Multiporphyrin arrays on cyclophosphazene scaffolds: synthesis and studies

The stable and robust cyclotriphosphazene and cyclotetraphosphazene rings were used as scaffolds to prepare hexa- and octaporphyrin arrays by treating N(3)P(3)Cl(6) and N(4)P(4)Cl(8), respectively, with 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl)porphyrin (N(4) core) or with its thiaporphyrin analogues (N(3)S and N(2)S(2) cores) in THF in the presence of Cs(2)CO(3) under simple reaction conditions. Thiaporphyrins were examined in addition to the normal porphyrin to tune the electronic properties of the resultant arrays. Observation of the molecular ion peaks in the mass spectra confirmed the molecular structures of the arrays. 1D and 2D NMR techniques were employed to characterize the multiporphyrin arrays in detail. The (1)H NMR spectra of the multiporphyrin arrays each show a systematic set of signals, indicating that the porphyrin units are arranged in a symmetrical fashion around the cyclophosphazene rings. All signals in the (1)H NMR spectra were assigned with the aid of COSY and NOESY experiments. The protons of each porphyrin unit are subject to upfield and downfield shifts because of the ring-current effects of neighboring porphyrin units. Optical, electrochemical, and fluorescence studies of the arrays indicated that the porphyrin units retain their independent ground- and excited-state characteristics. Cu(II) and Ni(II) derivatives of hexaporphyrin and octaporphyrin arrays containing N(4) porphyrin units and N(3)S porphyrin units were synthesized, and complete metalation of the arrays was confirmed by their mass spectra and by detailed NMR characterization of the Ni(II) derivatives of hexa- and octaporphyrin arrays containing N(4) porphyrin units. Electrochemical studies indicated that Cu(II) and Ni(II) ions present in the thiaporphyrin units of the arrays can be stabilized in the +1 oxidation state, which is not possible with arrays containing normal porphyrin units.     

Direct Esterification of Aromatic Aldehydes with Tetraphenylphosphonium Bromide under Oxidative N‐Heterocyclic Carbene Catalysis

An unconventional reagent, tetraphenylphosphonium bromide, was employed as a phenyl source in the direct transformation of aromatic aldehydes to the corresponding phenyl esters under oxidative N‐heterocyclic carbene (NHC) catalysis. The phenyl esters were obtained in moderate yields under mild and organocatalytic conditions.     

Banana Peel: A Potential Substrate for Laccase Production by <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis> VkJ2.4.5 in Solid-State Fermentation

In solid-state fermentation, among various solid supports evaluated, banana peel was found to be an ideal support and resulted into higher levels of laccase (6281.4 ± 63.60 U l⁻¹) along with notable levels of manganese peroxidase production (1339.0 ± 131.23 U l⁻¹) by Aspergillus fumigatus VkJ2.4.5. Maximum levels of laccase was achieved under derived conditions consisting of 80% of moisture level, 6 days of incubation period, 6% inoculum level, and an aeration level of 2.5 l min⁻¹. A column-tray bioreactor was designed to scale up and economize the enzyme production in three successive cycles of fermentation using the same fungal biomass. Thermal and pH stability profiles revealed that enzyme was stable up to 50°C and at varying pH range from 5–9 for up to 2 h. The apparent molecular weight of laccase was found to be 34 ± 1 kDa. MALDI-TOF/TOF analysis of the protein showed significant homology with maximum identity of 67% to other laccases reported in database.     

Some remarks on generalizations of countably compact spaces and Lindelöf spaces

We prove some propositions and present some examples concerning the properties between countably compact and pseudocompact and the properties between Lindelöf and pseudo-Lindelöf.     

Volume effect of laser produced plasma on X-ray emissions

An investigation of x-ray emission from Cu plasma produced by 1.054 μm Nd:glass laser pulses of 5 ns duration, at 2 × 10¹² − 2 × 10¹³ W cm⁻² is reported. The x-ray emission has been studied as a function of target position with respect to the laser beam focus position. It has been observed that x-ray emissions from ns duration plasma show a volume effect similar to subnanosecond plasmas. Due to this effect the x-ray yield increases when target is moved away relative to the best focal plane of the laser beam. This result supports the theoretical model of Tallents and has also been testified independently using suitably modified theoretical model for our experimental conditions. While above result is in good agreement with similar experimental results obtained for sub-nanosecond laser produced plasmas, it differs from result claiming filamentation rather than pure geometrical effect leading to x-ray enhancement for ns plasmas.     

Numerical analysis of SiGeSn/GeSn interband quantum well infrared photodetector

In this paper, detailed theoretical investigation on the frequency response and responsivity of a strain balanced SiGeSn/GeSn quantum well infrared photodetector (QWIP) is made. Rate equation and continuity equation in the well are solved simultaneously to obtain photo generated current. Quantum mechanical carrier transport like carrier capture in QW, escape of carrier from the well due to thermionic emission and tunneling are considered in this calculation. Impact of Sn composition in the GeSn well on the frequency response, bandwidth and responsivity are studied. Results show that Sn concentration in the GeSn active layer and applied bias have important role on the performance of the device. Significant bandwidth is obtained at low reverse bias voltage, e.g., 200?GHz is obtained at 0.28?V bias for a single Ge_0.83Sn_0.17 layer. Whereas, the maximum responsivity is of 8.6?mA/W at 0.5?V bias for the same structure. However, this can be enhanced by using MQW structure.     

Rapid Synthesis and Biological Activities of Some New Benzothiazol-2-Ylhexahydro-S- Triazine Derivatives

2,4,6-Substituted 1,3,5-tris(benzothiazolyl)hexahydro-1,3,5-triazine derivatives were synthesized by the condensation of substituted benzothiazoles with aldehydes by conventional as well as by microwave irradiation (solvent free and solid supported) methods. All compounds were tested for antibacterial and antifungal activities, and the results have been compared with standard drugs. Acaricidal and anti-feedant activities were also tested.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Bianchi Type V magnetized string dust cosmological models with Petrov-type degenerate

Bianchi Type V massive string cosmological models with free gravitational field of Petrov Type degenerate in the presence of magnetic field with variable magnetic permeability are investigated. The magnetic field is due to an electric current produced along the x-axis. The F ₂₃ is the only non-vanishing component of electromagnetic field tensor F _ij . Maxwell’s equations F _[ij;k] = 0 and F _;j ^ij = 0 are satisfied by F ₂₃ = constant. The behaviour of the model in the presence and absence of magnetic field and other physical aspects are also discussed.      

Sol–gel based anti-reflection coatings on wedged laser rods using a spin coater

Anti-reflection (AR) sol–gel coatings are deposited on wedge glass optics for high-power lasers using spin coating technique. Characterization of these coatings on BK-7 glass substrates is carried out in terms of thickness profile across the surface, thickness variation w.r.t. wedge angle, and its effect on AR coating reflectivity, at different wedge angles from 1° to 7°. Results of the study are used to deposit AR coatings on inclined end faces of Nd:phosphate glass laser rods.