A proton magnetic relaxation study has been carried out on a further seven polycrystalline amino acids from 130 to 500 K at 60·2 MHz, supplemented by measurements of the spectrum down to 4 K on five of them. These amino acids all have one or two methyl groups in their side chain, and exhibit two relaxation minima. Clear evidence is given that the relaxation minima at lower temperatures are attributable to reorientation of the methyl groups, while those at higher temperatures are attributable to reorientation of the -NH₃ groups in the zwitterion configuration of the molecules. Values of the relaxation constants, activation energies and time factors which best characterize the kinetics of both motions are tabulated. Effects of methyl group tunnelling are found for methionine and valine.

A proton magnetic resonance and relaxation study has been carried out on seven polycrystalline amino acids from 130 to 500 K at 60·2 MHz. These amino acids contain no methyl groups and all exhibit a single relaxation minimum. The measurements are well accounted for by the Kubo-Tomita theory of relaxation assuming a single correlation time which follows a simple activation law. In all cases the source of relaxation is provided by reorientation of the -NH₃ groups in the zwitterion form of the molecules; other protons are relaxed by spin-exchange with those of the -NH₃ group. The measured relaxation constants are consistent with inter-proton distances in the -NH₃ groups recently measured by neutron diffraction.

A proton magnetic relaxation investigation has been carried out on a further six polycrystalline amino acids from 130 to 500 K at 60·2 MHz and in two cases at 20·0 MHz also. Asparagine and glutamine with amide side chains exhibit closely similar relaxation minima well accounted for in terms of the Kubo-Tomita relaxation theory by NH₃ group reorientation in the zwitterion form of the molecules. Cysteine and phenylalanine exhibit two relaxation mechanisms, one at higher temperatures due to NH₃ group reorientation and a weaker mechanism at lower temperatures ascribed to motion of their side chains. The unusual relaxation behaviour of arginine arises from the protonation of the guadinium side group, so generating three reorienting amino groups in the molecule. The exceptionally long relaxation times of proline stem from the rigidity of its ring structure. Relaxation constants, activation energies and time factors for all the amino acids studied in this series are tabulated and discussed. For 18 amino acids the relaxation constants for NH₃ group reorientation follow well an inverse dependence on the number of molecular protons being relaxed, and their absolute values agree well with those calculated using proton separations determined by neutron diffraction. Activation energies for NH₃ group reorientation range from 28 to 52 kJ/mole. Highest values are for amino acids with hydrocarbon side chains suggesting the formation of stronger hydrogen bonds by NH₃ groups in the crystal when in the absence of competition from polar interactions. Methyl rotors, unencumbered by hydrogen bonding, are characterized by lower activation energies in the range 7 to 22 kJ/mole.

The aim of the study was to determine if an As-contaminated soil, stabilized using zerovalent iron (Fe0) and its combination with gypsum waste, coal fly ash, peat, or sewage sludge, could be used as a construction material at the top layer of the landfill cover. A reproduction of 2 m thick protection/vegetation layer of a landfill cover using a column setup was used to determine the ability of the amendments to reduce As solubility and stimulate soil functionality along the soil profile. Soil amendment with Fe0 was highly efficient in reducing As in soil porewater reaching 99 % reduction, but only at the soil surface. In the deeper soil layers (below 0.5 m), the Fe treatment had a reverse effect, As solubility increased dramatically exceeding that of the untreated soil or any other treatment by one to two orders of magnitude. A slight bioluminescence inhibition of Vibrio fischeri was detected in the Fe0 treatment. Soil amendment with iron and peat showed no toxicity to bacteria and was the most efficient in reducing dissolved As in soil porewater throughout the 2 m soil profile followed by iron and gypsum treatment, most likely resulting from a low soil density and a good air diffusion to the soil. The least suitable combination of soil amendments for As immobilization was a mixture of iron with coal fly ash. An increase in all measured enzyme activities was observed in all treatments, particularly those receiving organic matter. For As to be stable in soil, a combination of amendments that can keep the soil porous and ensure the air diffusion through the entire soil layer of the landfill cover is required.