Oleylamine as a reducing agent in syntheses of magic-size clusters and monodisperse quantum dots: optical and photoconductivity studies.

Separation of magic size clusters (MSCs) from monodisperse quantum dots (QDs) has generally been a difficult task while employing the commonly used synthesis procedure, where for preparation of PbSe QDs, Se-TOP (TOP = trioctylphosphine) is injected into Pb-oleate in 1-octadecene medium. In this study, we report for the first time a simple method to prepare MSCs, QDs and particles close to the bulk of PbSe using oleylamine (OAM) as the reducing agent, where the individual entities are efficiently separated. The chemical yield is found to be 95%. Studies on optical properties revealed the absorption and emission peaks of MSCs at fixed positions of 600 and 780 nm, respectively, while QDs exhibit significant shift to longer wavelengths for both the cases, depending on the particle size. Shift of the emission peak position for QDs is observed to be larger for initial stages of the waiting time as compared to those for longer waiting times. This can be attributed to two factors: faster growth in particle size is favoured kinetically in the initial stages, while thermodynamic stability occurs in the later stages, and reduction in surface to core contribution with increase of waiting time. QDs were found to emit at only one particular wavelength while they absorbed at two or more wavelengths. The quantum yields (QYs) of particles of sizes 4.1 and 5.1 nm are found to be 80 and 30%, respectively. The lifetime values are found to be 1.0-1.3 µs for QDs having an emission peak in the range of 1300-1500 nm. The hybrid device of PbSe (5 nm size) and MEHPPV (2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) shows increased conductivity both in the dark and in light, due to absorption in the region of NIR photons in the former and additionally in the visible region in the latter.

Disordered self assembled monolayer dielectric induced hysteresis in organic field effect transistors.

A memory device using an organic field effect transistor (OFET) with copper phthalocyanine (CuPc) as active material was fabricated and studied. For this purpose, SiO2 dielectric surface was modified with a disordered self assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) molecule which was found to induce large disorder in CuPc film thereby generating more traps for charge carriers. Drain current-drain voltage characteristics at zero gate voltage exhibited large hysteresis which was not observed in OFET devices with ordered OTS monolayer modified and unmodified SiO2 dielectrics. The extent of hysteresis and drain current on/off ratio, reading voltage etc. were found to be dependent on the sweep rate/step voltage employed during scanning. Highest hysteresis with on/off ratio of about 240 was obtained for an optimum step voltage of 2 V while it decreased with further reduction in the same. This was attributed to the longer scanning time leading to release of trapped carriers during forward scan itself. The OFET device was found to exhibit excellent memory retention capability where OFF and ON current measured for about 2 hours after stressing the device at write and erase voltages showed good retention of on/off ratio.

Anterior-cruciate-ligament reconstruction does not alter the knee-extensor moment arm during gait.

BACKGROUND: The ability of the quadriceps muscles to extend the knee depends on the moment arm of the knee-extensor mechanism, which is described by the moment arm of the patellar tendon at the knee. The knee-extensor moment may be altered by a change in quadriceps force, a change in the patellar tendon moment arm (PTMA), or both. A change in quadriceps muscle strength after anterior-cruciate-ligament-reconstruction (ACLR) surgery is well documented, however, there is limited knowledge about how this procedure affects the PTMA. RESEARCH QUESTION: Does ACLR surgery alter the moment arm of the knee-extensor mechanism during gait? METHODS: We measured the PTMA in both the ACLR knee and the uninjured contralateral knee in 10 young active individuals after unilateral ACLR surgery. Mobile biplane X-ray imaging was used to measure the three-dimensional positions of the femur, tibia and patella during level walking and downhill walking over ground. The PTMA was found from the location of the instantaneous axis of rotation at the knee and the line-of-action of the patellar tendon. RESULTS: There was a small but statistically significant difference in the mean PTMA calculated over one cycle of level walking between the ACLR knee and the contralateral knee, with the mean PTMA in the ACLR knee being 1.5 mm larger (p < 0.01). In downhill walking, statistically significant differences were found in the range 15°- 25° of knee flexion, where the PTMA was 4.7 mm larger in the ACLR knee compared to the contralateral knee (p < 0.01). SIGNIFICANCE: Significant differences were evident in the mean PTMA between the ACLR knee and the contralateral knee in both activities, however, the magnitudes of these differences were relatively small (range: 3-10%), indicating that ACLR surgery successfully restores the moment arm of the knee-extensor mechanism during dynamic activity.

Electrical characterization of self-assembled monolayers of alkyltrichlorosilanes on native oxide of silicon.

The octadecyltrichlorosilane (C18), dodecyltrichlorosilane (C12) and octyltrichlorosilane (C8) monolayers have been deposited on the native oxide of silicon by self-assembly technique. The morphology of the monolayers studied by atomic force microscopy revealed an average roughness of approximately 1.0 A. The Fourier Transform Infra Red Spectroscopic measurements revealed the presence of peaks at approximately 2848 and 2915 cm(-1) indicating the formation of densely packed monolayers. The current density versus voltage (J-V) measurements using mercury drop as counter electrode showed tunneling current between 10(-5) to 10(-8) A/cm2 at 1 V indicating the excellent dielectric behaviour of these monolayers. The J-V data were fitted to Simmons theory of tunneling which yielded an effective electron energy barrier height of 1.6 +/- 0.2 eV and the effective mass of electron tunneling through the barrier was found to be 0.3 +/- 0.03 m(e). The tunneling decay factor beta was estimated from the current density values measured as a function of thickness of the monolayer and was found to be 0.28 +/- 0.02 A(-1).

