Environment Present (environment + present)

Distribution by Scientific Domains

Selected Abstracts

Experimental and theoretical charge-density study of a tetranuclear cobalt carbonyl complex

Jacob Overgaard
Details of the complex bonding environment present in the molecular centre of an alkyne-bridged dicobalt complex have been examined using a combination of experimental and theoretical charge-density modelling for two compounds which share a central Co2C2 tetrahedral moiety as their common motif. Topological analysis of the experimental electron density illustrates the problem of separating the Co,C bond-critical points (b.c.p.s) from the intervening ring-critical point (r.c.p.), due largely to the flat nature of the electron density in the CoC2 triangles. Such a separation of critical points is immediately obtained from a topological analysis of the theoretical electron density as well as from the multipole-projected theoretical density; however, the addition of random noise to the theoretical structure factors prior to multipole modelling leads to a failure in consistently distinguishing two b.c.p.s and one r.c.p. in such close proximity within the particular environment of this Co2C2 centre. [source]

Intraovarian Localization of Growth Factors in Induced Cystic Ovaries in Rats

H. H. Ortega
Summary We hypothesized that the special hormonal environment present in animals with cystic ovarian disease (COD) interferes with cellular production of growth factors (GFs). The objective of the present study was to characterize the expression of insulin-like growth factor (IGF)-I, fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF) in induced COD using immunohistochemistry. We used an experimental model based on the exposure to constant light of adult rats during 15 weeks. We quantified the expression of GFs in cystic and normal ovaries by the Immunohistochemical Stained Area (IHCSA). In animals with COD, a significant reduction in the IHCSA of IGF-I in the follicular fluid, theca and granulosa layers of cysts occurred; and an increase in the interstitial tissue with regard to the control group. We found moderate immunoreactivity of FGF-2 in granulosa and theca layers of secondary and tertiary follicles and lower expression in the granulosa and theca interna layers of cystic follicles. Immunoexpression of VEGF was found in granulosa and theca cells of secondary and tertiary follicles. This study shows changes in the ovarian expression of IGF-I, FGF-2 and VEGF in induced COD. We can propose that an alteration in the control of the follicular dynamic, through the GFs, added to other features, could be involved in the ovarian cyst pathogenesis. [source]

Selenium- and Tellurium-Containing Multifunctional Redox Agents as Biochemical Redox Modulators with Selective Cytotoxicity

Dr. Vincent Jamier
Abstract Various human diseases, including different types of cancer, are associated with a disturbed intracellular redox balance and oxidative stress (OS). The past decade has witnessed the emergence of redox-modulating compounds able to utilize such pre-existing disturbances in the redox state of sick cells for therapeutic advantage. Selenium- and tellurium-based agents turn the oxidizing redox environment present in certain cancer cells into a lethal cocktail of reactive species that push these cells over a critical redox threshold and ultimately kill them through apoptosis. This kind of toxicity is highly selective: normal, healthy cells remain largely unaffected, since changes to their naturally low levels of oxidizing species produce little effect. To further improve selectivity, multifunctional sensor/effector agents are now required that recognize the biochemical signature of OS in target cells. The synthesis of such compounds provides interesting challenges for chemistry in the future. [source]

The Application of 199Hg NMR and 199mHg Perturbed Angular Correlation (PAC) Spectroscopy to Define the Biological Chemistry of HgII: A Case Study with Designed Two- and Three-Stranded Coiled Coils

Olga Iranzo Dr.
Abstract The use of de novo designed peptides is a powerful strategy to elucidate HgII,protein interactions and to gain insight into the chemistry of HgII in biological systems. Cysteine derivatives of the designed ,-helical peptides of the TRI family [Ac-G-(LaKbAcLdEeEfKg)4 -G-NH2] bind HgII at high pH values and at peptide/HgII ratios of 3:1 with an unusual trigonal thiolate coordination mode. The resulting HgII complexes are good water-soluble models for HgII binding to the protein MerR. We have carried out a parallel study using 199Hg NMR and 199mHg perturbed angular correlation (PAC) spectroscopy to characterize the distinct species that are generated under different pH conditions and peptide TRI,L9C/HgII ratios. These studies prove for the first time the formation of [Hg{(TRI,L9C)2 -(TRI,L9CH)}], a dithiolate,HgII complex in the hydrophobic interior of the three-stranded coiled coil (TRI,L9C)3. 199Hg NMR and 199mHg PAC data demonstrate that this dithiolate,HgII complex is different from the dithiolate [Hg(TRI,L9C)2], and that the presence of third ,-helix, containing a protonated cysteine, breaks the symmetry of the coordination environment present in the complex [Hg(TRI,L9C)2]. As the pH is raised, the deprotonation of this third cysteine generates the trigonal thiolate,HgII complex Hg(TRI,L9C)3, on a timescale that is slower than the NMR timescale (0.01,10,ms). The formation of the species [Hg{(TRI,L9C)2(TRI,L9CH)}] is the result of a compromise between the high affinity of HgII to form dithiolate complexes and the preference of the peptide to form a three-stranded coiled coil. [source]