Photo, thermal, and ultrasonic degradation of EGDMA-crosslinked poly(acrylic acid-co-sodium acrylate-co-acrylamide) superabsorbents

Superabsorbent polymers (SAPs) based on acrylic acid (AA), sodium acrylate (SA), and acrylamide (AM) were synthesized by inverse suspension polymerization using ethylene glycol dimethacrylate as the crosslinking agent. The equilibrium swelling capacities and the rates of swelling of SAPs varied with the AM content and followed first-order kinetics. The photodegradation of SAPs in their equilibrium swollen state was carried out by monitoring their swelling capacity and the residual weight fraction. The SAPs degraded in two stages, wherein the swelling capacity increased to a maximum and then subsequently decreased. Thermogravimetric analysis of the SAPs indicated that the copolymeric superabsorbents had intermediate thermal stability between the homopolymeric superabsorbents. The activation energies of SAPs with 0, 20, and 100 mol % AM content were determined by Kissinger method and were found to be 299, 248, and 147 kJ mol-1, respectively. The ultrasonic degradation of the superabsorbents was carried out in their equilibrium swollen state, and the change in the viscosity with ultrasonication time was used to quantify the degradation. The ultrasonic degradation of AA/SA superabsorbent was also investigated at various ultrasound intensities. The degradation rate coefficients were found to increase with the intensity of ultrasound. The ultrasonic degradation of AA/SA/AM (20% AM) was also carried out, and degradation rate was found to be more than that of the AA/SA superabsorbent. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Unusual co-crystal of isonicotinamide: the structural landscape in crystal engineering

The idea of a structural landscape is based on the fact that a large number of crystal structures can be associated with a particular organic molecule. Taken together, all these structures constitute the landscape. The landscape includes polymorphs, pseudopolymorphs and solvates. Under certain circumstances, it may also include multicomponent crystals (or co-crystals) that contain the reference molecule as one of the components. Under still other circumstances, the landscape may include the crystal structures of molecules that are closely related to the reference molecule. The idea of a landscape is to facilitate the understanding of the process of crystallization. It includes all minima that can, in principle, be accessed by the molecule in question as it traverses the path from solution to the crystal. Isonicotinamide is a molecule that is known to form many co-crystals. We report here a 2 : 1 co-crystal of this amide with 3,5-dinitrobenzoic acid, wherein an unusual N-H center dot center dot center dot N hydrogen-bonded pattern is observed. This crystal structure offers some hints about the recognition processes between molecules that might be implicated during crystallization. Also included is a review of other recent results that illustrate the concept of the structural landscape.

Kinetics of adsorption of methylene blue and rhodamine 6G on acrylic acid-based superabsorbents

Superabsorbent polymers (SAPs) of acrylic acid, sodium acrylate, and acrylamide (AM), crosslinked with ethylene glycol dimethacrylate, were synthesized by inverse suspension polymerization. The equilibrium swelling capacities of the SAPs were determined and these decreased with increasing AM content. The adsorption of the two cationic dyes, methylene blue and rhodamine 6G, on the dry as well as equilibrium swollen SAPs was investigated. The amount of the dye adsorbed at equilibrium per unit weight of the SAPs and the rate constants of adsorption were determined. The amount of the dye adsorbed at equilibrium by the SAPs decreased with increasing mol % of AM in the SAPs. The amount of the dye adsorbed at equilibrium was almost equal for the dry and equilibrium swollen SAPs. However, the equilibrium swollen SAPs adsorbed dyes at a higher rate than the dry SAPs. The higher rate of adsorption was attributed to the availability of all the anionic groups present in the fully elongated conformation of the SAPs in the equilibrium swollen state. The effect of initial dye concentration on the adsorption was also investigated and the adsorption was described by Langmuir adsorption isotherms. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Crystal Engineering in the Desiraju Research Group in Bangalore

Over the years, crystal engineering has transformed into a mature and multidisciplinary subject. New understanding, challenges, and opportunities have emerged in the design of complex structures and structure-property evaluation. Revolutionary pathways adopted by many leaders have shaped and directed this subject. In this short essay to celebrate the 60th birthday of Prof. Gautam R. Desiraju, we, his current research group members, contemplate the development of some of the topics explored by our group in the context of the overall subject. These topics, though not entirely new, are of significant interest to the crystal engineering community.

