M.R. Infante

Cationic Surfactants Derived from Lysine: Effects of Their Structure and Charge Type on Antimicrobial and Hemolytic Activities

Three different sets of cationic surfactants from lysine have been synthesized. The first group consists of three monocatenary surfactants with one lysine as the cationic polar head with one cationic charge. The second consists of three monocatenary surfactants with two amino acids as cationic polar head with two positive charges. Finally, four gemini surfactants were synthesized in which the spacer chain and the number and type of cationic charges have been regulated. The micellization process, antimicrobial activity, and hemolytic activity were evaluated. The critical micelle concentration was dependent only on the hydrophobic character of the molecules. Nevertheless, the antimicrobial and hemolytic activities were related to the structure of the compounds as well as the type of cationic charges. The most active surfactants against the bacteria were those with a cationic charge on the trimethylated amino group, whereas all of these surfactants showed low hemolytic character.

Preliminary studies of the toxic effects of non-ionic surfactants derived from lysine

The toxic effects of new synthetic monodisperse non-ionic long-chain N alpha, N epsilon-diacyl lysine polyoxyethylene glycol amide compounds with a structural resemblance to natural lecithin phospholipids were studied by the haemolytic method and the test of the chorioallantoic membrane of the hens egg (HET-CAM). The following compounds were tested: symmetrical N alpha,N epsilon-diacyl lysine homologues (N alpha,N epsilon-dihexanoyl, N alpha,N epsilon-dioctanoyl and N alpha,N epsilon-didecanoyl lysine) with one methyl ether polyoxyethylene glycol chain of different oxyethylene units (dioxyethylene glycol, tetraoxyethylene glycol and hexaoxyethylene glycol) as headgroup; symmetrical N alpha,N epsilon-diacyl lysine homologues with two methyl ether dioxyethylene glycol chains and the asymmetrical N alpha-butanoyl, N epsilon-dodecyl lysine with two hydrophilic methyl ether dioxyethylene glycol chains as headgroup. A commercial (polydisperse) oleoyl polyoxyethylene glycol diethanolamide with an average of eight units of ethylene oxide was used as control. All the synthesized tested compounds appeared to be less haemolytic and less irritant than the control. The synthesized products were studied with regard to their hydrophobic and hydrophilic chains in order to evaluate the influence of their structure on their haemolytic and irritative action. The results of this study show that the acyl chain distribution of these compounds greatly influence toxic effects: the asymmetrical compound N alpha-butanoyl,N epsilon-dodecyl lysine-bis[methyl ether diethylene glycol]amide was found to be the most haemolytic and irritating compound. Among the symmetrical homologues, the shortest-chain compounds N alpha,N epsilon-dihexanoyl lysine methyl ether polyoxyethylene glycol amides present the least haemolytic and irritating activity, independently of the number and length of the hydrophilic methyl ether polyoxyethylene glycol chains. Taking into account their surface activity properties and their less haemolytic and irritant action, the compound N alpha,N epsilon-dioctanoyl lysine-bis[methyl ether diethylene glycol]amide would be the most suitable for practical purposes.

Assessment of the potential skin irritation of lysine-derivative anionic surfactants using mouse fibroblasts and human keratinocytes as an alternative to animal testing.

AbstractPurpose. The aim of this study was to identify new surfactants with low skin irritant properties for use in pharmaceutical and cosmetic formulations, employing cell culture as an alternative method to in vivo testing. In addition, we sought to establish whether potential cytotoxic properties were related to the size of the counterions bound to the surfactants. Methods. Cytotoxicity was assessed in the mouse fibroblast cell line 3T6 and the human keratinocyte cell line NCTC 2544 using the MTT assay and uptake of the vital dye neutral red 24 h after dosing (NRU). Results. Lysine-derivative surfactants showed higher IC50s than did commercial anionic irritant compounds such as sodium dodecyl sulfate, proving to be no more harmful than amphoteric betaines. The aggressiveness of the surfactants depended on the size of their constituent counterions: surfactants associated with lighter counterions showed a proportionally higher aggressivity than those with heavier ones. Conclusions. Synthetic lysine-derivative anionic surfactants are less irritant than commercial surfactants such as sodium dodecyl sulfate and hexadecyltrimethylammonium bromide and are similar to betaines. These surfactants may offer promising applications in pharmaceutical and cosmetic preparations, representing a potential alternative to commercial anionic surfactants as a result of their low irritancy potential.

