Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C1275122 (TEM)
 21,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

All three classes of serine beta-lactamases are inhibited at micromolar levels by 1:1 complexes of catechols with vanadate. Vanadate reacts with catechols at submillimolar concentrations in aqueous buffer at neutral pH in several steps, initially forming 1:1, 1:2, and, possibly, 1:3 complexes. Formation of these complexes is followed by the slower reduction of vanadate (V (V)) to vanadyl (V (IV)) and oxidation of the catechol. Vanadyl-catechol complexes, however, do not inhibit the beta-lactamases. Rate and equilibrium constants of formation of the 1:1 and 1:2 complexes of vanadate with catechol itself and with 2,3-dihydroxynaphthalene were measured by stopped-flow spectrophotometry. Typical examples of all three classes of serine beta-lactamases (the class A TEM-2, class C P99, and class D OXA-1 enzymes) were competitively inhibited by the 1:1 vanadate-catechol complexes. The inhibition was modestly enhanced by hydrophobic substituents on the catechol. The 1:1 vanadate complexes are considerably better inhibitors of the P99 beta-lactamase than 1:1 complexes of catechol with boric acid and are likely to contain penta- or hexacoordinated vanadium rather than tetracooordinated. Molecular modeling showed that a pentacoordinated 1:1 vanadate-catechol complex readily fits into the class C beta-lactamase active site with coordination to the nucleophilic serine hydroxyl oxygen. Such complexes may resemble the pentacoordinated transition states of phosphyl transfer, a reaction also catalyzed by beta-lactamases.
 ...
PMID:Inhibition of serine beta-lactamases by vanadate-catechol complexes. 1870 3

Highly monodisperse silicon nanoparticles (1.57 +/- 0.21 nm) are synthesized with a covalently attached alkyl monolayer on a gram scale. Infrared spectroscopy shows that these silicon nanoparticles contain only a few oxygen atoms per nanoparticle. XPS spectra clearly show the presence of unoxidized Si and attached alkyl chains. Owing to the relatively efficient synthesis (yields approximately 100-fold higher than of those previously reported) the molar extinction coefficient epsilon can be measured: epsilon(max) = 1.7 x 10(-4) M(-1)cm(-1), only a factor of 4 lower than that of CdS and CdSe nanoparticles of that size. The quantum yield of emission ranges from 0.12 (C(10)H(21)-capping) to 0.23 (C(16)H(33)-capping). UV/Vis absorption and emission spectroscopy show clear vibrational progressions (974 +/- 14 cm(-1); up to five vibrational bands visible at room temperature), resembling bulk SiC phonons, which support the monodispersity observed by TEM. This was also confirmed by time-resolved fluorescence anisotropy measurements, which display a strictly monoexponential decay that can only be indicative of monodisperse, ball-shaped nanoparticles.
 ...
PMID:Alkyl-functionalized oxide-free silicon nanoparticles: synthesis and optical properties. 1875 8

In this study, chitosan nanoparticles were prepared and incorporated in hydroxypropyl methylcellulose (HPMC) films under different conditions. Mechanical properties, water vapor and oxygen permeability, water solubility, and scanning and transmission electron microscopy (SEM and TEM) results were analyzed. Incorporation of chitosan nanoparticles in the films improved their mechanical properties significantly, while also improving film barrier properties significantly. The chitosan poly(methacrylic acid) (CS-PMAA) nanoparticles tend to occupy the empty spaces in the pores of the HPMC matrix, inducing the collapse of the pores and thereby improving film tensile and barrier properties. This study is the first to investigate the use of nanoparticles for the purpose of strengthening HPMC films.
 ...
PMID:Properties of novel hydroxypropyl methylcellulose films containing chitosan nanoparticles. 1880 24

The electrochemical activation of multiwalled carbon nanotubes (MWCNTs) (at potentials of 1.5-2.0 V vs Ag/AgCl for 60-360 s) results in significantly increased rate constants (k(0)((obs))) for heterogeneous electron-transfer with [Fe(CN)(6)](3-/4-) (from 8.34 x 10(-5) cm s(-1) for as-received MWCNTs to 3.67 x 10(-3) cm s(-1) for MWCNTs that were electrochemically activated at 2.0 V for 180 s). The increase in the value of k(0)((obs)) arises from the introduction of wall defects exposing edge planes of the MWCNTs, as observed by high-resolution TEM. The density of the edge plane defects increases from almost zero (for as-received MWCNTs) to 3.7 % (for MWCNTs electrochemically activated at 2.0 V for 180 s). High-resolution X-ray photoelectron spectroscopy (HR-XPS), Raman spectroscopy, and electrochemical impedance spectroscopy were used to gain a better understanding of the phenomena. HR-XPS revealed that the increase in electrochemical activation potential increases the number of oxygen-containing groups on the surface of carbon nanotubes.
 ...
PMID:Relationship between carbon nanotube structure and electrochemical behavior: heterogeneous electron transfer at electrochemically activated carbon nanotubes. 1881 Jul 41

Carbon nanotubes fabricated by the dc arc discharge method (ADCNTs) and chemical vapor deposition method (CVDCNTs) were oxidized with concentrated HNO 3 to modify their surface chemistry. The materials were characterized using SEM, TEM, FTIR, XPS, potentiometric titration, and nitrogen adsorption. The initial and oxidized materials were used as adsorbents of cadmium from aqueous solutions with different pH. Langmuir and Freundlich adsorption models were applied to fit the isotherm data, and both models fit the experimental data very well. The acid oxidation resulted in an increase in the number of oxygen-containing groups without drastic changes in the texture of the adsorbents. Although the small volume of micropores is present, the nanotube structure can be considered as nonporous. The lack of developed microporosity in carbonaceous materials eliminates the inner surface diffusion problems and makes the vast majority of surface groups available for adsorption of cadmium. The availability of these centers depends on the pH of the solution, which controls the protonation level. In spite of the fact that the pH of the solution affects the speciation of cadmium to some degree, the surface chemistry is the predominant force for adsorption at the pH range adopted in the present study, while the texture of materials also affects the nanotube's cadmium-adsorbing performance.
 ...
PMID:Investigation of the role of surface chemistry and accessibility of cadmium adsorption sites on open-surface carbonaceous materials. 1881 19

