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Metallosurfactants
Provides up-to-date coverage of the synthesis, properties, and applications of metallosurfactants
Metallosurfactants: From Fundamentals to Catalytic and Biomedical Applications is a thorough introduction to amphiphilic compounds that allow to incorporate metal ions in the surfactant system. This comprehensive reference and guide describes the fundamentals of metal surfactant complexes, highlights recent advances in the field, and explores current and future applications and research areas. Gradually progressing from basic to advanced topics, the authors first explain the classification and characterization of metallosurfactants before delving into more complex concepts and various catalytic, sensing, and biomedical applications.
The book begins with coverage of the synthesis of metallosurfactants and their surface, interfacial, and aggregation behavior. Subsequent chapters discuss applications of metallosurfactants in areas such as drug delivery, molecular machines, transfection, nanoparticle synthesis, and carbon monoxide-releasing molecules (CORMs). Other topics include the use of metallosurfactants as catalysts in organic reactions, and as anticancer and antimicrobial agents in drug delivery and formulation. This unique reference
- Provides an overview of the structure-function relationship, synthesis methods, and characterization of metallosurfactants
- Reviews current trends in metallosurfactant development and research
- Examines the use of metallosurfactants in a wide range of reactions, including esterolytic reactions and hydrogen generation
- Discusses advanced applications of metallosurfactants, e.g. as nanoreactors for nanoparticle synthesis, non-viral transfection vectors, and sensors
Metallosurfactants: From Fundamentals to Catalytic and Biomedical Applications is an excellent introduction to the growing field of metallosurfactant chemistry as well as a concise, highly useful reference for researchers and scientists in both academia and industry.
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Veröffentlichungsjahr: 2022
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Table of Contents
Cover
Title Page
Copyright
Preface
1 Metallosurfactants, a “
Novel Portmanteau
”: A Holistic Insight into the Structural–Physiognomies Relationships, Synthesis Stratagems, and Characterization
1.1 Introduction
1.2 Intrinsic Physiognomies of Metallosurfactants
1.3 Classification of Metallosurfactants
1.4 Syntheses Stratagems and Characterization of Metallosurfactants
1.5 Conclusion
References
2 Metallosurfactants: A Surface and Interface Perspective
2.1 Introduction
2.2 Micellization and Surface Parameters
2.3 Adsorption of Surfactant Monolayers
2.4 Conclusions
References
3 Metallosurfactant Self‐Assembly: Structures and Chemistry of Interfacial, Biphasic, and Phase Transfer Catalysis
3.1 Introduction
3.2 Self‐Aggregation Behavior
3.3 Chemistry of Catalysis
3.4 Conclusions
Acknowledgment
References
4 Hydrolytic Metallosurfactants: Nanocatalysts for Esterolytic Reactions
4.1 Introduction
4.2 Metallosurfactants as Nanocatalyst for Esterolytic Reactions
4.3 Catalytic Hydrolysis of Carboxylate Esters
4.4 Catalytic Hydrolysis of Phosphate Esters
4.5 Quantitative Treatment of Observed Rates: Application of Kinetic Models
4.6 Conclusion
References
5 Metallosurfactants as Catalysts in Organic Reactions and Energy‐Based Applications
5.1 Introduction
5.2 Metallosurfactants as Catalysts in Organic Reactions
5.3 Metallosurfactants as Catalyst in Water Oxidation
5.4 Light‐Driven Hydrogen Generation
5.5 Conclusions
References
6 Metallosurfactants as Drug‐Delivery Vehicles
6.1 Introduction
6.2 Distinct Assemblies of Metallosurfactants in Drug Delivery
6.3 Metallosurfactants as MRI Contrast Agents
6.4 Conclusion
Acknowledgments
References
7 Metallosurfactants as Molecular Machines for the Preparation of Hybrid Silica‐Based Porous Material
7.1 Introduction
7.2 Porous Silica‐Based Materials
7.3 Different Types of Porous Silica‐Based Material
7.4 Future Perspectives
7.5 Conclusion
References
8 Metallosurfactants as Non‐viral Vectors in Transfection
8.1 Introduction
8.2 Metallosurfactant Monomers
8.3 Metallomicelles
8.4 Metalloliposomes (Metallosomes)
8.5 Future Perspectives
Acknowledgments
References
9 Metallosurfactants as Nanoreactors for Nanoparticle Synthesis
9.1 Introduction
9.2 Metallosurfactants as Reactors for Nanoparticle Synthesis
9.3 Future Perspective
9.4 Conclusion
Acknowledgments
References
Note
10 Metallosurfactants and Their Biological Attributes: Anticancer and Antimicrobial Properties
10.1 Introduction
10.2 Antimicrobial Activity
10.3 Anticancer Activity
10.4 Conclusion and Future Challenges
References
11 Metallosurfactants as Carbon Monoxide‐Releasing Molecules
11.1 Why CO?
11.2 How to Deliver CO?
11.3 CO‐releasing Metallosurfactants
11.4 Conclusions
Acknowledgments
References
12 Supramolecular Metal‐Modified Nanocontainers Based on Amphiphilic and Hybrid Matrix: Self‐Assembling Behavior and Practical Applications
12.1 Introduction
12.2 Structure, Properties, and Biomedical Application of Metallosurfactants
12.3 Amphiphilic System Based on Metallosurfactants and Macrocycles
12.4 Nanocomposites Based on Amphiphilic Resorcinarenes and Metal Nanoparticles
12.5 Conclusions
Acknowledgments
References
13 Metallosurfactants in Nanoscale Molecular Containers as Sensors
13.1 Introduction
13.2 Metallosurfactants as Nanosized Containers for Self‐assembled Molecular Devices
13.3 Surfactant Aggregates in Chemical Detection
13.4 Self‐Assembled Moieties as Fluorescent Sensors
13.5 Metallosurfactants and Detection Protocol
13.6 Conclusions
Acknowledgments
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Characterization of MTS via state‐of‐art analytical techniques.
Chapter 2
Table 2.1 Critical micelle concentration (CMC) and area occupied per molecul...
Table 2.2 The CMC values of the various Cr(III) coordination complexes at 30...
Table 2.3 Comparison of CMC values and thermodynamic parameters for Pt‐CPC a...
Table 2.4 Calculated parameters from surface tension measurements: critical ...
Chapter 3
Table 3.1 Several reactions catalyzed by vesicles (vscl) and amorphous (amps...
Chapter 5
Table 5.1 Reaction of 2‐aminobenzophenone 1a with ethyl acetoacetate 2a cata...
