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251.
Losito I Carbonara T Domenica De Bari M Gobbetti M Palmisano F Rizzello CG Zambonin PG 《Rapid communications in mass spectrometry : RCM》2006,20(3):447-455
Electrospray ionization ion trap mass spectrometry (ESI-ITMS) coupled to a two-dimensional liquid chromatographic separation was applied to the identification of peptides in antimicrobial fractions of the aqueous extracts of nine Italian cheese varieties. In particular, the chromatographic fractions collected during a preliminary fast protein liquid chromatography (FPLC) separation on the cheese extracts were assayed for antimicrobial activity towards Lactobacillus sakei A15. Active fractions were subsequently analyzed by reversed-phase high-performance liquid chromatography electrospray ionization sequential mass spectrometry (HPLC/ESI)-ITMSn, with n up to 3. Peptide identification was then performed starting from a conventional proteomics approach based on tandem mass spectrometric (MS/MS) analysis followed by database searching. In many cases this strategy had to be integrated by a careful correlation between spectral information and predicted peptide fragmentation, in order to reach unambiguous identifications. When even this integrated approach failed, MS3 measurements provided decisive information on the amino acid sequence of some peptides, through fragmentation of pendant groups along the peptide chain. As a result, 45 peptides, all arising from hydrolysis of milk caseins, were identified in nine antimicrobial FPLC fractions of aqueous extracts obtained from five of the nine cheese varieties considered. Many of them corresponded to peptides already known to exhibit biological activity. 相似文献
252.
Ytterbium is efficiently chelated by 1,2-diols in a variety of very different solvents. We found a set of solution equilibria among three complexes of minimum formula [Yb·(diol)], [Yb·(diol)2] and [Yb·(diol)3]. By extensive near-Infrared circular dichroism (NIR CD) investigation, we determined fingerprint CD spectra of the di- and tri-chelated species and the relative formation constants. Since NIR CD is sensitive only to chiral Yb-species, NIR CD can be very useful for studying complex mixtures, such as those used in enantioselective catalysis and involving a chiral non-racemic diol as an auxiliary and an ytterbium salt. The chiroptical spectra show completely conserved features through very different diol structures, demonstrating the identity of the coordination polyhedron around Yb(III) and giving rise to a new empirical method for assigning 1,2-diols absolute configuration. 相似文献
253.
An extraction system consisting of trilaurylamine N-oxide and benzene has been identified as a possible extractant for tracer arsenic (<10–3 M) from hydrochloric or sulfuric acid solutions with or without iodide. Benzene alone is less efficient as an extractant for arsenic when compared with trilaurylamine oxide dissolved in benzene. The mechanism of extraction is attributed to the formation of hydrated AsCl3, while the iodide complex is most probably AsI
4
–
. The role of the solvent and the other parameters affecting the extraction have been investigated. The results have been employed to determine arsenic in water samples by spectrophotometry using the molybdenum blue method. The extraction procedure was used for the analysis of 10 ml water samples containing 0.2–0.5 g of arsenic. 相似文献
254.
K. Uzelac Z. Glumac O. S. Barišić 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):101-108
We present numerical investigations of the short-time dynamics at criticality in the 1D Potts model with power-law decaying
interactions of the form 1/r1+σ. The scaling properties of the magnetization, autocorrelation function and time correlations of the magnetization are studied.
The dynamical critical exponents θ' and z are derived in the cases q=2 and q=3 for several values of the parameter σ belonging
to the nontrivial critical regime. 相似文献
255.
Luka Bilić Dr. Danijela Barić Dr. Gregory M. Sandala Dr. David Mathew Smith Dr. Borislav Kovačević 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(29):7930-7941
Diol dehydratase, dependent on coenzyme B12 (B12-dDDH), displays a peculiar feature of being inactivated by its native substrate glycerol (GOL). Surprisingly, the isofunctional enzyme, B12-independent glycerol dehydratase (B12-iGDH), does not undergo suicide inactivation by GOL. Herein we present a series of QM/MM and MD calculations aimed at understanding the mechanisms of substrate-induced suicide inactivation in B12-dDDH and that of resistance of B12-iGDH to inactivation. We show that the first step in the enzymatic transformation of GOL, hydrogen abstraction, can occur from both ends of the substrate (either C1 or C3 of GOL). Whereas C1 abstraction in both enzymes leads to product formation, C3 abstraction in B12-dDDH results in the formation of a low energy radical intermediate, which is effectively trapped within a deep well on the potential energy surface. The long lifetime of this radical intermediate likely enables its side reactions, leading to inactivation. In B12-iGDH, by comparison, C3 abstraction is an endothermic step; consequently, the resultant radical intermediate is not of low energy, and the reverse process of reforming the reactant is possible. 相似文献
256.
Monika Kovačević Lidija Barišić Rosana Ribić Vesna Petrović Peroković Srđanka Tomić Vladimir Rapić 《应用有机金属化学》2012,26(2):74-79
Bacterial adhesion, mediated through interaction of bacterial lectins with carbohydrate structures presented on the surface of the host cells, is a prerequisite for infection. Anti‐adhesion therapy, based on the inhibition of lectins by suitable carbohydrates, has been considered as a weapon for the combat of microbial diseases. Structural alteration of aglycon portions of mannose derivatives strongly influences their inhibitory potency toward type 1 fimbriated Escherichia coli. Thus several conjugates of mannose‐containing ferrocene aglycon moieties were synthesized and tested. The novel ferrocene conjugates 10, 12 and 14 were obtained by esterification of O‐mannosylated propionic acid 1 with ferrocene alcohols R‐Fn‐(CH2)n‐OH (Fn = 1,1'‐ferrocenylene; 2, n = 1, R = COOMe; 7, n = 1, R = NHBoc; 8, n = 2, R = H) in the presence of Boc2O/DMAP with subsequent debenzylation of the intermediate O‐protected esters. Performed hemagglutination inhibitory tests showed that the examined bioorganometallics exhibit better inhibitory activity than known inhibitor methyl α‐d ‐mannoside. Thus ferrocene–mannose conjugate 14 with the dimethylene spacer between ferrocene core and chiral linker displayed the best inhibitory efficiency. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献