SciCombinator

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Concept: Quaternary ammonium cation

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Dimeric quaternary alkylammonium salts possess a favourable surface and antimicrobial activity. In this paper we describe synthesis, spectroscopic analysis, surface and antimicrobial activity as well as biodegradability of polymethylene-α,ω-bis(N,N-dialkyl-N-deoxy-D-glucitolammonium iodides), a new group of dimeric quaternary ammonium salts. This new group of gemini surfactants can be produced from chemicals which come from renewable sources. The structure of products has been determined by the FTIR and (1)H and (13)C NMR spectroscopy. The biodegradability, surface activity and antimicrobial efficacy against Escherichia coli, Staphylococcus aureus, Candida albicans, Aspergillus niger and Penicillium chrysogenum were determined. The influence of the number of alkyl chains and their lengths on surface and antimicrobial properties has been shown. In general, dimeric quaternary alkyldeoxy-D-glucitolammonium salts with long alkyl substituents show favourable surface properties and an excellent antimicrobial activity.

Concepts: Spectroscopy, Surfactant, Quaternary ammonium cation, Ammonium, Ascomycota, Salt, Cocamidopropyl betaine, Fabric softener

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Subsequent to binding pocket modifications designed to provide dual d-Ala-d-Ala/d-Ala-d-Lac binding that directly overcome the molecular basis of vancomycin resistance, peripheral structural changes have been explored to improve antimicrobial potency and provide additional synergistic mechanisms of action. A C-terminal peripheral modification, introducing a quaternary ammonium salt, is reported and was found to provide a binding pocket-modified vancomycin analog with a second mechanism of action that is independent of d-Ala-d-Ala/d-Ala-d-Lac binding. This modification, which induces cell wall permeability and is complementary to the glycopeptide inhibition of cell wall synthesis, was found to provide improvements in antimicrobial potency (200-fold) against vancomycin-resistant Enterococci (VRE). Furthermore, it is shown that this type of C-terminal modification may be combined with a second peripheral (4-chlorobiphenyl)methyl (CBP) addition to the vancomycin disaccharide to provide even more potent antimicrobial agents [VRE minimum inhibitory concentration (MIC) = 0.01-0.005 μg/mL] with activity that can be attributed to three independent and synergistic mechanisms of action, only one of which requires d-Ala-d-Ala/d-Ala-d-Lac binding. Finally, it is shown that such peripherally and binding pocket-modified vancomycin analogs display little propensity for acquired resistance by VRE and that their durability against such challenges as well as their antimicrobial potency follow now predictable trends (three > two > one mechanisms of action). Such antibiotics are expected to display durable antimicrobial activity not prone to rapidly acquired clinical resistance.

Concepts: Antibiotic resistance, Cell wall, Vancomycin, Quaternary ammonium cation, Ammonium, Enterococcus, Vancomycin-resistant enterococcus, Antimicrobial

28

A model for the limiting surface tension of surfactant solutions (surface tension at and above the critical micelle concentration, cmc) was developed. This model takes advantage of the equilibrium between the surfactant molecules on the liquid/vacuum surface and in micelles in the bulk at the cmc. An approximate analytical equation for the surface tension at the cmc was obtained. The derived equation contains two parameters, which characterize the intermolecular interactions in the micelles, and the third parameter, which is the surface area per surfactant molecule at the interface. These parameters were calculated using a new atomistic modeling approach. The performed calculations of the limiting surface tension for four simple surfactants show good agreement with experimental data (∼30% accuracy). The developed model provides the guidance for design of surfactants with low surface tension values.

