Biosurfactants for a Sustainable Future E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1259

Veröffentlichungsjahr: 2021

Beschreibung

Biosurfactants for a Sustainable Future Explore the state-of-the-art in biosurfactant technology and its applications in environmental remediation, biomedicine, and biotechnology Biosurfactants for a Sustainable Future explores recent developments in biosurfactants and their use in a variety of cutting-edge applications. The book opens a window on the rapid development of microbiology by explaining how microbes and their products are used in advanced medical technology and in the sustainable remediation of emerging environmental contaminants. The book emphasizes the different techniques that are used for the production of biosurfactants from microorganisms and their characterization. Various aspects of biosurfactants, including structural characteristics, developments, production, bio-economics and their sustainable use in the environment and biomedicine, are addressed, and the book also presents metagenomic strategies to facilitate the discovery of novel biosurfactants producing microorganisms. Readers will benefit from the inclusion of: * A thorough introduction to the state-of-the-art in biosurfactant technology, techniques, and applications * An exploration of biosurfactant enhanced remediation of sediments contaminated with organics and inorganics * A discussion of perspectives for biomedical and biotechnological applications of biosurfactants * A review of the antiviral, antimicrobial, and antibiofilm potential of biosurfactants against multi-drug-resistant pathogens. * An examination of biosurfactant-inspired control of methicillin-resistant Staphylococcus aureus Perfect for academic researchers and scientists working in the petrochemical industry, pharmaceutical industry, and in the agroindustry, Biosurfactants for a Sustainable Future will also earn a place in the libraries of scientists working in environmental biotechnology, environmental science, and biomedical engineering.

Leseprobe

Biosurfactants for a Sustainable Future

Production and Applications in the Environment and Biomedicine

Edited by

Hemen Sarma

Department of BotanyNanda Nath Saika CollegeTitabar, Assam, India

Majeti Narasimha Vara Prasad

School of Life SciencesUniversity of Hyderabad (an Institution of Eminence)Hyderabad, Telangana, India

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Library of Congress Cataloging‐in‐Publication Data

Names: Sarma, Hemen, editor. | Prasad, Majeti Narasimha Vara editor.Title: Biosurfactants for a sustainable future : production and applications in the environment and biomedicine / Hemen Sarma, Nanda Nath Saika College, Department of Botany, 785630, Titabar, India; Majeti Narasimha Vara Prasad, University of Hyderabad, School of Life Sciences, 500046 Hyderabad, India.Description: Hoboken, NJ : Wiley, 2021. | Includes bibliographical references and index.Identifiers: LCCN 2020051310 (print) | LCCN 2020051311 (ebook) | ISBN 9781119671008 (cloth) | ISBN 9781119671039 (adobe pdf) | ISBN 9781119671053 (epub)Subjects: LCSH: Biosurfactants.Classification: LCC TP248.B57 B565 2021 (print) | LCC TP248.B57 (ebook) | DDC 668/.1–dc23LC record available at https://lccn.loc.gov/2020051310LC ebook record available at https://lccn.loc.gov/2020051311

Cover Design: WileyCover Image: @Kennia Barrantes

List of Contributors

Shashi Bhushan AgrawalDepartment of BotanyInstitute of ScienceBanaras Hindu UniversityVaranasiUttar PradeshIndia

Akil AhmadSchool of Industrial TechnologyUniversiti Sains MalaysiaGelugorPenangMalaysia

Subramania AngaiahElectro‐Materials Research LabCentre for Nanoscience and TechnologyPondicherry UniversityPuducherryIndia

Juan José ArayaEscuela de QuímicaCentro de Investigaciónen Electroquímica yEnergía Química (CELEQ)Universidad de Costa RicaSan JoséCosta Rica

Zarith Asyikin Abdul AzizSchool of Chemical and Energy EngineeringFaculty of EngineeringUniversity Teknologi MalaysiaJohor BahruJohor Malaysia

Kenia BarrantesNutrition and Infection SectionHealth Research InstituteUniversity of Costa RicaSan JoseCosta Rica

Káren Gercyane Oliveira BezerraNortheastern Network of BiotechnologyFederal Rural University of PernambucoRecifePernambucoBrazil

Advanced Institute of Technology and Innovation (IATI)RecifePernambucoBrazil

Catholic University of PernambucoRecifePernambucoBrazil

Siddhartha Narayan BorahRoyal School of BiosciencesRoyal Global UniversityGuwahatiAssam, India

