Chemical Bonding 2: Modern Theories of Chemical Bonding

Chemical Bonding II: Modern Theories of Chemical Bonding explains four bonding theories related to molecular geometry and bonding. Lewis structures and the Valence-Shell Electron-Pair Repulsion (VSEPR) model are used to describe and predict the electron group geometry, molecular geometry and shapes of molecules. The VSEPR model is then used to predict molecular polarity as a function of shape. This leads to Valence Bond Theory, which uses the principles of orbital overlap and hybridization of atomic orbitals to describe chemical bonding. Finally the Molecular Orbital Theory (MOT) based on electron delocalization is discussed in terms of bonding and anti-bonding molecular orbitals.

Synthesis of pyrano[3,2-c]quinoline derivatives using catalyst prepared from L-proline and p-toluenesulfonic acid

This research prepared new generation of ionic liquid (Deep eutectic solvent, DES) from L-proline and p-toluenesulfonic acid. The ionic liquid has an asymmetric center in its structure because the original amino acid has an asymmetric center. Subsequently, the ionic liquid was studied catalytic activity in reactions of quinoline[3,2-c]pyrano derivatives synthesis. Conditions affecting the reaction and rate of the two products were also investigated. The results of the reaction conditions showed that aprotic polar solvents gave better yields and the best reaction conditions were: temperature: 50oC, time: 2 h, catalytic amount: 35% mol . The ratios of two product isomers showed that the reaction always forms a mixture of two diastereomers and the trans products were synthesized with moderate enantiomeric excess (40% for four derivatives) compared with the cis products. In addition, the results on catalytic reuse also showed that the catalyst had good usability without significant decreasing activity. When benzaldehyde and aniline were changed with their derivates bearing donating electron group (-CH3), the reaction yields slightly decrease. However, benzaldehyde bearing withdrawing electron group (-F) gave moderate yield.

Role of thylakoid membranes in oxygenic photosynthesis: A comparative perspective using murburn concept

Murburn concept is a new redox metabolic paradigm which advocates that several redox enzymes generate/stabilize diffusible reactive (oxygen) species (DRS or DROS) to carry out useful electron/moiety transfer reactions at biological membrane interfaces (Manoj 2020a). Herein, we show that the components and principles of redox reactions within chloroplasts/cyanobacteria share several similarities with soluble and simple extracellular or peroxisomal heme-enzymes that carry out electron/group transfer. We explore the comparison in detail with membrane-embedded and complex systems that catalyze: (i) microsomal xenobiotic metabolism and (ii) mitochondrial oxidative phosphorylation. We point out that the murburn interpretations of catalytic phenomena are consistent through the various reaction systems cited above. Further, we argue that evolutionary constraints and the physiological restrictions of neutral pH ranges discount proton-gradient based explanations for bioenergetic phosphorylations in chloroplasts. Therefore, we propose that the highly packed thylakoid membranes with minute aqueous volumes serve to enhance the lifetimes of oxygen-centered radicals and intermediates. The murburn perspective could also potentially explain protein supercomplexes in chloroplasts, and generation of ATP in mitochondria by photo-activation. Our proposal also highlights the evolutionary significance of lipid membranes and utility of oxygen in diverse life processes.

Analytical calculation of electron group velocity surfaces in uniform strained graphene

Electron group velocity for graphene under uniform strain is obtained analytically by using the tight-binding (TB) approximation. Such closed analytical expressions are useful in order to calculate the electronic, thermal and optical properties of strained graphene. These results allow to understand the behavior of electrons when graphene is subjected to strong strain and nonlinear corrections, for which the usual Dirac approach is no longer valid. Some particular cases of uniaxial and shear strain were analyzed. The evolution of the electron group velocity indicates a break-up of the trigonal warping symmetry, which is replaced by a warping consistent with the symmetry of the strained reciprocal lattice. To do this, analytical expressions for the shape of the first Brillouin zone (BZ) of the honeycomb strained reciprocal lattice are provided. Finally, the Fermi velocity becomes strongly anisotropic, i.e., for a strong pure shear strain (20% of the lattice parameter), the two inequivalent Dirac cones merge and the Fermi velocity is zero in one of the principal axis of deformation. We found that nonlinear terms are essential to describe the effects of deformation for electrons near or at the Fermi energy.

A Simple Method of Cyclization of the 2'-Hydroxychalcone with Polystyrene-Pyridine Resine under Mild Conditions

The satisfying cyclization of 2’-hydroxy chalcone to flavanone using polystyrene-pyridine resine as catalyst and methanol as solvent under mild conditions is reported here. The method is appropriate for 2’-hydroxy chalcone derivatives with electron group in B-ring.