Comparative study of surface-active properties and antimicrobial activities of disaccharide monoesters

Sugar-Based Monoester Surfactants: Synthetic Methodologies, Properties, and Biological Activities

Glycolipids are biocompatible and biodegradable amphiphilic compounds characterized by a great scientific interest for their potential applications in various technological areas, including pharmaceuticals, cosmetics, agriculture, and food production. This report summarizes the available synthetic methodologies, physicochemical properties, and biological activity of sugar fatty acid ester surfactants, with a particular focus on 6-O-glucose, 6-O-mannose, 6-O-sucrose, and 6'-O-lactose ones. In detail, the synthetic approaches to this class of compounds, such as enzymatic lipase-catalyzed and traditional chemical (e.g., acyl chloride, Steglich, Mitsunobu) esterifications, are reported. Moreover, aspects related to the surface activity of these amphiphiles, such as their ability to decrease surface tension, critical micelle concentration, and emulsifying and foaming ability, are described. Biological applications with a focus on the permeability-enhancing effect across the skin or mucosa, antimicrobial and antifungal activities, as well as antibiofilm properties, are also presented. The information reported here on sugar-based ester surfactants is helpful to broaden the interest and the possible innovative applications of this class of amphiphiles in different technological fields in the future.

The useful biological properties of sucrose esters: Opportunities for the development of new functional foods

Sucrose esters have been deployed as surfactants in many food products since the 1950s. In addition to their useful physical characteristics, sucrose esters also have interesting biological properties that enhance their utility. This review critically examines the broad suite of biological activities that has been attributed to both synthetically-derived and naturally-occurring sucrose esters. These include insecticidal, molluscicidal, plant growth-regulating, anti-microbial, anti-tumor, anti-oxidant, anti-depressive, neuro-protective, anti-inflammatory and anti-plasmodial effects. In addition to providing a summary of the structure-activity profiles of sucrose esters, the various known mechanisms-of action of these compounds are also discussed. Furthermore, since sucrose esters are well-known surfactants, the potential to advantageously apply their industrially desirable physical characteristics in combination with their biological properties is considered. Recent advances in synthetic chemistry that have facilitated the deployment of biologically active sucrose esters as food additives are also described.

Interactions of Surfactants with the Bacterial Cell Wall and Inner Membrane: Revealing the Link between Aggregation and Antimicrobial Activity

Surfactants with their intrinsic ability to solubilize lipid membranes are widely used as antibacterial agents, and their interactions with the bacterial cell envelope are complicated by their differential aggregation tendencies. We present a combined experimental and molecular dynamics investigation to unravel the molecular basis for the superior antimicrobial activity and faster kill kinetics of shorter-chain fatty acid surfactant, laurate, when compared with the longer-chain surfactants studied in contact time assays with live Escherichia coli (E. coli). From all-atom molecular dynamics simulations, translocation events across peptidoglycan were the highest for laurate followed by sodium dodecyl sulfate, myristate, palmitate, oleate, and stearate. The translocation kinetics were positively correlated with the critical micellar concentration, which determined the free monomer surfactant concentration available for translocation across peptidoglycan. Interestingly, aggregates showed a lower propensity to translocate across the peptidoglycan layer and longer translocation times were observed for oleate, thereby revealing an intrinsic sieving property of the bacterial cell wall. Molecular dynamics simulations with surfactant-incorporated bacterial inner membranes revealed the greatest hydrophobic mismatch and membrane thinning in the presence of laurate when compared with the other surfactants. The enhanced antimicrobial efficacy of laurate over oleate was further verified by experiments with giant unilamellar vesicles, and electroporation molecular dynamics simulations revealed greater inner membrane poration tendency in the presence of laurate when compared with the longer-chain surfactants. Our study provides molecular insights into surfactant translocation across peptidoglycan and chain length-induced structural disruption of the inner membrane, which correlate with contact time kill efficacies observed as a function of chain length with E. coli. The insights gained from our study uncover unexplored barrier properties of the bacterial cell envelope to rationalize the development of antimicrobial formulations and therapeutics.

