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991.
H. Y. Hou Y. S. Duh W. H. Lin C. M. Shu 《Journal of Thermal Analysis and Calorimetry》2006,85(1):145-150
Cumene hydroperoxide
(CHP) is classified as a flammable hazard in NFPA 43B. Fires or explosions
induced by thermal hazards ascribed to the unstable hydroperoxyl or peroxyl
groups are often reported. This sequence studies is aimed at the decomposition
phenomena associated with the reactive and incompatible characteristics of
CHP mixed with alkaline solutions. Various alkalines were used for comparing
the relative impact of bases and effects on concentrations. Exothermic onset
temperatures and heats of decomposition of these incompatible mixtures were
performed by differential scanning calorimetry (DSC). Comparisons of exothermic
onset temperature, peak power, heat of decomposition, etc., were assessed
to verify the severity of incompatible hazards in these systems. When mixed
with a small amount of the hydroxides (in the production or storage of CHP),
CHP will be more labile or unstable because of lower exothermic temperature.
In addition, to elucidate the final products and propose mechanisms of the
reaction of CHP mixed with alkaline solution, the analytical results were
carried out by GC/MS and IR. The exhibited reactivity was complicated and
significantly affected by the alkaline solutions. The reaction schemes have
been proposed in this study. These results are especially important in process
safety design for producing CHP and its related compounds, such as phenol, α-cumyl
alcohol (CA), acetophenone (AP), and dicumyl peroxide (DCPO). 相似文献
992.
V. A. Milyukov A. V. Kataev O. G. Sinyashin E. Hey-Hawkins 《Russian Chemical Bulletin》2006,55(7):1297-1299
Heating of a mixture of white phosphorus and sodium in diethylene glycol dimethyl ether in the presence of catalytic amounts
of dibenzo-18-crown-6 affords a pure solution of sodium pentaphosphacyclopentadienide NaP5. One of the intermediate products is trisodium heptaphosphide Na3P7. The influence of the nature of a metal (Li, Na, K) on the formation of the pentaphosphacyclopentadienide anion was studied.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1249–1251, July, 2006. 相似文献
993.
Usherov-Marshak A. Pershina L. Krivenko P. 《Journal of Thermal Analysis and Calorimetry》1998,54(1):57-61
This paper presents results of thermochemical and thermokinetic studies of the hydration of portland cement, alkaline cements
with mineral additives and slag alkaline binder. The influence of the modulus of basicity of the binders on the thermochemical
and thermokinetic characteristics of hydration was estimated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
994.
Hilgeroth A Fleischer R Wiese M Heinemann FW 《Journal of computer-aided molecular design》1999,13(3):233-242
The functional groups of cage dimeric N-alkyl substituted 3,5-bis(hydroxymethyl)-4-(4-methoxyphenyl)-1,4-dihydropyridines are similar to those of cyclic and azacyclic ureas that are potent inhibitors of HIV-1 protease of the dihydroxyethylene- and hydroxyethylene type, respectively. In the following study the conformity of common functional groups is investigated concerning their orientation in space as well as in the enzyme HIV-1 protease. Starting from X-ray crystal data of the centrosymmetric cage dimeric N-benzyl derivative with ester groups, the derivative with hydroxymethylene groups was built and a systematic conformational search was performed for the conformationally important torsion angles considering electrostatic and van der Waals interactions. From the huge number of conformations those comprising centrosymmetrical and C2-symmetrical energy minima were selected and minimized. The three remaining conformers were fitted to the azacyclic urea A-98881 selected from the HIV-1 protease enzyme- inhibitor complex using the centroids of the corresponding aromatic residues and additionally by the field fit option of the Advanced CoMFA module of SYBYL. Interestingly, the energetically most favourable one, which, additionally, possesses C2-symmetry like the active site cavity of HIV-1 protease, showed the best fit. Comparing the electrostatic potential (EP) of the latter with the EP of A-98881 the aromatic residues show excellent accordance. Slight differences in the extent of the EP were found in the areas of the hydroxymethylene groups of the cage dimer and the single hydroxy group as well as the urea carbonyl group of A- 98881, respectively. In order to compare the binding possibilities to the enzyme HIV-1 protease for the cage dimer and A-98881, their interaction fields with certain probes (CH3 for alkyl, NHamide, and carbonyl, O– of COO–), representing the decisive functional groups of the active site, have been calculated using GRID and projected into the enzyme placing the structures according to the position of A-98881 in the enzyme- inhibitor complex. The strongest calculated fields of the O– probe were found near Asp 25 for both structures. Another respective conformity consists in the overlap of the fields for the NHamide probe near Ile 50 and 50 for the investigated cage dimer and A-98881. 相似文献
995.
