Phys Chem Chem Phys Phys Chem Chem Phys

Norbadione A (NBA) is a pigment present in edible mushrooms which is presumed to selectively complex Cs+ cations. Due to a very uncommon complexation mechanism, we used a combination of several experimental techniques, including H-1-NMR, Cs-133-NMR, isothermal calorimetric, potentiometric titrations and molecular dynamics MD simulations to determine the nature of the complexed species, as well as their stability constants for the NBA-M+ systems (M+ = Cs+, K+, Na+) in methanol : water 80 : 20 solutions at 25.0 degrees C. We show that almost no complexation occurs below pH 7.5, as long as a proton, involved in a strong hydrogen bond, bridges both carboxylic and enolic groups of each pulvinic moiety of NBA. Thus, neutralization of that proton is necessary to both set free potential coordination sites and to trigger a conformational change, two conditions needed to bind successively a first, then a second metallic cation. The stability constants determined in this study are in good agreement with each other, leading to the stability order Cs+ > K+ > Na+ for both mono- and bimetallic complexes, which is the reversed order to the one generally observed for low molecular weight carboxylic ligands in water. According to MD simulations in solution, complexation involves a mixture of Z/E isomers and conformers of NBA with a broad diversity of binding modes. Some pH and environment dependent aggregation phenomena are considered to also contribute to the binding process, and to possibly explain the accumulation of radionuclides in mushrooms.515mr Times Cited:4 Cited References Count:3

Carbon-13 longitudinal relaxation time measurements and DFT-GIAO NMR computations for two ammonium ions of a tetraazamacrocyclic scorpiand system

Spin-lattice relaxation times, T1s, for 13C nuclei in two cations Hn1n+ (n = 1, 5)of N-(2-amino-ethyl)-cyclam (1, scorpiand) were determined by means of 13C{1H} NMR experiments in aqueous solution at pH 11.5 and 0.2. The theoretical study [modeling with OPLS-AA, B3LYP/6-31G(d) geometry optimizations, dispersion-corrected energies (DFT-D3), and DFT-GIAO predictions of the NMR chemical shifts (including an IEF-PCM simulation of hydration)] was also done for several conformers of the tautomer iso-H414+ not investigated before. The binding directions in protonated polyamino receptors necessary for efficient complexation of the nitrate anion(s) were briefly outlined, as well. All these results were discussed in terms of 'abnormal' 13C chemical shift changes found previously for the side-chain carbons of amine 1 in strongly acidic solution (HNO3). In conclusion, an earlier proposal of its association with NO3- at pH=1 was rejected. Instead, the participation of small amounts of a microspecies iso-H414+Dhydr under such conditions can be proposed.Publikacja w ramach programu Springer Open Choice/Open Access finansowanego przez Ministerstwo Nauki i Szkolnictwa Wyższego i realizowanego w ramach umowy na narodową licencję akademicką na czasopisma Springer w latach 2010-2013

Biodynamers: Self-Organization-Driven Formation of Doubly Dynamic Proteoids

Polypeptide-type dynamic biopolymers (biodynamers) have been generated by polycondensation via acylhydrazone and imine formation of amino-acid-derived components that polymerize driven by self-organization. They have been characterized as globular particles, reminiscent of folded proteins, by cryo-TEM, LS, DOSY NMR, and SANS studies. The reversible polymers obtained show remarkably low dispersity and feature double covalent dynamics allowing for fine-tuning of both exchange and incorporation processes through pH control. In the course of build-up, they perform a selection of the most suitable building block, as indicated by the preferential incorporation of the more hydrophobic amino-acid component with increased rate and higher molecular weight of the polymer formed. The system described displays nucleation-elongation behavior driven by hydrophobic effects and represents a model for the operation of adaptation processes in the evolution of complex matter.