Emulsion Properties during Microencapsulation of Cannabis Oil Based on Protein and Sucrose Esters as Emulsifiers: Stability and Rheological Behavior

The effects of different emulsifiers, such as soy protein isolate-sucrose ester (SPI-SE) and whey protein isolate-sucrose ester (WPI-SE), on the properties of the emulsion during the microencapsulation of cannabis oil were studied. The influence of SE concentration on the emulsion properties of the two emulsifying systems was analyzed. The results of the adsorption kinetics show that SE can decrease the interfacial tension, particle size and zeta potential of the emulsions. The results of the interfacial protein concentration show that SE could competitively replace the protein at the oil-water interface and change the strength of the interfacial film. The results of the viscoelastic properties show that the emulsion structure of the two emulsion systems results in the maximum value when the concentration of SE is 0.75% (w/v), and the elastic modulus (G') of the emulsion prepared with SPI-SE is high. The viscosity results show that all emulsions show shear-thinning behavior and the curve fits well with the Ostwald-Dewaele model. The addition of SE in the emulsions of the two emulsion systems can effectively stabilize the emulsion and change the composition and strength of the oil-water interface of the emulsion. The cannabis oil microcapsules prepared with protein-SE as an emulsion system exhibit high quality.

Synthesis and characterization of a lactose-based biosurfactant by a novel nanodendritic catalyst and evaluating its efficacy as an emulsifier in a food emulsion system

Nonionic lactose fatty acid esters are a class of synthetic biosurfactants with various uses in the food, pharmaceutical, personal care, and cosmetic industries. The objective of this research was the preparation and full characterization of a series of novel metallic encapsulated magnetic core/dendrimer shell composites as catalysts (CoII/MnII G2.0L1/2@SCMBNP) and their use in the chemo- and regioselective synthesis of a biosurfactant for the first time. Surface-active properties (such as contact angle (CA), surface tension (SFT), interfacial tension (IFT), critical micelle concentration (CMC), hydrophilic-lipophilic balance (HLB), foamability (FA) & foam stability (FS), emulsion ability (EmA) & emulsion stability (EmS), surface excess (Γ) and free energy of adsorption (ΔG) were also determined for all synthesized biosurfactants. In comparison to other works, these results suggested that the synthesized lactose fatty acid esters have potential application as synthetic emulsifiers featuring surface properties and are comparable with Ryoto sugar ester L-1695 (sucrose laurate) & Tween-20 (polysorbate 20) as industrial emulsifiers. The optimized conditions for biosurfactant syntheses are 8 days at 2 : 1 molar ratio of lactose sugar to lauric acid at 50 °C. Lactose ester as a biosurfactant exhibited a decrease of SFT & IFT and was able to stabilize a 20% soybean O/W emulsion. Furthermore, high conversion & yield, excellent chemo- and regioselectivity, and high operational stability over 5 runs were achieved for CoII/MnII-G2.0L1/2@SCMBNP, indicating the suitable efficiency of the catalytic process.

Enzymatic Glycerolysis of Palm Kernel Olein-Stearin Blend for Monolaurin Synthesis as an Emulsifier and Antibacterial

Monolaurin is a monoacylglycerol, which can act as an emulsifier and antibacterial. Palm kernel oil is a monolaurin raw material that can be fractionated into palm kernel olein (PKOo) and palm kernel stearin (PKS). Therefore, this study prepares monolaurin through enzymatic glycerolysis of the PKOo-PKS blend. The effects of enzyme concentration, molar ratio of oil to glycerol, solvent to oil ratio, and reaction temperature on the products of glycerolysis were investigated. The best conditions were selected for further production, purification, and characterization of the monolaurin. The results showed that the best glycerolysis condition was obtained with an enzyme concentration of 10% w/w, an oil–glycerol molar ratio of 1:4, a solvent–oil ratio of 2:1 v/w, and a glycerolysis temperature of 40 °C with a stirring speed of 600 rpm based on the monoacylglycerol (MAG) concentration. The identification of the sample with FTIR and NMR indicated that the purified glycerolysis product is the monolaurin. The thermal analysis showed a large endothermic peak with a melting point of 35.56 °C. The purified monolaurin has a HLB value of 5.92, and an emulsion capacity and stability of 93.66 ± 1.85% and 89.54 ± 3.36%, respectively. The minimum inhibitory concentration (MIC) of the monolaurin for Escherichia coli FNCC 0091 and Staphylococcus aureus FNCC 0047 were at 500 ppm, and 100 ppm for Bacillus subtilis FNCC 0060.

