The Effect of Temperature on Nucleation of Condensed Water Phase on the Surface of a β-AgI Crystal. 2. Formation Work

In the condensation mechanism of heterogeneous ice formation, water crystallization occurs after a necessary amount of the liquid phase has accumulated on a substrate surface. In this way, the ice-forming activity of the surface is governed by its adsorption ability with respect to water vapor. The Monte Carlo canonical statistical ensemble method has been used to calculate the free energy, entropy, and work of nucleation of a disordered condensed water phase on the surface of crystalline silver iodide and to determine the surface tension. Comparative calculations have been performed at 260 and 320 K for the defect-free surface of a basal face of a crystal. The surface of a β-AgI crystal is completely covered with a monomolecular film even in unsaturated water vapors. The surface tension at the growing nucleus–substrate interface substantially increases due to the formation of the underlying film, and the growth of the nucleus becomes possible only in a supersaturated vapor. As the vapor density increases, the thickness of the condensed water layer grows, and, at negative Celsius temperatures, conditions are created for its crystallization. The underlying film with pronounced hydrophobic properties hinders nucleation, thereby decreasing the ice-forming activity of the surface in the condensation process. Under these conditions, the observed abnormally high ice-forming activity of silver-iodide aerosol particles may be explained by the presence of numerous crystal defects on the particle surface, with these defects representing channels that provide overcoming the hindering action of the film.     

Synthesis based on β-phenylethylamines. IX. Synthesis of sulfides of β-phenylethylamines and of N-benzyltetrahydroisoquinolines

New bimolecular sulfur-containing -phenylethylamines and N-benzyltetrahydroisoquinolines have been synthesized from formyl derivatives of diaryl sulfides. The possibility of using metals as catalysts for obtaining diaryl sulfides in the reaction of ortho-substituted benzaldehydes with SCl₂ has been shown for the first time.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 731–735, September–October, 1995. Original article submitted November 11, 1994.     

Study on Reactivity of Five-co-ordinate Bicycloazastannoxides. Ⅲ. Bromination with Bromine

In earlier our studies, we have determined that the structure of pentacoordinate bicycloazastannoxides with Schifibase derived from amino acids is similar to that of the metal vitamin B₆ chelates by X-ray method[l-3]. Recently we investigated the condensation of pentacoordinate bicycloazastannoxides with aldehydes[4] and first determined the thermodynamic α-CH acidity (pKa value) of pentacoordinate bicycloazastannoxides by the accurate spectrophotometeric method for relative equilibrium acidities of weak carbon acids in dimethyl sulfoxide[5]. It was found that the effect of the effect of α-CH acidity and stability of α-carbanions on condensation is important. The bulkiness of the amino acid moieties affects the α-CH acidity directly, and the effect of the bulkiness of amino acid moieties on.their α-CH acidities was interpreted by the Taft equation.     

Studies on Agarofurans VIII. Synthesis of the Metabolites of 4-Butyl-a-agarofuran

Agarofurans have been found to be active on the nervous system in our institute. 4-Butyl-a-agarofuran 1 is a promising drug candidate. In order to explore the pharmacokinetics of 1, the metabolism of 1 in vitro was studied with liver microsomes from rats. Five metabolites were isolated and structures were identified as compounds 2-6. But the absolute configuration of 2,4,5 and the position of carbonyl in 3 could not be unambiguously determined. Further determination was limited by the smal…     

Comment on “the effect of reagent rotation on steric requirements of elementary exchange reactions” by H. Kornweitz,A. Persky and R.D. Levine

The conclusion that reagent rotation in O+HCl enhances reactivity at high impact parameter, but suppresses reactivity at low impact parameter has been examined. It is found instead that rotation enhances reactivity as effectively for low as for high impact parameter.     

Studies on sulfinatodehalogenation ⅩⅩⅣ.Further study on sodium dithionite-initiated perfluoroalkylation of electron-rich aromatics

The application ot the sulfinatodehalogenation reaction system for the perfluoroalkylationof electron-rich aromatics is further studied.It was shown that perfluoroalkyl iodides reacted withpolyhydric phenols,N,N-dialkylanilines,2,5-dimethylpyrrole,N-methylpyrrole initiated by Na_2S_2O_4-NaHCO_3 gave the corresponding perfluoroalkylated products in moderate to good yields.     

Prediction of enthalpies of vaporization based on modified Randič indices. Esters

In the work a prediction method based on modified Randi? indices to estimate the enthalpies of vaporization under standard conditions Δ_vapH⁰(298.2) is proposed for esters with different structures and numbers of ester groups. It is shown that the proposed method enables the prediction of enthalpies of vaporization of esters with an accuracy as good as experimental.     

