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31.
A method for the determination of cadmium microamounts in mixtures with metallic ions withE
1/2 near toE
1/2 of cadmium is discussed. For higher selectivity cadmium was extracted in the form of the pyridin-thiocyanate complexes prior to polarography.
Bestimmung von Cadmium(II) neben anderen Metallionen
Zusammenfassung Es wird eine polarographische Methode zur Bestimmung von Cd(II) neben anderen Metallionen mitE 1/2 naheE 1/2(Cd) diskutiert. Zur Erhöhung der Selektivität und Genauigkeit wird eine Pyridin-Thiocyanat-Extraktion vorgeschalten.相似文献
32.
Anna M. Maj Albert Demonceau Alfred F. Noels 《Journal of organometallic chemistry》2007,692(14):3048-3056
A range of new imidazolium and imidazolinium chlorides bearing biphenyl units on their nitrogen atoms was synthesized. They differed by the electron-withdrawing or -donating nature and the steric bulk of the substituents on their aromatic rings. These various N-heterocyclic carbene (NHC) precursors were combined with the [RuCl2(p-cymene)]2 dimer and potassium tert-butoxide to generate the corresponding ruthenium-arene complexes [RuCl2(p-cymene)(NHC)] in situ. The catalytic activity of these species was investigated in the photoinduced ring-opening metathesis polymerization (ROMP) of cyclooctene. The results obtained confirmed the necessity of blocking the ortho-positions of the phenyl rings in the vicinity of the metal center in order to attain high catalytic efficiencies. They also showed that changing the steric and electronic properties of the substituents on the remote phenyl rings of the biphenyl units had no significant influence on the outcome of the polymerization. 相似文献
33.
Gibasiewicz K Szrajner A Ihalainen JA Germano M Dekker JP van Grondelle R 《The journal of physical chemistry. B》2005,109(44):21180-21186
Almost all photosystem I (PSI) complexes from oxygenic photosynthetic organisms contain chlorophylls that absorb at longer wavelength than that of the primary electron donor P700. We demonstrate here that the low-energy pool of chlorophylls in the PSI-LHCI complex from the green alga Chlamydomonas reinhardtii, containing five to six pigments, is significantly blue-shifted (A(max) at 700 nm at 4 K) compared to that in the PSI core preparations from several species of cyanobacteria and in PSI-LHCI particles from higher plants. This makes them almost isoenergetic with the primary donor. However, they keep the other characteristic features of "red" chlorophylls: clear spectral separation from the bulk chlorophylls, big Stokes shift revealing pronounced electron-phonon coupling, and large homogeneous and inhomogeneous broadening of approximately 170 and approximately 310 cm(-1), respectively. 相似文献
34.
Many abiotic and biotic factors can influence the partitioning equilibrium of heavy metals, thus influencing metal impact on aquatic environments. Unicellular algal species release soluble organic substances able to complex metals. In our laboratory a Cr-tolerant strain was selected and isolated from a wild type strain of Scenedesmus acutus. The exudates released by the two strains counteracted the growth inhibition caused by Cr(VI) and the exudates of the Cr-tolerant strain were more effective. On the contrary, the exudates did not reduce chromium toxicity to the cladoceran Daphnia magna. The reduction of chromium effect on algae seems the consequence of an algae-specific interaction among Cr(VI), exudates and algal cells. Chromium uptake resulted to be energy-dependent since bioaccumulation rate in subdued light condition was lower than at high light intensity. The effect of Cr(VI) on algae changed depending on metabolism of the cells and in particular it seemed to be related to the bioaccumulation rate. Tolerance in the selected strain could not be ascribed to a lower uptake of chromium. The difference in sensitivity to chromium between the two strains was exploited to evaluate if tolerance acquired by algae could have consequences for Daphnia. After treatment with Cr(VI), the two strains of S. acutus were used as food source for D. magna. The results indicate that chromium is accumulated by algae in a form not available for daphnids and that Cr tolerance acquired by the algae can be of some advantage to the consumer organism. 相似文献
35.
Gallium metal is effective in mediating the allylation of various carbonyl compounds and imines under solvent-free conditions, with the application of sonic energy, affording the corresponding homoallylic alcohols and amines. The imines themselves were also prepared under solventless conditions in high yield, thereby establishing a two-step solvent-free synthesis of homoallylic amines. In comparison, indium metal produced a mixture of the desired homoallylic secondary amine and the bis-allylated species via an iminium ion intermediate. 相似文献
36.
