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Conformational Isomers (conformational + isomer)

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Chemistry85%

Selected Abstracts

1H,NMR Spectroscopic Studies of the Conformational Isomers of Pyrrolidinofullerenes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007
Olena Lukoyanova
Abstract Mixed bis-adduct derivatives of C60 containing a pyrrolidine and a malonate methano group were synthesized. Three regioisomers, the e,, the trans -2, and the trans -3, were isolated and characterized. In-depth NMR studies of these methano-pyrrolidinofullerenes showed that the nitrogen inversion on the pyrrolidine moiety is not a fast event in the 1H,NMR time scale as previously regarded. Solvent effects, variable temperature experiments, and protonation of the pyrrolidine nitrogen are addressed. [source]

Conformational isomers of the [(5-methyl-2-pyridinio)aminomethylene]diphosphonate dianion and [(5-methyl-2-pyridyl)aminomethylene]diphosphonate trianion in salts with 4-aminopyridine and ammonia

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2009
Ewa Matczak-Jon
The crystal structures of two salts, products of the reactions between [(5-methyl-2-pyridyl)aminomethylene]bis(phosphonic acid) and 4-aminopyridine or ammonia, namely bis(4-aminopyridinium) hydrogen [(5-methyl-2-pyridinio)aminomethylene]diphosphonate 2.4-hydrate, 2C5H7N2+·C7H10N2O6P22,·2.4H2O, (I), and triammonium hydrogen [(5-methyl-2-pyridyl)aminomethylene]diphosphonate monohydrate, 3NH4+·C7H9N2O6P23,·H2O, (II), have been determined. In (I), the Z configuration of the ring N,C and amino N,H bonds of the bisphosphonate dianion with respect to the Cring,Namino bond is consistent with that of the parent zwitterion. Removing the H atom from the pyridyl N atom results in the opposite E configuration of the bisphosphonate trianion in (II). Compound (I) exhibits a three-dimensional hydrogen-bonded network, in which 4-aminopyridinium cations and water molecules are joined to ribbons composed of anionic dimers linked by O,H...O and N,H...O hydrogen bonds. The supramolecular motif resulting from a combination of these three interactions is a common phenomenon in crystals of all of the Z -isomeric zwitterions of 4- and 5-substituted (2-pyridylaminomethylene)bis(phosphonic acid)s studied to date. In (II), ammonium cations and water molecules are linked to chains of trianions, resulting in the formation of double layers. [source]

Conformational isomers of neutral trans -di­nitro­cobalt(III) complexes

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2001
Hyungphil Chun
The reaction of Co(acac)3 with N -(2-amino­ethyl)-1,3-propane­di­amine in the presence of NaNO2 results in the preparation of an unexpected di­nitro­cobalt(III) compound, (11-amino-4-methyl-5,8-di­aza­undeca-2,4-dien-2-olato-,4­N5,8,11,O)-di­nitrocobalt(III), [Co(C10H20N3O)(NO2)2], containing the tetra­dentate anion of 11-amino-4-methyl-5,8-diazaundeca-2,4-dien-­2-ol. Two isomers of the compound were obtained by recrystallization of the crude product. In one isomer, the two trans nitro groups are staggered, and in the other they are eclipsed. [source]

Synthesis and reactions of conformational isomers of a stable selenenic acid bearing a bridged calix[6]arene framework

HETEROATOM CHEMISTRY, Issue 4 2001
Kei Goto
A stable selenenic acid bearing a bridged calix[6]arene framework fixed in the 1,2,3-alternate conformation was synthesized. Its properties were compared with those of its conformational isomer fixed in the cone conformation, indicating that the reactivity of the endohedral SeOH group can be regulated by the conformation of the calix[6]arene framework. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:195,197, 2001 [source]

Synthesis and X-ray structure of two conformational isomers of [Zn(medpt)(SCN)2], medpt = bis (3 , aminopropyl)methylamine

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2006
S. Guha
Abstract Two conformational isomers of [Zn (medpt)(NCS)2], medpt=bis(3-aminopropyl) methylamine, (1) and (2) have been synthesised and the crystal structures are determined using single crystal X-ray diffraction. The structures of the complexes have been solved by Patterson method and refined by full-matrix least- squares techniques to R1 = 0.0524 for (1) and R1 = 0.0506 for (2), respectively. The geometry around the Zn(II) centre in both isomers is distorted trigonal bipyramidal. The two pendent thiocyanate moieties in (1), with Zn,N,C angles 167.9(4),173.9(4)º, coordinate the mental centre almost linearly while the corresponding coordinations in (2) are significantly bent [Zn,N,C angles 150.8(3),153.1(2)°]. Intermolecular N,H,S hydrogen bonds stabilise the crystal packing in the complexes forming infinite chains parallel to the [100] direction. The combinations of molecular chains generate three/two dimensional supramolecular framework in complexes (1) and (2). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis and reactions of conformational isomers of a stable selenenic acid bearing a bridged calix[6]arene framework

