ABSTRACT
The present work shows, for the first time, the application of laser ablation connected to inductively coupled plasma mass spectrometry (LA-ICP-MS) to the localized quantitative analysis of inclusions in polymeric industrial films. The multielemental mapping capabilities of LA-ICP-MS has allowed to chemically examine unique defects appeared during the plastic processing. This analytical tool is perfectly suited to detect elements such as Al, Mg, Zr, Ti, Cr, P, Pb, Sb, Zn, and Si in those inclusions. A method for multielemental quantitative analysis of these defects has been developed in the present work. The profiling for more than 100 different defects in three samples has demonstrated that more than 50% of these inclusions contain aggregates of some of the aforementioned elements. Therefore, the distribution of elements used as additives or present in catalysts must be carefully controlled during the production of polymeric films in order to avoid degradation in their performance.
ABSTRACT
Locked nucleic acids (LNA), conformationally restricted nucleotide analogues, are known to enhance pairing stability and selectivity toward complementary strands. With the aim to contribute to a better understanding of the origin of these effects, the structure, thermal stability, hybridization thermodynamics, and base-pair dynamics of a full-LNA:DNA heteroduplex and of its isosequential DNA:DNA homoduplex were monitored and compared. CD measurements highlight differences in the duplex structures: the homoduplex and heteroduplex present B-type and A-type helical conformations, respectively. The pairing of the hybrid duplex is characterized, at all temperatures monitored (between 15 and 37 degrees C), by a larger stability constant but a less favorable enthalpic term. A major contribution to this thermodynamic profile emanates from the presence of a hairpin structure in the LNA single strand which contributes favorably to the entropy of interaction but leads to an enthalpy penalty upon duplex formation. The base-pair opening dynamics of both systems was monitored by NMR spectroscopy via imino protons exchange measurements. The measurements highlight that hybrid G-C base-pairs present a longer base-pair lifetime and higher stability than natural G-C base-pairs, but that an LNA substitution in an A-T base-pair does not have a favorable effect on the stability. The thermodynamic and dynamic data confirm a more favorable stacking of the bases in the hybrid duplex. This study emphasizes the complementarities between dynamic and thermodynamical studies for the elucidation of the relevant factors in binding events.
