Electron spin resonance spectra of some phosphonyl radicals and related species

The isotropic ESR spectra of a number of phosphonyl radicals (X₂$\text{P}$O), the dimethylphosphinyl radical, and the phosphoranyl radical (MeO)₃$\text{P}$OBu-t, are described, and accurate values of the phosphorus hyperfine splittings and g-factors are reported. For X₂$\text{P}$O, the value of a(P) increases and the g-factor decreases as the electronegativity of X increases. There is a linear relationship between a(P) for X₂$\text{P}$O and ¹J(PH) for X₂P(O)H, but the same relationship does not hold for Me₂P- and Me₂PH. The spectrum of the di-n-hexylphosphonyl radical shows coupling to two pairs of α-methylene protons, and this non-equivalence is attributed to the pyramidal structure of the phosphonyl radical.     

Estrogen receptor ligands. 12. Synthesis of the major metabolites of an ERalpha-selective, dihydrobenzoxathiin antagonist for osteoporosis

[reaction: see text] During the course of drug metabolism studies, a major metabolite of compound 1 was detected in rhesus monkeys and assigned structure 4. The intriguing biotransformation of 1 leading to 4 was confirmed by a 19-step total synthesis starting from resorcinol (11), the key feature of which was the construction of the oxygen bridge utilizing a phenolic oxidation and trapping sequence. In addition, the synthesis of a related metabolite (5) is described.     

Infrared-induced conformational isomerization and vibrational relaxation dynamics in melatonin and 5-methoxy-N-acetyl tryptophan methyl amide

The conformational isomerization dynamics of melatonin and 5-methoxy N-acetyltryptophan methyl amide (5-methoxy NATMA) have been studied using the methods of IR-UV hole-filling spectroscopy and IR-induced population transfer spectroscopy. Using these techniques, single conformers of melatonin were excited via a well-defined NH stretch fundamental with an IR pump laser. This excess energy was used to drive conformational isomerization. By carrying out the infrared excitation early in a supersonic expansion, the excited molecules were re-cooled into their zero-point levels, partially re-filling the hole created in the ground state population of the excited conformer, and creating gains in population of the other conformers. These changes in population were detected using laser-induced fluorescence downstream in the expansion via an UV probe laser. The isomerization quantum yields for melatonin show some conformation specificity but no hint of vibrational mode specificity. In 5-methoxy NATMA, no isomerization was observed out of the single conformational well populated in the expansion in the absence of the infrared excitation. In order to study the dependence of the isomerization on the cooling rate, the experimental arrangement was modified so that faster cooling conditions could be studied. In this arrangement, the pump and probe lasers were overlapped in space in the high density region of the expansion, and the time dependence of the zero-point level populations of the conformers was probed following selective excitation of a single conformation. The analysis needed to extract isomerization quantum yields from the timing scans was developed and applied to the melatonin timing scans. Comparison between the frequency and time domain isomerization quantum yields under identical experimental conditions produced similar results. Under fast cooling conditions, the product quantum yields were shifted from their values under standard conditions. The results for melatonin are compared with those for N-acetyl tryptophan methyl amide.     

Quantitative analysis of the low molecular weight serum proteome using 18O stable isotope labeling in a lung tumor xenograft mouse model

With advancements in the analytical technologies and methodologies in proteomics, there is great interest in biomarker discovery in biofluids such as serum and plasma. Current hypotheses suggest that the low molecular weight (LMW) serum proteome possesses an archive of clipped and cleaved protein fragments that may provide insight into disease development. Though these biofluids represent attractive samples from which new and more accurate disease biomarkers may be found, the intrinsic person-to-person variability in these samples complicates their discovery. Mice are one of the most extensively used animal models for studying human disease because they represent a highly controllable experimental model system. In this study, the LMW serum proteome was compared between xenografted tumor-bearing mice and control mice by differential labeling utilizing trypsin-mediated incorporation of the stable isotope of oxygen, 18O. The digestates were combined, fractionated by strong cation exchange chromatography, and analyzed by nanoflow reversed-phase liquid chromatography coupled online with tandem mass spectrometry, resulting in the identification of 6003 proteins identified by at least a single, fully tryptic peptide. Almost 1650 proteins were identified and quantitated by two or more fully tryptic peptides. The methodology adopted in this work provides the means for future quantitative measurements in comparative animal models of disease and in human disease cohorts.     