Chapter 9
Table 9.1 Some examples of metallosurfactants as nanoreactors.
Chapter 12
Table 12.1 Different types of metallosurfactant structures.
Table 12.2 Catalytic activity of nanocomposites based on resorcinarene nanoc...
Table 12.3 Suzuki reaction using Pd, Ni nanocomposite with p(MVCA‐St).
List of Illustrations
Chapter 1
Figure 1.1 Schematic representation of surfactant.
Chapter 2
Figure 2.1 Potential self‐assembly structures possible for metallosurfactant...
Figure 2.2 (a) Structure of ligand L where R = C
10
H
21,
L1 and L2 (b) Surface...
Scheme 2.1 Structure of the metal–surfactant complex or metallosurfactant co...
Figure 2.3 Proposed organization of copper surfactant complex (a) at the air...
Scheme 2.2 Schematic representations of complexes in the interface showing t...
Figure 2.4 (a) The structure for redox active, amphiphilic metal complexes (...
Chapter 3
Figure 3.1 Representative structure of a metallomicelle (Green sphere: head ...
Figure 3.2 Structures of synthesized [Cu(
1
)]Cl
2
and [Cu(
2
)]Cl
2
metallosurfac...
Scheme 3.1 Schematic representation of ruthenium and iridium metallosurfacta...
Figure 3.3 (a) Structure and (b), (c) TEM images for [
2
][NO
3
]
4
, M = Pd and [
Figure 3.4 Cryo‐TEM images for 1 wt% solution of Co(III) surfactant showing ...
Figure 3.5 Ru metallosurfactant (a) Representation of inverted aggregates of...
Figure 3.6 (a) Fourier transforms of Fe(III) sites in sedimented Cd(II)‐ and...
Figure 3.7 (a) Preparation of molybdenum metallosurfactants [4–9] (L = 1, 2,...
Scheme 3.2 (a) Molecular structure of Ru metallosurfactant and image represe...
Figure 3.8 Structures of (a) PQS, (b) PQS‐attached Grubbs–Hoveyda‐1 metathes...
Scheme 3.3 (a) As‐synthesized Hoveyda‐type surface active catalysts – 2,3 (b...
Figure 3.9 Proposed mechanism of the ATH using chiral surfactant‐type cataly...
Scheme 3.4 (a) Vesicle formation via self‐assembly of amphiphilic pincer com...
Figure 3.10 Proposed mechanism of interfacial catalysis in bifacial esterifi...
Chapter 4
Figure 4.1 (a) Structure of common surfactant, (b) structure of metallosurfa...
Figure 4.2 Commonly investigated carboxylate and phosphate esters: (a) PNPA;...
Figure 4.3 Imidazole‐based metallosurfactant ligands prepared by Tagaki et a...
Figure 4.4 Selective activation of primary and secondary –OH groups of ligan...
Figure 4.5 Pyridine‐based ligands prepared by Tonellato and coworkers.
Figure 4.6 Phenanthroline‐based ligands synthesized by Engbersen and coworke...
Figure 4.7 Proposed mechanisms of hydrolytic cleavage of PNPP catalyzed by Z...
Figure 4.8 PNPP hydrolysis by Cu
2+
‐metallomicelles in the presence of ge...
Figure 4.9 Active species formed by the tetradentate ligand.
Figure 4.10 Proposed mechanism of the BNPP hydrolysis by metallomicelles of
Figure 4.11 Proposed mechanism for metallosurfactant‐mediated breakdown of B...
Scheme 4.1 (a) general scheme for partitioning of the reactants between the ...
Chapter 5
Figure 5.1 Effect of the length of catalyst chain on the ATH of aliphatical ...
Figure 5.2 Recycling test of the catalyst Mo1.
Figure 5.3 Kinetics of our authors' model reaction with different alkyl chai...
Scheme 5.1 Schematic representation of synthesis and self‐assembly of surfac...
Figure 5.4 (a) Polarization curves of CPC, PdCPC(I), and Pt/C, (b) Tafel slo...
Figure 5.5 (a) Cyclic voltammetry of CoCPC(I) in 0.5 N H
2
SO
4
at 100 mV s
−1
...
Figure 5.6 Polarization curves, initial and after 100 cycles at pH 11 for 1 ...
Figure 5.7 CV measurement (black) and Randles–Sevcik plot (blue); OER = circ...
Figure 5.8 Solvent study. Variation of organic solvent, with the final solut...
Figure 5.9 Kinetic traces at 510 nm for the back reactions of (a) [Ru(bpy)
2
M...
Chapter 6
Figure 6.1 Representation of a cobalt‐based metallosurfactant complex.
Figure 6.2 [Ru(bipy)(4,4′‐diheptadecyl‐2,2′‐bipyridine)
2
]Cl
2
metallosurfacta...
Figure 6.3 Structure of molybdenum metallosurfactant (left) and TEM image of...
Figure 6.4 Schematic diagram of metallosomes comprising a metal complex (DAC...
Figure 6.5 Construction of pH‐responsive mesostructured surfactant silica hy...
Figure 6.6 HIFU‐responsive process of Cu(II)‐terpyridine bonds containing bl...
Figure 6.7 Fabrication of reversible metallo‐supramolecular pH and thermores...
Figure 6.8 An illustration of synthetic route for
carbon dot
s (
CD
s) and self...
Figure 6.9 Illustration of fabrication of bimodal nanoparticular contrast ag...
Chapter 7
Figure 7.1 Porous materials with different size of pores.
Figure 7.2 Structural representation of a Catenanes.
Figure 7.3 Pictorial representation of surfactant‐based template synthesis o...
Figure 7.4 Copper surfactants based on sarcophagine and TEM image of mesopor...
Figure 7.5 Crystal structure of deprotonated and protonated bistable copper ...
Figure 7.6 Ruthenium metallosurfactant used as template for porous silicate ...
Figure 7.7 Representation of templating phenomena of Co soap.
Figure 7.8 Schematic illustration of synthetic pathway for magnetic mesoporo...
Figure 7.9 Graphical representation of single iron atom‐loaded mesoporous si...
Figure 7.10 Schematic representation of the strategy used for the encapsulat...
Chapter 8
Figure 8.1 Structures of different viral vectors.
Figure 8.2 Structures of different non‐viral vectors.
Figure 8.3 Stages involved in gene transfection process using surfactant mon...
Figure 8.4 Structures of the Ru metallosurfactants.
Figure 8.5 Structural representations of RuC11C11/cyclodextrin complexes wit...
