One-Dimensional Random Walk of a Synthetic Small Molecule Toward a Thermodynamic Sink

We report on the spontaneous intramolecular migration of α-methylene-4-nitrostyrene from amine group to amine group along oligoethyleneimine tracks up to eight repeat units in length (number of amine footholds, <i>n</i> = 3, 5, 9). Each track consists of <i>n</i> – 1 aliphatic secondary amine footholds plus a naphthylmethylamine group foothold situated at one end of the track. Under basic conditions the α-methylene-4-nitrostyrene unit undergoes a series of reversible intramolecular Michael–retro-Michael reactions between adjacent amine groups that move it up and down the track. For <i>n</i> = 3 and 5 it is possible to monitor the population of every positional isomer on the track by ¹H NMR spectroscopy. On the longest track (<i>n</i> = 9) the fraction of walkers on each end-foothold can be quantified with respect to those on the inner footholds. In all cases the naphthylmethylamine foothold acts as a thermodynamic sink with the steady-state distribution significantly biased in favor of the walker at that site. The dynamics of the walker migration is well described by the random walk of a Brownian particle in one dimension

Overview of Metabolism and Bioavailability Enhancement of Polyphenols

A proper diet is one of major factors contributing to good health and is directly related to general condition of the organism. Phenolic compounds are abundant in foods and beverages (fresh and processed fruits and vegetables, leguminous plants, cereals, herbs, spices, tea, coffee, wine, beer) and their pleiotropic biological activities result in numerous health beneficial effects. On the other hand, high reactivity and very large diversity in terms of structure and molecular weight renders polyphenols one of the most difficult groups of compounds to investigate, as evidenced by ambiguous and sometimes contradictory results of many studies. Furthermore, phenolics undergo metabolic transformations, which significantly change their biological activities. Here, we discuss some aspects of metabolism and absorption of phenolic compounds. On the basis of information reported in the literature as well as in summaries of clinical trials and patent applications, we also give an overview of strategies for enhancing their bioavailability

Exploring the Activation Modes of a Rotaxane-Based Switchable Organocatalyst

The reactivity of a rotaxane that acts as an aminocatalyst for the functionalization of carbonyl compounds through HOMO and LUMO activation pathways has been studied. Its catalytic activity is explored for C–C and C–S bond forming reactions through iminium catalysis, in nucleophilic substitutions and additions through enamine intermediates, in Diels–Alder reactions via trienamine catalysis, and in a tandem iminium-ion/enamine reaction. The catalyst can be switched “on” or “off”, effectively controlling the rate of all of these chemical transformations, by the <i>in situ</i> change of the position of the macrocycle between two different binding sites on the rotaxane thread