40 research outputs found
Self-Excited Vibration of Statically Unloaded Pads in Tilting-Pad Journal Bearings
load characteristics are satisfactory if ^m«0.66ap, but these pads do not have tendencies to loose their stability
Direct Scaling of Primitive Valence Force Constants:Â An Alternative Approach to Scaled Quantum Mechanical Force Fields
DFT analysis of Co-alkyl and Co-adenosyl vibrational modes in B12-cofactors
Density functional theory (DFT)-based normal mode calculations have been carried out on models for B12-cofactors to assign reported isotope-edited resonance Raman spectra, which isolate vibrations of the organo-Co group. Interpretation is straightforward for alkyl-Co derivatives, which display prominent Co-C stretching vibrational bands. DFT correctly reproduces Co-C distances and frequencies for the methyl and ethyl derivatives. However, spectra are complex for adenosyl derivatives, due to mixing of Co-C stretching with a ribose deformation coordinate and to activation of modes involving Co-C-C bending and Co-adenosyl torsion. Despite this complexity, the computed spectra provide a satisfactory re-assignment of the experimental data. Reported trends in adenosyl-cobalamin spectra upon binding to the methylmalonyl CoA mutase enzyme, as well as on subsequent binding of substrates and inhibitors, provide support for an activation mechanism involving substrate-induced deformation of the adenosyl ligand.NRC publication: Ye
Preparation of titanocene-gold compounds based on highly active gold(I)-N-heterocyclic carbene anticancer agents: Preliminary inâ vitro studies in renal and prostate cancer cell lines
Heterometallic titanocene-based compounds containing gold(I)-phosphane fragments have been extremely successful against renal cancer inâ
vitro and inâ
vivo. The exchange of phosphane by N-heterocyclic carbene ligands to improve or modulate their pharmacological profile afforded bimetallic complexes effective against prostate cancer, but less effective against renal cancer inâ
vitro. Herein we report the synthesis of new bimetallic Ti-Au compounds by the incorporation of two previously reported highly active gold(I)-N-heterocyclic carbene fragments derived from 4,5-diarylimidazoles. The two new compounds [(η5 -C5 H5 )2 TiMe(ÎŒ-mba)Au(NHC)] (where NHC=1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene, NHC-Bn 2âa; or 1,3-diethyl-4,5-diphenylimidazol-2-ylidene, NHC-Et 2âb) with the dual linker (-OC(O)-p-C6 H4 -S-) containing both a carboxylate and a thiolate group were evaluated inâ
vitro against renal and prostate cancer cell lines. The compounds were found to be more cytotoxic than previously described Ti-Au compounds containing non-optimized gold(I)-N-heterocyclic fragments. We present studies to evaluate their effects on cell death pathways, migration, inhibition of thioredoxin reductase (TrxR) and vascular endothelial growth factor (VEGF) in the PC3 prostate cancer cell line. The results show that the incorporation of a second metallic fragment such as titanocene into biologically active gold(I) compounds improves their pharmacological profile.This work was supported by the US National Cancer Institute and the US National Institute for General Medical Sciences (NIGMS) grants 1SC1CA182844 and 2SC1GM127278â05A1 (to M.C.). N.C. acknowledges a postdoctoral fellowship from the FundaciĂłn Alfonso MartĂn Escudero (Spain). N.G. thanks the Universidad de la Rioja (Spain) for a doctoral fellowship and a travel scholarship. M.A. thanks the Ministerio de EconomĂa y Ciencia (MINECO, Spain) for a doctoral fellowship and a travel scholarship.Peer reviewe
Mode Recognition in UV Resonance Raman Spectra of Imidazole: Histidine Monitoring in Proteins
The imidazole side-chains of histidine residues perform
key roles
in proteins, and spectroscopic markers are of great interest. The
imidazole Raman spectrum is subject to resonance enhancement at UV
wavelengths, and a number of UVRR markers of structure have been investigated.
We report a systematic experimental and computational study of imidazole
UVRR spectra, which elucidates the band pattern, and the effects of
protonation and deprotonation, of H/D exchange, of metal complexation,
and of addition of a methyl substituent, modeling histidine itself.
A consistent assignment scheme is proposed, which permits tracking
of the bands through these chemical variations. The intensities are
dominated by normal mode contributions from stretching of the strongest
ring bonds, C<sub>2</sub>N and C<sub>4</sub>C<sub>5</sub>, consistent
with enhancement via resonance with a dominant imidazole ÏâÏ*
transition