Luz ChacónNutrition and Infection SectionHealth Research InstituteUniversity of Costa RicaSan Jose, Costa Rica

Liang ChengSchool of Environment and SafetyEngineeringJiangsu UniversityZhengjiangChina

Jéssica CorreiaCEB – Centre of Biological EngineeringUniversity of MinhoBragaPortugal

Suresh DekaEnvironmental Biotechnology LaboratoryResource Management and EnvironmentSectionLife Sciences DivisionInstitute of Advanced Study in Science and Technology (IASST)GuwahatiAssamIndia

Santiago de FrutosDepartamento de Química FísicaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

Maribel FarfánDepartment of BiologyHealthcare and the EnvironmentSection of MicrobiologyUniversity of BarcelonaBarcelonaSpain

Francisco FragaDepartamento de Física AplicadaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

S. J. GeethaDepartment of BiologyCollege of ScienceSultan Qaboos UniversityMuscatOman

Madhurankhi GoswamiEnvironmental Biotechnology LaboratoryResource Management and Environment SectionLife Sciences DivisionInstitute of Advanced Study in Science and Technology (IASST)GuwahatiAssamIndia

Eduardo J. GudiñaCEB – Centre of Biological EngineeringUniversity of MinhoBragaPortugal

Sonam GuptaDepartment of BiotechnologyNational Institute of Technology RaipurRaipurChhattisgarhIndia

Gabriel IbarraDepartment of Public Health SciencesCollege of Health SciencesUniversity of Texas at El PasoEl PasoTXUSA

Nazim F. IslamDepartment of BotanyN N Saikia CollegeAssamIndia

Sanket J. JoshiOil & Gas Research CenterCentral Analytical and Applied Research UnitSultan Qaboos UniversityMuscatOman

Aida JoverDepartamento de Química FísicaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

Arun KarnwalDepartment of MicrobiologySchool of Bioengineering and BiosciencesLovely Professional UniversityPhagwaraPunjabIndia

Asma KhatoonCentre of Lipids Engineering and Applied Research (CLEAR)Universiti Teknologi MalaysiaJohor BahruJohorMalaysia

Anand K. KondapiLaboratory for Molecular TherapeuticsDepartment of Biotechnology and BioinformaticsSchool of Life Sciences, University of HyderabadHyderabadIndia

Current address: Department of MicrobiologyImmunology and PathologyColorado State UniversityFort CollinsCOUSA

Fernanda LugoDepartment of Public Health SciencesCollege of Health SciencesUniversity of Texas at El PasoEl PasoTX, USA

Chandana MalakarInstitute of Advanced Study in Science and Technology (IASST)GarchukAssamIndia

Ana María MarquésDepartment of BiologyHealthcare and the EnvironmentSection of MicrobiologyUniversity of BarcelonaBarcelonaSpain

Francisco MeijideDepartamento de Química FísicaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

Monoj Kumar MondalDepartment of Chemical Engineering and TechnologyIndian Institute of Technology (Banaras Hindu University)VaranasiUttar PradeshIndia

Amy R. NavaDepartment of Interdisciplinary Health SciencesCollege of Health SciencesUniversity of TexasEl PasoTX, USA

Kannan PakshirajanDepartment of Biosciences and BioengineeringIndian Institute of Technology GuwahatiGuwahatiAssamIndia

Punniyakotti ParthipanElectro‐Materials Research LabCentre for Nanoscience and TechnologyPondicherry UniversityPuducherryIndia

Yogesh PatilSymbiosis Centre for Research and InnovationSymbiosis International UniversityPune MaharashtraIndia

Lourdes PérezDepartment of Surfactant and NanobiotechnologyIQAC, CSICBarcelonaSpain

Aurora PinazoDepartment of Surfactant and NanobiotechnologyIQAC, CSICBarcelonaSpain

Rolando Procupez‐SchtirbuGeneral ChemistryDepartment of ChemistryUniversity of Costa RicaSan JoseCosta Rica

Vikas PruthiDepartment of BiotechnologyIndian Institute of Technology RoorkeeRoorkeeUttarakhandIndia

Aruliah RajasekarEnvironmental Molecular Microbiology Research LaboratoryDepartment of BiotechnologyThiruvalluvar UniversityVelloreTamilnaduIndia

Ashwini N. RaneDepartment of Environmental ScienceSavitribai Phule Pune UniversityPuneMaharashtraIndia

Selvan RavindranSymbiosis School of Biological SciencesSymbiosis International UniversityPuneMaharashtraIndia