Photochemistry of molecules adsorbed on alkali ion exchanged zeolites. A “Lebensraum” effect on product formation.

The products of the photolysis of dibenzyl ketone adsorbed on faujasite zeolites are found to be a strong function of the Si/Al composition of the zeolite and of the exchangeable cations associated with the internal framework.     

The impact of dihydrogen phosphate anions on the excited-state proton transfer of harmane. Effect of β-cyclodextrin on these photoreactions

Photoinduced proton transfer reactions of harmane (1-methyl-9H-pyrido[3,4-b]indole) (HAR) in the presence of a proton donor/acceptor such as dihydrogen phosphate anions in aqueous solution have been studied by stationary and time-resolved fluorescence spectroscopy. The presence of high amounts of dihydrogen phosphate ions modifies the acid/base properties of this alkaloid. Thus, by keeping the pH constant at pH 8.8 and by increasing the amount of NaH(2)PO(4) in the solution, it is possible to reproduce the same spectral profiles as those obtained in high alkaline solutions (pH >12) in the absence of NaH(2)PO(4). Under these conditions, a new fluorescence profile appears at around 520 nm. This result could be related to the results of a recent investigation which suggests that a high intake of phosphates may promote skin tumorigenesis. The presence of β-cyclodextrin (β-CD) avoids the proton transfer reactions in this alkaloid by means the formation of an inclusion complex between β-CD and HAR. The formation of this complex originates a remarkable enhancement of the emission intensity from the neutral form in contrast to the cationic and zwitterionic forms. A new lifetime was obtained at 360 nm (2.5 ns), which was associated with the emission of this inclusion complex. At this wavelength, the fluorescence intensity decay of HAR can be described by a linear combination of two exponentials. From the ratio between the pre-exponential factors, we have obtained a value of K = 501 M for the equilibrium of formation of this complex.     

Study on degrees of mesomorphic zone of polymer. Ⅲ.Determination of the degree of crystallinity of Eucommia Ulmoides gum by VTFTIR and VTWAXD

Eucommia Ulmoides (EU) gum will crystallize easily at room temperature due to the regular trans-1,4-polyisoprene (TPI) molecular structure. Around the skeleton stretching vibration band of TPI, its FTIR spectrum showed 5 weak crystalline peaks decrease as temperature increase, and there are also two amorphous peaks (845 cm⁻¹ and 668 cm⁻¹) increase as temperature increase. According to this phenomenon, Variable Temperature Fourier Transform Infrared Spectrum (VTFTIR) and Variable Temperature Wide Angle X-ray Diffraction (VTWAXD) have been taken to analyze the degree of crystallinity of EU gum. In addition to the ratio of crystalline zone, the result determined by VTFTIR also involve the mesomorphic zone, which make it higher than the result determined by VTWAXD. Through the comparative analysis of VTFTIR and VTWAXD, it has been proved that the ratio of crystalline zone, mesomorphic zone, amorphous zone in EU gum were respectively 39.8%, 27.6%, 32.6% at room temperature. Based on the Density Measurement and the three-phase model theory, the density gradient function of the mesomorphic zone of EU gum was firstly proposed. Below 60 °C, the density of the mesomorphic does not change with the temperature, approximately 0.931g/cm⁻³. Above 60 °C, the density of the mesomorphic decreases with the temperature increasing, and finally drops to 0.905g/cm⁻³ at 80 °C, which is equal to the density of the complete amorphous zone.     

Theoretical studies on the influence of molecular interactions on the mechanism of electron transfer in photosynthetic reaction center of Rps.viridis

Based on the QM/MM optimized X-ray crystal structure of the photosynthetic reaction center (PRC) of purple bacteria Rhodopseudomonas (Rps.) viridis, quantum chemistry density functional method (DFT, B3LYP/6-31G) has been performed to study the interactions between the pigment molecules and either the surrounded amino acid residues or water molecules that are either axially coordinated or hydrogen bonded with the pigment molecules, leading to an explanation of the mechanism of the primary electron-transfer (ET) reactions in the PRC. Results show that the axial coordination of amino acid residues greatly raises the ELUMO of pigment molecules and it is important for the possibility of ET to take place. Different hydrogen bonds between amino acid residues, water molecules and pigment molecules decrease the ELUMO of the pigment molecules to different extents. It is crucial for the ET taking place from excited P along L branch and sustains that the ET is a one-step reaction without through accessory bacterioc     

Studies on Chemical Composition of Anemone Altaica C.A.May (Ⅱ)

A new dispirolactone compound,C10H12O6 m.p.224-226℃,wasisolated from the ethyl acetate extract of the roots of anemone aJ-taica C.A.May,the Chinese medicinal herb,by using Si gel column chromatography.Its structure was determined as: 1,6,9,13-tetra-oxadispiro[4,2,4,2]tetradecane-2,10-dione by means of IR,NMR,MS spectra and X-ray diffraction analysis.     

