Quantum Impurity Rotator in a Matrix of Quantum Rotors: Electron Paramagnetic Resonance Dynamics of CH3 in Solid CD4 Matrix.

The rotational dynamics and the geometry of a light and flexible impurity molecule like methyl, matrix isolated in van der Waals solid, are supposed to be sensitive to the host molecule dynamics and order alterations of the matrix. In addition, the location of the impurity and its interaction with the matrix molecules is of prime importance. Large energy gaps between rotation levels of quantum rotators allow precise investigation of temperature-assisted quantum tunneling effects. The molecular rotation of methyl radicals isolated in the deuterated solid methane isotopomer, CD4, was investigated both by experimental and theoretical electron paramagnetic resonance (EPR) methods. The reduction of the quantum rotation frequency evident from the EPR spectrum of methyl radical at liquid-He temperatures was explained and connected to the irregular ratio of the central doublet to the outer quartet hf transitions. The involvement of temperature in the alteration of methyl symmetry between the C3 and D3 groups and the molecular host-host and guest-host interaction strengths were also examined by constructing temperature profiles of the rotation correlation times in the three phases of solid methane. The present study proves the deep impact that a van der Waals matrix may have on the geometry and the rotation levels of a substitutionally trapped quantum impurity rotor, effects that are yet very little known. This close correlation between dynamics of an impurity particle and the matrix molecules has great potential in developing sensitive physicochemical probes for van der Waals solids.

Conformation and bioactivity. Design and discovery of novel antihypertensive drugs.

Peptidomimitism is applied to the medicinal chemistry in order to synthesize drugs that devoid of the disadvantages of peptides. AT1 antagonists constitute a new generation of drugs for the treatment of hypertension designed and synthesized to mimic the C-terminal segment of Angiotensin II and to block its binding action on AT1 receptor. An effort was made to understand the molecular basis of hypertension by studying the conformational analysis of Ang II and its derivatives as well as the AT1 antagonists belonging to SARTANs class of molecules. Such studies offer the possibility to reveal the stereoelectronic factors responsible for bioactivity of AT1 antagonists and to design and synthesize new analogs. An example will be given which proves that drugs with better pharmacological and financial profiles may arise based on this rational design.