In chapter 2-4 , the five-membered exocyclic DNA adducts are biologically very significant because of their potential to block DNA replication and transcription, induce DNA strand breaks, trigger, apoptosis, and cause gene mutations and chromosomal aberrations. These effects could lead directly to carcinogenesis. Common exocyclic DNA adducts, such as 1,N6-ethenoadenine (εA), 3,N4-ethenocytosine (εC), N2,3-ethenoguanine (N2,3-εG), and 1,N2-ethenoguanine (1,N2-εG), are responsible for blocking Watson-Crick base pairing. The present study provides useful information, such as geometric characteristics, electronic properties, and physical parameters, for the misincorporation of DNA nucleotides in the exocyclic adduct, based on different conformations and unique mutagenic properties that are essential for the continuous effort to understand the base-pairing specificity toward the determination of cancer etiology. From our results, it can be observed that the exocyclic DNA adducts readily paired with thymine which are in good agreement with the experimental observations. In chapter 5, the preferential interactions of glycine betaine (GB) with solvent components and the effect of solvent on its stability have been examined. In particular, the microsolvation of organic osmolyte and widely important osmoprotectant in nature as glycine betaine has been reported by using M06, MP2 and CCSD (T) method. A number of configurations of the clusters for one to seven water molecules have been considered for the microsolvation. Structures of stable conformers are obtained and denoted as b1a, b2a, b3a, b4a, b5a, b6a and b7a. It is observed from the interaction energy difference (ΔE) that only seven water molecules can be accommodated in the first solvation shell to stabilize GB. In chapter 6, DNA base pair A-T has been investigated by IR and NMR spectroscopy using DFT methods. The results have been analyzed in terms of infrared vibrational frequencies and 1H-NMR chemical shifts. Different types of interactions N-H…N, N-H…O and C-H…O types have been investigated in DNA base pairs. Although, previous reports argued about the third C-H…O type interaction in A-T base pair, such typical interaction has been analyzed thoroughly by IR and NMR spectroscopy using DFT methods. Our result shows that the CH...O interaction in the A-T base pair is a weak interaction compared to normal hydrogen bond interactions. In chapter 7, Ionic liquids are novel solvents of interest as greener alternatives to conventional organic solvents aimed at facilitating sustainable chemistry. As a consequence of their unusual physical properties, reusability, and eco-friendly nature, ionic liquids have attracted the attention of organic chemists. Numerous reports have revealed that many catalysts and reagents were supported in the ionic liquid phase, resulting in enhanced reactivity and selectivity in various important reaction transformations. However, synthetic chemists cannot ignore the stability data and intermolecular interactions, or even reactions that are directly applicable to organic reactions in ionic liquids. It is becoming evident from the increasing number of reports on use of ionic liquids as solvents, catalysts, and reagents in organic synthesis that they are not totally inert under many reaction conditions. While in some cases, their unexpected reactivity has proven fortuitous and in others, it is imperative that when selecting an ionic liquid for a particular synthetic application, attention must be paid to its compatibility with the reaction conditions. Even though, more than 200 room temperature ionic liquids are known, only a few reports have commented their effects on reaction mechanisms or rate/stability. Therefore, rather than attempting to give a comprehensive overview of ionic liquid chemistry, this review focuses on the non-innocent nature of ionic liquids, with a decided emphasis to clearly illuminate the ability of ionic liquids to affect the mechanistic aspects of some organic reactions thereby affecting and promoting the yield and selectivity.
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