Microwave-assisted rapid extracellular synthesis of stable bio-functionalized silver nanoparticles from guava (<Emphasis Type="Italic">Psidium guajava</Emphasis>) leaf extract

Our research interest centers on microwave-assisted rapid extracellular synthesis of bio-functionalized silver nanoparticles of 26 ± 5 nm from guava (Psidium guajava) leaf extract with control over dimension and composition. The reaction occurs very rapidly as the formation of spherical nanoparticles almost completed within 90 s. The probable pathway of the biosynthesis is suggested. Appearance, crystalline nature, size and shape of nanoparticles are understood by UV–vis (UV–vis spectroscopy), FTIR (fourier transform infrared spectroscopy), XRD (X-ray diffraction), FESEM (field emission scanning electron microscopy) and TEM (transmission electron microscopy) techniques. Microwave-assisted route is selected for the synthesis of silver nanoparticles to carry out the reaction fast, suppress the enzymatic action and to keep the process environmentally clean and green.     

Experimental Investigation into the Mechanical Behavior of Textile Composites with Various Fiber Reinforcement Architectures

Mechanics of Composite Materials - The role of fiber reinforcement architecture in adjusting the mechanical properties of glass-fiber-reinforced epoxy composite materials is studied. Fibrous...     

Overcrowding estimates for zeroes of Planar and Hyperbolic Gaussian analytic functions

We consider the point process of zeroes of certain Gaussian analytic functions and find the asymptotics for the probability that there are more than m points of the process in a fixed disk of radius r, as . For the planar Gaussian analytic function, , we show that this probability is asymptotic to . For the hyperbolic Gaussian analytic functions, , we show that this probability decays like .In the planar case, we also consider the problem posed by Mikhail Sodin² on moderate and very large deviations in a disk of radius r, as . We partially solve the problem by showing that there is a qualitative change in the asymptotics of the probability as we move from the large deviation regime to the moderate.Research supported by NSF grant #DMS-0104073 and NSF-FRG grant #DMS-0244479.     

Synthesis of Novel 4‐Substituted Coumarins,Docking Studies,and DHODH Inhibitory Activity

Coumarins are the important class of naturally occurring heterocyclic compounds. Activities like antioxidant, antibacterial, anti‐inflammatory, and anticancer have been reported for coumarin derivatives. Present work details the synthesis of substituted coumarin‐4‐pyrrolones as well as coumarin‐4‐acetyl amino acids and their DHODH inhibitory activity, which is a dual target for malaria and cancer. Coumarin‐4‐acetic acids ( 2a – c ) were coupled with different methyl esters of α‐amino acids ( 3 ) giving rise to corresponding coumarin‐4‐acetyl amino acid methyl esters ( 4a – o ), which on hydrolysis under basic condition underwent cyclization forming substituted dihydropyrrole‐2‐ones ( 5a – i ), dihydroindolizine‐3‐ones ( 5j – l ), and dihydropyrrolizin‐3‐one ( 5m – o ). Acidic hydrolysis of the compounds ( 4a – o ) yielded corresponding coumarin‐4‐acetyl amino acids ( 6a – f ). The docking study was performed with the protein 4IGH (obtained from PDB) using Surflex–Dock module. The newly synthesized compounds were tested for DHODH inhibitory activity using Brequinar as the standard. Compound 6b showed remarkable inhibition compared with the standard, and the other compounds with terminal COOH showed moderate inhibition.     

Mesoporous Foam TiO2 Nanomaterials for Effective Hydrogen Production

Hydrolysis of TiCl₄ in a diether‐functionalized imidazolium ionic liquid (IL), namely 1‐methyl‐3‐[2‐(2‐methoxy(ethoxy)ethyl]imidazolium methane sulfonate (M(MEE)I ? CH₃SO₃), results in a heterostructured organic/inorganic and sponge‐like porous TiO₂ material. The thermal treatment (300 °C) followed by calcination (500 °C) affords highly porous TiO₂. The characterization of the obtained samples (with and without IL, before and after calcination) by XRD, SEM, and TEM reveals TiO₂ anatase crystalline phases and irregular‐shaped particles with different porous structures. These hierarchical‐structured mesoporous TiO₂ nanomaterials were employed as efficient photocatalysts in the water‐splitting process, yielding up to 1304 μmol g^?1 on hydrogen production.     

