Tandem mass spectrometry (MS/MS) molecular networking guided profiling of small molecules from Aquilaria sinensis (Lour.) Gilg leaves and their bioactivity evaluation.

INTRODUCTION: Agarwood, a fragrant resinous wood mainly formed by Aquilaria spp., is used worldwide as a natural fragrance and traditional medicine. A large amount of Aquilaria sinensis (Lour.) Gilg leaves are underutilised during the process of the agarwood industry, and the development of A. sinensis leaves as tea has recently attracted more and more attention. However, the small molecule profile of A. sinensis leaves and their bioactivities has been rarely reported. OBJECTIVE: To conduct a rapid untargeted liquid chromatography-mass spectrometry (LC-MS) analysis of A. sinensis leaves with a molecular networking (MN) strategy and evaluate its antioxidant and antidiabetic value. METHOD: A MN-assisted tandem mass spectrometry (MS/MS) analysis strategy was used to investigate the small molecule profile of A. sinensis leaves. Additionally, the integration of antioxidant and α-glucosidase inhibitory assays with MN analysis was executed to expeditiously characterise the bioactive compounds for potential prospective application. RESULTS: Five main chemical groups including phenol C-glycosides, organic acids, 2-(2-phenylethyl) chromones, benzophenone O-glycosides and flavonoids were rapidly revealed from the A. sinensis leaves. Eighty-one compounds were provisionally identified by comparing their MS/MS fragments with canonical pathways. The featured xanthone C-glycosides and benzophenone C-glycosides were recognised as the primary components of A. sinensis leaves. Several dimers and a trimer of mangiferin were reported firstly in A. sinensis leaves. Furthermore, 17 and 14 potential bioactive molecules were rapidly annotated from antioxidant and α-glucosidase inhibitory fraction, respectively. CONCLUSION: Our findings will help expand the utilisation of A. sinensis leaves and thus promote the high-quality development of agarwood industry.

Shielding Effects of Aromatic (Indole) Ring for Structural Analysis.

This review provides a critical analysis of shielding effects induced by an aromatic (indole) ring of small molecules mainly including three members of naturally occurring secondary metabolites asterric acid analogs, diketopiperazines (DKPs) possessing an aromatic or an indole ring, and rubrolides. Empirical rules about the shielding effects induced by an aromatic (indole) ring are classified, based on which some 1H NMR chemical shift values in the A-ring and structures of asterric acid analogs are revised, and the relative configurations of some DKPs possessing an indole ring are also assigned or revised. The empirical rules could provide an efficient and convenient method for NMR data analysis and configuration determination for the three members of small molecules mentioned above.

Physical Origin of Dual-Emission of Au-Ag Bimetallic Nanoclusters.

On the origin of photoluminescence of noble metal NCs, there are always hot debates: metal-centered quantum-size confinement effect VS ligand-centered surface state mechanism. Herein, we provided solid evidence that structural water molecules (SWs) confined in the nanocavity formed by surface-protective-ligand packing on the metal NCs are the real luminescent emitters of Au-Ag bimetal NCs. The Ag cation mediated Au-Ag bimetal NCs exhibit the unique pH-dependent dual-emission characteristic with larger Stokes shift up to 200 nm, which could be used as potential ratiometric nanosensors for pH detection. Our results provide a completely new insight on the understanding of the origin of photoluminescence of metal NCs, which elucidates the abnormal PL emission phenomena, including solvent effect, pH-dependent behavior, surface ligand effect, multiple emitter centers, and large-Stoke's shift.