The thesis presents synthesis and characterization of a family of low valent (PDI)Mn complexes. Detailed electronic structure evaluation from spectroscopic and crystallographic data revealed electron transfer from the reduced metal center to the accessible ligand orbitals. One particular (PDI)Mn variant, (5-Ph2PPrPDI)Mn has been found to be the most efficient carbonyl hydrosilylation catalyst reported till date, achieving a maximum turnover frequency of up to 4950 min-1. This observation demanded a thorough investigation of the operative mechanism. A series of controlled stoichiometric reactions, detailed kinetic analysis, and relevant intermediate isolation suggest a mechanism that involves oxidative addition, carbonyl insertion, and reductive elimination. Noticing such remarkable efficiency of the (PDI)Mn system, it has been tested for application in renewable fuel generation. A modest efficiency for H2 production at an apparent pH of 8.4 have been achieved using a cationic Mn complex, [(Ph2PPrPDI)Mn(CO)]Br. Although, a detailed mechanistic investigation remained challenging due to complex instability, a set of relevant Mn(-I) intermediates have been isolated and characterized thoroughly.
The dissertation also includes synthesis, characterization, and electronic structure evaluation of a series of Triphos supported iron complexes. Using this pincer chelate and either 2,2’-bipyridine (bpy) or 1,3,5,7-cyclooctatetraene (COT), a set of electronically interesting complexes have been isolated. Detailed electronic structure investigation using spectroscopy, magnetometry, crystallography, and DFT calculations revealed redox non-innocent behavior in the Bpy and COT ligands. Additionally, CO binding to the (Triphos)Fe system followed by reaction with borohydride reagents allowed for the isolation of some catalytically relevant and reactive iron hydride complexes.
Background: Staphylococcus aureus and S. epidermidis biofilms differ in structure, growth and regulation, and thus the high-throughput method of evaluating biofilm susceptibility that has been published for S. epidermidis cannot be applied to S. aureus without first evaluating the assay's reproducibility and reliability with S. aureus biofilms.
Methods: Staphylococcus aureus biofilms were treated with eleven approved antibiotics, lysostaphin, or Conflikt®, exposed to the oxidation reduction indicator Alamar blue, and reduction relative to untreated controls was determined visually and spectrophotometrically. The minimum biofilm inhibitory concentration (MBIC) was defined as ≤ 50% Alamar blue reduction and a purple/blue well 60 min after the addition of Alamar blue. Because all of the approved antibiotics had MBICs >128 μg/ml (most >2048 μg/ml), lysostaphin and Conflikt®, with relatively low MBICs, were used to correlate Alamar blue reduction with 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction and viable counts (CFU/ml) for S. aureus ATCC 29213 and three clinical isolates. Alamar blue's stability and lack of toxicity allowed CFU/ml to be determined from the same wells as Alamar blue absorbances.
Results: Overall, Alamar blue reduction had excellent correlation with XTT reduction and with CFU/ml. For ATCC 29213 and two clinical isolates treated with lysostaphin or Conflikt®, Alamar blue reduction had excellent correlation with XTT reduction (r = 0.93-0.99) and with CFU/ml (r = 0.92-0.98). For one of the clinical isolates, the results were moderately correlated for Conflikt® (r = 0.76, Alamar blue vs. XTT; r = 0.81, Alamar blue vs. CFU/ml) and had excellent correlation for lysostaphin (r = 0.95, Alamar blue vs. XTT; r = 0.97, Alamar blue vs. CFU/ml).
Conclusion: A reliable, reproducible method for evaluating biofilm susceptibility was successfully applied to S. aureus biofilms. The described method provides researchers with a simple, nontoxic, relatively inexpensive, high throughput measure of viability after drug treatment. A standardized biofilm Alamar blue assay should greatly increase the rate of discovery of S. aureus biofilm specific agents.