Syntheses,structure, and photoluminescence properties of the 1-dimensional chain compounds [(TPA)(2)Au][Au(CN)(2)] and (TPA)AuCl (TPA = 1,3,5-triaza-7-phosphaadamantane)

The structures and temperature-dependent photoluminescence properties of the one-dimensional compounds [(TPA)(2)Au][Au(CN)(2)], 1, and (TPA)AuCl, 2, are reported. An extended linear chain with weak Au.Au interactions along the c-axis is evident in the structure of 1, and a helical chain with a pitch of 3.271 A is seen for 2. The intrachain Au...Au separation is 3.457(1) and 3.396(2) A in 1 and 2, respectively. As a result of this weak Au...Au interaction, the physical properties of these compounds are anisotropic. Scanning electron microscopy (SEM) studies indicate that single crystals of both compounds are noninsulating. Single crystals of 1 do not luminesce visibly, but grinding the crystals finely initiates a strong green emission under UV irradiation at room temperature. Further interesting optical properties include the dependence of the emission profile of the powder on the exciting wavelength and luminescence thermochromism. When excited at wavelengths < 360 nm, the powder exhibits a blue emission at 425 nm while excitation with longer wavelengths leads to a green emission near 500 nm. While the green emission dominates at ambient temperature, cooling to cryogenic temperatures leads to the dominance of the blue emission. Fibers of 2 are luminescent at 78 K with an emission band centered at 580 nm. Compound 1 crystallizes in the orthorhombic space group Cccm (No. 66), with Z = 2, a = 6.011(1) A, b = 23.877(6) A, c = 6.914(1) A, V = 992.3(3) A(3), and R = 0.0337. Compound 2 crystallizes in the trigonal space group R3 (No. 148), with Z = 18, a = 22.587(2) A, b = 22.587(2) A, c = 9.814(2) A, V = 4336 A(3), and R = 0.0283.     

Pentakis(methoxycarbonyl)cyclopentadiene,a strong organic acid: Crystal and molecular structures of HC5(CO)2Me)5 and Li[C5(CO2Me)5](H2O)

Contrary to some previously depicted structures, the proton in HC₅(CO₂Me)₅ is bonded to two oxygens rather than to carbon; the lithium ion in Li[C₅(CO₂Me)₅] (H₂O) is tetrahedrally coordinated by two carbonyl oxygens from one C₅ anion, one from a second anion, and a water molecule.     

Styrene emulsion polymerization: Particle-size distributions

Data are presented on the time evolution of particle-size distributions (PSDs) in seeded and ab initio styrene emulsion polymerization systems. Initiation was by chemical reagent (potassium persulfate) or γ-radiation. The unswollen PSDs at various times during interval II of the polymerization were obtained by direct measurement of calibrated electron micrographs. Experimental results were fitted with the equations that describe the time evolution of an initial PSD. Analytic solutions to these equations that allow for entry, exit, and propagation of free radicals were obtained. The values of the rate coefficients for these processes used to fit the experimental data were in excellent agreement with those obtained from dilatometric kinetics experiments.     

Intramolecular azide-diene cycloadditions. An approach to fused bicyclic 3-pyrrolines based on a one-pot nitrene-diene cycloaddition equivalent.

Cyclization of heterosubstituted ω-azidodienes 11 provides fused bicyclic 3-pyrrolines 12 in one operation. These pyrrolines are potentially useful intermediates for natural products synthesis, as illustrated by further functionalization.     

Nickelocene chemistry : II. New methylidyne trinickel cluster compounds

The new methylidene trinickel cluster complexes, [RCNi₃(η⁵-C₅H₅₃] (R  CMe₃ or SiMe₃) and [Me₃SiCNi₃(η⁵-C₅H₅)2(η⁵-C₅H₄CH₂SiMe₃)] have been isolated in low yield from reactions between nickelocene and the corresponding alkyllithium reagents, RCH₂Li. The compounds [RCNi₃(η⁵-C₅H₅)₃] (R  Ph, CMe₃ or SiMe₃) have also been obtained by treatment of the σ-alkylnickel complexes [(η⁵-C₅H₅)Ni(CH₂R)(PPh₃)] with n-BuLi in the presence of an excess of nickelocene, but under similar conditions [(η⁵-C₅H₅)Ni(CH₂C_1OH₇-2)-(PPh₃)] (where C_1OH₇-2  2-naphthyl) failed to give [2-C_1OH₇CNi₃(η⁵-C₅H₅)₃]. The attempted synthesis of [(η⁵-C₅H₅)Ni(CH₂CCH)(PPh₃)] from [(η⁵-C₅H₅)-NiBr(PPh₃)] and CHCCH₂MgBr gave only [(η⁵-C₅H₅)Ni(CCMe)(PPh₃)] by an unusual rearrangement reaction.