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PubMed2005

Di-u-hydroxo-bis{(acetonitrile)dibenzyl(6-methyl-2-pyridylmethyl)-amine-kappa2N,N]copper(II)} bis(perchlorate).

The title compound corresponds to a copper(II) dimer, [Cu2(OH)2(C2H3N)2(C21H22N2)2](ClO4)2, where the metal centres are mu2-bridged by hydroxo groups. The coordination of each copper(II) centre is a slightly distorted square-based pyramid, with two N atoms from dibenzyl(6-methyl-2-pyridylmethyl)amine (BiBzMePMA) and two hydroxo O atoms occupying the basal positions, and the acetonitrile N atom at the apical position. The dimer is centrosymmetric, with a crystallographic inversion centre midway between the two Cu atoms [Cu...Cu = 2.9522 (9) A].

Acetonitriles↗
PubMed2006

Bis[bis(2-pyridylcarbonyl)aminato]iron(III) perchlorate acetonitrile disolvate.

The title compound, [Fe(C12H8N3O2)2]ClO4.2C2H3N, contains Fe(III) in a distorted octahedral coordination environment, with the Fe-N(pyridine) bonds significantly longer than the Fe-N(amine) bonds. The crystal packing involves a bifurcated C-H...(O,O) contact that is also found in all other [M(C12H8N3O2)2] complexes reported previously.

Acetonitriles↗
PubMed1996

The effects of sodium perchlorate on rabbit muscle enolase--Spectral characterization of the monomer.

Incubation of rabbit beta beta enolase in NaClO4 (< or = O.3 M) results in a loss of enzymatic activity and striking changes in the second-derivative ultraviolet spectrum of enolase. HPLC gel filtration shows that dissociation of the dimeric enzyme is occurring. We have used molecular modelling, fluorescence and circular dichroic spectroscopy to examine the structural differences between the monomeric and dimeric forms of this protein. In the dimer, the tyrosine residues are in a non-polar environment; upon dissociation, two of them that were at the dimer interface become exposed. This results in large changes in the second-derivative spectrum. Both the tryptophan fluorescence emission spectrum and the aromatic region of the CD spectrum indicate that there are also changes in the environment of other aromatic residues. No perturbations in the peptide bond region of the CD spectrum are observed. We propose that the major structural effect of NaClO4 is to increase the flexibility of the loops connecting the helices and strands of the alpha/beta barrel of enolase. These loops, which contain about half of the aromatic residues, contain some of the residues of the active site and other residues involved in subunit contacts. Increased flexibility of the loops could disrupt both subunit interactions and the structure of the active site.

Amino Acids↗
PubMed1990

Chloranil-photosensitized monomerization of dimethylthymine cyclobutane dimers and effect of magnesium perchlorate.

The photosensitized monomerization of the cyclobutane dimers of 1,3-dimethylthymine by p-chloranil was investigated by means of steady-state irradiation and laser-flash photolysis. Quantum yields for the monomerization are 0.34 for the cis,syn dimer, 0.39 for the trans,syn dimer, and much less than 10(-2) for the cis,anti isomer. Formation of the chloranil anion radical associated with quenching of triplet chloranil by the dimers demonstrates that electron transfer from dimers to triplet chloranil occurs to initiate the monomerization. Kinetic analysis suggested that the syn-dimer cation radicals undergo the ring cleavage at greater than or equal to 10(9) s-1 before escaping from the solvent cage, while the reactivity of the anti-dimer cation radical is very low. The different reactivities of the syn and anti dimer cation radicals are discussed in terms of through-bond coupling between the n orbitals of N(1) and N(1') involving the cyclobutane-ring sigma orbitals. In the cases of the syn-dimers, the sensitizer-dimer ion-radical pairs undergo the rapid geminate recombination that works as a major energy dissipating channel responsible for the lower-than-unity quantum yields. It has been found that the presence of Mg(ClO4)2 at 0.1 M enhances approximately 1.5 times either the monomerization of the syn dimers or the formation of the chloranil anion radical. A laser-flash photolysis study shows that Mg2+ forms a complex with either the triplet or the anion radical of chloranil. The net salt effects are attributed to the retardation of the rapid geminate recombination by the participation of Mg2+ in the sensitizer-dimer ion-radical pairs.

Chloranil↗