Prebiotically Plausible Organocatalysts Enabling a Selective Photoredox α-Alkylation of Aldehydes on the Early Earth.

Organocatalysis is a powerful approach to extend and (enantio-) selectively modify molecular structures. Adapting this concept to the Early Earth scenario offers a promising solution to explain their evolution into a complex homochiral world. Herein, we present a class of imidazolidine-4-thione organocatalysts, easily accessible from simple molecules available on an Early Earth under highly plausible prebiotic reaction conditions.

Nucleophilicity and Electrophilicity Parameters for Predicting Absolute Rate Constants of Highly Asynchronous 1,3-Dipolar Cycloadditions of Aryldiazomethanes.

Kinetics of the reactions of aryldiazomethanes (ArCHN) with benzhydrylium ions (ArCH) have been measured photometrically in dichloromethane. The resulting second-order rate constants correlate linearly with the electrophilicities E of the benzhydrylium ions which allowed us to use the correlation lg k = s( N + E) (eq 1) for determining the nucleophile-specific parameters N and s of the diazo compounds. UV-vis spectroscopy was analogously employed to measure the rates of the 1,3-dipolar cycloadditions of these aryldiazomethanes with acceptor-substituted ethylenes of known electrophilicities E.

Thermoluminescence solid-state nanodosimetry--the peak 5A/5 dosemeter.

The shape of composite peak 5 in the glow curve of LiF:Mg,Ti (TLD-100) following (90)Sr/(90)Y beta irradiation, previously demonstrated to be dependent on the cooling rate used in the 400°C pre-irradiation anneal, is shown to be dependent on ionisation density in both naturally cooled and slow-cooled samples. Following heavy-charged particle high-ionisation density (HID) irradiation, the temperature of composite peak 5 decreases by ∼5°C and the peak becomes broader. This behaviour is attributed to an increase in the relative intensity of peak 5a (a low-temperature satellite of peak 5).

Mysteries of LiF TLD response following high ionisation density irradiation: nanodosimetry and track structure theory, dose response and glow curve shapes.

Three outstanding effects of ionisation density on the thermoluminescence (TL) mechanisms giving rise to the glow peaks of LiF:Mg,Ti (TLD-100) are currently under investigation: (1) the dependence of the heavy charged particle (HCP) relative efficiency with increasing ionisation density and the effectiveness of its modelling by track structure theory (TST), (2) the behaviour of the TL efficiency, f(D), as a function of photon energy and dose. These studies are intended to promote the development of a firm theoretical basis for the evaluation of relative TL efficiencies to assist in their application in mixed radiation fields. And (3) the shape of composite peak 5 in the glow curve for various HCP types and energies and following high-dose electron irradiation, i.

The effects of ionisation density on the glow curve structure of LiF:Mg,Ti (TLD-100): the behaviour of composite glow peak 5 in 'slow-cooled' material.

The effects of ionisation density on the structure of the glow curve of LiF:Mg,Ti (TLD-100) are briefly reviewed and discussed within the framework of the spatially correlated TC/LC model and localised recombination. The effects of 'slow-cooling' on the structure of composite peak 5 following low-ionisation density beta/gamma irradiation are described and analysed in both 'slow-cooled' and 'normally cooled' samples. It is demonstrated that 'slow-cooling' using a cooling rate of 30 degrees C h(-1) increases the relative intensity of glow peak 5a to composite glow peak 5 from approximately 0.

Advanced multistage deconvolution applied to composite glow peak 5 in LiF:Mg,Ti (TLD-100).

The effects of 'slow-cooling' on the structure of composite peak 5 following low-ionisation density beta/gamma irradiation are described and analysed in both 'slow-cooled' and 'normally-cooled' samples. Computerised glow curve deconvolution is employed with constrained 'peak-shape' parameters deduced from anciliary studies using 4 eV and 5 eV optical excitation.

On the use of LiF:Mg,Ti thermoluminescence dosemeters in space--a critical review.

The use of LiF:Mg,Ti thermoluminescence dosemeters (TLDs) in space radiation fields is reviewed. It is demonstrated in the context of modified track structure theory and microdosimetric track structure theory that there is no unique correlation between the relative thermoluminescence (TL) efficiency of heavy charged particles, neutrons of all energies and linear energy transfer (LET). Many experimental measurements dating back more than two decades also demonstrate the multivalued, non-universal, relationship between relative TL efficiency and LET.