Nucleophilic additions are an important class of reactions in the preparation of several organic compounds. Metals facilitate nucleophilic additions in many cases. The present work Mechanistic Investigation of Metal Promoted Nucleophilic additions is an attempt to understand the mechanism of nucleophilic additions to imines and carbonyl compounds mediated by the transition metal complexes. Understanding the mechanism of metal promoted nucleophilic additions can facilitate the design and synthesis of more efficient catalysts. Chapter 1 provides a brief introduction to nucleophilic addition. A few named reactions that involve nucleophilic addition are described. An overview of the metal promoted nucleophilic addition reactions and their mechanisms are presented. A short note on the importance of understanding the mechanism of metal promoted nucleophilic addition is included. This section ends with the scope of the present work. Chapter 2 “Mechanistic Investigation of Titanium Mediated Reactions of Imines” deals with two reactions. The first reaction is the formation of reduced amines on reduction of imines. Amines and diamines are synthesized often from imines. A convenient route to such nitrogen containing compounds is through reduction of imines and through reductive coupling of imines respectively. Since both reactions occur in a parallel fashion, during the synthesis of diamines, amines are obtained as side products and vice versa. This problem is acute in the case of titanium based reducing agents. These reducing agents are called low valent titanium reagents because low valent titanium species are generated in situ either from titanium(IV) or titanium(III) reagents. There is no clear understanding of the nature of the low valent titanium involved in the reaction. To rectify this, a mechanistic understanding of this reaction is essential. An attempt was made to probe the mechanism of formation of amines using low valent titanium formed by using two different reducing agents namely phenylsilane and zinc. With the help of isotopic labelling studies, it was found that the mechanism of formation of an amine with phenylsilane involves a direct hydrogen transfer from phenylsilane to an imine. This was verified using deuterium labelled phenylsilane. With zinc, it follows a traditional titanacycle pathway which was verified by quenching with the deuterium oxide. A second reaction that has been probed is the alkylation of imines by Grignard reagents using chiral titanium complexes. Alkylation of imines is one of the suitable routes to prepare chiral amines. Alkylation of imines employing a Grignard reagent with Ti(OiPr)4 can proceed through two different pathways depending on the amount of the Grignard reagent used. Alkylation reaction with one equivalent of Grignard reagent can proceed through a Ti(IV) species and the alkylation reaction with two equivalents of the Grignard reagent can proceed through a Ti(II) species. The reaction proceeding through Ti(IV) is less wasteful as it only requires one equivalent of the Grignard reagent. The two pathways differ from each other in the nature of the transition state where the C-C bond is formed. To verify the favourable pathway, chiral titanium complexes were prepared and alkylation carried out. The alkylation results suggest that one equivalent of Grignard is sufficient to give good yields of the alkylated product and the reaction may proceed through a Ti(IV) promoted path. It was reported in the literature that at least three equivalents of Grignard reagent are required to get good yields of the alkylated product with zirconium complexes. This work suggests a greener alternate to alkylation of imines. Chapter 3 “Asymmetric Transfer Hydrogenation Reaction of Ketones in Water” deals with the synthesis of chiral ruthenium half-sandwich complexes employing a proline diamine ligand which has phenyl, ethyl, benzyl, or hydrogen as a substituent. These complexes were characterized by X-ray diffraction. In addition, all these complexes were obtained as single diastereoisomers. These complexes were used as catalysts for the reduction of a variety of ketones to chiral alcohols in water using sodium formate as a hydride source. Stoichiometric reaction between sodium formate and the catalysts showed the formation of hydride complexes as the active species. Based on the electronic effects observed, the key step is found to be a nucleophilic attack of hydride on the carbonyl carbon of ketones. In the transfer hydrogenation reaction with DCOONa, more of 1-phenylethanol- 1-2H1 was observed with all the ruthenium catalysts suggesting that the hydrogen from sodium formate is transformed into a metal hydride which is subsequently transferred to the ketones to form chiral alcohols. The catalysts were optimized with acetophenone as a model substrate. Only in the case of a catalyst which has a phenyl substituent, silver nitrate was found to enhance the formation of aqua complex which in turn resulted in good yields of the chiral alcohols. Among all the complexes studied, the catalyst bearing a phenyl group induces greatest enantioselectivity. It can also be recycled. Chapter 4 “On the Formation of a Ruthenium-PPh2H Complex