Theoretical study of enzymatically catalyzed tautomerization of carbon acids in aqueous solution: quantum calculations and steered molecular dynamics simulations

Differences in the torsional anharmonicity between reactant and transition state: the case of 3-butenal + H abstraction reactions

Thermal rate coefficients for the hydrogen-abstraction reactions of 3-butenal by a hydrogen atom were obtained applying multipath canonical variational theory with small-curvature tunneling (MP-CVT/SCT). Torsional anharmonicity due to the hindered rotors was taken into account by calculating the rovibrational partition function using the extended two-dimensional torsional (E2DT) method. For comparison, rovibrational partition functions were also estimated using the multistructural method with torsional anharmonicity based on a coupled torsional potential (MS-T(C)). By contrast, with (E)-2-butenal reactions, the abstraction reactions of 3-butenal proceed via five reaction channels (R1)-(R5). In a conformational search, 45 distinguishable structures of transition states were found, including enantiomers, which were separated into six conformational reaction channels (CRCs). The individual reactive paths were constructed, the recrossing and semiclassical transmission coefficients estimated, and the multipath rate constants were obtained. High torsional barriers between the wells of CRC2/CRC6 indicate a harmonic behavior. Consequently, a difference between the torsional anharmonicity of 3-butenal and the transition states is responsible for the increase in the thermal rate constants for channel (R2). Analysis of the contributions of each conformer of the transition state shows an important contribution of the high-energy rotamers in the total flux of (R1)-(R5). After fitting the rate constants in a four-parameter equation, the activation energy estimation showed a strong temperature dependence.

Endowing Hydrochromism to Fluorans via Bioinspired Alteration of Molecular Structures and Microenvironments and Expanding Their Potential for Rewritable Paper

Interest and effort toward new materials for rewritable paper have increased dramatically because of the exciting advantages for sustainable development and better nature life cycle. Inspired by how nature works within living systems, herein, we have used fluorans, as a concept verification, to endow original acidochromic, basochromic or photochromic molecules with broader properties, such as switchable with solvent, water, heat, electricity, stress, other force, etc., via simplified methods (i.e., via variation of submolecular structure or microenvironments). The hydrochromic visual change and reversible behavior of selected molecules have been explored, and the primary mechanism at the atomic or subatomic level has been hypothesized. In addition, several newly demonstrated hydrochromic fluorans have been utilized for water-jet rewritable paper (WJRP), which exhibit great photostability, high hydrochromic contrast, and fast responsive rate and which can be reused at least 30 times without significant variation. The water-jet prints have good resolution and various colors and can keep legibility after a few months or years. This improved performance is a major step toward practical applications of WJRP.