Dendrimer Assisted Dispersion of Carbon Nanotubes: A Molecular Dynamics Study

Various unique physical, chemical, mechanical and electronic properties of carbon nanotube (CNT) make it very useful materials for diverse potential application in many fields. Experimentally synthesized CNTs are generally found in bundle geometry with a mixture of different chirality and present a unique challenge to separate them. In this paper we have proposed the PAMAM dendrimer to be an ideal candidate for this separation. To estimate efficiency of the dendrimer in dispersion of CNTs from the bundle geometry, we have calculated potential of mean forces (PMF). Our PMF study of two dendrimer wrapped CNTs shows lesser binding affinity compared to the two bare CNTs. PMF study shows that the binding affinity decreases for non-protonated dendrimer and for the protonated case, the interaction is fully repulsive in nature. For both the non-protonated as well as protonated cases, the PMF increases with increasing dendrimer generations from 2 to 4 gradually compare to the bare PMF. We have performed PMF calculations with (6,5) and (6,6) chirality to study the chirality dependence of PMF. Calculated PMF for protonated dendrimer wrapped chiral CNTs is more compared to the protonated dendrimer wrapped armchair CNTs for all the generations studied. However, for non-protonated dendrimer wrapped CNTs such chirality dependence is not very prominent. Our study suggests that the dispersion efficiency of protonated dendrimer is more compared to the non-protonated dendrimer and can be used as an effective dispersing agent in dispersion of CNT from the bundle geometry.Comment: 22 pages, 8 figure

Structure of Carbon Nanotube-dendrimer composite

Using all atomistic molecular dynamics (MD) simulations we report the microscopic picture of the nanotube-dendrimer complex for PAMAM dendrimer of generation 2 to 4 and carbon nanotube of chirality (6,5). We find compact wrapping conformations of dendrimer onto the nanotube surface for all the three generations of PAMAM dendrimer. The degree of wrapping is more for non-protonated dendrimer compared to the protonated dendrimer. For comparison we also study the interaction of another dendrimer, poly(propyl ether imine) (PETIM), with nanotube and show that PAMAM dendrimer interacts strongly as compared to PETIM dendrimer as is evident from the distance of closest approach as well as the number of close contacts between the nanotube and dendrimer. We also calculate the binding energy between the nanotube and the dendrimer using MM/PBSA methods and attribute the strong binding to the charge transfer between them. Dendrimer wrapping on CNT will make it soluble and can act as an efficient dispersing agent for nanotube

Memecylon macneillianum (Melastomataceae), a new species from South Andaman, India

Memecylon macneillianum M. Das Das, G. S. Giri, A. Pramanik and D. Maity, a new species from the southern Andaman Islands in India, is described and illustrated. It differs from its closely related species M. oleifolium Blume by having both terminal and axillary inflorescences, a higher number (mostly 3–7) inflorescences per node, longer and acutely quadrangular, distinctly furrowed primary inflorescence axes, distinct calyx lobes, and globose fruits. Moreover, in M. macneillianum the leaves are thicker, coriaceous and yellowish on both surfaces when dry, whereas in M. oleifolium the leaves are thin, chartaceous and olive green with a distinctive rusty-red blush around the midvein on drying

Kinetics and mechanism of formation of tris(methyl 2-pyridyl ketoxime) complex of iron (II), its isomerisation, dissociation and oxidation to the iron(III) complex in solution

826-829Kinetics of formation of the tris chelate complex of Fe(II) with methyl 2-pyridyl ketoxime, its geometrical isomerisation (fac to mer), acid assisted dissociation and oxidation to the Fe(III) complex by perdisulphate in aqueous solution have been studied under a variety of conditions. The results have been interpreted with plausible mechanisms and compared with results available in literature on analogous systems

DNA-Assisted Dispersion of Carbon Nanotubes and Comparison with Other Dispersing Agents

