Synthesis and characterization of new di- and tri-nuclear cyano-bridged bis(dioximato)cobalt(III) complexes

Summary Several new neutral and cationic di- and tri-nuclear cyano-bridged bis(dioximato)cobalt(III) complexes have been synthesized and characterized (dioximato = dimethylglyoximato or diphenylglyoximato). These compounds are obtained through substitution of labile axial ligands by the nitrogen of the cyano-group in [Co(dioximato)₂(CN)₂]^– or [LCo(dioximato)₂(CN)] (L = H₂O, NH₃, or py). In the first case, the existence of only one band in the CN-stretching region of the i.r. spectrum at 2190–2200 cm^–1 is indicative of a trinuclear compound, while the presence of a second band at 2140 cm^–1 attributable to a terminal cyano-group indicates a dinuclear structure. In the presence of water, aquation of axial positions may take place at the same time as bridge formation, whereas the use of a non-aqueous solvent allows the preparation of complexes with pyridine or NH₃.     

A mew method of synthesis of 1,2,3,4-telrahydro-5H-5-oxo-1,4-benzodiazepines

A new one-step facile method for the synthesis of 1,12,3,4-tetrahydro5H-5-oxo-1,4-benzo-diuzepines is described. The method involves the addition of methyl anlhranilates to elhyl-enimine followed by intramolecular cyclizalion of the resulting intermediate compounds. Another attempted method starting from β-anilinoethylisocyanales is also described.     

A field theoretical approach to calculate electronic Born-Oppenheimer coupling terms

In this paper we suggest to consider the spatial distribution of the Born-Oppenheimer nonadiabatic coupling terms as fields which are created by sources, located at degeneracy points, and which can be derived using the ordinary mathematical tools of field theory. It is shown that the curl-divergence equations as formed within a given Hilbert space [M. Baer, Chem. Phys. Lett. 35, 112 (1975)] can be converted into a set of inhomogeneous coupled Poisson equations which are solved for a given set of boundary conditions. The method is applied to the three-state Hilbert subspace of the H(3) system. The numerical results are compared with ab initio calculations for which a very encouraging fit is found.     

Validity of the Hammond postulate and constraints on general one-dimensional reaction barriers

The Hammond postulate is a useful, qualitative tool that interrelates structural similarities between reactants, transition structures, and products with the exo- or endothermicity of reactions. It applies to most chemical reactions, although several exceptions are known. In this study the following problem is addressed: is it possible to formulate conditions for the validity of the quantitative Hammond postulate in terms of simple physical quantities characteristic to the molecules involved? A detailed analysis is given for the conditions of validity of the postulate, in terms of bounds on the internal forces and force constants of nuclear arrangements encountered along a reaction path. We have determined a broad class of constraints on barrier shapes that must be satisfied in order to obtain a critical situation that violates the Hammond postulate: a reactant-like transition structure (“transition state”) for endothermic reactions, and a product-like one for exothermic reactions. The general constraints are formulated in terms of physically meaningful quantities: (i) energy differences, (ii) restrictions on slopes (e.g., an upper bound on internal forces), and (iii) restrictions on curvatures (e.g., upper bounds on force constants) along potential curves.     

Application of capillary zone electrophoresis and reversed-phase high-performance liquid chromatography in the biopharmaceutical industry for the quantitative analysis of the monosaccharides released from a highly glycosylated therapeutic protein

Two assays for the quantitative determination of the neutral and amino-monosaccharides attached to a therapeutic glycoprotein were developed using capillary zone electrophoresis (CZE) and RP-HPLC. These assays meet the strict batch release requirements of the quality control in biopharmaceutical industry. The monosaccharides were released from the glycoprotein by hydrolysis with 2N trifluoroacetic acid. In the CZE assay the monosaccharides were reacetylated prior to derivatization with 8-aminopyrenesulfonic acid (APTS), reacetylation in the glycoprotein matrix was investigated in detail. The RP-HPLC method used pre-column derivatization with anthranilic acid in methanol-acetate-borate reaction medium; reacetylation was not necessary. However, epimerization of the different monosaccharides was observed and studied in detail. For the quantitative assay, separation of the amino-monosaccharide epimers had to be developed. The HPLC assay was validated.     

Darstellung und Struktur von Pyrazolyl-Kationen mit Polymethin- und Methan-Gerüst

The 4-pyrazoline-3-one1 reacts with 4-dimethylaminobenzaldehyde to yield the stable asymmetric cyanine dye2b which reacts with1 to give the colorless (aryl) (dipyrazolyl) methane3b. Using aldehydes with less cationstabilizing groups the polymethines2 are not isolated but only the methanes3. The structures of2b and3 are discussed by¹ H,¹³C and Hetero NMR spectra.     

Reactions of pyrrolidine enamines of cyclic and acyclic 3,4-dioxobutanoic acid Derivatives with dimethyl acetylenedicarboxylate. A new case of atropoisomerism.

Reaction conditions and structure of the starting enamines (cyclic or open-chain) determine greatly the final products of the title reactions. Whereas in benzene and acetonitrile, DMAD and 1 give a mixture of the diastereoisomeric dienamines 5, in methanol they afford pirrolizine 3. Enaminofuranones 2 and 10 furnish the corresponding “Michael adducts” 7a,b,c and 11a,b,c but fail to yield pirrolizines. It has been demonstrated that above b and c adducts differ exclusively on the arrangement of groups around a chiral axis.     

Reaction-based machine learning representations for predicting the enantioselectivity of organocatalysts

Hundreds of catalytic methods are developed each year to meet the demand for high-purity chiral compounds. The computational design of enantioselective organocatalysts remains a significant challenge, as catalysts are typically discovered through experimental screening. Recent advances in combining quantum chemical computations and machine learning (ML) hold great potential to propel the next leap forward in asymmetric catalysis. Within the context of quantum chemical machine learning (QML, or atomistic ML), the ML representations used to encode the three-dimensional structure of molecules and evaluate their similarity cannot easily capture the subtle energy differences that govern enantioselectivity. Here, we present a general strategy for improving molecular representations within an atomistic machine learning model to predict the DFT-computed enantiomeric excess of asymmetric propargylation organocatalysts solely from the structure of catalytic cycle intermediates. Mean absolute errors as low as 0.25 kcal mol⁻¹ were achieved in predictions of the activation energy with respect to DFT computations. By virtue of its design, this strategy is generalisable to other ML models, to experimental data and to any catalytic asymmetric reaction, enabling the rapid screening of structurally diverse organocatalysts from available structural information.

A machine learning model for enantioselectivity prediction using reaction-based molecular representations.     

Identification of a series of C25-C40 acyclic isoprenoid hydrocarbons in crude oils

The identification of acyclic isoprenoid hydrocarbons in organic extracts of geological samples and particularly in petroleum deserves a great interest from the biological origin of the sedimentary organic matter and the understanding of geochemical processes.     

Degradation of ²-O-4 lignin model and related compounds by the ascomyceteChrysonilia sitophila (TFB 27441 strain)

Growth of the ascomyceteChrysonilia sitophila during degradation of lignin model dimers and monomers was compared to a glucose control. An inhibition of growth by Cα-carbonyl monomers and stimulation by β-O-4 lignin model and vanillyl alcohol were observed. A comparison of the degradation by this ascomycete with the basidiomycetePhanerochaete chrysosoporium showed similarities in relation to the type of degradation caused.