Andriy Durygin

Tetragonal to orthorhombic phase transition of ammonia borane at low temperature and high pressure

The effect of pressure on the low temperature tetragonal (I4mm) to orthorhombic (Pmn21) phase transition of a potential hydrogen storage compound ammonia borane (NH3BH3) was investigated in diamond anvil cell using Raman spectroscopy. With applied pressure, the transition occurs at higher temperature, which indicates that pressure enhances the ordering of the structure. The positive Clapeyron slope of the transition was determined to be dP/dTu2009=u2009∼25.7u2009MPa/K, indicating the transformation is of exothermic. Appearance of some of the characteristic Raman modes of orthorhombic phase requires undercooling of around ∼15 K below the transition, indicating possible existence of an intermediate phase.

An experimental investigation of mesoporous MgO as a potential pre-combustion CO2 sorbent

We examined the CO2 capture capacity of mesoporous MgO (325 mesh size, surface areaxa0=xa095.08xa0±xa01.5xa0m2/g) as a potential pre-combustion CO2 sorbent. Our results show that 96.96xa0% of MgO was converted to MgCO3 at 350xa0°C and 10xa0bars CO2 pressure. The sorbent could be completely regenerated at 550xa0°C under argon flow. The sorption rate parameters such as surface area and pore size were investigated.

Characterization of Nanodiamond-based anti-HIV drug Delivery to the Brain

Human Immunodeficiency Virus Type 1 (HIV-1) remains one of the leading causes of death worldwide. Present combination antiretroviral therapy has substantially improved HIV-1 related pathology. However, delivery of therapeutic agents to the HIV reservoir organ like Central nervous system (CNS) remains a major challenge primarily due to the ineffective transmigration of drugs through Blood Brain Barrier (BBB). The recent advent of nanomedicine-based drug delivery has stimulated the development of innovative systems for drug delivery. In this regard, particular focus has been given to nanodiamond due to its natural biocompatibility and non-toxic nature–making it a more efficient drug carrier than other carbon-based materials. Considering its potential and importance, we have characterized unmodified and surface-modified (-COOH and -NH2) nanodiamond for its capacity to load the anti-HIV-1 drug efavirenz and cytotoxicity, in vitro. Overall, our study has established that unmodified nanodiamond conjugated drug formulation has significantly higher drug loading capacity than surface-modified nanodiamond with minimum toxicity. Further, this nanodrug formulation was characterized by its drug dissolution profile, transmigration through the BBB, and its therapeutic efficacy. The present biological characterizations provide a foundation for further study of in-vivo pharmacokinetics and pharmacodynamics of nanodiamond-based anti-HIV drugs.

High pressure Raman and x-ray diffraction studies on the decomposition of tungsten carbonyl

Polycrystalline tungsten hexacarbonyl, W(CO)6, was studied using in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD) at high pressures up to 60 GPa in a diamond anvil cell. High pressure causes collapse of the Oh molecular symmetry in W(CO)6 leading to decomposition of the carbonyl compound. The decomposed material has characteristic of δ(OCO), v(C=C), v(C=O), and adsorbed CO Raman features. High pressure XRD results showed the irreversible amorphization of tungsten hexacarbonyl. A solid state vibrational coupling mechanism is proposed to explain the formation of δ(OCO) units. Further, the high pressure Raman results of W, Mo, and Cr hexacarbonyls are compared and the breakdown of the Dewar-Chatt-Duncanson model in this family is qualitatively discussed.