Enzymatic Production of Lauroyl and Stearoyl Monoesters of d-Xylose, l-Arabinose, and d-Glucose as Potential Lignocellulosic-Derived Products, and Their Evaluation as Antimicrobial Agents

Forestry and agricultural industries constitute highly relevant economic activities globally. They generate large amounts of residues rich in lignocellulose that have the potential to be valorized and used in different industrial processes. Producing renewable fuels and high-value-added compounds from lignocellulosic biomass is a key aspect of sustainable strategies and is central to the biorefinery concept. In this study, the use of biomass-derived monosaccharides for the enzymatic synthesis of sugar fatty acid esters (SFAEs) with antimicrobial activity was investigated to valorize these agro-industrial residues. With the aim to evaluate if lignocellulosic monosaccharides could be substrates for the synthesis of SFAEs, d-xylose, l-arabinose, and d-glucose, lauroyl and stearoyl monoesters were synthetized by transesterification reactions catalyzed by Lipozyme RM IM as biocatalyst. The reactions were performed using commercial d-xylose, l-arabinose, and d-glucose separately as substrates, and a 74:13:13 mixture of these sugars. The proportion of monosaccharides in the latter mixture corresponds to the composition found in hemicellulose from sugarcane bagasse and switchgrass, as previously described in the literature. Products were characterized using nuclear magnetic resonance (NMR) spectroscopy and showed that only the primary hydroxyl group of these monosaccharides is involved in the esterification reaction. Antimicrobial activity assay using several microorganisms showed that 5-O-lauroyl-d-xylofuranose and 5-O-lauroyl-l-arabinofuranose have the ability to inhibit the growth of Gram-positive bacteria separately and in the products mix. Furthermore, 5-O-lauroyl-l-arabinofuranose was the only product that exhibited activity against Candida albicans yeast, and the four tested filamentous fungi. These results suggest that sugar fatty acid esters obtained from sustainable and renewable resources and produced by green methods are promising antimicrobial agents.

Synthesis and Biological Characterization of the New Glycolipid Lactose Undecylenate (URB1418)

As a follow-up to our previous studies on glycolipid surfactants, a new molecule, that is lactose 6′-O-undecylenate (URB1418), was investigated. To this end, a practical synthesis and studies aimed at exploring its specific properties were carried out. URB1418 showed antifungal activities against Trichophyton rubrum F2 and Candida albicans ATCC 10231 (MIC 512 μg/mL) and no significant antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa. At the same time, it presented anti-inflammatory properties, as documented by the dose-dependent reduction in LPS-induced NO release in RAW 264.7 cells, while a low antioxidant capacity in the range of concentrations tested (EC50 > 200 µM) was also observed. Moreover, URB1418 offers the advantage of being more stable than the reference polyunsaturated lactose esters and of being synthesized using a “green” procedure, involving an enzymatic method, high yield and low manufacturing cost. For all these reasons and the absence of toxicity (HaCaT cells), the new glycolipid presented herein could be considered an interesting compound for applications in various fields.

New, Biocompatible, Chitosan-Gelled Microemulsions Based on Essential Oils and Sucrose Esters as Nanocarriers for Topical Delivery of Fluconazole

Biocompatible gel microemulsions containing natural origin excipients are promising nanocarrier systems for the safe and effective topical application of hydrophobic drugs, including antifungals. Recently, to improve fluconazole skin permeation, tolerability and therapeutic efficacy, we developed topical biocompatible microemulsions based on cinnamon, oregano or clove essential oil (CIN, ORG or CLV) as the oil phase and sucrose laurate (D1216) or sucrose palmitate (D1616) as surfactants, excipients also possessing intrinsic antifungal activity. To follow up this research, this study aimed to improve the adhesiveness of respective fluconazole microemulsions using chitosan (a biopolymer with intrinsic antifungal activity) as gellator and to evaluate the formulation variables' effect (composition and concentration of essential oil, sucrose ester structure) on the gel microemulsions' (MEGELs) properties. All MEGELs were evaluated for drug content, pH, rheological behavior, viscosity, spreadability, in vitro drug release and skin permeation and antifungal activity. The results showed that formulation variables determined distinctive changes in the MEGELs' properties, which were nevertheless in accordance with official requirements for semisolid preparations. The highest flux and release rate values and large diameters of the fungal growth inhibition zone were produced by formulations MEGEL-FZ-D1616-CIN 10%, MEGEL-FZ-D1216-CIN 10% and MEGEL-FZ-D1616-ORG 10%. In conclusion, these MEGELs were demonstrated to be effective platforms for fluconazole topical delivery.

