Steepest descent reaction path integration using a first-order predictor-corrector method

The theoretical treatment of chemical reactions inevitably includes the integration of reaction pathways. After reactant, transition structure, and product stationary points on the potential energy surface are located, steepest descent reaction path following provides a means for verifying reaction mechanisms. Accurately integrated paths are also needed when evaluating reaction rates using variational transition state theory or reaction path Hamiltonian models. In this work an Euler-based predictor-corrector integrator is presented and tested using one analytic model surface and five chemical reactions. The use of Hessian updating, as a means for reducing the overall computational cost of the reaction path calculation, is also discussed.     

Nonresonant optical activity of isolated organic molecules

Cavity ring-down polarimetry (CRDP) has been exploited to interrogate the nonresonant optical activity (or circular birefringence) of prototypical organic compounds in the vapor phase, thereby revealing the intrinsic chiro-optical response evoked from isolated (solvent-free) molecules. Specific polarization rotation parameters have been measured at two distinct excitation wavelengths (355 nm and 633 nm) for a variety of gas-phase species drawn from the terpene, epoxide, and alkane/alkene families, with complementary solution-phase polarimetric studies serving to highlight the pronounced influence of solute-solvent interactions. Time-dependent linear response calculations performed at high levels of density functional theory have been enlisted to unravel the structural and electronic origins for observed behavior. Aside from elucidating the complex solvation processes that mediate chiro-optical phenomena taking place in condensed media, this study affords a critical assessment for emerging ab initio predictions of nonresonant optical activity and for their promising ability to assist in the determination of absolute molecular stereochemistry.     

A Generalized Two-Agent Location Problem: Asymmetric Dynamics and Coordination

We generalize a static two-agent location problem into dynamic, asymmetric settings. The dynamics is due to the ability of the agents to move at limited speeds. Since each agent has its own objective (demand) function and these functions are interdependent, decisions made by each agent may affect the performance of the other agent and thus affect the overall performance of the system. We show that, under a broad range of system’s parameters, centralized (system-wide optimal) and non-cooperative (Nash) behavior of the agents are characterized by a similar structure. The timing of these trajectories and the intermediate speeds are however different. Moreover, non-cooperative agents travel more and may never rest and thus the system performance deteriorates under decentralized decision-making. We show that a static linear reward approach, recently developed in Golany and Rothblum (Nav. Res. Logist. 53(1):1–15, 2006), can be generalized to provide coordination of the moving agents and suggest its dynamic modification. When the reward scheme is applied, the agents are induced to choose the system-wide optimal solution, even though they operate in a decentralized decision-making mode.     

The Application of Ultrasound in Honey: Antioxidant Activity,Inhibitory Effect on α-amylase and α-glucosidase,and In Vitro Digestibility Assessment

In the present study, the effects of ultrasound (10, 20, and 30 min) on the bioactive compounds, antioxidant capacity, enzymatic inhibition, and in vitro digestion of six honey extracts from the Oaxaca state, Mexico, were analyzed. Significant differences were found in each honey extract with respect to the ultrasonic treatment applied (p < 0.05). In the honey extract P-A1 treated with 20 min of ultrasound, the phenols reached a maximum concentration of 29.91 ± 1.56 mg EQ/100 g, and the flavonoids of 1.92 ± 0.01 mg EQ/100 g; in addition, an inhibition of α-amylase of 37.14 ± 0.09% was noted. There were also differences in the phases of intestinal and gastric digestion, presenting a decrease in phenols (3.92 ± 0.042 mg EQ/100 g), flavonoids (0.61 ± 0.17 mg EAG/100 mg), antioxidant capacity (8.89 ± 0.56 mg EAG/100 mg), and amylase inhibition (9.59 ± 1.38%). The results obtained from this study indicate that, in some honeys, the processing method could increase the concentration of bioactive compounds, the antioxidant capacity, and the enzymatic inhibition; however, when subjected to in vitro digestion, the properties of honey are modified. The results obtained could aid in the development of these compounds for use in traditional medicine as a natural source of bioactive compounds.     

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