Research in Chemistry
The great development of our understanding of transition metal catalysis in organic chemistry has opened a major avenue for invention of new processes and improvement of existing ones. Palladium enjoys two stable oxidation states, the +2 state and the Zerovalent state and it is the facile redox interchange between these oxidation states which is responsible for the rich reaction chemistry that palladium complexes display. More recently, it is found that potassium organotrifluoroborates show very high reactivity in palladium catalyzed cross-coupling reactions. Potassium organotrifluoroborate is very reactive, non-toxic, environmentally labile and water soluble organic species. In modern chemistry, it is novel and it has tremendous aspect in organic transformations and this field will be explored.
Three project abstracts
Anticancer drug discovery and development by chemical modification: This research has focus on the cytotoxic agents. The drug discovery paradigms selected agents that had significant cytostatic or cytotoxic activity on tumor cell lines. This will increase the possibility of finding selective anticancer drugs that eliminates the cytotoxic side effects associated with conventional cancer chemotherapy. Therefore the focus of this research is based on uncovering many novel molecular targets that are “cancer-specific”, which will allow the targeting of cancer cells while normal cells are spared. The chemical modification of conventional anticancer drugs is a practical approach to diminish their side effects by improving their cellular uptake.
Synthesis and application of phosphorylated nucleotides as anti-HIV agents: Anti-HIV nucleoside have limited cellular uptake due to the presence of negatively charged groups. On entering the cell, the majority of antiviral nucleosides are phosphorylated to monophosphate, diphosphate, and triphosphate forms, respectively, by cellular kinases to show activity. In attempts to bypass the first rate-limiting phosphorylation step in the metabolic conversion of nucleoside analogs, design and synthesis of the phosphorylated nucleoside prodrugs is the subject of this research. The main purpose of this research is developing phosphorylated multifunctional anti-HIV nucleoside analogs by combining agents having different mechanisms of action.
Synthesis and evaluation of modified oligodeoxynucleotides: During the past two decades, chemically modified oligodeoxynucleotides (ODNs) have received much attention in search for potential therapeutic and diagnostic agents and in the study of numerous biochemical and biological processes.To a great extent, these modifications have focused on replacing the phosphodiester group by phosphodiester mimics. Studies of the effects of backbone modifications on the conformational, physical and biological properties of nucleic acids are crucial importance in realizing the therapeutic goals. These studies can be feasible by new and improved methods for the solid phase synthesis of backbone modified ODNs. The long-term objective of this research is to synthesize of novel modified ODNs and oligomers with optimized bio-physical properties. The focus of this project is to synthesis and evaluate different classes of ODNs and oligomers containing novel linkages.
Oxy radicals, including superoxide anions, and oxidative stress may be key factors in the onset of certain diseases, including cancer (1). Oxy radicals, play important roles in the initiation, promotion and progression of carcinogenesis (1). It is considered that a significant event in oxy radical-mediated carcinogenesis is extensive oxidative damage to the nuclear fractions (2), which leads to deoxyribonucleic acid (DNA) damage such as DNA single-strand breaks and the enhancement of carcinogenesis (1). Thus, to prevent some cellular damage leading to cancer caused by oxy radicals, the level of tissue antioxidant is critical (1).