Figure 8.6 Dependence of both the apparent emission intensity values (EI) an...
Figure 8.7 Sigmoidal dependence of the binding constant
K
b
with the [DNA] fo...
Figure 8.8 Structural representations of RuC19C19/cyclodextrin complexes wit...
Figure 8.9 AFM images of DNA (a) and RuC1C19/DNA complexes at [S]/[DNA] = 0....
Figure 8.10 Metallosurfactant [Pt(L)
2
Cl
4
].
Figure 8.11 Metallosurfactant [Cu(L)Br
3
].
Figure 8.12 Metallosurfactants [Cu(L
dt
)
2
]
2+
and [Cu(L
ot
)
2
]
2+
.
Figure 8.13 Cu‐based metallosurfactants.
Chapter 9
Figure 9.1 Proposed organization of metallo‐surfactants, (a) at the air–wate...
Figure 9.2 Schematic representation of the steps involved in the formation o...
Figure 9.3
High resolution transmission electron microscope
(
HRTEM
) images o...
Figure 9.4 TEM images and corresponding histograms of CeO
2
NPs obtained afte...
Figure 9.5 TEM of gold particles: (a) CPC1 (20 mmol dm
−3
), irradiation...
Figure 9.6 Schematic illustration of NPs structure: (a) the normal bilayer b...
Figure 9.7 (a) Schematic illustration of NPs synthesis using water‐in‐oil in...
Figure 9.8 Representation of the apparatus employed by the authors for synth...
Figure 9.9 (a) TEM image of TiO
2
particles obtained by injecting
dimethyl su
...
Figure 9.10 Synthetic procedure for obtaining monodisperse g‐Fe
2
O
3
NPs.Sourc...
Figure 9.11 TEM images of MnS nanocrystals. (a) MnS nanorods. Inset is an HR...
Figure 9.12 Schematic representation of metal NPs fabrication using various ...
Figure 9.13 (a) TEM image (b) XRD pattern (c)
Field emission scanning electr
...
Figure 9.14 Schematic representation of Pd(0) NPs via two‐phase redox reacti...
Figure 9.15 Pictorial representation of CuNP synthesis. Source: Kaur et al. ...
Chapter 10
Figure 10.1 Metallosurfactants and their biological attributes: anticancer a...
Figure 10.2 Heterocyclic cationic surfactant with tin and copper as counteri...
Scheme 10.1 Micelles containing chelated cisplatin for anticancer therapy by...
Figure 10.3 (a) Activation of photodissociative amphiphilic Ru(II) complex a...
Figure 10.4 Concentration‐dependent mechanisms of cell death in amphiphilic ...
Figure 10.5 Blueprint of an emissive Ru(II) amphiphilic complex depicting re...
Chapter 11
Figure 11.1 Successive steps of the degradation of heme group and release of...
Figure 11.2 Examples of several CORM structures.
Figure 11.3 Metallosurfactant with the metal–carbonyl complex into the headg...
Figure 11.4 (a) Synthesis of the ligand (L) with 6 carbon atoms (L6). (b) Sy...
Figure 11.5 Center: scheme of the obtention of Mo‐CORMs/phosphatidylcholine ...
Chapter 12
Scheme 12.1 One‐stage synthesis of metallosurfactant with Cu(II) in the head...
Scheme 12.2 Two‐stage synthesis of metallosurfactant with Co(III) in the hea...
Scheme 12.3 Two‐stage synthesis of metallosurfactants with Cu(II), Ni(II) in...
Scheme 12.4 Chemical formulas of sulfonate calix[4]resorcinarene and complex...
Scheme 12.5 Synthesis of Ag@p(CRA‐B) and Ag@CRA‐C10.
Figure 12.1 Plots of ln(
A
/
A
0
) versus time for the catalytic reduction of
p
‐n...
Scheme 12.6 Synthesis of p(MVCA‐St) nanocomposites with PdNPs on the surface...
Chapter 13
Figure 13.1 Basic components of a surfactant.
Figure 13.2 Micellar, bilayer, and vesicular arrangements.
Figure 13.3 Chemical structure of lipids
1a
,
1b
, and
2
.
Figure 13.4 Structure of the lipids
1
–
4
.
Figure 13.5 Schematic representation of the self‐assembled chemosensor. (a) ...
Figure 13.6 Schematic illustration of synthetic process of hybrid QC
12
Et
3
Br‐...
Figure 13.7 Schematic representation of complexes 1 and 2 and their self‐agg...
Figure 13.8 Typical time‐resolved intensity decay curves of four‐month‐old R...
Figure 13.9 Schematic illustration of the fabrication of the bio‐modal nanop...
Figure 13.10 Schematic diagram of attachment of complexes and surfactants to...
Figure 13.11 Schematic representation of the formation of the iridium aggreg...
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Begin Reading
Index
Wiley End User License Agreement
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Metallosurfactants
From Fundamentals to Catalytic and Biomedical Applications
Edited bySurinder K. MehtaRavneet Kaur
Editors
Prof. Surinder K. MehtaPanjab UniversityDepartment of Chemistry160014 ChandigarhIndia
Dr. Ravneet KaurIvy Tech Community College3100 Ivy Tech Drive, ValparaisoIndiana 46383United States
Cover Image: © Tom Biegalski/Shutterstock
All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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© 2022 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany
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Print ISBN: 978‐3‐527‐34868‐8ePDF ISBN: 978‐3‐527‐83127‐2ePub ISBN: 978‐3‐527‐83129‐6oBook ISBN: 978‐3‐527‐83128‐9
Preface
This book introduces its readers to a very special class of amphiphiles termed as “metallosurfactants” from here on, incorporating a metal in the usual surfactant system. A book in this area has been long outstanding. When we started working on the metallosurfactants a few years back, we always felt the need for a holy grail or a guiding text to delve deeper into the realm of metal surfactant complexes or metallosurfactants. Something which could explain the fundamentals of the metal surfactant complexes in detail while highlighting the current progress as well as the future prospective. Back then, we would have been thrilled to get our hands on something like this. So, a lot of the topics included in this book stem from the difficulties we faced while doing the literature survey and understanding this complex topic a little better. The book has, therefore, been designed in such a way to provide a gradual evolution starting from the very basics to the more advanced concepts and then finally dealing with the applications of metallosurfactants including but not limited to catalytic, sensing, and biomedical fields. The book has been divided into 13 chapters. The first three chapters are associated with the synthesis and characterization of metallosurfactants followed by an investigation of their surface, interfacial and aggregation behavior. Accordingly, building on their properties, a variety of applications for the metallosurfactants have been discussed, highlighting the current status and development in the areas including catalysts for organic and esterolytic reactions, hydrogen generation, drug‐delivery vehicles, molecular machines, transfection, nanoparticle synthesis, anticancer and antimicrobial activities, CORMs, and sensors in the subsequent Chapters 4–13. This book is intended for introductory graduate‐level metallosurfactant chemistry and the researchers working in this field. We believe that fellow scientists from both academia and industry would find this book to be a concise, informative yet interesting read.