Thin film processing of axially modified phthalocyanine derivatives

A new class of hydroxyl terminated silicon phthalocyanine (SiPc) derivatives was prepared by capping dihydroxy SiPc with a variety of compounds containing two or more hydroxyl groups. The unique feature of these polyhydroxy SiPc derivatives is their function as crosslinkers that allows their processability into polyurethane films on reacting with isophorone diisocyanate. The films possess high impact resistance, thermostability at 125°C for over 10 h, and low absorption in the visible region. Solid polymeric films incorporating over 20% (w/w) of Pc rings were prepared without phase segregation. The kinetic parameters of polymerization, such as reaction conversion versus time and temperature, heat of reaction (ΔH), activation energy (ΔE), and reaction order (n) were investigated. Some of the polyhydroxy SiPc derivatives exhibit very high solubility in common organic solvents and possess adequate optical transparency for use as nonlinear optical materials in vision protection against laser light. © 1996 John Wiley & Sons, Inc.     

Strong persistence of an attractor and generalized partial synchronization in a coupled chaotic system

It is widely believed that when two discrete time chaotic systems are coupled together then there is a contraction in the phase space (where the essential dynamics takes place) when compared with the phase space in the uncoupled case. Contrary to such a popular belief, we produce a counter example--we consider two discrete time chaotic systems both with an identical attractor A, and show that the two systems could be nonlinearly coupled in a way such that the coupled system's attractor persists strongly, i.e., it is A?×?A despite the coupling strength is varied from zero to a nonzero value. To show this, we prove robust topological mixing on A?×?A. Also, it is of interest that the studied coupled system can exhibit a type of synchronization called generalized partial synchronization which is also robust.     

Preparation and properties of Zn<Subscript>0.9</Subscript>Ni<Subscript>0.1</Subscript>O diluted magnetic semiconductor nanoparticles

With a view to study the structural, electronic, magnetic, and electrical properties of Zn_0.9Ni_0.1O diluted magnetic semiconductor nanoparticles, systematic investigation has been undertaken. Samples were prepared for the first time by hydrazine-assisted polyol method, and the powders were annealed at various temperatures in order to obtain the samples with different grain sizes. From the Rietveld refined XRD data, lattice parameters, the average crystallite size values, and r.m.s micro-strain values were computed. From the AFM and TEM studies, the average particle sizes were obtained and are found to be in the range 12–46 nm. XPS measurements clearly indicate that the chemical states as +2 for both Zn and Ni ions and are stable with varying annealing temperature. Further, using XPS and optical studies, the electronic structure of the materials was analyzed. A careful phase analysis of the Rietveld refined XRD data (at logarithmic scale) selected area electron diffraction patterns, FTIR, Raman, and XPS studies; it was concluded that all the samples are having hexagonal wurtzite structure without any detectable impurity phases. The optical band gap values are found to exhibit a clear blue shift. The influence of oxygen vacancies on the emission spectra was studied by Photo Luminescence measurement. The magnetization studies were undertaken by VSM, MFM, and FMR techniques and confirmed the presence of clear room temperature ferromagnetism without any magnetic clusters. The carrier concentration (n) values obtained from the thermo power studies are found to decrease with increasing annealing temperature and depend on the local defects which are critically influenced by the annealing temperature and crystallite size of the nanomaterials.     

Total Synthesis of Myceliothermophins C,D, and E

The total synthesis of cytotoxic polyketides myceliothermophins E ( 1 ), C ( 2 ), and D ( 3 ) through a cascade‐based cyclization to form the trans‐fused decalin system is described. The convergent synthesis delivered all three natural products through late‐stage divergence and facilitated unambiguous C21 structural assignments for 2 and 3 through X‐ray crystallographic analysis, which revealed an interesting dimeric structure between its enantiomeric forms.