Tuning the leaving group in 2-deoxy-2-fluoroglucoside results in improved activity-based retaining β-glucosidase probes

The potency of 2-deoxy-2-fluoroglycosides in activity-based profiling of human acid β-glucosidase is drastically improved by introducing an N-phenyl trifluoroacetimidate leaving group at the anomeric center. Protonation by the general acid-base catalyst in the active site turned out to be a prerequisite, making the imidate probe a genuine mechanism-based glycosidase inactivator.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

Oscillation in the KMnO_4-NH_2CH_2COOH CSTR System

ＯｓｃｉｌｌａｔｉｏｎｉｎｔｈｅＫＭｎＯ_４－ＮＨ_２ＣＨ_２ＣＯＯＨＣＳＴＲＳｙｓｔｅｍＨｅＸｉｎｇＬＩａｎｄＸｉａｏＪｕｎＨＵＡＮＧ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，ＳｈａｎｇｈａｉＮｏｒｍａｌＵｎｉｖｅｒｓｉｔｙＳｈａｎｇｈａｉ２００?..     

Synthesis of (VO)2P2O7 catalystsvia exfoliation-reduction of VOPO4·2H2O in butanol in the presence of ethanol

The exfoliation-reduction of VOPO₄·2H₂O in l-butanol oriso-butanol alone, and in a l-butanol/ethanol oriso-butanol/ethanol mixture, were conducted. Although all precursors were composed of a lamellar compound with intercalated alcohol molecules, VOHPO₄·0.5H₂O was formed when the exfoliation-reduction process was carried out in the mixed alcohol. All precursors transformed to a single phase of (VO)₂P₂O₇ under the reaction conditions forn-butane oxidation, but the crystallinity of (VO)₂P₂O₇ was different. The catalyst synthesized iniso-butanol/ethanol was well crystalline (VO)₂P₂O₇, and exhibited higher selectivity to maleic anhydride than that synthesized iniso-butanol alone for then-butane oxidation.     

Solid solution in the LiAlO2LiCrO2 ternary oxide system

The solid solution LiAl_xCr_1−xO₂ has been synthesized over the complete range 0 ⩽ x ⩽ 1. The syntheses at the high aluminum compositions (x ⩾ 0.60) have been achieved through stabilization of the α-LiAlO₂ structure with chromium ions in octahedral coordination.     

Phase Relations in The V2O5–MoO3–α-Sb2O4 System in The Solid State in Air Atmosphere

The phase equilibria established in the V₂O₅–MoO₃–α-Sb₂O₄ system in the solid state in an air atmosphere were examined by using XRD and DTA methods. The obtained results allowed us to find that in this system a novel compound is formed involving three oxides. Its formula can be written as Sb₃V₂Mo₃O₂₁. The synthesis of this compound requires picking up the atmospheric oxygen. X-ray characteristics of this compound were determined and it was found that it melted incongruently at 740°C. The results obtained until now allow us to divide the investigated V₂O₅–MoO₃–α-Sb₂O₄ system into five partial subsystems. This revised version was published online in July 2006 with corrections to the Cover Date.     

High Temperature Phase Transitions in Na_xCoO_2 Materials

1 INTRODUCTION In recent years, much attention has been focused on the NaxCoO2 system due to its notable properties and potential technologic applications as a cathode material in high-energy density, reversible solid state battery systems[1, 2]. Recently, large thermoelectric power[3～6] in NaxCoO2 and superconductivity (～4 K) in hydrated NaxCoO2yH2O (x = 0.35, y = 1.33) ma- terial have been observed[7]. This hydrated layered phase is the first 3d-transition metal oxide with superco…     

Die Bestimmung von ?thylendiamin in 2-Methylpiperazin

Ohne Zusammenfassung     

Calculated energy barriers for the identity SN2 reaction H2O + CH3OH2+ → +H2OCH3 + OH2 in the gas phase,in water clusters,and in aqueous solution

The bimolecular nucleophilic substitution reaction H₂O + CH₃OH₂⁺ → ⁺H₂OCH₃ + OH₂ has been studied using various quantum chemical methods. Accurate barriers for the reaction in the gas phase are presented and discussed. The effect of microsolvation by water molecules in small clusters has been investigated. Extrapolation of the barrier obtained in the small clusters, using a linear relationship between the activation energy and the proton affinity of water clusters, gives a barrier for the reaction in aqueous solution which is in good agreement with that obtained in separate model calculations (polarized continuum model of a super molecule with the first solvation shell included).     

