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91.
This work studies the partitioning of the electron density into two contributions which are interpreted as the paired and the effectively unpaired electron densities. The topological features of each density field as well as of the total density are described localizing the corresponding critical points in simple selected molecules (local formalism). The results show that unpaired electron-density concentrations occur out of the topological bonding regions whereas the paired electron densities present accumulations inside those regions. A comparison of these results with those arising from population analysis techniques (nonlocal or integrated formalisms) is reported. 相似文献
92.
Aimée Arias-Carbajal Reádigos Roberto Cao Vázquez José R. del Bosque Arin 《Transition Metal Chemistry》1989,14(1):42-44
Summary The electronic properties of a series of cobalt(III)trans-furyldioximato-complexes of the type [CoB(FH)2X] (B=NH3, X=Cl, Br, I or NO2; B=pyridine (py) or thiocarbamide (thio), X=Cl or Br; B=imidazole (imid), X=Br), [Co(FH2)(FH)Cl2] and [Co(thio)2(FH)2]NO3 were studied by i.r., u.v. and1H and13C n.m.r. spectra The results were compared with those from the corresponding dimethylglyoximato-complexes. It was concluded that -conjugation over the equatorial plane in the furyldioximates is greater than in the dimethylglyoximates. There is some evidence of thetrans-influence of the anionic ligands in the ammines which are in the order NO
2
–
>Br–>Cl–. 相似文献
93.
Izaskun Bustero García Ainara Obieta Isabel Muñoz Roberto Rincón Inés Arteche Amaya 《Mikrochimica acta》2006,152(3-4):239-247
Interest in carbon nanotubes (CNT) has grown at a very rapid rate in the last decade. Their interesting physical and chemical
properties open attractive possibilities in many application areas. These properties depend on the process conditions during
synthesis and on subsequent purification steps. Recent studies have demonstrated that CNT can promote the electron transfer
of biomolecules. These exceptional properties make them attractive for use in electrochemical biosensors.
Multi walled nanotubes have been synthesized by the Chemical Vapor Deposition (CVD) method using methane as a carbon source
and Ni–Al2O3–SiO2 as the catalyst. The influence of the variation of certain reaction parameters such as feed gas composition, catalyst mass,
temperature and reaction time in the yield of the CVD process has been established. In addition, the structural and chemical
characteristics of the CNTs have been studied and a purification process to eliminate the catalyst and amorphous carbon has
been developed that involves a gaseous oxidative process and acid treatment. The efficiency of the purification step has been
determined by analytical techniques.
Atomic force microscopy, Raman scattering, thermogravimetric analysis, inductively coupled plasma atomic spectroscopy are
the characterization techniques employed in this work. 相似文献
94.
The two hexamines (H2N? CH2? CH2? )2N? (CH2)n? N(? CH2? CH2? NH2)2, «penten» (n = 2) and «ptetraen» (n=3) have been investigated as chelating agents for COIII (preparative Study) and some of the divalent metal ions (potentiometric and calorimetric studies). Both amines function as sexadentate ligands for CoIII, CoII and NiII, but one of the terminal aminogroups is much easier detached from the metal in case of M (penten)v+ than in case of M(ptetraen)v+, thus revealing more strain in the fivemembered chelate rings of the girdle plane of the «penten» complexes. On the other hand, the sixmembered chelate ring in M(ptetraen)v+ is more strained than the five-membered ring comprising the tertiary nitrogen atoms of M(penten)v+ CuII and ZnII coordinate with both ligands only 5 of the 6 basic nitrogen atoms present. Both hexaamines function as sexadentates again with MnII, but the metal is coordinated with a molecule of water in addition to the 6 nitrogen atoms in the «penten» complex in contrast to the «ptetraen» complex. The thermodynamic functions for the protonation of the hexamines and for the addition of metal ions in aqueous solution are understood in almost every detail. The dielectric shielding of the charges of the reactants exerted by the solvent has to be taken into account; it is reduced by electrostriction as well as by an increase in temperature. It is shown that the approach of charges of equal sign often is an exothermic process. 相似文献
95.