Ana I. RodriguesCEB – Centre of Biological EngineeringUniversity of MinhoBragaPortugal

Lígia R. RodriguesCEB – Centre of Biological EngineeringUniversity of MinhoBragaPortugal

Rashmi Rekha SaikiaDepartment of ZoologyJagannath Barooah CollegeJorhatAssamIndia

Hemen SarmaDepartment of BotanyN N Saikia CollegeTitabarAssamIndia

Leonie Asfora SarubboAdvanced Institute of Technology and Innovation (AITI)RecifePernambucoBrazil

Catholic University of PernambucoRecifePernambucoBrazil

Julio A. SeijasDepartamento de Química OrgánicaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

Suparna SenEnvironmental Biotechnology LaboratoryResource Management and Environment SectionLife Sciences DivisionInstitute of Advanced Study in Science and TechnologyGuwahatiAssamIndia

Siti Hamidah Mohd SetaparSchool of Chemical and Energy EngineeringFaculty of Engineering, Universiti Teknologi MalaysiaJohor BahruJohorMalaysia;

Department of Chemical ProcessesMalaysia‐JapanInternational Institute of TechnologyUniversity Teknologi MalaysiaSkudaiJohorMalaysia

SHE Empire Sdn., Jalan Pulai RiaBandar Baru Kangkar PulaiSkudaiJohorMalaysia

Pooja SinghSymbiosis School of Biological SciencesSymbiosis International UniversityPuneMaharashtraIndia

Victor H. SotoSchool of ChemistryResearch Center in Electrochemistry and Chemical Energy (CELEQ)University of Costa RicaCosta Rica

Shalini SrivastavaDepartment of BotanyInstitute of ScienceBanaras Hindu UniversityVaranasiUttar PradeshIndia

José A. TeixeiraCEB – Centre of Biological EngineeringUniversity of MinhoBragaPortugal

José Vázquez‐TatoDepartamento de Química FísicaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

M. Pilar Vázquez‐TatoDepartamento de Química OrgánicaFacultad de CienciasUniversidad de Santiago de CompostelaLugoSpain

Preface

This book is useful for the petrochemical industry (enhanced oil recovery from sludge), the pharmaceutical industry (developed technology for controlling multidrug‐resistant pathogens), and the agro‐industry (using byproducts), as well as environmental scientists and engineers (developing sustainable remediation technologies). As bioremediation is becoming green and a sustainable approach to environmental pollution control, the articles in this book will be relevant for future research that could benefit our stakeholders. The chapters in this reference book may be a unique collection that has been covered by most of the recent studies and provides systematic material produced by contemporary experts in the field. Focusing on research and development over the last 10 years, the study highlights relevant developments in the field. We hope that this book will support researchers by adding a new dimension to environmental studies and the remediation of emerging pollutants. A further benefit would be the understanding of the processes involved from the production to the sustainable use of biosurfactants in the environment and biomedicine.

This book explains how various methods can be used to recognize and classify microorganism‐producing biosurfactants in the environment. In addition, the various aspects of biosurfactants, including structural characteristics, developments, production, bioeconomics and their sustainable use in the environment, and biomedicine, are addressed. It presents metagenomic strategies to facilitate the discovery of novel biosurfactants (mechanistic understanding and future prospects) for the sustainable remediation of emerging pollutants.

The use of microbes for human well‐being is a prospective challenge, as they have developed novel chemicals and their metabolic pathway could be altered through omics approaches to the production of high‐value chemicals (HVCs), including biosurfactants. These chemicals may be used in sustainable remediation techniques such as the regulation of the antibiotic resistance gene (AGR) and microbe‐enhanced oil recovery (MEOR). We continue to face new and difficult challenges in the restoration of the environment, because current methods of remediation require so many chemicals that have again polluted the environment. There is a need to turn to more efficient alternative approaches and to find environmentally friendly chemicals for sustainability. As a result, the microbial world has the option of offering a replacement for green high‐value chemicals to replace certain hazardous compounds already used in environmental reclamation.

This book opens a window on the rapid development of microbiology sciences by explaining how microbes and their products are used in advanced medical technology and in the sustainable remediation of emerging environmental contaminants. The authors concentrate on the environment as well as the biomedical field and highlight the role of microbes in the real world. This book will be updated to reflect current knowledge, the latest developments in the field of biosurfactants, sustainable remediation applications, and applied medical sciences, and the biotechnological strategies being developed to improve production processes. The most important goal of writing this book will be to communicate current advances and challenges in biosurfactant research. This will allow the reader to understand the dynamics of applied science that underlie microbially derived surfactants, called biosurfactants, and their use in sustainable remediation technology. The basic aim is to include updated content throughout in order to keep pace with this advancing field.

