Antibacterial growth effects and speciation of several vanadium salts and complexes
Date
2023
Journal Title
Journal ISSN
Volume Title
Abstract
Vanadium (V) is a first-row transition metal ion that acts as a phosphatase inhibitor with a wide variety of biochemical and physiological functions. The ability of vanadium to form stable polyoxovanadates (POVs) and organometallic complexes has attracted attention for studying the properties and effects of these compounds in various biological systems. In my research, I used the bacterium species Mycobacterium smegmatis (M. smeg), which has undergone reclassification and is now classified as Mycolicibacterium smegmatis. Despite the taxonomic change, both the previous and current classifications use the same abbreviation, M. smeg. I also carried out some studies in Mycobacterium tuberculosis (M. tb). In my work, I explored the properties of several types of vanadium compounds including salts, oxometalates, and coordination complexes to investigate how they impact cellular growth. The first chapter of this dissertation focuses on determining the growth inhibitory effects of decavanadate (V10) and rapidly exchanging oxovanadates on the growth of two mycobacterial species: M. tb and M. smeg. Speciation analysis, utilizing 51V NMR spectroscopy, was employed to document that one specific oxometalate exhibits greater potency as a growth inhibitor for these mycobacterial species compared to other oxovanadates, indicating selectivity in its cellular interaction. Oxometalates have been involved in numerous applications in biological and medical studies, including their ability in addressing the phase-problem in X-ray crystallography of the ribosome. This study investigated the effect of different vanadate salts on the growth of M. smeg and M. tb, highlighting the critical role of speciation in the observed growth inhibition. Specifically, the large orange-colored sodium decavanadate (V10O286−) anion was found to be a stronger growth inhibitor for these bacteria compared to the colorless oxovanadate derived from sodium metavanadate. The 51V NMR spectroscopy and speciation calculations were employed to monitor the vanadium(V) speciation in the growth media and its conversion among species under growth conditions. Our results show that the decavanadate was 200-20 times more potent in inhibiting growth dependent the consideration of molecules or total vanadium content. The findings presented in this work are particularly important in the context of the numerous applications of polyoxometalates in biological and medical studies. The second chapter focuses on investigating the inhibitory effects of two monosubstituted decavanadates (V10): monoplatino(IV)nonavanadate(V) ([H2PtIVV9O28]5−, V9Pt), and by MoIV in monomolybdo(VI)nonavanadate(V) ([MoVIV9O28]5−,V9Mo) on the growth of M. smeg. The inhibitory effects of V9Pt and V9Mo were examined against the growth of M. smeg with EC50 values of 0.0048 mM and 0.015 mM, respectively. These values were compared to the reported inhibitory value of decavanadate ([V10O28]6−/[HV10O28]5−, V10) on M. smeg (EC50 = 0.0037 mM). Time-dependent 51V NMR spectroscopic studies were carried out for all three polyanions in aqueous solution, biological medium (7H9), and heated and non-heated supernatant. These studies aimed to evaluate their stability in their respective media, monitor their hydrolysis over time to form different oxovanadates, and calculate the corresponding EC50 values. The results presented in this study indicate that the two related derived decavanadate derivatives (V9Pt and V9Mo) and V10 exhibited greater potency as growth inhibitors of M. smeg, compared to monomeric vanadate (V1). The spectroscopic characterization conducted in the growth medium led to the conclusion that both the decavanadate structure and its properties play significant roles in their growth effects. In the third chapter in this dissertation, we investigated the growth effects of an anticarcinogenic non-toxic Schiff base oxidovanadium(V) complex (N-(salicylideneaminato)-N'-(2-hydroxyethyl) ethane-1,2-diamine) coordinated to the 3,5-di-tert-butylcatecholato ligand on a representative bacterium, M. smeg.. In addition, we synthesized a series of the Schiff base V-complexes based on previously reported methods and examined the effect of complexes as well as the free catecholates on the bacterial growth. To determine the inhibition activity of these complexes on M. smeg., the biological studies were complemented by spectroscopic studies using UV-Vis spectrophotometry and NMR spectroscopy. These spectroscopic studies determine which complexes remained intact under biologically relevant conditions. In this work, we examine (1) the growth effects of Schiff base oxidovanadium complexes coordinated to a catechol, (2) the growth effects of the respective free catecholates on M. smeg., and (3) the effects of the scaffold. These studies allowed us to demonstrate that some metal coordination complex exhibited greater potency than the ligand alone under biological conditions, whereas others showed greater effects of the free catecholate ligand and in one case the effects were similar of complex and catecholate ligand. The findings from these studies revealed that the observed effects of the Schiff base V-catecholate complex were influenced by the properties of the catechol, including toxicity, hydrophobicity, and steric factors. Finally, the fourth chapter presents preliminary research data on the antimicrobial effects of two pseudospherical mixed-valence polyoxovanadates (MV-POVs), namely K(NH4)4[H6PVIV2VV12O42]·11H2O (V14) and (Me4N)6[VIV8VV7O36(Cl)] (V15) on the growth of M. smeg. These MV-POVs showed complex effects on cell growth, as many of these systems are not stable under biological conditions. To investigate the vanadium(V) speciation in aqueous solutions and growth media, as well as to monitor any conversion among species under growth conditions, 51V NMR spectroscopy was employed. The 51V NMR spectra revealed some hydrolysis and more extensive oxidation of vanadium(IV) in V14 compared to V15 in both aqueous solutions and media. The studies show that both MV-POVs are effective growth inhibitors. The combined findings from the studies described in all the chapters of this dissertation indicate that the stability of the vanadium compound and its structure plays a significant role in the ability of the vanadium complexes to inhibit bacterial growth. These studies highlight the importance of speciation in the biological activity of vanadium complexes.
Description
Rights Access
Embargo expires: 08/28/2024.
Subject
catecholates
nuclear magnetic resonance (NMR) and UV-Vis spectroscopy
vanadium
Mycobcaterium tuberculosis
Mycobacterium smegmatis
antibacterial activities
speciation