Gas phase SN2 reactions of halide ions with trifluoromethyl halides: front- and back-side attack vs. complex formation.

Density functional theory computations and pulsed-ionization high-pressure mass spectrometry experiments have been used to explore the potential energy surfaces for gas-phase S(N)2 reactions between halide ions and trifluoromethyl halides, X(-) + CF(3)Y --> Y(-) + CF(3)X. Structures of neutrals, ion-molecule complexes, and transition states show the possibility of two mechanisms: back- and front-side attack. From pulsed-ionization high-pressure mass spectrometry, enthalpy and entropy changes for the equilibrium clustering reactions for the formation of Cl(-)(BrCF(3)) (-16.5 +/- 0.2 kcal mol(-1) and -24.5 +/- 1 cal mol(-1) K(-1)), Cl(-)(ICF(3)) (-23.6 +/- 0.2 kcal mol(-1)), and Br(-)(BrCF(3)) (-13.9 +/- 0.2 kcal mol(-1) and -22.2 +/- 1 cal mol(-1) K(-1)) have been determined. These are in good to excellent agreement with computations at the B3LYP/6-311+G(3df)//B3LYP/6-311+G(d) level of theory. It is shown that complex formation takes place by a front-side attack complex, while the lowest energy S(N)2 reaction proceeds through a back-side attack transition state. This latter mechanism involves a potential energy profile which closely resembles a condensed phase S(N)2 reaction energy profile. It is also shown that the Cl(-) + CF(3)Br --> Br(-) + CF(3)Cl S(N)2 reaction can be interpreted using Marcus theory, in which case the reaction is described as being initiated by electron transfer. A potential energy surface at the B3LYP/6-311+G(d) level of theory confirms that the F(-) + CF(3)Br --> Br(-) + CF(4) S(N)2 reaction proceeds through a Walden inversion transition state.

[Prophylaxis of postgastrectomy complications in patients with gastric cancer].

There are presented the results of surgical treatment of 447 patients. suffering gastric cancer, in whom gastrectomy was performed. Esophago-initestinal anastomosis was performed according to method of G. V. Bondahr. Interintestinal anastomosis (IIA) was formed using traditional Braun method and also was applied the longitudinal-transversal method, elaborated in the clinic. Usage of the method proposed did not worsen the immediate and late results, but have promoted significant improvement of the gastrectomy functional results. The method application secures the trustworthy lowering of the postgastrectomy complications rate while performing gastrectomy (dumping syndrome, reflux-esophagitis, the adduced loop syndrome) comparing with such, using Braun IIA--accordingly 30.5 and 52.8% (P = 0.016); fair, good and excellent the patients quality of life--accordingly in 67.8 and 47.2% (P = 0.024). The elaborated procedure of the IIA formation constitutes the method of choice while performing gastrectomy.

[Genetic polymorphism of a pelagic fish species, little Baikal oilfish Comephorus dybowski, deduced from analysis of microsatellite loci].

Intraspecific genetic polymorphism of a Baikal Lake endemic, little Baikal oilfish (Comephorus dybowski Korotneff, 1905), was evaluated based on microsatellite analysis. Six microsatellite loci designed for the European sculpin, Cottus gobio, were used. Each locus was typed using 25 to 35 individuals from each of the Baikal trenches (southern, middle, and northern). Analysis of genetic differentiation (F(ST) and R(ST)) revealed no statistical significant differences between the samples. The data showed that the target species was represented by a single panmictic stable population.

[New approach to determining sensitive innervation zones]. / Novyi podkhod k opredeleniiu zon chuvstvitel'noi innervatsii.

Despite a vast body of studies carried out over the past years, there is no single definite opinion about the topography of sensitive innervation zones. The reason, underlying such a situation, is analyzed in the report. Based on laser dopplerfluorometry and evoked somato-sensory potentials, an original method for determining autonomic innervation zones is described. High sensitivity of the method allows measuring dermatome topography in the absence of corresponding clinical disorders.

Structural and rheological properties of methacrylamide modified gelatin hydrogels.

