10 research outputs found
Contribution of Phosphates and Adenine to the Potency of Adenophostins at the IP3 Receptor: Synthesis of All Possible Bisphosphates of Adenophostin A
The Magnitude and Mechanism of Charge Enhancement of CH∙∙O H-bonds
Quantum calculations find that neutral methylamines and thioethers form complexes, with N-methylacetamide (NMA) as proton acceptor, with binding energies of 2–5 kcal/mol. This interaction is magnified by a factor of 4–9, bringing the binding energy up to as much as 20 kcal/mol, when a CH3+ group is added to the proton donor. Complexes prefer trifurcated arrangements, wherein three separate methyl groups donate a proton to the O acceptor. Binding energies lessen when the systems are immersed in solvents of increasing polarity, but the ionic complexes retain their favored status even in water. The binding energy is reduced when the methyl groups are replaced by longer alkyl chains. The proton acceptor prefers to associate with those CH groups that are as close as possible to the S/N center of the formal positive charge. A single linear CH··O hydrogen bond (H-bond) is less favorable than is trifurcation with three separate methyl groups. A trifurcated arrangement with three H atoms of the same methyl group is even less favorable. Various means of analysis, including NBO, SAPT, NMR, and electron density shifts, all identify the +CH··O interaction as a true H-bond
A Cluster Expansion Method for the Complete Resolution of Microscopic Ionization Equilibria from NMR Titrations
Relations between Protonation Constants and Titration Curves in Polyprotic Acids: A Critical View
Stimulation of Inositol 1,4,5-Trisphosphate (IP3) Receptor Subtypes by Adenophostin A and Its Analogues
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