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Crystal X-ray Structures (crystal + x-ray_structure)
Selected AbstractsAzotobacter vinelandii Metal Storage Protein: "Classical" Inorganic Chemistry Involved in Mo/W Uptake and Release ProcessesCHEMBIOCHEM, Issue 4 2008Jörg Schemberg Dr. Abstract The release of Mo (as molybdate) from the Mo storage protein (MoSto), which is unique among all existing metalloproteins, is strongly influenced by temperature and pH value; other factors (incubation time, protein concentration, degree of purity) have minor, though significant effects. A detailed pH titration at 12,°C revealed that three different steps can be distinguished for the Mo-release process. A proportion of ,15,% at pH 6.8,7.0, an additional 25,% at pH 7.2,7.5 and ca. 50,% (up to 90,% in total) at pH 7.6,7.8. This triphasic process supports the assumption of the presence of different types of molybdenum-oxide-based clusters that exhibit different pH lability. The complete release of Mo was achieved by increasing the temperature to 30,°C and the pH value to >7.5. The Mo-release process does not require ATP; on the contrary, ATP prevents, or at least reduces the degree of metal release, depending on the concentration of the nucleotide. From this point of view, the intracellular ATP concentration is suggested to play,in addition to the pH value,an indirect but crucial role in controlling the extent of Mo release in the cell. The binding of molybdenum to the apoprotein (reconstitution process) was confirmed to be directly dependent on the presence of a nucleotide (preferably ATP) and MgCl2. Maximal reincorporation of Mo required 1 mM ATP, which could partly be replaced by GTP. When the storage protein was purified in the presence of ATP and MgCl2 (1 mM each), the final preparation contained 80 Mo atoms per protein molecule. Maximal metal loading (110,115 atoms/MoSto molecule) was only achieved, if Mo was first completely released from the native protein and subsequently (re-) bound under optimal reconstitution conditions: 1 h incubation at pH 6.5 and 12,°C in the presence of ATP, MgCl2 and excess molybdate. A corresponding tungsten-containing storage protein ("WSto") could not only be synthesized in vivo by growing cells, but could also be constructed in vitro by a metalate,ion exchange procedure by using the isolated MoSto protein. The high W content of the isolated cell-made WSto (,110 atoms/protein molecule) and the relatively low amount of tungstate that was released from the protein under optimal "release conditions", demonstrates that the W-oxide-based clusters are more stable inside the protein cavity than the Mo-oxide analogues, as expected from the corresponding findings in polyoxometalate chemistry. The optimized isolation of the W-loaded protein form allowed us to get single crystals, and to determine the crystal X-ray structure. This proved that the protein contains remarkably different types of polyoxotungstates, the formation of which is templated in an unprecedented process by the different protein pockets. (Angew. Chem. Int. Ed.2007, 46, 2408,2413). [source] Synthesis and Characterization of CuII Complexes with Amino Acid Substituted Di(2-pyridyl)amine LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2007ko I. Kirin Abstract The two-step syntheses of the substituted di(2-pyridyl)amine ligands (dpa), dpa-CH2CO2H (1) and dpa-PhCO2H (2), are described. Ligands 1 and 2 are successfully coupled to the amino acid phenylalanine, yielding the derivatives 4 and 6, respectively. Four CuII(dpa)2 complexes, [Cu(dpa-CH2CO2tBu)2(NO3)2] (3Cu), [Cu(dpa-CH2CO-PheOMe)2(H2O)2](NO3)2·2MeOH (4Cu), [Cu(dpa-PhCO2Me)2 (MeOH)2](ClO4)2 (5Cu) and [Cu(dpa-PhCO-PheOMe)2(ClO4)2] (6Cu) have been prepared and characterized, including their single crystal X-ray structures. Fluorescence emission at UV (for 3 and 4) or blue (for 5 and 6) wavelengths of the free ligands is preserved in the corresponding Cu complexes, although with lower intensity. X-band EPR spectra of 4Cu and 6Cu both revealed one axial CuII signal with hyperfine and superhyperfine splittings. Complexes 4Cu and 6Cu are chiral inorganic complexes with amino acid bioconjugates that may serve as nucleoside analogs in modified peptide nucleic acids (PNA). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Self-Organization of Dipolar 4,4,-Disubstituted 2,2,-Bipyridine Metal Complexes into Luminescent Lamellar Liquid CrystalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2003Daniela Pucci Abstract Mononuclear cis -dichloro complexes, [LnMCl2], with different metal centres (PtII, NiII, and ZnII) and a series of palladium and platinum derivatives, [L2MX2], in which chloride groups are replaced with iodide, bromide, and azide ligands, have been synthesized from 4,4,-disubstituted-2,2,-bipyridines. Upon complexation of these non-mesogenic ligands, the peculiar structural arrangement, characterized by intermolecular associations of the new derivatives, induces mesomorphism in most [L2MX2] complexes, confirming the importance of coordination chemistry in metal-mediated formation of liquid crystals. Single crystal X-ray structures have been determined for dihexadecyl 2,2,-bipyridyl-4,4,-dicarboxylatopalladium and -zinc dichloride derivatives. Both the metal centres and the ancillary ligands have been varied to use dipole coupling as a tool to control molecular architecture: thermal, as well as spectroscopic properties, depend strongly upon molecular dipolar interactions. Tunable red and blue emitters based on PdII and PtII, both in solution and in the solid state, have been obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Comparison of 17,-estradiol structures from x-ray diffraction and solution NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2005Fernando Commodari Abstract The NMR-derived structure of estrogen (17,-estradiol, E2), the drug of choice for postmenopausal women, was compared with a recent literature crystal x-ray structure of Fab-bound E2. 1H and 13C NMR spectra of E2 were acquired in DMSO- d6. Assignments were obtained from an analysis of DQF-COSY, TOCSY, HETCOR, HMQC and HMBC 2D NMR spectra. The 1H and 13C NMR assignments are the first reported for E2 in DMSO- d6. Two solution structures, S1 and S2, were obtained with molecular modeling using NOE constraints. S1 overlaps with the crystal structure for all rings. S2 shows prominent differences in the C-ring (C9C11C12C13) segment, which deviates from a chair conformation, and excellent overlap in the A-, B- and D-rings of E2. The C-ring in S2 adopts a boat conformation as opposed to a chair conformation in the x-ray and S1 structures. The S2 structure is about 6° more twisted than the bound x-ray and S1 models. The S1, S2 and x-ray structures had ring bowing values of 10.1 ± 0.3, 11 ± 1 and 10.37°, respectively. Of the 100 solution conformers generated, 83 had S1 conformation and 17 had S2 conformation, with average internal energies of 112 ± 2 and 141 ± 2 kcal mol,1, respectively. The 100 S1 - and S2 - derived conformers showed a r.m.s.d. of 0.72 Å for all atoms. The x-ray, S1 and S2 C18O17 distances were 2.93, 2.92 ± 0.01 and 2.93 ± 0.01 Å, respectively, and the O3O17 distances were 11.06, 11.18 ± 0.12, and 10.89 ± 0.05 Å, respectively. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||