6'-O-Lactose Ester Surfactants as an Innovative Opportunity in the Pharmaceutical Field: From Synthetic Methods to Biological Applications

Glycolipid surfactants are biocompatible and biodegradable compounds characterized by potential applications in various sectors including pharmaceuticals, cosmetics, agriculture, and food production. A specific overview regarding synthetic methodologies and properties of 6′-lactose-based surfactants is presented herein, particularly all the synthetic approaches to this class of lactose esters, such as enzymatic and traditional organic syntheses. Moreover, detailed descriptions of physicochemical data and biocompatibility properties of these molecules, that is, surface tension, critical micelle concentration, emulsifying ability, foaming, particle size distribution, biocompatibility, and safety, are described. Biological applications with a focus on permeability enhancing, antimicrobial activity, and antibiofilm properties of 6′-lactose-based esters are also reported.

Interactions between poloxamer, PEOx-PPOy-PEOx, and non-ionic surfactant, sucrose monolaurate: A study on potential allergenic effect using model phospholipid membrane

Sugar-based surfactants are involved in skin related allergy cases in the past decade. Skin irritation starts with the interaction of the surfactant with the skin lipids leading to lipid emulsification and eventual barrier damage. Polymers or co-surfactants can be used to mitigate the allergenic effect but the mechanism of formulation mildness on skin remains unclear. We have used the quartz crystal microbalance (QCM) together with dissipative particle dynamics (DPD) simulation, small angle x-ray scattering (SAXS) as well as cell viability tests to decipher the interactions between poloxamers and sucrose monolaurate (SML), and how these interactions could prevent the disruption of a model supported phospholipid bilayer (SLB). Poloxamer addition to the SML solution can delay or totally prevent the disruption of the SLB depending on poloxamer type and concentration. Poloxamer P407 (Pluronic® F127) delays the onset of disruption while poloxamer P188 (Pluronic® F68) does not preserve the bilayer integrity even at high concentration of up to 15% w/w. Preservation of the SLB is likely due to the differences in the aggregates formation between SML-F127 and SML-F68 mixtures with corresponding retarded motion of SML micelles through the SML-F127 polymer matrix that improved cell viability.

Sustainable Production of Glycolipids by Biocatalyst on Renewable Deep Eutectic Solvents

Glycolipids have become an ecofriendly alternative to chemically obtained surfactants, mainly for the cosmetic, pharmaceutical, and food industries. However, the sustainable production of these compounds is still challenging, because: (i) water is a recognized inhibitor, (ii) multiphases make the use of cosolvent reaction medium necessary, and (iii) there are difficulties in finding a source for both starting materials. This study used sugars and lipids from peach palm fruit shells or model compounds as substrates to synthesize glycolipids on five different renewable deep eutectic solvents (Re-DES) alone or with a cosolvent system. Substrate conversions up to 24.84% (so far, the highest reported for this reaction on DES), showing (1) the non-precipitation of glucose in the solvent, (2) emulsification and (3) low viscosity (e.g., more favorable mass transfer) as the main limiting factors for these heterogeneous enzymatic processes. The resulting conversion was reached using a cosolvent system Re-DES:DMSO:t-butanol that was robust enough to allow conversions in the range 19–25%, using either model compounds or sugar and fatty acid extracts, with free or immobilized enzymes. Finally, the characterization of the in-house synthesized glycolipids by surface tension demonstrated their potential as biosurfactants, for instance, as an alternative to alcohol ethoxylates, industrially produced using less sustainable methods.

A novel strategy to fabricate stable oil foams with sucrose ester surfactant

HYPOTHESIS

Can a mixture of sucrose ester surfactant in vegetable oil be aerated to yield stable oleofoams? Is foaming achievable from one-phase molecular solutions and/or two-phase crystal dispersions? Does cooling a foam after formation induce surfactant crystallisation and enhance foam stability?

