| Chromium(â…¢) is an essential trace element for mammals and is required for maintenance of proper carbohydrate and lipid metabolism. Chromium(â…¢) helps insulin metabolize fat, turn protein into muscle and convert sugar into energy. It also plays a role in regulating appetite, reducing sugar cravings and increasing lean body mass. Additional chromium supplementation also favorably influences glucose/insulin metabolism in chronic hemodialysis patients. Cellular chromium potentiates insulin signaling by increasing insulin receptor kinase activity. Nutritional and pharmacological therapies complement one to combat typeâ…¡diabete.What is the physical form of Cr(â…¢) in the bloodstream? How is Cr(â…¢) transported and exchanged between ligands in the serum? Is transport specific? What structure/activity relationship exists in Cr(â…¢) complexes to allow their transport across biological membranes? At this point, there exist significant gaps in understanding the possible biochemistry of Cr(â…¢) and what molecular processes it may affect.In this thesis, the series of salicylic acid metal complexes were synthesized first. The physical chemistry properties were studied; the interaction of the chromium complexes and HSA, apoOTf and pBR322 DNA was carried out. The mechanism of endocytosis and release of Cr-Tf by K562 cells were studied.Chapterâ… : Review.The biological role for chromium is elucidatd in this chapter. Chromium is an essential trace element for mammals and is required for maintenance of proper carbohydrate and lipid metabolism. However, elucidating its function at a molecular level has proved to be problematic.Chapterâ…¡: Synthesis and expression of salicylic-chromium complexes.High dose of salicylic acid has been used, more than a century ago, to reduce the symptoms related to typeâ…¡diabetes. Salicylic acid is known to be a weak competitive inhibitor of PTP1B, with an inhibition constant of 19.4 mmol·T-1. More recently, many laboratories have reported that polymeric substances, containing multiple salicylic acid moieties, are potent inhibitors of PTPases. These compound prevented increases in the plasma triglyceride, cholesterol, and nonesterified fatty acid concentrations.The salicylic acid was selected to reacted with chromium(â…¢) to synthesize the chromium complexes such as [Cr(â…¢)(SA)(en)2]Cl,Cr(â…¢)(SSA)(en)2,[Cr(â…¢)(4-ASA)(en)2]C,[Cr(â…¢)(HNA)(en)2]Cl,[Cr2(CH2SA2)(en)4]Cl2 and [Cr2(CH2NSA2)(en)4]Cl2, [en=ethylenediamine, 4-ASA=4-aminosalicylic acid, SA=salicylic acid, SSA=5-sulfosalicylic acid, HNA=3-Hydroxy-2-naphthoic acid, CH2NSA2 = 4,4'-Methylenebis (3-Hydroxy-2-naphthoic acid)], which were characterized by mean of chemical analyses, fluorescence spectra, absorption spectra and single crystal X-ray diffraction, The chromium(â…¢) is at the centre of a compressed octahedron formed by four nitrogen atoms from two en molecules, one phenolic hydroxyl oxygen and one carboxylate oxygen from the SA ligand. The characteristic absorption peak of the free H2SA (Ï€-Ï€*) occurs at 298 nm, while in the complex this peak exhibits a considerable red shift to 326 nm. The fluorescence spectrum of the free H2SA at pH 7.4 displays maximum emissions speak near 410 nm, while in the complex the fluorescence intensity at 410 nm is quenched. The significant changes in the complex's absorption and fluorescence spectra will be benefited for the following studies such as the reactivity and stabilities.Chapterâ…¢: Physics-chemistry properties of the chromium(â…¢) complexes.Chromium(â…¢) because of its d3 electronic configuration forms stable and substitution inert metal complexes. The photochemistry reaction of the chromium complex has been the century theme of inorganic photochemistry reaction since 1960s. The stability under different tempreture, different pH environments and irradiation condition of the complex are discussed by means of UV-Visible, fluorescence spectra, conductivity mensuration, pH mensuration and electrospray ionization mass spectrometry. It shows that the complex is stable at room temperature, pH 7.4, while it will be decomposed in acid environment. It shows that the ion photoaquated to a monodentate protonated ethylenediamine (en) complex which then underwent further aquation thermally with loss of the en ligand. Finally a hydrolyzed, multinuclear Cr cluster predominates at neutral pH.The reaction of the complexes with EDTA and H2O2 indicated that that the irritated complex is unstable compared to the complex.Chapterâ…£: Interaction of chromium complexes with human serum albumin (HSA).The X-ray crystallographic data for HSA reveal it actually to be a 585 amino acid residue (66.5 kDa) monomer containing three homologousα-helical domainsâ… ,â…¡, andâ…¢. Serum albumins are the most abundant and the most important proteins in the circulatory system of a wide variety of organisms, being the major macromolecules contributing to the osmotic blood pressure. Many drugs, metal ions (Cu2+,Ca2+,Zn2+,Ni2+), hormone, amino acid and fatty acid are reversibly bound to albumins, which then function as carrier. Therefore, it is imperative to