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991.
Johnston CA Willard FS Ramer JK Blaesius R Roques CN Siderovski DP 《Combinatorial chemistry & high throughput screening》2008,11(5):370-381
Heterotrimeric G-proteins, comprising Galpha, Gbeta, and Ggamma subunits, are molecular switches that regulate numerous signaling pathways involved in cellular physiology. This characteristic is achieved by the adoption of two principal states: an inactive state in which GDP-bound Galpha is complexed with the Gbetagamma dimer, and an active state in which GTP-bound Galpha is freed of its Gbetagamma binding partner. Structural studies have illustrated the basis for the distinct conformations of these states which are regulated by alterations in three precise 'switch regions' of the Galpha subunit. Discrete differences in conformation between GDP- and GTP-bound Galpha underlie its nucleotide-dependent protein-protein interactions (e.g., with Gbetagamma/receptor and effectors, respectively) that are critical for maintaining their proper nucleotide cycling and signaling properties. Recently, several screening approaches have been used to identify peptide sequences capable of interacting with Galpha (and free Gbetagamma) in nucleotide-dependent fashions. These peptides have demonstrated applications in direct modulation of the nucleotide cycle, assessing the structural basis for aspects of Galpha and Gbetagamma signaling, and serving as biosensor tools in assays for Galpha activation including high throughput drug screening. In this review, we highlight some of the methods used for such discoveries and discuss the insights that can be gleaned from application of these identified peptides. 相似文献
992.
A series of "push-pull" salts substituted with an electron-donating bis(N,N-dimethyl)aniline unit and different electron-withdrawing methyl or chelating pyridinium units have been designed and synthesized from Michler's ketone. The spectroscopic and electronic properties were investigated and compared to their DAST homologues. The studies revealed that a lower HOMO-LUMO gap is obtained in all cases, showing the ability of our donor to increase the "push-pull" effect. Two chromophores with a terpyridine as acceptor end group have also been prepared. 相似文献
993.
Dominique R. Duguay Matthew T. Zamora Johanna M. Blacquiere Francis E. Appoh Christopher M. Vogels Susan L. Wheaton Felix J. Baerlocher Andreas Decken Stephen A. Westcott 《Central European Journal of Chemistry》2008,6(4):562-568
The addition of formylphenylboronic acid derivatives to thiourea and ethyl acetoacetate proceeds in the presence of an additional
Lewis acid catalyst to give the corresponding 3,4-dihydropyrimidin-2(1H)-(thio)ones (Biginelli products) in moderate yield.
Compounds were tested for antifungal activity against pure cultures of Aspergillus niger, Aspergillus flavus, Candida albicans and Saccharomyces cerevisiae but, unfortunately, none showed any appreciable activity.
相似文献
994.
Pichon C Dolbecq A Mialane P Marrot J Rivière E Goral M Zynek M McCormac T Borshch SA Zueva E Sécheresse F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(10):3189-3199
While the reaction of [PW(11)O(39)](7-) with first row transition-metal ions M(n+) under usual bench conditions only leads to monosubstituted {PW(11)O(39)M(H(2)O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe(II)(bpy)(3)][PW(11)O(39)Fe(2) (III)(OH)(bpy)(2)]12 H(2)O (bpy=bipyridine) complex (1) contains the dinuclear {Fe(micro-O(W))(micro-OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe(III) centers in complex 1 are weakly antiferromagnetically coupled (J=-11.2 cm(-1), H=-JS(1)S(2)) compared to other {Fe(micro-O)(micro-OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy](2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]14 H(2)O (2) (dmbpy=5,5'-dimethyl-2,2'-bipyridine) and H(2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]10 H(2)O (3) represent the first butterfly-like POM complexes. In these species, a tetranuclear Fe(III) complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe(III) cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the chi(M)T=f(T) curve leads to J(wb)=-59.6 cm(-1) and J(bb)=-10.2 cm(-1) (H=-J(wb)(S(1)S(2)+S(1)S(2*)+S(1*)S(2)+S(1*)S(2*))-J(bb)(S(2)S(2*))). While the J(bb) value is within the range of related exchange parameters previously reported for non-POM butterfly systems, the J(wb) constant is significantly lower. As for complex 1, this can be justified considering Fe(w)--O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH(3))(4)](10)[(PW(11)O(39)Fe(III))(2)O]12 H(2)O (4) has been isolated. In this complex, the two single oxo-bridged Fe(III) centers are very strongly antiferromagnetically coupled (J=-211.7 cm(-1), H=-JS(1)S(2)). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2, which is insoluble in common solvents, have been studied in the solid state. 相似文献
995.
996.
Murielle Rivenet Pascal Roussel Francis Abraham 《Journal of solid state chemistry》2008,181(10):2586-2590
Single crystals of Bi(C2O4)OH were obtained by the slow diffusion of Bi3+ cations through silica gel impregnated with oxalic acid. The structure was solved in the Pnma space group with a=6.0853(2) Å, b=11.4479(3) Å, c=5.9722(2) Å, leading to R=0.0188 and wR=0.0190 from 513 unique reflections. The bismuth coordination polyhedron is a BiO6E pentagonal bipyramid with the lone pair E sitting at an axial vertex. The opposite axial vertex is occupied by a hydroxyl oxygen atom, which is also an equatorial corner of a neighboring BiO6E bipyramid. The sharing of the hydroxyl oxygen atoms build zig-zag chains running down the [100] direction. These chains are aligned in a sheet parallel to the (010) plane and are further connected through oxalate ions to form a three-dimensional arrangement. On heating, Bi(C2O4)OH decomposes to the meta-stable quadratic β-Bi2O3 phase. 相似文献
997.
Exposure of a mixture of propargyl vinyl ketone and a nucleophilic primary or secondary amine to activated dry silica gel in the absence of solvent leads to a cascade of reactions that results in the formation of an aminocyclopentenone. The reaction with triethylamine leads to a cross-conjugated cyclopentadienone. 相似文献
998.
The collision-induced dissociation of lasalocid and monensin A bound to alkali metal cations has been investigated using electrospray MS/MS. The binding affinity for the metal cations, as measured with collision-induced dissociation, was found to depend on their ionic radius, decreasing with increasing radius. Monensin A was observed to have a greater binding affinity for alkali metal cations than lasalocid acid. 相似文献
999.
[reaction: see text] In an effort to develop new ways of synthesizing polycyclic alkaloids, we successfully added silyl enol ethers, allylsilanes, and enamines to iminium ions generated from amides. Because of their higher oxidation state, such iminiums show a yet unexploited advantage of potential double cyclizations over standard Mannich monocyclizations. We report herein the first example of tethered nonaromatic carbon nucleophiles adding to activated amides for the generation of enaminals of various ring sizes, with endo- or exo-cyclic nitrogen. 相似文献
1000.
Gibson AM Brookes MJ Kim SS Francis ST Morris PG 《Solid state nuclear magnetic resonance》2005,28(2-4):258-265
It is generally accepted that the temporal resolution of blood oxygenation level dependent functional MRI is limited due to the inherent latency and longevity of the haemodynamic response. However, in this study we introduce a technique for measurement of timing differences from within the same brain region in two (or more) separate tasks that allows accurate determination of cortical timing differences 200 ms. Our technique, based on a novel use of linear regression analysis, is shown to yield accurate results both in simulated and experimental data. We show that cortical timing differences measured using fMRI are consistent with published electrophysiological results. Measurement of timing differences using this technique could prove a useful strategy for identifying neural network components in a wide range of cognitive paradigms. 相似文献