The flavonoids (Fig.1) have long been suggested to act as antioxidants, due to their radical-scavenging and metal-chelating capabilities. They are representatives of a multitude of phenolic compounds exclusively present in plants. They occur in fruits, vegetables, nuts, seeds and leaves. The average daily (Western) diet contains about 1 g of mixed flavonoids, an amount that might be sufficient to achieve pharmacologically significant concentrations in tissues. Di Carlo et al.(3) have recently suggested that, though vitamins A, C and E have been traditionally regarded as antioxidants in fruits and vegetables, there is a possibility that plant flavonoids show a protective effect against oxidative DNA damages caused by not only gamma-ray radiation but also UV irradiation, chemicals and endogenous oxidative stress. Secondly, the above authors indicated that, flavonoids are capable of modulating the activity of enzymes and affect the behavior of many cell systems, suggesting that the compounds may possess significant antihepatoxic, antiallergic, anti-inflammatory, antiosteoporotic and even antitumor activities. Pharmacological doses of vitamins E, C and b-carotene sometimes have beneficial, but often also no effect or harmful effects, so that, for a more reliable antioxidant action, adequate dietary supply of a mixture of flavonoids seems preferable (4). Our laboratory is currently involved in studies aimed at:
1. The potential use of the flavonoids (i.e., kaempferol, quercitin, luteonin, genistein and eridictyol) as antioxidants against prooxidants (e.g., Heavy Metals & Enediynes, peroxynitrate etc.) We are currently concentrating our efforts on copper (Cu) and iron (Fe) induced oxidative DNA damage under in vitro conditions. Cu and Fe are physiologically important metals that may play a significant role in the endogenous oxidative DNA damage involved in aging and cancer (5). These metals have been classified as tumor promoters due to their ability to generate high levels of reactive oxygen species (ROS). The major intracellular ROS are superoxide anion radical (O2.-), hydrogen peroxide (H2O2) and hydroxyl radical (.OH). H2O2, in the presence of a transition metal such as Fe2+ or Cu+, produces .OH via the fenton reaction (5). The .OH radical is the most electrophilic radical that DNA is exposed to (5), causing a large number of lesions that include strand breaks and oxidized bases (e.g., the formation of 8-hydroxyguanine), that are involved in carcinogenesis. The significance of this work is that it will reveal a novel route to the prevention of heavy metal oxidation and intoxication using flavonoids.
2. The use of flavonoids against the formation of endogenous DNA adducts (Fig. 2) resulting
from oxidation by the said metals. The hypothesis to be tested is that, the above metals can cause abstraction of hydrogens from deoxyribose of DNA to produce products (e.g., the formation of furfural and 5'-nucleoside aldehyde) which can react with DNA, and thus serve as a source of endogenous DNA adducts. We will investigate the potential use of the flavonoids against the formation of these products. The levels of base adducts following exposure to these metals will be monitored by reverse phase high pressure liquid chromatography (RP-HPLC). We believe that, our studies will reveal a more concise picture of how flavonoids control endogenous adduct formation than our current understanding.
Information on the potential use of flavonoids as either antioxidants or supplements is essential to health especially for the elderly.
1. Yano, T., Ishikawa, G., and Ichikawa, T. (1993) Is vitamin E a useful agent against oxy radical-promoted lung tumnorigenesis in ddY mice? Carcinogenesis 14, 1133-1136.
2. Floyd, R. A. (1990) The role of 8-hydroxyguanine in carcinogenesis. Carcinogenesis, 11, 1447-1450.
3. Di Carlo, G., Mascolo, N., Izzo, A. A. and Capasso, F. (1999) Flavonoids: old and new aspects of a class of natural therapeutic drugs. Life Sci. 65, 337-353.
4. Hassig, A., Liang. W. X., Schwabl, H. and Stampli, K. (1999) Flavonoids and tannins: plant-based antioxidants with vitamin character. Med. Hypothesis 52, 479-481.
5. Kennedy, L. J., Moore Kenneth Jr., Caufield, J. L., Tannenbaum, S. R., and Dedon, P. C. (1997) Quantitation of 8-oxoguanine and strand breaks produced by four oxidizing agents. Chem. Res. Toxicol. 10, 386-392.
Dr. Theodore Duello
Dr. Duello's research interests are in Analytical Environmental Contaminants and Environmental Methods. Presently, work with Gas-Chromatography utilizing Electron Capture Detection for the pollutant, Pentachlorophenol in various matrices including biological materials is of most interest.
