Loss in a rectangular optical waveguide induced by the crossover of a second waveguide

We calculate the loss induced in a single-mode rectangular optical waveguide by the presence of a second waveguide, perpendicular to the first, which crosses over the first waveguide at a variable distance d. Our calculation is applied to the analysis of several doped silica waveguides of practical importance for optical circuit design.     

A new one-pot three-component condensation reaction for the synthesis of 5-deaza-5,8-dihydropterins

The one-pot cyclocondensation of 2,6-diaminopyrimidin-4-one, an aromatic or aliphatic aldehyde and a beta-ketoester in acetic acid, or dimethyl sulfoxide in the presence of zinc(II) bromide, under thermal conditions provided dihydropyrido[2,3-d]pyrimidin-4(3H)-ones in good yield and with total regiocontrol.     

The diazo route to diazonamide A: studies on the tyrosine-derived fragment

Various approaches to the tyrosine-derived fragment of the marine secondary metabolite diazonamide A are described. Initial efforts were focused on the originally proposed structure of the natural product, and a feasibility study established that a model 4-aryltryptamine could be readily prepared. Protected 4-bromotryptamine underwent Pd0-catalyzed coupling with the boronic acid derived from 2-bromophenyl allyl ether by Claisen rearrangement, O-methylation and lithiation-boration. The resulting biaryl was elaborated into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Z-valinamide gave the desired tryptamine-oxazole following cyclodehydration of the intermediate ketoamide. A potential precursor to the benzofuran ring of the original structure of diazonamide A was prepared in eight steps from N-Z-tyrosine tert-butyl ester. Iodination, O-protection and Stille coupling gave the cinnamyl alcohol 25, converted via the bromide into the allyl aryl ether 27. Subsequent Claisen rearrangement and oxidative cleavage of the alkene gave the lactol 29, converted into the desired benzofuranone 31. The revision in the structure of diazonamide A to 2 resulted in the targeting of an alternative tyrosine-derived model benzofuranone 41 synthesized in four steps from N-Z-tyrosine methyl ester 36 by a route involving Claisen rearrangement of cinnamyl ether 37. Poor yields in this sequence prompted an investigation into the intramolecular Heck reaction as a route to benzofuranone 50. Coupling of 3-iodotyrosine 44 with 2-phenylbutenoic acid 48 gave ester 49 that readily underwent intramolecular Heck reaction to give benzofuranone 50, albeit with poor stereocontrol.     

DETECTION OF DNA-PSORALEN PHOTOADDUCTS in situ

Abstract— An immunological method, with the use of specific immune serum, has been developed for detection of 8-methoxypsoralen (8-MOP) photoadducts to DNA, formed in situ in cell nuclei, after combined treatment with 8MOP and UV-A irradiation (Zarçbska et al. , 1978). Lymphocytes fixed on slides or in suspension, and cryostat sections of different mammalian tissues, served as antigenic substrate, after treatment with 8-MOP and UV-A in vitro. Specific fluorescence in these substrates was detected in the nuclei after treatment with 30 ˜ 140 kJ/m² UV-A in the presence of 0.1-0.3 μg/cm² 8-MOP. PHA-stimulated-lymphocytes appeared to be the most sensitive substrate.
However, hairless mice treated with high doses of UV-A in vivo , 70 ˜ 360 kJ/m² did not reveal a specific fluorescence of epidermal nuclei, unless a high local concentration of 8-MOP was attained.
The apparent discrepancy in the level of photoadduct detection between the in vitro and in vivo treated specimens was explained by the low number of DNA-8-MOP-photoadducts formed in vivo under these experimental conditions. The relevance of these findings to the role of DNA-8-MOP-photoadducts formed during PUVA photochemotherapy is discussed.     

The first photocrystallographic evidence for light-induced metastable linkage isomers of ruthenium sulfur dioxide complexes

Light-induced metastable linkage isomers of trans-[Ru(NH(3))(4)Cl(SO(2))]Cl and trans-[Ru(NH(3))(4)(H(2)O)(SO(2))](C(6)H(5)SO(3))(2) have been identified for the first time using photocrystallographic methods. In both linkage isomers the SO(2) ligand is side bound, but the Ru-O and Ru-S distances are considerably longer and almost equal in the trans-H(2)O isomer. DFT calculations confirm that both isomers correspond to minima on the ground-state potential energy surface and also predict the existence of a second oxygen-bound isomer for both compounds. The decay of the light-induced species has been studied by both DSC and IR. Activation energies for the thermal back-reaction, as derived from the temperature-dependent disappearance of light-induced IR bands, are 50.0 and 58.4 kJ/mol for the two isomers, which is larger than the corresponding numbers for photoinduced side-bound nitrosyl linkage isomers.     

Solvent-Free Synthesis of Core-Functionalised Naphthalene Diimides by Using a Vibratory Ball Mill: Suzuki,Sonogashira and Buchwald–Hartwig Reactions

Solvent-free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’-bis(2-ethylhexyl)-2,6-dibromo-1,4,5,8-naphthalenetetracarboxylic acid (Br₂-NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)₂) and are tolerant to air and atmospheric moisture. Furthermore, the real-world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs.     

Adult neurogenesis and specific replacement of interneuron subtypes in the mouse main olfactory bulb

Background  

New neurons are generated in the adult brain from stem cells found in the subventricular zone (SVZ). These cells proliferate in the SVZ, generating neuroblasts which then migrate to the main olfactory bulb (MOB), ending their migration in the glomerular layer (GLL) and the granule cell layer (GCL) of the MOB. Neuronal populations in these layers undergo turnover throughout life, but whether all neuronal subtypes found in these areas are replaced and when neurons begin to express subtype-specific markers is not known.