A method for highly precise and high-resolution imaging and location of oxygen-containing groups on the walls of carbon nanotubes (CNTs) is presented. The soft-chemistry approach is used by means of tagging oxygen-containing groups on the surface of CNTs with Eu(III) through coordinate covalent bonds. Eu(III) ions bonded to oxygen-containing groups are observed by high-angle annular dark-field scanning TEM.
 ...
PMID:Imaging of oxygen-containing groups on walls of carbon nanotubes. 1900 31

One kind of novel hierarchical carbon nanotubes/bamboo charcoal (CNTs/BC) was prepared by CVD growth of CNTs on low-cost bamboo charcoal (BC). The obtained CNTs/BC composites were characterized by SEM and TEM observations. Adsorption of copper ions by CNTs/BC in aqueous solution was investigated. The adsorbed copper species were analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that the CNTs/BC composites exhibited higher adsorption capacities toward aqueous copper ions than the pristine BCs and commercial activated bamboo charcoals (ABCs) with a specific surface area of over 1000 m(2) g(-1). The adsorption capacity increases with nanotube growth time. Moreover, nitric acid treatment was used for the oxidation of the carbon surface. The surface functional groups of carbon samples were analyzed by Fourier transform infrared spectroscopy (FT-IR), Boehm's titration method, and zeta potential analysis. It was found that nitric acid treatment for CNTs/BC produced more oxygen-containing functional groups, leading to a higher copper ion adsorption capability than conventional carbon adsorbents under the same treatment condition.
 ...
PMID:Effect of growing CNTs onto bamboo charcoals on adsorption of copper ions in aqueous solution. 1905 22

This study is to test the sensitivities of different tumor cells to ultrasound irradiation at the frequency of 2.2 MHz for 60 s duration, and investigate the potential mechanism underlying different sensitivities. Three murine tumor models with distinct aggressiveness (S180, H-22 and EAC) were exposed to ultrasound to evaluate their sonodynamic efficiencies, and several biological parameters such as cell membrane permeability, lipid peroxidation (LPO), ultra-structure observation, intracellular reactive oxygen species (ROS) and mitochondria membrane potential (MMP) were analyzed after exposures. The results showed that cellular responses of different cells were distinct, of interest to note, the aggressive S180 cells were much more sensitive than others, whereas EAC cells were relatively more resistant to ultrasound irradiation. The direct comparisons among different types of cells indicate that the sono-sensitization seems to depend on the physiological and chemical properties of tumor cells. Perhaps sections of cell membrane became destabilized following the initial radical attack and LPO reaction, which caused S180 cells more susceptible to mechanical stresses during sonolysis. This study provides important implications for cancer therapy.
 ...
PMID:Comparisons among sensitivities of different tumor cells to focused ultrasound in vitro. 1927 8

SBA-15 functionalization with mercaptopropyltrimethoxysilane has been used to prepare supported gold catalysts for the low temperature CO oxidation reaction. Supports and catalysts have been characterized by chemical analysis, CHS analysis, XRD, TGA, nitrogen adsorption-desorption at 77 K, TEM, CPMAS NMR, XPS and EPR. Catalytic runs have been carried out at atmospheric pressure and 313-623 K and the influence of diverse thermal treatments of the samples prior to reaction has been investigated. The presence of organic residues and the size of the gold nanoparticles strongly affect catalytic activity. Only high-temperature calcination in air followed by treatment under H2 atmosphere leads to active catalysts. After complete elimination of the functionalizing agent, caused by the calcination step, a gold-mediated "activation" process of the silica support takes place during the hydrogen treatment. As a consequence, active catalysts for the low temperature CO oxidation are obtained, even though the size of the Au particles is too large for establishing direct Au-oxygen interactions, usually assumed to be essential for the reaction over silica-supported gold catalysts.
 ...
PMID:Modifications induced by pretreatments on Au/SBA-15 and their influence on the catalytic activity for low temperature CO oxidation. 1928 78

In this study, highly porous carbon nanofibers (CNFs) were prepared by chemical activation in order to develop promising energy storage materials. The activation was performed at a temperature of 850 degrees C by using different metal hydroxides as the activating agents. Pore structures of the CNFs were analyzed using N(2)/77K adsorption isotherms. The presence of oxygen groups was analyzed by means of acid-base titration. The structural order (crystallinity) of the materials was studied by XRD and TGA analysis and the morphology and diameter distributions by means of TEM. The use of hydroxide of alkaline metals of low melting and boiling points (K, Rb, and Cs) led to the best results of porosity development. On the contrary, the pore opening was lower if the alkaline metal had a high boiling point (Na) or when alkali earth cations were used as activating agents. After the activation, the porous CNFs showed a decrease in diameter and scratches on their surfaces, as a consequence of the surface oxidation and opening of the graphitic layers, respectively. It was found that the specific surface area of the porous CNFs prepared using KOH and RbOH was more than 400 and 280 m(2) g(-1), respectively, without loss of their fiber shape.
 ...
PMID:Influence of the nature of the metal hydroxide in the porosity development of carbon nanofibers. 1941 31


<< Previous 1 2 3 4 5 6 7 8 9 10