Toshifumi Miyazawa Kiwamu Imagawa Hiroe Minowa Toyoko Miyamoto Takashi Yamada 《Tetrahedron》2005,61(43):10254-10261
In the Aspergillus oryzae protease-catalyzed ester hydrolysis, substitution of N-unprotected amino acid esters for the corresponding N-protected amino acid esters resulted in a large enhancement of the hydrolysis rate, while the enantioselectivity was deteriorated strikingly when the substrates employed were the conventional methyl esters. This difficulty was overcome by employing esters bearing a longer alkyl chain such as the isobutyl ester. Utilizing this ester, amino acids carrying an aromatic side chain were resolved with excellent enantioselectivities (E=50 to >200). With amino acids bearing an aliphatic side chain also, good results in terms of the hydrolysis rate and enantioselectivity were obtained by employing such an ester as the isobutyl ester. Moreover, the enantioselectivity proved to be enhanced further by conducting the reaction at low temperature. This procedure was applicable to the case where the enantioselectivity was not high enough even by the use of the isobutyl ester. 相似文献
996.
The activity and stability of alkaline phosphatase in solutions of water and the fused salt ethylammonium nitrate 总被引:4,自引:0,他引:4
David K. Magnuson James W. Bodley D. Fennell Evans 《Journal of solution chemistry》1984,13(8):583-587
The fused salt ethylamonium nitrate has several properties which resemble those of the biologically important solvent water. In order to shed light on the role of solvent in determining protein structure we have examined the influence of ethylammonium nitrate on the activity and stability of the enzyme alkaline phosphatase. Significantly, although reduced enzymatic activity was observed in ethylammonium nitrate solutions up to 60% (v/v) in water, the enzyme was stable to brief exposure to solutions as high as 80% (v/v) in the fused salt. 相似文献
997.
《Arabian Journal of Chemistry》2022,15(12):104334
Targeting SARS-CoV-2 papain-like protease using inhibitors is a suitable approach for inhibition of virus replication and dysregulation of host anti-viral immunity. Engaging all five binding sites far from the catalytic site of PLpro is essential for developing a potent inhibitor. We developed and validated a structure-based pharmacophore model with 9 features of a potent PLpro inhibitor. The pharmacophore model-aided virtual screening of the comprehensive marine natural product database predicted 66 initial hits. This hit library was downsized by filtration through a molecular weight filter of ≤ 500 g/mol. The 50 resultant hits were screened by comparative molecular docking using AutoDock and AutoDock Vina. Comparative molecular docking enables benchmarking docking and relieves the disparities in the search and scoring functions of docking engines. Both docking engines retrieved 3 same compounds at different positions in the top 1 % rank, hence consensus scoring was applied, through which CMNPD28766, aspergillipeptide F emerged as the best PLpro inhibitor. Aspergillipeptide F topped the 50-hit library with a pharmacophore-fit score of 75.916. Favorable binding interactions were predicted between aspergillipeptide F and PLpro similar to the native ligand XR8-24. Aspergillipeptide F was able to engage all the 5 binding sites including the newly discovered BL2 groove, site V. Molecular dynamics for quantification of Cα-atom movements of PLpro after ligand binding indicated that it exhibits highly correlated domain movements contributing to the low free energy of binding and a stable conformation. Thus, aspergillipeptide F is a promising candidate for pharmaceutical and clinical development as a potent SARS-CoV-2 PLpro inhibitor. 相似文献
998.