Key features:

Addresses the applications of biosurfactants in sustainable remediation technology, for example, as agents to form emulsions and biofilm formation for desorption of hydrophobic pollutants.

Discusses the current state of understanding of the different microbial surfactants, their classifications, properties, how to achieve higher yields, and new applications.

There is a substantial research result on biosurfactants that envisages our capacity to build a consolidated framework for further development of applications. Biosurfactants for sustainable remediation technology should fill this need, covering the latest trend on biosurfactant research and their applications.

The book was contributed by 56 authors from leading surfactants research groups from Brazil, Costa Rica, China, India, Malaysia, Oman, Portugal, Spain, and the United States, comprising 22 chapters.

Introduction to Biosurfactants

Metagenomics Approach for Selection of Biosurfactant Producing Bacteria from Oil Contaminated Soils: An Insight into Its Technology

Biosurfactant Production Using Bioreactors from Industrial Byproducts

Biosurfactants for Heavy Metal Remediation and Bioeconomics

Application of Biosurfactants for Microbial Enhanced Oil Recovery (MEOR)

Biosurfactant Enhanced Sustainable Remediation of Petroleum Contaminated Soil

Microbial Surfactants Are Next‐Generation Biomolecules for Sustainable Remediation of Polyaromatic Hydrocarbons

Biosurfactants for Enhanced Bioavailability of Micronutrients in Soil: A Sustainable Approach

Biosurfactants: Production and Role in Synthesis of Nanoparticles for Environmental Applications

Green Surfactants: Production, Properties, and Application in Advanced Medical Technologies

Antiviral, Antimicrobial, and Antibiofilm Properties of Biosurfactants: Sustainable Use in Food and Pharmaceuticals

Biosurfactant‐Based Antibiofilm Nano Materials

Biosurfactants from Bacteria and Fungi: Perspectives on Advanced Biomedical Applications

Biosurfactant‐Inspired Control of Methicillin‐Resistant

Staphylococcus aureus

(MRSA)

Exploiting the Significance of Biosurfactant for the Treatment of Multidrug‐Resistant Pathogenic Infections

Biosurfactants Against Drug‐Resistant Human and Plant Pathogens: Recent Advances

Surfactant‐ and Biosurfactant‐based Therapeutics: Structures, Properties, and Recent Developments in Drug Delivery and Therapeutic Applications

The Potential Use of Biosurfactants in Cosmetics and Dermatological Products: Current Trends and Future Prospects

Cosmeceutical Applications of Biosurfactants: Challenges and Perspectives

Biotechnologically Derived Bioactive Molecules for Skin and Hair‐Care Application

Biosurfactants as Biocontrol Agents Against Mycotoxigenic Fungi

Biosurfactant‐Mediated Biocontrol of Pathogenic Microbes of Crop Plants

The book explores how these twenty‐first century multifunctional biomolecules improve or replace chemically synthesized surface‐active agents with the aid of the industrial application of biosurfactant production based on renewable resources. This book is also useful for scholars, academicians in bioengineering and biomedical sciences, undergraduate and graduate students in microbiology, environmental biotechnology, health, clinical, and pharmaceutical sciences.

1Introduction to Biosurfactants

José Vázquez Tato1, Julio A. Seijas2, M. Pilar Vázquez‐Tato2, Francisco Meijide1, Santiago de Frutos1, Aida Jover1, Francisco Fraga3, and Victor H. Soto4

1 Departamento de Química Física, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda, Lugo, Spain

2 Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda, Lugo, Spain

3 Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda, Lugo, Spain

4 Escuela de Química, Centro de Investigación en Electroquímica y Energía Química (CELEQ), Universidad de Costa Rica, San José, Costa Rica

