Reactions of triosmium clusters with indole: X-ray structures of [Os3(CO)10(μ-OH)(μ-OMeCO)] and [Os3(μ-H)(CO)10(μ-1, 2-η2-NC8H6)]

Treatment of [Os₃(CO)₁₂] with indole in presence of a methanolic solution of Me₃NO⋅2H₂O at 60^∘C afforded the previously reported compounds [(μ-H)Os₃(CO)₁₀(μ-OMe)] 2, [(μ-H)Os₃(CO)₁₀(μ-OH)] 3 and [Os₃(CO)₁₀(μ-OH)(μ-OMeCO)] 4 in 10, 5 and 20% yields, respectively. The reaction of [Os₃(CO)₁₀(MeCN)₂] with indole at room temperature gave [(μ-H)Os₃(CO)₁₀(μ-1,2-η²-NC₈H₆)] 5 in 40% yield. Compounds 4 and 5 have been characterized by single crystal X-ray diffraction studies. Compound 4 crystallizes in the monoclinic space group P2(1)/c with a = 23.1239(3), b = 9.8087(4), c = 16.9017(6) ?, β = 92.6998(14)^∘, Z = 8 and V = 3829.3(2) ?³ and 5 crystallizes in the monoclinic space group P2(1)/c with a = 9.009(3), b = 9.764(4), c = 24.906(6) ?, β = 93.452(14)^∘, Z = 4 and V = 2186.9(13) ?³. Compound 4 consists of an open cluster of three osmium atoms with the hydroxy and methoxycarbonyl ligands bridging the open Os–Os edge. Compound 5 consists of an isosceles triangle of osmium atoms with one elongated Os–Os edge which is bridged by the hydride and the indolyl ligands.     

White-beam X-ray diffraction and radiography studies on high-boron-containing borosilicate glass at high pressures

ABSTRACT

Multi-angle energy-dispersive X-ray diffraction studies and white-beam X-ray radiography were conducted with a cylindrically shaped (1?mm diameter and 0.7?mm high) high-boron-content borosilicate glass sample (17.6% B₂O₃) to a pressure of 13.7?GPa using a Paris-Edinburgh (PE) press at Beamline 16-BM-B, HPCAT of the Advanced Photon Source. The measured structure factor S(q) to large q?=?19 Å^?1 is used to determine information about the internuclear bond distances between various species of atoms within the glass sample. Sample pressure was determined with gold as a pressure standard. The sample height as measured by radiography showed an overall uniaxial compression of 22.5% at 13.7?GPa with 10.6% permanent compaction after decompression to ambient conditions. The reduced pair distribution function G(r) was extracted and Si–O, O–O and Si–Si bond distances were measured as a function of pressure. Raman spectroscopy of the pressure recovered sample as compared to starting material showed blue-shift and changes in intensity and widths of Raman bands associated with silicate and four-coordinated boron.     

Fluorimetric study of interaction of merbromin with trypsin

Interaction of merbromin with trypsin is of bovine origin has been studied by monitoring the absorption steady-state and time-resolved fluorescence spectral properties of the dye. Studies have been done in media of varying pH at different trypsin concentrations. It has been observed that trypsin brings about a quenching of fluorescence of the dye. The quenching is static in nature and the equilibrium constant of dye-trypsin interaction in the ground-state has been determined from quenching studies. Steady-state anisotropy of the dye increases in presence of trypsin in the medium. Values of micro-viscosity in the vicinity of the fluorophore in media containing trypsin have been determined from measurements of fluorescence anisotropy. Time-resolved fluorescence studies indicate the existence of two decaying states for the dye. The fractional contribution to the time-resolved decay changes with pH. The average lifetime, however, does not depend on the concentration of trypsin.     

3,6-bis(2'-pyridyl)pyridazine (L) and its deprotonated form (L - H+)- as ligands for {(acac)2Ru(n+)} or {(bpy)2Ru(m+)}: investigation of mixed valency in [{(acac)2Ru}2(mu-L - H+)]0 and [{(bpy)2Ru}2(mu-L - H+)]4+ by spectroelectrochemistry and EPR