Using 1- Phenylethane-1,2-diol” deals with the mechanism of formation of PPh2H from PPh2Cl. This unique transformation involves a ruthenium-cymene dimer, PPh2Cl and 1-phenylethane-1,2- diol. In the attempted synthesis of a ruthenium bisphosphinite complex, using the ruthenium-cymene dimer, chlorodiphenylphosphine and 1-phenylethane-1,2-diol, the formation of [Ru(η6-cymene)Cl2PPh2H] was observed in good yield. Formation of the expected ruthenium bisphosphinite complex was not observed. The reaction was carried out in the absence of 1-phenylethane-1,2-diol resulted in the formation of [Ru(η6- cymene)Cl2PPh2Cl] suggests that the diol acts as a reducing agent. To verify the source of hydrogen in the 1-phenylethane-1,2-diol, deuterated diols were prepared. The reactions with the deuterated diols revealed several interesting aspects of the formation of the Ru-PPh2H complex. Chapter 5 “Mechanistic Studies on the Diazo Transfer Reaction” deals with the synthesis of labelled azides and the labelled azidating reagent to probe the mechanism of the diazo transfer reaction. Azides are important precursors used for a variety of chemical transformations including the celebrated Cu(I) catalyzed click reaction. Azides are also used as protecting groups for amines as they can be conveniently reduced to amines. Azidation of amines usually yield azides, with retention of stereochemistry. There is a possibility that the azide formation can occur through the SNi mechanism with retention of configuration where nitrogen in the starting material will not be retained after forming an azide. The reaction was carried out with 13C and 15N labelled L-valine and L-isoleucine to probe this possibility. The resultant labelled azide has 15N retained in its position. This excluded the SNi pathway. To show where the nucleophilic amine group is attacking the azide, labelled imidazole-1¬sulfonyl azide was synthesized from NaN215N. Reactions were carried out with L-valine (labelled and unlabelled) in the presence of a metal catalyst and with unlabelled L-valine in the absence of catalyst. These results confirm the postulated pathways described in the literature.

This thesis describes the study on structure and dynamics of various kinds of molecular membranes in general. We have studied the morphological transition of colloidal as well as biologically relevant membranes and qualitatively argued regarding the interplay between structure and dynamics. Systematic measurements have been performed to address the issue of ambiguous behavior of molecules under stress when its confined at the interface. The structural and dynamical effect on interfacial membranes have been studied for soft colloidal free standing langmuir monolayer as well as for the quasi two dimensional lipid membranes on solid supports. For organic nanoparticle monolayer we have observed a correlation between the nanoparticle raft dynamics and the underlying morphological transition. In this study we have also found a non-monotonic behavior of dynamical heterogeneity with time which is unusual for a colloidal system in common and beyond the prediction of Mode Coupling Theory. In the case of lipid membrane, we have given an experimental evidence of lipid molecular rearrangement process at molecular level when its perturbed by foreign entities. Using sophisticated X-Ray scattering techniques, we were able to capture the subtle changes happening in the assembly of lipid molecules in a planar bilayer structure when it interacts with molecules having biological relevance. In the next level we have used lipid membranes as an active plat-form to study the physical interaction with several kinds of nanoparticles and explored the mechanism of active participation of lipid molecules in self assembly process. Besides with the help of Fluorescence Correlation Spectroscopy, we have also studied the effect of nanoparticles assemblies on the dynamics of lipid molecules itself. In Chapter 1, we have provided the background along with a brief review of the existing literature for understanding the results represented in the subsequent chapters. This includes discussion on the various physical properties of our systems of interest, including dynamic behavior of colloidal particles in different concentration regime and a detailed theoretical understanding regarding the glass transition and jamming transition for a highly dense colloidal packing. In this section we have also discussed the advantages of interfacial microrheology technique over conventional bulk rheology in terms of efficiency and sensitivity. Here we have also pointed out the formulation of the multi-particle tracking method for achieving different parameters which are correlated in space and time for a given system. Followed by that the Dynamical Susceptibility and the anomaly in Van Hove correlation function, for a heterogeneous system has been argued thoroughly. Towards the end we have discussed about the general features of another type of two dimensional membrane i.e. the lipid membrane at interface. Using raft theory we have also tried to give a plausible explanation of the dynamical heterogeneity of the real cell membrane which is mimicked by the model supported lipid