High-temperature kinetics of the reaction between CN and hydrocarbons using a novel high-enthalpy flow tube

More than 70 molecules of varied nature have been identified in the envelopes of carbon-rich stars through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals, and a significant number are unique to the circumstellar medium. The determination of relevant laboratory kinetics data is critical to keep up with the development of the high spectral and spatial resolution observations and of the refinement of chemical models. Neutralneutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures and deserve a detailed laboratory investigation. The approach we have developed aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high-enthalpy source with a flow tube and a pulsed laser photolysislaser-induced fluorescence system to probe the undergoing chemical reactions. The high-enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane (C3H8), propene (C3H6), allene (C3H4), 1,3-butadiene (1,3-C4H6), and 1-butyne (C4H6) over a temperature range extending from 300 to 1200 K. All studied reactions of CN with unsaturated hydrocarbons are rapid, with rate coefficients greater than 10-10 cm3 center dot molecule-1 center dot s-1 and exhibit slight negative temperature dependence above room temperature. (c) 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 753766, 2012

LbL-coated microcapsules as systems for encapsulation of optical brightening agent

We report the encapsulation of optical brightening agent (OBA) into hollow microcapsules prepared by the controlled Layer- by-Layer (LbL) self-assembly process, achieved by the sequential adsorption of oppositely charged polyelectrolytes using negatively charged silica template. Loading takes place by spontaneous deposition method which was proved by confocal laser scanning microscopy (CLSM) using rhodamine 6G (Rd6G) as a fluorescent probe. The loading of the OBA into the microcapsules was found to be dependent on the feeding concentration, pH of the medium, and loading temperature. The encapsulation efficiency of OBA decreased on increasing feeding concentration. Maximum loading was observed at pH 4 and amount of OBA loaded decreased with increase in pH. The loaded OBA was released in a sustained manner for 8 h. No degradation of the OBA was observed during the process of encapsulation and release. Polyelectrolyte capsules potentially offer an innovative way of encapsulating large amounts of active materials for a variety of applications. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 1609-1614, 2013

Adsorption of anionic dyes on a reversibly swelling cationic superabsorbent polymer

A cationic monomer 2-(methacryloyloxy)ethyl]trimethylammonium chloride was polymerized using N,N'-methylenebisacrylamide as the crosslinker to obtain a cationic superabsorbent polymer (SAP). This SAP was characterized by Fourier transform-infrared spectroscopy, and the equilibrium swelling capacity was determined by swelling in water. The SAP was subjected to cyclic swelling/deswelling in water and NaCl solution. The conductivity of the swelling medium was monitored during the swelling/deswelling and was related to the swelling/deswelling characteristics of the SAP. The adsorption of five anionic dyes of different classes on the SAP was carried out and was found to follow the first-order kinetics. The Langmuir adsorption isotherms were found to fit the equilibrium adsorption data. The dye adsorption capacity of the SAP synthesized in this study was higher than that obtained for other hydrogels reported in the literature. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Demonstrating the Usefulness of CAELinux for Computer Aided Engineering using an Example of the Three Dimensional Reconstruction of a Pig Liver

CAELinux is a Linux distribution which is bundled with free software packages related to Computer Aided Engineering (CAE). The free software packages include software that can build a three dimensional solid model, programs that can mesh a geometry, software for carrying out Finite Element Analysis (FEA), programs that can carry out image processing etc. Present work has two goals: 1) To give a brief description of CAELinux 2) To demonstrate that CAELinux could be useful for Computer Aided Engineering, using an example of the three dimensional reconstruction of a pig liver from a stack of CT-scan images. One can note that instead of using CAELinux, using commercial software for reconstructing the liver would cost a lot of money. One can also note that CAELinux is a free and open source operating system and all software packages that are included in the operating system are also free. Hence one can conclude that CAELinux could be a very useful tool in application areas like surgical simulation which require three dimensional reconstructions of biological organs. Also, one can see that CAELinux could be a very useful tool for Computer Aided Engineering, in general.

Point Spread Function Engineering for Super-Resolution Single-Photon and Multiphoton Fluorescence Microscopy

Super-resolution imaging techniques are of paramount interest for applications in bioimaging and fluorescence microscopy. Recent advances in bioimaging demand application-tailored point spread functions. Here, we present some approaches for generating application-tailored point spread functions along with fast imaging capabilities. Aperture engineering techniques provide interesting solutions for obtaining desired system point spread functions. Specially designed spatial filters—realized by optical mask—are outlined both in a single-lens and 4Pi configuration. Applications include depth imaging, multifocal imaging, and super-resolution imaging. Such an approach is suitable for fruitful integration with most existing state-of-art imaging microscopy modalities.

Nanoindentation in Crystal Engineering: Quantifying Mechanical Properties of Molecular Crystals

Nanoindentation is a technique for measuring the elastic modulus and hardness of small amounts of materials. This method, which has been used extensively for characterizing metallic and inorganic solids, is now being applied to organic and metalorganic crystals, and has also become relevant to the subject of crystal engineering, which is concerned with the design of molecular solids with desired properties and functions. Through nanoindentation it is possible to correlate molecular-level properties such as crystal packing, interaction characteristics, and the inherent anisotropy with micro/macroscopic events such as desolvation, domain coexistence, layer migration, polymorphism, and solid-state reactivity. Recent developments and exciting opportunities in this area are highlighted in this Minireview.

