9 research outputs found

    Investigating the Structural and Metal Binding Properties of an Ancestral Eye Lens Crystallin

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    βγ-crystallins are structural proteins in the eye lens that refract light to produce an image. These proteins are found at extremely high concentrations in the lens and must remain sol- uble and transparent. If their solubility is perturbed due to a mutation, chemical damage, or a disturbance in metal ion homeostasis, then cataract can develop and cloud the eye lens. In order to understand more about the evolutionary origin of the structure and aggrega- tion of these proteins in the human eye lens, the structure and metal binding properties of an ancestral Ca2+ binding βγ-crystallin found in the Ciona intestinalis tunicate were investigated using biophysical characterization techniques such as fluorescence, CD, ITC, DLS and solution-state NMR. It was found that the tunicate crystallin has a conformational change upon addition of Ca2+ and other divalent cations. This protein is highly stabilized both chemically and thermally upon binding to Ca2+ and it binds more strongly than has been previously reported for other Ca2+ binding βγ-crystallins. It was also found that this crystallin interacts with other divalent cations, all of which thermally stabilize the protein. Although divalent metal ions raise the melting temperature of the tunicate crystallin, aggre- gation is induced by the interaction with some of these metal ions well below the melting temperature. Several solution-state NMR techniques were developed in order to solve the structure of this tunicate βγ-crystallin and other related biomolecules in the presence of divalent metal ions. One of the methods uses DLPC/DHPC bicelles, a low-temperature alignment medium, to obtain long range distance and angular restraints of dynamic and heat sensitive biomolecules in the presence of divalent metal ions. These restraints are de- termined via measurement of residual dipolar couplings, where J-couplings of a biomolecule in isotropic solution are compared with the J+D values for the biomolecule in the presence of an alignment medium. If there is a change in this peak splitting, then alignment of the biomolecule is occuring. Another technique involves using a small molecular probe dCDP and 31P NMR to determine the macromolecule-free and macromolecule-bound divalent metal ion concentrations in NMR samples out of a total amount of divalent metal ions put into the system

    Syntheses and the Characterization of Schiff Base Copper Complexes and their Interaction with ct-DNA and Plasmid DNA

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    Transition metal complexes are among metal-based complexes generating interest as anticancer agents. Previous research has shown that copper complexes have the potential for chemotherapeutic activity. Hydrolysis of phosphodiester bonds found in the backbone of DNA as well as intercalation between the DNA base pairs are two ways of how the complexes have shown to decrease the proliferation of cancer cells. A number of Schiff base ligands, MICQ, APMIC, and AQC, have been synthesized. The ligands have reacted with different copper salts to produce five corresponding Schiff base copper complexes. The complexes have been characterized via infrared spectroscopy, uv/vis spectroscopy, cyclic voltammetry and elemental analysis. An x-ray crystal structure of one of the complexes has also been determined. A square base pyramidal geometry was observed from the structure with the complex being the square base and the chlorine being the apex of the pyramid. Reactivity studies of the complexes with a model compound of DNA as well as with DNA have been performed. Some of the reactivity studies include ethidium bromide competitive binding studies, absorption titration studies and DNA cleavage experiments

    Synthesis and the Characterization of Schiff-based Copper Complexes: Reactivity with DNA, 4-NPP and BNPP

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    Two new copper Schiff-base complexes have been synthesized and characterized by use of spectroscopic techniques. The Schiff-base ligands, (E)-N-((1-methyl-1H-imidazol-2-yl)methylene)quinolin-8-amine, MICQ and (E)-1-((quinolin-8-ylimino)methyl)naphthalen-2-ol, TL1 were obtained from the reaction of 8-aminoquinoline with 1-methyl-2-imidazolecarboxaldehyde and 2-hydroxy-1-napthaldehyde respectively. The reaction of MICQ with copper(II) chloride produced complex 1, [Cu(MICQ)Cl](PF6), whereas the reaction of TL1 with copper(II) acetate resulted in complex 2, Cu(TL1)(OAc)·CH3OH. The single crystal X-ray structure determination of both complexes show distorted square planar geometries around the copper center. The reactivity of the complexes with calf thymus DNA, CT-DNA and plasmid DNA have been studied using ethidium bromide displacement fluorescence emission, electronic absorption spectroscopy and agarose gel electrophoresis analysis. From the fluorescence emission studies Ksv values of 3.70 × 103 M−1 and 7.82 × 103 M−1 were obtained for complexes 1 and 2, respectively. The absorption titration resulted in Kb values of 1.52 × 105 M−1 for complex 1 and 5.00 × 105 M−1 for complex 2. The results indicate that both complexes significantly interact with CT-DNA and also show cleavage of supercoiled DNA. In addition, complex 2 was found to hydrolyze the DNA model compounds bis(4-nitrophenyl) phosphate, BNPP and 4-nitrophenyl phosphate, 4-NPP

    Cyclizing Pentapeptides: Mechanism and Application of Dehydrophenylalanine as a Traceless Turn-Inducer

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    Dehydrophenylalanine is used as a traceless turn-inducer in the total synthesis of dichotomin E. Macrocyclization of the monomer is achieved in high yields and selectivity over cyclodimerization under conditions 100 times more concentrated than previously achieved. The enamide facilitates ring closing, and Rh-catalyzed hydrogenation of the unsaturated cyclic peptide results in selective formation of the natural product or its epimer, depending on our choice of phosphine ligand. NMR analysis and molecular modeling revealed that the linear peptide adopts a left-handed α-turn that preorganizes the N- and C-termini toward macrocyclization
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