1Metallosurfactants, a “Novel Portmanteau”: A Holistic Insight into the Structural–Physiognomies Relationships, Synthesis Stratagems, and Characterization
Ankush Parmar1, Shilpee Sachar2, and Shweta Sharma1
1Panjab University, Institute of Forensic Science and Criminology, Chandigarh, 160014, India
2University of Mumbai, Department of Chemistry, Vidyanagari, Santacruz (E), Mumbai, 400098, India
1.1 Introduction
Recently, “surface chemistry” has gained enormous amount of attention in bringing the vivid paradigm of synthetic chemistry [1]. Owing to the splendid attributes, being offered by it, a vast majority of the leading researchers, scientists, and physical chemists across the globe are putting their exertions to envisage noble advancements in this illustrious domain [2]. The inception of this field can be dated back to the late seventeenth century. It was through the numerous experiments (to study the phenomenon responsible for spontaneous spreading of oil‐on‐water) conducted by the famous physician Sir Benjamin Franklin that the early breakthroughs in this domain were achieved [3]. This innovation later on proved to be a souvenir and became the underlying fundamental basis for the upcoming research and development in this field [4].
In subsequent decades, a colossal growth has been witnessed in the dominion of surface chemistry, and the corresponding systematic findings have actually transformed variegated scientific disciplines [5]. It is because of this particular realm that the eminent fields such as colloid chemistry, interface science and surface engineering came into existence.
Several other eminent and impending disciplines viz. nanoscience, energy conversion, and catalysis have also momentously gained from it [6]. In other words, surface chemistry has essentially laid down the underpinning stone for voluminous superlative fields [7]. Henceforth, it can be rightly said that “surfactants, a portmanteau of surface‐active agents” as we call them have proven to be highly potent agents (Figure 1.1) [8–11]. Amidst, all the molecules investigated in the realm of chemistry, surfactants are most exclusively studied. Owing to their exceptional solution and interfacial properties, they are currently being utilized on a widespread level in several fields.
Surfactants can be defined as the “materials which when present at low concentrations, alters the interfacial free energies of the interfaces via adsorbing themselves onto the interface/surface of the system” [8,12–20]. They generally fall under the category of organic compounds and are truly amphiphilic in nature [21].
Figure 1.1 Schematic representation of surfactant.
When it comes to structural organization, surfactants usually comprises of two vital components the first one being the head (polar) group, which is hydrophilic in nature [22,23], and the second part often referred to as the tail (non‐polar) group is hydrophobic (lipophilic) in nature [24]. It is mostly observed that the polar head group varies greatly in structure and can be multifaceted, while the tail group demonstrates less diversity and as a rule it primarily comprises of a hydrocarbon (alkyl) chain with 8–20 carbon atoms. Broadly speaking, the tail can be branched/linear hydrocarbon, aliphatic, alkyl/aryl, short/long whereas; the head group can be ionic/non‐ionic [21–23]. These chemical moieties have an innate ability to affect the air–water interface in an articulate fashion. This might be attributed to the reduction in the surface tension (interfacial tension) of water and formation of assorted assemblies (micelles) at the interface [10,25]. Upon adsorption at the interface, the two characteristic portions of the surfactants viz. head and tail group align themselves according to their polarities/preferential solubilities. The polar head group align itself toward the aqueous (water) part, while the tail group orient itself away from the water (outward direction) thereby resulting in the formation of micelles [26].
When dispersed in aqueous phase, at low concentration these surfactants generally exist in monomeric/dimeric state. An increase in their concentration beyond a designated threshold (viz. critical micellar concentration [CMC]) leads to the spontaneous accumulation of surfactant monomers. This further results in the formation of assemblies/colloidal‐sized clusters also commonly referred to as “micelles” [4,7,26,27]. A major share of this potential breakthrough goes to James William McBain, whose discovery inevitably changed the dynamics and lead to significant advancements in the field of surface/surfactant chemistry [12,27–29]. It was in the year 1916, while conducting his research experiments, he observed infrequent alteration in the electro‐conductive physiognomies as a function of soap concentration and he coined the term “micelles” [30].
Nowadays, a dire need is felt for the upgradation and development of novel technologies, which will play an intricate role in improvising the varied aspects of human lives. This upsurge calls for a quick modification of the surfaces in order to perfectly align with these rapid advancements [31]. Herein, the innate potential to alter the interfaces as per the requisite demand plays a pivotal role in envisaging and devising innovative technological advancements, ranging from energy production to biomedical implants, which will offer promising outcomes [12,27]. Incessant strides are being made in the field of science and technology on a regular basis to attain the aforementioned goal.
Irrespective of the fact that these chemical moieties possess such dynamic properties yet, they have not been able to secure a place for themselves among the “catalogue of advanced materials” [32]. In lieu of this, unique complexes with pre‐selected functionalities (viz. proteins, carbohydrates, and metal ions) have been developed, which comprehensively aided in triumphing the lacunas associated with conventional surfactant systems. Additionally, incorporation of such modalities resulted in the fabrication of novel surfactants with engineered interfacial attributes [31]. Among all functional groups/modalities, metal ions have played a pivotal role in escalating the physicochemical attributes of the conventional surfactants exponentially. This in particular has lately led to the emergence of remarkable, and idiosyncratic complexes commonly referred to as metallosurfactants (MTS) [33].
1.2 Intrinsic Physiognomies of Metallosurfactants
Self‐aggregation/association/assembly above CMC is an intrinsic property, which makes these surfactants and amphiphilic structures an invigorated tool. Length and volume of lipophilic component, size and charge of the polar head group, type of interaction with the solvent system, ionic strength, and molecular framework of the system are some of domineering factors, which tend to govern the hydrodynamic radii (particle size), and surface charge (zeta potential) of these singular entities [34–36]. The whole credit for this fundamental concept of aggregation goes to Zhulina et al. [35]. It was because of their incessant attempts that a comprehensive overview of this distinguishing phenomenon could be deciphered more than 30 years ago [37,38].
