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101.
Sénèque O Rager MN Giorgi M Prangé T Tomas A Reinaud O 《Journal of the American Chemical Society》2005,127(42):14833-14840
The coordination chemistry of Zn in an N(3)ArOH environment has been explored. The ligands are based on calix[6]arenes that present two imidazole arms and an amino phenol moiety at the narrow rim. Three different types of complexes have been characterized. One is dicationic with Zn(2+) coordinated to the three nitrogen atoms and to the oxygen of the phenol group of the calix[6]ligand. This complex is very sensitive to exogenous coordinating molecules and exists as a 5-coordinate species due to the endo-complexation of a guest. The second species is a monocationic complex for which the phenol group has been deprotonated. The resulting N(3)ArOZn complex can also bind a guest ligand albeit with a lower affinity than the dicationic complex. The third species is neutral. It can be obtained upon reaction with a base to yield a hydroxo complex or with an anion such as a chloride that coordinates the metal center from the outside of the calixarene cavity. The simultaneous binding of two anionic donors decreases the Zn Lewis acidity, allowing an impressive conformational reorganization of the system. One imidazole arm is released by the metal center. The other one undergoes self-inclusion into the pi-basic calixarene cavity because the low affinity of the metal center for neutral ligand does not allow the endo-coordination of an exogenous guest. Hence, the calix[6]N(3)ArOH-based Zn complexes act as an acid-base switch for guest binding. Several aspects of this system appear reminiscent of Zn-peptidases of the astacin and serralisin families. 相似文献
102.
Treatment of 1,3-dienes and 1,3,5-cycloheptatriene by chlorotrimethylsilane in the presence of wire of lithium led mainly to reductive dimerization with formation of bis(allylsilane) derivatives. Bis-silyl compounds obtained: from 1,3-butadiene, 1,8-bis(trimethylsilyl)-2,6-octadiene (70%); from isoprene, (Z,Z)-2,7-dimethyl-1,8-bis(trimethylsilyl)-2,6-octadiene (44%) and 2,6-dimethyl-1,8-bis(trimethylsilyl)-2,6-octadiene (19%); from butadiene-isoprene mixture (1:1), 3-methyl-1,8-bis(trimethylsilyl)-2,6-octadiene (55%); from 2,3-dimethylbutadiene, (E,E)-2,3,6,7-tetramethyl-1,8-bis(trimethylsilyl)-2,6-octadiene (36%), from 1,3-cyclohexadiene, 4,4′-bis(trimethylsilyl)-bicyclohexyl-2,2′-diene (48%); from 1,3,5-cycloheptatriene, 1,1′-bi[(S∗,S∗)-6-(trimethylsilyl)cyclohepta-2,4-dien-1-yl] (53%). The structure of the various intermediates (radical anion, dianion, silylated radical, silylated anion) has been established by calculations at the B3LYP/6-311++G(d,p) level of theory with zero-point energy correction. These results are in accordance with a pathway including the formation of a radical anion, its silylation furnishing to a γ-silylated allylic radical followed by a dimerization reaction in the head to head manner. 相似文献
103.
József Kaizer József Pap Gábor Speier Marius Réglier Michel Giorgi 《Transition Metal Chemistry》2004,29(6):630-633
The preparation, spectroscopic properties, and crystal structure of [Cu(ind)(mco)] [ind is the anion of 1,3-bis(2-pyridylimino)isoindoline and mco is the anion of 3-hydroxy-(4H)-benzopyran-4-one] are reported. The complex exhibits a distorted square pyramidal geometry. The oxygenation of the title compound results in oxidative cleavage of the heterocyclic ring to give the (acetylsalicylato)copper(II) complex [Cu(asp)(ind)] (asp is the anion of acetylsalicylic acid) and CO as primary products, which reaction resembles the enzymatic reaction of quercetinase. 相似文献
104.
Arduini A Brindani E Giorgi G Pochini A Secchi A 《The Journal of organic chemistry》2002,67(17):6188-6194
A novel heteroditopic receptor (5) based on a rigid calix[4]arene cavity bearing at the upper rim four arylsulfonamido binding sites has been synthesized. The binding abilities of this new host have been investigated in apolar solvents toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) and compared with those of monotopic and heteroditopic calix[4]arene-bis(crown-3)-based receptors 1 and 2 in order to evaluate the role of the anion on ion-pair recognition. While monotopic host 1 shows an efficiency order toward the different salts that increases when the anion is less interactive (Hofmeister trend), an opposite role of the counteranion on the recognition process was observed with host 5 (anti-Hofmeister trend). A more complex behavior is experienced by host 2, which shows a high and leveled efficiency for all the anions tested. The results obtained were explained on the basis of the different types of ion pairs present in the recognition process. Further information on the role of the anion were obtained by the "dual host" strategy utilizing the tri-n-butylthioureido derivative of tren 7, which forms a stable complex with chloride anion. The very high efficiency shown by these heteroditopic hosts opens new routes in supramolecular projects and is a very interesting tool in the molecular recognition of ion-pairs and its applications. 相似文献
105.
