Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self-assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary-functionalized naphthalenediimides (NCDPs 1-6) have been prepared and their chiral self-assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1-3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M- to P-type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid-state thin-film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4-6), with an achiral or D-isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π-π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P-) and left (M-) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent-induced helical assembly and reversible chiroptical switching of naphthalenediimides.

First examples of racemization of tetrahedral tetracoordinated centers via a planar transition state or an intermediate structure.

Transannular Diels-Alder (TADA) reactions that occur between the diene and dienophile moieties located on a single macrocyclic triene molecule have been recognized as effective synthetic routes toward realizing complex tricyclic molecules in a single step. In this paper, we report a comprehensive study on the TADA reactions of 14-membered cyclic triene macrocycles to yield A.B.C[6.6.6] tricycles using quantum chemical methods and using classical molecular dynamics simulations. A benchmark study has been performed to examine the reliability of the commonly used ab initio methods and hybrid density functional levels of theory in comparison with results from CCSD(T) calculations to accurately model TADA reactions. The energy barriers obtained using the M06-2X functional were found to be in quantitative agreement with the CCSD(T) level of theory using a reasonably large basis set. Conformational properties of the reactants have been systematically studied using extensive molecular dynamics (MD) simulations. For this purpose, model systems were conceived, and force field parameters corresponding to the dihedral terms in the potential energy function were obtained. Linear relationship between the activation energies corresponding to the TADA reactions and the probability of finding the reactant in certain conformational states was obtained. A clustering method along with optimizations at the molecular mechanics and density functional M06-2X levels has been used to locate the most stable conformation of each of the trienes.

Background: The present research paper described about the optimization of various zero order and first order UV spectrophotometric method using different buffers. Validation study was performed to develop a simple, sensitive, rapid, accurate and economical Ultra Violet spectrophotometric method for the estimation of Valganciclovir. Methods: UV 1800 double beam UV Visible Spectrophotometer with a pair of 10mm path length matched quartz cells were used for the study. Method A (Water), Method B (phosphate buffer pH2), Method C (Phosphate buffer pH4) and Method D (phosphate buffer pH5) were developed for estimation of Valganciclovir by zero-order and first-order derivative. Results: Linearity was carried out in the concentration range of 5-60 µg/ml and the correlation coefficient were found to be 0.999. The percentage recoveries were found to be 98-102%. The relative standard deviation was found to be <2%. The LOD and LOQ were found to be 0.3241 µg/ml and 0.8227 µg/ml respectively. Conclusion: Hence, the methods were validated according to ICH guidelines and can be adopted for the routine analysis of Valganciclovir in pure and tablet dosage form.

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