Search results for "Activation"

Trapping of Different Lipase Conformers in Water-Restricted Environments

1996

Based on a recently reported strategy to rationally activate lipolytic enzymes for use in nonaqueous media [Mingarro, I., et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 3308-3312], we compared the behavior in water-restricted environments of activated vs nonactivated forms of different lipases toward their natural substrates, triacylglycerols. To this end, nine lipases from varied origins (mammalian, fungal, and bacterial) were assayed using simple acidolyses as nonaqueous model reactions. The experimental results for several (though not all) lipases, discussed in the light of current structural and functional information, were collectively consistent with a model where, depending on the "…

Metabolic Inactivation of Reactive Metabolites

1978

ABSTRACT Many compounds which are not electrophilically reactive as such are transformed by mammalian enzymes to reactive metabolites which are, in many cases, responsible for cytotoxic, mutagenic and/or carcinogenic effects of the compounds in question. The essential role of activating systems in this situation has become common knowledge during the last decade. However, many reactive metabolites are also subject to inactivation by mammalian enzymes. This important parameter is frequently not taken into account. Compounds possessing aromatic or olefinic moieties are very widely occurring and activation of these often proceeds via an electrophilically reactive epoxide. This may be transform…

Mo-Based Oxidizers as Powerful Tools for the Synthesis of Thia- and Selenaheterocycles.

2019

A highly efficient synthetic protocol for the synthesis of thia- and selenaheterocycles has been developed. By employing a MoCl5 -mediated intramolecular dehydrogenative coupling reaction, a broad variety of structural motifs was isolated in yields up to 94 %. The electrophilic key transformation is tolerated by several labile moieties like halides and tertiary alkyl groups. Due to the use of disulfide or diselenide precursors, a high atom efficiency was achieved.

Implication of eNOS Uncoupling in Cardiovascular Disease

2017

Under physiological conditions, nitric oxide (NO) is produced in the vasculature mainly by the endothelial nitric oxide synthase (eNOS). Endothelial NO relaxes blood vessels, inhibits platelet activity, and protects against atherosclerosis. Under pathological conditions such as hypertension, diabetes, and hypercholesterolemia, eNOS may become uncoupled. Uncoupled eNOS generates superoxide at the expense of NO and contributes substantially to oxidative stress and endothelial dysfunction. Major mechanisms of eNOS uncoupling include deficiency of the eNOS cofactor tetrahydrobiopterin, deficiency of the eNOS substrate L-arginine, and eNOS S-glutathionylation. Reversal of eNOS uncoupling may rep…

Sorption Kinetics of Benzene and p-Xylene on Template Supported Synthesized Gallosilicates

1993

Adsorption equilibria and kinetics of benzene and p-xylene on microporous gallosilicates (Ga-MFI) were measured piezometrically to ascertain the role of Ga in the system and to compare it with Ga-free MFI structures. The intracrystalline mobility of benzene follows a diffusional mechanism throughout the entire concentration range with an energy of activation that considerably exceeds that for the Ga-free species (78 kJmol−1 and 26 kJmol−1, respectively). For p-xylene, the kinetics indicate the existence of three sorption states. Sorbing species become highly immobile at a pore filling of ca n > 4 molecules per unit cell, i.e. in the range of concentration where isotherm hysteresis occurs. T…

1978

A newly designed automatically controlled stirred reactor suitable for kinetic measurements of reactions with half lives ≥2s has been applied to follow the anionic polymerization of methyl methacrylate in THF with Na+ as a counter ion in the presence of an excess of NaB(C6H5)4. As initiators were used: benzylsodium reacted with α-methylstyrene (I), fluorenylsodium (II), and 9-methylfluorenylsodium (III). With I the initiation is fast as compared with the polymerization reaction which is first order in monomer concentration. Within the range of −50°C to −100°C an almost unperturbed “living” polymerization is observed. The Arrhenius plot of the rate constants results in a straight line with a…

Trace element determination in sediments: a comparative study between neutron activation analysis (NAA) and inductively coupled plasma-mass spectrome…

2000

An inductively coupled plasma-mass spectrometry (ICP-MS) method has been employed for trace element determination in five real sediment samples and a standard reference material. These samples were mineralized by dry ashing at 550°C and fused at 1100°C for 30 min with lithium metaborate. Dissolved samples were measured by a semiquantitative methodology with external calibration and with Rh as an internal standard. More than 50 elements have been measured. As a reference technique, a direct analysis of the solid samples was carried out by neutron activation analysis. Results obtained by ICP-MS have been compared with those obtained by neutron activation analysis (NAA) by applying the paired …

Effect of Temperature on Isobutyric Acid Loss during Roasting of Carob Kibble

1997

The high content of isobutyric acid in carob (Ceratonia siliqua L.) constitutes a handicap for some of its potential uses due to the undesirable smell produced by that compound. In this study the loss of isobutyric acid during roasting was approached by heating the carob kibble at temperatures from 120 to 180 °C in two local cultivars (Matalafera and Lisa). The initial content of isobutyric acid varied between 6.3 (Lisa) and 9.4 (Matalafera) g isobutyric acid/kg dry solid. Results showed that the process can be described by a diffusive model. The activation energy of the process is about 55 kJ/mol for both cultivars. Keywords: Carob pod; roasting; isobutyric acid; diffusion

A dft study of the regioselectivity in intramolecular diels-alder reactions with formation of a tricyclodecane skeleton

2011

Three different intramolecular Diels-Alder (IMDA) reactions associated with the formation of fused and bridged tricyclodecane skeletons have been studied at the B3LYP/6-31G(d) computational level. While substitution on the diene and dienophile fragments modulates the polar character of the reaction, the strain effect produced by the methylene tether affects the activation energy, and its torsion controls the different regioisomeric channels of the IMDA process. Analysis of the reactivity indices recently proposed (J. Soto-Delgado et al., Org. Biomol. Chem., 2010, 8, 3678) within the conceptual density functional theory allows for the characterization of the mechanism including the charge tr…

A Versatile Palladium/Triphosphane System for Direct Arylation of Heteroarenes with Chloroarenes at Low Catalyst Loading

2010

International audience; Put a ring on it: The use of an air-stable, robust palladium/tridentate phosphane catalyst in direct C[BOND]H and C[BOND]Cl activation reactions is reported (see scheme; DMAc=N,N-dimethylacetamide, TBAB=tetra-n-butylammonium bromide). Electron-rich, electron-poor, and polysubstituted furans (X=O), thiophenes (X=S), pyrroles (X=NR5), and thiazoles were arylated with chloroarenes in the presence of the catalyst.