Singlet molecular oxygen quantum yield measurements of some porphyrins and metalloporphyrins

Hematoporphyrin IX dimethyl ester (HPDME), tetraphenylporphyrin (TPP), tetra(4-methoxyphenyl)porphyrin (TMPP), tetra(3,4-dimethoxyphenyl)porphyrin (TDMPP), tetra(3,4,5-trimethoxyphenyl)porphyrin (TTMPP), tetraanthrylporphyrin (TAP) and tetraacridylporphyrin (TACP), and their Zn²⁺, SnX ₂ ²⁺ , Pd²⁺ and Pt²⁺ complexes have been prepared and characterized. The singlet molecular oxygen quantum yield (ϕ_Δ) values of the above porphyrins and their metal derivatives in N,N-dimethyl formamide (DMF) have been measured in the presence of 1,3-diphenylisobenzofuran (DPBF) as¹O₂ acceptor using steady state technique after correcting for the intensity of light absorbed by the photosensitizers. The ϕ_Δ values for the free base porphyrins are usually around 0.60. Hematoporphyrin IX dimethyl ester and its metal derivatives follow the order: HPDME (ϕ_Δ = 0.60) > Zn HPDME (0.40) > PdHPDME (0.34) > Sn(OH)₂ HPDME (0.28) > PtHPDME (0.24). Zinc(II) complexes of tetraarylporphyrins show about 65% efficiency in ϕ_Δ values are compared to the ϕ_Δ values of their corresponding free base porphyrins. These results can be explained on the basis of catalyzed intersystem crossing to the ground state. The ϕ_λ values of the above free base porphyrins and their metal complexes in DMF in presence of DPBF using single-pulsed laser excitation technique follow similar trends.     

Single crystal EPR studies of Mn(II) doped into zinc ammonium phosphate hexahydrate (ZnNH4PO4·6H2O): A case of interstitial site for bio-mineral analogue

Single crystal EPR studies of Mn(II)-doped zinc ammonium phosphate hexahydrate (ZnNH₄PC₄·6H₂O) have been reinvestigated at room temperature. Single crystal rotations along the three orthogonal axes indicate that the spin Hamiltonian parameters for the interstitial site are:g _xx = 1.966,g _yy = 1.972,g _zz = 1.976;D _xx = -12.28 mT,D _yy = -2.09 mT andD _zz = 14.37 mT;A _xx = 9.06 mT,A _yy = 9.06 mT andA _zz = 11.09 mT;a = -0.11 mT. These parameters differ considerably from the previous report of Chand and Agarwal and indicate the orthorhombic nature of the paramagnetic impurity. The impurity is found to enter the lattice interstitially, in contrast to earlier prediction of substitutional position. The percentage covalency of the Mn-0 bond has been estimated.     

Electron density distribution in GaAs using MEM

Electron density distribution of GaAs is determined by means of the maximum entropy method (MEM) using reasonably good X-ray data collected at room temperature and 200 K. The bonding electron distributions are clearly visible in the MEM map and the mixed covalent-ionic character in GaAs is evidenced. The density distributions at 200 K show more condensed electronic clouds as compared to the room temperature map, preserving the trend in the bonding characters. The electron densities at the middle of the bond are 0.79 and 0.70 e/ų at 200 K and at room temperature, respectively. The refined harmonic thermal factors are in good agreement with the published values.     

Origin of room-temperature ferromagnetism in cobalt-doped ZnO

Thin films of ZnO doped with cobalt have been grown by the pulsed laser deposition (PLD) technique in different temperatures ranging from 500°C to 650°C. The films grown on sapphire c-plane single crystal were found to be highly epitaxial. Magnetic properties of these films were studied, and the films exhibited ferromagnetic characteristics at room temperature. Detailed structural and microstructural characterization was performed to correlate the fate of the magnetic impurities, i.e., cobalt, and the cause of magnetic properties. It is established from this work that the magnetic properties of these films are inherent to the system, and any presence of second phase/nanoclusters/precipitates are ruled out as the cause of magnetic properties. The techniques used to establish these were conventional and high-resolution transmission electron microscopy (HRTEM) along with electron-energy loss spectroscopy (EELS) and scanning transmission electron microscopy-atomic number (STEM-Z) contrast studies.     

Shape preserving interpolation using quadratic X-splines

In this note, we use a new approach to define the Quadratic X-splines and then examine it for preserving shape when applied to strictly convex data. Here, the construction of the Quadratic X-Spline interpolation becomes straight forward.     