The primary focus of Dr. Guha's research is the use of theoretical methods to investigate the structures, spectroscopy, energies, and kinetics of complexes and transition states involved in novel catalytic reactions occurring between free radicals and molecules in the Earth's atmosphere. Free radicals play important roles in various oxidation processes, and it is critical to determine their reaction mechanisms. Of particular importance are the radicals that are produced by photodecomposition during catalytic cycles involving hydrogen, halogen, oxygen, sulfur, carbon, and nitrogen families, as they affect the presence of the ozone layer in the upper atmosphere. Information regarding the reactivity of radicals is important for determining the pathways by which multi-step atmospheric reactions occur. Dr. Guha is interested in analyzing the photochemistry of small molecules in order to understand the reaction mechanisms of upper atmospheric species that have not yet been addressed. The information gained from such studies can be used in developing predictive models of the gas-phase reactivity of atmospheric species.
Dr. Guha's areas of interest (major themes) are: (A) Complex formation in atmospheric reactions, (B) Kinetics of atmospheric reactions, and (C) Excited state photochemistry of atmospheric species. Progress in each of these areas is essential to understanding the occurrence of chemical processes in the atmosphere and their implications. Such studies are performed by using computational programs such as GAUSSIAN and MOLPRO and applying state-of-the-art ab initio molecular orbital computational methods, such as Moeller-Plesset, coupled-cluster, and quadratic configuration quantum mechanical methods in conjunction with sophisticated basis sets, depending upon the size and complexity of the processes.
The application of high-level computational techniques to study gas-phase reactions represents a novel approach that provides new insights into the fundamental details of reactivity of atmospheric species. Through these studies, the chemistry of atmospheric oxidation processes can be probed into, and their influence on the existence of life on Earth assessed. The results of Dr. GuhaÃ¢â‚¬â„¢s work prove to be invaluable in aiding experimental analysis and can be used as input into chemical models to address critical issues such as global warming and ozone depletion.
Synthesis and Characterization of New Schiff bases: There is a continuing interest in the design and synthesis of molecules that efficiently bind to DNA and cleave it. In particular, the study of organic chelating agents containing nitrogen and sulfur as the donor atoms and their metal complexes has become a subject of intensive investigation. In this regard, the use of bidentate NN chelating agents such as 1, 10-phenanthroline (phen) has played an important role in synthetic and medicinal chemistry. 1,10-Phenanthroline has also been used extensively as a ligand in both analytical and preparative coordination chemistry as well as in the preparation of many mixed-ligand complexes. 1,10- Phenanthroline and ligands derived from it as well as some of their metal complexes have also been found to be widely used in areas such as molecular catalysis, solar energy conversion, calorimetric analysis, herbicides, molecular recognition, self-assembly, antineoplastic agents, and nucleic acid probes. It has been found that Schiff bases formed by condensation of S-alkyl/aryl esters of dithiocarbazaic acid with heterocyclic aldehydes and ketones contain both ‘hard’ nitrogen and ‘soft’ sulfur donor atoms. Consequently, they are capable of forming stable complexes with a wide variety of metal ions, some of which have also been found to exhibit interesting physico-chemical properties and potentially useful chemotherapeutic properties.
Since organic and polymeric magnets offer advantages over traditional magnets because of the diversity of their structures, low density, low magnetic loss and process of preparation without metallurgy at high temperature, studies involving the synthesis of Schiff bases using 1,10-phenanthroline-2,9-dicarboxaldehyde and sulfur-containing primary amines deserve more attention. We, therefore, have undertaken the synthesis and characterization of new Schiff bases formed from 1,10-phenanthroline-2,9-dialdehyde and some sulfur-containing amines.
Synthesis of Curcumol: Curcuma wenyujin was used in traditional Chinese medicine for the treatment of various cancers including cervical carcinoma, vulva cancer, skin neoplasm, thyroid tumor, esophageal neoplasm, gastric, and intestinal cancer. Curcumol, one of the major components of the essential oil with the structure of sesquiterpene hemiacetal was found to have obvious anti-tumor activity. The structure of Curcumol has been established in 1965, and later it’s stereostructure was confirmed by X-ray analysis in 1984. This compound showed a very strong toxicity (ID50 of rats is 250mg/kg). Thus further structural modifications of curcumol to generate new analogs with increased water solubility, improved bioactivity and less toxic may provide high utility in cancer and other diseases treatment. Several metabolites from microbial transformation of curcumol has been isolated and structures were determined. [Chem Pharm Bull., 55(3) 451-454 (2007)]. Bioactivity of these metabolites has not yet been studied. We propose here a flexible synthetic route to these compounds which would allow us to synthesize a variety of these groups of compounds by slight modification of the starting materials.