EXPERIMENTS

Concentrating on extra virgin olive oil, we first study the effect of aeration temperature and surfactant concentration on foamability and foam stability of mixtures cooled from a one-phase oil solution. Based on this, we introduce a strategy to increase foam stability by rapidly cooling foam prepared at high temperature which induces surfactant crystallisation in situ. Differential scanning calorimetry, X-ray diffraction, infra-red spectroscopy, surface tension and rheology are used to elucidate the mechanisms.

FINDINGS

Unlike previous reports, both foamability and foam stability decrease upon decreasing the aeration temperature into the two-phase region containing surfactant crystals. At high temperature in the one-phase region, substantial foaming is achieved (over-run 170%) within minutes of whipping but foams ultimately collapse within a week. We show that surfactant molecules are surface-active at high temperature and that hydrogen bonds form between surfactant and oil molecules. Cooling these foams substantially increases foam stability due to both interfacial and bulk surfactant crystallisation. The generic nature of our findings is demonstrated for a range of vegetable oil foams with a maximum over-run of 330% and the absence of drainage, coalescence and disproportionation being achievable.

A Review on Recent Progress of Glycan-Based Surfactant Micelles as Nanoreactor Systems for Chemical Synthesis Applications

The nanoreactor concept and its application as a modality to carry out chemical reactions in confined and compartmentalized structures continues to receive increasing attention. Micelle-based nanoreactors derived from various classes of surfactant demonstrate outstanding potential for chemical synthesis. Polysaccharide (glycan-based) surfactants are an emerging class of biodegradable, non-toxic, and sustainable alternatives over conventional surfactant systems. The unique structure of glycan-based surfactants and their micellar structures provide a nanoenvironment that differs from that of the bulk solution, and supported by chemical reactions with uniquely different reaction rates and mechanisms. In this review, the aggregation of glycan-based surfactants to afford micelles and their utility for the synthesis of selected classes of reactions by the nanoreactor technique is discussed. Glycan-based surfactants are ecofriendly and promising surfactants over conventional synthetic analogues. This contribution aims to highlight recent developments in the field of glycan-based surfactants that are relevant to nanoreactors, along with future opportunities for research. In turn, coverage of research for glycan-based surfactants in nanoreactor assemblies with tailored volume and functionality is anticipated to motivate advanced research for the synthesis of diverse chemical species.

Topical Biocompatible Fluconazole-Loaded Microemulsions Based on Essential Oils and Sucrose Esters: Formulation Design Based on Pseudo-Ternary Phase Diagrams and Physicochemical Characterization

To initiate our research into the development of biocompatiîle gelled-microemulsions based on essential oils (EOs) and sucrose esters (SEs) for the topical delivery of fluconazole, this formulation study investigated the usefulness of two relatively harmless natural non-ionic surfactants from the group of SEs (sucrose laurate and stearate) to form, in the presence of antifungal EOs, stable, isotropic microemulsions effective on fluconazole solubilization. Fluconazole’s solubility in EO significantly depended on their chemical composition, showing higher values for cinnamon, oregano and clove essential oils, further selected as oil phase components for microemulsion formulations. The phase behavior of several EO–isopropyl miristate/SE–isopropanol/water systems was assessed through pseudo-ternary phase diagrams constructed by microplate dilution technique. The hydrocarbon chain length of the SE and EO type strongly influenced the size of the microemulsion region in the pseudo-ternary phase diagrams. Ten microemulsion formulations containing 2% fluconazole, 6% or 10% oil mixture of EO–isopropyl myristate in 1:1 ratio, 45% SE-isopropanol mixture and water, were selected and evaluated for physicochemical properties (droplet size, polydispersity, viscosity, refractive index, zeta potential and pH). All formulations were physicochemically acceptable, but viscosity enhancement and further in vitro and in vivo tests are required for the development of biocompatible, clinically safe and effective fluconazole topical preparations.

Enzymatically-synthesized xylo-oligosaccharides laurate esters as surfactants of interest

Lipase-catalyzed synthesis of xylo-oligosaccharides esters from pure xylobiose, xylotriose and xylotetraose in the presence of vinyl laurate was investigated. The influence of different experimental parameters such as the loading of lipase, the reaction duration or the use of a co-solvent was studied and the reaction conditions were optimized with xylobiose. Under the best conditions, a regioselective esterification occurred to yield a monoester with the acyl chain at the OH-4 of the xylose unit at the non-reducing end. Surface-active properties of these pure xylo-oligosaccharides fatty esters have been evaluated. They display interesting surfactant activities that differ according to the degree of polymerization (DP) of the glycone moiety.

