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991.
Dias AR Martins AM Ascenso JR Ferreira H Duarte MT Henriques RT 《Inorganic chemistry》2003,42(8):2675-2682
The preparations of 1,4,7-(NHPhSiMe(2))(3)-1,4,7-triazacyclononane (H(3)N(3)-tacn) and its lithium and sodium derivatives are described. The X-ray structure of the THF adduct of the lithium derivative, Li(3)N(3)-tacn(THF)(2), shows that one of the macrocycle pendant arms is bent to allow the coordination of the its lithium ion to two tacn amines. In solution, a fluxional process makes all the pending arms magnetically equivalent. The reactions of Li(3)N(3)-tacn or Na(3)N(3)-tacn with either TiCl(4) and TiCl(3)(THF)(3) led to the formation of [Ti(N(3)-tacn)], 5. The oxidation of 5 with various oxidizing reagents gave cationic complexes [Ti(N(3)-tacn)]X, 6 (X = I, Cl, SCN, PF(6), BPh(4)), that exist as a pair of enantiomers, lambda(lambdalambdalambda)/delta(deltadeltadelta), which interconvert in solution. The molecular structures of 5 and 6 (X = I, BPh(4)) show the coordination of the six nitrogen donor set to the titanium. Due to the short length of the tacn pendant arms, the hexadentate bonding mode of the ligand is mainly achieved through the sharpening of the N-Si-N angles. The reaction of [Ti(N(3)-tacn)]I, 6a, with W(CO)(6) led to the synthesis of [Ti(N(3)-tacn)][W(CO)(5)I], 7. 相似文献
992.
For the first time the millimeter-wave spectra of the trans-35ClHC=CHF and trans-37ClHC=CHF isotopomers have been observed in natural abundance. Many DeltaJ=0, +/-1 DeltaK(-1)=+1 transitions for 35ClHC=CHF and DeltaJ=0 DeltaK(-1)=+1 transitions for 37ClHC=CHF have been detected and assigned. This allowed us to accurately determine the vibrational ground-state rotational constants, quartic and some sextic centrifugal distortion constants, and nuclear quadrupole coupling constants for both 35Cl and 37Cl. The experimental investigation has been supported by highly accurate theoretical predictions. As far as ab initio computations are concerned, the complete set of cubic and quartic force constants have been evaluated by numerical differentiation of the analytic second-order M?ller-Plesset many-body perturbation theory/correlation consistent polarized valence triple zeta second derivatives. The anharmonic part of the force field completes the theoretical study on the equilibrium structure, dipole moment, chlorine quadrupolar tensor, and harmonic force field previously carried out by the same authors. 相似文献
993.
Alberto TárragaPedro Molina Juan L. LópezMa? Desamparados Velasco 《Tetrahedron letters》2003,44(16):3371-3375
Ferrocenophane derivatives 3 act as electrochemical sensors of Mg2+ ions: a new redox peak appears in the CVs anodically shifted compared to the E1/2 of the free receptors by 268-382 mV. Receptors 3a, 3c and 3d are selective for Mg2+, whilst 3b is also responsive to Ca2+ ion (302 mV shift). Receptor 3c also gave a highly visual output response in the presence of Mg2+ consisting of a deep purple colour. 相似文献
994.
Coded amino acids in gas phase: the shape of isoleucine 总被引:1,自引:0,他引:1
Lesarri A Sánchez R Cocinero EJ López JC Alonso JL 《Journal of the American Chemical Society》2005,127(37):12952-12956
The solid alpha-amino acid isoleucine has been vaporized by laser ablation and expanded in a supersonic jet, where the molecular conformations of the isolated molecule were probed using Fourier transform microwave spectroscopy. Two conformers of neutral isoleucine have been detected in gas phase, the most stable being stabilized by an intramolecular hydrogen bond N-H...O=C and a cis-COOH arrangement. The higher energy form is stabilized by an intramolecular hydrogen bond N...H-O. The sec-butyl side chain of the amino acid adopts the same configuration in the two observed conformers, with a staggered configuration at Cbeta similar to that observed in valine and a trans arrangement of Calpha and Cdelta. Ab initio calculations at MP2/6-311++G(d,p) level reproduce satisfactorily the experimental results. 相似文献
995.
