New Spin Probes: Tri- and Hexacationic Derivatives of Stable Tetrathiatriarylmethyl Radicals

Russian Journal of Organic Chemistry - The reaction of Finland trityl with tertiary aliphatic alcohols containing a terminal tertiary amino group, followed by quaternization of the amino groups,...     

Orientational self-pumped phase conjugation of a light beam in a layer of a nematic liquid crystal with nonreciprocal feedback

Self-pumped phase conjugation of a Nd: YAG laser beam by forward stimulated orientational scattering in a nematic liquid crystal layer with a nonreciprocal feedback loop is investigated. It is found that the threshold of phase-conjugate wave generation is the lowest when the phase shift difference of pumping and scattering waves in the loop is /2.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 304–311, March–April, 1995.     

Nondegenerate four-wave-mixing measurements of a resonantly induced refractive-index grating in a Nd:YAG amplifier

Two optical waves (at 1064 nm) were used to resonantly induce a population grating in a flash-lamp-pumped Nd:YAG rod, and a nonresonant wave (at 1054 or 694 nm) was used to read (with a diffraction efficiency of as much as 1% or 0.3%, respectively) the refractive-index grating caused by the difference in the polarizability of the excited and the unexcited Nd ions. Comparisons of experimental results and numerical calculations gave the dependence of the ratio of the real and the imaginary parts of the resonant susceptibility of Nd:YAG at 1064 nm on the pump power.     

Methanethiosulfonate Derivative of OX063 Trityl: A Promising and Efficient Reagent for Side-Directed Spin Labeling of Proteins

Trityl radicals (TAMs) have recently appeared as an alternative source of spin labels for measuring long distances in biological systems. Finland trityl radical (FTAM) served as the basis for this new generation of spin labels, but FTAM is rather lipophilic and susceptible to self-aggregation, noncovalent binding with lipophilic sites of proteins, and noncovalent docking at the termini of duplex DNA. In this paper the very hydrophilic OX063 TAM with very low toxicity and little tendency for aggregation is used as the basis for a spin label. Human serum albumin (HSA) labeled with OX063 has an intense narrow line typical of TAM radicals in solution, whereas HSA labeled with FTAM shows broad lines and extensive aggregation. In pulse EPR measurements, the measured phase memory time T_M for HSA labeled with OX063 is 6.3 μs at 50 K, the longest yet obtained with a TAM-based spin label. The lowered lipophilicity also decreases side products in the labeling reaction.     

Stimulated resonance scattering of light waves in laser crystals with a population inversion

A new type of stimulated scattering of light is discovered in a Nd:YAG laser crystal with a population inversion. The scattering occurs for light at the resonance frequency of the laser transition, with a small anti-Stokes shift. It is shown that the effect is due to the appearance of a wave of population of the metastable level and the associated traveling index grating in a laser medium with different polarizability of the excited and unexcited atoms. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 13–18 (10 January 1996)     

Novel materials from bis(arene)metal‐containing polyacrylonitrile

Novel bis(arene)metal‐containing polyacrylonitrile materials have been prepared by the polycyanoethylation reaction between acrylonitrile and (arene)₂M (M = Cr or V; arene = PhH, C₆H₄Et₂ or mesitylene) in the absence of solvent. The resulting star‐shaped molecules consist of a central (arene)₂M species with up to four polyacrylonitrile arms covalently bonded to the arene ligands. The materials are readily soluble and films can be cast from solutions in acetonitrile. The IR and solid state ¹³C NMR spectra (or EPR spectrum for the oxidized chromium‐containing polymer) are consistent with the presence of a metal–arene bond and confirm the persistence of the sandwich structure. The properties of the thermolysed materials are consistent with the formation of conjugated naphthyridine‐type structures. The value of |n₂| determined by the degenerate four‐wave mixing technique at 1064 nm with a 6 ns pulse duration for a solution in conc. H₂SO₄ (1 g l⁻¹) of the chromium‐containing polymer pyrolysed at 350 °C was found to be 0.8 × 10⁻¹³ cm² W⁻¹ corresponding to |lRe _χ⁽³⁾| = 0.4 × 10⁻¹¹ esu.     

DOPA Residues Endow Collagen with Radical Scavenging Capacity**

Here we uncover collagen, the main structural protein of all connective tissues, as a redox-active material. We identify dihydroxyphenylalanine (DOPA) residues, post-translational oxidation products of tyrosine residues, to be common in collagen derived from different connective tissues. We observe that these DOPA residues endow collagen with substantial radical scavenging capacity. When reducing radicals, DOPA residues work as redox relay: they convert to the quinone and generate hydrogen peroxide. In this dual function, DOPA outcompetes its amino acid precursors and ascorbic acid. Our results establish DOPA residues as redox-active side chains of collagens, probably protecting connective tissues against radicals formed under mechanical stress and/or inflammation.     

Silicon-containing polymers for non-linear optics

A variety of novel poly[ethynediyl-arylidene-ethynediyl-silylene]s (PEAES), including those containing hypercoordinate silicon atom as well as donor and acceptor groups, has been synthesized. The presence of hypercoordinate silicon favours high values of fast Kerr-type non-linearities, and the incorporation of amide groups gives rise to good optical quality nanocomposites in a silica matrix. The inorganic-organic hybrid sol-gel film incorporating 5–14 mass% of the polymer containing pentacoordinate silicon showed Re ⁽³⁾ = –9.5 ×10^–11 esu. The predominant rôle of the electron nonlinear mechanism has been demonstrated by using test beams with linear and circular polarizations. The photorefractive properties of composites based on PEAES as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N-ethylcarbazole and phenyltrimethoxysilane as plasticizer, and fullerenes as charge generators have been investigated. The nonlinear optical effects, including four-wave mixing and two-beam coupling were studied at 633 nm without preliminary electric poling. The photorefractive origin of the refractive index changes was confirmed by the high two-beam gain under an externally applied electric field. Refractive index gratings affording two-beam gain can also be written under zero field conditions. To explain this unique property of the materials it is suggested that chromophore orientation asymmetry arises either during film formation or is induced by the longitudinal intensity gradient.     

Self-organised poly[(ethynediyl)(arylene)(ethynediyl)silylene]/<Emphasis Type="Italic">N</Emphasis>-ethylcarbazole/polyphenylsilsesquioxane hybrid nanomaterials: photoconductivity and electro-optic response at telecommunication wavelengths

The photoconductivity and electro-optic response of a self-organised nanostructured poly[(ethynediyl)(arylene)(ethynediyl)silylene]/N-ethylcarbazole/polyphenylsilsesquioxane composite have been investigated with a cw diode laser at a wavelength of 1500 nm. For electric field 25 V µm^–1 and beam intensity 18 W cm^–2, the photosensitivity was 0.5 pS cm^–1 (W cm^–2)^–1. The dark conductivity was found to be much less than the photoconductivity and the composite shows photo charge generation at this wavelength. The value of the composite electro-optic coefficient is in agreement with data for polymeric materials active in the visible range. Orientational effects have been observed with modulation frequencies down to several Hz, and quite slow dynamics of the response can be expected.Based on the report presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30–June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1897–1901, September, 2004.