Crystallographically characterised 3,6-bis(2'-pyridyl)pyridazine (L) forms complexes with {(acac)2Ru} or {(bpy)2Ru2+}via one pyridyl-N/pyridazyl-N chelate site in mononuclear Ru(II) complexes (acac)2Ru(L), 1, and [(bpy)2Ru(L)](ClO4)2, [3](ClO4)2. Coordination of a second metal complex fragment is accompanied by deprotonation at the pyridazyl-C5 carbon {L --> (L - H+)-} to yield cyclometallated, asymmetrically bridged dinuclear complexes [(acac)2Ru(III)(mu-L - H+)Ru(III)(acac)2](ClO4), [2](ClO4), and [(bpy)2Ru(II)(mu-L - H+)Ru(II)(bpy)2](ClO4)3, [4](ClO4)3. The different electronic characteristics of the co-ligands, sigma donating acac- and pi accepting bpy, cause a wide variation in metal redox potentials which facilitates the isolation of the diruthenium(III) form in [2](ClO4) with antiferromagnetically coupled Ru(III) centres (J = -11.5 cm(-1)) and of a luminescent diruthenium(II) species in [4](ClO4)3. The electrogenerated mixed-valent Ru(II)Ru(III) states 2 and [4]4+ with comproportionation constants Kc > 10(8) are assumed to be localised with the Ru(III) ion bonded via the negatively charged pyridyl-N/pyridazyl-C5 chelate site of the bridging (L - H+)- ligand. In spectroelectrochemical experiments they show similar intervalence charge transfer bands of moderate intensity around 1300 nm and comparable g anisotropies (g1-g3 approximatly 0.5) in the EPR spectra. However, the individual g tensor components are distinctly higher for the pi acceptor ligated system [4]4+, signifying stabilised metal d orbitals.     

Development and laboratory evaluation of a rheometer for soil visco-plastic parameters

A motorized rheometer was developed for determining soil visco-plastic parameters that works on the principle of torsional shear applied to a standard vane with controlled strain rate. Rheological measurements were carried at different soil moisture contents (10%, 13%, 17% and 20% dry basis (gravimetric)) and soil compaction levels (100, 150, 200, 300 and 400 kPa) to find their effects on soil viscosity and yield strength. The values of viscosity of the clay loam soil (29% clay, 24% silt and 47% sand) were found to spread in the range of 53–283 kPa s, and yield stress variation had a span of 4–28 kPa. Increase in soil compaction was accompanied by a sharp increase in soil viscosity, while moisture content affected soil viscosity negatively. Effect of both these parameters was statistically significant (95% confidence interval). Yield stress was positively related to soil compaction and the effect was statistically significant. However, it was negatively related to moisture content and the effect was not statistically significant for the levels of moisture content tested.     

On the temperature dependent frequency factor in thermoluminescence

In thermoluminescence (TL), frequency factor might not always be temperature independent. In the present article we consider a method of two heating rates for evaluation of temperature exponent for the case of temperature dependent frequency factor in TL. The method has been analysed by applying it both to numerical and experimental TL peaks.     

High-affinity DNA targeting using readily accessible mimics of N2'-functionalized 2'-amino-α-L-LNA

N2'-Pyrene-functionalized 2'-amino-α-L-LNAs (locked nucleic acids) display extraordinary affinity toward complementary DNA targets due to favorable preorganization of the pyrene moieties for hybridization-induced intercalation. Unfortunately, the synthesis of these monomers is challenging (~20 steps, <3% overall yield), which has precluded full characterization of DNA-targeting applications based on these materials. Access to more readily accessible functional mimics would be highly desirable. Here we describe short synthetic routes to a series of O2'-intercalator-functionalized uridine and N2'-intercalator-functionalized 2'-N-methyl-2'-aminouridine monomers and demonstrate, via thermal denaturation, UV-vis absorption and fluorescence spectroscopy experiments, that several of them mimic the DNA-hybridization properties of N2'-pyrene-functionalized 2'-amino-α-L-LNAs. For example, oligodeoxyribonucleotides (ONs) modified with 2'-O-(coronen-1-yl)methyluridine monomer Z, 2'-O-(pyren-1-yl)methyluridine monomer Y, or 2'-N-(pyren-1-ylmethyl)-2'-N-methylaminouridine monomer Q display prominent increases in thermal affinity toward complementary DNA relative to reference strands (average ΔT(m)/mod up to +12 °C), pronounced DNA-selectivity, and higher target specificity than 2'-amino-α-L-LNA benchmark probes. In contrast, ONs modified with 2'-O-(2-napthyl)uridine monomer W, 2'-O-(pyren-1-yl)uridine monomer X or 2'-N-(pyren-1-ylcarbonyl)-2'-N-methylaminouridine monomer S display very low affinity toward DNA targets. This demonstrates that even conservative alterations in linker chemistry, linker length, and surface area of the appended intercalators have marked impact on DNA-hybridization characteristics. Straightforward access to high-affinity building blocks such as Q, Y, and Z is likely to accelerate their use in DNA-targeting applications within nucleic acid based diagnostics, therapeutics, and material science.