CHAPTER MENU

1.1 Introduction and Historical Perspective

1.2 Micelle Formation

1.3 Average Aggregation Numbers

1.4 Packing Properties of Amphiphiles

1.5 Biosurfactants

1.6 Sophorolipids

1.7 Surfactin

1.8 Final Comments

Acknowledgement

References

1.1 Introduction and Historical Perspective

Surface tension is a property that involves the common frontier (boundary surface) between two media or phases. Strictly speaking, the surface tension of a liquid should mean the surface tension of the liquid in contact and equilibrium with its own vapor. However, as the gas phase has normally a small influence on the surface, the term is generally applied to the liquid–air boundary. The phases can also be two liquids (interfacial tension) or a liquid and solid. According to IUPAC, the surface tension is the work required to increase a surface area divided by that area [1]. This is the reversible work required to carry the molecules or ions from the bulk phase into the surface implying its enlargement and corresponds to the increase in Gibbs free energy (G) of the system per unit surface area (A),

(1.1)

where γ is the interfacial tension. Therefore, the units of γ are J/m2 or N/m, but it is normally recorded in mN/m (because it coincides with the value in dyn/cm of the cgs system). In 1944, Taylor and Alexander [2] collected some representative published (1885–1939) values for the surface tension of water at 20 °C. Their own value was 72.70 ± 0.07 mN/m (calculated by extrapolation) in agreement with more recent determinations, the accepted value being 71.99 ± 0.36 mN/m at 25 °C [3]. This is a rather high value when it is compared with those of other common solvents as ethanol (22.39 ± 0.06 mN/m), acetic acid (27.59 ± 0.09 mN/m), or acetone (29.26 ± 0.05 mN/m) (values from [4]) at 20 °C.

The decrease in the surface tension of water has been traditionally achieved by using soaps or soap‐like compounds. According to IUPAC a “soap is a salt of a fatty acid, saturated or unsaturated, containing at least eight carbon atoms or a mixture of such salts. A neat soap is a lamellar structure containing much (e.g. 75%) soap and little (e.g. 25%) water. Soaps have the property of reducing the surface tension of water when they are dissolved in soap‐like compounds in water.” This reduction facilitates personal care, washing of clothes and other fabrics, etc. The early documents with descriptions of soaps and their uses are typically related with medicinal aspects, and nowadays there is almost a specific type of soap for each requirement. Levey [5] has reviewed the early history of “soaps” used in medicine, cleansing, and personal care. For instance, he mentions that “in a prescription of the seventh century BC, soap made from castor oil (source of ricinoleic [12‐hydroxy‐9‐cis‐octadecenoic] acid) and horned alkali is used… as a mouth cleanser, in enemata, and also to wash the head.” However, Levey concludes that a true soap using caustic alkali was probably not produced in antiquity but “evidence has been adduced to indicate that salting out was in use in early Sumerian times.” In his Naturalis Historia, Pliny the Elder [6] refers to soap (sapo) as prodest et sapo, Galliarum hoc inventum rutilandis capillis. fit ex sebo et cinere, optimus fagino et caprino, duobus modis, spissus ac liquidus, uterque apud Germanos maiore in usu viris quam feminis, which may be translated as “There is also soap, an invention of the Gauls for making their hair shiny (or glossy). It is made from suet and ashes, the best from beechwood ash and goat suet, and exists in two forms, thick and liquid, both being used among the Germans, more by men than by women.”

Hunt [7] indicates that centers of soap production by the end of the first millennium were in Marseilles (France) and Savona (Italy), while in Britain some references appear in the literature around 1000 AD. For instance, in 1192 the monk Richard of Devizes referred to the number of “soap makers in Bristol and the unpleasant smells which their activities produced.” Hunt also resumed other aspects as the chemistry of soap, the British alkali industry, the expansion of soap production, soap manufacturers, and manufacturing methods. As early as 1858, Campbell presented a USA patent [8] for the production of soaps. He described the process as consisting in “the use of powdered carbonate of soda for saponifying the fatty acids generally, and more particularly the red oil or ‘red (oleic) acid oil’ and converting them, by direct combination, into soap in open pans or kettles, at temperatures between 32 and 500 °F.” Mitchell [9] revised the Jabón de Castilla or Castile soap (named from the central region of Spain), probably the first white hard soap. It was an olive oil‐based soap and soaps with this name can still be bought today. Traditional recipes and videos can be easily found on the Internet. In the paper “Literature of Soaps and Synthetic Detergents”, Schulze [10] recorded the literature (including books, periodicals, abstracts, indexes, information services, patent publications, association publications, conference proceedings) on soaps, surfactants, and synthetic detergents up to 1966.

Nowadays descriptions for soap‐making from fats and oils are frequent for teaching purposes. For instance, Phanstiel et al. [11] have described the saponification process (basic hydrolysis of fats). It involves heating either animal fat or vegetable oil in an alkaline solution. The alkaline solution hydrolyses the triglyceride into glycerol and salts of the long‐chain carboxylic acids (Scheme 1.1).

