Isomeric Effect on H/D Exchange of Resveratrol Studied by NMR Spectroscopy

Abstract

Resveratrol (3,5,4'-trihydroxylstilbene), a phytoalexin in response to injury or fungal attack, is found in grapes and other food products. It has been well documented that the compound has beneficial effects as hypolipidemic, anticancer, antiviral, neuroprotective, antiaging, and anti-inflammatory natural active principle. It was observed that both trans-and cis-resveratrols undergo hydrogen-deuterium (H/D) exchange at H-2,6 and H-4 positions of the A-ring. The exchange rates were determined by 1 H NMR spectroscopy. The results reveal that the exchange rates are configuration and pH dependent. Derivative of 2-O-β-D-glucoside can significantly speed up the H/D exchange reactions for both isomers. The trans-resveratrol experiences faster H/D exchanging than the cis-resveratrol. Such isomeric effect is possibly due to the factor that the trans-resveratrol is in favor of forming larger/super conjugative system and has less spatial interference. Theoretical calculation shows that electronegativity at these positions is in the order of H-2,6＞H-4, which is in consistent with the exchange rates observed by NMR. The results may be of help in understanding the properties of resveratrol, and in analysis of resveratrol in natural products or body fluids using mass spectroscopy that occasionally requires stable deuterium isotope labeling.

N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(ii) and chromium(i)

“…The magnetic moment µ eff in solution was determined to µ eff = 4.84µ B , which accounts for four unpaired electrons per chromium atom. Our results and the molecular structure obtained from XRD are in agreement with the molecular structure reported previously by Zhu et al 28 [{Cr(IMe Me ) (THF)Cl(µ-Cl)} 2 ] defied isolation, but attempts to isolate this complex by crystallization lead to formation of small amounts of a number of single crystals suitable for XRD. The resulting molecular structures reveal that the situation is most probably more complicated as different isomers have been characterized, either isolated molecules [{Cr(IMe Me )(THF)Cl(µ-Cl)} 2 ] (ESI, Fig.…”

“…It was reported previously that the reaction of CrCl 2 with two equivalents IiPr Me afforded a the chromium complex [Cr (IiPr Me ) 2 Cl 2 ], whereas the reaction using just one equivalent led to formation of dinuclear [{Cr(IiPr Me )(THF)Cl(µ-Cl)} 2 ], which can be regarded as intermediate in the formation of the former. 28,29 We can confirm these results for all NHCs used in this study. The reactions of freshly prepared [CrCl 2 (THF) 2 ] with one equivalent of the free carbenes IMe Me , IiPr Me , IMes, IDipp, and cAAC Me led immediately to intensely blue colored solutions, which obtain their color from initially formed chloride bridged dimers of the type [{Cr(L)(THF)Cl(µ-Cl)} 2 ] or [{Cr(L)Cl (µ-Cl)} 2 ] (L = NHC, cAAC Me ), respectively.…”

“…27 For example, in 2010 Zhu and coworkers reported the molecular structures of the di-and mononuclear complexes [{Cr(IiPr Me )Cl(µ-Cl)(thf )} 2 ] (vide infra) and [Cr(IiPr Me ) 2 Cl 2 ], yet a derivatization of the latter with NaC 5 H 5 proved to be unsuccessful (vide infra). 28 Despite the early advances made in the synthetic approaches to untethered carbene ligated chromium complexes, chromium(II) and chromium(III) half-sandwich complexes ligated with monodentate NHCs are rather rare and have prepared so far according to four established routes (Scheme 1).…”

The unique catalytic role of water in aromatic C–H activation at neutral pH: a combined NMR and DFT study of polyphenolic compounds

“…It has been suggested that the mechanism of H/D exchange reaction of aromatic C-H protons in acid or basic conditions of polyphenolic compounds [37][38][39][40][41] follows a two-step process, 41 as shown in Fig. 2.…”

Novel Functional Mesoporous Silicas for Separating and Pre-Concentrating Trace Chromium Ion in Fireworks and Firecracker

“…Fireworks and firecracker is one of the most well-known consumer goods around the world. The heavy metal contamination coming from fireworks and firecracker 1,2 is of increasing concern because of its great threaten to human health [3][4][5] . Lead, mercury and chromium identified as highly toxic elements will be gradually accumulated in organism body and further threaten human health through food chains.…”