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Group Present (group + present)
Selected AbstractsThe reactivity of Ni(II) toward aspartic and glutamic monohydroxamatesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2006Fawzia Al-Sogair The formation of complexes of Ni(II) with aspartic and glutamic acid hydroxamates was determined by potentiometric methods at I = 0.15 M NaCl and T = 25°C. The equilibrium study of Ni(II) with ASX or GLX revealed that the predominant species formed in solution were (M:L:H+): (1:1:0), (1:1:1), (2:1:0), and (2:1:1) in the whole pH range (,3,11). The formation of polymeric species was not observed. The octahedral structures were predicted in which the ligands act as tridentate ligands. The kinetics of complex formation between Ni(II) with ASX system as well as Ni(II) with GLX were also studied in a wide pH range. The observed rate constants for the Ni(II)-hydroxamates were found to be dependent on the total concentration of hydroxamates at a given pH through the following relations: kobs = Y0 + Z(TASX) and kobs = Y0 + Z(TGLX) + W(TGLX)2. The trans effect of the hydroxyl group present in the reacting species of Ni(OH)+ as well as a ring closure resulted from ligand chelation are introduced as explanations for the rate constants obtained for the reactions of Ni(II) with ASX or GLX. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 540,552, 2006 [source] NMR and UPLC-qTOF-MS/MS characterisation of novel phenylethanol derivatives of phenylpropanoid glucosides from the leaves of strawberry (Fragaria × ananassa cv. Jonsok)PHYTOCHEMICAL ANALYSIS, Issue 5 2009Kati Hanhineva Abstract Introduction Strawberry (Fragaria × ananassa) is rich in polyphenols, particularly anthocyanins, flavonols, condensed tannins and ellagic tannins. In addition to the fruits, the leaves of strawberry also contain a wide range of phenolic compound classes, but have not been investigated to the same extent as the fruit. Objective To characterise a metabolite group present in the leaves of strawberry, that was not amenable for identification based on earlier information available in the literature. Methodology Methanolic extracts of strawberry leaves were analysed by UPLC-qTOF-MS/MS and iterative quantum mechanical NMR spectral analysis. Results The structures of phenylethanol derivatives of phenylpropanoid glucosides Eutigoside A ( F4) and its two isomeric forms 2-(4-hydroxyphenyl)ethyl-[6- O -(Z)-coumaroyl]- ,- d -glucopyranoside ( F6) and 4-(2-hydroxyethyl)phenyl-[6- O -(e)-coumaroyl]- ,- d -glucopyranoside ( F1) were resolved by NMR and UPLC-qTOF-MS/MS. In addition, two other derivatives of phenylpropanoid glucosides similar to Eutigoside A but possessing different phenolic acid moieties, namely Grayanoside A ( F5) and 2-(4-hydroxyphenyl)ethyl-[6- O -(e)-caffeoyl]- ,- d -glucopyranoside ( F14), were similarly identified. Also, accurate characteristic coupling constants for the subunits are reported and their usefulness in structural analysis is highlighted. Conclusion Chemical analysis of the leaves of strawberry (Fragaria × ananassa cv. Jonsok) resulted in the identification of a compound class, phenylethanol derivatives of phenylpropanoid glycosides, not previously found in strawberry. Copyright © 2009 John Wiley & Sons, Ltd. [source] Thermally induced intramolecular oxygen migration of N -oxides in atmospheric pressure chemical ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2010Xin Wang N -Oxides are known to undergo three main thermal degradation reactions, namely deoxygenation, Cope elimination (for N -oxides containing a ,-hydrogen) and Meisenheimer rearrangement, in atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The ions corresponding to these thermal degradants observed in the ensuing APCI mass spectra have been used to identify N -oxides as well as to determine the N -oxidation site when the analyte contains multiple tertiary amine groups. In this paper, we report a thermally induced oxygen migration from one N -oxide amine to another tert -amine group present in the same molecule through a six-membered ring transition state during APCI-MS analysis. The observed intramolecular oxygen migration resulted in the formation of a new isomeric N -oxide, rendering the results of the APCI-MS analysis more difficult to interpret and potentially misleading. In addition, we observed novel degradation behavior that happened after the Meisenheimer rearrangement of the newly formed N -oxide: a homolytic cleavage of the NO bond instead of elimination of an aldehyde or a ketone that usually follows the rearrangement. Understanding of these unusual degradation pathways, which have not been reported previously, should facilitate structural elucidation of N -oxides using APCI-MS analysis. Copyright © 2010 John Wiley & Sons, Ltd. [source] Conformational evaluation of labeled C3,-O-P- 13CH2 -O-C4, phosphonate internucleotide linkage, a phosphodiester isostereBIOPOLYMERS, Issue 7 2009Abstract Modified internucleotide linkage featuring the C3,-O-P-CH2 -O-C4, phosphonate grouping as an isosteric alternative to the phosphodiester C3,-O-P-O-CH2 -C4, bond was studied in order to learn more on its stereochemical arrangement, which we showed earlier to be of prime importance for the properties of the respective oligonucleotide analogues. Two approaches were pursued: First, the attempt to prepare the model dinucleoside phosphonate with 13C-labeled CH2 group present in the modified internucleotide linkage that would allow for a more detailed evaluation of the linkage conformation by NMR spectroscopy. Second, the use of ab initio calculations along with molecular dynamics (MD) simulations in order to observe the most populated conformations and specify main structural elements governing the conformational preferences. To deal with the former aim, a novel synthesis of key labeled reagent (CH3O)2P(O)13CH2OH for dimer preparation had to be elaborated using aqueous 13C-formaldehyde. The results from both approaches were compared and found consistent. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 514,529, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Leucine Side-Chain Conformation and Dynamics in Proteins from 13C NMR Chemical ShiftsCHEMBIOCHEM, Issue 9 2009Frans A. A. Mulder Dr. Abstract Look to the left: The carbon nucleus of a substituent in the gauche position about a subtending dihedral angle experiences an NMR chemical shift of about 5 ppm relative to the same chemical group present in the trans position. We demonstrate that this ",-gauche effect" can be utilized to determine the conformation and extent of rotameric averaging for leucine amino acid side chains in the protein calbindin D9k. The success of this approach suggests that rules can be established to define the orientation of other side chains in proteins as well, offering an easy gauge of protein side-chain flexibility, as well as avenues to advance protein structure determination by using side-chain chemical shifts. [source] | ||||||||||