Home About us Contact
|
Home About us Contact | ||
|
|
||
NH Groups (nh + groups)
Selected AbstractsThe First Stable Monomeric Triaminostannane of Composition [(Me3Si)3CSn(NHtBu)3] Containing Three Substituted NH GroupsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2003Jörg Janssen Abstract Triaminostannanes of secondary amines have been known since 1977 and are widely used in tin organic chemistry. However, the corresponding nitrogen substituted stannanes of primary amines are not cited in the literature. Herein we report on the ammonolysis reaction of [(Me3Si)3CSnCl3] with tBuNH2 in the presence of a strong base and the X-ray structural analysis of [(Me3Si)3CSn(NHtBu)3], the first monomeric triaminostannane containing protons at the nitrogen atoms. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Cobalt(III) Complexes of a Tripodal Ligand Containing Three Imidazole Groups: Properties and Structures of Racemic and Optically Active SpeciesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008Hirofumi Nakamura Abstract The complex [Co(H3L)](ClO4)3·H2O (1), where H3L {tris[2-(4-imidazoylmethylideneamino)ethyl]amine} is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 molar ratio, was synthesized and optically resolved by fractional crystallization of the diastereomeric salt with [Sb2{(R,R)-tart}2]2, [(R,R)-tart = (2R,3R)-tartrate(4,) ion]. From the less soluble part, ,-[Co(H2L)][Sb2{(R,R)-tart}2]·4H2O (2) was isolated. Starting from 2, two optically active complexes, ,-[Co(H3L)](ClO4)3·1.5H2O (,- 1) and ,-[Co(L)] (,- 3), were obtained. The crystal structures of these complexes are compared with those of the racemic structures. ,- 1 shows an unusually strong circular dichroism (, = 488 nm, ,, = ,7.74 M,1,cm,1) in the first d,d absorption band region. The effects of deprotonation,reprotonation of the uncoordinated imidazole NH groups of ,-[Co(H3L)]3+ on the UV/Vis and CD spectra and on the cyclic voltammograms were studied in methanol. Although the deprotonation,reprotonation reactions are reversible, the redox couple for the completely deprotonated species [CoIII/II(L)]0/, is not observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Zinc Hydrazide and Zinc Alkoxide Hydrazide Cages with Zn4N8 and Zn4N6O Cores , Cluster Isomerism as a Result of Subtle Changes in Ligand SizeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2006Surajit Jana Abstract The hydrazide cluster [(iPrZn)4(NHNMe2)4] (1) was synthesised by the reaction of diisopropylzinc with N,N -dimethylhydrazine and was characterised by 1H- and 13C NMR and IR spectroscopy, mass spectrometry, elemental analysis and X-ray crystallography. This compound forms asymmetric aggregates containing Zn4N8 cores. The Zn atoms in these aggregates are arranged in topological tetrahedra in which the triangular faces are bridged by NHNMe2 substituents. Each NH group is connected to two Zn atoms and each NMe2 group to one Zn atom. Alkoxide clusters were prepared in one-pot syntheses by treating diisopropylzinc solutions with mixtures of N,N -dimethylhydrazine and ROH (R = Et, iPr). The resulting compounds have the formula [(iPrZn)4(NHNMe2)3(OR)] [R = Et (3), iPr(4)] and contain Zn4N6O cages, such that one NHNMe2 in 1 is replaced by one alkoxide group. Two different aggregation modes were found for these Zn4N6O cages. In compound 3, one Zn atom is bound to two NMe2 groups and one NH group. The other three Zn atoms each have three bonds to NH groups and one dative bond to an NMe2 group. The cage consists of one four-membered and one six-membered ring as well as four five-membered rings. In compound 4, the fourth zinc atom is exclusively bonded to three anionic NH functions in such a way that the rings in the cage are all five-membered. Compounds 3 and 4 were characterised by NMR spectroscopy and single-crystal X-ray diffraction. Hydrazide hydroxide clusters were also obtained through the reaction of a diisopropylzinc solution with N,N -dimethylhydrazine and a small amount of water. The structure of the resulting cocrystalline material, [(iPrZn)4(NHNMe2)4]·[(iPrZn)4(NHNMe2)3(OH)] (2), was also confirmed by X-ray diffraction. The hydroxide cluster in 2 contains a Zn4N6O cage, with a similar aggregation mode to that of 4. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis and Structure of Macrolactams of 3,-Aminodeoxycholanic AcidEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2006Martin Feigel Abstract The macrolactams cyclo(3,-aminodeoxycholic amide)2 (1) and cyclo(3,-aminodeoxycholic amide)3 (2) were prepared in high yields (1: 32,%; 2: 41,%) from the pentafluorophenyl esters of the linear precursors. The solid-state structures of both macrocycles were determined by X-ray diffraction. Compound 1 forms a cleft of C2 symmetry which holds two methanol and two water molecules fixed by hydrogen bonds. The crystals of compound 2 contain two slightly different macrolactam rings of 7,8 Å diameter. The polar ,-surface of the deoxycholanic parts and the amide NH groups are oriented into the center of the rings. The cavity formed by the ring system and the void volume between the macrocycles is filled by disordered solvent molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Hybrid ,/,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] Striking changes in molecular recognition by deuteration of aqueous binary solventsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2005Tadashi Endo Abstract Oxidation of a pair of associating thiols 1 and 2 with oxygen, each with a binding site [,C(O)NHC(O)NH,] and a recognition site (R1 or R2), is examined at various temperatures in aqueous binary solvents of water or deuterium oxide with ethanol, acetonitrile or methanol. The selectivity (r),a measure of the degree of molecular recognition in the oxidation,represented by the logarithmic ratio of the yield of the unsymmetrical disulfide (4) to twice that of the symmetrical disulfide (3) was examined as a function of the mole fractions of water (xw) and deuterium oxide (xdo). It is found that, on deuteration of aqueous binary solvents containing ethanol (xw=,0.50 and 0.75), the temperature dependence of molecular recognition (r) alters strikingly from a clear bell-shaped type (a maximum at 35°C) to a plateau-like type in the range 20,70°C. It is clarified further that, in aqueous acetonitrile at xw=,0.20 and 0.75, deuteration of water causes the temperature dependence of r to become fairly dull. In contrast, it is found that the deuteration effect in water,methanol is much less than that in water,ethanol or in water,acetonitrile. Furthermore, conversion of the NH groups in 1 and 2 to the ND groups occurs very quickly. A possible cause of the large deuterium effect is discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Poly[bis(,-benzene-1,4-dicarboxylato)bis[,-6-(4-pyridyl)-5H -imidazolo[4,5- f][1,10]phenanthroline]dilead(II)]: an interpenetrating ,-Po netACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Zhan-Lin Xu The asymmetric unit of the title compound, [Pb2(C8H4O4)2(C18H11N5)2]n, contains two PbII atoms, two benzene-1,4-dicarboxylate (1,4-bdc) dianions and two 6-(4-pyridyl)-5H -imidazolo[4,5- f][1,10]phenanthroline (L) ligands. Each PbII atom is eight-coordinated by three N atoms from two different L ligands and five carboxylate O atoms from three different 1,4-bdc dianions. The two 1,4-bdc dianions (1,4-bdc1 and 1,4-bdc2) show different coordination modes. Each 1,4-bdc1 coordinates to two PbII atoms in a chelating bis-bidentate mode. Each carboxylate group of the 1,4-bdc2 anion connects two PbII atoms in a chelating,bridging tridentate mode to form a dinuclear unit. Neighbouring dinuclear units are connected together by the aromatic backbone of the 1,4-bdc dianions and the L ligands into a three-dimensional six-connected ,-polonium framework. The most striking feature is that two identical three-dimensional single ,-polonium nets are interlocked with each other, thus leading directly to the formation of a twofold interpenetrated three-dimensional ,-polonium architecture. The framework is held together in part by strong N,H...O hydrogen bonds between the imidazole NH groups of the L ligands and the carboxylate O atoms of 1,4-bdc dianions within different ,-polonium nets. [source] Bis[bis(methoxycarbimido)aminato]copper(II) 1-methylpyrrolidin-2-one disolvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009Ann M. Chippindale The title compound, [Cu(C4H8N3O2)2]·2C5H9NO, consists of a neutral copper complex, in which the CuII centre coordinates to two bis(methoxycarbimido)aminate ligands, solvated by two molecules of 1-methylpyrrolidin-2-one. The complex is planar and centrosymmetric, with the CuII centre occupying a crystallographic inversion centre and adopting approximately square-planar geometry. N,H...O hydrogen-bonding interactions exist between the amine