investigate the binding interaction between chromium(â…¢) and serum albumin for the better understanding of the existing states, transportation, absorption, metabolism and pharmacodynamic properties of the drugs.In this paper we describe the effect of the nature of chromium(â…¢) complexes on its ability to bind to HSA. All the chromium(â…¢) complexes employed in this study have been found to quench the fluorescence intensity of tryptophanyl residue. The binding constant, Kb as estimated from the fluorescence quenching studies has been found to be 8.70×103, 1.69×104, 7.40×103, 2.80×104 mol-1·L for the [Cr(SA)(en)2]Cl, [Cr(ASA)(en)2]Cl and [Cr(SSA)(en)2], [Cr(HNA)(en)2]Cl respectively. One of our concerns is the stability of the complexes in the presence of HSA. Both the UV and fluorescence spectra show that the complex is stable and the Cr(â…¢) ions could not be transferred to HSA. According to the Forster non-radiative energy transfer theory, the distance between Cr(â…¢) complex and HSA were calculated. The forces acting between the complex and HSA were evaluated. According to the theory of Ross, the date obtained indicated that protein association progress is involved in hydrophobic interaction and the other crucial types of interaction such as electrostatic interaction and hydrogen bonds.Chapterâ…¤: Kinetics reaction of the chromium complex with ovotransferrin (OTf).Up to date, the mechanisms of absorption of chromic ions are uncertain. The iron-transport protein transferrin has been proposed to serve as the major chromium transport agent. As a result of the in vivo and in vitro studies, it reasonably has been assumed that transferrin was involved in chromium transport, although transport has not conclusively demonstrated in vivo. In order to explore the transfer mechanism of chromium(â…¢) in mammals, the combination of UV-Vis and fluorescence spectra are used to study the transfer manner of Cr(â…¢) from the complex to EDTA and apoOTf. The second order rate constants were obtained. It was found the transfer manner to EDTA and apoOTf is different. Cr(â…¢) are combined to EDTA, and SA or en ligands are competitively replaced. In the reaction of [Cr(SA)(en)2]Cl with apoOTf, two Cr-en bonds are broken and [Cr(SA)]-apoOTf bonds are formed. That is to say, Cr(â…¢) can be transferred from the title complex to apoOTf with the retention of the salicylate, and a stable ternary complex S A-Cr(â…¢)- transferrin was formed. Salicylate serves as the role of synergistically bound anion when Cr(â…¢) is transferred to the protein. Similarly, ASA2- and SSA2- also serve as the role of synergistically bound anion. The transfer of Cr from complex [Cr(â…¢)(SA)(en)2]Cl to apoOTf is slowly, k=(1.4±0.2)×10-1 mor-1·L·s-1.Chapterâ…¥: Mechanism of transferrin-receptor meditated chromium-transferrin at cell level.Cell-associated count studies on the uptake of 125I labeled transferrin contain Cr3+ species by K562 cells showed that like apoTf, Cr-Tf, and Cr2-Tf can bind to cell receptors. The sequence of three species binding to transferrin is apoTf < Cr-Tf 2-Tf. NaN3 worked on the binding and release of Cr-Tf with the cells, which shows both processes demand energy. The binding and internalization of Cr2-Tf could be competitively inhibited by nonradioactive apoOTf. The results demonstrate the Cr-Transferrin can be recognized by the TfR and the TfR-mediated mechanism is a possible pathway for Cr3+ from blood or plasma to chromodulin by which proposed mechanism for the activation of insulin receptor activity.Chapterâ…¦: DNA and protein damage by chromium complexes.Formation of DNA lesions, including strand breaks, abasic sites and Cr(â…¢)-DNA cross-links in Cr(â…¥)-exposed cells is believed to be the primary cause of Cr(â…¥)-induced carcinogenicity. Complexes of Cr(â…¤/â…£) with peroxo and/or superoxo ligands have been implicated as likely reactive species that cause oxidative DNA damage on exposure to either the Cr(â…¥) + reductant+O2, or Cr(â…¢)+H2O2 systems (Cr(â…¥) itself does not react with isolated DNA). In order to evaluated the DNA and protein damage by chromium complex, some experiments ware carried out in the following:1. Gel electrophoresis of plasmid DNA in the presence of irritated complexes of 6μmol·L-1 [Cr(â…¢)(SA)(en)2]+,[Cr(â…¢)(4-ASA)(en)2]+ and Cr(â…¢)(SSA)(en)2 shows that they can efficiently promote the cleavage of pBR 322 DNA into smaller fragments in a time- and concentration-dependent fashion. However, those chromium complexes can not cause any damage to DNA. The irritated products can efficiently cleavage pBR 322 DNA even after 12 months. The cleavage experiments in the presence of -OH radical scavenger indicated the irritated products promote hydrolysis of the DNA phosphodiester.2. SDS-PAGE of the samples reveals that the three complexes in the presence of hydrogen peroxide produced no damage to the protein. Meanwhile, no marked changes have been observed in the protein absorption band in the presence of the three complexes, indicating that these chromium(â…¢) complexes do not bring about any major tertiary structure changes. |
PDF Full Text Request