Scheme 1.1 Alkaline hydrolysis of a triglyceride to obtain soaps.

To overcome the shortcomings of the carboxylic group of soaps, during the first decades of the twentieth century, new surface‐active agents were obtained in chemistry laboratories. Kastens and Ayo [12] and Kosswig [13] reviewed the main achievements of these decades. The first result of this search was Nekal, an alkyl naphthalene sulfonate, although it probably was a mixture of various homologs [14]. Other pioneer compounds were Avirol series (sulfuric acid esters of butyl ricinoleic acid), Igepon A series (fatty acid esters of hydroxyethanesulfonic acid), Igepon T series (amide‐derivatives of taurine). All these products represented different approaches to the elimination of the carboxylic group of soaps. IUPAC defines a surfactant as a substance that lowers the surface tension of the medium in which it is dissolved and/or the interfacial tension with other phases, and, accordingly, is positively adsorbed at the liquid/vapor and/or at other interfaces. By detergent, IUPAC refers to a surfactant (or a mixture containing one or more surfactants) having cleaning properties in dilute solutions. Thus, soaps are surfactants and detergents.

It is not easy to whom the use of the word surfactant should be ascribed for the first time. A search in SciFinder® suggests that the word was first used by Bellon and LeTellier in a French patent (1943) [15]. The SciFinder abstract of this patent indicates that “Surfactants such as wetting agents, detergents, emulsifiers, and stickers are prepared by treating by‐product materials containing starches, cellulose, amino acids, and smaller quantities of inedible fats with NaOH and neutralizing the reaction product.”

Because of their physicochemical properties, surfactants have found applications in almost any kind of industry. A list of the relevant ISO and DIN regulations for a utility evaluation of surfactants has been provided by Kosswig [13]. For instance, in 1950 Lucas and Brown [16] measured the wetting power of 13 surfactants to find a wetting agent that would enable sulfuric acid to wet peaches quickly and uniformly so as to permit acid peeling. Anionic, cationic, and neutral surfactants were tested. In the Application Guide appendix of the book Chemistry and Technology of Surfactants[17] there is a list that illustrates the variety of surfactants and their versatility in a wide range of applications. Among others the following are mentioned: Agrochemical formulations, Civil engineering, Cosmetics and toiletries, Detergents, Household products, Miscellaneous industrial applications, Leather, Metal and engineering, Paints, inks, coatings, and adhesives, Paper and pulp, Petroleum and oil, Plastics, rubber, and resins, and Textiles and fibers. For instance, their wetting properties have been early used in food technology. We have already mentioned the early connection of soap and medicine and correspondingly the use of surfactants in pharmacy in the formulation (as emulsifying agents, solubilizers, dispersants, for suspensions) and as wetting agents, which cannot be a surprise [18]. Nursing care makes a continuous use of surface‐active agents.

The soaps of Scheme 1.1 show the most important structural characteristic of surfactants: the coexistence of one lyophilic group (alkyl chain) and one lyophobic group (carboxylate ion). In aqueous solutions, it is more frequent to use the terms hydrophilic and hydrophobic. A graphical representation head–tail (hydrophobic group–hydrophilic group) is widely used, the alkyl chain being the tail and the carboxylate group the head (Figure 1.1). This structure gives the amphiphile character to surfactant compounds.

Figure 1.1 Schematic representation of the structure of some surfactants.

More generally, the head can be any polar group and the tail any apolar group, leading to a wide range of structures and types of surfactants. Among anionic heads, typical groups are carboxylate, sulfate, sulfonate, and phosphate, while the most frequent counterions are monovalent and divalent cations. Polycharged heads are also common, EDTA derivatives being well‐known examples [19]. Cyclopeptides constitute another important group [20]. Among cationic heads, typical groups are tetralkylammonium, N,N‐dialkylimidazolinium and N‐alkylpyridinium ions, while chloride and bromide are the most common counterions. Among neutral heads, polyethylene glycol ethers, polyglycol ethers, and carbohydrates can be mentioned. Zwitterionic heads are very important as phospholipids belong to this group, as well as sulfobetaines and trialkylamine oxides. Many examples can be found elsewhere [13].