Role of aggregate size in the hemolytic and antimicrobial activity of colloidal solutions based on single and gemini surfactants from arginine

Cationic colloidal systems composed of arginine based surfactants (single or gemini structures) and membrane additive compounds such as DLPC or cholesterol have been characterized by means of size distribution and zeta-potential measurements. The single or monocatenary surfactant (LAM) as well as the gemini with the shortest spacer chain (C6(LA)2) formed micelles, while aqueous solutions of pure gemini surfactants with longer spacers (C9(LA)2 and C12(LA)2) formed very big aggregates. The addition of phospholipids or cholesterol changed drastically the aggregation behaviour. In the case of LAM and C6(LA)2, the incorporation of additives gave rise to the formation of cationic vesicles. For C9(LA)2 and C12(LA)2, this type of additives promoted the formation of smaller aggregates. All the formulations had positive zeta-potential values and in general exhibited high colloidal stability. We also evaluated the hemolysis and the antimicrobial activity of these systems. The capability of disrupting erythrocyte membranes depends on the hydrophobicity of the molecules and the size of aggregates in the solution. Gemini surfactants with short spacer chains are more hemolytic than their single chain homologue, while gemini surfactants with long spacers are much less hemolytic than their single chain counterpart. Moreover, for the same formulation, the hemolysis depends on the initial concentration of the stock solution used to set up the hemolysis/concentration curve. Results show that small aggregates interact easily with these biological membranes. The alkyl spacer chain and the presence of additives also play an important role in the antimicrobial activity, and, in general, the interaction with bacteria and erythrocytes is affected by the same parameters. The physico-chemical and biological characterization of these systems might be important for several biotechnological applications in which cationic vesicular systems are involved.

Synthesis and properties of cationic surfactants containing a disulfide bond

Two new cationic surfactants containing a disulfide bond were synthesized, and the physical chemical characteristics and the fundamental surface-active properties were determined. These new surfactants have potential applications in the textile and cosmetic field. These compounds have been prepared by condensation of a commercial Nα,Nα-dimethyl amino betaine with cystine dimethyl ester or cystamine by means of the mixed anhydride method. The study of their properties revealed that these molecules are soluble in water (stable at pH⩽8) and show surface activity with similar low critical micelle concentration values. Microscopic examination of water/surfactant systems containing these compounds shows that they form liquid crystals with patterns corresponding to typical hexagonal and lamellar structures.

Ribbon-type and cluster-type lipoplexes constituted by a chiral lysine based cationic gemini lipid and plasmid DNA

Lipoplexes constituted by plasmid DNA pEGFP-C3 (pDNA) or linear double-stranded calf thymus DNA (ctDNA) and mixed cationic liposomes consisting of several percentages of the cationic lysine derived lipid C6(LL)2 and the zwitterionic lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) have been analyzed by both experimental and theoretical approaches. Experimental studies, consisting of electrophoretic mobility/zeta potential, small angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), negatively stained transmission electron microscopy (NS-TEM), and GelRed f1uorescence intercalation assays, have been carried out at several liposome and lipoplex compositions, defined in terms of cationic lipid molar fraction and either the mass or charge ratios of the lipoplex. The electrochemical study confirms that, in the presence of the mixed lipids and in contrast with what has usually been found for linear DNA, the plasmid DNA is compacted with a large number of its Na+ counterions, thus yielding a much lower effective negative charge (q−pDNA) than that for ctDNA (q−ctDNA), as reported recently by us (J. Am. Chem. Soc., 2011) for other lipoplexes. This finding is revealed as crucial for an optimum and efficient lipoplex preparation, since a lower effective negative charge implies a lower quantity of cationic lipid and, accordingly, a potential lower cytotoxicity. TEM experiments reveal a complex scenario of multilamellar nanostructures, from ribbon-type (typically present for chiral lipids) to cluster-type structures (usually found in cationic lipid/DOPE systems), the composition of the mixed liposome playing an important role in the final morphology of the lipoplex. SAXS diffractograms confirm the existence of these two types of multilamellar structures through a deconvolution process of the first peak of diffractograms into two overlapping bands. On the other hand, a theoretical complexation model is employed to determine the net charge of the lipoplexes studied in this work. The model allows analysis and comparison of the electrochemical behaviour of lipoplexes containing linear DNA vs. those constituted by a supercoiled DNA, confirming the experimental findings.