Implementation of an 8-Core, 64-Thread, Power-Efficient SPARC Server on a Chip

The second in the Niagara series of processors (Niagara2) from Sun Microsystems is based on the power-efficient chip multi-threading (CMT) architecture optimized for Space, Watts (Power), and Performance (SWaP) [SWap Rating = Performance/(Space _* Power) ]. It doubles the throughput performance and performance/watt, and provides >10times improvement in floating point throughput performance as compared to UltraSPARC T1 (Niagara1). There are two 10 Gb Ethernet ports on chip. Niagara2 has eight SPARC cores, each supporting concurrent execution of eight threads for 64 threads total. Each SPARC core has a floating point and graphics unit and an advanced cryptographic unit which provides high enough bandwidth to run the two 10 Gb Ethernet ports encrypted at wire speeds. There is a 4 MB Level2 cache on chip. Each of the four on-chip memory controllers controls two FBDIMM channels. Niagara2 has 503 million transistors on a 342 mm² die packaged in a flip-chip glass ceramic package with 1831 pins. The chip is built in Texas Instruments' 65 nm 11LM triple-Vt CMOS process. It operates at 1.4 GHz at 1.1 V and consumes 84 W.     

Identification of regions of fastest mixing in a system of point vortices

This paper describes a numerical method for efficiently identifying the regions of fastest mixing of a passive dye in a flow due to a system of point vortices. Results obtained from computations are presented for systems of three and four point vortices, both in the unbounded domain and inside a circular cylinder. The flow is two‐dimensional and the fluid is incompressible. The regions where mixing is possible are found by studying the largest Lagrangian Lyapunov exponent distribution with respect to various initial positions of tracer particles. The regions of fastest mixing are then identified from the Lyapunov exponent distribution at small times. The results of the method are verified by quantifying the mixing by using a traditional box counting technique. The technique is then applied to several different initial configurations of vortices and some interesting results are obtained. Some numerical findings about the nature of the exponents computed are also discussed. Copyright © 2002 John Wiley Sons, Ltd.     

Generation of femtosecond pulses at 1350 nm by Cerenkov radiation in higher-order-mode fiber

We demonstrate a method of generating short pulses at 1350 nm by exciting Cerenkov radiation in a higher-order-mode fiber with a 1064 nm femtosecond fiber laser. We measure a 106 fs, 0.66 nJ output pulse. Cerenkov radiation in fibers allows for energy transfer between a soliton and a dispersive wave, providing an effective and engineerable platform to shift the wavelength of a femtosecond source. With appropriate design of the higher-order-mode fiber, this method of generating short pulses at 1350 nm can be extended to other wavelengths and to higher pulse energies.     

An Approach to NMR Assignment of Intrinsically Disordered Proteins

An efficient approach to NMR assignments in intrinsically disordered proteins is presented, making use of the good dispersion of cross peaks observed in [¹⁵N,¹³C′]‐ and [¹³C′,¹H^N]‐correlation spectra. The method involves the simultaneous collection of {3D (H)NCO(CAN)H and 3D (HACA)CON(CA)HA} spectra for backbone assignments via sequential H^N and H^α correlations and {3D (H)NCO(CACS)HS and 3D (HS)CS(CA)CO(N)H} spectra for side‐chain ¹H and ¹³C assignments, employing sequential ¹H data acquisitions with direct detection of both the amide and aliphatic protons. The efficacy of the approach for obtaining resonance assignments with complete backbone and side‐chain chemical shifts is demonstrated experimentally for the 61‐residue [¹³C,¹⁵N]‐labelled peptide of a voltage‐gated potassium channel protein of the Kv1.4 channel subunit. The general applicability of the approach for the characterisation of moderately sized globular proteins is also demonstrated.     

Gastroprotective potentials of the ethanolic extract of Mukia maderaspatana against indomethacin-induced gastric ulcer in rats

This study investigated the protective effects of the ethanolic extract of Mukia maderaspatana against indomethacin-induced gastric ulcer in rats. Gastric ulceration was induced by single intraperitoneal injection of indomethacin (30 mg/kg b.wt.). M. maderaspatana extract produced significant reduction in gastric mucosal lesions, malondialdehyde and serum tumour necrosis factor-α associated with a significant increase in gastric juice mucin content and gastric mucosal catalase, nitric oxide and prostaglandin E2 levels. The volume and acidity of the gastric juice decreased in pretreated rats. The plant extract was evaluated in the gastric juice of rats, untreated has showed near normal levels in pretreated rats. The M. maderaspatana was able to decrease acidity and increase the mucosal defence in the gastric area, therefore justifying its use as an antiulcerogenic agent. Ranitidine significantly increased pH value and decreased pepsin activity and gastric juice free and total acidity. The anti-ulcer effect was further confirmed histologically.