Multicomponent ligand interactions are involved in essentially all nanoparticle (NP) applications. However, the ligand conformation and ligand binding mechanisms on NPs are highly controversial. The research reported here is focused on deepening the fundamental understanding of multicomponent ligand interactions with gold and silver nanoparticles (AuNPs and AgNPs) in water. We demonstrated that AuNPs passivated by saturated layer of poly(ethylene glycol) (PEG-SH) have large fractions of AuNP surface area available for ligand adsorption and exchange. The fraction of AuNP surface area passivated by PEG-SH with molecular weights of 2000, 5000, and 30000 g/mol was calculated to be ~ 25%, ~20%, and ~9% using 2-mercaptobenzimidazole and adenine as model ligands. The effect of both reduced and oxidized protein cysteine residues on protein interactions with AgNPs was investigated. The model proteins included wild-type and mutated GB3 variants with 0, 1, or 2 reduced cysteine residues. Bovine serum albumin containing 34 oxidized (disulfide-linked) and 1 reduced cysteine residues was also included. Protein cysteine content that were found to have no detectable effect on kinetics of protein/AgNP binding. However, only proteins that contain reduced cysteine induced significant AgNP dissolution. We further demonstrated that organothiols can induce both AgNP disintegration and formation under ambient conditions by simply mixing organothiols with AgNPs or AgNO3, respectively. Surface plasmon- and fluorescence-active AgNPs formed by changing the concentration ratio between Ag+ and organothiol. Organothiols also induced AuNP formation by mixing HAuCl4 with organothiols, but no AuNP disintegration occured. Finally, we proposed that multicomponent ligand binding to AuNPs can be highly dependent on the sequence of ligand mixing with AuNPs. Quantitative studies revealed that competitive adenine and glutathione adsorption onto both as-synthesized and PEG-SH functionalized AuNPs is predominantly a kinetically controlled process. Besides providing new insights on multicomponent ligand interactions with colloidal AuNPs and AgNPs, this study opens a new avenue for fabrication of novel nanomaterials in biological/biomedical applications.

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This thesis reports on the synthesis, characterisation, enantiomeric resolution, 1H NMR structural study and physical evaluation of a series of certain bidentate ligand metal complexes, where ‘L-L’ denotes the ancillary bidentate ligand and ‘intercalator’ indicates the intercalating bidentate ligand. The L-L series varies in size and shape. Results of many tests and projects conducted are explained in detail. / Master of Science (Hons)

Six novel platinum(II) intercalators of the form [Pt(AL)(IL)]Cl2, where AL = ethylenediamine (en), 1R,2R-diaminocyclohexane (R,R-dach), or 1S,2S-diaminocyclohexane (S,S-dach) and IL = 4,7-dihydroxy-1,10-phenanthroline (4,7-dhp) or 4,7-dicarboxy-1,10-phenanthroline (4,7-dcp), were synthesised. All complexes were prepared by the addition of the intercalating ligand followed by the addition of the diamine ancillary ligand. The complexes with 4,7-dhp were soluble in DMSO and were characterised by 1H, 13C, and 195Pt NMR, elemental analysis, UV-vis, ESI-MS, and CD. The complexes with 4,7-dcp were only soluble in a highly acidic solution and, therefore, were characterised only by 1H NMR and elemental analysis. The cytotoxicity of the 4,7-dhp complexes was tested in the L1210 murine leukaemia cell line. [Pt(S,S-dach)(4,7-dhp)]Cl2 showed an IC50 value of > 80 μM. The antitumour and antibacterial activities of all six complexes were tested in vitro using the Kirby-Bauer disc diffusion method with Staphylococcus aureus and Agrobacterium tumefaciens. The 4,7-dhp complexes showed no activity to these bacteria strains. The activities of the 4,7-dcp complexes were not able to be tested due to their solubility only in acidic solutions, which itself inhibits cell growth. The diffusion coefficients of the Pt(II) intercalators of the form [Pt(AL)(IL)]Cl2, where AL = en, R,R-dach, or S,S-dach and IL = phen, 4-mp, 4,7-dmp, 4,7-dhp, 4,7-dcp or 3,4,7,8-tmp and various starting materials used during the synthesis of these complexes were measured using pulsed gradient spin-echo (PGSE) NMR. The diffusion coefficients of both 4,7-dcp and [Pt(4,7-dcp)Cl2] were observed to be lower than other compounds with similar molecular weights indicating dimerisation of the compounds. The binding studies of the systems, [Pt(en)(phen)]Cl2 to (i) BSA, (ii) delipidated BSA, and (iii) d(GTCGAC)2 were studied using a simple two-site binding model with diffusion NMR. The binding of [Pt(en)(phen)]Cl2 – BSA was well described by the model giving the values Kd = 0.0021 ± 0.0002 M and n = 5.85 ± 0.31. On the contrary, the binding of [Pt(en)(phen)]Cl2 – delipidated BSA showed a poor fit to the model. From the poor fit of the data, it was speculated that the transverse relaxation of BSA largely affected the system. The binding of [Pt(en)(phen)]Cl2 – d(GTCGAC)2 showed results where the diffusion coefficient decreases as the concentration of the drug increases but an opposite effect was observed from the point where the drug reached equimolar concentrations to d(GTCGAC)2. It was speculated that the drug undergoes allosteric binding to the biomolecule or that a conformational change occurred as the drug concentration increases in the system. A further study of [Pt(en)(phen)]Cl2 and K2PtCl4 using 195Pt diffusion NMR was conducted giving a diffusion coefficient of 3.08 ± 0.04 × 10-10 m2 s-1 for K2PtCl4. The diffusion coefficient of [Pt(en)(phen)]Cl2, however, were unobtainable due to the short transverse relaxation of the Pt complex. / Master of Science (M.Sc.) (Hons)

