Gábor Schubert

Determination of the retention behavior of barbituric acid derivatives in reversed-phase high-performance liquid chromatography by using quantitative structure–retention relationships

Retention parameters of 45 barbituric acid derivatives were determined on an amide embedded RP silica column using non-buffered water-dioxan eluent systems. Linear correlations were calculated between the logarithm of the capacity factor and the dioxan concentration in the eluent. Six different retention parameters of each barbituric acid derivative were correlated with different conventional and quantum chemical structural descriptors using quantitative structure-retention relationship (QSRR). The different parameters were: intercept (log k0) and slope (b) values of the linear, the combined retention parameter (log k0/b), asymmetry factor (AF5) and theoretical plate values (N(USP) and N(JP), according to the United States and Japanese Pharmacopoeia calculations). Stepwise regression analysis (SRA) and principal component analysis (PCA) followed by two-dimensional nonlinear mapping were used to determine the retention behavior of barbituric acid derivatives. SRA and PCA led to similar results. The results indicated that the retention of barbituric acid derivatives are mainly governed by the polaric and steric parameters of the substituents.

Unprecedented formal ‘2+2’ addition of allene to CO2 promoted by [RhCl(C2H4)(PiPr3)]2: direct synthesis of the four membered lactone α-methylene-β-oxiethanone. The intermediacy of [RhH2Cl(PiPr3)]2: theoretical aspects and experiments

Abstract In this paper the reaction of allene with carbon dioxide is discussed, using [RhCl(C2H4)(PiPr3)]2 as catalyst. An unprecedented formal ‘2+2’ allene–CO2 reaction to afford a four-membered lactone is described. The influence of the temperature and pressure on the reaction of allene and CO2 is highlighted. The role of addition of hydrogen to the reaction system, as modulator of the products distribution is discussed. The behavior of the catalyst [RhCl(C2H4)(PiPr3)]2 towards H2 is also described and the structure of the resulting Rhhydride species inferred through a theoretical study.

PCA, followed by two-dimensional nonlinear mapping and cluster analysis, versus multilinear regression in QSRR

Retention parameters of 45 different barbituric acid derivatives were determined on an amide embedded RP silica column (Discovery RP-AmideC16) using non-buffered tetrahydrofuran-water mixtures as eluents. Linear correlations were calculated between the lgk values and the tetrahydrofuran concentration in the eluent. Chromatographic parameters of barbituric acid derivatives were correlated with different conventional and quantum chemical structural descriptors in QSRR study (the different parameters were: intercept (lg k 0) and slope (b) values of the linear, the combined retention parameter (lg k 0/b), asymmetry factor (AF) and theoretical plate values (N)). Multilinear regression analysis (SRA) and principal component analysis (PCA), followed by two dimensional nonlinear mapping and cluster analysis techniques, were used to determine the retention behavior of barbituric acid derivatives. Different mathematical-statistical methods indicated that the hydrophobic characteristics of the solutes have marked influence on the retention behavior of barbituric acid derivatives on this amide embedded RP silica column in tetrahydrofuran-water eluent systems. The significant effect of the hydrophobic characteristics of the analytes in the retention behavior indicated that the effects of the interaction between the analytes and the residual silica silanol groups are negligible.

Theoretical analysis of bis(ethylene) complexes of molybdenum and tungsten

Abstract Density functional calculations on the zero-valent bis(ethylene) trans -[M(C 2 H 4 ) 2 (PH 3 ) 4 ] model complexes and the actual trans -[M(C 2 H 4 ) 2 (PMe 3 ) 4 ] (M=Mo, W) compounds were carried out at the BPW91 level of theory. The experimentally characterised molecular structures of both molybdenum and tungsten complexes were properly reproduced by the energy optimised geometries only when the trimethylphosphine ligands were used. The experimentally observed ruffling of the phosphine ligands was not detected when the simplified model was considered. This discrepancy was interpreted as a consequence of different steric interactions between the PH 3 and PMe 3 ligands. The theoretical analysis gives a good account of some chemical properties observed in these compounds. In particular, the low PMe 3 dissociation energies calculated for these compounds are in agreement with the experimental observation of free phosphine dissociation in the solutions of trans -[M(C 2 H 4 ) 2 (PMe 3 ) 4 ] compounds. The comparison of energy data for PH 3 and PMe 3 complexes corroborates the experimental hypothesis that phosphine dissociation has a steric origin.

Peer Reviewed: The Most Cited Books in Analytical Chemistry.

A survey of references in analytical chemistry over the past decade shows the importance of books.

Study of the retention parameters of barbituric acid derivatives in reversed phase HPLC by using quantitative structure-retention relationships

SummaryRetention parameters of 45 different barbituric acid derivatives were determined on an amide embedded RP silica column (Discovery RP-AmideC16) using non-buffered methanol-water mixtures as eluents. Linear correlations were calculated between the logk values and the methanol concentration in the eluent. The intercept (logk0) and slope (b) values of the line, the combined retention parameter (logk0/b), asymmetry factor (AF5) and theoretical plate (N) value of each barbituric acid derivative were correlated with different conventional and quantum chemical structural descriptors using Quantitative Structure-Retention Relationship (QSRR). The SRA (stepwise regression analysis) results indicated that the retention is mainly governed by the steric and the lipophilicity properties of the barbituric acid derivatives in water-methanol eluent mixtures.

Inorganica chimica acta: Its publications, references and citations. An update for 1995-1996

Abstract Scientometric techniques have been used to characterize the journal Inorganica Chimica Acta during the 1995–1996 period. The results are compared to those of a previous study for the 1990–1994 period, with attempts to pinpoint characteristic trends and patterns. An epistemological analysis based on title words is used to locate ‘creative foci’ of research.

A tudománymetria törvényalkotó „úttörői”

Absztrakt A tudomanymetria harom sokat emlegetett es idezett torvenye a Bradford-, a Lotka- es a Zipf-torveny. A szerzők roviden bemutatjak a harom torveny nevadojanak tudomanyos palyajat, es hogy hogyan jutottak el a roluk elnevezett torvenyek megalkotasaig. Vazoljak a torvenyek es nevadoik munkassaganak utoeletet is. Orv. Hetil., 2016, 157(2), 74–78.