However, the structures of surfactants may be more complex than the head–tail model suggests. For instance, the number of polar and non‐polar groups can be higher than one, the phospholipid phosphatidylcholine with two alkyl–allyl chains and a zwitterion as the head being an example. Gemini surfactants are dimeric surfactants [21] carrying two charged groups and two alkyl groups. The two amphiphilic moieties are connected at the level of the head groups, which are separated by a spacer group. They are characterized by critical micelle concentrations that are one to two orders of magnitude lower than those corresponding to conventional (monomeric) surfactants [22].

Bolaamphiphilic molecules contain a hydrophobic skeleton (e.g. one, two, or three alkyl chains, a steroid, or a porphyrin) and two water‐soluble groups on both ends [23]. They can be symmetric or asymmetric [24, 25]. Recent examples of bolaamphiphilic, Y‐shaped and divalent surfactants have been published by Baccile et al. [26] (Figure 1.1).

Some surfactants, instead of the mentioned head–tail structure, present a bifacial polarity with the hydrophilic and hydrophobic characteristics at two opposite sides of the molecule. The best‐known examples are bile salts (see Figure 1.2) [27, 28]. Many membrane‐active compounds are facial amphiphiles including cationic peptide antibiotics [29]. The facial amphiphilic conformation adopted by these peptides is a consequence of their secondary and tertiary structures, allowing that one face of the molecule presents cationic groups (protonated amines or guanidines) and the other face contains hydrophobic groups. An example may be magainin I [30]. Among other surfactant structures, diblock copolymers and polymeric surfactants, fluorosurfactants and silicone‐based surfactants can be mentioned [13].

Figure 1.2 Bifacial structure of cholic acid.

1.2 Micelle Formation

The necessity of a quantitative measurement of the surface tension of soap solutions was soon evident. By the time that I. Traube published his earliest paper in 1884, significant theories of capillarity from La Place, Poisson, or Gauss were known [31]. Early measurements of the surface tension only imply inorganic salts, acids, and bases. In 1864 Guthrie [32, 33] measured some organic liquids. At the same time, Musculus [34] studied the capillarity of aqueous solution of alcohol observing that “the capillarity of the water decreases considerably with the addition of the least amount of alcohol, in the beginning, much faster than in the presence of more alcohol.” He also noticed that “all derivatives of ethyl alcohol which are soluble in water (as acetic acid) behave like this, and probably this is also the case with the other alcohols,” but substances such as “sugars, and salts if they are not present in a great amount, almost do not influence the capillarity of water.” He proposed the use of capillarity for measuring the concentration of alcohol and acetic acid in water, among other reasons, because “it offers the advantage that one needs only very little fluid for analysis, one drop being enough.” He continued that, as “the animal fluids, such as blood serum, urine, have a capillarity which is equal to that of water, it is possible to detect and quantify substances in the urine,” making reference, for instance, to bile.

Traube started the measurement of the influence of many organic substances on the surface tension of water in the period 1884–1885 [31] and observed that “the surface tension of capillary‐active compounds belonging to one homologous series decreased with each additional CH2 group in a constant ratio which is approximately 3:1,” leading him to propose Traube's Rule.

A nice historical paper was published by Traube [31] in 1940, in which he mentioned previous works related to the investigation of aqueous solutions of inorganic salts, acids, and bases, employing the method of capillary tubes, and, particularly, the dropping method applied by Quinke. Traube developed this method and designed a simple instrument, the stalagmometer – together with the stagonometer – which found general application in science and industry. In the mentioned paper, Traube refers mainly to his publications that appeared in the period 1886–1887. By 1906, the measurement of the surface tension by the capillary rise was so important that it was included in the book Practical Physical Chemistry by A. Findlay. The use of Traube's stalagmometer for such a purpose was proposed in the 3rd edition of the book, published in 1915. The experiment is still proposed in recent textbooks on practical Physical Chemistry [35].

Seventeen of the more important methods of measuring surface tension were described in 1926 by Dorsey [36]. According to his own words, “The list of references does not pretend to be complete but is intended merely to direct the reader to one or more of the sources from which the required information can be obtained most satisfactorily.” Even so, the number of cited papers was greater than 110, while the number of citations corresponding to the nineteenth century was 63 (56%). Eminent scientists such as Bohr, Rayleigh, Thomson, Kelvin, Maxwell, Laplace, and Poisson were among them. Tate [37] published his famous law in 1864 and Wilhelmy in 1863.