Maria Antonietta Zoroddu Roberto Dallocchio Maria Antonietta Cabras 《Transition Metal Chemistry》1987,12(4):356-358
Summary Copper(II) complexes with 6-benzylaminopurine (BAPH) of the types Cu(BAPH)2(ClO4)2·2H2O (1) Cu(BAP)2·4H2O (2), and Cu(BAPH2)Cl3·MeOH (3), have been synthesized and characterized by conductivity, magnetic measurements, i.r., electronic and e.s.r. spectroscopy. 相似文献
96.
Mandrioli R Musenga A Ferranti A Lasaponara SS Fanali S Raggi MA 《Journal of separation science》2005,28(9-10):966-972
A micellar electrokinetic chromatographic method was developed and applied for the first time to the separation and quantification of the main components of cloves, namely eugenol and beta-caryophyllene. The analytes were separated in less than ten minutes in an unmodified fused silica capillary (effective length: 40.0 cm) using a background electrolyte composed of 25 mM carbonate buffer (pH 10.0) and 60 mM sodium dodecylsulfate. Analyte concentrations were determined in clove oil and in methanolic clove extracts after simple sequential dilution with methanol and background electrolyte, and the resulting electropherograms showed no interference due to other components. Precision assays gave satisfactory results, with mean standard deviation of peak areas lower than 4.7% (lower than 1.5% for migration times). The eugenol content of a commercial clove oil was about 70% (RSD% = 3.2), while that of beta-caryophyllene was about 15% (RSD% = 4.2); in clove extracts, on the other hand, eugenol was approximately 15% (RSD% = 4.7) and beta-caryophyllene 4% (RSD% = 5.1). Accuracy was also good (mean recovery >98%). 相似文献
97.
98.
Luigi Fabbrizzi Piero Paoletti Markus C. Zobrist Gerold Schwarzenbach 《Helvetica chimica acta》1973,56(2):670-680
The thermodynamic functions of the proton transfer H2tn2++tn → 2 Htn+ (tn = 1,3-diaminopropane) have been determined in aqueous solutions containing different amounts of KCl (0.05 ? μ ? 3.01). The free energy (?ΔG) of the process decreases, whereas the enthalpy (-ΔH) increases with μ. There is reason to believe that the reaction is entirely controlled by the Coulomb forces between the two protonic charges. The electrostatic energy involved can be described in terms of a model incorporating an effective dielectric constant εe, such that δεe/δμ and δ2εe/δμδT are both positive. The polarisation of pure water is produced by orientation of hydrogen-bonded dipole molecules H2O, whereas the electrolyte solution is polarised in addition by dislocation of the ions K+ and Cl?. Our results demonstrate that the former type of polarisation is much more temperature dependent than the latter. 相似文献
99.
Roberto Dovesi 《International journal of quantum chemistry》1986,29(6):1755-1774
The symmetry properties of the mono- and bielectronic terms contributing to the Fock matrix in the ab initio Hartree–Fock treatment of periodic systems are discussed. A computational scheme which takes full advantage of the point symmetry is presented; in this respect, it represents a generalization of the scheme proposed in Int. J. Quantum Chem. 17 , 501 (1980). Computational details and numerical examples are reported; it is shown that with respect to two of the bottlenecks of this kind of calculation, namely, computer time and backing storage required for the bielectronic integrals, it is possible to obtain saving factors as large as h and h2, respectively, where h is the order of the point group. Preliminary tests are reported which indicate that the study of relatively complicated systems, like quartz or corundum (9 and 10 atoms in the unit cell, respectively) at an ab initio Hartree–Fock level is now within reach. 相似文献
100.
Fabio Ponticelli Enrico Marinello Roberto Pagani Lucia Terzuoli 《Journal of heterocyclic chemistry》1991,28(5):1225-1227
The reaction of B6 vitamins 1–3 with cyanate, in the presence of equivalent amounts of hydrochloric acid, yields different adducts according to the structure of the starting material. Regiospecific attack on the amino group or the phenolic hydroxy group was found for 2a,b and 3a,b , respectively. From the aldehydes 1a,b , the 2H-pyrido[3,4-e]-1,3-oxazin-2-ones 7a,b were obtained through an attack on both the phenolic and aldehyde group. 相似文献