Ester- and amide-containing multiQACs: Exploring multicationic soft antimicrobial agents

Quaternary ammonium compounds (QACs) are ubiquitous antiseptics whose chemical stability is both an aid to prolonged antibacterial activity and a liability to the environment. Soft antimicrobials, such as QACs designed to decompose in relatively short times, show the promise to kill bacteria effectively but not leave a lasting footprint. We have designed and prepared 40 soft QAC compounds based on both ester and amide linkages, in a systematic study of mono-, bis-, and tris-cationic QAC species. Antimicrobial activity, red blood cell lysis, and chemical stability were assessed. Antiseptic activity was strong against a panel of six bacteria including two MRSA strains, with low micromolar activity seen in many compounds; amide analogs showed superior activity over ester analogs, with one bisQAC displaying average MIC activity of ∼1μM. For a small subset of highly bioactive compounds, hydrolysis rates in pure water as well as buffers of pH =4, 7, and 10 were tracked by LCMS, and indicated good stability for amides while rapid hydrolysis was observed for all compounds in acidic conditions.

Novel gemini cationic surfactants based on N, N-dimethyl fatty hydrazide and 1,3-dibromopropane: synthesis, evaluation of surface and antimicrobial properties

A fatty hydrazide based cationic gemini surfactants, 1,3-bis (N'-acyl-N,N-dimethylhydrazinium) propane dibromide which possess hydrolyzable amido moieties in the lipophilic portions, were prepared by reacting 1,3-bromopropane with N,N-dimethyl fatty hydrazide. The surface properties were explained and discussed based on the effect of their chemical structures. The micelle-forming ability, foaming ability, and foam stability were evaluated. The prepared surfactants also showed some antimicrobial activity against gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus) but they were not active against gram negative bacteria (Escherichia coli, P. aeruginosa), yeast (Candida albicans), and molds (Aspergillus niger).

Aggregation behavior of gemini surfactants and their interaction with macromolecules in aqueous solution

Gemini surfactants are constructed by two hydrophobic chains and two polar/ionic head groups covalently connected by a spacer group at the level of the head groups. Gemini surfactants possess unique structural variations and display special aggregate transitions. Their aggregation ability and aggregate structures can be more effectively adjusted through changing their molecular structures compared with the corresponding monomeric surfactants. Moreover, gemini surfactants exhibit special and useful properties while interacting with polymers and biomacromolecules. Their strong self-aggregation ability can be applied to effectively influence the aggregation behavior of both polymers and biomacromolecules. This short review is focused on the performances of gemini surfactants in aqueous solutions investigated in the last few years, and summarizes the effects of molecular structures on aggregation behavior of gemini surfactants in aqueous solution as well as the interaction of gemini surfactants with polymers and biomacromolecules respectively.

Hydrophilic carotenoids: surface properties and aggregation of an astaxanthin-lysine conjugate, a rigid, long-chain, highly unsaturated and highly water-soluble tetracationic bolaamphiphile

The surface and aggregation properties of a synthetic, highly water-soluble carotenoid, the tetracationic astaxanthin-lysine conjugate (Asly), have been examined through measurements of surface tension, optical absorption and dynamic light scattering. The following parameters were determined: critical aggregation concentration c(M), surface concentration Gamma, molecular area a(m), free energy of adsorption and aggregation (DeltaG(ad) degrees and DeltaG(M) degrees , respectively), and the aggregate size r(H). The compound forms true monomolecular solutions in water below c(M); aggregates emerge only at rather high concentrations (> or =2.18 mM).

Effects of ethylene glycol addition on the aggregation and micellar growth of gemini surfactants

Micellization of three didodecyl dicationic dibromide gemini surfactants with different methylene spacer lengths, 12-s-12,2Br- where s = 3-5 methylene groups, has been investigated in water-ethylene glycol, EG, mixtures with weight percentages of EG up to 50%. Subsequently, effects of the addition of the organic solvent on the micellar growth of these surfactants and on the surfactant concentration range where sphere-to-rod transitions occur were studied by means of steady-state and time-resolved fluorescence quenching and spectroscopic measurements. Results show that an increase in the weight percentage of ethylene glycol added to aqueous 12-s-12,2Br- (s = 3-5) micellar solutions causes the sphere-to-rod transition to occur at higher surfactant concentrations than in pure water. The diminution in the average aggregation number, N(agg), when wt % EG increases, provoked by the decrease in the interfacial Gibbs energy contribution to DeltaG degrees M, is the main factor responsible for this observation. The decrease in N(agg) is accompanied by a decrease in the ionic interactions and the extra packing contribution to the deformation of the surfactants tails, making formation of cylindrical micelles less favorable. Besides, an increase in the solvent content and polarity of the interfacial region does not favor formation of direct ion pairs, decreasing the tendency of micelles to grow.

Aggregation Properties of Sodium Hyaluronate with Alkanediyl-alpha,omega-bis(dimethylalkylammonium Bromide) Surfactants in Aqueous Sodium Chloride Solution

Aggregation properties of sodium hyaluronate (NaHA) with alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants (referred to as dimeric surfactants) in aqueous sodium chloride solutions have been studied as a function of surfactant chemical structure. Surface tension measurements indicate the unusual parabolic dependence of surface tension vs log surfactant concentration with a surface tension minimum at concentration c(min). The increase of surface tension above c(min) may be related to the formation of clusters consisting of NaHA chain and dimeric surfactants at the air-water interface and in the bulk. From light scattering measurements, molecular weight, hydrodynamic radius, and second virial coefficient have been calculated. The simple calculation of the ratio of positive charge of dimeric surfactant unit per one negatively charged hyaluronate disaccharidic unit in NaHA-surfactant complex reveals that there is a slight excess of positive surfactant charges per one negatively charged disaccharidic unit in the region around c(min) and the NaHA-surfactant complex is not far from electroneutrality. The nonlinear behavior of viscosity vs surfactant concentration in the NaHA-dimeric surfactant system depends on surfactant chemical structure. The behavior is concerned with the size increase due to complex growth and with the size shrinkage above c(min). A model describing the behavior of NaHA-surfactant complex in the bulk and at the interface is suggested. Copyright 2000 Academic Press.