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71.
Christian Bellec Marie-Claude Bellassoued-Fargeau Bernadette Graffe Marie-Claude Sacquet Pierre Maitte 《Journal of heterocyclic chemistry》1990,27(3):551-555
The chemical reduction of 5H-[1]benzopyranno[4,3-d]pyrimidines with lithium aluminum hydrrde leads to 3,4-dihydro derivations. The electro-chemical reducation in acidic medium shows two monoelectronic cathodic waves. In netural or basic medium, substituted compounds in 2 position show a single bielectronic wave while two bielectronic waves are observed for unsubstituted compounds In all cases, preparative electrolysis lead to a hydrodimer in the 4,4′-positiom. 相似文献
72.
Demetrio De Calle García M. Reichenbächer Klaus Danzer Christian Hurlbeck Christine Bartzsch Karl-Heinz Feller 《Analytical and bioanalytical chemistry》1998,360(7-8):784-787
The extraction of wine aroma compounds was studied by direct-SPME (DI/SPME), headspace-SPME (HS/SPME) and multiple-headspace-extraction-SPME
(MHE/SPME). The aromagrams obtained by HS/SPME-CGC were evaluated with chemometrical methods for the varietal classification
of wines.
Received: 25 July 1997 / Revised: 24 September 1997 / Accepted: 7 October 1997 相似文献
73.
We explore here an approach to mimic the structures and biological functions of protein loops in small synthetic molecules, by grafting the loop of interest onto an organic template comprising a bicyclic diketopiperazine, prepared by the formal coupling of (2S,4S)-4-aminoproline (Pro(NH2)) and aspartic acid (Asp). The Fmoc-protected template 4 is used to prepare cyclo(-Ala1-Asn2-Pro3-Asn4-Ala5- Ala6-Temp-) ( 5 ) and cyclo(-Ala1-Arg2-Gly3-Asp4-Temp-) ( 6 ) (where Temp = template derived from 4 ), containing the Asn-Pro-Asn-Ala (NPNA) and Arg-Gly-Asp (RGD) motifs. The conformational properties of these molecules are studied in aqueous solution by NMR and simulated-annealing methods. The NPNA motif, an immunodominant epitope on the circumsporozoite surface protein of the malaria parasite Plasmodium falciparum, is shown to adopt a stable type-I β-turn in 5 . The template in 5 adopts a preferred conformation with Pro(NH2)χ1 ≈? ?35° and the Asp moiety χ1 ≈? 70°. A different template conformation is inferred for 6 , with Pro(NH2)χ1 ≈? 0°, but the ARGD loop appears by NMR to undergo rapid conformational averaging. Solid-phase binding assays reveal that 6 displays modest antagonist activity towards both the integrin αIIbβ3 and αvβ3 receptors. 相似文献
74.
Vanommeslaeghe K Van Alsenoy C De Proft F Martins JC Tourwé D Geerlings P 《Organic & biomolecular chemistry》2003,1(16):2951-2957
Histone deacetylase (HDAC) inhibitors have recently attracted considerable interest because of their therapeutic potential for the treatment of cell proliferative diseases. An X-ray structure of a very potent inhibitor, Trichostatin A (TSA), bound to HDLP (an HDAC analogue isolated from Aquifex aeolicus), is available. From this structure, an active site model (322 atoms), relevant for the binding of TSA and structural analogues, has been derived, and TSA has been minimized in this active site at HF 3-21G* level. The resulting conformation is in excellent accordance with the X-ray structure, and indicates a deprotonation of the hydroxamic acid in TSA by His 131. Also, a water molecule was minimized in the active site. In addition to a similar deprotonation, in accordance with a possible catalytic mechanism of HDAC as proposed by Finnin et al. (M. S. Finnin, J. R. Donigian, A. Cohen, V. M. Richon, R. A. Rifkind and P. A. Marks, Nature, 1999, 401, 188-193), a displacement of the resulting OH- ion in the active site was observed. Based on these results, the difference in energy of binding between TSA and water was calculated. The resulting value is realistic in respect to experimental binding affinities. Furthermore, the mechanism of action of the His 131-Asp 166 charge relay system was investigated. Although the Asp residue in this motif is known to substantially increase the basicity of the His residue, no proton transfer from His 131 to Asp 166 was observed on binding of TSA or water. However, in the empty protonated active site, this proton transfer does occur. 相似文献
75.
Hydroxylamine-O-sulfonic acid: a convenient reagent for the conversion of aldehydes into nitriles . Hydroxylamine-O-sulfonic acid (HAS) proved to be an excellent reagent for the conversion of aliphatic, aromatic and heteroatomic aldehydes into nitriles. There, aldehydes in the form of suspension in HAS water solution, react rapidely to give the corresponding nitriles in high yield. Only with formylpyridines could the intermediate oxime-O-sulfonic acids be isolated. 相似文献
76.
cis- and trans-3,4-Dichlorocyclobutene (I) react with Ni(CO)4 and AlCl3 to give (C4H4)NiCl2 · AlCl3 (II), while the bromo- and iodo-substituted cyclobutenes (III) without AlCl3 yield the complexes (C4H4)NiX2 (IVa, X Br; IVb, X I). Properties of II and IV are discussed and the presence of a C4H4 ring attached to nickel is likely from the results obtained. 相似文献
77.
