Reaction of carboxylic acid esters with phenolates in oil-in-water microemulsions based on cetyltrimethylammonium bromide

A kinetic study of reactions of carboxylic acid esters with phenols activated with alkalis or amines in microemulsions based on cationic surfactants showed that the phenolates formed upon activation exhibit different nucleophilicity depending on the value of the negative charge on the oxygen atom, which is determined by the properties of the phenol, ionizing agent, and solvent.     

Structure and Properties of Water-Oil Microemulsions

The parameters determining the structure and properties (surface potential and size of microdrops) of oil-water microemulsions containing various surfactants, and also the distribution of components between the dispersed phase and dispersing medium were determined by the kinetic method and by high-resolution ¹H NMR spectroscopy with a pulse magnetic field gradient.     

Aqueous solutions of geminal alkylammonium surfactants as a medium for reactions of long-chain amines

The formation of surfactant-hydrophobic amine mixed aggregates reduces the pK _a of long-chain amines by 1–1.5 units compared with those in molecular solutions and is an important factor responsible for the high catalytic effect of the system in ester bond cleavage. In aqueous solution of geminal surfactants, the rate of azomethine formation in the reaction of long-chain amines with benzaldehydes is an order-of-magnitude higher than in ethanol.     

Cetylpyridinium bromide-catalyzed reaction of ortho-aminomethylphenols with para-nitrophenyldiphenyl phosphate

Cetylpyridinium bromide micelles accelerate the reaction of paranitrophenyldiphenyl phosphate with orthoaminomethylphenol by more than an order of magnitude in aqueous micellar solutions. The rate constants for this reaction are, however, about 50 times lower in the micellar phase than in water, i.e., the principal factor responsible for micellar catalysis in this reaction is concentration of the reagent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1126–1129, May, 1990.     

Towards the standard-module approach to disulfide-linked polypeptide nanostructures. I. Methodological prerequisites and mass spectrometric characterization of the test two-loop structure

Potentially biologically-active nanostructures can be created from single chains of unmodified peptides by cross-linking different regions of the chain by disulfide bonds and cleaving the chain at specified sites to obtain the final configuration. The availability of techniques for assembly and characterization of such structures was tested on a two-loop structure created from a 21-residue linear peptide. Directed intra-molecular disulfide bond formation was performed by inserting partial sequences favoring intra-molecular SS bond formation ("loops") separated by partial sequences disfavoring such a process ("spacers") into the precursor sequence. Peptide bond cleavage by partial acid hydrolysis at specific sites (GG, NP/DP) inside the loops opened them; the same process in the spacer separated the loops. Synthesis, oxidation and bond cleavage were monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI ToF MS). The hydrolysis fragments of the produced nanostructures were characterized by tandem electrospray ionization Fourier transform mass spectrometry (ESI FT-MS) with collisional and electron capture dissociations. The latter technique was especially useful as it cleaves SS bonds preferentially. The feasibility of the proposed synthesis approach and the adequacy of the analysis techniques for the test structure were demonstrated.     

Acid-base properties and nucleophilicity of o-aminomethylphenols in aqueous micellar solutions and microemulsions

The pK _a values and constants of tautomeric equilibrium of several o-aminomethylphenols with different hydrophilic-lipophilic ability were measured in aqueous micellar solutions and in direct microemulsions based on cetyltrimethylammonium bromide. The kinetics of hydrolysis of p-nitrophenyl acetate at different pH and concentrations of aminomethylphenol and surfactant was studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1724–1729, October, 2006     

Kinetics of the reactions of esters and primary amines in “oil-water” type microemulsions

The possibilities of using “oil-water” type microemulsions as a medium for reactions of nucleophilic substitution in esters have been considered. The kinetics of the reactions ofp-nitrophenyl acetate and caprylate with primary amines in the medium indicated has been studied. The hydrophoby factor, being of great importance for micellar solutions of surfactants, is not substantially manifested in detergent microemulsions: the rate constants of the reactions studied are in fact independent of the length of the alkyl radical of the nucleophile.     

A general method for precalculation of parameters for sustained off resonance irradiation/collision-induced dissociation

Sustained off resonance irradiation (SORI) collision-induced dissociation (CID) is a commonly used method of collisionally activating ions for fragmentation in Fourier transform mass spectrometric experiments. To achieve the degree of fragmentation desired, both the irradiation frequency and amplitude must be optimized. This is a time-consuming procedure, particularly when the m/z values of the precursor ions vary over a broad range. We present an approach that simplifies this optimization by precalculating the irradiation frequency of the ions to be fragmented as a constant percentage of the reduced cyclotron frequency. Using this approach, the optimal amplitude was found to be significantly less dependent on the m/z value of the precursor ion, and therefore required little or no adjustment. This method considerably simplified optimization of SORI-CID for analysis of carbohydrates, glycoconjugates, and peptides over the mass range m/z 300-3500, requiring optimization of only a single experimental parameter, the irradiation amplitude, and only for the first MS/MS stage.     

Application of nonionic amphiphiles for increasing solubility in water of alkylated bibenzimidazole derivatives

Solubilization capacity of a number of nonionic micelle-forming compounds toward 2,2´-bibenzimidazole and its alkylated derivatives was determined by spectrophotometry. It was found that as the hydrophilic lipophilic balance of the studied amphiphiles grows, their solubilization effect toward 2,2´-bibenzimidazoles increases and reaches the highest value in the case of pluronic F127. The conversion of bibenzimidazoles to the cationic form induced by lowering the medium pH improves efficiency of the solubilizers.     

The influence of hydrophobic amines on hydrolysis of bis(p-nitrophenyl) methylphosphonate in micellar solutions of cetylpyridinium bromide

The kinetics of hydrolysis of bis(p-nitrophenyl) methylphosphonate in the presence of primary aliphatic amines in aqueous micellar solutions of cetylpyridinium bromide was studied. The reaction proceedsvia two routes, alkaline hydrolysis and amine-catalyzed hydrolysis according to the general basic catalysis mechanism. The contributions of these routes and the catalytic effect of micelles depend on the hydrophobicity of the amines. The formation of different types of micelles was found, and their characteristic parameters were determined by tensiometry and high-resolution¹H NMR spectroscopy with a magnetic field pulse gradient. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 2, pp. 267–272, February, 2000.