The synthesis and structural characterization of Os3(CO)8[Si(OMe)3][μ-PMe2(C6H4](μ-H)2: An unusual unsaturated triosmium cluster complex

The reaction of Os₃(CO)₁₀(NCMe)[Si(OMe)₃](-H),1, with PMe₂Ph yielded the new complex Os₃(CO)₁₀(PMe₂Ph)[Si(OMe)₃](-H),2 by substitution of the MeCn ligand with the phosphine ligand. When heated to 125°C compound2 was decarbonylated and transformed into the new unsaturated cluster complex Os₃(CO)₈[-PMe₂(C₆H₄)][Si(OMe)₃](-H)₂,3 in 54% yield. Compound3 was characterized by a single crystal X-ray diffraction analysis, osmium bonds. The phenyl ring of the phosphine ligand has undergoneortho-metallation by a neighboring metal atom. A terminally coordinated Si(OMe)₃ ligand is coordinated to the third osmium atom. The cluster is unsaturated by the amount of 2 electrons, and there is an open coordination site on the siloxyl substituted osmium atom that is partially filled by a weak interaction with one of the -bonds of theortho-metalled phenyl ring. Complex3 reacts with CO at 1 atm to reform compound2 in 85% yield in 5 h at 40°C. Crystal Data: for3: space group = P2₁/n,a = 9.911(2) Å,b = 18.451(6) Å,c = 14.872(2) Å, = 95.64(2)°,Z = 4, 1994 reflections,R = 0.028.     

Fast peroxyoxalate chemiluminescence for minimized analytical separation systems

The maximum intensity, Imax, and time required to reach the maximum emission, taumax, for 1-aminopyrene monitored in 1,1'-oxalyldi-4-methylimidazole (OD4MI) chemiluminescence (CL) reactions are approximately 61 times higher and 16 times faster than their respective values for bis(2,4,6-trichlorophenyl)oxalate (TCPO) CL reactions in the presence of imidazole (ImH).     

Conformational identification and dipole moment of 4-fluoro-1-butene by microwave spectroscopy

The microwave spectrum of 4-fluoro-1-butene has been recorded in the frequency region 26.5–40.0 GHz. A-type rotational transitions in the ground vibrational state have been assigned. The effective rotational constants and centrifugal distortion constants were determined to be A = 19 196 ± 323, B = 2132.48 ± 0.01, C = 2112.52 ± 0.01 MHz, D_J = 0.70 ± 0.03 and D_JK = −26.16 ± 0.05 kHz. Analysis of the measured Stark effects gave a dipole moment of 1.80 D with components of |u_a| = 1.62 ± 0.01, |u_b| = 0.68 ± 0.05 and |u_c| = 0.39 ± 0.14 D. From the experimental rotational constants and dipole moments, it is suggested that the assigned spectra have resulted from the skew—trans conformer.     

Self-repairing polymers: poly(dioxaborolane)s containing trigonal planar boron

The molecular weight of poly(dioxaborolane)s can be controlled during the polymerization reaction or through post-polymerization processing in such a manner that hydrolytic damage to these materials may be repaired, thereby regenerating the polymer.     

Structure of slope-critical configurations

In 1970, P. R. Scott conjectured, and recently P. Ungar proved, that n noncollinear points in the plane determine at least n–1 directions. The goal here is to obtain information on the structure of the critical sets where the minimum of n–1 is attained. Such a set is distributed in a rather regular way onto spokes radiating out from a centrex point. If the number of spoke-pairs is even, the set must be centrally symmetric. Moreover, some bounds on the number of points per spoke are obtained. These results lead to the characterization, for small n, of certain types of slope-critical configurations.Dedicated to M. S. Irani on his 90th birthday 25 February, 1984Research supported in part by NSF EPSCoR Grant IPS-80-11451.     

Determination of arsenic in sediments, coal and fly ash slurries after ultrasonic treatment by hydride generation atomic absorption spectrometry and trapping in an iridium-treated graphite tube