HETEROATOM CHEMISTRY, Issue 4 2001
Kei Goto
A stable selenenic acid bearing a bridged calix[6]arene framework fixed in the 1,2,3-alternate conformation was synthesized. Its properties were compared with those of its conformational isomer fixed in the cone conformation, indicating that the reactivity of the endohedral SeOH group can be regulated by the conformation of the calix[6]arene framework. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:195,197, 2001 [source]

Highly Efficient Rhodium Catalysts for the Asymmetric Hydroformylation of Vinyl and Allyl Ethers using C1 -Symmetrical Diphosphite Ligands

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
Aitor Gual
Abstract Here, we describe the successful application of novel glucofuranose-derived 1,3-diphosphites in the rhodium-catalysed asymmetric hydroformylation of vinyl acetate, 2,5-dihydrofuran and 2,3-dihydrofuran. In the hydroformylation of vinyl acetate, total regioselectivity and high ee (up to 73%) were obtained. When 2,3- and 2,5-dihydrofuran were the substrates, total chemo- and regioselectivities were achieved together with ees up to 88%. These results correspond to the highest ee values reported to date in the asymmetric hydroformylation of these substrates. The HP-NMR studies of the [RhH(CO)2(L)] species (L=15 and 17) demonstrated that both ligands coordinate to the Rh centre in an eq-eq fashion. The complex [RhH(CO)2(15)] was detected as a single isomer with characteristic features of eq-eq coordination. However, the broadening of the corresponding signals indicated that this species is rapidly interchanging in solution. In contrast, complex [RhH(CO)2(17)] was detected as a mixture of two conformational isomers at low temperature due to the greater flexibility of the monocyclic backbone of this ligand. [source]

Conformational analysis of a potent SSTR3-selective somatostatin analogue by NMR in water solution

JOURNAL OF PEPTIDE SCIENCE, Issue 2 2006
Margarida Gairí
Abstract The three-dimensional structure of a potent SSTR3-selective analogue of somatostatin, cyclo(3,14)H-Cys3 -Phe6 -Tyr7 - D -Agl8(N, Me, 2-naphthoyl)-Lys9 -Thr10 -Phe11 -Cys14 -OH (des-AA1, 2, 4, 5, 12, 13[Tyr7, D -Agl8(N, Me, 2-naphthoyl)]-SRIF) (peptide 1) has been determined by 1H NMR in water and molecular dynamics (MD) simulations. The peptide exists in two conformational isomers differing mainly by the cis/trans isomerization of the side chain in residue 8. The structure of 1 is compared with the consensus structural motifs of other somatostatin analogues that bind predominantly to SSTR1, SSTR2/SSTR5 and SSTR4 receptors, and to the 3D structure of a non-selective SRIF analogue, cyclo(3,14)H-Cys3 -Phe6 -Tyr7 - D -2Nal8 -Lys9 -Thr10 -Phe11 -Cys14 -OH (des-AA1, 2, 4, 5, 12, 13[Tyr7, D -2Nal8]-SRIF) (peptide 2). The structural determinant factors that could explain selectivity of peptide 1 for SSTR3 receptors are discussed. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. [source]

Multiple diverse ligands binding at a single protein site: A matter of pre-existing populations