Cembranoid Natural Products: Cembranoids are 14-membered ring containing diterpenes, found in marine invertebrates as well as in some plants and insects. Cembranoid diterpenes have been found to have a variety of biomedical applications, and hence synthetic investigations of these compounds have been carried out by many groups. A convergent retrosynthetic strategy has played a key role in designing the synthetic strategy of the Cembranoid key structure in our study. Few interesting reactions are planned to construct the key structure of Cembranoid. The detailed forward synthesis of these substructures and finally to target compound are planned.
Dr. Moore's research interests lie in the areas of synthetic inorganic chemistry, materials chemistry, and nanomaterials. The research efforts in Dr Moore's laboratory center on the synthesis of novel inorganic materials at both the macro- and nano-scales. A fundamental theme present in this research effort is the use of chemically "soft" methods (i.e. solution-based, room temperature, or low temperature routes) for material preparation. Several specific areas are of interest:
Ceramic Nanocomposite Materials
Sol-gel chemistry is a facile, solution-based method for the preparation of metal oxide materials, and composite materials thereof. Research in this area focuses on the covalent incorporation of nanocrystal precursors into a ceramic, sol-gel matrix. Thermal treatment of these intermediate precursor/ceramic composites yields nanocomposites consisting of nanocrystals of a desired material widely dispersed throughout a ceramic matrix.
Optical Materials (Rare-Earth Molybdates and Rare-Earth Oxides)
Materials having the basic formula Re2(MoO4)3, where Re = rare earth (lanthanide) ion, have interesting optical properties. These materials are luminescent and may also possess non-linear optical properties (second harmonic generation). Enhancement of the optical properties of these materials may be achieved by restricting the Re2(MoO4)3 materials to the nano size regime. Preparation of these nanomaterials will be prepared using water-in-oil microemulsions (aqueous “nano-reactors") to facilitate the production of Re2(MoO4)3 nanoparticles.
Metal sulfides are a technologically important class of materials with applications ranging from light harvesting components in solar cells to catalysis to solid-state lubrication. Research in this area will probe new methods for the room temperature or low temperature preparation of various metal sulfides, including pH dependant decomposition of molecular precursors and “thio" sol-gel reactions.
Nsoki Phambu obtained a BS in physical chemistry from Denis Diderot University (Paris VII), followed by a MS and PhD in chemistry and molecular physical chemistry at Henri Poincare University of Nancy in France. In 1999, Dr. Phambu joined the faculty in the department of Natural Sciences at Johnson C. Smith University, Charlotte NC. In 2004, Dr. Phambu joined the faculty in the department of chemistry at Tennessee State University. His research interests include investigating the interactions between different biological systems and membrane constituents, with special emphasis on the role of endogenous/exogenous metal ions. Biophysical approaches such as Raman (main tool), infrared (IR), circular dichroism (CD), NMR, fluorescence, UV visible and scattering techniques are employed. Current research projects are:
A. Interactions between antimicrobial peptides and model membranes in the presence of metal ions
The objective is to investigate the effect of metal ion binding on the secondary and tertiary structure of antimicrobial peptides in the presence and absence of phospholipids using infrared, Raman, CD, UV visible, and fluorescence techniques as well as NMR. Several spectroscopic techniques such as IR, Raman, NMR, fluorescence, and UV visible techniques are used in a complementary way to discern structural changes in both antimicrobial peptides and phospholipid membranes in the presence of selected cations.
B. Identification and mapping of compounds such as pharmaceuticals, proteins, vitamins, carbohydrates in natural products or biological samples using Raman microspectroscopy.