Separation and sorting of pristine carbon nanotubes (CNTs) from bundle geometry is a very challenging task due to the insoluble and nondispersive nature of CNTs in aqueous medium. Recently, many studies have been performed to address this problem using various organic and inorganic solutions, surfactant molecules, and biomolecules as dispersing agents. Recent experimental studies have reported the DNA to be highly efficient in dispersing CNTs from bundle geometry. However, there is no microscopic study and also quantitative estimation of the dispersion efficiency of the DNA. Using all-atom molecular dynamics simulation, we study the structure and stability of single-stranded DNA (ssDNA)-single-walled carbon nanotube (SWNT) (6,5) complex. To quantify the dispersion efficiency of various DNA sequences, we perform potential of mean forces (PMF) calculation between two bare SWNTs as well ssDNA-wrapped CNTs for different base sequences. From the PMF calculation, we find the PMF between two bare (6,5) SWNTs to be approximately -29 kcal/mol. For the ssDNA-wrapped SWNTs, the PMF reduces significantly and becomes repulsive. In the presence of ssDNA of different polynucleotide bases (A, T, G, and C), we present a microscopic picture of the ssDNA SWNT (6,5) complex and also a quantitative estimate of the interaction strength between nanotubes from PMF calculation. From PMF, we show the sequence of dispersion efficiency for four different nucleic bases to be T > A > C > G. We have also presented a comparison of the dispersion efficiencies of ssDNA, flavin mononucleotide surfactant, and poly(amidoamine) (PAMAM) dendrimer by comparing their respective PMF values

Lectotypification of Memecylon flavescens Gamble (Memecylaceae DC.)

The Lectotype of Memecylon flavescens Gamble is designated here

Parcel wise crop discrimination and web based information generation using remote sensing and open source software

The present study aims to develop a paradigm for parcel level horticultural crop identification and web based geospatial information generation using high resolution satellite data and open source GIS software. Initially to get the spectral differences among the crops both visual as well as digital classifications were performed particularly a number band ratios were generated. Based on the obtained NDVI values the crop classes were categorized and then matched with the plot based GPS survey data including the farmers information. The achieved discrimination was cross checked with the statistical analysis of data (ANOVA) obtained from the same spectral regions of the image where the maximum discriminations were noticed. Then a web based information development application was designed and managed with the help of QuantumGIS and published on the web through web2 leaflet along with the basic functionalities such as advanced queries, overlay analysis of vector layers, PAN, Zoom etc., with a view to provide the users an easy access to GIS data as well as on the internet with a minimum technological knowhow. That published web information can be managed and updated in future as per requirement by the authorized administrator only. Keywords: Crop discrimination, ANOVA, NDVI, GPS, QuantumGIS, Web2 leafle

Myoblast differentiation of human mesenchymal stem cells on graphene oxide and electrospun graphene oxide-polymer composite fibrous meshes: importance of graphene oxide conductivity and dielectric constant on their biocompatibility

Recently graphene and graphene based composites are emerging as better materials to fabricate scaffolds. Addition of graphene oxide (GO) nanoplatelets (GOnPs) in bioactive polymers was found to enhance its conductivity (sigma) and, dielectric permittivity (epsilon) along with biocompatibility. In this paper, human cord blood derived mesenchymal stem cells (CB-hMSCs) were differentiated to skeletal muscle cells (hSkMCs) on spin coated thin GO sheets composed of GOnPs and on electrospun fibrous meshes of GO-PCL (poly-caprolactone) composite. Both substrates exhibited excellent myoblast differentiations and promoted self-alignedmyotubesformation similar to natural orientation. sigma, epsilon, microstructural and vibration spectroscopic studies were carried out for the characterizations of GO sheet and the composite scaffolds. Significantly enhanced values of both s and e of the GO-PCL composite were considered to provide favourable cues for the formation of superior multinucleated myotubes on the electrospun meshes compared to those on thin GO sheets. The present results demonstrated that both substrates might be used as potential candidates for CB-hMSCs differentiation and proliferation for human skeletal muscle tissue regeneration