Sucrose fatty acid esters: synthesis, emulsifying capacities, biological activities and structure-property profiles

The notable physical and chemical properties of sucrose fatty acid esters have prompted their use in the chemical industry, especially as surfactants, since 1939. Recently, their now well-recognized value as nutraceuticals and as additives in cosmetics has significantly increased demand for ready access to them. As such a review of current methods for the preparation of sucrose fatty acid esters by both chemical and enzymatic means is warranted and is presented here together with an account of the historical development of these compounds as surfactants (emulsifiers). The somewhat belated recognition of the antimicrobial, anticancer and insecticidal activities of sucrose esters is also discussed along with a commentary on their structure-property profiles.

Direct and selective enzymatic synthesis of trehalose unsaturated fatty acid diesters and evaluation of foaming and emulsifying properties

Trehalose diesters are Gemini-type surfactants that might have better surface activity than conventional surfactants. A one-step method for the preparation of trehalose unsaturated fatty acid diesters has been successfully developed. The yield of trehalose diester of different unsaturated fatty acids was between 78 % and 88 % under optimal conditions: 25 mmol/L trehalose, 100 mmol/L unsaturated fatty acid, 60 g/L 3 Å molecular sieves and 20 g/L lipase at 150 rpm and 50 °C for 42 h in 15 mL of acetone. Additionally, trehalose diester was the sole product obtained with Novozym 435 in acetone. The chemical structures of 6,6'-di-O-oleoyltrehalose, 6,6'-di-O-linoleoyltrehalose, 6,6'-di-O-eicosenoyltrehalose and 6,6'-di-O-erucoyltrehalose were confirmed by FTIR, MS and NMR. Moreover, the hydrophile-lipophile balance (HLB) values, foaming properties and emulsifying properties of trehalose diesters were assessed, showing the potentials of these diesters as naturally derived surfactants for the food industry.

Atypical Reaction Media and Organized Systems for the Synthesis of Low-Substitution Sugar Esters

Sugar esters are non-ionic surfactants with amphiphilic properties of interest for the formulation of various products in the fields of detergents, foods, medicines, pharmaceuticals, agriculture, and cosmetics. The properties of sugar esters depend on their degree of substitution (we consider degrees of substitution between 1 and 3 here) which guides their use. Sugar esters are biodegradable and non-toxic, and the demand for these compounds is high and continuing to increase. Indeed, interest in these compounds stems from the natural origin of the raw materials, the synthetic processes involved and the performance of the final product. The choice of reaction medium is crucial, to facilitate contact between reactants and prevent hydrolysis of the products. In this review, we provide an overview of the processes and synthesis routes for sugar ester production, ionic liquids and deep eutectic solvent as non-usual media or with organized systems.

Methacrylate saccharide-based monomers for dental adhesive systems

The aim of this in vitro study was to synthesize three new methacrylate monomers based on the modification of saccharides structures (glucose-Gluc, sucrose-Sucr and chitosan-Chit) with glycidyl methacrylate, and to use them in the composition of dental adhesives. Three methacrylate saccharide monomers were synthesized and characterized by mid-IR, ¹H and ¹³C NMR, antioxidant activity and cytotoxic effect. Monomers included: one monosaccharide - Gluc-MA; one disaccharide - Sucr-MA; and one polysaccharide - Chit-MA. Primers containing HEMA, methacrylate saccharide monomers at concentrations of 0 (control), 1, 2 or 4 wt%, 60 wt% ethanol aqueous solution (pH3.0) and initiator system were formulated. Primers were used in conjunction with a bond step and composite paste to restore caries-free third molars, and dentin bond strength (24 hours and 6 month of storage in water), and antimicrobial activity (Alamar Blue test) were tested. Degree of conversion (DC) and maximum rate of polymerization (Rp_max) of the primers themselves were also analyzed. The mid-IR, ¹H and ¹³C spectrum confirmed the presence of vinyl group on the structure of saccharides. Chit-MA showed low antioxidant activity and did not present a cytotoxic effect. Gluc-MA and Sucr-MA possess antioxidant and cytotoxic activity, concentration dependent. In the presence of methacrylate saccharide monomers, the primers showed DC comparable to the control group, except Gluc-MA4%, Sucr-MA4% and Chit-MA1%, which showed a range of 64.6 from 58.5 %DC. Rp_max was not statistically different for all the groups (p = 0.01). The bond strength of Sucr-MA1% increased from 25.7 (±2.8) to 40.6 (±5.3) MPa after 6 months of storage. All the synthesized monomers showed some antimicrobial activity after polymerization. Gluc-MA and Chit-MA 4% and Sucr-MA 1, 2 and 4% led to decrease bacterial metabolism. Sucr-MA 1% showed better results regarding the decrease in bacterial metabolism and increasing the bond strength after 6 months of storage.