In vitro cytocompatibility assessment of amorphous carbon structures using neuroblastoma and Schwann cells

The development of scaffolds for neural tissue engineering application requires an understanding of cell adhesion, proliferation, and migration of neuronal cells. Considering the potential application of carbon as scaffold materials and the lack of understanding of compatibility of amorphous carbon with neuronal cells, the carbon-based materials in the forms of carbon films and continuous electrospun carbon nanofibers having average diameter of approximate to 200 nm are being investigated with or without ultraviolet (UV) and oxy-plasma (OP) treatments for cytocompatibility property using mouse Neuroblastoma (N2a) and rat Schwann cells (RT4-D6P2T). The use of Raman spectroscopy in combination with Fourier transform infrared (FTIR) and X-ray diffraction establishes the amorphous nature and surface-bonding characteristics of the studied carbon materials. Although both UV and OP treatments make carbon surfaces more hydrophilic, the cell viability of N2a cells is statistically more significant on OP treated fibers/films compared to UV fiber/film substrates after 4 days in culture. The electrospun carbon fibrous substrate provides the physical guidance to the cultured Schwann cells. Overall, the experimental results of this study demonstrate that the electrospun amorphous carbon nanofibrous scaffolds can be used as a suitable biomaterial substrate for supporting cell adhesion and proliferation of neuronal cells in the context of their applications as artificial nerve implants. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

Engineering Gold Nanoparticle Interaction by PAMAM Dendrimer

Bare faceted gold nanoparticles (AuNPs) have a tendency to aggregate through a preferred attachment of the 111] surfaces. We have used fully atomistic classical molecular dynamics simulations to obtain a quantitative estimate of this surface interaction using umbrella sampling (US) at various temperatures. To tune this surface interaction, we use polyamidoamine (PAMAM) dendrimer to coat the gold surface under various conditions. We observe a spontaneous adsorption of the protonated as well as nonprotonated PAMAM dendrimer on the AuNP surface. The adsorbed dendrimer on the nanoparticle surface strongly alters the interaction between the nanoparticles. We calculate the interaction between dendrimercoated AuNPs using US and show how the interaction between two bare faceted AuNPs can be tuned as a function of dendrimer concentration and charge (pH dependent) With appropriate choice of the dendrimer concentration and charge, two strongly interacting AuNPs can be made effectively noninteracting. Our simulation results demonstrate a strategy to tune the nanoparticle interaction, which can help in engineering self-assembly of such nanoparticles.

Scaffolds for bone tissue engineering: role of surface patterning on osteoblast response

The fabrication of tissue engineering scaffolds necessitates amalgamation of a multitude of attributes including a desirable porosity to encourage vascular invasion, desired surface chemistry for controlled deposition of calcium phosphate-based mineral as well as ability to support attachment, proliferation, and differentiation of lineage specific progenitor cells. Scaffold fabrication often includes additional surface treatments to bring about desired changes in the surface chemistry. In this perspective, this review documents the important natural and synthetic scaffolds fabricated for bone tissue engineering applications in tandem with the surface treatment techniques to maneuver the biocompatibility of engineered scaffolds. This review begins with a discussion on the fundamental concepts related to biocompatibility as well as the characteristics of the biological micro-environment. The primary focus is to discuss the effects of surface micro/nano patterning on the modulation of bone cell response. Apart from reviewing a host of experimental studies reporting the functionality of osteoblast-like bone cells and stem cells on surface modified or textured bioceramic/biopolymer scaffolds, theoretical insights to predict cell behavior on a scaffold with different topographical features are also briefly analyzed.

Crystal engineering: from molecule to crystal

How do molecules aggregate in solution, and how do these aggregates consolidate themselves in crystals? What is the relationship between the structure of a molecule and the structure of the crystal it forms? Why do some molecules adopt more than one crystal structure? Why do some crystal structures contain solvent? How does one design a crystal structure with a specified topology of molecules, or a specified coordination of molecules and/or ions, or with a specified property? What are the relationships between crystal structures and properties for molecular crystals? These are some of the questions that are being addressed today by the crystal engineering community, a group that draws from the larger communities of organic, inorganic, and physical chemists, crystallographers, and solid state scientists. This Perspective provides a brief historical introduction to crystal engineering itself and an assessment of the importance and utility of the supramolecular synthon, which is one of the most important concepts in the practical use and implementation of crystal design. It also provides a look to the future from the viewpoint of the author, and indicates some directions in which this field might be moving.