Search results for "conformation"

Increased conformational rigidity of humic substances by oxidative biomimetic catalysis

2005

A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials. High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS-(13)C NMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mw(a)) occurred invariably for all humic substances with the oxidative polymerization catalyzed …

Conformational investigation of α,β‐dehydropeptides. XV: N‐acetyl‐α,β‐dehydroamino acid N ′N ′‐dimethylamides: conformational properties from infrare…

2005

The FTIR spectra were analysed in the region of the nu(s)(N-H), AI(C=O) and nu(s)(Calpha=Cbeta) bands for a series of Ac-DeltaXaa-NMe2, where DeltaXaa = DeltaAla, (Z)-DeltaAbu, (Z)-DeltaLeu, (Z)-DeltaPhe and DeltaVal, to determine a predominant solution conformation of these alpha,beta-dehydropeptide-related molecules. Measurements were taken in CCl4, DCM and MeCN solutions. In the same way, spectra of saturated analogues Ac-Xaa-NMe2, where Xaa = Ala, Abu, Leu, Phe and Val, were investigated. To help interpret the spectroscopic results, conformational maps were calculated by the B3LYP/6-31+G** method. Also, the relative energies of all conformers of the dehydro compounds in vacuo as well as…

Partial thioamide scan on the lipopeptaibiotic trichogin GA IV. Effects on folding and bioactivity

2012

Backbone modification is a common chemical tool to control the conformation of linear peptides and to explore potentially useful effects on their biochemical and biophysical properties. The thioamide, ψ[CS-NH], group is a nearly isosteric structural mimic of the amide (peptide) functionality. In this paper, we describe the solution synthesis, chemical characterization, preferred conformation, and membrane and biological activities of three, carefully selected, peptide analogues of the lipopeptaibiotic [Leu11-OMe] trichogin GA IV. In each analogue, a single thioamide replacement was incorporated. Sequence positions near the N-terminus, at the center, and near the C-terminus were investigated…

Crystal structure of (E)-4-methyl-N-{2-[2-(4-nitrobenzylidene)hydrazin-1-yl]-2-oxoethyl}benzenesulfonamideN,N-dimethylformamide monosolvate

2017

The molecule of the title Schiff base compound, C16H16N4O5S·C3H7NO, displays atransconformation with respect to the C=N double bond. The C—N and N—N bonds are relatively short compared to their normal bond lengths, indicating some degree of delocalization in the molecule. The molecule is bent at the S atom, with an S—N—C—C torsion angle of 164.48 (11)°. The dihedral angle between the two aromatic rings is 84.594 (7)°. Intermolecular N—H...O and C —H...O hydrogen bonds connect centrosymmetrically related molecules into dimers forming rings ofR33(11) andR22(10) graph-set motif stacked along theaaxis into a columnar arrangement. The molecular columns are further linked into a three-dimensional…

Crystal structure of the tripeptideN-(benzyloxycarbonyl)glycylglycyl-L-norvaline

2015

The title tripeptide, C17H23N3O6, contains a nonproteinogenic C-terminal amino acid residue, norvaline, which is an isomer of the amino acid valine. Norvaline, unlike valine, has an unbranched side chain. The molecule has a Gly–Gly segment which adopts an extended conformation. The norvaline residue also adopts an extended backbone conformation while its side chain has ag+tconformation. In the crystal lattice, N—H...O and O—H...O hydrogen bonds stabilize the packing. Molecules translated along the crystallographicaaxis associate through an N—H...O hydrogen bond. The remaining three hydrogen bonds are between molecules related by a21screw axis.

Triclinic conformational polymorph of N,N,N′,N′-tetrakis(2-cyanoethyl)-1,2-ethylenediamine (TCED)

2018

Abstract The crystal and molecular structures of two polymorphs of N,N,N′,N′-tetrakis(2-cyanoethyl)-1,2-ethylenediamine have been characterized by X-ray diffraction along with density functional theory (DFT) studies. The molecules differ from each other by conformation. N,N,N′,N′-tetrakis(2-cyanoethyl)-1,2-ethylenediamine has been synthesized by cyanoethylation of ethylenediamine. Cyanoethylation of vicinal diamines is important for the synthesis of hyperbranched polymeric materials applied as catalysts, surfactants and encapsulating agents in drug delivery systems. The molecular geometry of N,N,N′,N′-tetracyanoethyl-1,2-ethylenediamine is similar to that of homologous compounds. DFT calcul…

Conformational investigation of α,β‐dehydropeptides Part VI. Molecular and crystal structure of benzyloxycarbonylglycyl‐(Z )‐dehydrophenylalanine

1994

The structure of a peptide containing C-terminal dehydrophenylalanine, Z-Gly-(Z)-delta Phe (C19H18N2O5, MW = 354) was determined from single-crystal X-ray diffraction data. Needle-shaped crystals were grown from a 1:1 mixture of methanol-acetone in the monoclinic space group P2(1) with a = 14.717(4), b = 4.941(2), c = 12.073(4) A, beta = 103.72(4) degrees; V = 852.86(8) A3, Z = 2 and Dc = 1.32 g cm-3. The structure was solved by direct methods using SHELXS-86 and refined to a final R-index of 0.032 for 1714 observed reflections. The peptide adopts a conformation folded at the glycine residue, and principal torsion angles are omega 0 = -167.6(2) degrees, phi 1 = -71.8(3) degrees, psi 1 = -31…

Synthèse et étude physico-chimique de ligands macrocycliques, macrobicycliques et macrotricycliques dérivés du 5,12-dioxocyclame

2002

The synthesis and the physico-chemical studies of macropolycyclic ligands based on 5,12-dioxocyclam L1 are presented. The first part of this dissertation presents the structural and physico-chemical properties of L1 and its N-substituted derivatives L2 and L3. A potentiometric study reveald a cooperative protonation of the two macrocyclic ligands L1 and L2 whereas the study of the macrotricycle L3 in a methanol-water mixture revealed a sequential cooperative diprotonation of the four tertiary amines. The square planar nickel and copper complexes were synthesized and characterized using infrared, UV-vis and ESR spectgroscopy. The spectroscopic studies showed the presence of intermolecular hy…

STUDIO QUANTOMECCANICO STRUTTURALE E CONFORMAZIONALE DELL'INSETTICIDA ROTENONE

2008

Effetto della flessibilità conformazionale sull'equilibrio di interconversione tra aldosi e chetosi

2008

Le reazioni di interconversione tra gli aldosi e i chetosi sono importanti trasformazioni, di interesse biochimico, che si presentano in parecchi stadi sia del catabolismo (glicolisi, via dei pentosofosfati) che dell'anabolismo (ciclo di Calvin) dei glucidi. Il meccanismo di reazione accettato, che coinvolge intermedi 1,2-endiolici, è talvolta riferito come una doppia tautomeria acido-catalizzata. Poiché, d'altro canto, reagenti, prodotti ed intermedi presentano tutti un'elevata flessibilità molecolare, ogni indagine computazionale sufficientemente accurata deve comprendere necessariamente l'analisi conformazionale di ciascun substrato coinvolto nell'equilibrio chimico. Tale analisi è stata…