Natalia I. Larionov Inna P. Gladysheva Olga V. Polekhina Lidiya P. Kurochkina Elena N. Gorbatova 《Applied biochemistry and biotechnology》1996,61(1-2):139-148
The modification of Bowman-Birk soybean protease inhibitor (BBI) with the monoaldehyde derivative of block copolymer of ethylene
oxide and propylene oxide (PE),M
r
2000 is described. The conjugate contains five covalently bound polymer chains per protein molecule, and retains the ability
to inhibit trypsin and chymotrypsinlike proteinases. The distribution of native BBI and the BBI-PE conjugate was examined
in mice. After iv injection of [125I]BBI and [125I]BBIPE, both inhibitors distributed very rapidly to the liver, kidney, and lungs, and more slowly to the brain. At the same
time-points (up to 24 h), radioactivity in the blood and organs of mice injected with modified inhibitor was higher than that
of the native inhibitor. The blood concentration time profile following iv administration of two BBI preparations at a dose
3 mg/kg was reasonable well described by a two-compartment open model with first-order elimination kinetics. The total clearance
of BBI-PE decreased by a factor of 8, body mean residence time increased by a factor of 5 in comparison with BBI. A physiological
pharmacokinetic model was developed to describe the tissue-to-blood distribution of two inhibitors. One-compartment physiological
organ model (flow limited) was used to describe of timecourse profiles of BBI concentration in organs. A two-compartment physiological
organ model (membrane limited) was used to predict tissue-to-blood distribution of conjugated BBI in some organs of mice (liver,
lungs). The predicted concentration curves of BBI and BBI-PE in blood and organs in mice (with the exception of kidney) showed
good agreement with the observed values. 相似文献
999.
Carlos A Martinez 《Tetrahedron》2004,60(3):759-764
The development of an efficient route for the preparation of (2S)-2-[3-{[(5-methylisoxazol-3-yl)carbonyl]amino}-2-oxopyridin-1(2H)-yl]pent-4-ynoic acid (4), a key intermediate in the synthesis of a human rhinovirus (HRV) protease inhibitor, is presented. In the presence of 40% acetonitrile, the alkaline protease from Bacillus lentus can catalyze the kinetic resolution of racemic ester 7 to afford (S)-acid 4 in 49% chemical yield/per cycle with 98% ee and >98% HPLC purity. The (R)-ester can then be readily recycled via a DBU catalyzed epimerization. The enzymatic preparation described here is superior to the existing chemical resolution route, exhibiting lower costs as well as higher yields, enantioselectivity, and substrate loads. In addition, this protease displays broad substrate specificity toward this class of compounds and can be easily extended to the preparation of other tripeptide mimetics of rhinovirus protease inhibitors. 相似文献
1000.
L. S. Kosheleva 《Russian Chemical Bulletin》1994,43(3):346-350
The change in the structure of NH4NaY zeolite (53 % NH4
+, Si/Al = 2.37) after hydrothermal treatment at 873 K followed by modification with aqueous KOH solution at 353 K was studied by IR and29Si NMR spectroscopy. It has been shown that hydrolytic cleavage of the Al-O bond of the deammoniated zeolite sites by hydrothermal treatment predominates in the framework groups Si(OAl)
n
(OSi)4–n
,n=2, 3. Molecular water adsorbed on such a sample exists as hydrogen-bonded associates with hydrogen bonds of various strengths reaching that in ice-like structures (the band at 2468 cm–1). Treatment with an alkali results in partial regeneration of the normal bridge bonds. The exchange of the protons of the terminal silanol groups with the alkaline cation prevents those groups from participating in the regeneration process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 387–391, March, 1994. 相似文献