Photolytic cyclopentadienyl ligand exchange between dicyclopentadienylzirconium dichloride and related systems.

Irradition of benzene solutions of zirconocene dichloride and zirconocene- d₁₀ dichloride with 313 nm light leads to the formation of zirconocene-d₅ dichloride with a quantum yield of 0.021 mol/Ei. The equilibrium constant is 2.8 Zirconocene dichloride exchanges a cyclopentadienyl ligand photolytically with bis(methylcyclopentadienyl)zirconium dichloride with the constant equal to 2.3.     

Cubic twists of <Emphasis Type="Italic">GL</Emphasis>(2) automorphic L-functions

Let and let be a cuspidal automorphic representation of . Consider the family of twisted L-functions L(s,) where ranges over the cubic Hecke characters of K. In this paper the mean value of this family of L-functions is computed; the result is consistent with the generalized Lindelöf hypothesis. From this mean value result a nonvanishing theorem is established: for given s there are infinitely many cubic twists such that the L-value at s is nonzero. At the center of the critical strip the number of such characters of norm less than X is . These results are obtained by introducing and studying three different families of weighted double Dirichlet series. These series are related by functional equations, some of which are obtained through the study of higher metaplectic Eisenstein series and the Hasse-Davenport relation. The authors establish the continuation of such series and then obtain their main result by Tauberian methods. Mathematics Subject Classification (1991) 11F66, 11F70, 11M41, 11N75, 22E55     

Development of an analytical methodology for sarin (GB) and soman (GD) in various military-related wastes

The Army requires analytical methods that can detect chemical agents down to the low part-per-billion (ppb) levels in their waste streams in order to meet various state regulations regarding the classification of hazardous waste. Analytical methods were developed for the measurement of sarin (GB) and soman (GD) at ppb levels that involved preconcentration of relatively large volumes (40-150 microliters) of a chloroform extract onto a sorbent cartridge, followed by thermal desorption and analysis by GC-flame photometric detection. Certified reporting limits (CRLs) achieved with these methods ranged from 8.3 to 19 ppb for GB and from 1.8 to 5.3 ppb for GD in the three matrices screened. Method detection limits (MDLs) achieved with these methods ranged from 1.7 to 8.2 ppb for GB and from 0.39 to 1.2 ppb for GD. The methods are capable of achieving lower CRLs and MDLs with only minor modification.     

Substituted 2-Pyrones and 5,6-Dihydropyrones

A series of substituted 2-pyrones and 5,6-dihydropyrones have been synthesized and investigated for their inhibitory activity toward human leukocyte elastase, procine pancreatic elastase and chymotrypsin.     

Dynamic NMR studies of ferrocenylsulphide-palladium(II) and -platinum(II) complexes

The stereodynamics of ferrocenylsulphide-palladium(II) and -platinum(II) complexes, Fe(C₅H₄SR)₂MX₂, (M = Pd^II, Pt^II; X = Cl, Br; R = Ph, i-Pr and i-Bu), have been examined by variable temperature NMR. At temperatures down to ca. ?100° C, the pyramidal inversion of the S atoms could be slowed down sufficiently to yield accurate energy data, while the reversal of the ferrocenophane ring remained fast on the NMR time scale. ΔG^≠ data for the S inversion process were in the range 47 to 65 kJ mol^?1 and were influenced to varying extents by the nature of the transition metal, the halogen, and the R substituent on the sulphur.     

A cyclopentadienyl ring exchange method for the attachment of early transition metal metallocene dichlorides to a polymer support

PMR and mass spectral analysis have been used to study the interchange of π-bonded cyclopentadienyl rings with σ-bonded cyclopentadienyl rings in the compounds (C₅H₅)₄M (M = Ti, Zr, Hf, Nb, Ta, Mo and W) and (C₅H₅)₃V or a-bonded benzylcyclopentadienyl rings in the compounds (C₆H₅CH₂C₅H₄) (C₅H₅)₂MC1 (M = Ti, Zr, Hf, Nb, Ta, Mo and W). As soon as the Cp₄M species are generated (indicated by a color change), the interchange occurs and the equilibrium is established. As reported, no such interchange was observed in (C₅H₅) ₄Mo in the PMR time scale; however, it does occur after a longer time. By using this interchange behavior of the cyclopentadienyl ring, metallocene dichlorides of Ti, Zr, Hf, V, Nb, Ta, Mo and W have been attached to polystyrene-divinylbenzene beads.     

A practical, enantioselective synthetic route to a key precursor to the tetracycline antibiotics

A practical, enantioselective synthetic route to a key precursor to the tetracycline antibiotics is reported. The route proceeds in nine steps (21% yield) from the commercial substance methyl 3-hydroxy-5-isoxazolecarboxylate. Key steps in the route involve enantioselective addition of divinylzinc to 3-benzyloxy-5-isoxazolecarboxaldehyde and an endo-selective intramolecular furan Diels-Alder cycloaddition reaction. The route described has provided more than 40 g of chromatographically pure 1 with 93% ee.     

Illusory continuity of interrupted speech: speech rate determines durational limits

Deleted segments of speech can be restored perceptually if they are replaced by a louder noise. An earlier study of this "phonemic restoration effect" found that, when recorded discourse was interrupted periodically by noise, the durational limit for illusory continuity corresponded to the average word duration. The present study employed a different passage of discourse recorded by a different speaker. Durational limits for apparent continuity of discourse interrupted by noise were measured at the normal (original) playback speed, as well as at rates that were 15% greater and 15% less. At the normal playback rate, once again the limit of continuity approximated the average word duration--but of especial interest was the finding that changes in playback rate produced proportional changes in continuity limits. These results, together with other evidence, suggest that phonemic restorations represent a special linguistic application of a general auditory mechanism (auditory induction) producing appropriate syntheses of obliterated sounds, and that for discourse the limits of illusory continuity correspond to a fixed amount of verbal information, and not a fixed temporal value.     

One-step synthesis of low polydispersity, biotinylated poly(N-isopropylacrylamide) by ATRP

Low polydispersity poly(N-isopropylacrylamide) with a biotin end-group was obtained in one step from a biotinylated initiator for atom transfer radical polymerization and interacted with streptavidin to generate the thermosensitive polymer-protein conjugate.     

Determination of non-ortho polychlorinated biphenyls in environmental Standard Reference Materials

The concentrations of three non-ortho ("coplanar") polychlorinated biphenyls, 3,3',4,4'-tetrachlorobiphenyl (IUPAC PCB 77), 3,3',4,4',5-pentachlorobiphenyl (IUPAC PCB 126), and 3,3',4,4',5,5'-hexachlorobiphenyl (IUPAC PCB 169), were determined in five NIST Standard Reference Materials (SRMs) of environmental and biological interest. The measured levels were approximately between (0.2 to 1.3) ng/g in SRM 1588a (Organics in Cod Liver Oil), (0.3 to 9) ng/g in SRM 1944 (New York/New Jersey Waterway Sediment), (0.2 to 0.4) ng/g in SRM 1945 (Organics in Whale Blubber), (1 to 18) ng/g in SRM 2974 (Organics in Freeze-dried Mussel Tissue [Mytilus edulis]), and (0.1 to 0.4) ng/g in candidate SRM 1946 (Lake Superior Fish Tissue). PCB 169 was present at < 0.1 ng/g in SRMs 1944 and 2974.