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31.
Roccatano D Sbardella G Aschi M Amicosante G Bossa C Di Nola A Mazza F 《Journal of computer-aided molecular design》2005,19(5):329-340
The dynamical aspects of the fully hydrated TEM-1 β-lactamase have been determined by a 5 ns Molecular Dynamics simulation.
Starting from the crystallographic coordinates, the protein shows a relaxation in water with an overall root mean square deviation
from the crystal structure increasing up to 0.17 nm, within the first nanosecond. Then a plateau is reached and the molecule
fluctuates around an equilibrium conformation. The results obtained in the first nanosecond are in agreement with those of
a previous simulation (Diaz et al., J. Am. Chem. Soc., (2003) 125, 672–684). The successive equilibrium conformation in solution
shows an increased mobility characterized by the following aspects. A flap-like translational motion anchores the Ω-loop to
the body of the enzyme. A relevant part of the backbone dynamics implies a rotational motion of one domain relative to the
other. The water molecules in the active site can exchange with different residence times. The H-bonding networks formed by
the catalytic residues are frequently interrupted by water molecules that could favour proton transfer reactions. An additional
simulation, where the aspartyl dyad D214–D233 was considered fully deprotonated, shows that the active site is destabilized. 相似文献
32.
Dr. Adrián Leandro Lewandowski Dr. Sergio Tosoni Leonard Gura Dr. Zechao Yang Dr. Alexander Fuhrich Dr. Mauricio J. Prieto Dr. Thomas Schmidt Dr. Denis Usvyat Prof. Wolf-Dieter Schneider Dr. Markus Heyde Prof. Gianfranco Pacchioni Prof. Hans-Joachim Freund 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(6):1870-1885
The present review reports on the preparation and atomic-scale characterization of the thinnest possible films of the glass-forming materials silica and germania. To this end state-of-the-art surface science techniques, in particular scanning probe microscopy, and density functional theory calculations have been employed. The investigated films range from monolayer to bilayer coverage where both, the crystalline and the amorphous films, contain characteristic XO4 (X=Si,Ge) building blocks. A side-by-side comparison of silica and germania monolayer, zigzag phase and bilayer films supported on Mo(112), Ru(0001), Pt(111), and Au(111) leads to a more general comprehension of the network structure of glass former materials. This allows us to understand the crucial role of the metal support for the pathway from crystalline to amorphous ultrathin film growth. 相似文献
33.
Tozzi C Anfossi L Baggiani C Giovannoli C Giraudi G 《Analytical and bioanalytical chemistry》2003,375(8):994-999
In our work we performed a combinatorial solid-phase synthesis in aqueous medium to prepare peptide libraries from which to select an amino acid sequence with binding properties towards aflatoxins.We used polystyrene beads, functionalised with carboxylic groups as solid support and eight amino acids as monomers. During the first step 64 different sequences of two amino acids were prepared by exploiting the principles of combinatorial chemistry; then the binding properties of all sequences towards aflatoxin B(1 )were checked. We determined binding constants towards aflatoxin B(1) and towards aflatoxins B(2), G(1) and G(2). Results were promising, so we prepared a new library by using the selected dipeptide as the starting solid phase. After selecting the best tetrapeptide sequences, we determined binding constants towards the quoted aflatoxins. We obtained binding constants ( K>10(4) M(-1)) similar to those shown by human serum albumin for similar compounds. Preliminary studies on an extraction column were promising for the development of an SPE system and for its application in food matrices. 相似文献
34.
Gianfranco Denti Scolastica Serroni Giovanni Sindona Nicola Uccella 《Journal of the American Society for Mass Spectrometry》1993,4(4):306-311
Fast-atom bombardment (FAB) mass spectrometry in the negative ionization mode enables the sputtering into the gas phase of the ruthenium complexes [Ru(2,2′-bipyridine[bpy])2(2,5-bis) (pyrydil)pyrazine[dpp])](PF6)2; [Ru(bpy)2,(2,3dpp)](PF6)2;[Ru(bpy)2,(2,3-dpp-Me)]( PF6)3; and [Ru(bpy)2(?-2,3-dpp)]2 RuCl2(PF6)4 as intact radical anions. These data, combined with those avaiiable from the positive FAB spectra allow a full characterization of the analytes. 相似文献
35.