Protein-ligand and protein-protein interactions are critical to cellular function. Most cellular metabolic and signal tranduction pathways are influenced by these interactions, consequently molecular level understanding of these associations is an important area of biochemical research. We have examined the thermodynamics of several protein-protein associations and the protein-ligand interactions that mediate them. Using Fluorescence Correlation Spectroscopy, we have examined the putative interaction between pig heart malate dehydrogenase (MDH) and citrate synthase (CTS). We demonstrate a specific, low-affinity interaction between these enzymes. The association is highly polyethylene glycol (PEG)-dependent, and at high concentrations of NaCl or PEG, non-specific aggregates are formed. We demonstrate that oxaloacetate, the intermediate common to both CTS and MDH, induces the association at concentrations below the Km of CTS, suggesting that the open conformation of CTS is involved in the association. Using several biophysical techniques, we have examined the subunit associations of B. stearothermophilus phosphofructokinase (PFK). We demonstrate that the inhibitor bound conformation of the enzyme has reduced subunit affinity. The kinetics and thermodynamics of the phosphoenolpyrvuate (PEP)-induced dissociation of PFK have been quantified. Binding substrate, fructose-6-phosphate (F6P), stabilizes the enzyme to inhibitor-induced dissociation by 132-fold. These data suggest that subunit associations may play a role in the allosteric inhibition of PFK by PEP. The thermodynamics of the protein-ligand associations and allosteric inhibition of E. coli phosphofructokinase have been examined using intrinsic fluorescence and hydrostatic pressure. Both ligand-binding affinity and PEP inhibition are diminished by pressure, whereas substrate-binding affinity for inhibitor-bound enzyme is pressure-insensitive. Larger entropic than enthalpic changes with pressure lead to the overall reduction in free energies. Using a fluorescence-based assay, we have developed a series of baroresistant buffer mixtures. By combining a buffer with acid dissociation of negative volume with a buffer of positive volume, a pressure-resistant mixture is produced. Alteration of the molar ratio of the two component buffers yields mixtures that are pressure-insensitive at pH values around neutrality.

Title from title page of PDF (University of Missouri--St. Louis, viewed March 3, 2010). Vita. Includes bibliographical references (p. 109-113).

Many anticancer and antibacterial therapies are based on the interaction of small molecule drugs with DNA. Increasing interest in the development of DNA-interactive agents has fostered the need for sensitive and versatile analytical techniques that are capable of characterizing the DNA/ligand interactions and are compatible with librarybased screening methods. Electrospray ionization mass spectrometry (ESI-MS) has emerged as a useful technique for the analysis of non-covalent complexes formed between DNA and small molecules due to its low sample consumption and fast analysis time. The work presented in this dissertation is aimed at exploring, optimizing, and validating ESI-MS methods for characterizing DNA-ligand interactions. ESI-MS is first used to assess the binding of threading bis-intercalators to duplexes containing different sequences to determine high affinity binding sites of the ligands. Preliminary DNAse footprinting experiments identified possible specific binding sites of the ligands and ESI-MS experiments revealed that the ligands bound to DNA duplexes containing the respective specific binding sequences. The metal-mediated binding of benzoxazole ligands with different side chains to duplex DNA is also examined. Cu²⁺ and Ni⁺ were found to promote the most dramatic increase in ligand binding, and ligands exhibiting the most dramatic metal-mediated or metal-enhanced binding were also determined to be the most cytotoxic. The quadruplex DNA binding selectivity of perylene diimides is evaluated by screening the binding of the ligands to quadruplex, duplex and single strand DNA by ESI-MS. Three ligands, one containing basic side chains, one containing anionic sidechains, and one benzannulated compound were determined to be the most-quadruplex selective. The ESI-MS results correlated well with spectroscopic experiments. The relative gas-phase stabilities of different quadruplex DNA structures were investigated using molecular dynamics simulations and ESI-MS. The stabilities from the E[subscript 1/2] values generally paralleled the RMSD and relative free energies of the quadruplexes based on MD energy analysis. Finally an ESI-MS technique employing the KMnO₄ reaction with DNA to determine conformational changes to the duplex structure upon ligand binding is detailed. Thymines in most intercalator/duplex complexes are more susceptible to oxidation by KMnO₄ than those in duplex DNA. CAD and IRMPD experiments are used to identify the site of oxidation. / text

Not available / text

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.