With an advent in time, several triumphant advancements have been accomplished in the field of surfactant chemistry. These progressions have broadened up the horizons of our understanding in lieu of surfactants. Similarly, the underlying concepts providing an inclusive aftermath of the phenomenon have also upgraded in recent years. This upgradation vindicated the fact that it is the metal ion, which plays a pivotal role in regulating the self‐aggregation behavior of MTS/MTSC, respectively [34]. Whilst, the positioning of the metal ion component (counter ion/integral component) in the base matrix does not seem to have an obligatory effect on the assembling phenomenon.
When dispersed in aqueous media, these MTS tends to “diminish the characteristic qualities of metalloenzymes” [39]. Therefore, the MTSC felicitates a self‐aggregation/association of distinct metal‐complex‐based aggregates reciprocating the aggregation number equivalent to their counterparts viz. surfactants [15,39]. This distinguishing property to self‐aggregate, and formulate idiosyncratic complexes bestow these MTS with unique potential applications, which can prove to be handy in real‐time scenario [39]. Additionally, the complexes so generated possess multiphasic properties, and can solubilize an array of diverse chemical moieties i.e. lipophilic/hydrophilic, and ionic components [13]. Depending upon the CMC value, distinctive structures illustrating assorted geometrical facets viz. micelles (spherical, oblate/prolate/ellipsoid, hybrid crystals with layered perovskite structure), and aggregates (vesicles, bilayers, helixes, tubules) are customarily formed by this special class of metallic surfactants [40–43].
As compared to their conventional counterparts, CMC of these metal‐based surfactant complexes is very less. Henceforth, the presence of MTS at a miniscule concentration is potent enough to bring a substantial saturation at the interfacial point along with a significant micelle formation [44]. Apart from these facts and findings, it has also been deciphered by studies that the self‐assembly of MTS is greatly affected by two key factors i.e. nature of transition metal ion and differences in coordination at atomic scale. To gain a holistic view of the aforementioned fact, let us briefly discuss the effects of ions, solvents, and structures on micellar morphology with some examples:
Metal ion
– If a conventional surfactant is dispersed in water, a simple micelle is formed, while incorporation of a metal ion in the base structure results in a significant alteration in the geometrical facet, and surface charge of the MTS. In place of the micelle, formation of a vesicle takes place usually [
45
–
47
].
Solvent system
– A reverse micelle having a metallic amphiphilic bilayer is formed upon the dispersion of an MTS (having multiple alkyl chains attached to a metal ion) in non‐polar solvent while, such a phenomenon is absent in conventional surfactant systems [
18
,
48
,
49
]. Upon dispersion into less polar organic solvents (
viz
. chloroform, and diethyl ether), these MTS tends to aggregate, and formulation of inverted metallomicelles takes place. This phenomenon can be principally attributed to the non‐covalent interactions which encourage the orientation of the reactive head group in a miniscule volume thereby ultimately resulting in the generation of a highly concentrated and catalytically active cavity of colloidal frameworks.
Structural factor –
Formation of micelle takes place in case of an aqueous dispersion of single‐chain MTS while vesicles are formed upon dispersion of double‐chain MTS in aqueous media [
50
–
52
]. This can be further explained based upon the morphology of the metallic surfactants. Cylindrical morphology of the double‐chain MTS, and interaction of metal ion with two surfactant molecules results in the formation of a
pseudo‐double‐chain surfactant
(
PDCS
). During the PDCS generation, the molecules orient themselves in such a manner, that the packing assumes a vesicular structure [
53
–
55
].
Apart from this, the cross‐sectional area of both the vital components i.e. head and tail region is altered due to the incorporation of metallic ion in the core structure. This alteration creates a demarcating change in the packing volume, thereby inducing a series of phase transition in the metalloaggregates. The phase transitions ultimately result in the fabrication of vesicles with vivid structural forms (viz. unilamellar, multi‐lamellar/vesicular) [56–58].
With the aid of MTS, an assortment of vivid physicochemical attributes of metal ions can be localized at air–water/oil–water interface. Henceforth, it would be apposite to state, “the MTS are an exceptional class of surfactant system, which technically amalgamated two diverse area of science i.e. co‐ordination and surface chemistry in a coherent manner” and this leads to the emergence of a noble omnipotent scientific domain. Amidst a wide array of characteristics, redox activity is deemed to be the predominant one. The inculcated metallic ion tends to possess a variable oxidation state, and it is because of this inherent property that these MTS are able to illustrate such a noteworthy ability. The traditional surfactant systems lacks this capability as their core framework is largely composed of elements‐like carbon, oxygen and sulfur [45].
On a comparative note, it has been established repeatedly, that MTS essentially bestow enhanced chemical reactivity as compared to their conventional counterparts. Charge, valency, and empty d/f orbitals entangled with metal ions are some of the pivotal factors, which escalates the chemical reactivity of these superior class of metal surfactants to many fold times [18]. In other words, it can be righteously stated that the “base surfactant itself does not have any chemical reactivity” [18,45]. However, it is the embodiment of the metal ion, which brings a radical change in the chemical state of the pristine surfactant, thereby efficaciously circumventing the existing lacuna associated with the traditional surfactant systems [45].
Incorporating metal ions possessing energy levels equivalent to those of the visible transitions (taking place in the UV–visible region) imparts a chromophoric ability to the MTS. It is because of this intricate potential that these metal‐based surfactants exhibit illustrious and bright colors (e.g. Cu2+ [blue], Fe2+/Fe3+ [yellowish red], and Ni2+ [green]). This might be attributed to the d–d transition of the metal ion, which is positioned in the visible region of the electromagnetic spectrum. Additionally, it is well versed that the alteration in color is exclusively dependent upon the surrounding chemical milieu. This facilitates the user with a tranquil access where he/she can control the reaction conditions in a complacent manner [45].
In an analogous manner, inculcation of a paramagnetic/ferromagnetic metal ion within the framework of the soft matter imparts magnetic properties to the surfactants, which are fundamentally diamagnetic in nature [18]. The stimuli (magnetic field)‐responsive surfactants depicts a novel class of surfactants, wherein the surface tension can be simply modulated by switching on/off the applied magnetic field. Distinct from all of this Lewis acidity, pH responsiveness, and structural diversity are some of the other striking attributes, which are exemplified by these MTS [51,54,57].
