Anisotropic spin—lattice relaxation in the triplet state of naphtralene-h8 in n-pentane

The temperature dependence of the individual spin—lattice relaxation rate constants (W_ij) between the lowest triplet sublevels of naphthalene-h₈ in a polycrystalline Shpol'skii matrix of n-pentane have been measured between 1.2 and 2.4 K in zero field. The total sublevel decay constants are evaluated and found to be independent of temperature. The W_ij are found to be highly anisotropic, but the anisotropy pattern differs from that observed previously in a durene matrix.     

The relative biological effectiveness of a high energy neutron beam for micronuclei induction in T-lymphocytes of different individuals

In assessing the radiation risk of personnel exposed to cosmic radiation fields as it pertains to radiological damage during travel in civilian aircrafts, it is particularly important to know the relative biological effectiveness (RBE) for high energy neutrons. It has been the subject of numerous investigations in recent years using different neutron energies and cytogenetic examinations. Variations in the radiosensitivity of white blood cells for different individuals are likely to influence the estimate of the relative biological effectiveness for high energy neutrons. This as such observations have been noted in the response of different cancer cell lines with varying inherent sensitivities. In this work the radiosensitivities of T-lymphocytes of different individuals to the p(66)/Be neutron beam at iThemba LABS were measured using micronuclei formations and compared to that noted following exposure to ⁶⁰Co γ-rays. The principle objective of this investigation was to establish if a relationship between neutron RBE and variation in biological response to ⁶⁰Co γ-rays for lymphocytes from different individuals could be determined. Peripheral blood samples were collected from four healthy donors and isolated lymphocytes were exposed to different doses of ⁶⁰Co γ-rays (1–5 Gy) and p(66)/Be neutrons (0.5–2.5 Gy). One sample per donor was not exposed to radiation and served as a control. Lymphocytes were stimulated using PHA and cultured to induce micronuclei in cytokinesis-blocked cells. Micronuclei yields were numerated using fluorescent microscopy. Radiosensitivities and RBE values were calculated from the fitted parameters describing the micronuclei frequency dose response data. Dissimilar dose response curves for different donors were observed reflecting varying inherent sensitivities to both neutron and gamma radiation. A clear reduction in the dose limiting RBE_M is noted for donors with lymphocytes more sensitive to γ-rays (p = 0.032, R² = 0.94). Unlike observations made with different cancer cell lines exposed to the same clinical neutron beam, the variations in neutron RBE observed in T-lymphocytes of different individuals is related to the cellular radioresistance to photons.     

Maximizing Coordination Capsule–Guest Polar Interactions in Apolar Solvents Reveals Significant Binding

Guest encapsulation underpins the functional properties of self‐assembled capsules yet identifying systems capable of strongly binding small organic molecules in solution remains a challenge. Most coordination capsules rely on the hydrophobic effect to ensure effective solution‐phase association. In contrast, we show that using non‐interacting anions in apolar solvents can maximize favorable interactions between a cationic Pd₂L₄ host and charge‐neutral guests resulting in a dramatic increase in binding strength. With quinone‐type guests, association constants in excess of 10⁸ m ^?1 were observed, comparable to the highest previously recorded constant for a metallosupramolecular capsule. Modulation of optoelectronic properties of the guests was also observed, with encapsulation either changing or switching‐on luminescence not present in the bulk phase.