Mechanism of the hydroperoxide destruction in the oxidized methyl oleate,oleyl alcohol,and oleic acid

The differentiated mechanism of destruction of hydroperoxides derived from methyl oleate, oleyl alcohol and oleic acid was explained with the influence of the hydrogen-bond interactions. The evidence for the proposed models was given through the quantitative yields of the five classes of the secondary products of autoxidation: monohydroxy-, dihydroxy-, keto-, ketohydroxyderivatives and monofunctional products of degradation of the oxidized molecules.     

Gas chromatographic and NMR spectroscopic study of the interactions between the tris β-diketone chelates of europium and aliphatic nucleophiles

Summary The aim of this work was to study the utilisation of coordinative europium compounds as stationary phase additives in gas chromatography. The following series of aliphatic nucleophilic compounds were used as solutes: n-alcohols, carboxylic acid methyl esters, ketones, ethers and 1-alkenes. A correlation was established between the chromatographic retention values and the NMR chemical shift changes induced by interactions of the organic molecules with the europium chelate. The agglomerate formation between the europium chelates and nucleophilic compounds involves changes in the NMR spectra and selective increases in the GC retention values when adding europium chelates to the stationary phases. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Physico-chemical modelling of solute retention in reversed-phase HPLC with methanol-water mobile phase

Chromatographia - A relationship is derived for the retention parameter (i. e. the retardation coefficient, RF of a solute chromatographed in reversed-phase HPLC using methanol-water mixtures as...     

Phase transitions and molecular motions in [Zn(NH3)4](BF4)2 studied by nuclear magnetic resonance, infrared and Raman spectroscopy

Middle infrared absorption, Raman scattering and proton magnetic resonance relaxation measurements were performed for [Zn(NH₃)₄](BF₄) in order to establish relationship between the observed phase transitions and reorientational motions of the NH₃ ligands and BF₄⁻ anions. The temperature dependence of spin-lattice relaxation time (T₁(¹H)) and of the full width at half maximum (FWHM) of the bands connected with ρ_r(NH₃), ν₂(BF₄) and ν₄(BF₄) modes in the infrared and in the Raman spectra have shown that in the high temperature phase of [Zn(NH₃)₄](BF₄)₂ all molecular groups perform the following stochastic reorientational motions: fast (τ_R≈10⁻¹² s) 120° flips of NH₃ ligands about three-fold axis, fast isotropic reorientation of BF₄⁻ anions and slow (τ_R≈10⁻⁴ s) isotropic reorientation (“tumbling”) of the whole [Zn(NH₃)₄]²⁺ cation. Mean values of the activation energies for uniaxial reorientation of NH₃ and isotropic reorientation of BF₄⁻ at phases I and II are ca. 3 kJ mol⁻¹ and ca. 5 kJ mol⁻¹, respectively. At phases III and IV the activation energies values for uniaxial reorientation of both NH₃ and of BF₄⁻ equal to ca. 7 kJ mol⁻¹. Nearly the same values of the activation energies, as well as of the reorientational correlation times, at phases III and IV well explain existence of the coupling between reorientational motions of NH₃ and BF₄⁻. Splitting some of the infrared bands at T_C2=117 K suggests reducing of crystal symmetry at this phase transition. Sudden narrowing of the bands connected with ν₂(BF₄), ν₄(BF₄) and ρ_r(NH₃) modes at T_C3=101 K implies slowing down (τ_R?10⁻¹⁰ s) of the fast uniaxial reorientational motions of the BF₄⁻ anions and NH₃ ligands at this phase transition.     

Synthesis and biological properties of 1,8‐naphthalimidebutylamines. Serotonin 5‐HT1A and 5‐HT7 binding data and pass‐assisted search

Syntheses of the N‐substituted butyl derivatives of 1,8‐naphthalimide ( 1‐8 ), containing various arylpiperazines, tetrahydroisoquinoline and methylhomopiperazine moieties attached at 4‐position of the butyl chain have been described. Biological activities were evaluated in vitro for their ability to bind to serotonin 5‐HT_1A and 5‐HT₇ receptors. Due to the structural similarity of derivatives 1‐8 to psychotropic agents, the pharmacological properties of target compounds were predicted using PASS program.     

