Beta-alpha correlation in the decay of 20Na

We have measured the β-α angular correlation in the allowed positron decay of ²⁰Na to the 7.42 MeV state of ²⁰Ne. The correlation is of the form $\text{1 +}\text{a}\text{cos}\text{θ +}\text{p}\text{cos}{}^2\text{θ}$. We find $\text{p}\text{= ?0.003 ± 0.005}$ in reasonable agreement with expectations based on the conserved vector current theory.     

Simultaneous selection,amplification and isolation of a pseudo-peptide receptor by an immobilised N-methyl ammonium ion template

Immobilised N-methyl ammonium ions have been used to simultaneously select, amplify and isolate a pseudo-peptide receptor from a dynamic library of hydrazones.     

Spin scattering and spin-orbit coupling in metals

An identity between ε, the probability of a spin disorientation at a metal surface with the ratio of the phonon resistivity scattering time, τ_ph, to the phonon spin scattering time, τ_2ph, in the bulk metal is established. Also it is shown that, for diffuse resistivity scattering, ε at a metal-metal interface is given by the $\text{τ}{}_{\mathrm{ph}}\text{τ}{}_{\mathrm{2ph}}\text{>}$ ratio in the bulk of the higher Z metal. Finally from an approximate fit of ε and the $\text{τ}{}_{\mathrm{ph}}\text{τ}{}_{\mathrm{2ph}}$ ratios to α⁴Z⁴ it is proposed that CESR may be readily observed in titanium and molybdenum.     

A Nuclear Singlet Lifetime of More than One Hour in Room‐Temperature Solution

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are supremely important techniques with numerous applications in almost all branches of science. However, until recently, NMR methodology was limited by the time constant T₁ for the decay of nuclear spin magnetization through contact with the thermal molecular environment. Long‐lived states, which are correlated quantum states of multiple nuclei, have decay time constants that may exceed T₁ by large factors. Here we demonstrate a nuclear long‐lived state comprising two ¹³C nuclei with a lifetime exceeding one hour in room‐temperature solution, which is around 50 times longer than T₁. This behavior is well‐predicted by a combination of quantum theory, molecular dynamics, and quantum chemistry. Such ultra‐long‐lived states are expected to be useful for the transport and application of nuclear hyperpolarization, which leads to NMR and MRI signals enhanced by up to five orders of magnitude.     

Rate of energy loss of relativistic μ-mesons

The rate of energy loss of relativistic μ-mesons by collision processes, bremsstrahlung, direct pair production and nuclear interactions is reviewed. The theory and experimental work associated with these individual mechanisms is discussed and, where relevant, similar work on protons and electrons included. The combination of the individual effects are involved in range energy measurements. Results of these experiments are presented and the factors which limit their value considered.     

Manipulation of the Phytochemical Profile of Tenderstem® Broccoli Florets by Short Duration,Pre-Harvest LED Lighting

Light quality has been reported to influence the phytochemical profile of broccoli sprouts/microgreens; however, few studies have researched the influence on mature broccoli. This is the first study to investigate how exposing a mature glasshouse grown vegetable brassica, Tenderstem^® broccoli, to different light wavelengths before harvest influences the phytochemical content. Sixty broccoli plants were grown in a controlled environment glasshouse under ambient light until axial meristems reached >1 cm diameter, whereupon a third were placed under either green/red/far-red LED, blue LED, or remained in the original compartment. Primary and secondary spears were harvested after one and three weeks, respectively. Plant morphology, glucosinolate, carotenoid, tocopherol, and total polyphenol content were determined for each sample. Exposure to green/red/far-red light increased the total polyphenol content by up to 13% and maintained a comparable total glucosinolate content to the control. Blue light increased three of the four indole glucosinolates studied. The effect of light treatments on carotenoid and tocopherol content was inconclusive due to inconsistencies between trials, indicating that they are more sensitive to other environmental factors. These results have shown that by carefully selecting the wavelength, the nutritional content of mature broccoli prior to harvest could be manipulated according to demand.     

Pseudohalogen chemistry—VII: Addition of thiocyanogen to alkynes

Thiocyanogen does not react with simple alkynes under heterolytic conditions in benzene at 20-25°. Under homolytic conditions, addition occurs readily giving mixtures of E- and Z- dithiocyanatoalkenes with high E:Z ratios; prolonged treatment with excess reagent also leads to mixtures of the dithiocyanatoalkenes but usually with lower E:Z ratios. A radical-chain mechanism, involving preferential anti-addition of thiocyanogen in an initial kinetically-controlled reaction and subsequent thermodynamically-controlled isomerisation of the adducts, is proposed. The influence of substituents on the reaction rates and product ratios is discussed in terms of their steric effects.     

Molecular shuttles by the protecting group approach

Two new [2]rotaxane-based molecular shuttles, in which a mechanically bound dibenzo[24]crown-8 (DB24C8) macroring shunts back and forth between two dialkylammonium recognition sites situated on a chemical dumbbell, have been constructed by a novel synthetic strategy that relies upon the use of the tert-butoxycarbonyl (Boc) protecting group. During the syntheses of both molecular shuttles, this protecting group masks a dialkylammonium recognition center which is liberated only after the [2]rotaxane constitution is established. In both cases, the molecular shuttles' other dialkylammonium center is essential for the rotaxane-forming reactions and it ensures that DB24C8 is interpenetrated by threadlike precursors, as a result of noncovalent bonding interactions, to produce [2]pseudorotaxanes which are stoppered subsequently through 1,3-dipolar cycloadditions between azides and bulky acetylenedicarboxylates. The new molecular shuttles have been examined by means of dynamic 1H NMR spectroscopy, which reveals that the movements of the DB24C8 macroring are very highly dependent both on solvent properties and on the nature of the spacer unit linking the two dialkylammonium centers. Thus, DB24C8 shunts facilely between the dialkylammonium centers when the shuttles are dissolved in solvents that readily donate their nonbonding electrons into noncovalent bonds, e.g., DMF, and when spacer units that do not offer much steric resistance to shuttling, e.g., hexamethylene, are used. On the other hand, shuttling is difficult in solvents that are less inclined to donate their electrons into noncovalent bonds, e.g., (CDCl2)2, and when relatively bulky benzenoid spacer units, e.g., p-xylylene, link the two dialkylammonium centers. It has been proposed that the DB24C8 might act as a "ferry" which carries a proton between dialkylammonium and dialkylamine moieties in a singly protonated [2]rotaxane by means of ion-dipole interactions.