Nuclear quantum effects in calculated NMR shieldings of benzene; a Feynman path integral study

The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window.     

Generation of Pseudocontact Shifts in Proteins with Lanthanides Using Small “Clickable” Nitrilotriacetic Acid and Iminodiacetic Acid Tags

Pseudocontact shifts (PCS) induced by paramagnetic lanthanide ions provide unique long‐range structural information in nuclear magnetic resonance (NMR) spectra, but the site‐specific attachment of lanthanide tags to proteins remains a challenge. Here we incorporated p‐azido‐phenylalanine (AzF) site‐specifically into the proteins ubiquitin and GB1, and ligated the AzF residue with alkyne derivatives of small nitrilotriacetic acid and iminodiacetic acid tags using the Cu^I‐catalysed “click” reaction. These tags form lanthanide complexes with no or only a small net charge and produced sizeable PCSs with paramagnetic lanthanide ions in all mutants tested. The PCSs were readily fitted by single magnetic susceptibility anisotropy tensors. Protein precipitation during the click reaction was greatly alleviated by the presence of 150 mM NaCl.     

Electrochemical reduction of some 3-aryl-2-cyanothioacrylamide derivatives at the DME

Summary The polarographic behaviour of the title compounds is reported and discussed in acid media. The obtained data indicate that these compounds undergo a four-electron reduction. A mechanism for the electrode process atpH<7 is proposed, discussed and clarified via identification of controlled potential electrolysis (CPE) product and application of cyclic voltammetry (CV).

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Die elektrochemische Reduktion einiger 3-Aryl-2-cyanothioacrylamid-Derivate an der DME

Zusammenfassung Es wurde das polarographische Verhalten der Titelverbindungen in saurem Medium untersucht. Die erhaltenen Daten zeigen, daß diese Verbindungen eine Vierelektronenreduktion eingehen. Es wird ein Mechanismus für den Elektrodenprozess beipH<7 vorgeschlagen und diskutiert. Zur Klärung der Verhältnisse wurden die mittels kontrollierter Potential-Elektrolyse (CPE) erhaltenen Produkte identifiziert und auch cyclische Voltammetrie eingesetzt.