Interaction of anesthetic molecules with α-helix and polyproline II extended helix of long-chain poly-l-lysine.

The effect of halothane, enflurane, sevoflurane, and isoflurane molecules, as volatile anesthetics, on the α-helices and polyproline II extended helices (PPII) of long-chain poly-l-lysine (PLL) were studied using Fourier-transform infrared and vibrational circular dichroism spectroscopy. Uncharged and charged α-helices, as well as charged extended PPII helices, were subjected to anesthetic actions in solvents with different pD values or methanol to water ratios. A crucial factor responsible for hindering the anesthetic-PLL interactions is shown to be the ionization of amino groups of the PLL side chains. The α-helix to ß-sheet transition was triggered only for the uncharged α-helical structures of PLL by the nonpolar anesthetics under study.

Ethanol- and trifluoroethanol-induced changes in phase states of DPPC membranes. Prodan emission-excitation fluorescence spectroscopy supported by PARAFAC analysis.

It has been shown that Prodan emission-excitation fluorescence spectroscopy supported by Parallel Factor (PARAFAC) analysis is a fast, simple and sensitive method used in the study of the phase transition from the noninterdigitated gel (Lß') state to the interdigitated gel (LßI) phase, triggered by ethanol and 2,2,2-trifluoroethanol (TFE) molecules in dipalmitoylphosphatidylcholines (DPPC) membranes. The relative contribution of lipid phases with spectral characteristics of each pure phase component has been presented as a function of an increase in alcohol concentration. It has been stated that both alcohol molecules can induce a formation of the LßI phase, but TFE is over six times stronger inducer of the interdigitated phase in DPPC membranes than ethanol molecules. Moreover, in the TFE-mixed DPPC membranes, the transition from the Lß' to LßI phase is accompanied by a formation of the fluid phase, which most probably serves as a boundary phase between the Lß' and LßI regions. Contrary to the three phase-state model of TFE-mixed DPPC membranes, in ethanol-mixed DPPC membranes only the two phase-state model has been detected.

Anesthetic-dependent changes in the chain-melting phase transition of DPPG liposomes studied using near-infrared spectroscopy supported by PCA.

The effect of inhalation anesthetics (enflurane, isoflurane, sevoflurane or halothane) on the lipid chain-melting phase transition of negatively charged phospholipid membranes was studied using near-infrared (NIR) spectroscopy supported by Principal Component Analysis (PCA). NIR spectra of anesthetics-mixed dipalmitoylphosphatidylglycerol (DPPG) membranes were recorded in a range of the first overtone of the symmetric and antisymmetric stretching vibrations of CH2 groups of lipid aliphatic chains as a function of increasing temperature. Anesthetic-dependent changes in the trans to gauche conformers ratio of CH2 groups in the hydrocarbon lipid chains were characterized in detail and compared with the zwitterionic lipid membranes, which were built of dipalmitoylphosphatidylcholine (DPPC) molecules.

Aggregation of N,N'-diallylurea and N,N'-diallylthiourea in solutions.

Joint studies by IR spectroscopy, dipole moments, average molecular weight measurements and DFT calculations on the self-aggregation of N,N'-diallylureas and N,N'-diallylthioureas in solvents of different polarities were performed. Simultaneous uses of all these methods are required for better understanding the mechanism of aggregation and the effects of different polarity of solvents. In this study also the measurements of IR spectra in polarized light were additionally performed, which gives information on arrangement of aggregates in liquid crystal matrix-built of 4-CN biphenyl derivative. It was demonstrated that in such conditions two forms of dimers the linear and cyclic ones are in equilibrium with different arrangements according the axis of CN group.

Self-aggregation mechanisms of N-alkyl derivatives of urea and thiourea.