Growth of highly oriented crystalline polyaniline films by self-organization.

Silicon substrates with (100) orientation were modified with amino-silane self-assembled monolayer (SAM) to provide amino (NH(2)) moieties at the substrate surface. Self-organization of polyaniline during chemical polymerization, on this modified surface, leads to the growth of highly oriented films at the substrate-polymer interface. The morphology studied using scanning electron microscopy and atomic force microscopy revealed the formation of polymer film with well faceted pyramidal crystallites. XPS and FTIR spectroscopy were used to analyze the chemical structure of the film. X-ray diffraction measurements show the crystalline nature of the polyaniline, whose lattice parameters are in agreement with the reported values. This study underlines the importance of a SAM in deciding the structure and morphology of the deposited polymer.

Human protein reference database as a discovery resource for proteomics.

The rapid pace at which genomic and proteomic data is being generated necessitates the development of tools and resources for managing data that allow integration of information from disparate sources. The Human Protein Reference Database (http://www.hprd.org) is a web-based resource based on open source technologies for protein information about several aspects of human proteins including protein-protein interactions, post-translational modifications, enzyme-substrate relationships and disease associations. This information was derived manually by a critical reading of the published literature by expert biologists and through bioinformatics analyses of the protein sequence. This database will assist in biomedical discoveries by serving as a resource of genomic and proteomic information and providing an integrated view of sequence, structure, function and protein networks in health and disease.

BioBuilder as a database development and functional annotation platform for proteins.

BACKGROUND: The explosion in biological information creates the need for databases that are easy to develop, easy to maintain and can be easily manipulated by annotators who are most likely to be biologists. However, deployment of scalable and extensible databases is not an easy task and generally requires substantial expertise in database development. RESULTS: BioBuilder is a Zope-based software tool that was developed to facilitate intuitive creation of protein databases. Protein data can be entered and annotated through web forms along with the flexibility to add customized annotation features to protein entries. A built-in review system permits a global team of scientists to coordinate their annotation efforts. We have already used BioBuilder to develop Human Protein Reference Database http://www.hprd.org, a comprehensive annotated repository of the human proteome. The data can be exported in the extensible markup language (XML) format, which is rapidly becoming as the standard format for data exchange. CONCLUSIONS: As the proteomic data for several organisms begins to accumulate, BioBuilder will prove to be an invaluable platform for functional annotation and development of customizable protein centric databases. BioBuilder is open source and is available under the terms of LGPL.

Diabetic Tongue - Could it be a Diagnostic Criterion?

Diabetes mellitus (DM) is a common disease which usually manifests in the form of polyuria, polydipsia, weight loss, fatigue, weakness, blurry vision, frequent skin infections, and slow healing of skin lesions. Taste disturbances like ageusia, hypogeusia and dysgeusia have been associated with DM. The early diagnosis of DM based on these symptoms is very important to start treatment early and thereby prevent complications. We present an interesting case of a female presenting with altered taste as the first symptom of DM.

PhoN-expressing, lyophilized, recombinant Deinococcus radiodurans cells for uranium bioprecipitation.

Employment of genetically engineered radiation resistant organisms to recover radionuclides/heavy metals from radioactive wastes is an attractive proposition. Cells of recombinant Deinococcus radiodurans strain expressing, a non-specific acid phosphatase encoding phoN gene, were lyophilized. Lyophilized recombinant Deinococcus cells retained viability and PhoN activity and could efficiently precipitate uranium from aqueous solutions for up to six months of storage at room temperature. Batch process for uranium removal using lyophilized cells was more efficient compared to a flow through system, in terms of percent uranium removed, substrate conservation and time taken. Lyophilized recombinant Deinococcus cells exhibited high loading of up to 5.7 g uranium/g dry weight of cells in a batch process at 20 mM input uranium concentration. Lyophilization deflated the cells but did not alter gross cell morphology or surface nucleation capability of cells for uranium precipitation. The precipitated uranyl phosphate remained tightly associated with the cell surface, thus facilitating easy recovery.

Development of human protein reference database as an initial platform for approaching systems biology in humans.

Human Protein Reference Database (HPRD) is an object database that integrates a wealth of information relevant to the function of human proteins in health and disease. Data pertaining to thousands of protein-protein interactions, posttranslational modifications, enzyme/substrate relationships, disease associations, tissue expression, and subcellular localization were extracted from the literature for a nonredundant set of 2750 human proteins. Almost all the information was obtained manually by biologists who read and interpreted >300,000 published articles during the annotation process. This database, which has an intuitive query interface allowing easy access to all the features of proteins, was built by using open source technologies and will be freely available at http://www.hprd.org to the academic community. This unified bioinformatics platform will be useful in cataloging and mining the large number of proteomic interactions and alterations that will be discovered in the postgenomic era.