Modification of guanine residues in PNA-synthesis by PyBOP

The phosphonium-type coupling reagent PyBOP, when applied to the synthesis of peptide nucleic acid (PNA) oligomers, was found to form O⁴-phosphonium compounds of the nucleobase guanine which can be converted into C⁴-modified guanine-derived PNAs by nucleophiles.     

Relative quantum yield for the production of O-atom and S-atom from the photodissociation of OCS in the vacuum UV

The relative efficiencies for two dissociative channels in the vacuum UV photolysis of carbonyl sulphide have been determined using the flash photolysis-resonance fluorescence technique to measure initial yields of atomic oxygen and atomic sulphur. At wavelengths above 105 nm, the dissociation of OCS to form atomic sulphur exceeded that for the formation of atomic oxygen to such an extent that only an upper limit could be placed on the minor process, Φ_S >/ 50 Φ_O. In addition, the flash photo-excitation of carbonyl sulphide produced a long-lived spontaneous emission in the UV and vacuum UV that might be due to molecular fluorescence from OCS.     

DETAILED ACTION SPECTRUM FOR THE DELAY SHIFT IN PUPAE EMERGENCE OF DROSOPHILA PSEUDOOBSCURA*

Abstract— Dose-response curves were measured for the delay phase shift of pupae emergence of Drosophila pseudoobscura. From these curves an action spectrum was determined for this process; it suggests a flavin to be the photoreceptor pigment.     

Theoretical rate constant calculations for O(3P) with saturated hydrocarbons

Theoretical rate constants have been calculated for O(³P) with five saturated hydrocarbons, CH₄, C₂H₆, C₃H₈, iso-C₄H₁₀, and neo-C₅H₁₂. The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(³P) + CH₄ is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO-ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.     

Chemistry of thienopyridines. XXXI. A new synthesis of thieno[3,2-b]pyridine and studies on direct substitution into its thiophene ring

Thieno[3,2-b]pyridine ( 1 ) is synthesized in 65% overall yield for two steps which consist of addition of toluene-α-thiol to 2-ethynylpyridine plus vacuum pyrolysis of the addend ( 7 ). Cis and trans forms of 7 are described. Compound 1 undergoes (a) electrophilic substitution at C-3 to give chloro, bromo, and iodo derivatives (44–57% yields) and (b) lithiation at C-2 (to give 1a ). Intermediate 1a is converted into derivatives of 1 with halo (19–48%), formyl (54%), acetyl, and hydroxymethyl (40%) substituents at C-2. Also described are 2-cyano and 2,3-dibromo derivatives of 1 . Structural assignments are based on chemical transformations plus ¹H and ¹³C nmr spectral data. The substitution pattern of 1 is compared with predictions made on the bases of analogous ring systems and molecular orbital calculations.     

The insertion and extrusion of heterosulfur bridges. XI. Desulfurizations of condensed thiophenes by means of methanol and a molybdena catalyst

Desulfurizations of 2-methyl- ( 1b ), 4-methyl- ( 1c ), and 4,6-dimethyldibenzothiophenes ( 1d ), benzo[b]thiophene ( 2 ), and benzo[b]naphtho[2,1-d]thiophene ( 5 ) were effected by means of methanol and a sulfided CMA catalyst [a mixed oxide of Co(II), Mo(VI), and Al(III)] at 450°. Desulfurization was accompanied by processes of demethylation and ring hydrogenation in the case of 1d and by both methylation and demethylation in the cases of 1b and 1c . Compound 2 gave ethylbenzene (80%), while 5 produced 2-phenylnaphthalene (69%).     

Chemistry of thienopyridines. XXXIV. Mass spectral fragmentation patterns of some secondary amines and related imines

The mass spectra of some secondary amines and aldimines in the thieno[2,3-b]pyridine ( 3 ) system are presented. α, α-Bis(4-thieno[2,3-b]pyridylamino)toluene ( 1 ) undergoes (a) electron impact-induced dissociation at 80° to give the spectrum of 4-amino- 3 (3b) and (b) thermal dissociation at 200° to give a composite spectrum of 3b and its benzylidene derivative. Spectra of benzylamino and dimethylaminobenzylamino derivatives of 3 are dominated by benzyl-type fragments, while benzylideneimino derivatives show more varied fragmentation.     

Arsenic in contaminated soil and river sediment

Different areas in the Erzgebirge mountains are contaminated by high arsenic concentration which is caused by the occurrence of ore and industrial sources. The study showed clearly a high concentration of arsenic in the surface and under soil (A and B horizons) in the Freiberg district. The distribution of the arsenic concentration in the area, the content of water soluble arsenic, the several oxidation states (As³⁺, As⁵⁺) and the bonding types have been analyzed.