Concepts: Chemistry, Surface tension, Surfactant, Micelle, Quaternary ammonium cation, Solution, Macromolecule, Colloidal chemistry

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The structure of solubilized water in water-in-n-heptane aggregates stabilized by mixtures of single- and double-tail quaternary ammonium surfactants, namely didodecyldimethylammonium chloride/dodecyltrimethylammonium chloride (DDAC/DTAC) or didodecyldimethylammonium bromide/dodecyltrimethylammonium bromide (DDAB/DTAB) was studied by two noninvasive techniques, (1)H NMR and FT-IR. In the former, the chemical shift data, δ(obs), were used to calculate the so-called deuterium/protium fractionation factor, φ(M), of the aggregate-solubilized water and were found to be unity. In the FT-IR study, upon increasing water/surfactant molar ratio, W, the frequency, ν(OD), of the HOD species decreases, while its full width at half height and its area increase. The results obtained from both techniques indicate that the water appears to be present as a single nano-phase and the structure varies continuously as a result of increasing W. In addition, the effect of changing the counter-ion (Br(-) or Cl(-)) on (1)H NMR and FT-IR results was investigated. In spite of the known difference in the dissociation of these counter-ions from micellar aggregates, this was found not to affect the state of solubilized water. This report gives further insight into the contradictory scientific debates on the structure of water in the polar nano-cores of microemulsions.

Concepts: Nuclear magnetic resonance, Addition, Emulsion, Surfactant, Micelle, Quaternary ammonium cation, Cocamidopropyl betaine, Fabric softener

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A previous study identified an association between high MICs of quaternary ammonium compounds (QACs) and antibiotic resistance. The current aim was to investigate the genetic background of this association.

Concepts: Bacteria, Antibiotic resistance, Escherichia coli, Quaternary ammonium cation, Ammonium, Salt, Quaternary ammonium compounds

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In this article we investigated effects of different types of conventional surfactants on exchange dynamics of quaternary ammonium dimeric surfactants, with chemical formula as C(14)H(29)N(+)(CH(3))(2)- (CH(2))(s)-N(+)(CH(3))(2)C(14)H(29)•2Br(-), short for 14-s-14. Two nonionic surfactants, TX-100 (TritonX-100) and Brij-35 [polyethylene glycol (23) laurylether], and one cationic surfactant, TTAB (n-tetradecyltrimethyl ammonium bromide), and one ionic surfactant, SDS (Sodium dodecyl sulfate) were chosen as typical conventional surfactants. Exchange rates of 14-s-14 (s=2, 3 and 4) between the micelle form and monomer in solution were detected by two NMR methods: one-dimensional (1D) line shape analysis and two dimensional (2D) exchange spectroscopy (EXSY). Results show that, the nonionic surfactants (TX-100 and Brij-35), the cationic surfactant (TTAB) and the ionic surfactant (SDS) respectively accelerated, barely influenced and slowed the exchange rate of 14-s-14. The effect mechanism was investigated by the self-diffusion experiment, relaxation time measurements (T(2)/T(1)), the fluorescence experiment (I(1)/I(3)) and the observed chemical shift variations. Results reveal that, nonionic conventional surfactants (TX-100 and Brij-35) loosened the molecule arrangement and decreased the hydrophobic interactions in the micelle, and thus accelerated the exchange rate of 14-s-14. The cationic conventional surfactant (TTAB) little changed the molecule arrangement and thus little influenced the exchange rate of 14-s-14. The ionic conventional surfactant (SDS) introduced the electrostatic attraction effect, tightened the molecule arrangement and increased the hydrophobic interactions in the micelle, and thus slowed down the exchange rate of 14-s-14. Besides, the two-stepwise exchange mechanism of 14-s-14 in the mixed solution was revealed through the interesting variation tendency of exchange rates of 14-s-14.

Concepts: Chemistry, Ion, Surfactant, Micelle, Quaternary ammonium cation, Solution, Cocamidopropyl betaine, Fabric softener

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This study uses molecular dynamics (MD) modeling to examine the interlayer microstructures of montmorillonite intercalated with single chain QACs. Three types of QACs-tetramethylammonium (TMA), decyltrimethylammonium (DTMA), and hexadecyltrimethylammonium (HDTMA)-were selected to synthesize the organoclay complex, and the surfactant arrangement was analyzed quantitatively in systems in the absence of water. A series of arrangement patterns of interlayer QAC surfactant were observed, including lateral monolayers, lateral bilayers, pseudotrilayers, and paraffin monolayers, in agreement with previous experimental results. The effects of increasing one carbon chain length and amount of loading of QAC on the resultant QAC arrangement are summarized, yielding a model that provides insight into the prediction of synthesized QAC-clay microstructure and engineering behavior in practice.

