A series of diferrocenylpolyenes of general formula Fc(CH=CH)(n)()Fc with n = 1-6 (Fc = ferrocenyl group) has been prepared and studied from the point of view of intervalence transitions in the mixed valence state. Well-resolved intervalence transitions are observed in dichloromethane upon partial electrolytic oxidation. Comproportionation constants have been determined from redox titration data and in some cases from electrochemical wave splitting. The corrected spectra of the mixed valence species have been deconvoluted to extract the parameters (position, intensity, width) of the intervalence bands, which allowed the determination of the metal-metal coupling (V(ab)) through the bridging unit using Hush's formula. The decay of V(ab) with distance is close to an exponential law with an exponent of 0.087 Å(-)(1), constituting one of the smallest attenuations reported so far. A small deviation to the exponential law is detected.

Females of internally fertilizing species can significantly extend sperm lifespan and functionality during sperm storage. The mechanisms for such delayed cellular senescence remain unknown. Here, we apply current hypotheses of cellular senescence developed for diploid cells to sperm cells, and empirically test opposing predictions on the relationship between sperm metabolic rate and oxygen radical production in an insect model, the cricket Gryllus bimaculatus. Using time-resolved microfluorimetry, we found a negative correlation between metabolic rate (proportion of protein-bound NAD[P]H) and in situ intracellular oxygen radicals production in freshly ejaculated sperm. In contrast, sperm stored by females for periods of 1 h to 26 days showed a positive correlation between metabolic rate and oxygen radicals production. At the same time, stored sperm showed a 37 per cent reduced metabolic rate, and 42 per cent reduced reactive oxygen species (ROS) production, compared with freshly ejaculated sperm. Rank differences between males in ROS production and metabolic rate observed in ejaculated sperm did not predict rank differences in stored sperm. Our method of simultaneously measuring ROS production and metabolic rate of the same sample has the advantage of providing data that are independent of sperm density and any extracellular antioxidants that are proteins. Our method also excludes effects owing to accumulated hydrogen peroxide. Our results unify aspects of competing theories of cellular ageing and suggest that reducing metabolic rate may be an important means of extending stored sperm lifespan and functionality in crickets. Our data also provide a possible explanation for why traits of ejaculates sampled from the male may be rather poor predictors of paternity in sexual selection studies and likelihood of pregnancy in reproductive medicine.

Intervalence transitions have been observed between pentaammineruthenium(II) and -ruthenium(III) groups linked by dipyridylpolyenes, dipyridylthiophene, and dipyridylfuran. For all compounds, the comproportionation constants have been determined, to obtain corrected spectra of the mixed-valence forms, and the intervalence band profiles have been obtained by spectral deconvolution. The longest dipyridylpolyenes (with 3 and 4 double bonds) give only ill-defined bands, which does not allow us to reach definitive conclusions on the decay law of the electronic interaction with distance. On the contrary, dipyridylthiophene and -furan present a better resolution of the intervalence transition, which is ascribed to a better coplanarity and rigidity.