NH groups of the ligands and the O atoms of the 1-methylpyrrolidin-2-one molecules. The associated units pack to form sheets. [source] Nickel and zinc complexes with a monodentate heterocycle and tridentate Schiff base ligands: self-assembly to one- and two-dimensional supramolecular networks via hydrogen bondingACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Xiao-Hua Chen In the complex (morpholine)[2-hydroxy- N,-(5-nitro-2-oxidobenzylidene)benzohydrazidato]nickel(II), [Ni(C14H9N3O5)(C4H9NO)], (I), the NiII center is in a square-planar N2O2 coordination geometry. The complex bis[,-2-hydroxy- N,-(2-oxidobenzylidene)benzohydrazidato]bis[(morpholine)zinc(II)], [Zn2(C14H10N2O3)2(C4H9NO)2], (II), consists of a neutral centrosymmetric dimer with a coplanar Zn2(,2 -O)2 core. The two ZnII centers are bridged by phenolate O atoms. Each ZnII center exhibits a distorted square-pyramidal stereochemistry, in which the four in-plane donors come from the O,N,O,-tridentate 2-hydroxy- N,-(2-oxidobenzylidene)benzohydrazidate(2,) ligand and a symmetry-related phenolate O atom, and the axial position is coordinated to the N atom from the morpholine molecule. There are intramolecular phenol,hydrazide O,H...N hydrogen bonds present in both (I) and (II). In (I), square-planar nickel complexes are linked by intermolecular morpholine,morpholine N,H...O hydrogen bonds, leading to a one-dimensional chain, while in (II) an infinite two-dimensional network is formed via intermolecular hydrogen bonds between the coordinated morpholine NH groups and the uncoordinated phenolate O atoms. [source] Two-dimensional hydrogen-bonded networks in two novel glycoluril derivativesACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2008Li-Ping Cao Two new glycoluril derivatives, namely diethyl 6-ethyl-1,4-dioxo-1,2,2a,3,4,6,7,7b-octahydro-5H -2,3,4a,6,7a-pentaazacyclopenta[cd]indene-2a,7b-dicarboxylate, C14H21N5O6, (I), and 6-ethyl-2a,7b-diphenyl-1,2,2a,3,4,6,7,7b-octahydro-5H -2,3,4a,6,7a-pentaazacyclopenta[cd]indene-1,4-dione, C20H21N5O2, (II), both bearing two free syn -urea NH groups and two ureidyl C=O groups, assemble the same one-dimensional chains in the solid state running parallel to the [010] direction via N,H...O hydrogen bonds. Furthermore, the chains of (I) are linked together into two-dimensional networks via C,H...O hydrogen bonds. [source] Tetraaquabis(2-methoxybenzaldehyde isonicotinoylhydrazone)cadmium(II) dinitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2007Zhongwu Fu The CdII centre in the title complex, [Cd(C14H13N3O2)2(H2O)4](NO3)2, occupies a crystallographic inversion centre and is coordinated by two donor N atoms from two 2-methoxybenzldehyde isonicotinoylhydrazone ligands and by four O atoms from four coordinated water molecules, giving a slightly distorted octahedral geometry. There is an extended three-dimensional network structure resulting from O,H...O hydrogen bonds between coordinated water and nitrate anions, and between coordinated water and carbonyl O atoms, and from N,H...O hydrogen bonds between NH groups and nitrate O atoms. [source] Solvent-dependent conformation of amylose tris(phenylcarbamate) as deduced from scattering and viscosity dataBIOPOLYMERS, Issue 9 2009Taichi Fujii Abstract The z -average mean-square radius of gyration ,S2,z, the particle scattering function P(k), the second virial coefficient, and the intrinsic viscosity [,] have been determined for amylose tris(phenylcarbamate) (ATPC) in methyl acetate (MEA) at 25°C, in ethyl acetate (EA) at 33°C, and in 4-methyl-2-pentanone (MIBK) at 25°C by light and small-angle X-ray scattering and viscometry as functions of the weight-average molecular weight in a range from 2 × 104 to 3 × 106. The first two solvents attain the theta state, whereas the last one is a good solvent for the amylose derivative. Analysis of the ,S2,z, P(k), and [,] data based on the wormlike chain yields h (the contour length or helix pitch per repeating unit) = 0.37 ± 0.02 and ,,1 (the Kuhn segment length) = 15 ± 2 nm in MEA, h = 0.39 ± 0.02 and ,,1 = 17 ± 2 nm in EA, and h = 0.42 ± 0.02 nm and ,,1 = 24 ± 2 nm in MIBK. These h values, comparable with the helix pitches (0.37,0.40 nm) per residue of amylose triesters in the crystalline state, are somewhat larger than the previously determined h of 0.33 ± 0.02 nm for ATPC in 1,4-dioxane and 2-ethoxyethanol, in which intramolecular hydrogen bonds are formed between the CO and NH groups of the neighbor repeating units. The slightly extended helices of ATPC in the ketone and ester solvents are most likely due to the replacement of those hydrogen bonds by intermolecular hydrogen bonds between the NH groups of the polymer and the carbonyl groups of the solvent. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 729,736, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Changes in protein conformation and dynamics upon complex formation of brain-derived neurotrophic factor and its receptor: Investigation by isotope-edited Fourier transform IR spectroscopyBIOPOLYMERS, Issue 1 2002Tiansheng Li Abstract The interactions of brain-derived neurotrophic factor (BDNF) with the extracellular domain of its receptor (trkB) are investigated by employing isotope-edited Fourier transform IR (FTIR) spectroscopy. The protein secondary structures of individual BDNF and trkB in solutions are compared with those in their complex. The temperature dependence of the secondary structures of BDNF, trkB, and their complex is also investigated. Consistent with the crystal structure, we observe by FTIR spectroscopy that BDNF in solution contains predominantly , strands (,53%) and relatively low contents of other secondary structures including , turns (,16%), disordered structures (,12%), and loops (,18%) and is deficient in , helix. We also observe that trkB in solution contains mostly , strands (52%) and little , helix. Conformational changes in both BDNF and trkB are observed upon complex formation. Specifically, upon binding of BDNF, the conformational changes in trkB appear to involve mostly , turns and disordered structures while the majority of the ,-strand conformation remains unchanged. The IR data indicate that some of the disordered structures in the loop regions are likely converted to , strands upon complex formation. The FTIR spectral data of BDNF, trkB, and their complex indicate that more amide NH groups of trkB undergo H,D exchange within the complex than those of the ligand-free receptor and that the thermal stability of trkB is decreased slightly upon binding of BDNF. The FT-Raman spectra of BDNF, trkB, and their complex show that the six intramolecular disulfide bonds of trkB undergo significant conformational changes upon binding of BDNF as a result of changes in the tertiary structure of trkB. Taken together, the FTIR and Raman data are consistent with the loosening of the tertiary structure of trkB upon binding of BDNF, which leads to more solvent exposure of the amide NH group and decreased thermal stability of trkB. This finding reveals an intriguing structural property of the neurotrophin ligand,receptor complex that is in contrast to other ligand,receptor complexes such as a cytokine,receptor complex that usually shows protection of the amide NH group and increased thermal stability upon complex formation. © 2002 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 67: 10,19, 2002; DOI 10.1002/bip.10038 [source] Effect of PbII on the Secondary Structure and Biological Activity of TrypsinCHEMBIOCHEM, Issue 7 2005Lin Yang Prof. Abstract The effects of PbIIon the secondary structure and biological activity of trypsin have been examined by monitoring changes in its conductivity and IR and circular dichroism (CD) spectra. The results show that PbIIreacts with trypsin, and that the binding sites might be OH and NH groups in pepsin. The CD spectra indicate that interaction with PbIIsignificantly affects the secondary structure of trypsin, the ,-sheet-structure content being increased by about 42,%, whilst those of ,-helix and ,-turn structures are decreased by 13,% and 21,%, respectively. The results clearly demonstrate that PbIIaffects the biological activity of trypsin by modifying its secondary structure. Most interesting is that PbIIup-regulates the activity of trypsin at low concentrations while down-regulating it at high concentrations. [source] Infrared Study of Intercomponent Interactions in a Switchable Hydrogen-Bonded RotaxaneCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008Dhiredj Abstract The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the CO groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the ,(CO) frequencies of the CO groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of ,(CO) bands of the CO groups residing inside the macrocycle cavity remain unaffected by the solvent polarity. [source] | ||||||||||