Dynamic shear oscillation measurements at small strain were used to characterize the viscoelastic properties and related differences in the molecular structure of hydrogels based on gelatin methacrylamide. Gelatin was derivatized with methacrylamide side groups and was subsequently cross-linked by radical polymerization via photoinitiation. The light treatment of methacrylamide gelatin solutions resulted in the production of hydrogel films with high storage modulus (G'). Mechanical spectra and thermal scanning rheology of the obtained hydrogels are described. The temperature scan of the network below and above melting point of gelatin allowed us to identify the respective contributions of chemical and physical cross-linkage to the hydrogel elastic modulus. The results indicate that the rheological properties of the gelatin-based hydrogels can be controlled by the degree of substitution, polymer concentration, initiator concentration, and UV irradiation conditions.

In vitro release characteristics of bioactive molecules from dextran dialdehyde cross-linked gelatin hydrogel films.

Hydrogel films, prepared by cross-linking of gelatin with dextran dialdehydes (weight ratio 2:1), and containing either fluorescein isothiocyanate dextran (Mw 70000) or polypeptides were evaluated in terms of their release characteristics and mechanical properties upon increasing storage time at 4 degrees C. Important changes in release kinetics and mechanical properties of the cross-linked gelatin films were observed, especially during the first week after the hydrogel production. Rheological and NMR measurements showed that the mechanical properties of the gelatin hydrogel films were improved with increasing storage time. It appeared that the process of chemical cross-linking and physical structuring of the gelatin hydrogel matrix did not occur instantaneously and substantially influenced the polypeptide release patterns. Cross-linked gelatin hydrogels were found to be appropriate release systems for medium-term sustained delivery of biologically active epidermal growth factor (EGF), but release characteristics were strongly dependent on the nature of the protein which was incorporated.

Chemical ionization of phenyl n-propyl ether and methyl substituted analogs: Propene loss initiated by competing proton transfer to the oxygen atom and the aromatic ring.

The mechanism of propene loss from protonated phenyl n-propyl ether and a series of mono-, di-, and trimethylphenyl n-propyl ethers has been examined by chemical ionization (CI) mass spectrometry in combination with tandem mass spectrometry experiments. The role of initial proton transfer to the oxygen atom and the aromatic ring, respectively, has been probed with the use of deuterated CI reagents, D2O, CD3OD, and CD3CN (given in order of increasing proton affinity), in combination with deuterium labeling of the ß position of the n-propyl group or the phenyl ring. The metastable [M + D](+) ions of phenyl n-propyl ether-formed with D2O as the CI reagent-eliminate C3H5D and C3H6 in a ratio of 10:90, which indicates that the added deuteron is incorporated to a minor extent in the expelled neutral species. In the experiments with CD3OD as the CI reagent, the ratio between the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of phenyl n-propyl ether is 18:82, whereas the ratio becomes 27:73 with CD3CN as the reagent. A similar trend in the tendency to expel a propene molecule that contains the added deuteron is observed for the metastable [M + D](+) ions of phenyl n-propyl ether labeled at the ß position of the alkyl group. Incorporation of a hydrogen atom that originates from the aromatic ring in the expelled propene molecule is of negligible importance as revealed by the minor loss of C3H5D from the metastable [M + H](+) ions of C6D5OCH2CH2CH3 irrespective of whether H2O, CH3OH, or CH3CN is the CI reagent. The combined results for the [M + D](+) ions of phenyl n-propyl ether and deuterium-labeled analogs are suggested to be in line with a model that assumes that propene loss occurs not only from species formed by deuteron transfer to the oxygen atom, but also from ions generated by deuteron transfer to the ring. This is substantiated by the results for the methyl-substituted ethers, which reveal that the position as well as the number of methyl groups bonded to the ring exert a marked effect on the relative importances of the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of the unlabeled methyl-substituted species.

[The functional role of monoaminergic and amino acid-ergic mechanisms of the locus coeruleus in anxiety from different aversive origins]. / Funktsional'naia rol' monoamin- i aminokislotergicheskikh mekhanizmov locus coeruleus v trevoge razlichnogo aversivnogo geneza.

Dopamine and glutamine acid microinjection in the locus coeruleus of rats does not influence the alarm state in the test of "Threatening situation" avoidance, but weakens the state of alarm in the test of "illuminated site" avoidance. The local injection of GABA and noradrenaline mesatone effect imitators in this brain formation weakens the alarm state in the test of "threatening situation" avoidance but is not effective in the test of "illuminated site" avoidance. On the contrary, the chemical stimulation of locus coeruleus by serotonin influences the anxiolytic effect in two different experimentally modelled states of alarm. The participation of locus coeruleus and acidergic mechanisms in anxiety of diverse aversive genesis is discussed.