Trends in analytical chemistry are towards simple and less time consuming analytical methods. We propose the use of Raman + infrared spectroscopes to fully characterize the components of natural products or any biological samples. The objective of this work is to identify the biomolecules present in a natural product or biological sample. The targeted biomolecules are proteins, carbohydrates, lipids, etc.. The conformation of proteins is determined using the decomposition of the infrared amide I band (self-deconvolution, second derivative enhancements techniques and curve-fitting procedures) and the special (physical) distribution of the biomolecules in natural products or biological samples is obtained using Raman spectral imaging.
General research area: Drug Design, Synthesis and Computational Chemistry
The development of small organic molecules with potential to impact human health and disease is an area of significant interest in the department. Medicinal chemistry involves organic synthesis, as well as studies designed to understand the molecular basis of drug action. Research studies in the Okoro’s group generally begins with lead compound discovery either by virtual screening, natural product isolation or by simplification of existing drugs to identify the essential pharmacophores. Next, analogs of the lead are synthesized for structure-activity relationship studies and compound optimization. In addition, molecular modeling studies are carried out to find out how the lead compounds interact with the intended macromolecular target. In particular, docking experiments are heavily used, since biochemical assay results show the highest correlation with computational drug design methods, such as docking;
bindingEscore α lnKI
Ongoing projects cover a broad spectrum of interests, such as the chemistry of fluorinated cyclic β-diketones as building block for heterocyclic synthesis, topoisomerase II poisons/catalytic inhibitors, anticonvulsant drug synthesis, and enzyme inhibitors for CDK5, Hsp90, Akt, and 4-HPPD.
Project: Container Molecule
This project focuses on the design and synthesis of molecules containing inner space, so called "container molecules". These molecules will be able to accommodate smaller molecules.
These are potential candidates for fuel (hydrogen) storage molecules. Their storage capacity when tuned with their binding affinity gives them their scavenging capability, which could potentially be used for absorbing toxic organic molecules and/or heavy metals. The target molecules are designed using economic building blocks (both yield and cost wise). The candidacy of the building block will be evaluated by economic computational studies. Organic, inorganic and organometallic chemistry are the synthetic tools for the target molecules. Characterization/analysis tool includes: infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet/visible spectroscopy, powder and single crystal X-ray diffraction studies.
This project involves the synthesis and functionalization of nanoparticles (magnetic). These nanoparticles will be functionalized with the container molecules. These modified nanoparticles will be used to fish out any toxic/environmentally hazardous material.
Project: Sensor Device
Molecules that can accommodate other smaller molecules serve as an antenna for certain kind of molecules. These antenna molecules when tethered to a surface, prepares the base for a sensor device. Surface spectroscopy serves as the output component for the sensor device.
Human natural killer (NK) lymphocytes play a central role in immune defense against viruses and tumors. NK cells are capable of killing (lysing) tumor cells and virally infected cells. They are responsible for limiting the spread of blood-borne metastases as well as limiting the development of primary tumors. Any agent that interferes with the ability of NK cells to lyse their targets could increase the risk of tumor incidence and/or viral infections. Studies in our laboratory have assessed the capacity of a variety of compounds, known to contaminate the environment, to interfere with this crucial immune function. Compounds found to interfere with the immune function of the NK cell are further examined for their capacity to alter the biochemical pathways needed by the NK cell to carry out its functions. This involves monitoring the effects of the compound on the expression of particular proteins such as those involved in the killing (lysis) of tumor and viral cells, granzyme B and perforin, as well as cell-surface proteins required for binding to tumor and virally-infected cells. Additionally, enzymes known to be important in regulating the lytic process such as protein tyrosine kinases, phospholipase C gamma, protein kinase C, and mitogen activated protein kinases (MAPK) are examined for changes in response to these compounds. To date we have screened more than 40 compounds for their ability to interfere with NK cell function and have found 19 compounds that interfere with function.
Department of Chemistry