Even at low concentrations, surfactants reduce the surface tension of water due to its tendency to migrate toward the air–water interface, forming a monolayer. This was first suggested in 1907 by Milner [38] and, previously, Marangoni in 1871 “suggested that this capability [local variation in the tension of its surface] is due to the presence on the surface of the film of a pellicle, composed of matter having a smaller capillary tension than that of water.” Milner clearly established that “in several organic solutions the surface tension is less than that of water, and there is consequently an excess of solute in the surface.” Later, Langmuir [39] indicated that “the ‐COOH, ‐CO, and –OH groups have more affinity for water than for hydrocarbons… [and] when an oil is placed on water, the –COO– groups combine with the water, while the hydrocarbon chains remain combined with each other.” In other words, the tail of a surfactant (the hydrocarbon chain) must be located at the air interface, with the tail upwards oriented and the head (hydrophilic groups) at the water interface.

Rising the surfactant concentration, the surface concentration increases as well until the full coverage of the interface by the molecules or ions. If the interface is completely covered, further increment of the surfactant concentration does not (almost) modify the surface tension. Furthermore, the additional surfactant molecules (or ions) have to remain in the bulk solution, and following Langmuir “hydrocarbon chains remain combined with each other, thus forming micelles” (or other aggregates).

The term micelle was commonly used by the first years of the twentieth century [40, 41] in relation to colloid solutions (frequently inorganic gels). In 1920 McBain and Salmon [42] (see also [43]) described a brief résumé of previous work, citing, for instance, Krafft's work. From the summary of this paper we extract the following sentences:

3. These colloidal electrolytes are salts in which one of the ions has been replaced by an ionic micelle.

5. This is exemplified by any one of the higher soaps simply on change of concentration. Thus, in concentrated solution there is little else present than colloid plus cation, whereas in dilute solution both undissociated and dissociated soap are crystalloids of simple molecular weight.

8. The ionic micelle in the case of soaps exhibits an equivalent conductivity quite equal to that of potassium ion. Its formula may correspond to

but more probably it is

, where

P

−

is the anion of the fatty acid in question.

Therefore, the essential definition of the present concept of a micelle was established. IUPAC indicates that “Surfactants in solution are often association colloids, that is, they tend to form aggregates of colloidal dimensions, which exist in equilibrium with the molecules or ions from which they are formed. Such aggregates are termed micelles.”

In 1922, McBain and Jenkins [44] studied solutions of sodium oleate and potassium laurate by ultrafiltration, using this technique for separating the ionic micelle from the neutral colloid. For both surfactants they showed that the proportion (simple potassium laurate or sodium oleate)/(ionic micelle) increases fast at low concentrations and reached a plateau at high concentrations (see graphs of the paper). They also concluded that the diameter of the ionic micelle is only a few times the length of the molecule and “the particles of sodium oleate are about ten times larger than those of potassium laurate.”

By the end of the twenties and the beginning of thirties of the twentieth century, the research activity on micelle‐forming substances experienced an extraordinary blooming spring. The paper by Grindley and Bury [45] is a landmark on the subject, being particularly illustrative for the purposes of this review. They represented the formation of micelles by butyric acid in solution by the equation

(1.2)

where n is “the number of simple molecules in a micelle” or aggregation number (which is a relatively large number) and write the equilibrium constant as

(1.3)

where s and m are the concentrations of butyric acid as monomers and as micelles, respectively. The previous equation can be written as

(1.4)

from which they deduced that if s/K is appreciably smaller than unity, the concentration of micelles will be negligible. Only when s approaches the value K does the concentration of micelles become appreciable, and “will rapidly increase as the total concentration increases.” From this analysis they conclude that “if any physical property of aqueous butyric acid solutions be plotted against the concentration, the slope of the curve will change abruptly near this point.” A few months later, Davies and Bury [46] named that concentration as the critical concentration for micelles.

Previous analysis constitutes the basis of all experimental techniques so far used for determining the critical concentration for micelles (from here cmc). For instance, the association of monomers in micelles reduces the number of particles in the solution and, consequently, colligative properties (freezing point, vapor pressure…) also drastically change at this concentration. Other properties such as solubilization of solutes as dyes or the conductivity of the solution also change significantly. As an example, we shall mention the paper by Powney and Addison [47] who measured the surface tension of aqueous solutions of sodium dodecyl, tetradecyl, hexadecyl, and octadecyl sulfates and plotted the results in the form of vs log (concentration), as we do nowadays. The curves showed breaks at critical concentrations, which correspond to transitions from single ions to micelles, these single ions constituting the surface‐active species. Figure 1.3