Betalains are natural plant pigments found in certain plants belonging to the order Caryophyllales. This work presents theoretical calculations on the excited state properties of three betalains: betanin, an almost non-fluorescent natural betacyanin; indicaxanthin, a weakly fluorescent natural betaxanthin; and cBeet120, a synthetic betaxanthin fluorescence probe that is also weakly fluorescent. Calculations at the algebraic diagrammatic construction (ADC (2)) level of theory, combined with the conductor-like screening model (COSMO) to simulate solvent effects, predict absorption spectra in good agreement with experiment for all three of these betalains. Several distinct theoretical approaches identify torsions of the molecular geometry that can lead to conical intersections between the excited singlet (S_1) and ground state (S_0) potential surfaces and identify probable geometries at the minimum on the crossing seam (MXS). The present results thus emphasize the central role played by torsional modes in determining the fluorescence properties of natural betalains and of most synthetic betalain analogs as well. A direct implication of the results is that the fluorescence quantum yields of natural or synthetic betalains can potentially be enhanced by introducing structural modifications that permit the molecule to avoid these MXS geometries and/or by incorporation into a more rigid environment that hinders the specific bond rotations involved in the non-radiative relaxation of the excited state.

Anthocyanins are the natural plant pigments responsible for most of the red, blue and purple colors of flowers and fruit. One method of stabilization of the color of anthocyanins in nature is intramolecular copigmentation, in which a copigment molecule covalently attached to one of the sugar residues complexes with the anthocyanin cation chromophore. In the present work, two quantum chemical methodologies, time-dependent density functional theory (TD-DFT) and second.order algebraic diagrammatic construction (ADC(2)), were employed to predict the absorption spectra in vacuum and conductor-like screening model (COSMO) water of a natural anthocyanin containing an ester of coumaric acid (copigment) bound to the sugar residue of a cyanidin chromophore. ADC(2) in water adequately reproduces the experimental spectra with and without intramolecular copigmentation, pointing to this theoretical technique as a promising approach for predicting the spectroscopic properties of natural (and nature-inspired) dyes and pigments.

A novel fluorescent sensor based on carbon dots (CDs) was synthesized for direct determination of glutathione (GSH), which bromoacetyl bromide was functionalized CDs (CDs-Br) sensing system for the first time. The bromoacetyl bromide functional groups (halogen moiety) can quench the fluorescence of CDs, which were substituted by the -SH group, could lead to a significant fluorescence increase of CDs-Br via the halogen substitution cyclization. This method could effectively immediately detect amino acids with thiols and it needn't to be combined with metal ions. Under optimum conditions, the probe has a good selectivity for GSH over other various biologically relevant species and even two other similar biothiols(Cys/Hcy) and could image GSH in living cells. (C) 2017 Elsevier B.V. All rights reserved.

Glutathione is a thiol-containing tripeptide which composed of glutamic acid, cysteine and glycine. Reduced glutathione possesses the function of anti-oxidation, toxin-removing and other crucial physiological functions. Abnormal level of it indicates the emergence of diseases such as hepatitis, pneumonia, AIDS or even cancer. Therefore real-time detection of it has the important significance of keeping normal physiological condition and monitoring certain diseases. The fluorescence technique has obvious advantages of swift response, high sensitivity and selectivity comparing with other detection methods. The detection of glutathione by fluorescent reagents has attracted much attention. In this review, we summarized fluorescent probes reported so far for glutathione according to the classification of organic and inorganic probes, including coumarin-based probes, BODIPY-based probes, quantum dots-based probes, carbon dots-based probes and so on, focusing on the detection process and mechanism. The review concluded with an outlook towards potential applications of all kinds of probes for glutathione detection.

We describe a new method for synthesis of water-soluble photoluminescent carbon dots (CDs) by one-pot hydrothermal treatment of adipic acid and triammonium citrate. The CDs have excitation/emission maxima of 340/440 nm, a quantum yield of 0.13, and are shown to be a viable fluorescent probe for the determination of Hg(II). It shows a linear relationship in the 4 to 18 μM mercury ion concentration range. The detection limit is as low as 2.47 μM. The CDs were applied to intracellular sensing and imaging of Hg(II) where they showed low toxicity.