The determination of the energetics of the temperature-dependent two-state N $ S pseudorotational equilibrium through 3JHH analysis in 36 nucleos(t)ides and 3 abasic sugars has allowed us for the first time to quantify the strength of various nucleobase-dependent anomeric and gauche effects, and how their interplay finally steers the sugar conformation. The plots of the pDdependent thermodynami...

The conformational characteristics of abasic 1-deoxy sugars 1,2, and 3 and pentofuranose moieties in 2‘,3‘dideoxy-[ddA (6), ddG (7), ddC (S)], 2’-deoxy-[dA (9), dG (lo), dC (ll)], and ribo-@-D-nucleosides [Ade (12), Gua (13), Cyt (14)] were established through the analysis of vicinal proton-proton coupling constants extracted from their 500-MHz lH-NMR spectra recorded at 20 K intervals in the t...

Karplus relationships for all 26 NMR spin-spin coupling constants (SSCCs) J of the pseudorotating tetrahydrofuran (THF) molecule were derived by expanding J as a function J(q,φ) of the puckering amplitude q and the pseudorotational phase angle φ. For this purpose, the conformational potential V(q,φ) of THF was determined at the MBPT(2)/ccpVTZ and B3LYP/6-31G(d,p) levels of theory. THF is a slig...

In the group-6 metal hexacarbonyls a number of metal-to-ligand charge-transfer (MLCT) and ligand-field (LF or d ! d) states can be excited in the near UV. The latter are repulsive. In equilibrium geometry, most of them are higher than the MLCT states. We probed the dynamics of photodissociation of M(CO)6 ! M(CO)5 + CO (M = Cr; some data also for M = Mo) with improved time resolution (10– 40 fs)...

The far-infrared vibration–rotation–tunneling spectrum of ~D2O!4 has been measured in the spectral region near 2.04 THz. Observation of additional transition doublets with a constant 5.6 MHz spacing in a parallel ~c-type! spectrum extends the first detailed study of this cluster @Science 271, 59 ~1996!#. Three possibilities are explored for the origin of this small splitting: tunneling between ...

Understanding microsecond-timescale dynamics is crucial to establish three-dimensional (3D) structure-activity relationships in sugars but has been intractable to experiments and simulations. As a consequence, whether arguably the most important chemical scaffold in glycobiology, N-acetyl-d-glucosamine (GlcNAc), deviates from a rigid (4)C(1) chair is unknown. Here, conformer populations and exc...

New evidence bearing upon the anomalous properties of xenon hexafluoride has been obtained via the ab initio molecular orbital approach applied successfully to the diand tetrafluorides in paper 1. Structures of both XeFt and XeF6 are governed by a stereochemically active lone pair. In the case of the square-pyramidal cation the F .. -Xe-Feq angle calculated for the bare ion is within 2° of the ...

This paper provides a first-principles theoretical investigation of the polytopal rearrangements and fluxional behavior of five-coordinate d-transition metal complexes. Our work is primarily based on a potential energy surface analysis of the iron tetracarbonyl hydride radical HFec(CO)4. We demonstrate the existence of distorted coordination geometries in this prototypical system and, for the f...

The conformations of MgATP and AMP bound to a monomeric tryptic fragment of methionyl tRNA synthetase have been investigated by two-dimensional proton transferred nuclear Overhauser effect spectroscopy (TRNOESY). The sample protocol was chosen to minimize contributions from adventitious binding of the nucleotides to the observed NOE. The experiments were performed at 500 MHz on three different ...