Chiral Photodetector Based on GaAsN

The detection of light helicity is key for various applications, from drug production to optical communications. However, the light helicity direct measurement is inherently impossible with conventional photodetectors based on III–V or IV–VI non-chiral semiconductors. The prior polarization analysis by often moving optical elements is necessary before light is sent to the detector. A method is here presented to effectively give the conventional dilute nitride GaAs-based semiconductor epilayer a chiral photoconductivity. The detection scheme relies on the giant spin-dependent recombination of conduction electrons and the accompanying spin polarization of the engineered defects to control the conduction band. As the conduction electron spin polarization is, in turn, intimately linked to the excitation light polarization, the light polarization state and intensity can be determined by a simple conductivity measurement. This approach, removing the need for any optical elements in front of a non-chiral detector, could offer easier integration and miniaturization. This new chiral photodetector could potentially operate in a spectral range from the visible to the infra-red using (InGaAl)AsN alloys or ion-implanted nitrogen-free III–V compounds.     

Laminated morphology of nontwisting beta-sheet fibrils constructed via peptide self-assembly

A synthetic peptide has been de novo designed that self-assembles into beta-sheet fibrils exhibiting a nontwisted, stacked morphology. The stacked morphology is constituted by 2.5 nm wide filaments that laterally associate to form flat fibril laminates exceeding 50 nm in width and micrometers in length. The height of each fibril is limited to the length of exactly one peptide monomer in an extended beta-strand conformation, approximately 7 nm. Once assembled, these highly ordered, 2-D structures are stable over a wide range of pH and temperature and exhibit characteristics similar to those of amyloid fibrils. Furthermore, the rate of assembly and degree of fibril lamination can be controlled with kinetic parameters of pH and temperature. Finally, the presence of a diproline peptide between two beta-sheet-forming strands in the peptide sequence is demonstrated to be an important factor in promoting the nontwisting, laminated fibril morphology.     

Reactivity and selectivity of the N-acetyl-Glu-P-1, N-acetyl-Glu-P-2, N-acetyl-MeIQx,and N-acetyl-IQx nitrenium ions: comparison to carbocyclic N-arylnitrenium ions

The model ultimate carcinogens 1a-d, related to the metabolites of the food-derived carcinogenic heterocyclic amines Glu-P-1, Glu-P-2, MeIQx, and IQx, spontaneously decompose in neutral aqueous solution to generate the heterocyclic nitrenium ions, 2a-d. The less reactive esters 1a and 1b also undergo acid-catalyzed ester hydrolysis to generate the corresponding hydroxamic acids at pH <2, while the more reactive 2c and 2d are prone to rearrangement in nonaqueous solvents. The reactions of the nitrenium ions with AcO(-), HPO(4)(2-), N(3)(-), and 2'-deoxyguanosine (d-G) were characterized in aqueous solution by using a combination of competitive trapping methods and product isolation and identification. The reactions with N(3)(-) and d-G generally follow patterns previously established for carbocyclic nitrenium ions, but the reactions with AcO(-) and HPO(4)(2-) are unusual. Similar reactions have previously only been reported for heterocyclic 1-alkyl-2-imidazolium ions. The N(3)(-)/solvent selectivities of these ions (5.1 x 10(6) M(-1) for 2a, 2.3 x 10(6) M(-1) for 2b, 1.2 x 10(5) M(-1) for 2c, and 5.2 x 10(4) M(-1) for 2d) are comparable to those of highly selective carbocyclic nitrenium ions. If k(az) for these ions is diffusion limited at ca. 5 x 10(9) M(-1) s(-1) the aqueous solution lifetimes of these ions range from 10 micros (2d) to 1 ms (2a). These ions are also highly selective for trapping by d-G, but comparisons to other nitrenium ions show that they are 10- to 50-fold less selective for trapping by d-G than they would be if both the N(3)(-) and d-G reactions were diffusion limited. This is not a consequence of their heterocyclic structures. Several carbocyclic ions show similar behavior. The relatively inefficient trapping of 2c and 2d by d-G may account for the observation of the unusual minor N-2 d-G adduct that is isolated for both of these nitrenium ions, but has not previously been observed for the reactions of other nitrenium ions with monomeric d-G.     

2,6-Diarylhexahydro-4-pyridazinols by acid-catalyzed cyclization of benzaldehyde aryl-2-(2-propenyl)hydrazones

Treatment of benzaldehyde l-(2-propenyl)-4-methylsulfonylphenylhydrazone ( 1f ) with 45% sulfuric acid gave 2-(4-methylsulfonylphenyl)-6-phenylhexahydro-4-pyridazinol ( 2f ) in 35% yield rather than the expected 1-(4-methylsulfonylphenyl)-1-(2-propenyl)hydrazine. The halogen-substituted hydrazones 1c-1e and benzaldehyde 1-(2-methyl-2-propenyl)phenylhydrazone ( 1b ) gave similar results.     

Novel routes for the generation of structurally diverse labdane diterpenes from andrographolide

Andrographolide 1, the major constituent of the Indian medicinal plant Andrographis paniculata (Acanthaceae) was converted into the key intermediate 4 by selective oxidative degradation of the C-12,13 olefin bond. The aldehyde functional group present in 4 has been utilized for synthesizing a number of structurally diverse labdane diterpenes. Synthesis and in vitro cytotoxic activity results of the compounds prepared are discussed.     

Thirteenth IUPAC Conference on Chemical Thermodynamics Joint Meeting with the Twenty-fifth AFCAT Conference July 17–22, 1994 Clermont-Ferrand,France

Meeting Notice

Thirteenth IUPAC Conference on Chemical Thermodynamics Joint Meeting with the Twenty-fifth AFCAT Conference July 17–22, 1994 Clermont-Ferrand, France     

Synthesis and photophysical properties of neutral luminescent rhenium-based molecular rectangles

A series of neutral luminescent molecular rectangles [[Re(CO)(3)(mu-bpy)Br][Re(CO)(3)(mu-L)Br]](2) (1-4) having fac-Re(CO)(3)Br as corners and 4,4'-bipyridine (bpy) as the bridging ligand on one side and other bipyridyl ligands of varying length (L) on the other side have been synthesized and characterized. The crystal structure of 1 shows a rectangular cavity with the dimensions of 11.44 x 7.21 A. When the cavity size is tuned from 1 to 4, a dimension of 11.4 x 20.8 A could be achieved, as revealed by the molecular modeling. These rectangles exhibit luminescence in solution at room temperature. In particular, compound 4 containing 1,4-bis(4'-pyridylethynyl)benzene (bpeb) as bridging ligand shows the excited-state lifetime of 495 ns. Fine-tuning of the cavity size of the rectangles improves their excited-state properties. These properties facilitate the study of excited-state electron-transfer reactions with electron acceptors and donors and host-guest binding. Crystallographic information: 1.6CH(3)COCH(3) is monoclinic, P2(1)/c, with a = 12.0890(2), b = 24.2982(2), and c = 12.8721(2) A, beta = 107.923(1) degrees, and Z = 2.     

Studien über antibakterielle Wirkstoffe, 5. Mitt.

Zusammenfassung Die Synthese einer Anzahl von 4-(Phenylthio-)-pyridinbzw.-chinolin-N-oxyden, deren Phenylkern halogen-und alkylsubstituiert ist und die möglicherweise antibakterielle Eigenschaften besitzen, wird beschrieben.