Physicochemical Parameters Affecting the Electrospray Ionization Efficiency of Amino Acids after Acylation.

Electrospray ionization (ESI) is widely used in liquid chromatography coupled to mass spectrometry (LC-MS) for the analysis of biomolecules. However, the ESI process is still not completely understood, and it is often a matter of trial and error to enhance ESI efficiency and, hence, the response of a given set of compounds. In this work we performed a systematic study of the ESI response of 14 amino acids that were acylated with organic acid anhydrides of increasing chain length and with poly(ethylene glycol) (PEG) changing certain physicochemical properties in a predictable manner.

Absorption, fluorescence, and acid-base equilibria of rhodamines in micellar media of sodium dodecyl sulfate.

Rhodamine dyes are widely used as molecular probes in different fields of science. The aim of this paper was to ascertain to what extent the structural peculiarities of the compounds influence their absorption, emission, and acid-base properties under unified conditions. The acid-base dissociation (HR(+)⇄R+H(+)) of a series of rhodamine dyes was studied in sodium n-dodecylsulfate micellar solutions.

Colloidal properties and behaviors of 3 nm primary particles of detonation nanodiamonds in aqueous media.

This study was aimed to reveal the principal colloidal properties of the aqueous dispersion of extremely small primary single-crystalline diamond particles in water. Together with the non-diamond layer, the size of the colloidal species is 2.8 ± 0.

Mercury ions complexation with a series of heterocyclic derivatives of 3-hydroxychromone: spectral effects and prospects for ultrasensitive Hg2+ probing.

Complexation of three 3-hydroxychromone derivatives bearing a nitrogen-containing heterocyclic moiety in the position 2 of the chromone bicycle - benzimidazole, quinoline, and 2,5-diphenyloxazole, with mercury(II) ions is reported. Formation of chelate complexes with the metal cations coordinated with the cavity formed by 3-OH and 4-C═O groups was shown, as well as the possibility of side moiety heteroatom participation in binding of metal ions. High sensitivity to mercury of 2,5-diphenyloxazole-substituted 3-hydroxychromone was elucidated, allowing to detect Hg(2+) below the maximum permissible concentration for drinking water.

Heterogeneous wide range pH-sensing materials allowing ratiometric fluorescence detection based on structurally rigid analogs of 2,6-distyrylpyridine.

The new sensing materials based on the microsized silica gel powder with non-covalently immobilized structurally rigid analogs of 2,6-distyrylpyrydine ((3E,5E)-3,5-dibenzylidene-8-phenyl-1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridines) were developed and tested. Most of the investigated compositions demonstrate linear ratiometric fluorescence response on pH in the physiologically important interval (pH 6-9). The compound with the greatest number of protolytic centers within the studied series demonstrated the widest pH sensitivity range, however in this case the analytical signal was the lowest.

Comparison of C18 silica bonded phases selectivity in micellar liquid chromatography.

The paper describes a new test designed in micellar LC (MLC) to compare the commercial C18 stationary phase properties. This test provides the total hydrophobicity, hydrophilicity, steric selectivity, hydrogen bonding, and ion-exchange capacity properties calculation of the ODS stationary phases. Both the test compounds and chromatographic separation conditions choice for column characterization in MLC are detailed.

Heteroscedasticity of retention factor and adequate modeling in micellar liquid chromatography.

The two concepts of micelle formation (pseudo-phase and mass-action) could be the basis of retention models in micellar liquid chromatography (MLC). The separation of 4-hydroxybenzoic acid esters and seven polyaromatic hydrocarbons were performed to study the repeatability of retention factor in MLC. The full two factor experimental design was used for studying the dependence of retention factor variance on mobile phase composition (sodium dodecylsulfate, 1-butanol).

Aliphatic carboxylic acids as new modifiers for separation of 2,4-dinitrophenyl amino acids by micellar liquid chromatography.

The possibilities of isocratic separation of 2,4-dinitrophenyl derivatives of 12 amino acids that considerably differ in hydrophobicity by micellar mobile phases with different organic modifiers have been discussed. For the first time aliphatic carboxylic acids have been used as modifiers of micellar eluent in micellar liquid chromatography with C18 columns. Elution strength of hybrid micellar phases on the basis of sodium dodecylsulfate and aliphatic carboxylic acids increases in sequence: acetic View Article and Find Full Text PDF

Electromagnetic phase differences in the coherent backscattering enhancement mechanism for random media consisting of large nontransparent spheres.

Phase curves of intensity are calculated for light scattering in media randomly packed with large nontransparent spheres (x=125), the surfaces of which reflect according to the Fresnel equations. We consider three values of refractive index: m = 0.73 + i5.

Fluorescence behavior of chromones containing several protolytic centers 3-Thiazolylchromones: Emission band assignment and pH dependent effects.

Fluorescence properties of 3-thiazolylchromones (TC) were studied in the wide H(0)/pH range -10 to 12. It was found that the number of the excited TC protolytic forms exceeds their quantity in the ground state. The formation of the new emitting species was explained as the result of the dramatic changes in the acid-base characteristics of three protolytic centers of TC molecules under the electronic excitation.

Micellar liquid chromatography retention model based on mass-action concept of micelle formation.

Mass-action model of surfactant micelle formation has been used to develop a conceptual retention model in micellar liquid chromatography (MLC). The retention model bases on the consideration of the changes of the sorbate microenvironment at its transferring from the mobile phase (hybrid micellar eluent) to the stationary phase (a modified surface of alkyl-bounded sorbent). Principal retention equation contains the characteristics of hybrid micelles (critical micelle concentration, degree of counterion binding, partition coefficient of modifier between aqueous solution and micellar pseudo-phase) as well as three fitting parameters.

Radiationless deactivation of the excited phototautomer form and molecular structure of ESIPT-compounds.

Correlation between the character of electronic density redistribution in the excited normal and phototautomer forms, which are involved in the excited state intramolecular proton transfer (ESIPT) reaction, and the rates of primary photoprocesses--proton phototransfer and radiationless deactivation of the phototautomer form--was analysed on the qualitative level. It was revealed that noticeable improvement of fluorescence properties of ESIPT molecules could be achieved by directed modification of their chemical structure, most importantly by the introduction of electron withdrawing substituents into their proton donor moieties. Several facts are presented in favour of the last statement.