Effect of Catalase on Biocatalytic Synthesis of Pyruvate by Enzymes from Pseudomonas sp.

Pyruvate was produced from DL-lactate by a kind of green-chemical biocatalyst --cell-free extract from bacterial strain Pseudomonas sp. SM-6. Catalase in cell-free extract, whichcould stabilize the pyruvate formed by lactate oxidase, played an important role in pyruvatepreparation. The effect of catalase in conversion process was evaluated.     

Studies on Agarofurans Ⅲ. The Synthesis of 3-Substituted Agarofurans

Agarotlirans were found to be bioactive on nervous system. 3,4-dihydroxy dihydroagarofuran (l)' is only one of this group of natural products, which has substituent on C3 position.We synthesized this compound by the reported nletllod' and tbund it to possess somespecific bioactivity on nervous system. In order to search for more active compounds, wedecided to modify agarofurans on C-3 position beginning with the synthesis of 14-nor-3oxodihydroagarofuran (2).In the initial stage of the synthes…     

Gas Hydrate Frameworks of Allen's Polyhedra. 1. Frameworks on 3–5 Nets

The structures of water molecule frameworks built up of 5¹², 5¹²6², 5¹²6³, and 5¹²6⁴ polyhedra are discussed. In the frameworks of such polyhedra, it is possible to distinguish layers; the centers of the polyhedra belonging to a layer are at the nodes of a planar network consisting of triangular, pentagonal, and hexagonal meshes. The structure of one layer entirely determines the structure of the whole framework. An analysis is given of the structure and topology of frameworks whose layers are constructed on pentagontrigonal nets. It is shown that these frameworks can be constructed from two types of polyhedral blocks closely packed in space.     

Studies on Agarofurans Ⅳ. The Synthesis of 4-Substitutioned Agarofurans

Agarowoodoilwasfoundtobebioactiveinpharmacologicalscreeningforthenervoussysteminourinstitute.AgarofuransareonesmicturaltypeoftheimportantconstituentSofagarowoodoil.Q-Agarofuran(lh),oneofthemanyconstitUentsoftheoil,issuspectedofbeinganimportantcontributortothebioactivity.AlthoughseveralsynthesisofQ-agarofuran(fo)havebeendescribed'-',theyarenotsuitableforthesynthesisofitsanalogs.Thebioactivitiespromptedustodevelopanewroutetoa-agarofuran(fo)anditsanalogs.EarliersynthesisofQ-agarofuran(lb),with…     

Synthesis of Nanostructured Carbon on Ni Deposited on Mesoporous Aluminum,and Titanium Oxides. Investigation of Biocatalytic Properties of Lipase Adsorbed on Carbon–Mineral Supports

This work is a continuation of the studies devoted to the synthesis of nanostructured carbon (NSC) as a result of the pyrolysis of a mixture of H₂ + C₃–C₄ alkanes on supported Ni catalysts. Mesoporous alumina (γ-Al₂O₃) and titania (TiO₂), on which Ni(II) compounds are deposited by impregnation or homogeneous precipitation, are studied as carriers. Using the methods of thermogravimetric analysis and scanning electron microscopy, it is shown that the activity of Ni catalysts (carbon yield) and the morphology of synthesized NSC are largely determined by the chemical nature of the support. It is found that the synthesis of NSC in the form of carbon nanofibers with a pronounced filamentary structure proceeds only on a Ni catalyst supported on titanium dioxide. The mesoporous carbon–mineral supports obtained after catalytic pyrolysis were studied in the adsorptive immobilization of the enzyme such as Thermomyces lanuginosus lipase. The adsorption properties of the supports, as well as the enzymatic activity and stability of the prepared biocatalysts in the esterification of saturated fatty acids (capric, C10: 0) with aliphatic alcohols (isopentanol, C₅) in the non-aqueous media of organic solvents (hexane and diethyl ether) at ambient temperature, are studied. Biocatalysts prepared by lipase adsorption on NSC/TiO₂ show the maximum esterification activity of 100 EA/g, which is 20–45 times higher than the activity of lipase adsorbed on NSC/Al₂O₃.     

Modifications based on coumarins. II. Synthesis ofα-monoglycerides of karatavic and galbanic acids and their phosphates

The synthesis has been performed of -monoglyceride derivatives of coumarins — karatavic and galbanic acids and their modified derivatives — phosphates. The structures of the compounds have been confirmed by IR, UV, PMR, and¹³C and³¹P NMR spectroscopies.A. B. Bekturov Institute of Chemical Sciences, Academy of Sciences of the Republic of Kazakhstan, Almaty Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 217–220, March–April, 1997.