Electronic and vibrational states of oxygen and sulfur molecular ions inside implanted SiO2 films

The paper presents the results of a low-temperature time-resolved photoluminescence (PL) investigation of thin SiO₂ films implanted with either oxygen or sulfur ions. Both PL and PLE spectra of the samples demonstrate vibronic oscillations which were attributed to the ground and excited states of sulfur- and oxygen-related molecular species. Vibrational frequencies and anharmonicity parameters calculated from the experimental data agree well with known literature. The most intensive excitation is observed in the spectral region of silica matrix excitons. It is established that such high-energy irradiation leads to non-bridging oxygen hole center creation as well as to the luminescence of molecular species. The results obtained on silica film modification could be of interest for future planar waveguides and thin oxide structure design.     

Reactive Acrylamide-Modified DNA Traps for Accurate Cross-Linking with Cysteine Residues in DNA–Protein Complexes Using Mismatch Repair Protein MutS as a Model

Covalent protein capture (cross-linking) by reactive DNA derivatives makes it possible to investigate structural features by fixing complexes at different stages of DNA–protein recognition. The most common cross-linking methods are based on reactive groups that interact with native or engineered cysteine residues. Nonetheless, high reactivity of most of such groups leads to preferential fixation of early-stage complexes or even non-selective cross-linking. We synthesised a set of DNA reagents carrying an acrylamide group attached to the C5 atom of a 2′-deoxyuridine moiety via various linkers and studied cross-linking with MutS as a model protein. MutS scans DNA for mismatches and damaged nucleobases and can form multiple non-specific complexes with DNA that may cause non-selective cross-linking. By varying the length of the linker between DNA and the acrylamide group and by changing the distance between the reactive nucleotide and a mismatch in the duplex, we showed that cross-linking occurs only if the distance between the acrylamide group and cysteine is optimal within the DNA–protein complex. Thus, acrylamide-modified DNA duplexes are excellent tools for studying DNA–protein interactions because of high selectivity of cysteine trapping.     

Time-resolved photoluminescence of implanted SiO2:Si+ films

In this paper we present results of a low-temperature time-resolved photoluminescence (PL) investigation of thin SiO₂ films implanted with silicon ions. In addition to the luminescence of well-known ODCs, some other bands are present in the low-energy region of PL spectra that are attributed to silicon nanoclusters (quantum dots – SiQDs), excitons and hydrogen-related species (HRS). Specific features of SiQD and HRS bands are the nanosecond kinetics and unusual “stepped” PL excitation spectrum in the 3.5–7.5 eV range. The possible origin of discovered phenomena is discussed. The obtained results are interpreted taking into account the interference of exciting radiation and dimensional quantization effects.