Sambasivarao Kotha

Synthesis and magnetic properties of polymer nanocomposites with embedded iron nanoparticles

Magnetic nanoparticles embedded in polymer matrices have excellent potential for electromagnetic device applications like electromagnetic interference suppression. We have synthesized polymer nanocomposites of poly(methylmethacrylate) doped with varying concentrations of iron nanoparticles (∼20 nm in size). The iron nanoparticles were produced using a microwave plasma technique and have a natural oxide surface layer for passivation. These nanocomposites were processed using melt blending technique. The polymer processing conditions were optimized to achieve good uniform dispersion of the nanoparticles in the polymer matrix. The concentration and dispersion of nanoparticles were varied in a controlled way. Surface characterization with scanning electron microscopy indicates that, to a large extent, the iron nanoparticles are embedded in the bulk; the surface mainly showed features associated with the polymer surface. Static magnetic properties such as susceptibility and M–H loops were studied using a physi...

Bidisperse Magnetorheological Fluids using Fe Particles at Nanometer and Micron Scale

Conventional magnetorheological (MR) fluids are suspensions of micron-sized particles in a hydraulic or silicone oil carrier fluid. Recently, research has been conducted on the advantages of using bidisperse fluids, which are mixtures of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron- sized particles and nanometer-sized particles. The settling rate of such bidisperse fluids using nanometer-sized particles is reduced because the nanoparticles fill pores created between the larger particles, thereby reducing fluid transport during creeping flow. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manifested by such an MR fluid at its saturation magnetization. There is a measurable and predictable variation in rheological properties as the weight percent (wt%) of the nanometer-sized particles is increased relative to the weight percent (wt%) of micron-sized particles, while maintaining a constant solids loading in the MR fluid samples. All bidisperse fluids tested in this study have a solids loading of 60 wt% of iron (Fe) particles. This study investigates the effect of increasing the wt% of 30 nm (nominal) Fe particles relative to 30 mm (nominal) Fe particles on rheological characteristics, such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid that provides the best combination of high yield stress and low settling rate based on empirical measurements. The applicability of the Bingham-plastic rheological model to the measured flow curves of these MR fluids is also presented.

Recent chemistry of benzocyclobutenes

This review covers aspects related to the synthesis, reactions and applications of benzocyclobutenes.

Advanced approach to polycyclics by a synergistic combination of enyne metathesis and Diels–Alder reaction

Enyne metathesis (EM) has widely been used to prepare various synthetic and natural products. Further, a sequential use of EM and Diels-Alder (DA) reactions generates highly functionalized and intricate polycarbocycles and heterocyclic frameworks. In this critical review we describe the application of a unique combination of EM and DA reactions to prepare various amino acid derivatives, natural products and heterocycles. Some of the heterocyclic targets include cyclic peroxides, siloxanes and various nitrogen (or oxygen) containing compounds. Use of ethylene and cyclooctadiene (COD) for improving the yield of EM products are also discussed (69 references).

Synthesis of unsual α-amino acids via a 2+2+2 cycloaddition strategy

A simple method for the preparation of diyne building block 5 and its use in the synthesis of indane-based α-amino acid derivatives via a 2+2+2 cycloaddition strategy is reported.

A retrospective on the design and synthesis of novel molecules through a strategic consideration of metathesis and Suzuki-Miyaura cross-coupling.

In recent years, ruthenium-catalyzed metathesis and palladium-catalyzed Suzuki-Miyaura cross-coupling reactions have proven to be the most efficient tools for carbon-carbon bond formation in synthetic organic chemistry. This is mainly because of the stability and remarkable functional-group tolerance of these catalysts. Therefore, the strategic consideration of these two powerful reactions can eventually minimize the synthetic steps for the construction of complex target molecules. In this perspective we summarize the efforts of many research groups who have used the combination of these two powerful reactions (either together in concert or separated by a few multistep sequences) for the synthesis of supramolecular ligands, polyaromatic compounds, and complex natural products.

Synthesis of constrained α-amino acid derivatives via enyne metathesis reaction

Synthesis of a diene building block via enyne metathesis reaction and its usage in the preparation of constrained α-amino acid derivatives is described.

Diversity-Oriented Approach to Macrocyclic Cyclophane Derivatives by Suzuki–Miyaura Cross-Coupling and Olefin Metathesis as Key Steps

Palladium-catalyzed Suzuki-Miyaura (SM) cross-coupling reaction with allylboronic acid pinacol ester and titanium assisted cross-metathesis (CM)/ring-closing metathesis (RCM) cascade has been used to synthesize macrocyclic cyclophane derivatives.

Diversity Oriented Approach to Crownophanes by Enyne Metathesis and Diels–Alder Reaction as Key Steps

Various crownophanes are assembled starting with simple phenol derivatives such as catechol, resorcinol, and hydroquinone. Here, cross-enyne metathesis (CEM) and Diels-Alder (DA) reaction have been used as key steps. This strategy has embedded six diversity points.

Synthesis of constrained α-amino acid derivatives via Diels-Alder approach

Synthesis of new five and seven membered outer ring diene building blocks containing α-amino acid moiety and their usage in the preparation of the constrained amino acid derivatives is described.