It seems from the aforementioned facts and findings, that the metal ion is the only component, which is responsible for allocating such eminent characteristics however, in real sense it is not so. The soft matter also adds significantly to the metal‐ion chemistry. Active transfer of the above‐mentioned attributes to the interface is typically accomplished due to the surface‐active property of the surfactant. Henceforth, it is the reunion of the characteristic chattels of both the components, which led to the acquirement of such distinctive physicochemical attributes [48]. Owing to such exceptional attributes, this special class of building blocks have been utilized in many fields vis‐à‐vis (i) surface activation agents, (ii) monolayers, (iii) emulsions, (iv) contrast agents (medical resonance imaging), (v) catalysts (homogenous photo catalysis), (vi) transporting and sensing agents (fluorescent sensors), (vii) binders and metal extractors, (viii) redox agents (biological system), (ix) vectors for drug delivery (nanoparticles), (x) thin‐film optoelectronic devices, (xi) solvatochromic probes, (xii) interfacial photo‐physical agents, (xiii) templates for fabrication of diverse frameworks (micelles, vesicles, bilayers, liquid crystals, mesoporous materials, and metallomesogens), and (xiv) antimicrobial agents (viz. antibacterial, antiparasitic, anthelminthic) [50,59,60].
1.3 Classification of Metallosurfactants
In pertinent literature, a vast majority of systems have been outlined, which tends to intrinsically categorize these tailored/engineered hybrid surface‐active moieties based upon certain distinctive characteristics. One such classification system relies upon the type of bonding between the metal ion, and the soft matter (surfactant). According to this system, surfactants comprising of inorganic moieties are generally referred to as inorganic surfactants (viz. I‐SURFs) [18,45]. I‐SURFs can be categorically sub‐divided into two major categories viz.
I‐SURFs type I
– These are the simplest type of surfactants, in which the metal ion is incorporated within the conventional surfactant. Herein, the metal ion plays a definitive role, and acts as a counter ion.
I‐SURFs type II
– In such kind of hybrid surfactants, the metal ion acts as an integral part of the polar head group. Type II I‐SURFs can be further divided into two prominent types i.e. type II a, and type II b. In type II I‐SURFS, the metal ion is localized within the polar head group component of the soft matter. In the latter one, the metal ion itself acts as the head group.
In the pertinent literature, another classification system, which shares analogous fundamental basics to the aforementioned system, has been reported. In this method, the MTS are chiefly classified into three major categories viz.
Group I –
In this kind of metal‐based surfactants, the hydrophilic head group acts as a housing cavity for the positioning of the metal ion. Further, attachment of this component with the hydrocarbon tail is accomplished via covalent binding
[61]
.
Group II
– These MTS represent a newer class of hybrid metallic surfactants. In these hybrid surfactants, the hydrophobic part of the soft matter provides accommodation to the metal ion. Herein, the metal ion acts as an integral part of the long alkyl chain, and it is with the help of co‐ordination chemistry that this ionic entity is connected with the hydrophobic segment
[62]
.
Group III
– In this type of hybrid surfactants, the counter ion of the soft matter provides a housing cavity to the metallic ion. Herein, the metal ion is weakly bonded with the surfactant and is localized within the counter ion segment
[63]
.
Based upon their dissociation in water, a third type of classification system categorizes the MTS into two chief classes viz.
Cationic
– Upon dispersion into an aqueous phase, these MTS are primarily dissociated into two key components i.e. an amphiphilic cation, and an anion. A major share of such MTS chiefly comprises of nitrogenous compounds such as fatty amine salts, and quaternary ammoniums. These nitrogenous functional groups are further attached to elongated single or multiple alkyl tails (e.g. bis(2‐phenylpyridine)(4,4‐diheptadecyl‐2,2‐bipyridine)‐iridium(III) chloride (Ir‐complex))
[64]
.
Anionic
– Unlike their predecessors, these MTS also dissociate into two major components upon dispersion into an aqueous phase. However, the demarcation lies in the fact that herein, an amphiphilic anion is generated in place of a cation followed by the generation of a cation. Anionic surfactant
viz
. sodium 1,4‐bis(neopentyloxy)‐3‐(neopentyloxycarbonyl)‐1,4‐dioxobutane‐2‐sulfonate (TCl
4
) would constitute a perfect example of such a system
[65]
The fourth classification system is distinctly apart from the earlier‐described systems. Herein, depending upon the localization of metal ion in the soft matter, the MTS can be classified into two broad categories as;
Metal ion in hydrophilic head group
– In this class of hybrid metal‐based surfactant, hydrophobic component of the MTS primarily comprises of the alkyl chain of the soft matter, while the metal ion along with its primary coordinated sphere constitutes the polar head group [
15
,
60
].
Metal ion in hydrophobic tail group
– This type of MTS depicts divergent attributes as juxtaposed to the former one. Herein, the metal ion is localized in the hydrophobic (alkyl chain) segment (tail) of the soft matter [
16
,
40
].
The fifth classification system can be considered as the core/base structural characterization scheme. According to this classification schema, the MTS can be classified into five major categories as;
Single chained
– In this class of MTS; the metal ion is incorporated with the polar head group of the soft matter. Herein, the metal ion tends to play a definitive role, and acts as a counter ion
[66]
.
Double chained
– This type of hybrid metallic surfactants possess an analogous structure to that of the single‐chain MTS. However, the major demarcation lies in tail group. Alike its predecessor, the metal ion along with its primary coordination sphere acquires the functionality of the polar (hydrophilic) head group. Whereas, on the other hand, the ligand along with the alkyl (hydrophobic) tail is coordinated to the metal ion [
67
,
68
].
Pseudogemini
– With an advent in time, surfactant chemistry exemplified astonishing progressions. These momentous advancements, paved a gallant way for the fabrication of interesting class of novel surfactants
viz
. pseudogemini surfactants. Pseudogemini MTS are single‐chain analogues of gemini surfactants
[69]
. They possess an explanatory complexed structure, in which the amphiphilic ligands are attached to a centrally coordinated metal ion. MTS complex of an “
alkylsulfonatephosphine‐functionalized alkyphenol ethoxylate
” symbolizes an interesting example of such a system
[44]
.
Mixed ligand coordination complexes
– These can be piously regarded as the exalted class of MTS. In such MTS, a transition metal complexed with an amphiphilic entity such as Schiff's base is incorporated within the core framework of a conventional surfactant
[70]
.
Organometallic surfactants
– These hybrid surfactants epitomizes the most advanced series of metallic surfactants. It can be astutely stated, “
it is because of such illustrious moieties that the dynamics of surfactant chemistry has metamorphosed colossally
.” Coming on to the schematic aspect, these MTS are analogous to the traditional surfactants, as they also tend to possess a head and tail group. Nonetheless, a major variance is generated due to the alteration in the chemical nature of the molecular entities, which constitutes both these pivotal segments. Herein, the head group usually constitutes of a transition metal embodied with one of the components of the soft matter. Whilst, in the second region, the alkyl chain is substituted with a functional group tagged π‐conjugated chain, which further acquires the functional role of the hydrophobic tail
[71]
.