Modeling of ion-exclusion and vacancy ion-exclusion chromatography in analytical and concentration overload conditions

Ion-exclusion chromatography (IEC) finds applications in various different analytical separations of weak acids. Pure, deionized water or a diluted, aqueous solution of a strong mineral acid (such as, e.g., sulphuric acid) is used as the mobile phase, whereas a typical stationary phase is a strongly acidic resin in the H(+) form (e.g., the sulfonated polystyrene-divinylbenzene resin with a high ion-exchange capacity, provided by the sulfonic acid groups). When pure water is used as the mobile phase, then the characteristic leading (i.e., frontally tailing) peaks are obtained, and the retention depends mainly on the concentration of the analyte. An alternative technique is vacancy ion-exclusion chromatography (v-IEC), in which the column is equilibrated with the sample solution, flowing as the mobile phase through the system, and pure water is injected as the sample. In this case, the symmetrical vacant peaks are obtained. The aim of this paper is to describe the retention mechanism in IEC and v-IEC for the adsorptive and nonadsorptive acids in analytical and concentration overload conditions, with pure water and the diluted sulphuric acid solution as the two different mobile phases. The retention times and the peak shapes predicted by the derived equations remain in a good qualitative and quantitative agreement with the experimental data. The model proposed in this paper predicts the new features characteristic of IEC for the adsorptive acids. These are, namely, an increase in the retention time of the peak apexes (up to a certain level and concurring with an increase in the acid concentration), followed by a subsequent decrease of the retention time (with the further growth of the acid concentration in the eluent). Similar changes in the retention time observed for v-IEC in the specific adsorption conditions were also correctly predicted by the model.     

Mathematical models of solute retention in gas chromatography as sources of thermodynamic data. Part IV. Aliphatic alcohols as the test analytes

This study is the fourth consecutive part belonging to the cycle devoted to an alternative approach to deriving certain thermodynamic magnitudes. The previous three papers were dedicated, respectively, to ketones, aldehydes, and alkylbenzenes. In our present study (similar to the previous ones) the following working procedure is adopted. With the aid of capillary gas chromatography, the retention times are obtained for a wide variety of the aliphatic alcohols. The analyses are carried out isothermally on stationary phases of different polarity and at five different measuring temperatures. These data constitute an experimental basis for further processing with the aid of the specially devised mathematical equations. The fitting parameters of these equations, due to their physicochemical meaning, enable determination of certain thermodynamic data. Nine equations used in this study are the relationships coupling the selected retention data [relative retention (r), non-reduced relative retention (rG), the retention factor (k), or the Kováts retention index (I)] and a variety of the physical magnitudes [the boiling point of the analyte (T(B)), its molar volume (Vm), or its molar refraction (Rm)]. These relationships are tested with respect to their performance to predict the molar enthalpy of vaporization (deltaHvap) of the analytes of interest (i.e., of aliphatic alcohols). Evaluation of the equations' performance is carried out through a comparison of the numerical values generated from this approach with those originating from the other methods, and a very good agreement was found between these two series of the data. The best molar enthalpy vaporization values (deltaHvap) are obtained from the retention data originating from the most polar of the three investigated stationary phases (i.e., DB-Wax). Models V and VIII proved the best performing ones among the nine models tested in this study.     

Circular dichroism and conformational dynamics of cephams and their carba and oxa analogues

The biological activity of bicyclic beta-lactam antibiotics depends strongly on the absolute configuration of the bridgehead carbon atom. Frelek and co-workers proposed an empirical helicity rule relating the configuration of the bridgehead carbon atom to the sign of the 220 nm band in the electronic circular dichroism (CD) spectrum of beta-lactams. Here we use synthetic organic chemistry, CD spectroscopy, and time-dependent density functional theory (TDDFT) to investigate the validity of this structure-property relationship for eight model compounds. For conformationally flexible beta-lactams, substantial thermal effects are found which must be included in calculations. To this end, we combine TDDFT calculations of CD with full quantum-mechanical Born-Oppenheimer molecular dynamics (MD) simulations for the first time. The CD spectra are sampled with ground-state density functional trajectories of up to 60 ps. The MD simulations show a surprisingly high sensitivity of the CD to the molecular conformation. On the other hand, the relation between CD and thermally averaged structural parameters is much less complex. While the helicity rule does not seem to hold for individual conformers, it is confirmed by the calculations for seven out of eight systems studied if thermally averaged CD spectra and structures are considered. Since thermal effects on CD can be larger than typical inherent inaccuracies of TDDFT, our results emphasize the need for a systematic treatment of conformational dynamics in CD calculations even for moderately flexible systems. Temperature-dependent CD measurements are very useful for this purpose. Our results also suggest that CD spectroscopy may be used as a sensitive probe of conformational dynamics if combined with electronic structure calculations.     

Secondary electron microscopy and transmission electron microscopy studies of carbon nanotubes in C-Ni films

Carbon nanotubes films have been studied with SEM and TEM. The studied films were obtained using a two step method: PVD process and CVD process. Strongly defected and curled carbon nanotubes containing Ni nanoparticles formed the film with thickness of about 300–400 nm. Observed carbon nanotubes were of lengths from 100 nm to 300 nm and did not stick to each other.