Mechanistic Insight into the Chemiluminescent Decomposition of Cypridina Dioxetanone and the Chemiluminescent, Fluorescent Properties of the Light Emitter of Cypridina Bioluminescence.

Cypridina bioluminescence has been increasingly used in bioimaging, bioanalysis, and biomedicine, due to high quantum yield and high signal-to-noise ratio. However, there is still no consensus regarding different aspects of the chemiluminescent mechanism of this system, which impairs the development of new applications. Herein, we have used a theoretical DFT and TD-DFT approach to (i) determine the identity of the dioxetanone species responsible for efficient chemiexcitation and (ii) identify the bioluminescent emitter and determine if light-emission occurs from the fluorescent or chemiluminescent state. Our results demonstrate that upon oxygenation of the imidazopyrazinone scaffold, a dioxetanone with a neutral amide group and a cationic guanidinopropyl group is formed. This species is efficiently chemiexcited (with no obvious charge transfer step) to the corresponding oxyluciferin with a neutral amide and cationic guanidinopropyl groups. After the "dark" chemiluminescent state, this oxyluciferin species is converted into a bright blue-emitting fluorescent state.

A Computational Investigation of the Equilibrium Constants for the Fluorescent and Chemiluminescent States of Coelenteramide.

In spite of recent advances in understanding the mechanism of coelenterate bioluminescence, there is no consensus about which coelenteramide specie and/or state are the light emitter. In this study, a systematic investigation of the geometries and spectra of all possible light emitters has been performed at the TD ωB97XD/6-31+G(d) level of theory, including various fluorescent and chemiluminescent states in vacuum, in a hydrophobic environment and in aqueous solution. To deduce the most probable form of the fluorescent and chemiluminescent coelenteramide emitter, the equilibrium constants for the fluorescent and chemiluminescent states connecting the various species have been calculated. ωB97XD gives a qualitatively good description of fluorescent and chemiluminescent structures. Coelenteramide is formed in a "dark" chemiluminescent state and must evolve to a bright fluorescent state. Moreover, the photoacidity of the phenol group is significantly higher in the fluorescent state than in the chemiluminescent state, which allows the formation of phenolate coelenteramide and clarifies its role as the bioluminescent emitter.

Diaqua-bis-(4,4'-bipyridine-κN)bis-(2,4,5-trifluoro-3-hy-droxy-benzoato-κO)manganese(II).

In the title compound, [Mn(C(7)H(2)F(3)O(3))(2)(C(10)H(8)N(2))(2)(H(2)O)(2)], the Mn(II) ion, situated on a centre of inversion, has a distorted octa-hedral coordination geometry and is coordinated by two N atoms from two 4,4'-bipyridine ligands, two O atoms from two 2,4,5-trifluoro-3-hy-droxy-benzoate ligands and two water mol-ecules. Inter-molecular O-H⋯N hydrogen bonds link the mol-ecules into a chain along the a axis. Inter-actions between neighboring chains occur through O-H⋯O hydrogen bonds, which link the chains into a two-dimensional supra-molecular network parallel to the ac plane. In addition, O-H⋯O hydrogen bonds between the water mol-ecules and carboxyl-ate groups also exist in the the crystal structure.