Influence of alkyl substituents in 1,3-diethyl-2-thiobarbituric acid on the coordination environment in M(H2O)2(1,3-diethyl-2-thiobarbiturate)2 M = Ca2+, Sr2+

Two new isostructural complexes, [Ca(H₂O)₂(μ₂-Detba-O,O′)₂]_n (1) and [Sr(H₂O)₂(μ₂-Detba-O,O′)₂]_n (2) (HDetba = 1,3-diethyl-2-thiobarbituric acid), were synthesized and characterized by single-crystal and powder X-ray diffraction analysis, TG-DSC, FT-IR, and emission spectroscopy. The single-crystal X-ray diffraction data revealed that 1 and 2 are polymeric where M²⁺ (M = Ca, Sr) is a six-coordinate octahedral binding four Detba^? ions and two water molecules. The octahedra are linked through bridging Detba^? ions forming a 2-D layer. Two intermolecular hydrogen bonds O–H…S in the crystal form a 3-D net. The comparison of M(Detba)₂ and M(Htba)₂ (H₂tba = 2-thiobarbituric acid) structures showed that the coordination number of metals in M(Detba)₂ does not exceed six and there are no π–π interactions, unlike compounds with Htba^?; Detba^? ions are only bridges in HDetba coordination compounds. Thermal decomposition of 1 and 2 includes dehydration, which mainly ends at 200 °C, and organic ligand oxidation at 300–350 °C with a release of CO₂, SO₂, H₂O, NH₃, and isocyanate. Upon excitation at 220 nm, 1 and 2 exhibit an intense emission maximum at 557 nm.     

Untersuchungen in den Dreistoffsystemen: Molybdän-Silizium-Bor,Wolfram-Silizium-Bor und in dem System: VSi2−TaSi2

Die grundsätzliche Aufteilung der Phasenfelder des Dreistoffsystems: Mo–Si–B wird in einem Schnitt bei 1600°C gegeben. Es tritt eine ternäre Mo₅(Si, B)₃-Phase mitT 2-Struktur auf, welche mit Mo-MK, Mo₃Si, Mo₅Si₃-T 1-Typ, Mo₂B und MoB im Gleichgewicht steht. Es existiert auch die isotype Kristallart im Dreistoffsystem: W–Si–B. Die Existenz eines borreichen Silicoborids wird wahrscheinlich gemacht. Silizium nimmt etwas Bor in fester Lösung auf. Zwischen VSi₂ und TaSi₂ besteht eine lückenlose Mischreihe.

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Mit 6 Abbildungen     

EuPtSn2 – A Stannide with Sn2 Dumbbells in a Three-dimensional [PtSn2]2– Polyanion

EuPtSn₂ was obtained by melting of the elements in a sealed tantalum ampoule followed by an annealing sequence for crystal growth. The EuPtSn₂ sample was studied through its Guinier powder pattern and the structure was refined from single-crystal X-ray diffractometer data: CeRhSn₂ type, Cmcm, a = 472.05(3), b = 1724.19(12), c = 957.36(7) pm, wR₂ = 0.0388, 879 F² values and 30 variables. The platinum and tin atoms build up a three-dimensional [PtSn₂]^2– polyanionic network which consists of distorted PtSn₅ square pyramids (265–278 pm Pt–Sn) and Sn₂ dumbbells with 281 and 299 pm Sn–Sn distances. The structural relationship with DyRhGe₂ and Ce₃Pt₄Ge₆ is discussed. EuPtSn₂ shows Curie–Weiss behavior with an experimental magnetic moment of 7.78(1) μ_B / Eu, indicating stable divalent europium. This is corroborated by ¹⁵¹Eu Mössbauer spectroscopy. Antiferromagnetic ordering is detected below 3.4 K. Specific heat measurements confirm the magnetic ordering and indicate a second phase transition through a clear λ-type signal at 7.3 K which might be associated with a structural distortion.     