Giampiero Bartocci Anna Spalletti Ugo Mazzucato 《Research on Chemical Intermediates》1995,21(7):735-747
A fluorimetric and photochemical study of cis-9-styrylanthracene as a function of temperature has been carried out in different solvents with the aim of answering some open questions about the behavior of its first excited singlet state, S1. In non-polar solvents, a parallel photoreactive pathway, leading to a cyclization adduct, was found to compete with fluorescence and isomerization already at 200 K, its contribution increasing markedly with temperature. The cis » trans photoisomerization occurs prevalently by a triplet mechanism, a detectable contribution of diabatic and adiabatic isomerization in S1 being operative in these solvents from room temperature upwards. In polar solvents, the main deactivation pathway competitive with fluorescence is isomerization to trans, which occurs prevalently through a mixed singlet mechanism with a major diabatic and a minor adiabatic components. 相似文献
37.
38.
Aviñó A Cubero E González C Eritja R Orozco M 《Journal of the American Chemical Society》2003,125(51):16127-16138
The structural, dynamical, and recognition properties of antiparallel DNA triplexes formed by the antiparallel d(G#G.C), d(A#A.T), and d(T#A.T) motifs (the pound sign and dot mean reverse-Hoogsteen and Watson-Crick hydrogen bonds, respectively) are studied by means of "state of the art" molecular dynamics simulations. Once the characteristics of the helix are defined, molecular dynamics and thermodynamic integration calculations are used to determine the expected stabilization of the antiparallel triplex caused by the introduction of 8-aminopurines. Finally, oligonucleotides containing 8-aminopurine derivatives are synthesized and tested experimentally using several approaches in a variety of systems. A very large stabilization of the triplex is found experimentally, as predicted by simulations. These results open the possibility for the use of oligonucleotides carrying 8-aminopurines to bind single-stranded nucleic acids by formation of antiparallel triplexes. 相似文献
39.
Bertosa B Kojić-Prodić B Wade RC Ramek M Piperaki S Tsantili-Kakoulidou A Tomić S 《Journal of chemical information and computer sciences》2003,43(5):1532-1541
The activity of a biological compound is dependent both on specific binding to a target receptor and its ADME (Absorption, Distribution, Metabolism, Excretion) properties. A challenge to predict biological activity is to consider both contributions simultaneously in deriving quantitative models. We present a novel approach to derive QSAR models combining similarity analysis of molecular interaction fields (MIFs) with prediction of logP and/or logD. This new classification method is applied to a set of about 100 compounds related to the auxin plant hormone. The classification based on similarity of their interaction fields is more successful for the indole than the phenoxy compounds. The classification of the phenoxy compounds is however improved by taking into account the influence of the logP and/or the logD values on biological activity. With the new combined method, the majority (8 out of 10) of the previously misclassified derivatives of phenoxy acetic acid are classified in accord with their bioassays. The recently determined crystal structure of the auxin-binding protein 1 (ABP1) enabled validation of our approach. The results of docking a few auxin related compounds with different biological activity to ABP1 correlate well with the classification based on similarity of MIFs only. Biological activity is, however, better predicted by a combined similarity of MIFs + logP/logD approach. 相似文献
40.
Johansson A Håkansson M Jagner S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(18):5311-5318
Stereochemically labile copper and zinc complexes with the N,N'-dimethylethylenediamine ligand (dmeda) have been shown to be promising precursors for the total spontaneous resolution of chiral covalent networks. (N,N')-[Cu(NO3)2(dmeda)]infinity crystallises as a conglomerate and yields either enantiopure (R,R)-1 or enantiopure (S,S)-1. A mixed-valence copper(I/II) complex, [{Cu(II)Br2(dmeda)}3(Cu(I)Br)2]infinity (2), which crystallises as a pair of interpenetrating chiral (10,3)-a nets, is formed from CuBr, CuBr2 and dmeda. One net contains ligands with solely (R,R) configuration and exhibits helices with (P) configuration while the other has solely (S,S)-dmeda ligands and gives rise to a net in which the helices have (M) configuration. The whole crystalline arrangement is racemic, because the interpenetrating chiral nets are of opposite handedness. With zinc chloride (R,S)-[ZnCl(dmeda)2]2[ZnCl4] (3) is obtained, which is a network structure, although not chiral. Total spontaneous resolution of stereochemically labile metal complexes formed from achiral or racemic building blocks is suggested as a viable route for the preparation of covalent chiral networks. Once the absolute structure of the compound has been determined by X-ray crystallography, a quantitative determination of the enantiomeric excess of the bulk product can be undertaken by means of solid-state CD spectroscopy. 相似文献