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Absorption of continuous wave and pulsed resonance radiation at a wavelength of 1.6 µm at the upward transition from the excited state $^{5}{\mathrm{I}}_{7}$ of holmium (Ho3+) ions in silica-based fiber has been studied. Analysis of experimental and simulated data of the absorption dynamics for the case of pulsed pumping of Ho-doped fiber allowed us to determine the previously unknown value of the absorption cross-section at the transition $^{5}{\mathrm{I}}_{7}{ \to }^{5}{\mathrm{I}}_{5}$ as 1.9×10–21 cm2. It allowed us to correctly simulate the relaxation process of the $^{5}{\mathrm{I}}_{7}$ level population averaged over the fiber length in the presence of stationary resonance radiation. The effect of pulsed resonance radiation with different peak powers (10 and 100 W) and pulse duration of 1 μs on the stationary active medium was considered. The mutual influence of the Ho-doped fiber characteristics and the resonance radiation at a wavelength of 1.6 μm was found. This allows the resonance radiation to be used as an attenuator or modulator of laser radiation at the $^{5}{\mathrm{I}}_{8}{ \to }^{5}{\mathrm{I}}_{7}$ transition in Ho-doped fibers.

Production of small discrete DNA nanostructures containing covalent junctions requires reliable methods for the synthesis and assembly of branched oligodeoxynucleotide (ODN) conjugates. This study reports an approach for self-assembly of hard-to-obtain primitive discrete DNA nanostructures—“nanoethylenes”, dimers formed by double-stranded oligonucleotides using V-shaped furcate blocks. We scaled up the synthesis of V-shaped oligonucleotide conjugates using pentaerythritol-based diazide and alkyne-modified oligonucleotides using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and optimized the conditions for “nanoethylene” formation. Next, we designed nanoethylene-based “nanomonomers” containing pendant adapters. They demonstrated smooth and high-yield spontaneous conversion into the smallest cyclic product, DNA tetragon aka“nano-methylcyclobutane”. Formation of DNA nanostructures was confirmed using native polyacrylamide gel electrophoresis (PAGE) and atomic force microscopy (AFM) and additionally studied by molecular modeling. The proposed facile approach to discrete DNA nanostructures using precise adapter-directed association expands the toolkit for the realm of DNA origami.

In this paper, we demonstrate the selection of radiation from the stimulated Raman scattered radiation, while using a spectral filter, based on a high-reflection fiber Bragg grating and an optical circulator. As a result, a stable pulsed signal was obtained at a wavelength of 1125 nm with a repetition rate of 1 MHz. The pulse duration and energy varied from 120 to 173 ps and 9 to 15 nJ, respectively, depending on the operating regimes of the master oscillator and amplifier.

Communicated by Ramaswamy H. Sarma

We demonstrate an all-fiber 2 μm holmium-doped laser hybrid mode locked by the co-action of nonlinear polarization evolution and absorption saturation of single-walled carbon nanotubes. The laser was pumped by a continuous-wave ytterbium-doped fiber laser at a wavelength of 1125 nm. The holmium laser generated 1.4 ps soliton pulses at a wavelength of 2082 nm with bandwidth up to 3.3 nm and repetition rate of 14.9 MHz. An average output power of 4.7 mW was obtained corresponding to pulse energy up to 0.3 nJ and peak power of 220 W.

Objective: To synthesize a novel chemotype based on the naphthoquinone scaffold with retained cytotoxicity and provisionally low intracellular oxidation potential. Background: Derivatives of naphthoquinone, although potent anticancer agents, can exert heart toxicity due to generation of free oxygen species. Methods: In this study, we modified the scaffold by replacing one carbonyl group with the oxime moiety. Interestingly, only one carbonyl group in 1-R-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione 2-oxides reacted with hydroxylamine. The spatial structure was determined by X-ray analysis. New compounds were tested for the ability to form stable complexes with double stranded DNA by spectroscopy and molecular docking and to induce death of tumor cell lines and non-malignant counterparts. Results: The resulting 1-R-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione 4-oxime 2-oxides were further acylated to produce a series of 1-R-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione 4-(O-acyloxime) 2-oxides. Newly synthesized compounds demonstrated a higher (in submicromolar or low micromolar range) cytotoxic potency against human colon and breast adenocarcinoma cell lines than to non-malignant skin fibroblasts. Spectroscopic measurements revealed that, unlike other classes of quinone derivatives, new naphthotriazoledione oxides did not form stable complexes with double stranded DNA regardless of their fitting to the DNA minor groove (as determined by molecular modeling). Conclusion: Thus, our chemical modifications yielded a new chemotype with good cytotoxic properties and yet-to-be-identified intracellular target(s).