Solubility in the ZnCl2-CO(NH2)2-HCl-H2O system at 25°C

The ZnCl₂-CO(NH₂)₂-HCl-H₂O quaternary system at 25°C was studied by the solubility method. The concentration boundaries of crystallization were established for the phases that correspond to the eutonic compositions of ternary systems, for double carbamide compounds with zinc chloride and hydrochloric acid, and for the compound ZnCl₂ · 2CO(NH₂)₂ · HCl.     

Energetics and structure in I 2 − (CO2) n clusters

We have implemented a model of I ₂ ^? (CO₂) _n (2 ≤n ≤ 17) clusters and present an analysis of the minimum energy structures obtained from a quenching procedure. A discussion of the importance of various potential contributions to the energetics of the clusters is also presented. Given the current state of understanding of structural control of caging and the time scales of recombination and evaporation, this model has important implications for understanding the picosecond dynamics observed by the Lineberger group and for rigorous studies of evaporation rates.     

Bioscillation and Birhythmicity in the H_2O_2-KSCN-CuSO_4-NaOH System

Two kinds of different mechanistic oscillations can be displayed in the H_2O_2-KSCN-CuSO_4-NaOH system. One discovered by this study is the pH oscillation in a continuous flow stirred tank reactor(CSTR) resulting from the oxidation of KSCN. The other is the oscillation of H_2O_2 decomposition in both CSTR and batch reactors(reported by Orbáin in 1986). Under appropriate experimental conditions, the system exhibits a birhythmicity in a CSTR. Two different pH oscillations are reported here. The pH oscillations which accompany the decomposition of H_2O_2 exist in the batch reactor and the CSTR at a high flowrate, but the pH oscillations in a CSTR at a low flowrate originates from proton positive and negative feedback in the oxidation of KSCN. The oscillation of non-catalyzed oxidation of KSCN by hydrogen peroxide in a CSTR can be found. Also we have observed whether Cu~(2+) exists or not in the batch system, the pH increases to near neutral ultimately after pH drops twice.     

6-Membered ring intermediates in polymerization of N-carboxyanhydride-L-α-arginine in H_2O

In polymerization of N-carboxyanhydride-L-α-arginine(L-Arg-NCA) in H2O,nucleophilic reaction of guanidine group with the carbonyl group of L-Arg-NCA leads to quick intramolecular rearrangement,yielding a 6-membered ring intermediate 1-amidino-3-amino-2-piperidone,which is either elongated by another L-Arg-NCA yielding arginyl-1-amidino-3-amino-2-piperidone or hydrolyzed to L-α-arginine.The oligoarginines are formed mainly through hydrolysis of arginyl-1-amidino-3-amino-2-piperidones.This is a unique pathway...     

STS study of TiO_2 film and Pt-deposited TiO_2 film in air

Direct investigation of the electronic structure of catalyst surfaces on the near-atomic scale in general has not been impossible in the past. However, with the advent of the scanning tunneling microscope (STM), the opportunity arises for incorporating the scanning tunneling spectroscopy (STS) for correlation in-situ surface electronic structure with topography on a sub-nanometer scale. In this paper, we report the STS results of thin film TiO2 and Pt-deposited TiO2 annealed at 450℃. It…     

Oxidation of n-Butanol and 2-Pentanol with Molecular Oxygen in Supercritical CO2

Oxidation of n-butanol and 2-pentanol using molecular oxygen in supercritical (SC) CO2 with and without co-solvent is investigated. The results showed that the reaction selectivity is high when the reaction is carried out in SC CO2. It has been observed that co-solvent affects conversion and selectivity of the reaction considerably.