Effect of Variations in the Fatty Acid Residue of Lactose Monoesters on Their Emulsifying Properties and Biological Activities

Lactose fatty acid esters are high-value-added derivatives of lactose and represent a class of biodegradable, non-ionic, low-molecular-weight surfactants (emulsifiers) that have considerable potential in the food, cosmetic, and pharmaceutical industries. Certain lactose esters have also garnered attention for their biological activities. In this work, we detail syntheses of a homologous series of 6'- O-acyllactose esters of varying alkyl chain length (from 6 to 18 carbons) and report on their activities as surfactants as well as their antimicrobial and cytotoxic properties. The structure-property profiles established in this work revealed that while the medium-chain esters displayed excellent emulsifying properties and moderate antimicrobial activities, their longer chain congeners exhibited the highest cytotoxicities. As such, we have established that certain 6'- O-acyllactose esters are superior to their sucrose-derived and commercially exploited counterparts. These results will serve as a useful guide for the development of lactose esters as, inter alia, emulsifiers in the food industry.

Comparative Study of the Emulsifying Properties of a Homologous Series of Long-Chain 6'- O-Acylmaltose Esters

Emulsifiers derived from renewable resources such as sucrose and fatty acids are high volume commodity chemicals and currently produced by traditional chemical synthesis techniques that lack the capacity to form the most desirable monoesters (of sucrose) in a selective and efficient fashion. The development of new emulsifiers (surfactants) from alternate, structurally simpler but nevertheless abundant disaccharides such as maltose represents a possible solution to this problem. Herein, we report the facile enzymatic preparation of a homologous series of 6'- O-acylmaltose esters and an in-depth evaluation of them revealing that their surfactant properties and thermal stabilities are largely determined by the length of the fatty acid chain. In the first such comparison, we show that the foaming and emulsifying effects of certain of these maltose monoesters are superior to those of their sucrose-derived and commercially exploited counterparts. As such, maltose esters have considerable potential as emulsifiers for use in, for example, the food industry.

Synthesis, Structure⁻Activity Relationships and In Vitro Toxicity Profile of Lactose-Based Fatty Acid Monoesters as Possible Drug Permeability Enhancers

Permeability enhancers are receiving increased attention arising from their ability to increase transepithelial permeability and thus, bioavailability of orally or pulmonary administered biopharmaceutics. Here we present the synthesis and the in vitro assaying of a series of lactose-based non-ionic surfactants, highlighting the relationship between their structure and biological effect. Using tensiometric measurements the critical micelle concentrations (CMCs) of the surfactants were determined and demonstrate that increasing hydrophobic chain length reduces surfactant CMC. In vitro testing on Caco-2 intestinal and Calu-3 airway epithelia revealed that cytotoxicity, assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release assays, is presented for most of the surfactants at concentrations greater than their CMCs. Further biological study demonstrates that application of cytotoxic concentrations of the surfactants is associated with depolarizing mitochondrial membrane potential, increasing nuclear membrane permeability and activation of effector caspases. It is, therefore, proposed that when applied at cytotoxic levels, the surfactants are inducing apoptosis in both cell lines tested. Importantly, through the culture of epithelial monolayers on Transwell^® supports, the surfactants demonstrate the ability to reversibly modulate transepithelial electrical resistance (TEER), and thus open tight junctions, at non-toxic concentrations, emphasizing their potential application as safe permeability enhancers in vivo.

