H,C, Pt NMR study on platinum(II) interaction with sulphur containing Amadori compounds

The NMR study on the interaction of Pt(II) with Amadori compounds is performed. The Amadori compounds are derived from the reaction of β-d-glucose with l-cystine leading to N,N′-di-(1-deoxy-β-fructos-1-yl)-l-cystine [FruCyscys], and with l-methionine leading to N-(1-deoxy-β-fructos-1-yl)-l-methionine [FruMet].     

Reaction between quinone and thiazolidine. A study on the formation mechanism of new antiproliferative quinolindiones

Reaction between quinolinquinone and thiazolidine in basic medium was investigated. 2-Arylthiazolidine-4-carboxylic acid ethyl esters undergo two different cleavages in basic medium, yielding the 1-aryl-2-azadiene and a thiolic species. In the presence of quinolinquinone, the isomeric 1-aryl-3-ethoxycarbonyl-pyridoisoquinolin-5,10-diones and 3-amino-3-ethoxycarbonyl-dihydrothienoquinolin-4,9-diones are formed by a hetero-Diels-Alder reaction and 1,4-Michael addition reaction, respectively. A mechanism for the formation of the reaction products is presented.     

Multivariate calibration techniques applied to the spectrophotometric analysis of one-to-four component systems

The UV spectrophotometric analysis of a multicomponent mixture containing paracetamol, caffeine, tripelenamine and salicylamide by using multivariate calibration methods, such as principal component regression (PCR) and partial least-squares regression (PLS), was described. The calibration set was based on 47 reference samples, consisting of quaternary, ternary, binary and single-component mixtures, with the aim to develop models able to predict the concentrations of unknown samples containing as many as one-to-four components. The calibration models were optimized by an appropriate selection of the number of factors as well as wavelength ranges to be used for building up the data matrix and excluding any information about the interfering excipients included in pharmaceutics. The PCR and PLS models were compared and their predictive performance was inferred by a successful application to the assays of synthetic mixtures and pharmaceutical formulations.     

Proteomics of gluten: mapping of the 1Bx7 glutenin subunit in Chinese Spring cultivar by matrix-assisted laser desorption/ionization

The verification of the cDNA-deduced sequence of the high molecular weight glutenin subunit 1Bx7 in Chinese Spring cultivar was achieved by direct matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of the tryptic fragments. The published sequence of the 1Bx7 subunit contains 5 Lys and 15 Arg residues but, due to the presence of three Arg-Pro bonds, which are generally resistant to cleavage by trypsin, or cleaved to a very limited extent by trypsin, 19 peptides can be predicted. The identification of the tryptic fragments was achieved by direct MALDI-MS analysis by using three different matrices (DHB, SA and HCCA) in combination with the most compatible sample preparation procedures in order to obtain the maximum sequence coverage. MALDI analysis of the 1Bx7 tryptic digest resulted in the identification of the expected peptides and additional fragments arising from non-specific cleavages; the fragments that were not detected are peptides with low mass (from 147.2 to 317.4), so we obtained a sequence coverage of 98.8%. The results reported here also indicated that the sequence of the 1Bx7 subunit from cv. Chinese Spring is different from the cDNA-deduced sequence reported in the literature; in particular, a possible insertion of the hexapeptide QPGQGQ within the sequence Gln630-Tyr725 was suggested. Finally, it is possible to rule out glycosylation of the 1Bx7 subunit, or any other post-translational modification, to within the detection limits of the method.     

Comparisons of NMR spectral quality and success in crystallization demonstrate that NMR and X-ray crystallography are complementary methods for small protein structure determination

X-ray crystallography and NMR spectroscopy provide the only sources of experimental data from which protein structures can be analyzed at high or even atomic resolution. The degree to which these methods complement each other as sources of structural knowledge is a matter of debate; it is often proposed that small proteins yielding high quality, readily analyzed NMR spectra are a subset of those that readily yield strongly diffracting crystals. We have examined the correlation between NMR spectral quality and success in structure determination by X-ray crystallography for 159 prokaryotic and eukaryotic proteins, prescreened to avoid proteins providing polydisperse and/or aggregated samples. This study demonstrates that, across this protein sample set, the quality of a protein's [15N-1H]-heteronuclear correlation (HSQC) spectrum recorded under conditions generally suitable for 3D structure determination by NMR, a key predictor of the ability to determine a structure by NMR, is not correlated with successful crystallization and structure determination by X-ray crystallography. These results, together with similar results of an independent study presented in the accompanying paper (Yee, et al., J. Am. Chem. Soc., accompanying paper), demonstrate that X-ray crystallography and NMR often provide complementary sources of structural data and that both methods are required in order to optimize success for as many targets as possible in large-scale structural proteomics efforts.     

Nonspecular total internal reflection of spatial solitons at the interface between highly birefringent media

We investigate total internal reflection of nonlocal spatial optical solitons at the interface between two differently oriented regions of a highly birefringent nematic liquid crystal. The solitons survive the interaction with an induced index mismatch and undergo nonspecular reflection, with an emerging angle differing appreciably from the incidence angle.