Dehydroaromatization of quinoxalines: one-step syntheses of trinuclear 1,6,7,12,13,18-hexaazatrinaphthylene titanium complexes

We report the spontaneous coupling of N-heterocycles, initiated by C-H bond activation reactions. The reaction of quinoxalines and the titanocene acetylene complex Cp2Ti{eta2-C2(SiMe3)2}, as an excellent titanocene source, results in the formation of trinuclear 1,6,7,12,13,18-hexaazatrinaphthylene (HATN) titanium complexes. These HATN titanium complexes are thermally stable but sensitive to air and moisture. A three-fold dehydrogenative C-C coupling is proposed as the main step in the presented synthetic procedure. Particularly using commercial starting materials, an efficient route for the dehydrogenative coupling of N-heterocycles, leading to multidentate ligands, has been established.     

Enhanced ALA-induced fluorescence in hyperparathyroidism

INTRODUCTION: Intraoperative localization of parathyroid glands can be challenging especially in minimally invasive surgery. Fluorescence diagnosis using the photosensitizer aminolevulinic acid (ALA) has been described to identify normal parathyroid glands during experimental bilateral neck exploration. The present study evaluated fluorescence differences between hyperplastic and normal parathyroid glands as a precondition for a clinical application of the technique. MATERIALS AND METHODS: Polycystic kidney disease (PKD) rats with hyperparathyroidism due to hyperplastic parathyroid glands and Wistar rats with normal parathyroid glands were photosensitized by peritoneal lavage with ALA solution. After surgical exposure of thyroid and parathyroid glands the operative site was observed under blue light conditions using the d-light system to assess fluorescence characteristics of each tissue. Fluorescence intensities of parathyroid glands and surrounding thyroid tissue were measured by spectrometry. Parathyroid hormone in serum of the rats was determined by enzyme-linked immunosorbent assay (ELISA). RESULTS: Observation of the exposed thyroid site showed a subjectively stronger red fluorescence of the parathyroid glands in the PKD rats in comparison to the Wistar rats, whereas thyroid tissue appeared equally fluorescent. In the PKD animals, spectrometric fluorescence intensity was 10 times higher in the parathyroid glands than in the thyroid gland, whereas in the Wistar rats the ratio was 3.2:1. Fluorescence intensity in the parathyroid glands was more than twice in the PKD rats than in the Wistar rats, however slightly lower in the thyroid tissue. ELISA confirmed the pathophysiological change of a hyperparathyroidism with significantly increased serum levels of parathyroid hormone in the PKD rats. DISCUSSION: Hyperparathyroidism enhances ALA-induced fluorescence of the parathyroid glands. A combined surgical fluorescence strategy may justify a unilateral, minimally invasive approach in selected patients and serve to improve the capability of the surgeon to safely and efficiently manage parathyroid diseases.     

Anionic triazine systems

The synthesis of TAS+ C3N3F4- (1) (TAS+ = (Me2N)3S+) and the reactions of 1 with Me3SiOSiMe3 and Me3SiCF3 to give TAS+ C3N3F2O- (2) and TAS+[(NCF)(NCCF3)(NC(CF3)(2)]- (4) are reported. An isomer of 4, TAS+[(NCCF3)2(NCFCF3)]-, compound 6, was obtained by fluoride ion addition to (CF3CN)3. From the reactions with Me3SiNMe2 neutral fluoroamino triazines C3N3Fn(NMe2)(n-1) (n = 1, 2) were isolated. Possible reaction pathways are discussed, the X-ray structures of 1, 2, 4 and 6 were determined.     

Vibrational spectra and gas phase structure of N-cyanoimidosulfurous difluoride, NCN=SF2

The vibrational spectra, IR (gas) and Raman (liquid) of N-cyanoimidosulfurous difluoride, NCN=SF2, were recorded, and the molecular structure was determined by gas electron diffraction. The spectra were assigned by comparing the vibrational frequencies with those in related molecules and with calculated (HF, MP2, B3LYP with 6-31G(d) basis sets) values, and a normal coordinate analysis was performed. The molecule possesses a syn conformation (Ctriple bondN syn with respect to the bisector of the SF2 angle). This has been rationalized by orbital interactions of the electron lone pairs of sulfur and nitrogen with the N-C and S-F bonds, respectively, which are antiperiplanar or anticlinal to these lone pairs (anomeric effects). Quantum chemical calculations with the B3LYP and MP2 methods reproduce the experimental structure reasonably well if large basis sets (6-311G(2d,f)) are used.     

Novel 3-deoxy analogs of the anti-HBV agent entecavir: synthesis of enantiomers from a single chiral epoxide

A synthesis of novel 3^′-deoxy analogs of the anti-HBV agent entecavir (BMS-200475) was devised using regioselective ring opening of suitable cyclopentene epoxides as the key step. This versatile approach afforded access to an enantiomeric pair of carbocyclic nucleosides from a single chiral intermediate.     

