NMR spectroscopy is a very powerful technique for the characterization of structure and dynamics of a variety of systems starting from small organic molecules to large biological macromolecules. In solids, the study of protons becomes more interesting because they are very sensitive to inter-molecular packing and are directly involved in hydrogen-bonding and aromatic π-π interactions, etc. The present thesis is devoted essentially to utilizing information from proton resonances obtained using multinuclear and multiple-quantum approaches. The thesis has two parts. The first part deals with methodological developments in the area of solid-state NMR, relevant to the study of rigid powder samples as well as partially ordered liquid crystalline materials. Methods have been proposed to investigate the structure of small molecules at moderate spinning frequencies and thermotropic liquid crystals at static conditions. Proton detected heteronuclear experimental methods based on both first and second-order cross polarization at moderate and ultra-fast magic angle spinning rates are also proposed. The second part of the thesis deals with the application of both newly proposed and existing solid state NMR methods to the study of several biologically relevant systems. These include the study of several designed as well as naturally occurring peptides. The use of first-principles calculations based on GIPAW method for supporting the experimentally obtained results has also been made. The thesis is divided into five chapters. In the second chapter, a new pulse sequence to correlate Double Quantum (DQ) proton frequencies to carbon Single Quantum (SQ) chemical shifts in the solid state has been proposed. In this sequence, named as MAS-J-1H (DQ)-13C-HMQC, the correlation between 1H and 13C is achieved through scalar coupling, while the double-quantum coherence among protons is generated through dipolar couplings. This experiment is particularly suited for the study of 13C in natural abundance. The advantages of the technique with applications to alanine, histidine and a model liquid crystalline material have been demonstrated. The assignment of 13C spectra of partially ordered systems has also been considered. In this case the assignment of the spectrum is a major challenge due to the interplay of anisotropic order and chemical shift parameters. The DQ-SQ correlation experiment described in the thesis has been applied to a well known liquid crystal and also to a novel thiophene based liquid crystal and the local order parameters of the liquid-crystal have been obtained. The thesis also presents results on the azelaic acid -isonicotinamide co-crystal as well as the drug ibuprofen obtained by using novel methodologies. In the case of the former, the problem of overlap of resonances was overcome with the use of the REVERSE-CP approach to separate out the carbon attached protons from the rest of the protons. Subsequently, by the use of several combined approaches, the structural features were identified. A new heteronuclear correlation pulse sequence for solids under fast MAS conditions has also been tested. With low r.f powers, a second-order dipolar term mediated transfer of magnetization between I and S spin known as second order cross-polarization (SOCP) was exploited to obtain the entire spin system connectivity. Both carbon detected and proton detected experiments have been carried out and their utility evaluated. Similar approaches to shed light on the structure and conformation of a set of proline and pseudoproline based designed β-turn peptides that are used as templates for understanding protein folding have been made. Results of studies on two biologically important forms of the short-chain peptides namely glutathione reduced (GSH) and oxidized (GSSG) tripeptides are also presented.

Spin selective MQ-SQ correlation has been demonstrated by either selective pulses in homo-nuclear spin systems in isotropic and weakly orienting chiral media or by nonselective pulses in hetero-nuclear spin systems in strongly aligned media. As a consequence of the spin selective correlation, the coherence transfer pathway from MQ to SQ is spin state selective. This two dimensional approach enables the utilization of the passive couplings (remote couplings) to break a complex one dimensional spectrum into many sub spectra. Each sub spectrum contains fewer transitions and hence fewer couplings (active couplings). The role of the passive couplings is to displace the sub spectra and measurement of the displacements taking into account their relative tilt provides the magnitude of the passive couplings along with relative signs. Further possibility of a spin state selective MQ-SQ resolved experiment to determine very small remote couplings otherwise buried within linewidth in one dimensional spectrum has been demonstrated. The resolution of the multiple quantum spectrum in indirect dimension has also been exploited to separate the sub spectra. The technique renders the analysis of complex spectrum in isotropic system much simpler. The potentialities of the technique have also been demonstrated for discrimination of optical enantiomers and derivation of the residual dipolar couplings from very complicated spectrum. The second order spectrum in strongly aligned media restrict selective excitation, however in hetero-nuclear spin system the nonselective pulses on protons do not interact with the hetero-nuclear spins. Thus the weakly coupled part of a strongly coupled spectrum has been exploited for simplifying the second order spectrum and thereby its analysis. Thus several methodologies derived from spin selective correlation has been demonstrated. Enantiopure spectrum has been recorded from a mixture of R and S enantiomers by a novel pulse scheme called Double Quantum Selective Refocusing Experiment. The dipolar coupled methyl protons in weakly orienting media are utilized. The selective excitation of double quantum coherence reduces the three spin system into a two spin system and remote couplings are refocused which otherwise leads to broadening. The sum of passive couplings being different for the enantiomers resolution in the DQ dimension is enhanced and thereby their discrimination. Finally several decoupling schemes has been compared in the indirect dimension of HSQC experiment to resolve 13C satellite spectra otherwise buried within line width for increased confidence in determining hetero-nuclear framework information.