Synthesis and characterization of lactose fatty acid ester biosurfactants using free and immobilized lipases in organic solvents

In this work, lactose fatty acid esters were enzymatically synthesized from fatty acids and lactose using Candida antarctica B lipase (CALB) in organic solvents. Products were purified using a solvent extraction method and analyzed using ATR-FTIR and surface-active properties measurements. Results showed that hexanes and acetonitrile provide the highest conversions for both free and immobilized lipases, up to 77% and 93% respectively. The conversion rate of esterification is solvent-dependent for free lipase; the conversion rate of immobilized lipase still shows solvent dependency, but to a lesser degree. Surface tension, interfacial tension, critical micelle concentration (CMC), and contact angles were also measured for all of the samples, showing the potentials of these sugar esters as naturally derived surfactants for the food industry.

Enzymatic Preparation of a Homologous Series of Long-Chain 6- O-Acylglucose Esters and Their Evaluation as Emulsifiers

Sugar fatty acid esters are nonionic surfactants that are widely exploited in the food and cosmetics industries, as well as in the oral care and medical supply fields. Accordingly, new methods for their selective synthesis and the "tuning" of their emulsifying properties are of considerable interest. Herein we report simple and irreversible enzymatic esterifications of d-glucose with seven fatty acid vinyl esters. The foaming and emulsifying effects of the resulting 6- O-acylglucose esters were then evaluated. In accord with expectations, when the length of the alkyl side chain associated with the 6- O-acylglucose esters increases, then their hydrophilic-lipophilic balance (HLB) values decrease, while the stabilities of the derived emulsions improve. In order to maintain good foaming properties, alkyl side chains of at least 9 to 11 carbons in length are required. In the first such assays on 6- O-acylglucose esters, most of those described herein are shown to be nontoxic to the HepG2, MCF-7, LNacp, SW549, and LO-2 cell lines.

Enzymatic Synthesis and Characterization of Sucrose Erucate

The enzyme catalyzed synthesis is a environmentally friendly route compared to traditional syntheses. The lipase-catalyzed synthesis of sucrose erucate was achieved in a solvent mixture of t-butanol and dimethyl sulfoxide (4: 1) by esterification of sucrose with erucic acid using the immobilized Thermomyces lanuginosus lipase. Various process parameters like temperature, substrate molar ratio, solvent, time, and enzyme loading were studied. The optimal conditions for the esterification reaction obtained were 10 %(w/w) enzyme loading, a molar ratio sucrose/fatty acid 1: 1, mild reaction conditions (50 °C and atmospheric pressure) and reaction time (40 h with 55.6 % conversion). The sugar esters were characterized for surfactant properties at different concentration. Sucrose erucate showed a surface tension of (32.73 ± 0.01) mN m−1at a critical micellar concentration of 9.8 × 10−5 mol L−1 and good emulsification power.

Lipase-catalyzed synthesis of sucrose monoester: Increased productivity by combining enzyme pretreatment and non-aqueous biphasic medium

Sucrose monocaprate was synthesized by carrying out a lipase-catalyzed transesterification in a non-aqueous biphasic medium. Vinyl caprate was mechanically dispersed into a solution of sucrose in DMSO. The use of DMSO allowed increasing sucrose concentration up to 0.7M (in DMSO). The denaturing effect of DMSO on lipase was avoided by pretreatment of lipase by pH adjustment in the presence of crown ether. This pretreatment maintained a significant catalytic activity which led to 0.2M sucrose monoester within 1h at 50°C, which represented higher productivity than already reported. Detailed structural characterization revealed that only monoester was recovered and the 2-O-acylated sucrose monocaprate was the major isomer in the final product.

Lactose esters: synthesis and biotechnological applications

Biodegradable nonionic sugar esters-based surfactants have been gaining more and more attention in recent years due to their chemical plasticity that enables the various applications of these molecules. In this review, various synthesis methods and biotechnological implications of lactose esters (LEs) uses are considered. Several chemical and enzymatic approaches are described for the synthesis of LEs, together with their applications, i.e. function in detergents formulation and as additives that not only stabilize food products but also protect food from undesired microbial contamination. Further, this article discusses medical applications of LEs in cancer treatment, especially their uses as biosensors, halogenated anticancer drugs, and photosensitizing agents for photodynamic therapy of cancer and photodynamic inactivation of microorganisms.