1.4 Syntheses Stratagems and Characterization of Metallosurfactants
The facts and findings discussed above have provided us with a comprehensive overview of the MTS and their intricate physiognomies. Now, it has become clear that MTS are technically “amphiphilic entities comprising of coordinated metal ion/ions.” Coming on to the syntheses part, polar or organic solvents play a vivacious role in the syntheses of these exceptional classes of hybrid surfactants. Till date, three distinctive synthesis routes have been devised for the syntheses of MTS;
1.4.1 Metathesis Reaction
A highly sophisticated and arduous methodology becomes pre‐requisite when it comes to the development of MTS possessing cationic metal species, and aliphatic tails. In such circumstances, the following stratagem i.e. metathesis reaction (MR), appears to be a unique one and offers several lucrative advantages viz. [72]
One‐pot synthesis.
Ease of extraction and cost effectiveness.
Efficient recovery of catalyst
– Employment of water‐soluble catalyst circumvents the need for re‐extraction.
Minimized solvent consumption/wastage
– Tranquil extraction of catalyst can be accomplished with an aqueous phase. The aqueous phase can be reused as such for subsequent reactions (continuous batch production).
Ordinary reaction conditions
– Does not require any specific reaction conditions such as inert atmosphere, and degassing. The entire reaction can be carried out at room temperature.
In general terms, an MR can be defined as a “reaction in which two distinct chemical entities react in an aqueous phase to form a novel product.” Herein, the formation of the new product usually takes place due to the double decomposition/displacement reaction (interchanging of the radicals or ions of the reactant species). MR, in other words, can be technically referred to as “the phenomenon of cation, and anion exchange in a polar/aqueous phase” [73].
To understand the dynamics of the aforementioned synthesis schema, let us consider certain examples. Lipshutz et al. carried out the synthesis of a “designer surfactant” viz. PQS (nanomicelle‐forming amphiphile) using a metathesis reaction [74]. Herein, a well‐versed ring‐closing ruthenium catalyst i.e. Grubbs Hoveyda 1 Ru(II) was employed as an intermediate substrate for the catalyzing the entire reaction. The present experiment exhibited promising outcomes and the results came out to be extremely significant. Proposed methodology, i.e. micellar catalysis/ring catalysis metathesis (RCM) allowed a successful covalent linking of the Ru carbene with the designated chemical moiety, thereby, leading to a successful synthesis of the novel MTS [74]. The synthesized PQS MTS offered three vivid key elements viz. lipophilic segment (site for solubilization of insoluble organic substrates), hydrophilic segment (solubilizes PQS in polar/aqueous solvent such as water), and free –OH residue within the hydrophobic core (site bearing the metallic part). The proposed methodology also offered a potent solution to overcome the pre‐existing lacunas of the conventional methodology. Pure water acted as the solvent system, and during the entire reaction, room‐temperature conditions were maintained. The catalyst used was water soluble, and no re‐isolation steps were further carried out. Additionally, the proposed methodology facilitated the RCM of water‐insoluble dienic substrates [74].
1.4.2 Ligand Substitution Reaction
Ligand substitution reaction (LSR) is the second most preferred type of reaction, when it comes to the synthesis of hybrid metal‐based surfactants. As the name itself suggests, the method generally involves the substitution of lesser labile ligands with more labile ligands. In other words, it can be righteously said, that in these types of reactions, interchange of highly susceptible ligands takes place via the lesser ones. In lieu of this, Veeralakshmi et al. synthesized varied types of single‐ and double‐chained MTS possessing idiosyncratic biological functionalities [75]. Facile employment of LSR led to the efficacious synthesis of hybrid ligand‐anchored metallic surfactant complexes. Herein, Co(dien)Cl3 acted as the precursor excipient whilst, diethylenetriamine (dien), dodecylamine (DA), and hexadecylamine (HA) were chosen as the model ligands. In the present experiment, one or two amine groups of the alkylamine ligand base played an active role and led to the substitution of one or two labile chloride ligands. This ligand‐mediated substitution ultimately resulted in the synthesis of four different types of MTS viz. [Co(dien)(HA)Cl2]ClO4(III), [Co(dien)(DA)Cl2]ClO4(IV) [Co(dien)(HA)2Cl](ClO4)2(V), and [Co(dien)(DA)2Cl](ClO4)2(VI) [75].
1.4.3 Ligand Insertion Reaction
Last but not the least, ligand insertion reaction (LIR) is the third type of reaction, which is predominantly employed for the synthesis of MTS. A distinctive feature of this method is the maintenance of the integral nature of all the excipients being employed during the reaction. Unlike, its predecessor i.e. LSR, this method does not involve any substitution/elimination. The method preferred is the fabrication of hybrid metal‐surfactant complexes via interjecting a chemical moiety (usually a ligand) into another molecule or a bond [19]. Following this approach, Wagay et al. synthesized a hybrid MTS named cis‐chlorobis(ethylenediamine)dodecylamine cobalt(III) nitrate(I) (viz. CDCN) [67,68,76]. Herein, a dropwise addition of the ligand i.e. dodecylamine (ethanolic solution) to trans‐[Co(en)2Cl2]Cl (aqueous solution) resulted in the attainment of the desired metal surfactant complex.
In another experiment, a double‐chained MTS viz. cis‐bis(1,3‐diaminopropane) bis(dodecylamine)cobalt(III) nitrate(II) (DDCN) was synthesized by the same group using LIR methodology [76]. Analogous to the aforementioned methodology, the preset method also involved a dropwise addition of ethanolic dodecylamine solution (ligand) to an aqueous solution of trans‐[Co(tmd)2Cl2]ClO (aqueous solution). This in turn led to a successful synthesis of the desired hybrid metal–surfactant complex i.e. DDCN.
Characterization plays an imperative role in deciphering the electro‐physicochemical, structural, and morphological attributes of the synthesized MTS. Determination of such imperious traits can further aid in exploring the practical utility of these versatile systems in real‐time scenario. Not only this, the characterization of synthesized MTS using high‐tech analytical techniques gives an edge to the researchers/chemists, and allows them to develop versatile MTS with tailored properties. A wide array of analytical techniques ranging from simplistic spectrophotometer to advanced techniques such as electron/ atomic microscopy has been widely employed for the facile elucidation of intricate physiognomies. Table 1.1 illustrates the varied analytical techniques being employed for the characterization of novel MTS.