Cationic vesicles based on biocompatible diacyl glycerol-arginine surfactants: Physicochemical properties, antimicrobial activity, encapsulation efficiency and drug release

Physicochemical characteristics of cationic vesicular systems prepared from biocompatible diacyl glycerol-arginine surfactants are investigated. These systems form stable cationic vesicles by themselves and the average diameter of the vesicles decreases as the alkyl chain length of the surfactant increases. The addition of DPPC also modifies the physicochemical properties of these vesicles. Among the drugs these cationic formulations can encapsulate, we have considered Ciprofloxacin and 5-Fluorouracil (5-FU). We show that the percentage of encapsulated drug depends on both the physicochemical properties of the carrier and the type of drug. The capacity of these systems to carry different molecules was evaluated performing in vitro drug release studies. Finally, the antimicrobial activity of empty and Ciprofloxacin-loaded vesicles against Gram-positive and Gram-negative bacteria has been determined. Three bacteria were tested: Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. The in vitro drug release from all formulations was effectively delayed. Empty cationic vesicles showed antimicrobial activity and Ciprofloxacin-loaded vesicles showed similar or higher antimicrobial activity than the free drug solution. These results suggest that our formulations represent a great innovation in the pharmaceutical field, due to their dual pharmacological function: one related to the nature of the vehiculated drug and the other related to the innate antibacterial properties of the surfactant-based carriers.

Highly concentrated emulsions as novel reaction media

Abstract Synthesis of a cationic surfactant, Nα-lauroyl arginine methyl ester hydrochloride (LAM) has been carried out in gel emulsions of the system water/C14E4/decane. The yields of LAM synthesized in gel emulsions are comparable to those obtained in conventional dimethylformamide (DMF) media. The rate of LAM formation is faster in gel emulsions at short times, the reaction taking place without mechanical energy input and at 25°C.

Surface tension properties of aqueous solutions of disulfur betaine derivatives

Abstract The equilibrium and dynamic surface tensions of aqueous solutions of two newly synthesized surfactants relevant to wool dyeing were studied by means of the Wilhelmy plate and a bubble method. The surfactants ( N α , N α ′-bis( N -dodecyl- N , N -dimethylglycine cystine dimethyl ester dihydrochloride) and ( N α , N α ′-bis( N -dodecyl- N , N -dimethylglycine) cystamine dihydrochloride), are double-chain and bicationic in character. Their CMCs and Langmuir adsorption equilibrium parameters were determined at 25°C. Both molecules are very efficient surfactants. Their surface tensions equilibrate in time-scales ranging from seconds to hours (concentration c =1000—2 μM). Their dynamic surface tensions under constant and pulsating area conditions indicate that there is a strong barrier to adsorption at the air—water interface. The presence of the micelles accelerates the net rate of adsorption, suggesting fast micellar dissociation.

Irritancy potential induced by surfactants derived from lysine

The ocular irritancy potential of surfactants of the anionic and non-ionic type, derived from lysine has been tested by the hens egg test-choriollantoic membrane (HET-CAM) to correlate the potential irritation with the structure of the surfactant, in order to synthesize the less irritant surfactant for their use in the pharmaceutical and cosmetics industry. The anionic compounds, independently of the counterion, showed an irritant action higher than non-ionic surfactants. Among the anionic surfactants the presence of lysine as cation reduced the degree of irritation; nevertheless, the salt of lysine of lauric acid was a severe irritant. The non-ionic surfactant with two chains was less irritant than the corresponding compound with one chain and represented the best compound for ocular application. The time of appearance of haemorrhage, vasoconstriction and coagulation is used to evaluate the degree of irritation. There was a close relationship between the concentration and the time of the appearance of vasoconstriction at the concentrations tested.