Self-capping

QM/MD Simulations of High-Temperature SWCNT Self-capping... 

In 2003, Han et al. reported a theoretical study of the self-capping of zigzag n, 0) SWCNTs using classical MD techniques based on a semi-empirical reactive bond order [8] (Tersoff) force field at 3000 Kelvin [9]. They found the importance of... 

Fig. 4.3 Plots of average time length of self-capping time. Temperature (a) 2500 K, (b) 3000 K, (c) 3500 K. T] is the time of closing of the first end, and T2 is that of the other end. Error bars indicate maximum and minimum time length for the same n and temperature...

The average values of ti and T2 over the 3 RANDOM SEED trajectories is shown in Fig. 4.3. Minimal time of both-sides self-capping was found for n = 6 at 2500 K and 3000 K, and n = 5 at 3500 K. The value of T2 is roughly the twice of ti but in some case, (6, 6), (8, 8) and (9, 9) at 3500 K for instance, T2 less than the twice of Ti. The reason for such strange step-wise self-capping sequence (first one end caps, then the other), is likely to And in the flying-ice-cube problem of the velocity scaling thermostat [17]. 

Fig. 4.4 Snapshots of CUT (10,10) SWCNT self-capping process at 3500 K. C-C bonds are drawn with a threshold of 1.8 A. Each snapshot figure is composed of three perspectives From the left end, from the side, and from the right end...

We have performed simulations of the thermally activated self-capping process of carbon-only (CUT) and edge-oxidized (OX) models of open-ended SWCNTs, using quantum chemical molecular dynamics (QM/MD) simulations. We observed the following important features in trajectories up to 150 picoseconds ... 

V. Edge-oxidized SWCNTs lose their edge functional groups very quickly, except for edge C-H bonds. The presence of hydrogen on the rim decreases the probability of self-capping, similar as in the prohibitive role of hydrogen in the fullerene formation process in combustion synthesis [19]. 

Acetic anhydride may also react with the protected exocyclic amino groups of the nucleobases. The product of this reaction is a potent acetylating agent itself and is stable to the TFA deprotection procedure. The result is an observed self-capping of the PNA in the neutralization step after TFA treatment (unpublished results). The inclusion of a DMF-piperidine (19 1) wash following the capping protocol nullifies the acetyl-nucleobase intermediate. 

A number of exciting recent developments have been made in this area. The asymmetric complex [Cd S2CNMe(CigH37) 2] has been used for the generation of self-capped CdS quantum dots, simply prepared upon thermolysis in a... 

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