We describe the synthesis of 3-(2-thienyl)pyridazine and of some of its derivatives substituted on the 6 position eg., ethoxy, hydrazino and azido. Some of these compounds have lead to condensed rings systems, namely, triazolo- and tetrazolopyridazines. 相似文献
78.
Kritsana Jitmanee Jaroon Jakmunee Somchai Lapanantnoppakhun Sunanta Wangkarn Norio Teshima Tadao Sakai Gary D. Christian Kate Grudpan 《Microchemical Journal》2007,86(2):195-203
Derivative techniques for analytical signal processing are useful for solving some noise and signal resolution problems in various fields of study such as titrimetry, spectrophotometry, chromatography and electrochemistry. The broad use of these techniques, however, is often limited by costly inflexible built-in software packages in commercial analytical instruments. We propose here the application of commercial simple software packages such as Microsoft® Excel and Microcal Origin for signal smoothing and fitting, and for obtaining derivative analytical signals in batch and flow-based analyses, including potentiometric titration, spectrophotometry, chromatography, voltammetry and sequential injection analysis (SIA). The worldwide (especially Excel) software packages are easy-to-use for less experienced users and have also capabilities for advanced users, and therefore employing such packages can result in expansion of useful derivative techniques. We demonstrate application of the available package-aided derivative capabilities for enhancing some chemical analyses, including potentiometric acid–base titration, Bradford assay of protein, chromatographic separation of ajmaline and reserpine and anodic stripping voltammetry of copper. The derivative signals from smoothed and fitted curves offer better accuracy and precision, even for non-resolving peaks and tailing peaks. In some cases, the optimization of experimental conditions is not further required, which can lead to fast method development. 相似文献
79.
Structures and Molecular Properties of Charge-Pertubed Molecules. 2, 3-Diphenylquinoxaline Radical Anions in Solution and in Crystals The Na⊕ and K⊕ radical-ion salts of 2, 3-diphenylquinoxaline seem to be (according to a structural database search) among the first ones of N-heterocyclic radical anions in crystals. The one-electron reduction in aprotic 1, 2-dimethoxyethan (DME) solution at metal mirrors and the crystallization under Ar have been preceded by cyclovoltammetric (CV) and ESR/ENDOR measurement. The first electron insertion at ?1.63 V proves to be reversible, whereas the irreversible second step, which is accompanied by an overcrossing of the CV line, can be rationalized by an ‘ECE-DISP’ mechanism via a dianion redox disproportionation. The ENDOR spectrum resolves four 1H couplings and allows to simulate the ESR spectrum including the 14N hyperfine splittings. Both dark-blue single crystals of the radical ion salts $[2,3{\rm - diphenylquinoxaline}^{{.} \ominus} {\rm Met}^ \oplus ({\rm DME})]^.$ show unexpected similarities for Met⊕ = Na⊕, K⊕ despite the 36-pm difference in their ionic radii. The largest structural changes inflicted by the one-electron reduction of the N-heterocyclic molecule are observed in the vicinity of the N-centers bearing the highest effective nuclear charge. The DME-chelated metal cations coordinate at the N electron pairs and form Met⊕(DME)-bridged polymer chains of the radical anion, which are differently ondulated in the Na⊕ and K⊕ radical anion salts. The take-home lesson suggests that many more N-heterocyclic molecules might be analogously reduced under optimized conditions and isolated as single crystals. 相似文献
80.
Thorsten Oldag Thomas Aussieker Hans‐Lothar Keller Christian Preitschaft Arno Pfitzner 《无机化学与普通化学杂志》2005,631(4):677-682
Solvothermal Synthesis and Crystal Structure Determination of AgBiI4 and Ag3BiI6 AgBiI4 and Ag3BiI6 were synthesized by solvothermal reaction from AgI and BiI3 in diluted HI‐solution (20 %) at a temperature of 160 °C. The greyish‐black crystals grow as octahedra (AgBiI4) or hexagonal/trigonal platelets (Ag3BiI6). AgBiI4 crystallizes in space group Fd3¯m with a = 1222.3(1) pm (300 K) and Z = 8 whereas Ag3BiI6 shows the space group R3¯m with a = 435.37(6) pm, c = 2081.0(4) pm (300 K) and Z = 1. Both crystal structures show stacking sequence abcabc… of hexagonal layers containing Iodine. Bismuth and silver are sharing octahedral sites with different mass ratio in both structures. The part of silver which could be localized varies with temperature. This behaviour indicates mobility of silver within the crystal structure. The ionic conductivity of AgBiI4 is explored. AgBiI4 and Ag3BiI6 show close structural relationship, with AgBiI4 as a variant with a higher degree of order. 相似文献