Phase Transition and Self-assembly of Lower Diamondoids and Derivatives.
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Phase Transition and Self-assembly of Lower Diamondoids and Derivatives. Yong Xue 1, G. Ali Mansoori 2 1 Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA 2 Department of BioEngineering, University of Illinois at Chicago, Chicago, IL 60607, USA ABSTRACT Applying ab initio calculation and molecular dynamics simulation methods, we have been calculating and predicting the essential phase transition and self-assembly of two lower diamondoids (adamantane and diamantane), three of their important derivatives (amantadine, memantine and rimantadine), and two organometallic molecules that are built by substituting one hydrogen ion with one sodium ion in both adamantane and diamantine molecules (ADM•Na and Optimized DIM•Na). To study their self-assembly and phase transition behaviors, we built seven different MD simulation systems, and each system consisting of 125 molecules. We obtained self-assembly structures and simulation trajectories for the seven molecules. Radial distribution function studies showed clear phase transitions for the seven molecules. Higher aggregation temperatures were observed for diamondoid derivatives. We also studied the density dependence of the phase transition which demonstrates that the higher the density - the higher the phase transition points. INTRODUCTION Diamondoids and their derivatives have found major applications as templates and as molecular building blocks in nanotechnology [1-3]. They have been drawn more and more researchers’ attentions to their highly symmetrical and strain free structures, controllable nanostructural characteristics, non-toxicity and their applications in producing variety of nanostructure shapes, in molecular manufacturing, in nanotechnology and in NEMS and MEMS. It is important and necessary to study self-assembly of these molecules in order to obtain reference data, such as temperature, pressure, bonding properties, etc. for application in nanotechnology e.g. building molecular electronic devices. THEORY Two lower diamondoids, three adamantane derivatives and two artificial molecules (substituting one hydrogen atom in adamantane and diamantine with one sodium atom) are studied in this report. We classified them into three groups as shown in Table I. Group 1: Adamantane (ADM) and Diamantane (DIM), the lowest two diamondoids. Due to their six or more linking groups, they have found major applications as templates and as molecular building blocks in nanotechnology, polymer synthesis, drug delivery, drug targeting, DNA-directed assembly, DNA-amino acid nanostructure formation, and host-guest chemistry [13]. However these diamondoids do not have good electronic properties which are necessary for building molecular electronics, but some of their derivatives do. Group 2: Memantine, Rimantadine and Amantadine, the three derivatives of adamantane, which have medical applications as antiviral agents and due to their amino groups, they could be treated as molecular
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semiconductors [4]. Group 3: ADM•Na, DIM•Na, the two organometallic mol
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