Monica Bartolomei Maurizio Cignitti Marina Cotta Ramusino Gianfranco La Manna 《Journal of Molecular Structure》1995,330(1-3):431-435
7,8-dihydroquinoline-4,5 (1H,6H)-dione (1) and 7,8-dihydroquinoline-2,5-(1H,6H)-dione (2) in their tautomeric oxo and hydroxy forms have been studied by ab initio Hartree-Fock calculations; tautomerization energies predict a more stable hydroxy structure having an intramolecular hydrogen bond for compound 1, whereas the oxo form is slightly-preferred for compound 2. Fourier Transform-Infra Red (FT-IR) spectra in CHCl3 solution indicate that the predicted most stable tautomers in the vapour phase remain as such. 相似文献
36.
Daniel Wright Mariagioia Zampagni Elisa Evangelisti Simona Conti Giampiero D'Adamio Andrea Goti Matteo Becatti Claudia Fiorillo Niccolò Taddei Gianfranco Liguri 《Photochemistry and photobiology》2013,89(2):442-452
UV‐induced toxicity is characterized by marked oxidative stress, accompanied by the depletion of key cellular antioxidants, particularly glutathione (GSH). Replenishing cellular GSH may represent a means of counteracting UV‐induced toxicity: however, treatment with free GSH is not therapeutically effective due to its unfavorable pharmacokinetic properties. In this study, we show that S‐acyl‐glutathione (acyl‐SG) derivatives, which consist of an acyl chain (of variable length and saturation) linked via a thioester bond to GSH, increase intracellular levels of reduced GSH in primary skin fibroblasts, adenocarcinoma HeLa and neuroblastoma SH‐SY5Y cells. Consistent with this, acyl‐SG derivatives protect against UV‐induced reactive oxygen species (ROS) production and UV‐B/C‐mediated lipid peroxidation and caspase‐3 activation in the analyzed cell lines, with unsaturated thioesters displaying a significantly greater protective effect. Taken together, our findings suggest that acyl‐SG thioesters may be therapeutically effective in the treatment of UV‐related skin disorders and oxidative stress‐mediated conditions in general. 相似文献
37.
38.
More specific official methodology is needed to survey the illegal use of clenbuterol in animal production plus the synthesis of new compounds that currently elude routine analytical methods. The identification of a new adrenergic agonist, N1-(2-(4-amino-3,5-dichlorophenyl)-2-hydroxyethyl)-N1-isopropyl-propanamide (known as compound A) in animal feed has prompted studies to verify if the existing cleanup procedures developed for clenbuterol are really effective. This study considers the ion-exchange mechanism on cyanopropyl (CN), sulfonic cation exchange (SCX), mixed phase (MPH) (C8 + SCX), and nonendcapped C18 (C18NE) solid-phase extraction (SPE) columns. Results indicate that compound A (by contrast with clenbuterol) is not efficiently retained on the CN, SCX, and MPH SPE columns (recovery <10%). This finding thus leads to the development of a gas chromatography-tandem mass spectrometry procedure based on C18NE SPE that is able to purify both agonists from bovine livers spiked at 0.5, 1.0, and 2.0 ppb with a mean recovery of 93% for clenbuterol and 92% for compound A. 相似文献
39.
Brinchi L Di Profio P Germani R Savelli G Spreti N 《Journal of colloid and interface science》2002,247(2):429-436
The effects of ethanol on the critical micellar concentration (cmc) and the rates of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) have been investigated in aqueous cationic surfactants of the cetyltrialkylammonium family with bromide [CT(R)ABr], chloride [CT(R)ACl], and nitrate [CT(R)ANO3] counterions, and methyl (CTAX), n-propyl (CTPAX), and n-butyl (CTBAX) as the head group alkyl moieties. Effects upon cmc and reactivity are similar, featuring a break at the ethanol mole fraction, x(EtOH), of ca. 0.055; these effects have been related to changes in solvent structure, with formation of a clathrate at x(EtOH) = 0.055. Rate data in CTBABr were further investigated and fitting of raw kinetic data to the pseudophase model is possible up to x(EtOH) = 0.1, showing an unexpected decrease of rate constant values in the micellar pseudophase, kM', as ethanol content increases: a significant variation of micellar ionization degree could account for this kinetic effect. 相似文献
40.