1,2-oxaphosphorin-3-ene derivatives in the reaction of SO2Cl2 with dichlorides of 2-chloro-3-alkyl-1,3-alkadienephosphonic acids

2,4,5-Trichloro-2-oxo-1,2-oxaphosphorin-3-enes was sinthesised using the interaction of sulfuryl chloride with dichlorides of 2-chloro-3-alkyl-1,3-alkadienephosphonic acids.     

Synthesis of 2H‐chromeno[4,3‐b]pyridine‐2,5(1H)‐diones and related heterocycles via the erlenmeyer‐ploechl reaction

1,2‐Dihydro‐5H‐[1]benzopyrano[4,3‐b]pyridine‐2,5‐diones 4a‐j were synthesized from 4‐alkylamino‐coumarin‐3‐carbaldehydes 1 and 5(4H)‐oxazolinones (azalactones) derived from N‐acetylglycine ( 2a ) and hippuric acid ( 2b ). The intermediates 3 ( 3j isolated only) underwent spontaneous recyclization via opening of the azalactone and successive formation of the fused 2‐pyridones 4 . Attempts to synthesize the selected 2H‐chromeno[3,4‐f]‐1,7‐naphthyridine 6 by Vilsmeier reaction of 4e failed. Instead, N‐deacetylation took place, followed by formylation of the amino group to the formamidine 7a . In addition, pyranopyridine 9a was obtained by condensation of the 3‐formyl‐2‐pyridone 8 with the azalactone derived from 2a and acetic anhydride.     

Collision theory treatment of monomolecular and bimolecular gas reactions

An exact collision theory of unimolecular and bimolecular gas phase reactions is derived from a general quantum-mechanical formulation of reactions rates based on the assumption that the reactants are in thermal equilibrium. In this way the quantum corrections to the classical collision theory expressions are rigorously defined. Approximate formulas for these corrections make it possible to determine well the temperature ranges within which the classical and the semiclassical approximations are valid. A comparison is made between the collision and the transition state theory with emphasis on some conceptual difficulties of the latter in treating the simple decomposition and recombination reactions. It is shown that in the classical (high temperature) limit these theories are incompatible except when the reaction coordinate is entirely separable (i.e., when the transition state theory is no longer useful).     

Thermodynamics of formation of carnallite type double salts

The solubility of the systems RbCl–MgCl₂–H₂O, RbBr–MgBr₂–H₂O and CsBr–MgBr₂–H₂O have been investigated by the physicochemical analysis method at 25°C and formation of carnallite type double salts was established. The Pitzer model is used to calculate the thermodynamic functions needed to plot the solubility isotherms of the systems. The results obtained are in good agreement with the experimental data. The free energies of formation of carnallite and bromcarnallite type double salts from simple salts and the standard molar energies of formation are estimated.     

YfeX – A New Platform for Carbene Transferase Development with High Intrinsic Reactivity

Carbene transfer biocatalysis has evolved from basic science to an area with vast potential for the development of new industrial processes. In this study, we show that YfeX, naturally a peroxidase, has great potential for the development of new carbene transferases, due to its high intrinsic reactivity, especially for the N−H insertion reaction of aromatic and aliphatic primary and secondary amines. YfeX shows high stability against organic solvents (methanol and DMSO), greatly improving turnover of hydrophobic substrates. Interestingly, in styrene cyclopropanation, WT YfeX naturally shows high enantioselectivity, generating the trans product with 87 % selectivity for the (R,R) enantiomer. WT YfeX also catalyzes the Si−H insertion efficiently. Steric effects in the active site were further explored using the R232A variant. Quantum Mechanics/Molecular Mechanics (QM/MM) calculations reveal details on the mechanism of Si−H insertion. YfeX, and potentially other peroxidases, are exciting new targets for the development of improved carbene transferases.     

Identification of productive inhibitor binding orientation in fatty acid amide hydrolase (FAAH) by QM/MM mechanistic modelling

Modelling of the mechanism of covalent adduct formation by the inhibitor O-arylcarbamate URB524 in FAAH shows that only one of the two possible inhibitor binding orientations is consistent with the experimentally observed irreversible carbamoylation of the nucleophile serine: this is a potentially crucial insight for designing new covalent inhibitors of this promising drug target.     

Relationship between chiroptical properties, structural changes and interactions in enzymes: a computational study on beta-lactamases from class A

Enzyme functions such as catalysis, binding and regulation are directly related to a variety of conformational changes. A sensitive and useful method for their investigation is circular dichroism (CD) and a rotational strength (R) is its fundamental characteristic. In this study, we show how the sensitivity of the mechanisms of rotational strengths to important conformational changes depends on the chromophore environment in two beta-lactamases from class A (from Escherichia coli and B. licheniformis). Rotational strengths have been calculated using the matrix method and including the effects of local environment (LE). X-ray structures (of protein components) of several enzyme-ligand complexes from the catalytic cycle of the TEM-1 enzyme and for both crystallographic monomers of the enzyme from B. licheniformis were used. An analysis of the relative degree of perturbation of the rotational strengths upon local interactions is performed.