Proof of formation of an unstable conjugated triene on decomposition of gibberellin A3 in water
It has been shown by the methods of1H NMR and high-performance liquid chromatography with recording of UV spectra that in aqueous solutions of gibberellin A3, via gibberellenic acid, an unstable conjugated triene having λmax 326 nm is formed which is readily converted into allogibberic acid and is isolated as a mixture (1:2) with this acid. In the1H NMR spectrum of the triene, confirming its structure, spin-spin coupling both of the H-5 proton and of the protons of the methyl group with all the H-1, H-2, and the H-3 protons is observed. The precursor of allogibberic acid has been ascribed the structure of (−)-13-hydroxy-19,20-dinorgibberella-1,3,9,16-tetraen-7-oic acid with a conjugated 1,3,9-trienic system.
Photochemical and mass spectrometric transformation of gibberellenic acid to 9-epiallogibberic acid
Gibberellenic acid (2) reacted thermally in a modified immersion photochemical reactor, to give an intermediate triene (3). This triene then isomerized photochemically, via suprafacial [1,3]-hydrogen migration, to 9-epiallogibberic acid (5). On the other hand, comparison of the positive mass spectra of gibberellenic acid (2), allogibberic acid (4), and 9-epiallogibberic acid (5) showed that gibberellenic acid underwent electron impact fragmentation to the triene 3 cation. This cation then rearranged through suprafacial [1,3]-hydrogen migration to the 9-epiallogibberic acid (5) cation.
Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.