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Crystal State (crystal + state)
Selected AbstractsHybrid ,/,3 -peptides with proteinogenic side chains. monosubstituted analogues of the chemotactic tripeptide For-Met-Leu-Phe-OMeJOURNAL OF PEPTIDE SCIENCE, Issue 8 2004Cesare Giordano Abstract The ,/,3 -mixed tripeptides R-CO-,3 -HMet-Leu-Phe-OMe (1a,b), R-CO-Met-,3 -HLeu-Phe-OMe (2a,b) and R-CO-Met-Leu-,3 -HPhe-OMe (3a,b) (a, R = tert -butyloxy-; b, R = H,), analogues of the potent chemoattractant For-Met-Leu-Phe-OMe, have been synthesized by classical solution methods and fully characterized. The activities of the new analogues as chemoattractants, superoxide anion producers and lysozyme releasers have been determined on human neutrophils. Whereas all of the three N -formyl derivatives are significantly less active than the parent tripeptide as chemoattractants, compound 1b has been found to be highly active as a superoxide anion producer and 3b as a lysozyme releaser. The results show that the replacement of the native Leu residue at the central position is, in each of the examined cases, the least favourable modification. The three N -Boc derivatives are, as expected, devoid of activity as agonists, but they are all good inhibitors of chemotaxis. Information on the solution conformation has been obtained by examining the involvement of the NH groups in intramolecular H-bonds using 1H NMR. The conformation of the N -Boc analogue 1a has also been determined in the crystal state by x-ray diffraction analysis. The molecule is extended at the ,3 -HMet residue (,1 = ,87°;,1 = 172°;,1 = 126° ) and no intramolecular H-bond is present. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] Grp94, the endoplasmic reticulum Hsp90, has a similar solution conformation to cytosolic Hsp90 in the absence of nucleotidePROTEIN SCIENCE, Issue 9 2009Kristin A. Krukenberg Abstract The molecular chaperone, Hsp90, is an essential eukaryotic protein that assists in the maturation and activation of client proteins. Hsp90 function depends upon the binding and hydrolysis of ATP, which causes large conformational rearrangements in the chaperone. Hsp90 is highly conserved from bacteria to eukaryotes, and similar nucleotide-dependent conformations have been demonstrated for the bacterial, yeast, and human proteins. There are, however, important species-specific differences in the ability of nucleotide to shift the conformation from one state to another. Although the role of nucleotide in conformation has been well studied for the cytosolic yeast and human proteins, the conformations found in the absence of nucleotide are less well understood. In contrast to cytosolic Hsp90, crystal structures of the endoplasmic reticulum homolog, Grp94, show the same conformation in the presence of both ADP and AMPPNP. This conformation differs from the yeast AMPPNP-bound crystal state, suggesting that Grp94 may have a different conformational cycle. In this study, we use small angle X-ray scattering and rigid body modeling to study the nucleotide free states of cytosolic yeast and human Hsp90s, as well as mouse Grp94. We show that all three proteins adopt an extended, chair-like conformation distinct from the extended conformation observed for the bacterial Hsp90. For Grp94, we also show that nucleotide causes a small shift toward the crystal state, although the extended state persists as the major population. These results provide the first evidence that Grp94 shares a conformational state with other Hsp90 homologs. [source] Rotationally disordered phase of 1,3-dibromo-5-iodo-2,4,6-trimethylbenzene at 293 KACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Soumia Ghanemi In the crystal state at room temperature, the molecule of dibromoiodomesitylene (1,3-dibromo-5-iodo-2,4,6-trimethylbenzene), C9H9Br2I, is prone to strong disorder, apparently involving only the three halogen sites (occupied identically by 66.7% Br and 33.3% I). This disorder, of the rotational type according to previously published NMR measurements, corresponds to fast 2,/3 stochastic in-plane reorientations of the whole molecule between three discernable locations. This kind of rotational disorder can be revealed for the first time by diffractometry thanks to the C2v idealized molecular symmetry of the title compound, although it has been indirectly suspected at room temperature in other trihalogenomesitylenes of similar crystal packing but of D3h molecular symmetry. The average endocyclic angles facing the Br/I sites and the methyl groups are 124.14,(6) and 115.85,(2)°, respectively. The angle between the normal to the aromatic ring and the normal to the (100) plane is 4.1°. TLS analysis indicates that only the aromatic ring and the methyl groups behave as a rigid body with respect to the thermal librations. [source] Total Synthesis, Characterization, and Conformational Analysis of the Naturally Occurring Hexadecapeptide Integramide,A and a DiastereomerCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2010Marta De, Zotti Dr. Abstract Integramide,A is a 16-amino acid peptide inhibitor of the enzyme HIV-1 integrase. We have recently reported that the absolute stereochemistries of the dipeptide sequence near the C terminus are L -Iva14 - D -Iva15. Herein, we describe the syntheses of the natural compound and its D -Iva14 - L -Iva15 diastereomer, and the results of their chromatographic/mass spectrometric analyses. We present the conformational analysis of the two compounds and some of their synthetic intermediates of different main-chain length in the crystal state (by X-ray diffraction) and in solvents of different polarities (using circular dichroism, FTIR absorption, and 2D NMR techniques). These data shed light on the mechanism of inhibition of HIV-1 integrase, which is an important target for anti-HIV therapy. [source] Studies on Properties of p -Nitrophenylazo Calix[4]arene DerivativesCHINESE JOURNAL OF CHEMISTRY, Issue 2 2003Jin Chuan-Ming Abstract The p -nitrophenylazo calix[4]arene derivatives 1a-1d with nonlinear optical (NLO) properties were prepared by the diazo-coupling reaction of calix[4]arene with p -nitrophenyl diazonium. The diazotization reaction of p -nitroaniline was carried out with isoamyl nitrite as a source of nitrous add in EtONa/EtOH under refluxing condition. X-Ray crystallographic analysis and 1H NMR spectra reveal that they exist as cone conformation in crystal state or in solution. HRS measurements at 1064 nm in THF indicate that p -nitro-phenylazo calix[4]arenes have higher hyperpolarizability ,z values than the corresponding reference compound 4-(4-nitrophenylazo)-2, 6-dimethyl-phenol, without red shift of the charge transfer band. The tetrakis p -nitrophenylazo calix[4]arene (2) with longer alkyl chains can form monolayer at the air/water interface. [source] | ||||||||||