Cryoprotectants: the essential antifreezes to protect life in the frozen state

In the fifty years since the establishment of the cryoprotective effect of glycerol, cell banking by cryopreservation has become routine in many areas of biotechnology and medicine. Cryoprotectant addition has become a rather mundane step within the overall protocol. However, for future advances in cryobiology and to meet new challenges in the clinical use of cryopreserved cells or tissues, it will be essential to have an understanding of the development and current status of the biological and chemical knowledge on cryoprotectants (CPA). This review was undertaken to outline the history of CPA use, the important properties of CPA in relation to freezing damage, and what can be learnt from natural freezing-tolerant organisms. The conflicting effects of protection and toxicity resulting from use of CPA are discussed, and the role of CPA in enhancing glassy states in the emerging field of vitrification are also set out.     

Computer simulation studies of anisotropic systems. XI. Second- and fourth-rank molecular interactions

The Maier-Saupe theory for nematic liquid crystals provides a reasonable account of their orientational order and its temperature dependence. The theory is based on second-rank anisotropic interactions and its predictions can be improved by the introduction of higher-rank terms as in the Humphries-James-Luckhurst theory. However comparison with the properties of real nematogens does not allow an unambiguous test of the theory because the form of the pair potential is unknown. This is not the case for computer simulations where the intermolecular potential is defined. We have therefore undertaken a Monte Carlo study of the influence fourth-rank interactions on nematic behaviour and report the results of our simulations here. The model nematogen used as a reference is that developed by Lebwohl and Lasher in which the particles are confined to the sites of a simple cubic lattice and interact via a second-rank anisotropic potential. The simulation gives the internal energy, the heat capacity at constant volume and the second-rank order parameter as a function of temperature, as well as the nematic-isotropic transition temperature. These results are used to provide the first unambiguous test of the Humphries-James-Luckhurst theory. We also discuss the changes in the transition temperature which are caused by the introduction of the fourth-rank term in the pair potential using thermodynamic perturbation theory for the Helmoltz free energy.     

The application of correlated SIMS and RBS techniques to the measurement of ion implanted range profiles

A simple, inexpensive secondary ion mass spectrometer (SIMS) instrument is de. scribed and its application to the determination of the range profiles of 20–30 keV Cs⁺ ions implanted into silicon and aluminium targets is demonstrated. The results are compared with those obtained by the alternative method of Rutherford backscattering (RBS) analysis and it is shown that provided the SIMS sputtering yield, S, (which is required for the calculation of the depth scale of the SIMS data) is chosen as a fitting constant, the agreement between the two techniques is excellent. On this basis, therefore, it is proposed that, provided a trace implant of Cs⁺ is included to provide an in-built calibration of S, the SIMS apparatus offers a universal technique for the determination of the profiles of impurities present at concentrations of 1–100 ppm.     

Adsorption von Argon, Stickstoff und Wasserdampf an Zirkoniumoxid

Ohne Zusammenfassung     

Neutrino mass hierarchy and stepwise spectral swapping of supernova neutrino flavors

We examine a phenomenon recently predicted by numerical simulations of supernova neutrino flavor evolution: the swapping of supernova nu(e) and nu(mu,tau) energy spectra below (above) energy E(C) for the normal (inverted) neutrino mass hierarchy. We present the results of large-scale numerical calculations which show that in the normal neutrino mass hierarchy case, E(C) decreases as the assumed effective 2x2 vacuum nu(e)<==>nu(mu,tau) mixing angle (approximately theta13) is decreased. In contrast, these calculations indicate that E(C) is essentially independent of the vacuum mixing angle in the inverted neutrino mass hierarchy case. With a good neutrino signal from a future galactic supernova, the above results could be used to determine the neutrino mass hierarchy even if theta13 is too small to be measured by terrestrial neutrino oscillation experiments.     

An immunoaffinity tandem mass spectrometry (iMALDI) assay for detection of Francisella tularensis

Francisella tularensis (F. tularensis) has been designated by the CDC as 1 of the 10 organisms most likely to be engineered for bioterrorism. Symptoms of tularemia in humans are non-specific, thus making the disease difficult to diagnose. If not quickly diagnosed and treated, the disease has a high mortality rate - thus methods for early and specific diagnosis are of critical importance.This immunoaffinity MALDI MS/MS (iMALDI) assay provides unambiguous detection of F. tularensis peptides at attomole levels from peptide solutions, and at low CFU levels from bacteria. The addition of stable-labeled versions of the peptide as internal standards allows absolute quantitation of F. tularensis peptides with a linear dynamic range spanning two orders of magnitude. The ability of mass spectrometry to obtain amino acid sequence data on affinity-captured peptides provides absolute specificity and avoids “false positives” from the non-specific binding. The F. tularensis iMALDI assay has been applied to different samples, such as nasal swabs.This novel quantitative diagnostic F. tularensis iMALDI assay allows the safe, sensitive, and specific detection of F. tularensis. The assay can be easily adapted to other target peptides and therefore has broad application potential in clinical diagnosis of other pathogens and diseases.