Search results for "Dimer"

HPLC in the characterisation of conformational species of linear gramicidins

1997

Abstract High-performance size-exclusion chromatography (HPSEC) has proved to be a highly simplified and rapid procedure to investigate the conformational behaviour of gramicidin A inserted in different model membrane systems (lipid dispersions, liposomes, micelles) based on the separation of double-stranded dimers and monomers present in the lipid assemblies. The HPSEC approach has been extended to the characterisation of acylated analogs of gramicidin (palmitoyl- and oleoyl-derivatives) and a series of peptide analogs where tryptophan residues were chemically modified or replaced by less polar residues (phenylalanine or naphtylalanine) lacking H-bonding ability. The Chromatographic result…

Capping α-Cyclodextrin with Cyclotriveratrylene by Triple Disulfide-Bridge Formation

2013

Disulfide-bond formation is an expeditious coupling reaction to make macropolycyclic symmetrical receptors. It is used here for the preparation of unsymmetrical cavitands based on α-cyclodextrin (α-CDX) and cyclotriveratrylene (CTV) analogues. Accordingly, diastereomeric hemicryptophanes 2a and 2b were obtained in 11 % isolated yield by the iodine oxidation of a 1:1 mixture of racemic cyclotrithiophenolene (3) and the C3-symmetric trithiol derivative of permethylated α-cyclodextrin (PM α-CDX) 4. Remarkably, the target hemicryptophanes were obtained in a 5:3 diastereomeric ratio. The reaction produced mainly (34 %) a singly disulfide-bridged PM α-CDX dimer 7, however no traces of triply disu…

Spectroscopic behavior of metal–drug complexes. Infrared spectra of Cu(II) dimer complexes with acetazolamide (H2acm) and an analogue sulfonamide (B-…

1999

Abstract The infrared spectra of the drugs H2acm and B-H2ats, and their copper(II) dimer complexes with stoichiometries [Cu(acm)(NH3)2(OH2)]2·H2O and [Cu(B-ats)(NH3)2]2 are reported and discussed. The Raman spectra of H2acm and B-H2ats are also reported. An assignment of H2acm and B-H2ats modes in the complexes is proposed in comparison with the modes of the free ligands. The spectral modifications due to the deprotonation and coordination effects are analyzed. The ν(N–H) modes of the sulfonamido, carbonamido and Nring–H of the imine tautomer have been accurately assigned. Important information about the S–O and S–N vibrations has been obtained.

2020

Reduction of the aluminum iodide AlI2AriPr8 (1; AriPr8 = C6H-2,6-(C6H2-2,4,6-Pri3)2-3,5-Pri2) with 5% w/w Na/NaCl in hexanes gave a dark red solution from which the monomeric alanediyl :AlAriPr8 (2) was isolated in ca. 28% yield as yellow-orange crystals. Compounds 1 and 2 were characterized by X-ray crystallography, electronic and NMR spectroscopy, and theoretical calculations. The Al atom in 2 is one-coordinate, and the compound displays two absorptions in its electronic spectrum at 354 and 455 nm. It reacts with H2 under ambient conditions to give the aluminum hydride {AlH(μ-H)AriPr8}2, probably via a weakly bound dimer of 2 as an intermediate.

DFT study of the interaction free energy of p–p complexes of fullerenes with buckybowls and viologen dimers

2011

We present a theoretical investigation, by means of DFT protocols, of the complexation thermodynamics of (i) complexes of C70 and C60 fullerenes with bowl-shaped hexabenzocoronene derivatives and (ii) complexes of C60 with viologen dimers. The recent functionals of the M06 family, accounting for p-p interactions to a good level of approximation, have been used to calculate the interaction free energies. For the former complexes, the good agreement between the calculated results and the experimental data confirms the reliability of the protocol used. On these grounds, we then checked the stability of a series of complexes of C60 with some viologen dimers, 1BPnBP1 (n = 6-9), where two N-methy…

A novel germacranolide-aminoacid adduct dimer from centaurea aspera

1991

Abstract The novel germacronolide-valine adduct dimer 1 has been isolated from aerial parts of Centaurea aspera var. aspera . Its structure has been determined by spectroscopic methods.

5-Amino-1-phenyl-3-trifluoromethyl-1H-pyrazole-4-carboxylic acid

2009

In the title compound, C11H8F3N3O2, there are two molecules in the asymmetric unit wherein the phenyl rings make dihedral angles of 65.3 (2) and 85.6 (2)° with the pyrazole rings. In the crystal, pairs of molecules are held together by O—H...O hydrogen bonds between the carboxyl groups, forming a centrosymmetric dimer with an R22(8) motif. Intramolecular N—H...O interactions are also present.

Association of model peptides and dehydropeptides: N-acetyl-L-butyrine and (Z)-dehydrobutyrine N',N'-dimethylamides.

2006

These comparative studies on the aggregation behaviour of Ac-(Z)-DeltaAbu-NMe(2) and Ac-L-Abu-NMe(2) in carbon tetrachloride were performed by the analysis of their FTIR spectra and by theoretical calculations. The percentage of the monomeric form (alpha) decreased as concentration increased and this occurred to a higher degree for the (Z)-DeltaAbu derivative than for its saturated analogue. The dimerization constant K(D), calculated on the basis of the intensity of the monomer and associate bands in the nu(s)(N-H) vibration region, is by three orders of magnitude larger for Ac-(Z)-DeltaAbu-NMe(2) than for Ac-L-Abu-NMe(2). The obtained dimer geometries of the dehydro- compound were calculat…

Association of model peptides and dehydropeptides: N-acetyl-l-alanine- and dehydroalanine N′,N′-dimethylamides

2005

Abstract The comparative studies on the association of Ac-ΔAla-NMe 2 and Ac- l -Ala-NMe 2 in carbon tetrachloride were performed by the analysis of their average molecular weight, dipole moments and FTIR spectra. To aid spectroscopic interpretation and gain some deeper insight into the nature of associates, the geometries of the minimum energy of the dimers of Ac-ΔAla-NMe 2 and Ac- l -Ala-NMe 2 were calculated by the B3LYP/6-31+G** method. The average molecular weight in the studied concentration range, for the ΔAla and l -Ala peptide, as determined by the osmometric method, did not exceed 1.5 and 1.2 of the monomeric mass, respectively. Accordingly, the percentage of the monomeric form (α)…

Bridgehead isomer effects in bis(phosphido)-bridged diiron hexacarbonyl proton reduction electrocatalysts

2017

The influence of the substitution, orientation and structure of the phosphido bridges in [Fe2(CO)6(μ-PR2)2] electrocatalysts of proton reduction has been studied. The isomers e,a-[Fe2(CO)6{μ-P(Ar)H}2] (1a(Ar): Ar = Ph, 2′-methoxy-1,1′-binaphthyl (bn′)), e,e-[Fe2(CO)6{μ-P(Ar)H}2] (1b(Ar): Ar = Ph, bn′) were isolated from reactions of iron pentacarbonyl and the corresponding primary phosphine, syntheses that also afforded the phosphinidene-capped tri-iron clusters, [Fe3(CO)9(μ-CO)(μ3-Pbn′)] (2) and [Fe3(CO)9(μ3-PAr)2] (3(Ar), Ar = Ph, bn′). A ferrocenyl (Fc)-substituted dimer [Fe2(CO)6{μ:μ′-1,2-(P(CH2Fc)CH2)2C6H4}] (4), in which the two phosphido bridges are linked by an o-xylyl group, was al…