membrane. Here we have argued about the structural six fold symmetry of a compact monolayer. Finally in the last part we have summarized the theoretical aspects of the lipid molecule mediated self assembly process and the how the lipid diffusion plays a vital role in it. Chapter 2 deals with the aspect of measuring the morphological transition and its effect on the dynamics for a two dimensional membrane at air/water interface. It starts with the discussion on the synthesis method for various types of organic molecule grafted nanoparticles like Cadmium Selenide(CdSe Quantum Dots) and Gold Nanoparticle(Au NPs) of different size and properties and followed by a preparation method of 2D film at air/water interface and on solid substrate using Langmuir-Blodgett method. In this chapter we have discussed about the basic principles of several experimental tools like Brewster Angle Microscopy(BAM), Laser Scanning Confocal Microscopy(LSCM), Atomic Force Microscopy(AFM), Thermogravimetric Analysis(TGA), X Ray Reflectivity(XRR), Grazing Incidence Diffraction(GID), Fluorescence Correlation Spectroscopy(FCS) etc. Chapter 3 explains the main aspects of the microscopic dynamics in dense amorphous nanoparticle monolayer at the air-water interface. In this study we have found a transition in mechanical properties, tracked down through the systematic variation of isothermal compressibility(�) with increasing two dimensional packing fraction of nanoparticle rafts up to the area fraction of Φ∼0.82 using Laser Scanning Confocal Microscope. Here we have used multi particle tracking method for a close packed gold monolayer with CdSe tracer to estimate different dynamical properties like Mean Square Displacement(MSD), Dynamical Heterogeneity etc. These calculations indeed point out the non-monotonic variation of the amplitude in the four-point dynamic susceptibility (χ4), a signature of spatio-temporal extension of correlated domains. Along with that we have also observed the anomaly in trend for the inherent relaxation time τ∗with increasing area fraction(Φ). Interestingly the variation in χ4exactly follows the systematic we found for the isothermal compressibility( �) with increasing Φ and that indicates the connection between the observed macroscopic transitions in mechanical properties and the microscopic dynamical phase transitions. Finally we have given a possible explanation of these kind of events in terms of the interaction between this sterically stabilized nanoparticle domains with the help of interpenetration of the capping long chain polymers of the neighboring nanoparticle. Chapter 4 opens up the possibilities of probing the hidden features of biomembranes at molecular scale with the help of very precise techniques based on synchrotron X ray diffraction. Here we have studied the rearrangement of the lipid molecules of an artificial membrane on a solid support as an effect of ad-sorption of organic branched molecules. In this work we have used non toxic PETIM dendrimers of two different generations, i.e. G3and G4which differs a lot in terms of size, no of termination groups, molecular weights and protonation states. Our initial measurements shows quantitatively the in-plane and out of plane symmetry breaking of the lipid bilayer as a result of the interaction with these two types of molecules. The molecular adsorption effect was quantified in terms of thickness reduction and the change in the scattering length density(SLD) or the electron density of the top layer in out of plane reflectivity model. Interestingly both the dendrimers showed different behavior and the interaction reflected in terms of membrane penetration was found stronger for higher generation. On the other hand the GID measurement indicates an enhancement of the in plane unit cell dimension and associated parameters of the arrangement of lipid molecules as a result of interaction with dendrimers. The combined XRR and GID measurements indicate a local fluidization of lipid packing as an outcome of charged branched molecules adsorption on the membrane surface. Chapter 5 is summarizes the lipid mediated self assembly process of nanoparticles on a bilayer and how the interaction changes the local properties of the bilayer represented by the molecular diffusivity. In this study we have used particles of wide variety of features in terms of size, charge, functionality, polarity etc and found a quite dramatic effect in the nanoparticle adsorption event on a solid supported Lαphased DMPC lipid bilayer. We have also seen that de-pending on the concentration and amount of surface charge the nanoparticles form two dimensional regular self assembled patterns on the bilayer surface. In FCS measurement, we have also found a second group of dynamics ( distribution of diffusivity) along with the normal bilayer diffusion which has been identified as the diffusion of the lipid molecules where nanoparticles are adsorbed. The inherent increment in diffusivity supports the argument of local fluidization in lipid membrane in presence of charged nanoparticle as we have observed in our XRR and GID data described in chapter 4. Chapter 6 contains the summary and the future perspective of the work presented here.