A high performance lipase preparation: characterization and atomic force microscopy

The goal of obtaining enzyme forms which show greater stability, higher catalytic efficiency, and reusability has been pursued since last several decades. Some novel biocatalyst designs have been evolved and protein coated micro-crystals (PCMCs) is one of them. Pseudomonas cepacia lipase coated micro-crystals were prepared by simultaneous precipitation of mixture of aqueous lipase solution and salts such as potassium sulphate by organic solvents. This resulted in lipase coated micro-crystals. The structures of micro-crystals were studied by atomic force microscopy (AFM). The AFM picture confirmed the enzyme coating over the potassium sulphate crystals. These PCMCs are in the size range of 500-1000 nm. These enzyme coated micro-crystals showed enhanced transesterification rates. Also, the PCMC were stable at 60 degrees C whereas the free enzyme lost all its activity. The enzyme coated micro-crystals prepared by 50 mg Pseudomonas cepacia lipase gave 96% conversion in 90 min whereas free enzyme gave 8% conversion. Even PCMCs prepared from 3.12 mg lipase gave 90% conversion in 10 h at 60 degrees C where as free lipase was inactive at 60 degrees C.     

Melting of Ni and Fe nanoparticles: a molecular dynamics study with application to carbon nanotube synthesis

Molecular dynamics simulations with many-body interatomic potentials are used to study melting of Ni and Fe nanoparticles with diameters that range between 2 and 12 nm. Two different embedded-atom method interatomic potentials are used for each element. The capability of each interatomic potential to model (i) size-dependent melting in nanoparticles and (ii) the bulk melting temperature of Ni or Fe is explored. In agreement with existing theory, molecular dynamics simulations show that the melting temperature of non-supported nanoparticles decreases with decreasing nanoparticle size, displaying a linear relationship with the inverse of nanoparticle diameter. However, molecular dynamics simulations using the interatomic potentials considered in this work provide a lower estimate than existing theory for the sensitivity of the melting temperature to nanoparticle size (slope of linear relationship). Molecular dynamics simulations demonstrate that melting is surface initiated and that a finite temperature range exists in which partial melting of the nanoparticle occurs. This observation is very important in the development of advanced vapor-liquid-solid models for catalyst-assisted single-walled carbon nanotube synthesis.     

Mathematical modeling and process parameters optimization of ultrasonic assisted electrochemical magnetic abrasive machining

Journal of Mechanical Science and Technology - A new machining technique called ultrasonic assisted electrochemical magnetic abrasive machining integrates ultrasonic vibrations, electrochemical...     

Oil–water transport in clay-hosted nanopores: Effects of long-range electrostatic forces

Charged clay surfaces can impact the storage and mobility of hydrocarbon and water mixtures. Here, we use equilibrium molecular dynamics (MD) and nonequilibrium MD simulations to investigate hydrocarbon-water mixtures and their transport in slit-shaped illite nanopores. We construct two illite pore models with different surface chemistries: potassium–hydroxyl (PH) and hydroxyl–hydroxyl (HH) structures. In HH nanopore, we observe water adsorption on the clay surfaces. In PH nanopores, however, we observe the formation of water bridges because of the existence of a local, long-range electric field. Our NEMD simulations demonstrate that the velocity profiles across the pore depend strongly on water concentration, pore width and the presence or absence of the water bridge. This fundamental study provides a theoretical basis for understanding nanofluidics with charged surfaces and can be applied in such as biological processes, chemical and physical fields, and the oil and gas extraction in clay-rich formations.     

Traceability Issue in PM2.5 and PM10 Measurements

Nowadays particle size and mass concentration measurements are the important parameter of the ambient air quality standards of several countries. The regulatory limits of mass concentration of particulate matter (PM) for the size classes of PM_2.5 and PM₁₀, i.e., particle sizes of less than or equal to 2.5 and 10 μm in aerodynamic diameter, respectively in air are defined on yearly and hourly time-weighted-average basis. However, these limits are different in different regulations of the countries. Both of the parameters relate with the human health, climate and other issues, therefore accurate and precise measurement of these parameters are very important. Despite this, so far not much work has progressed in national metrology institutes (NMIs) worldwide on calibration and traceability issue of PM measurements. In this paper in context of PM measurement traceability, we present systematically the (1) air quality regulation in different countries, (2) reference methods for size and mass measurements, (3) variation/error and limitations of PM measurements based on the current results in this study and previously published results, (4) current status of PM size and mass calibration facility, (5) expected uncertainty in PM measurements, (6) add-on uncertainty in other parameters of national ambient air quality standards due to PM measurements, (7) where does traceability of PM issue stand against other parameters of air quality standards and its impact on health and climate, (8) NMIs working on this issue, (9) status at Bureau International des Poids et Mesures (BIPM), France and (10) conclusion. The aim of this paper is to better understand the importance of international system of units (SI) traceability issue in PM measurements, so wherever and whenever it is measured, should be acceptable everywhere, and data should be comparable for improving air quality and thus the quality of life. Funding agencies should be aware of this issue, and accept the results from the principle investigators and team only when their results have the traceability link to SI. NMIs should make program to involve industries in gas and aerosol metrology work to fulfill the requirement of calibration and standards. The regulatory authorities/ministry should work together with NMIs to improve the data quality of ambient measurements. This will greatly help to better make the policies and decisions on the related impacts. These were also the ultimate goals of “one-day pre-AdMet workshop” organized at National Physical Laboratory, New Delhi, India on February 20th, 2013.     

