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Teaching practical laboratory skills is a key component of preparing undergraduate students for future careers in chemistry and elsewhere. In this paper, we present our new strategy to teach practical skills to undergraduate chemistry students. We report a Skills Inventory, a list of the suggested practical skills a graduate chemist should possess; this list was compiled by chemists across the UK. In our new practical course we begin by decoupling the practical skill from the theoretical background, compelling students to first master the basic processes needed to carry out a specific technique. In what we have termed a ‘spiral curriculum’ approach, skills are revisited on multiple occasions, with increasing complexity and greater emphasis on underlying theory. The new course makes links across traditional subdisciplines of chemistry to avoid compartmentalisation of ideas.

The nature of the first genetic polymer is the subject of major debate.sup.1. Although the 'RNA world' theory suggests that RNA was the first replicable information carrier of the prebiotic era--that is, prior to the dawn of life.sup.2,3--other evidence implies that life may have started with a heterogeneous nucleic acid genetic system that included both RNA and DNA.sup.4. Such a theory streamlines the eventual 'genetic takeover' of homogeneous DNA from RNA as the principal information-storage molecule, but requires a selective abiotic synthesis of both RNA and DNA building blocks in the same local primordial geochemical scenario. Here we demonstrate a high-yielding, completely stereo-, regio- and furanosyl-selective prebiotic synthesis of the purine deoxyribonucleosides: deoxyadenosine and deoxyinosine. Our synthesis uses key intermediates in the prebiotic synthesis of the canonical pyrimidine ribonucleosides (cytidine and uridine), and we show that, once generated, the pyrimidines persist throughout the synthesis of the purine deoxyribonucleosides, leading to a mixture of deoxyadenosine, deoxyinosine, cytidine and uridine. These results support the notion that purine deoxyribonucleosides and pyrimidine ribonucleosides may have coexisted before the emergence of life.sup.5. A prebiotic synthesis of the purine DNA nucleosides (deoxyadenosine and deoxyinosine) in which the pyrimidine RNA nucleosides (cytidine and uridine) persist has implications for the coexistence of DNA and RNA at the dawn of life., Author(s): Jianfeng Xu [sup.1] , Václav Chmela [sup.1] , Nicholas J. Green [sup.1] , David A. Russell [sup.1] , Mikolaj J. Janicki [sup.2] , Robert W. Góra [sup.2] , Rafal [...]

Collisional energy transfer in unimolecular systems is often described using a master equation. The lack of detailed knowledge of energy transfer events combined with the computationally intensive nature of this approach makes approximate methods attractive, especially for parametrizing experimental results. One such approximation is based on the diffusion equation. In this paper a number of diffusion equation approximations is examined. Troe and Nikitin have derived such approximations by truncation of the Kramers–Moyal expansion of the master equation. A new approximation, using a similar approach is presented here. The diffusion equation can also be obtained as the limit of a sequence of master equations as the collision energy transfer becomes infinitely small and frequent. The derivation of such a limiting diffusion equation is presented. A further set of approximations in which the energy transfer process is imbedded in a diffusion process is also examined. The accuracy of all approximations is assessed by comparison with full solutions of the corresponding master equations for energy transfer in azulene and ethane, and for the kinetics of methane dissociation. [ABSTRACT FROM AUTHOR]

Three models for the relaxation kinetics of a reversible unimolecular isomerization reaction are formulated and analyzed: a generalization of the simple Lindemann–Hinshelwood scheme, a detailed model with the strong collision approximation, and a master equation solution. For such systems the use of a classical relaxation analysis has been questioned. In each case it is found that the relaxation analysis does not give forward and reverse rate constants appropriate to the pure irreversible reactions, but that the rate constants so obtained can be interpreted in terms of irreversible schemes which allow for back reaction before collisional stabilization. The accuracy of this decomposition is linked with the applicability of the steady-state approximation for the populations of the reactive states, as is demonstrated analytically under the strong collision approximation, and numerically with the full master equation. An alternative approach using perturbation theory is shown to be unacceptably inaccurate. [ABSTRACT FROM AUTHOR]

Recently we presented [Chem. Phys. Lett. 142, 385 (1987)] a method for calculating the diffusion-controlled geminate escape probability of an ion pair in an anisotropic medium. The escape probability depends on both the length and the direction of the initial interion vector, and is reducible to a function of two dimensionless variables describing the overall anisotropy of the medium. In this paper the treatment is extended to include an initial distribution of interion distances and an external field. Inclusion of a field increases the number of independently variable parameters to five: two to describe the anisotropy of the medium and three to describe the intensity and direction of the applied field. It is shown that the effects of including anisotropy are not negligible for the typical case of anthracene and that the slope-to-intercept ratio of the field-dependent escape probability for a spherically averaged distribution depends on the direction of the applied field. [ABSTRACT FROM AUTHOR]