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1.
The trisilanol 1,3,5‐(HOi‐Bu2Si)3C6H3 ( 7 ), prepared in three steps from 1,3,5‐tribromobenzene via the intermediates 1,3,5‐(Hi‐Bu2Si)3C6H3 ( 8 ) and 1,3,5‐(Cli‐Bu2Si)3C6H3 ( 9 ) forms an equimolar complex with trans‐bis(4‐pyridyl)ethylene (bpe), 7 ·bpe, whose structure was investigated by X‐ray crystallography. The hydrogen‐bonded network features a number of SiO? H(H)Si and SiO? H hydrogen bridges. Evidence was found for cooperative strengthening within the sequential hydrogen bonds. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and 1H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M2L3], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (Nim, Ocarb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M5L4H−4], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all. 相似文献
3.
Conversion of adsorption properties of activated charcoal (C∗) by metal modification towards selenite, selenate and seleno-dl-methionine (Se-Met) was studied. Several metals were included in modification studies and also a procedure was developed for the separation and independent determination of microgram quantities of these selenium species in aqueous solution. Selenium species were collected one by one from the same sample solution onto collector material by adsorbing them directly or after complex formation onto different metal-loaded activated charcoals (MgC∗ and FeC∗). The mass of selenium in these collectors was measured directly by energy dispersive X-ray fluorescence spectrometry (EDXRF). Detection limits for all three selenium species were better than 6 μg corresponding to concentration of 60 μg/l with 0.100 l of initial sample volume. 相似文献
4.
Jo E Sanna MG Gonzalez-Cabrera PJ Thangada S Tigyi G Osborne DA Hla T Parrill AL Rosen H 《Chemistry & biology》2005,12(6):703-715
The essential role of the sphingosine 1-phosphate (S1P) receptor S1P(1) in regulating lymphocyte trafficking was demonstrated with the S1P(1)-selective nanomolar agonist, SEW2871. Despite its lack of charged headgroup, the tetraaromatic compound SEW2871 binds and activates S1P(1) through a combination of hydrophobic and ion-dipole interactions. Both S1P and SEW2871 activated ERK, Akt, and Rac signaling pathways and induced S1P(1) internalization and recycling, unlike FTY720-phosphate, which induces receptor degradation. Agonism with receptor recycling is sufficient for alteration of lymphocyte trafficking by S1P and SEW2871. S1P(1) modeling and mutagenesis studies revealed that residues binding the S1P headgroup are required for kinase activation by both S1P and SEW2871. Therefore, SEW2871 recapitulates the action of S1P in all the signaling pathways examined and overlaps in interactions with key headgroup binding receptor residues, presumably replacing salt-bridge interactions with ion-dipole interactions. 相似文献
5.
Sanna D Micera G Kallay C Rigo V Sovago I 《Dalton transactions (Cambridge, England : 2003)》2004,(17):2702-2707
Copper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (Nim, N-, Nim)-co-ordinated [CuH-1L]0+ complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L]-(0) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (Nim, N-, N-, Nim) in (7,5,6)-membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pH approximately 9 in all cases. 相似文献
6.
Xiao Yan Wu Sanna JÄÄskelÄinen Wu-Yen Linko 《Applied biochemistry and biotechnology》1996,59(2):145-158
A commercialRhizomucor miehei lipase was purified by ammonium sulfate precipitation. Phenyl Sepharose 6 Fast Row hydrophobic interaction chromatography,
and DEAE Sepharose Fast Flow anion-exchange chromatography. The recovery of lipase activity was 32% with a 42-fold purification.
The molecular size of the purified enzyme was 31,600 Dalton and the pI 3.8. The enzyme was stable for at least 24 h within
a pH range of 7.0-10.0, and 96.8% of the enzyme activity remained when kept at 30‡C for 24 h. Further, about 10–30% of the
lipase activity was inhibited by K+, Li+, Ni+, Co2+, Zn2+, Mg2+, Sn2+, Cu2+, Ba2+, Ca2+, and Fe2+ ions and by SDS, but EDTA had no effect. Under the experimental conditions, the optimum temperature for the hydrolysis of
olive oil was 50‡C (pH 8.0), and for the synthesis of 1-butyl oleate, 37‡C. It was concluded that hydrolytic activity of lipase
alone is not a sufficient criterion for its synthetic potential. The optimal molar ratio of oleic acid and 1-butanol was 2:1
for 1-butyl oleate synthesis. The 1-butyl oleate yield was unaffected by purification of the enzyme after 12 h. 相似文献
7.
