Analytical FT‐Raman spectroscopy to chemotype Leptospermum scoparium and generate predictive models for screening for dihydroxyacetone levels in floral nectar

Leptospermum scoparium (Mānuka) is the source of nectar for Unique Mānuka Factor (UMF) honey. The chemical component of interest to this study is dihydroxyacetone (DHA). DHA is the precursor for the chemical methylglyoxyl which is the main chemical responsible for the UMF activity in Manuka honey. Screening commercially bred plants for increased DHA synthesis in L. scoparium is a critical factor in growing the Manuka Honey industry in New Zealand. FT‐Raman spectroscopy, in combination with principal component analysis and partial least squares regression analysis, was investigated as an analytical tool for building a screening model for DHA in the nectar of L. scoparium. Leaf samples of seven cultivars of the species L. scoparium were collected in an attempt to correlate metabolic factors in the plant with DHA synthesis in the nectar. Leaf material was analysed using Fourier transform‐raman spectroscopy (FT‐Raman). The DHA levels in nectar samples of the same cultivars were measured using standard LC‐MS methods. This study showed that the application of multivariate analysis of FT‐Raman spectra from leaf material is a useful tool to screen for DHA potential in L. scoparium. The PLS regression shows that we can screen for DHA concentrations in the range of 3300–7600 mg/kg plus or minus 20% standard error and can distinguish low medium and high DHA synthesis in the group of plants studied. The model for predicting DHA concentrations is influenced by a significant contribution from the spectral variance due to beta‐carotene and other highly scattering compounds that are not directly correlated with UMF. Copyright © 2014 John Wiley & Sons, Ltd.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Mobility of electrons in supercritical krypton: role of density fluctuations

Excess electrons were generated in supercritical krypton by means of pulsed x-ray irradiation, and the electron transport phenomena were studied. Electron signals immediately after a 30 ps pulse showed a distinctive feature characteristic of the presence of the Ramsauer-Townsend minimum in the momentum transfer cross section. The dependence of the drift velocity v(D) on field strength was found to be concave upward in the low field region and then to go through a maximum with increasing field strength, which is also typical of the presence of a minimum in the scattering cross section at an intermediate field strength. A minimum in the electron mobility was observed at about one-half the critical density. The acoustical phonon scattering model, which successfully explained the mobility change in this density region in supercritical xenon, was again found to account for the mobility in supercritical krypton.     

Knotted Paths in Percolation

We study the topology of doubly-infinite paths in the bond percolation model on the three-dimensional cubic lattice. We propose a natural definition of a knotted doubly-infinite path. We prove the existence of a critical probability p _k satisfying p _c < p _k < 1 (where p _c is the usual percolation critical probability), such that for p _c < p < p _k , all doubly-infinite open paths are knotted, while for p > p _k there are unknotted doubly-infinite paths.     

Stacking of the mutagenic DNA base analog 5-bromouracil

The potential energy surface of the stacked 5-bromouracil/uracil (BrU/U) dimer has been investigated in the gas phase and in solution (water and 1,4-dioxane), modeled by a continuum solvent using the polarizable continuum model. Minima and transition states were optimized using DFT (the M06-2X density functional and the 6-31+G(d) basis set). Six stacked gas-phase BrU/U minima were located: four in the face-to-back orientation and two face-to-face. The global minimum in the gas phase is a face-to-face structure with a twist angle of 60° and a zero-point energy-corrected interaction energy of ?10.7 kcal/mol. The BrU/U potential energy surface is geometrically and energetically similar to that of U/U (Hunter and Van Mourik in J Comput Chem 33:2161, 2012). Energy calculations were also performed on experimental geometries of stacked dimers (47 containing BrU stacking with either adenine, cytosine, guanine or thymine and 51 containing thymine also stacking with one of those four bases) taken from DNA structures in the Protein Data Bank. Single-point interaction energies were computed at different levels of theory including MP2, CCSD(T) and DFT using the mPW2PLYP-D double-hybrid functional augmented with an empirical dispersion term, using basis sets ranging from aug-cc-pVDZ to aug-cc-pVQZ. No strong evidence was found for the suggestion that the mutagenicity of BrU is due to enhanced stacking of BrU compared to the corresponding stacked dimers involving thymine.