Rotational dynamics of confined C ₆₀ from near-infrared Raman studies under high pressure

Abstract

Peapods present a model system for studying the properties of dimensionally constrained crystal structures, whose dynamical properties are very important. We have recently studied the rotational dynamics of C 60 molecules confined inside single walled carbon nanotube (SWNT) by analyzing the intermediate frequency mode lattice vibrations using near-infrared Raman spectroscopy. The rotation of C 60 was tuned to a known state by applying high pressure, at which condition C60 first forms dimers at low pressure and then forms a single-chain, nonrotating, polymer structure at high pressure. In the latter state the molecules form chains with a 2-fold symmetry. We propose that the C 60 molecules in SWNT exhibit an unusual type of ratcheted rotation due to the interaction between C 60 and SWNT in the ''hexagon orientation,'' and the characteristic vibrations of ratcheted rotation becomes more obvious with decreasing temperature. molecular rotation ͉ peapods B ecause of its high symmetry and relatively weak intermolecular interactions, the fullerene C 60 presents a nearly ideal system for studying different crystal structures possible in onedimensionally constrained nanostructure systems, such as C 60 peapods [C 60 molecules inserted into single walled carbon nanotubes (SWNTs)] (1). Such nanostructures are emerging as a class of nanoscale materials with tunable mechanical, electronic, thermal, and optical properties (2, 3). In contrast to bulk C 60 crystals, C 60 inserted in SWNTs form monomeric linear chains in which each C 60 has only two nearest neighbors, as compared to 12 neighbors in crystalline bulk C 60 (4). As a result the intermolecular interactions in these self-assembled carbon nanostructures and the dynamic behavior of the encapsulated molecules are expected to be different from those in solid fullerenes. It is well known that the solid C 60 crystallizes into a face centered cubic structure at room temperature, and the molecules perform nearly free rotations (5). For the peapods, recent theoretical simulations suggest that the C 60 s have two different orientations with low potential energy when they are trapped into SWNTs, the pentagonal and hexagonal orientations (6-8) with a pentagon and a hexagon perpendicular to the tube axis, respectively. Very recent experimental studies on peapods by inelastic neutron scattering (INS) and nuclear magnetic resonance (NMR) suggest that the linear arrays of C 60 molecules still rotate inside SWNTs at room temperature, either showing quasi-free rotation or being dynamically disordered with high orientational mobility (9, 10). However, how the C 60 molecules rotate inside SWNTs, especially at room temperature, is still an interesting open question. It is not only necessary to search another effective experimental method to study the possible rotation of confined C 60 in detail, but also very important to study the rotation from a different perspective. Considering that C 60 rotates down to very low temperature, it would be helpful to employ other techniques to change the r...

Antigen Processing and Remodeling of the Endosomal Pathway: Requirements for Antigen Cross-Presentation

“…Similarly, Di Pucchio et al (2008) report cross-presentation of a viral antigen by plasmacytoid DC in a Brefeldin A-resistant, but primaquine-sensitive manner. Furthermore, silencing of the small GTPases Rab3b and 3c, that colocalize with class I MHC molecules in recycling endosomes (RE) of DC2.4 cells, inhibits cross-presentation (Zou et al, 2009). Finally, mouse DC lacking class I MHC in recycling compartments due to expression of class I MHC with an aberrant tyrosine-based motif, are defective in cross-presentation (Lizee et al, 2003).…”

Confined adamantane molecules assembled to one dimension in carbon nanotubes

“…In order to construct functional elements of diamondoid-based NEMS devices a controllable method to arrange and possibly connect the diamondoids with strong bonds is desirable. An intriguing possibility is to use carbon nanotubes (CNT) as vessels in the same way as for fullerenes [7][8][9][10][11][12][13][14], polymers [15] and other organic [13,[16][17][18] and inorganic materials [19][20][21][22]. Very soon after their discovery the nanotubes were proposed as possible nano sized vessels for chemical reactions [23,24].…”

Into the Intracellular Logistics of Cross-Presentation

“…This pathway would be simpler as it does not require (unknown) mechanisms for delivering antigens to the cytosol. Antigens would simply be degraded by endosomal proteases and peptides loaded on recycling MHC I. Peptide release and exchange can occur efficiently under mild acidic conditions, without the support of chaperones (Gromme et al, 1999; Burgdorf et al, 2006; Di Pucchio et al, 2008; Zou et al, 2009; Win et al, 2011). …”