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Modelling Calculations (modelling + calculation)

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Chemistry100%

Selected Abstracts

Evaluation of Cu,Ethylenediamine Metal Ion Buffers as Calibrants for Ion-Selective Electrode Measurement of Copper in Fresh Water Systems

ELECTROANALYSIS, Issue 10 2005
Ling Zeng
Abstract An investigation was made into the accuracy of cupric ion selective electrode (ISE) measurement of Cu in solutions approximating acidic freshwaters with Cu-ethylenediamine buffers used as the calibrants. This method overestimates the free Cu compared with calibration using Cu(NO3)2 standards, the standard addition method, and speciation modelling calculations. Statistical tests showed a small, but significant, difference between the intercepts of the linear Nernstian regressions of the calibration plots of Cu-en buffer standardisation and direct calibration with Cu(NO3)2 standards in matrix that matches the samples. The difference in the intercepts, which corresponds with Eo values of the electrode, is not well understood, but is possibly caused by potentially interfering cations such as Fe2+. The results of this study showed that down to 10,8,M Cu2+, where a linear Nernstian response is possible, the Cu ISE is probably better calibrated using Cu standards prepared in the same matrix as the sample solutions to avoid potential matrix effects. [source]

An Acyclic Aminonaphthyridine-Based Receptor for Carbohydrate Recognition: Binding Studies in Competitive Solvents

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2007
Monika Mazik
Abstract 1H NMR spectroscopic and microcalorimetric titrations revealed that receptor 3b, consisting of three protonated 2-amino-1,8-naphthyridine units, binds N -acetylneuraminic acid (Neu5Ac), the most commonly occurring sialic acid, with high affinity in competitive solvents such as water/dimethyl sulfoxide. Receptor 3b is able to form neutral/charge-reinforced hydrogen bonds and ion pairs with Neu5Ac, similar to sialic acid-binding proteins. Furthermore, indications for weak binding of neutral sugars, such as methyl ,- D -glucopyranoside, D -maltose and D -cellobiose were provided by NMR spectroscopy. Molecular modelling calculations, synthesis and binding studies in aqueous media are described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

2,3-,-Epoxyjaeschkeanadiol 5-benzoate from Ferula hermonis Boiss

FLAVOUR AND FRAGRANCE JOURNAL, Issue 6 2001
Youssef Diab
Abstract The new 2,3-,-epoxyjaeschkeanadiol 5-benzoate has been isolated and its 1H- and 13C-NMR signals were completely assigned by the application of the modern NMR techniques. Its conformations are discussed on the basis of molecular modelling calculations and nuclear Overhauser effect spectroscopy (NOESY) spectra. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Magnesium and biological activity of oxytocin analogues modified on aromatic ring of amino acid in position 2

JOURNAL OF PEPTIDE SCIENCE, Issue 8 2001
ina Slaninová
Abstract For the purpose of evaluating substitution effects in the ortho, meta or para positions of the aromatic ring of tyrosine or phenylalanine in position 2 of oxytocin on uterotonic activity in vitro in the presence and absence of magnesium ions, six new analogues of oxytocin ([,,- and ,,- m -methylphenylalanine2]oxytocin, [,,- and ,,- m -methoxyphenylalanine2]oxytocin and [,,- and ,,- o -methyltyrosine2]oxytocin) were synthesized and several previously described analogues resynthesized. For the phenylalanine series, it is found that, in the absence of magnesium ions, substitution of the ortho and meta positions leads to loss of intrinsic activity (the analogues are antagonists) in contrast to the para position. In the tyrosine series, only methyl substitution in the meta position has this effect (substitution of ortho position only attenuates the agonistic biological activity). Addition of Mg ions restores to a certain degree the agonistic activity in the case of the o -methylphenylalanine analogue and enhances the agonistic activity of o -methyltyrosine oxytocin. All other analogues keep the original qualities as in the absence of Mg. Molecular modelling calculations of the structure of the above analogues was carried out to help explain these findings of the molecular level. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source]