Central Ring Puckering Enhances the Stokes Shift of Xanthene Dyes.

Small-molecule dyes are generally designed based on well-understood electronic effects. However, steric hindrance can promote excited-state geometric relaxation, increasing the difference between the positions of absorption and emission bands (the Stokes shift). Accordingly, we hypothesized that sterically induced central ring puckering in xanthene dyes could be used to systematically increase their Stokes shift. Through a combined experimental/quantum-chemical approach, we screened a group of (9-acylimino)-pyronin dyes with a perturbed central ring geometry. Our results showed that an atom with sp3 hybridization in position 10 of (9-acylimino)-pyronins induces central ring puckering and facilitates excited-state geometric relaxation, thereby markedly enhancing their Stokes shifts (by up to ~2000 cm-1). Thus, we prepared fluorescent (9-acylimino)-pyronin pH sensors, which showed a Stokes shift disparity between acid and base forms of up to ~8700 cm-1. Moreover, the concept of ring puckering-enhanced Stokes shift can be applied to a wide range of xanthene analogues found in the literature. Therefore, central ring puckering may be reliably used as a strategy for enhancing Stokes shifts in the rational design of dyes.

Multiplicity-driven photochromism controls three-state fulgimide photoswitches.

Fulgimide photoswitches display three-state photoswitching between isomeric forms Z, E and C. Fulgimides have therefore access to both large steric change of double bond isomerization and the large spectral change induced by electrocyclization. By controlling the multiplicity and photoisomerization conditions, we achieved precise and near-quantitative control over both isomerization modes.

BODIPY phototether enables oligonucleotide cyclization and subsequent deprotection by tissue-transparent red light.

meso-methyl-BODIPY photocages release a leaving group upon visible light irradiation but often lack thermal stability. In turn, our thermally-stable, red-shifted BODIPY phototether allows oligonucleotide cyclization, preventing complementary strand hybridization. Hybridization resumes upon red-NIR irradiation, disconnecting the phototether by oxidative cleavage, which is easily monitored by a blue shift in fluorescence.

The effect of bee drone brood on the motility and viability of stallion spermatozoa-an in vitro study.

Bee drone brood is a beehive by-product with high hormonal activity used in natural medicine to treat male infertility. The aim of the study was to assess the effect of drone brood on stallion spermatozoa during a short-term incubation for its potential use in the equine semen extenders. Three different forms of fixed drone brood (frozen (FR), freeze-dried (FD), and dried extract (DE)) were used. Solutions of drone brood were compared in terms of testosterone, protein, total phenolic content, and antioxidant activity. The stallion semen was diluted with prepared drone brood solutions. The computer-assisted semen analysis (CASA) method was employed to evaluate the movement characteristics of the diluted ejaculate. To determine spermatozoa viability, the mitochondrial toxicity test (MTT) and Alamar Blue test were performed. In terms of testosterone content and antioxidant activity, a close likeness between FR and FD was found whereas DE's composition differed notably. FR had a positive effect mainly on progressive motility, but also on sperm distance and speed parameters after 2 and 3 h of incubation. On the contrary, FD and DE acted negatively, depending on increasing dose and time. For the first time, a positive dose-dependent effect of fixed drone brood on spermatozoa survival in vitro was demonstrated.