AgGaSe2 thin films grown by chemical close-spaced vapor transport for photovoltaic applications: structural, compositional and optical properties

Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum substrates using the technique of chemical close-spaced vapor transport. The high crystallinity of the samples is confirmed by grazing-incidence x-ray diffraction, scanning and transmission electron microscopy, and optical transmission/reflection spectroscopy. Here, two of the three expected direct optical bandgaps are found at 1.77(2) and 1.88(6) eV at 300 K. The lowest bandgap energy at 4 K is estimated to be 1.82(3) eV. Photoluminescence spectroscopy has further revealed the nature of the point defects within the AgGaSe(2), showing evidence for the existence of very shallow acceptor levels of 5(1) and 10(1) meV, and thus suggesting the AgGaSe(2) phase itself to exhibit a p-type conductivity. At the same time, electrical characterization by Hall, Seebeck and four-point-probe measurements indicate properties of a compensated semiconductor. The electrical properties of the investigated thin films are mainly influenced by the presence of Ag(2)Se and Ga(2)O(3) nanometer-scaled surface layers, as well as by Ag(2)Se inclusions in the bulk and Ag clusters at the layers' rear side.     

Reconfigurable wavefront sensor for ultrashort pulses

A highly flexible Shack-Hartmann wavefront sensor for ultrashort pulse diagnostics is presented. The temporal system performance is studied in detail. Reflective operation is enabled by programming tilt-tolerant microaxicons into a liquid-crystal-on-silicon spatial light modulator. Nearly undistorted pulse transfer is obtained by generating nondiffracting needle beams as subbeams. Reproducible wavefront analysis and spatially resolved second-order autocorrelation are demonstrated at incident angles up to 50° and pulse durations down to 6 fs.     

Microscale analysis of proteins in inner ear tissues and fluids with emphasis on endolymphatic sac, otoconia, and organ of Corti

Here we describe preparatory techniques adapted for the study of proteins of inner ear tissues and fluids that have allowed us to apply state-of-the-art analytical techniques in spite of the minute size and anatomical complexities of this organ. Illustrative examples address unresolved issues of functional and clinical significance. First, we demonstrate how quick-freezing and freeze drying prevents artifacts that arise from sampling endolymphatic sac (ES) content in the liquid state. This set the stage for the generation of the first protein profile of the ES. Identification of crucial proteins will help elucidate mechanisms of endolymph volume regulation and pathogenesis of Meniere's disease. Second, we show how a unique situation allowed identification of otoconial proteins by mass spectrometric analysis without prior separation and we discuss possible roles for these minor otoconins in otoconial development and prevention of degenerative diseases that affect balance. Finally, we demonstrate techniques for the precise dissection of organ of Corti and its substructures, while preserving their near normal chemical state. We extended an earlier study in which we identified a novel calcium-binding protein by IEF, oncomodulin, localized in the outer hair cells and show here the applicability of prefractionation for the screening of calcium-binding proteins of organ of Corti. These studies demonstrate how advanced preparatory and analytical techniques can be applied to studies of the inner ear.     

Functionality and Observed Versus Predicted Gel Points

An ambiguity in use of the term functionality is pointed out. The two most widely used relations (Flory, and Stockmayer and Kahn) connecting extent of reaction at the gel point and functionality are examined. The relations are shown mathematically to lead to the same result when all assumptions and definitions are considered. Measured gel points of polyesters are compared with those predicted by the equation. Deviations were less than 10% of the predicted values.

An ambiguity in definition has been observed for the word functionality which has led to unnecessary confusion of thought. It is believed that this confusion has often occurred and has been seen in the literature quite recently [1,2]. On the one hand, functionality has been used to mean the number of chain ends united at the branch points in a polymer network. Since branch points can unite no fewer than three chain ends, functionality in this sense can take on values of three or greater. Networks are most often three or four functional. If more than one type of branch point is present, the average functionality can be calculated as a fraction with a value above three.     

Structure Investigations on 4‐Halo‐1,2,3,5‐dithiadiazolyl Radicals XCNSSN• (X = F,Cl, Br): The Shortest Intradimer S···S Distance in Dithiadiazolyl Dimers

Crystals of the 4‐halo‐1,2,3,5‐dithiadiazolyl radicals (X = F, Cl, Br) were obtained by sublimation at 80 °C and 10^?2 Torr, and the structures were determined by X‐ray diffraction. The fluoro derivative crystallizes as a cisoid dimer in the space group P2₁/n, whereas the chloro and bromo derivatives crystallize isomorphous as twisted dimers in the space group C2/c. The chloro and bromo derivatives show the shortest intradimer S···S contacts of all known 1,2,3,5‐dithiadiazolyl dimers. In addition the obtained structure of ClCN₂S₂^? represents the fifth polymorph of ClCN₂S₂^? characterized by X‐ray crystallography. The structures and the packing including secondary interactions are discussed.