Enantioselective hydrolysis of a Schiff's base of D,L-Phenylalanine ethyl ester in water-poor media via the reaction catalyzed with α-chymotrypsin immobilized on hydrophilic macroporous gel support

The application of immobilized α-chymotrypsin for the purpose of enantioselective hydrolysis of a Schiff's base of D,L-Phe-OEt (D,L-SBPH) in the mixed water-acetonitrile media with the different content of water is described. The immobilized biocatalyst was prepared by the chemical coupling of the enzyme to poly(vinyl alcohol) (PVA) cryogel—the macroporous hydrogel prepared by means of the freezing-thawing techniques. SBPH is water insoluble, and, therefore, acetonitrile (MeCN) with minor water additives was used as a solvent for the reaction of enantics elective hydrolysis of the racemic substrate. The process was conducted for 96–200 h, and L-Phe with the purity up to 98% e.e. precipitated in both the reaction medium and gel-carrier bulk. Theproduct wasrecovered by washing the organo-insoluble sediment with aqueous ammonia. D-Phe with the purity up to 85% e.e. was recovered from the organic solution of D-ester after its acidic hydrolysis. The PVA-cryogel-attached enzyme was effective in SBPH hydrolysis in MeCN/water mixtures. The immobilized biocatalyst was active for more than 1 mo of application and could be successfully used after another 4 mo storage at +10°C.     

New synthesis of ortho esters of sugars

Summary A new synthesis of ortho esters of sugars has been proposed, starting with 1,2-cis-halogenoses in ethyl acetate medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12 p. 2214–2216, December, 1964     

Efficient catalysis of the Suzuki-Miyaura reaction under mild conditions with cyclopalladated N,N-dimethylaminomethylferrocene

High catalytic activity of N,N-dimethylaminomethylferrocene cyclopalladated derivative was demonstrated in the the Suzuki-Miyaura cross-coupling of aryl bromides with phenylboronic acid, which allowed us to carry out the reaction under extremely mild conditions.     

Near Infrared Phosphorescent,Non‐oxidizable Palladium and Platinum Perfluoro‐phthalocyanines

New Pd^II and Pt^II complexes with a highly electron‐deficient ligand (H₂PcF₆₄) were conveniently prepared in a three‐step synthesis. This is the first time that the phosphorescence of phthalocyanines with a H₂PcF₆₄ framework has been measured. Based on these measurements, the triplet‐state energies (E_T) were directly determined. Transient absorption experiments revealed broad T₁→T_n absorption spanning from ca. 350 to ca. 1000 nm and allowed determination of the triplet‐state lifetimes. Removal of the Pd or Pt from the perfluoro‐phthalocyanine resulted in a significant increase of the triplet lifetime for H₂PcF₆₄. The very efficient intersystem crossing observed for both PdPcF₆₄ and PtPcF₆₄ leads to residual fluorescence and suppresses the fluorescence lifetimes to less than 50 ps. The absence of Pd and Pt in the perfluoro‐phthalocyanine ligand, viz. H₂PcF₆₄, led to a recovery of fluorescence. Cyclic voltamperometry studies pointed to complete resistance of PdPcF₆₄ and PtPcF₆₄ to oxidation and very strong electron affinity, which rendered these materials very good electron acceptors (n‐type materials). The presence of d‐orbital metals such as Pd^II and Pt^II in the phthalocyanine ring stabilizes their reduced forms, as indicated by the spectroelectrochemical experiments. PdPcF₆₄ and PtPcF₆₄ easily sensitize singlet oxygen production with very high quantum yields. Both phthalocyanines presented resistance to photodegradation in the solid state under aerobic conditions and under intense irradiation.     

The Structure of N‐(1‐Deoxy‐β‐D‐fructopyranos‐1‐yl)‐L‐proline Monohydrate (“D‐Fructose‐L‐proline”) and N‐(1,6‐Dideoxy‐α‐L‐fructofuranos‐1‐yl)‐L‐proline (“L‐Rhamnulose‐L‐proline”)

Nano n-propylsulfonated γ-Fe₂O₃ was found to be a highly efficient, reusable heterogeneous catalyst for the conversion of a range of monosaccharides and some of their derivatives to the corresponding O-isopropylidene derivatives in good to excellent yields by refluxing the reaction mixture in dry acetone. The magnetic property of the catalyst enabled its separation from the reaction mixture by a simple process of filtration along with the aid of an external magnet. The efficiency of the catalyst was found to be largely unaffected for at least up to six cycles of reuse, thus proving the new methodology to be environmentally rewarding besides being simple and facile in operation.     

Retention Indices for Most Frequently Reported Essential Oil Compounds in GC

Retention indices were evaluated for one hundred most commonly reported essential oil compounds in gas chromatography (GC) using a large retention index database. Retention data are presented for three types of stationary phases: dimethyl silicone, dimethyl silicone with 5% phenyl groups, and polyethylene glycol stationary phases. The data evaluations are based on the treatment of multiple measurements with the number of data records ranging between 30 and 470 per compound. Data distribution analysis was limited to temperature programming conditions. Data reported include the most probable value of retention index, average and median values, standard deviation, and confidence intervals. The values of most probable retention indices correspond to frequently used GC conditions of measurements (temperature program, column parameters, gas flow conditions). The results are compared with data from several available retention index collections.     

Oxide‐Supported IrNiOx Core–Shell Particles as Efficient,Cost‐Effective,and Stable Catalysts for Electrochemical Water Splitting

Active and highly stable oxide‐supported IrNiO_x core–shell catalysts for electrochemical water splitting are presented. IrNi_x@IrO_x nanoparticles supported on high‐surface‐area mesoporous antimony‐doped tin oxide (IrNiO_x /Meso‐ATO) were synthesized from bimetallic IrNi_x precursor alloys (PA‐IrNi_x /Meso‐ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA‐IrNi_x /Meso‐ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiO_x /Meso‐ATO catalyst displayed high water‐splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.     

A Chemical Kinetic Mechanism for 2‐Bromo‐3,3,3‐trifluoropropene (2‐BTP) Flame Inhibition

In this work, we report a detailed chemical kinetic mechanism to describe the flame inhibition chemistry of the fire‐suppressant 2‐bromo‐3,3,3‐trifluoropropene (2‐BTP), under consideration as a replacement for CF₃Br. Under some conditions, the effectiveness of 2‐BTP is similar to that of CF₃Br; however, like other potential halon replacements, it failed an U.S. Federal Aviation Authority (FAA) qualifying test for its use in cargo bays. Large overpressures are observed in that test and indicate an exothermic reaction of the agent under those conditions. The kinetic model reported herein lays the groundwork to understand the seemingly conflicting behavior on a fundamental basis. The present mechanism and parameters are based on an extensive literature review supplemented with new quantum chemical calculations. The first part of the present article documents the information considered and provides traceability with respect to the reaction set, species thermochemistry, and kinetic parameters. In additional work, presented more fully elsewhere, we have combined the 2‐BTP chemical kinetic mechanism developed here with several other submodels from the literature and then used the combined mechanism to simulate premixed flames over a range of fuel/air stoichiometries and agent loadings. Overall, the modeling results qualitatively predicted observations found in cup‐burner tests and FAA Aerosol Can Tests, including the extinguishing concentrations required and the lean‐to‐rich dependence of mixtures. With these data in hand, in a second phase of the present work, we perform a reaction path analysis of major species under several modeled conditions. This analysis leads to a qualitative understanding of the ability of 2‐BTP to act as both an inhibitor and a fuel, depending on the conditions and suggests areas of the kinetic model that should be further investigated and refined.