Concepts: Scientific method, Atom, Surfactant, Quaternary ammonium cation, Ammonium, Salt, Cocamidopropyl betaine, Fabric softener

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The interaction between gamma-cyclodextrin and amphiphilic p-sulfonatocalix[4]-arenes was studied using NMR and isothermal titration calorimetry techniques. The results indicate that this calixarenes are able to form 1:1, 1:2 and 2:1 host-guest complexes with the cyclodextrin. The ROESY spectra suggest that the cyclodextrin binds the calixarenes trough the hydrophobic alkyl chains. p-Sulfonatocalix[4]arenes, which are traditionally used as host molecules, act as guests in the presence of gamma-cyclodextrin. However, their recognition site remains active upon complexation with the cyclodextrin, and ternary complexes can be devised. Here, we also demonstrate the formation of such complexes using tetramethylammonium chloride as a model guest. Moreover, it is also demonstrated that the recognition properties of the calixarene are unaffected upon complexation with the cyclodextrin.

Concepts: Ammonia, Ion, Demonstration, Supramolecular chemistry, Quaternary ammonium cation, Polyatomic ion, Host-guest chemistry, Calixarene

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Thermodynamically stable nanovesicular structures are of high interest for academia and industry in a wide variety of application fields, ranging from nanomaterials preparation to nanomedicine. Here we show the ability of quaternary ammonium surfactants and sterols to self-assemble forming stable amphiphilic bimolecular building-blocks with the appropriate structural characteristics to form, in aqueous phases, closed bilayers, named quatsomes, with outstanding stability with time and temperature. Molecular self-assembling of cholesterol (Chol) and surfactant cetyltrimethylammonium bromide (CTAB) was studied by quasi-elastic light scattering (QELS), cryogenic transmission electron microscopy (cryo-TEM), turbidity (optical density) measurements and molecular dynamic simulations (MD) with atomistic detail, upon varying the cholesterol-to-surfactant molar ratio. As pure species, CTAB forms micelles and insoluble cholesterol forms crystals in water. However, our molecular dynamic simulations reveal that the synergy between CTAB and cholesterol molecules makes them self-assemble into bimolecular amphiphiles and then into bilayers in the presence of water. These bilayers have the same structure of those formed by double tailed unimolecular amphiphiles.

Concepts: Cholesterol, Electron, Structure, Nanotechnology, Surfactant, Quaternary ammonium cation, Salt, Cocamidopropyl betaine

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Recent research has highlighted a growing focus on stimuli-responsive surfactant wormlike micelles (WLMs) particularly those with switchability. Here we report CO2-switchable WLMs based on the commercial anionic surfactant sodium dodecyl sulfate (SDS) and N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA) mixed in a mole ratio of 2:1. When CO2 is bubbled into an aqueous mixture of these reactants, the TMPDA molecules are protonated to form quaternary ammonium species, two of which in the same protonated TMPDA molecule “bridge” two SDS molecules by non-covalent electrostatic attraction, behaving like a “pseudo” gemini surfactant and forming viscoelastic WLMs verified by cryo-TEM. Upon removal of CO2, the quaternized spacers are deprotonated back into tertiary amines, dissociating the “pseudo” geminis back to conventional SDS molecules that form low viscosity spherical micelles. Such a reversible sphere-to-worm transition could be repeated several cycles without loss of response to CO2.

Concepts: Molecule, Chemistry, Atom, Viscosity, Surfactant, Quaternary ammonium cation, Salt, Mole