The mechanisms of self-aggregation of N-alkyl and N,N'-dialkyl derivatives of urea and thiourea in weakly polar solvents (chloroform and 1,2-dichloroethane) were examined. The C-H···O or C-H···S hydrogen bonds formed with these two acidic solvents compete with the N-H···O or N-H···S hydrogen bonds formed between solute molecules, influencing the self-aggregation of urea derivatives in a particular solvent. The peculiarities of the solvent interactions were discussed and the stronger interaction of chloroform was noted. Aggregation of the N-alkyl derivatives was followed using IR spectroscopy, with two gradual aggregation constants (K1 and K2) determined. The average molecular weight and dipole moments were shown to depend on the concentration, and the form of aggregation was analyzed through the study of the dipole moments. All of the urea derivatives demonstrated an increase in dipole moment with increased concentration, resulting in stronger NH2···O hydrogen bond interactions and leading to linear-type aggregation. Contrastingly, the dipole moments of the mono-N-alkyl-substituted thioureas decreased with concentration. Density-functional theory calculation of these processes showed that reliable results could only be obtained if solvent interactions were considered, with a specific combination of local and bulk effects. It was also shown that going from N,N'-disubstituted to N-monoalkyl derivatives the ability to aggregate increases, which is related to a diminished steric hindrance to hydrogen bonding. Finally, it was demonstrated that the mechanisms of self-aggregation depend on the acid-base properties of the solute, hydrogen bonding to the solvent molecules, and steric interactions of the aliphatic chains.

Correlation between structure and shape of the polarized infrared absorption spectra of 4-chloro-2'-hydroxy-4'-alkyloxyazobenzenes.

Polarized infrared spectra of liquid crystalline 4-chloro-2'-hydroxy-4'-alkyloxyazobenzenes (CHAB) with C(5), C(6), and C(7) alkyl chains measured at 25 °C were compared, with particular attention being paid to the influence of chain length on formation of ordered boundary layers. The effect of chain elongation is discussed on the basis of calculations of the optimized geometry of dimeric species, which reflects the role of association in ordered phases. The impact of the varying intermolecular interactions on the spectra of C(5), C(6), and C(7) derivatives measured as a function of the polarization angle is analyzed by principal component analysis (PCA). The polarization-angle-dependent results are contrasted with the transition moment directions obtained from the density functional theory (DFT) calculations. The continuum spread down to 500 cm(-1) and a pseudoband at ca. 600 cm(-1) ascribed to the Fermi resonance between ν(OH) and γ(OH) modes is an additional phenomenon whose features also depend on alkyl chain length.

Structure of aggregates of dialkyl urea derivatives in solutions.

Combined IR spectroscopy, dipole moment, and average molecular weight measurements and DFT calculations on the self-aggregation of N,N'- and N,N-dialkylureas in solvents of different polarities were performed. It was found that, to acquire a better understanding of the mechanisms of associations, the simultaneous use of all of these methods is required. It was found that symmetric dialkyl derivatives of urea associate much more strongly, giving in CCl(4) even a 12-fold mass of monomers, in contrast to asymmetric ones, where the average molecular weight reaches only a 2-fold mass of monomers. The very strong influence of solvents was discovered. The aggregation is much weaker in more polar chloroform and 1,2-dichloroethane leading to only a 2-fold increase in the average molecular weight. A strong influence of the symmetry of dialkylurea molecules was also found. Dipole moments of symmetric N,N'-dialkylurea increase with concentration, suggesting a rather linear arrangement of vectors in an aggregate. For asymmetric N,N-derivatives dipole moments decrease with concentration. DFT calculations were used to predict the form of aggregation.

Matrix-isolation FT-IR spectroscopic study and theoretical DFT(B3LYP)/6-31++G** calculations of the vibrational and conformational properties of tyrosine.

The complicated conformational isomerism of tyrosine is studied by experimental matrix-isolation FT-IR spectroscopy combined with theoretical DFT(B3LYP)/6-31++G** calculations. Not less than 18 possible conformations of tyrosine have been considered theoretically. The results revealed that the most and the less stable forms of neutral tyrosine have the same conformation of the main part of amino acid (conformation II) but they differ in orientation of the phenyl ring. The calculated values of the relative energies suggest that all conformations would be detectable in the experimental spectrum. However, it appeared that it is not possible to distinguish in the experimental spectrum between the bands due to the forms with the same conformation of the main part of amino acid but a different orientation of the phenol ring.

Influence of substituents on the anharmonicity of nus(OH) vibration in phenol derivatives explored by experimental and theoretical approach.

Very good reproducibility of the first five vibrational transitions of phenol in the gas phase by the MP2/ 6-31G potential for O-H bond stretching was found. The vibrational levels were calculated by a program for variational solving of the time-independent Schrödinger equation in one dimension. Relative intensities of particular transitions were determined on the basis of the function of the dipole moment. The substituent effects on the nu(s)(OH) transitions and on the intensity of these transitions, as well as on the structure of eleven phenols, was analyzed as a function of the pK(a) values.