To flame-seal or not to flame-seal NMR tubes: The role of liquid-vapor equilibria on the accuracy of variable temperature experiments.

In NMR experiments, it is crucial to control the temperature of the sample, especially when measuring kinetic parameters. Usually, it takes 2 to 5 min for the temperature of the sample inside the NMR probe to stabilize at a fixed value set for the experiment. However, the NMR sample tubes are flame-sealed in some cases, such as when working with volatile solvents, atmosphere-sensitive samples, or calibration samples for long-term use.

Validation of Enthalpy-Entropy Compensation Mechanism in Partial Amide Bond Rotation.

The concept of enthalpy-entropy compensation (EEC) is one of the highly debated areas of thermodynamics. The conformational change due to restricted double-bond rotation shows a classic two-site chemical exchange phenomenon and has been extensively studied. Fifty-four analogs of ,-diethyl--toluamide (DEET) as a model system were synthesized to study the thermodynamics of the partial amide bond character using nuclear magnetic resonance (NMR) spectroscopy.

Effects of structural and electronic characteristics of chalcones on the activation of peroxisome proliferator-activated receptor gamma.

Chalcones share some structural similarities with GW-1929, a highly-selective and potent agonist for peroxisome proliferator-activated receptor-gamma (PPARγ). In this study, we tested 53 structurally diverse chalcones to identify characteristics essential for PPARγ activation in a GAL4-based transactivation assay. This screen identified several novel chalcone agonists of PPARγ.

Design, synthesis and identification of a new class of triarylmethyl amine compounds as inhibitors of apolipoprotein E production.

We have identified a new class of triarylmethyl amine compounds that can inhibit apolipoprotein E (apoE) production. ApoE is a cholesterol- and lipid-carrier protein implicated in aging, atherosclerosis, Alzheimer's Disease (AD), and other neurological and lipid-related disorders. Attenuation of apoE production is generally considered to be of therapeutic value.

Modulations in restricted amide rotation by steric induced conformational trapping.

The rotation around the amide bond in N,N-diethyl-m-toluamide (m-DEET) has been studied extensively and often used in laboratory instructions to demonstrate the phenomenon of chemical exchange. Herein, we show that a simple modification to N,N-diethyl-o-toluamide (o-DEET) significantly alters the dynamics of the restricted rotation around the amide bond due to steric interactions between the ring methyl group and the two N-ethyl groups. This alters the classic two-site exchange due to restricted rotation around the amide bond, to a three-site exchange, with the third conformation trapped at a higher-energy state compared to the other two.

An unnatural amino acid that induces beta-sheet folding and interaction in peptides.

This paper introduces a unique amino acid that can readily be incorporated into peptides to make them fold into beta-sheetlike structures that dimerize through beta-sheet interactions. This new amino acid, Orn(i-PrCO-Hao), consists of an ornithine residue with the beta-strand-mimicking amino acid Hao [J. Am.