Molar and partial molar excess volumes of mixtures of benzene with several methyl esters (from methanoate to decanoate) were determined, over the whole concentration range, at 25°C and atmospheric pressure from experimental densities and correlated by a suitable equation. The applicability of the Flory and Priggogine–Flory–Pattersort models for predicting molar excess volumes is tested. The calculated values with Flory and Priggogine–Flory–Patterson are similar and agree poorly with the experimental data. 相似文献
996.
Antonio Javier Blasco Agustín González Crevillén María Cristina González Alberto Escarpa 《Electroanalysis》2007,19(22):2275-2286
This review highlights the role of electrochemical approaches in the sensing of antioxidants and their antioxidant capacity with especial attention to the analytical possibilities of electrochemistry in the direct evaluation of antioxidant capacity exhibited by food and biological samples due to the termed dietary, natural or biological antioxidants (mainly polyphenols, and vitamins C and E). The analytical potency of the electrochemistry is comprehensively stated and the selected results found in the literature are summarized and discussed critically. The main electrochemical approaches used have been cyclic voltammetry (CV) and flow injection analysis with amperometric detection (FIA‐ED). In addition, miniaturization is going to break new frontiers in the evaluation of antioxidant activity. 相似文献
997.
Sergio Auricchio Orso Vajna de Pava Pietro Traldi Alberto Griffini 《Journal of mass spectrometry : JMS》1982,17(1):34-41
The electron impact mass spectrometric behaviour of a series of macrocyclic-acyclic polyether-ester compounds containing an isoxazole, benzene or pyridine ring is discussed in detail with the aid of exact mass measurements and metastable ions (linked scans B/E and B2/E). The nature of unusual [M+H]+ species, present in the crown moieties only, is elucidated by means of low electron energy measurements and labelling experiments. The field desorption spectra show only intense peaks corresponding to [M+H]+ species and rule out the presence of dimeric moieties. 相似文献
998.
The formation of open chain polyammonium cation-fluoride and -carbonate complexes was studied by potentiometric and calorimetric techniques at t=25 °C. Several species of HiAL (A=amine; L=F−, CO32−) are formed in both systems with a mean stability (ζ=|zanion×zcation|) and for fluoride and carbonate, respectively. The comparison with analogous systems (chloride and acetate for fluoride and hydrogenphosphate, sulfate and malonate for carbonate) showed that fluoride and carbonate form the most stable species with open chain polyammonium cations, among low molecular weight anions. The N-alkyl substitution does not play negligible role in the stability of these complexes, the species formed by substituted amines being more stable. 相似文献
999.
The molecular structures and energetics of diazomethyl (HCNN) and cyanomidyl (HNCN) radicals and their related cations (HCNN(+),HNCN(+)) and anions (HCNN(-),HNCN(-)) are reported at a high level of accuracy. The singles and doubles coupled-cluster method including a perturbational correction for connected triple excitations with systematic sequences of correlation consistent basis sets have been employed. Extrapolation to the complete basis set limit has been used with accurate treatments of core-valence correlation effects in order to accurately predict molecular properties, ionization potentials, electron affinities as well as C-H and N-H bond dissociation energies. For all the species studied, harmonic vibrational frequencies have also been evaluated in order to obtain zero-point corrections to ionization potentials, electron affinities, and dissociation energies. 相似文献
1000.
New glycoclusters constituted of ribosylmethyl, galactosylmethyl, and glucosylmethyl fragments assembled on a calix[4]arene platform by means of propoxytetrazole spacers have been prepared by coupling the corresponding sugar azides with p-toluenesulfonyl cyanide, and then reacting 1-glycosylmethyl-5-sulfonyl-tetrazole derivatives thus formed with a calix[4]arene tetrol. 相似文献