Preparation and Optimization of Dry PLGA Nanoparticles by Spray Drying Technique

The aim of this article was to evaluate the potential of poly lactide-coglycolide (PLGA) nanoparticles (NPs) as carriers for controlling release of doxorubicin (DOX) via a spray drying technique. The challenge was to entrap a hydrophilic molecule into a lipophilic core molecule of PLGA. To achieve this objective, we modified conventional approach of drug loading to spray drying technique. The eight formulations of nanoparticles were prepared by modified double emulsion and solvent evaporation technique followed by spray drying using 2³ factorial designs. PLGA (A) and PVA (B) and stirring speed (C) were used as independent variables where particle size (Y₁), entrapment efficiency (Y₂) and percentage of drug release at the 32 hour (Y₃) were taken as dependant variables. The results showed that the method is easy and efficient for the entrapment of the drug as well as the formation of spherical nanoparticles. This modification improved DOX entrapment efficiency relative to controls real loadings up to 40%. The in vitro release studies indicated the DOX loaded PLGA nanoparticles provide controlled drug release over a period of 32 h. Hence, this investigation demonstrated the potential of the experimental design in understanding the effect of the formulation variables on the quality of DOX-PLGA nanoparticles.     

Osteoconduction of porous Ti metal enhanced by acid and heat treatments

Bone ingrowth into porous Ti metal is important for stable fixation of Ti metal implants to surrounding bone. However, without surface treatment this is limited to only a thin region of the outer surface of the Ti metal. In the present study, a porous Ti metal with a porosity of ~60 % and interpore connections of 70–200 micrometers in diameter was investigated in terms of its chemical and heat treatments, by implanting it into rabbit femur for periods varying from 3 to 12 weeks. The porous Ti metal subjected to heat treatment at 600 °C after H₂SO₄/HCl mixed acid treatment showed the largest bone ingrowth in comparison with those subjected to no treatment, only acid treatment, and only heat treatment even at an early stage after implantation, and remained as such even 12 weeks after implantation. Their bone ingrowths were well interpreted in terms of apatite-forming abilities of the Ti metals in body environment. Their apatite-forming abilities did not depend upon their surface roughness nor type of crystalline phase, but upon the positive surface charge.     

X-ray study of weak interactions in two flavonoids

X-ray diffraction studies were carried out on single crystals of two flavonoids, viz. 5-hydroxy-6,7,4′-trimethoxyflavone, C₁₈H₁₆O₆, (I) and 5-hydroxy-3,7,4′-trimethoxyflavone, C₁₈H₁₆O₆, (II). Crystal structures of both the flavonoids were solved by direct methods and refined by full-matrix least-squares procedures. In both the molecules, the benzopyran moiety is planar. The dihedral angle between the phenyl ring and the benzopyran portion is 5.50(4)° in (I) and 29.11(5)° in (II). In (I), the crystal packing is influenced by O-H…O hydrogen bonds, and weak C-H…O and π…π interactions whereas in (II) the crystal structure is stabilized by the presence of four intermolecular short contacts of the type C-H…O. There is also one C-H…π hydrogen bond with H… centroid distance of <2.7 Å. The molecules are further stabilized by π-π interactions.     

Optically driven nanorotors: experiments and model calculations

We show that asymmetric nanorods rotate under the laser radiation pressure, irrespective of the polarization of the light, when trapped in laser tweezers. If a nanorod is not quite transparent to the trapping laser radiation, the radiation pressure force generates a non zero torque on the asymmetric nanorods making them rotate at a moderate speed. Our experimental observations on radiation pressure driven rotations of MgO and Si nanorods in optical trap show that the efficiency of the rotors depends directly on their transmittance at the trapping wavelength. We propose theoretical models to estimate the rotational speed at different laser powers for a rotor with shape asymmetries or surface irregularities.     

Resistive switching in copper oxide nanorods: a bottom up approach applicable for enhanced scalability

Reversible, stable and reproducible resistive switching in a parallel network of Cu2O nanorods, observed in the present study, highlights the advantages of using nanorods in comparison to normally used thin films. Unipolar and symmetric current-voltage characteristics of the metal/insulator/metal structure consisting of Hg top contact/Copper oxide (Cu2O) nanorods/Ag bottom contact in a sandwich configuration shows electroforming at about 11 V, reproducible reset and set points at 0.53 +/- 0.03 and 4.2 +/- 0.02 V and a high OFF/ON resistance ratio > 10(3). Slope of current-voltage characteristics and current contrast in CAFM mapping indicate that filamentary conduction mechanism is responsible for resistive switching. This study sets the foundation for fabricating a nanorods based resistive random access memory device and thus a manifold increase in the device scalability.