Investigations on the Luminescence Properties of Quartz and Feldspars Extracted from Loess in the Canterbury Plains, New Zealand South Island

The applicability of the single-aliquot regenerative-dose (SAR) protocol, by using the optically stimulated lumi-nescence (OSL) signal of quartz as well as the post-infrared–infrared (pIRIR) signals of polymineral fine grains, namely pIRIR225 and pIRIR290, was assessed for dating loess in New Zealand South Island. OSL signals of quartz grains displayed low sensitivity. However, the application of repeated irradiation/bleaching cycles did not result in an increase in sensitivity; annealing in the 300–500°C temperature range generated the sensitisation of both the 110°C thermoluminescence (TL) peak as well as the OSL signal, likely by activation of yet unidentified luminescence centres. After heating, the quartz signal is comparable to that of ideal samples, but the annealing is precluding successful dating. On the other hand, feldspar infrared-stimulated signals displayed satisfactory properties, al-lowing estimation of ages ranging from 14 ± 1–29 ± 3 ka for the investigated deposit. It was shown that pIRIR225 and pIRIR290 methods have potential for dating loess in the South Island of New Zealand, based on the following observations: (i) Dose recovery tests were successful with recovered-to-given dose ratios with a <10% deviation from unity, (ii) constant residual values of about 4 Gy and about 10 Gy were obtained after exposures for 48 h in the case of pIRIR225 signals and 96 h in the case of pIRIR290 signals, respectively, (iii) while a slight dose-dependence of the residual was reported, and for a dose as large as 1600 Gy the residual values are ≅9 Gy and ≅19 Gy for pIRIR225 and pIRIR290 signals, respectively

Raman microspectroscopic study on low-pH-induced DNA structural transitions in the presence of magnesium ions

Low-pH-induced DNA structural changes were investigated in the pH range 6.8-2.10 by Raman microspectroscopy. Measurements were carried out on calf thymus DNA in the presence of low concentrations of Mg2+ ions. Vibrational spectra are presented in the wavenumber region 500-1650 cm-1. Large changes in the Raman spectra of calf-thymus DNA were observed on lowering the pH value. These are due to protonation and unstacking of the DNA bases during DNA melting and also to changes in the DNA backbone conformation. The intensities of the Raman bands of guanine (681 cm-1), adenine (728 cm-1), thymine (752 cm-1) and cytosine (785 cm-1), typical of the C2-endo-anti conformation of B-DNA, are discussed. The B-form marker near 835 cm-1 and the base vibrations in the higher wavenumber region (1200-1680 cm-1) are analysed. Effects of low pH value upon the protonation mechanism of opening AT and changing the protonation of GC base pairs in DNA are discussed