Summary In this work the main parameters which define the threshold, the temporal shape and the stability ofp-H2 Raman laser have been investigated. Our results show a very high-power conversion efficiency (130%) and for each pump CO2 line we can dispose of a correspondent line (pulse≥1J/50 ns) in the 16 μm range. This is foundamental as far as UF6 isotopic separation is concerned.
Riassunto In questo lavoro sono stati studiati i principali parametri che definiscono la soglia, la forma temporale e la stabilità di un laser Raman a para-idrogeno (16 μm). I nostri risultati mostrano un'alta efficienza di conversione di potenza (130%) per ciascuna riga del laser a CO2 permettendo una buona tunabilità nel range dei 16 μm. Questo è fondamentale per la separazione isotopica di UF6.
Резюме В этой работе исследуются основные параметры, которые определяют порог, временную форму и стабильностьp-H2 рамановского лазера. Наши результаты показывают очень высокую эффективность конверсии (130%). Для каждой линии CO2 накачки мы можем сопоставить соответствующую линию (импульс≥1 Дж/50 нс) в диапазоне 16 мкм. Это является основой для разделения изотопов UF6.相似文献
106.
M. Bernardini F. D''Amato M. Giorgi S. Marchetti 《International Journal of Infrared and Millimeter Waves》1989,10(1):31-41
Generally the quantum efficiency of FIR Raman generation in molecular gases is below the theoretical value. This disagreement is particularly evident in Raman scattering from pulsed sources with short pulse length, when the vibrational saturation limits the power conversion. Other nonlinear processes can overcome this saturation, but they require a very intense pump power for too short a time to use the FIR radiation in high sensitive experiments with heterodyne detection. This is the case, for instance, of RFWM. In this work we describe the experimental conditions to achieve a high efficiency 90 micron Raman conversion in ammonia, with both short and long pulses. 相似文献
107.
108.
Giuliana Biagi Irene Giorgi Oreste Livi Valerio Scartoni Silvia Velo Antonio Lucacchini Generoso Senatore Pier Luigi Barili 《Journal of heterocyclic chemistry》1995,32(1):169-176
Several new 1,2,3-triazolo[4,5-b][1,4]diazepines were prepared starting from 1-benzyl-1 and 1-phenethyl-4,5-diamino-1,2,3-triazole 2 (Scheme 1), by condensation reactions with β-diketones (Scheme 2), β-ketoesters (Scheme 3), and diethyl malonates (Scheme 4). In the first case we obtained compounds 3 and 4 with basic properties, while the ester function condensations gave cyclic amide derivatives 7, 8, 10, 12 and 13 with acid properties. Some N-methyl derivatives 11, 14 and 15 were obtained from the cyclic amide compounds. Most of compounds were tested for their ability to displace [3H]flunitrazepam from bovine brain membranes but no compound showed benzodiazepine receptor binding affinity. 相似文献
109.
Giuliana Biagi Irene Giorgi Oreste Livi Antonio Nardi Valerio Scartoni 《Journal of heterocyclic chemistry》2002,39(6):1293-1298
Four new triazolylbenzimidazolthione derivatives (2a‐d), analogous to triazolylbenzimidazolone derivatives previously tested as activators of the BKCa potassium channels, were prepared and assayed without success. Some derivatives of a new tricyclic nitrogen heterocycle, 1,2,3‐triazolo[1,5‐a][1,3,5]benzo‐triazepine, bearing a carboxamido group in the 3 position, other substituents in the 8 position and a carbonyl (5a‐d) or thione (6a‐c) or methylthio (7a‐c) function in the 5 position were synthesised. The nucleophilic displacement of the methylthio substituent with morpholine or cyclopentylamine provided the 5‐amino‐substituted tricyclic derivatives 8a‐d. Starting from the l‐(2‐nitrophenyl)‐4‐cyano‐5‐amino‐1,2,3‐triazole (9), the 3‐cyano‐triazolobenzotriazepin‐5‐one derivative 12 was also obtained. The majority of the new compounds were tested towards the BKCa potassium channels, the benzodiazepine and adenosine A1 and A2a receptors, but no remarkable activity was detected. 相似文献
110.
M. D. Crozet P. Vanelle M. Giorgi A. Gellis 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):o496-o498
The title compounds, C13H15N3O5S and C11H10N2O4S2, respectively, both contain a phenylsulfonyl group connected, through a methylene bridge, to either a substituted nitroimidazole or nitro‐1,3‐thiazole ring. In the imidazole‐containing molecule, the nitro and sulfonyl groups are trans relative to the sulfonyl–methyl bond, while in the thiazole‐containing molecule, these substituents are cis. The stabilizing interactions within the crystals are also different between the two compounds. 相似文献