A simple and reliable method for the determination of arsenic in sediment and in coal without sample digestion, based on hydride generation from slurry samples is proposed. After grinding the samples to a particle size of 50 μm, the sample powder was mixed with aqua regia and hydrofluoric acid in an ultrasonic bath for 30 min. After diluting the mixture with hydrochloric acid, the slurry was allowed to stand for 48 h, and an aliquot was used for hydride generation with sodium borohydride. More than 80% of the arsenic was leached to the aqueous phase under these conditions, except for one sediment sample with very high silica content. The generated arsine was collected in a graphite tube, treated with 0.5 mg of iridium as a permanent modifier, and the arsenic determination was carried out by electrothermal atomic absorption spectrometry. The same tube could be used for at least 160 cycles without any re-treatment. The greatest advantage of the method was that only a minimum of reagents and sample handling were required, reducing the risks of contamination and/or analyte loss. However, the addition calibration technique had to be used in order to obtain results within the 95% confidence level for 11 certified reference materials, 5 sediments, 5 coals and one coal fly ash. One certified sediment slurry was spiked with the analyte and the resulting addition calibration curve was used for the analysis of the certified sediments. Similarly, one certified coal was used to obtain the addition calibration curve for the coal and coal fly ash samples. The recoveries of the certified values, except for one sediment, were between 91 and 115%. The limits of detection in the samples were 0.54 and 0.7 μg g⁻¹ for the coal and sediment samples, respectively, obtained for 1 ml of slurry containing 1 mg of sample.     

Vibrational spectra,conformational equilibria,ab initio calculations and vibrational assignments of ethylmethylfluorosilane

The infrared spectra of ethylmethylfluorosilane (CH₃SiHFCH₂CH₃) have been recorded as a vapour, liquid and solid at 78 K in the 4000–50 cm⁻¹ range and isolated in an argon matrix at ca. 5 K. Infrared spectra of two different solid phases were obtained after annealing to temperatures of 120 and 130 K, and recooling to 78 K. Although the IR spectra were quite similar in the MIR region, certain differences were noted in the FIR region below 400 cm⁻¹. The most stable conformer MeMe was present after annealing to 130 K, but three bands belonging to MeH were detected after annealing to 120 K. Various infrared bands changed intensity when the argon matrix was annealed to temperatures between 20 and 35 K, and some of these were related to changes in the conformational abundance.Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of an amorphous and annealed solid were recorded at 78 K. In the variable temperature Raman spectra, various bands changed in intensity and were interpreted in terms of conformational equilibria between the three possible conformers. Complete assignments were made for all the bands of the most stable conformer MeMe. From various bands assigned to the three conformers, the conformational enthalpy difference ΔH from MeMe to the intermediate energy conformer MeH was found to be 0.5 kJ mol⁻¹ and to the highest conformer MeF was 0.7 kJ mol⁻¹. At ambient temperature this leads to 39% MeMe, 32% MeH and 29% of the MeF conformer in the liquid.Ab initio calculations in the RHF, MP2, DFT approximations and very accurate G2 calculations were carried out. With one exception, the MeMe conformer had the lowest enthalpy in all these calculations, the MeH had the intermediate and the MeF the highest enthalpy, and the calculations were in good agreement with the measurements.     

Hydrolytic protein cleavage mediated by unusual mononuclear copper(II) complexes: X-ray structures and solution studies

The crystal structures and redox and UV-vis/EPR spectroscopic properties of two new mononuclear copper(II) complexes, [Cu(HL1)Cl2] (1) and [Cu(L1)Cl] (2), prepared through the reaction between copper(II) chloride and the ligand 2-[(bis(pyridylmethyl)amino)methyl]-4-methyl-6-formylphenol (HL1) under distinct base conditions, are reported along with solution studies. Also, we demonstrate that these CuII complexes are able to cleave unactivated peptide bonds from bovine serum albumin (BSA) and the thermostable enzyme Taq DNA polymerase at micromolar concentration, under mild pH and temperature conditions. The cleavage activity seems to be specific with defined proteolytic fragments appearing after protein treatment. The location of the specific cleavage sites was tentatively assigned to solvent-accessible portions of the protein. These are two of the most active Cu(II) complexes described to date, since their cleavage activity is detected in minutes and evidence is here presented for a hydrolytic mechanism mediating protein cleavage by these complexes.     

Convergent solid phase peptide synthesis. I. Synthesis of protected segments on a hydroxymethylphenyloxymethyl resin using the base labile FMOC α-amine protection. Model synthesis of LHRH.

Convergent solid phase peptide synthesis has been applied to yield LHRH. The segments 1–6 and 7–10 of LHRH were synthesized on a hydroxymethylphenyloxymethyl resin using the base labile Fmoc protecting group on the α-amines. The side chains were protected by HF labile groups. Purification of the segments was performed on Sephadex LH-20 columns and by HPLC on Silica Gel 60 columns. The two segments were then assembled on an α-aminobenzyl resin to yield entire sequence of LHRH. After HF treatment and standard purification on Sephadex G-15 and carboxymethylcellulose CM-52 the desired LHRH was obtained. Synthesis of the segments by the same strategy on carbazoyloxymethylphenyloxymethyl resin showed up unexpected difficulties.