PROTEIN SCIENCE, Issue 2 2002
Buyong Ma
Abstract Here, we comment on the steadily increasing body of data showing that proteins with specificity actually bind ligands of diverse shapes, sizes, and composition. Such a phenomenon is not surprising when one considers that binding is a dynamic process with populations in equilibrium and that the shape of the binding site is strongly influenced by the molecular partner. It derives implicitly from the concept of populations. All proteins, specific and nonspecific, exist in ensembles of substates. If the library of ligands in solution is large enough, favorably matching ligands with altered shapes and sizes can be expected to bind, with a redistribution of the protein populations. Point mutations at spatially distant sites may exert large conformational rearrangements and hinge effects, consistent with mutations away from the binding site leading to population shifts and (cross-)drug resistance. A similar effect is observed in protein superfamilies, in which different sequences with similar topologies display similar large-scale dynamic motions. The hinges are frequently at analogous sites, yet with different substrate specificity. Similar topologies yield similar conformational isomers, although with different distributions of population times, owing to the change in the conditions, that is, the change in the sequences. In turn, different distributions relate to binding of different sizes and shapes. Hence, the binding site shape and size are defined by the ligand. They are not independent entities of fixed proportions and cannot be analyzed independently of the binding partner. Such a proposition derives from viewing proteins as dynamic distributions, presenting to the incoming ligands a range of binding site shapes. It illustrates how presumably specific binding molecules can bind multiple ligands. In terms of drug design, the ability of a single receptor to recognize many dissimilar ligands shows the need to consider more diverse molecules. It provides a rationale for higher affinity inhibitors that are not derived from substrates at their transition states and indicates flexible docking schemes. [source]

Crystal structure of the antibiotic albomycin in complex with the outer membrane transporter FhuA

PROTEIN SCIENCE, Issue 5 2000
Andrew D. Ferguson
Abstract One alternative method for drug delivery involves the use of siderophore-antibiotic conjugates. These compounds represent a specific means by which potent antimicrobial agents, covalently linked to iron-chelating siderophores, can be actively transported across the outer membrane of Gram-negative bacteria. These "Trojan Horse" antibiotics may prove useful as an efficient means to combat multi-drug,resistant bacterial infections. Here we present the crystallo-graphic structures of the natural siderophore-antibiotic conjugate albomycin and the siderophore phenylferricrocin, in complex with the active outer membrane transporter FhuA from Escherichia coli. To our knowledge, this represents the first structure of an antibiotic bound to its cognate transporter. Albomycins are broad-host range antibiotics that consist of a hydroxamate-type iron-chelating siderophore, and an antibiotically active, thioribosyl pyrimidine moiety. As observed with other hydroxamate-type siderophores, the three-dimensional structure of albomycin reveals an identical coordination geometry surrounding the ferric iron atom. Unexpectedly, this antibiotic assumes two conformational isomers in the binding site of FhuA, an extended and a compact form. The structural information derived from this study provides novel insights into the diverse array of antibiotic moieties that can be linked to the distal portion of iron-chelating siderophores and offers a structural platform for the rational design of hydroxamate-type siderophore-antibiotic conjugates. [source]

Cocrystal of cis - and trans - N -phenylformamide

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2008
Bernard Omondi
N -Phenylformamide, C7H7NO, crystallizes with two molecules in the asymmetric unit which have different conformations of the formylamino group, one being cis and the other trans. This is the first example of an arylformamide crystal containing both conformational isomers and it may thus be considered a cocrystal of the two conformers. The two molecules in the unit cell are linked through N,H...O hydrogen bonding to two other molecules, thereby forming hydrogen-bonded tetramers within the crystal structure. [source]

trans -Bis[1-benzyl-3-(2,3,4,5,6-penta­fluoro­benz­yl)benzimidazol-2-yl­idene]­dibromo­palladium(II)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2006
Aytaç Gürhan Gökçe
The title compound, [PdBr2(C21H13F5N2)2], crystallizes with two independent centrosymmetric conformational isomers having a square-planar coordination at the Pd atom. The conformational isomers differ by the ligands having a cis or trans orientation of their benzyl and pentafluorobenzyl rings with respect to the benzimidazole ring plane. The benzimidazole rings are rotated with respect to the coordination plane of the metal by 79.1,(2) and 75.2,(1)° for mol­ecules A and B, respectively. The Pd,Br bond lengths are 2.4218,(8) and 2.4407,(10),Å for mol­ecules A and B, respectively, and the Pd,C bond lengths are 2.030,(8) and 2.018,(9),Å. The crystal structure contains two types of C,H,F and one type of C,H,Br intra­molecular contact, as well as C,H,, inter­actions. [source]

trans -(2-Methyl­thio­benzoato- O)phenylbis­(tri­phenyl­phosphine)­palladium(II), two conformational isomers

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2000
Gert J. Kruger
The title compound, trans -[Pd(C6H5)(C8H7O2S)(C18H15P)2], crystallizes in two modifications differing only in the orientation of the 2-methyl­thio­benzoato ligand. In both cases, this ligand binds to the metal centre via one O atom in a monodentate fashion. The only significant difference is a rotation about the C(Ph),COO bond, with O,C,C,C torsion angles having values of 6.3,(7) and 157.3,(3)° in the two isomeric forms. [source]