The reaction of some primary amines with the methyl 2-[(α-oxobenzyl)-(α-bromo)methyl]phenylacetate ( 5 ) afforded the isoquinolinones 7a-d , which in turn were hydrogenated to 10a-d . The synthesis of these compounds was designed on the basis of a potential depressant and antiinflammatory activity found in other structurally related compounds. 相似文献
8.
Two optimal orthogonalization processes are devised toorthogonalize,possibly approximately,the columns of a very large and possiblysparse matrix A∈Cn×k.Algorithmically the aim is,at each step,to optimallydecrease nonorthogonality of all the columns of A.One process relies on using translated small rank corrections.Another is a polynomial orthogonalization process forperforming the L?wdin orthogonalization.The steps rely on using iterative methods combined,preferably,with preconditioning which can have a dramatic effect on how fast thenonorthogonality decreases.The speed of orthogonalization depends on howbunched the singular values of A are,modulo the number of steps taken.These methods put the steps of the Gram-Schmidt orthogonalizationprocess into perspective regardingtheir(lack of)optimality.The constructions are entirely operatortheoretic and can be extended to infinite dimensional Hilbert spaces. 相似文献
9.
M. Leino J. Uusitalo T. Enqvist K. Eskola A. Jokinen K. Loberg W. H. Trzaska J. Äystö 《Zeitschrift für Physik A Hadrons and Nuclei》1994,348(2):151-152
Two new neutron-deficient isotopes207,208Ac have been produced in fusion reactions with 5.2–5.6 MeV/nucleon40Ar ions on175Lu and identified on the basis of genetic correlations. The fusion evaporation products were separated on-line using a gas-filled magnetic recoil separator. The alpha energy and half-life of208Ac were determined to be (7572±15) keV and (95 ?16 +24 ) ms, respectively. A new alpha line with a half-life of (25 ?5 +9 ) ms and an energy of (7758±20) keV is assigned to the decay of an isomeric state in208Ac. Another new activity with a half-life of (22 ?9 +40 ) ms and an alpha energy of (7712±25) keV is assigned to207Ac. 相似文献
10.
M. Leino J. Uusitalo R. G. Allatt P. Armbruster T. Enqvist K. Eskola S. Hofmann S. Hurskanen A. Jokinen V. Ninov R. D. Page W. H. Trzaska 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):157-164
Neutron-deficient isotopes of radium have been produced in the reactions35Cl+175Lu,40Ar+170,171Yb, and36Ar+170,171Yb and separated in-flight with a gas-filled recoil separator. The activities have been identified on the basis of correlated alpha decay chains. The alpha particle energy Eα and the half-life T1/2 of an isomeric state of the new isotope,203m Ra, have been determined to be (7615±20) keV and (33 ?10 +22 ) ms, respectively. An assignment of another decay with Eα = (7577±20) keV and T1/2=(1.1 ?0.5 +5.0 ) ms to203g Ra is made on the basis of one observed three-decay chain. Tentative evidence for the production of the new isotope202Ra is also given. The values Eα = (7860±60) keV and T1/2=(0.7 ?0.3 +3.3 ) ms were measured. Improved decay data have been obtained for204Ra. The results are Eα = (7484±10) keV and T1/2=(59 ?9 +12 ) ms. Earlier findings concerning the decay of two states in205Ra and an isomer in207Ra have been confirmed. Approximate values for cross sections have been determined for202Ra, produced using the36Ar+170Yb reaction and for203Ra,204Ra, and205Ra using the35Cl+175Lu reaction. The results are 2 nb (202Ra), 4 nb (203Ra), 40 nb (204Ra), and 800 nb (205Ra). 相似文献