Table 1.1 Characterization of MTS via state‐of‐art analytical techniques.
Techniques
MTS explored
Characteristic attributes probed
Inference
References
Dynamic light scattering
(
DLS
)
Tetradecylpyridinium
(
TP
) TP
2
[MCl
4
] (M = Mn, Co, Ni, Cu, Zn)
Hydrodynamic radii (size) and surface charge
The micelles depicted ultrafine particle size of 4–7 nm, whilst the zeta potential was found to be +45 mV, respectively.
[68]
Scanning electron microscopy
(
SEM
)
Supramolecular MTS
(
SMMS
s)
Surface morphology
The fabricated SMMSs illustrated a spherical (polymeric) morphology. Highly dispersed polymeric SMMSs obtained with increase in the chain length
[77]
Biscetylpyridiniumtetrachloroplatinate (Pt‐CPC) MTS
Surface morphology
Surface pattern found to be profoundly dispersed, highly homogenous, and spherical in nature
[78]
Transmission electron microscopy
(
TEM
)
Double‐tailed metallosomes (
viz
. bishexa decylpyridinium metal tetrachloride (MCPC II) [M: Fe, Co, Ni, Cu])
Morphological attributes
Fabricated MTS (50–150 nm) possessed diverse morphologies
viz
. multivesicular and spherical
[73]
C
n
–Cu–C
n
(
n
= 8, 12, 16) MTS
Morphometric attributes
Primarily vesicular aggregates within a size range of 60–200 nm. Additionally microscopic studies revealed the presence of polydispersions and polyaggregates
[79]
Atomic force microscopy
(
AFM
)
CTA–AgB MTS
Molecular geometry
The aggregates were predominantly spherical
[80]
Copper(II)‐surfactant complexes
Molecular geometry
Metallovesicle
s (
MTV
s) in the size range of 20–50 nm were formed
[81]
Ultraviolet–Visible (UV–Vis) spectroscopy
Bishexadecyl pyridinium metal(II) tetrachloride (M CPC II) [M:Fe, Co, Ni]
Probabilistic mechanism responsible for binding of BSA to the corresponding MTS
Inclination in the intensity of the absorption maxima (static quenching) of BSA upon addition of MTS. Blue shift (protein stabilization/unfolding).
[82]
Chromium (III) MTS containing various chelating ligands (ethylenediamine (en), tri‐ethylenetetramine (trien), 2,2‐bipyridine (bpy), and 1,10‐phenanthroline (phen)), and axial amine (dodecylamine/cetylamine)
Geometrical configuration of the corresponding cations within the MTS
Escalated distortion of basal planes in case of “
phen
” complexes as compared to “
bpy
” complexes. Both the complexes (
viz. cis
‐[Cr(phen)
2
(C
12
H
25
NH
2
)
2
]
3+
and [Cr(bpy)
2
(C
16
H
33
NH
2
)
2
]
3
) possess an identical structure
[59]
Fourier transform infra‐red
(
FTIR
) spectroscopy
Hexadecyltrimethyl ammonium chromium trichloride (CrC I), hexadecyltrimethyl ammonium chromium tetrachloride (CrC II)
Elucidation of functional group bonds generated among the parent excipients.
Interaction of metal chloride with the ammonium group of the MTS resulted in an alteration in the chemical milieu (shifting of –C–N, and NH–Cl stretching band to a lower wavenumber)
[83]
Bistable copper(II) complex
Explication of linkage developed between the varied precursor materials
Free carbonyl groups (
v
O–H) played a pivotal role in establishing linkage with the silanol (
Si
–OH) groups present in the silica walls
[84]
Nuclear magnetic resonance
(
NMR
) spectroscopy
N‐heterocyclic carbene
(
NHC
)‐MTS
Vindicating the successful fabrication (linkage of two polymer blocks) of MTS.
Covalent linkage between PS and PMMA established. Fabricated MTS comprises of core‐shell‐shaped particles, resulting in the synthesis of block copolymer
[33]
FeCPC I, CoCPC I, NiCPC I MTS
—
Electronic interaction between the cationic (CP
+
) and anionic (MCl
3
) moieties resulted in the synthesis of corresponding MTS.
[2]
Small‐angle X‐ray scattering
(
SAXS
)
Lipid mimetic MTS
viz
. [Ru(bpy)2(dn‐bpy)]
2+
and [Ir(ppy)2(dn‐bpy)]
+
Determination of the structural aspects of the corresponding MTS
Sharp Bragg's peaks obtained indicating the formation of crystalline, hollow, and multilamellar (composed primarily of bilayer stacks) MTS‐based structures
[85]
MTS ionogels
Elucidation of the morphological attributes of the corresponding MTS.
All the three MTS ionogels possessed lamellar morphology.
[86]
X‐ray diffraction
(
XRD
)
Cetylpyridinium chloride
metallosome
s (
MET
s)
Establishment of the morphological arrangement of the as‐fabricated METs
METs possessed highly crystalline geometry along with a lamellar metallosomal bilayer
[73]
Differential scanning calorimetry
(
DSC
)
[M (CH
3
COO)
4
]
2−
[C
12
H
25
NH
+
3
]
2
Physicochemical characteristics of the MTS.
Decomposition occurs with melting in metal complexes, and metal oxides remained as final products. Activation energy order obtained was dependent on the size of transition metal ion and metal ligand bond strength
[87]
Thermogravimetry/ differential thermal analysis
(
TG‐DTA
)
Pt‐CPC MTS
Thermal behavior and stability of the MTS
The fabricated MTS depicted an enhanced thermal stability. The Pt‐CPC MTS illustrated an exothermic behavior prior to the
transition temperature
(
TT
) whereas; a
vice‐a‐versa
phenomenon was obtained on/after the TT.
[78]
1.5 Conclusion
MTS represents a class of supra‐molecular assemblies which can facilitate an effective bridging between both the explicit domains of chemistry viz. synthetic and inorganic. It is because of this unique bridging that these exhilarating moieties with tailored physiognomies can befabricated with ease. Apart from this, the inimitable metal‐phase behavior of the MTS bestows them with a unique ability to formulate an extensive array of supramolecular structures. Additionally, the existence of an interrelation between the two vivid domains viz. coordination chemistry and surfactant self‐assembly offers tremendous opportunities for these MTS to be applied on a full‐scale level in varied domains of science, and technology.
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