Folate antagonists. 17. Synthesis and biological properties of a 2,4-diamino-6-thioquinazoline analog of aminopterin

A multistep route for the synthesis of N-[4-[(2,4-diamino-6-quinazolinyl)thio]benzoyl]-L-glutamic acid (2) from 4-mercaptobenzoic acid and 5-chloro-2-nitrobenzonitrile is described. Although this aminopterin analog lacked significant antimalarial activity, it was a potent inhibitor of dihydrofolate reductase from Trypanosoma cruzi. The pteroic ester analog 11 , however, was active against Plasmodium berghei infections in mice at high doses.     

Revised structures of pratorinine and pratorimine

Two phenanthridone alkaloids isolated from the bulbs of $\text{Crinum bulbispermum}$ L. have been shown to be identical with pratorinine and pratorimine. The structure proposed earlier for pratorinine has been revised to 3 on the basis of an X-ray structure analysis and the structure of pratorimine has been shown to be 2.     

The NMR spectra of some 1,3-oxathians and the influence of heteroatoms on the coupling constants of adjacent protons

The preparation of 4-phenyl-1, 3-oxathian, 6-methyl-1, 3-oxathian, and some of their 2-substituted derivatives is described. Significant features of their NMR spectra are discussed with particular reference to the influence of the heteroatoms on the coupling constants of adjacent protons.     

Pre-scission particle and gamma-ray emission in heavy-ion-induced fission

An introduction is given to the physics of the equilibrium transition-state model and of dissipative nuclear dynamics. Experimental data on pre-scission particle and gamma-ray emission and their interpretation are reviewed. They appear to indicate overdamped motion of the nuclear fluid. A time scale for compound-nucleus fission of about 30 × 10⁻²¹ s or greater is indicated, whilst that for quasi- or fast-fission is somewhat shorter.     

Nuclear and radiochemistry training in the UK

Nuclear and radiochemistry training in the UK is described. A brief history of some of the departments is included.     

The Interaction of Shocks with Dispersive Waves I. Weak Coupling Limit

We introduce and analyze a model for the interaction of shocks with a dispersive wave envelope. The model mimicks the Zakharov system from weak plasma turbulence theory but replaces the linear wave equation in that system by a nonlinear wave equation allowing the formation of shocks. This paper considers a weak coupling in which the nonlinear wave evolves independently but appears as the potential in the time-dependent Schrodinger equation governing the dispersive wave. We first solve the Riemann problem for the system by constructing solutions to the Schrodinger equation that are steady in a frame of reference moving with the shock. Then we add a viscous diffusion term to the shock equation and by explicitly constructing asymptotic expansions in the (small) diffusion coefficient, we show that these solutions are zero diffusion limits of the regularized problem. The expansions are unusual in that it is necessary to keep track of exponentially small terms to obtain algebraically small terms. The expansions are compared to numerical solutions. We then construct a family of time-dependent solutions in the case that the initial data for the nonlinear wave equation evolves to a shock as t → t* < ∞. We prove that the shock formation drives a finite time blow-up in the phase gradient of the dispersive wave. While the shock develops algebraically in time, the phase gradient blows up logarithmically in time. We construct several explicit time-dependent solutions to the system, including ones that: (a) evolve to the steady states previously constructed, (b) evolve to steady states with phase discontinuities (which we call phase kinked steady states), (c) do not evolve to steady states.     

Exploiting and controlling gel-to-crystal transitions in multicomponent supramolecular gels

Multicomponent supramolecular gels provide opportunities to form materials that are not accessible when using the single components alone. Different scenarios are possible when mixing multiple components, from complete co-assembly (mixing of the components within the self-assembled structures formed) to complete self-sorting such that each structure contains only one of the components. Most examples of multicomponent gels that currently exist form stable gels. Here, we show that this can be used to control the mechanical properties of the gels, but what is probably most exciting is that we show that we can use a magnetic field to control the shape of the crystals. The gelling component aligns in a magnetic field and so results in anisotropic crystals being formed.

Multicomponent supramolecular gels provide opportunities to form materials that are not accessible when using the single components alone.     

Understanding the Development of Flexibility in Struggling Algebra Students

The ability to flexibly solve problems is considered an important outcome for school mathematics and is the focus of this paper. The paper describes the impact of a three-week summer course for students who struggle with algebra. During the course, students regularly compared and contrasted worked examples of algebra problems in order to promote flexible use of solution strategies. Assessments were designed to capture both knowledge and use of multiple strategies. The students were interviewed in order to understand their rationales for choosing particular strategies as well as their attitudes toward instruction that emphasized multiple strategies. Findings suggest that students gained both knowledge of and appreciation for multiple strategies, but they did not always use alternate strategies. Familiarity, understandability, efficiency, and form of the problem were all considerations for strategy choice. Practical and theoretical implications are discussed.