Interaction of two different samples of graphene with DNA nucleobases and nucleosides is investigated by isothermal titration calorimetry. The relative interaction energies of the nucleobases decrease in the order guanine (G)>adenine (A)>cytosine (C)>thymine (T) in aqueous solutions, although the positions of C and T seem to be interchangeable. The same trend is found with the nucleosides. Interaction energies of the A-T and G-C pairs are somewhere between those of the constituent bases. Theoretical calculations including van der Waals interaction and solvation energies give the trend G>A approximately T>C. The magnitudes of the interaction energies of the nucleobases with graphene are similar to those found with single-walled carbon nanotubes.
Interaction of electron donor and acceptor molecules with graphene samples prepared by different methods as well as with single-walled carbon nanotubes (SWNTs) has been investigated by isothermal titration calorimetry (ITC). The ITC interaction energies of the graphene samples and SWNTs with electron acceptor molecules are higher than those with electron donor molecules. Thus, tetracyanoethylene (TCNE) shows the highest interaction energy with both graphene and SWNTs. The interaction energy with acceptor molecules varies with the electron affinity as well as with the charge-transfer transition energy for different aromatics. Metallic SWNTs interact reversibly with electron acceptor molecules, resulting in the opening of a gap.
The growth of gold nanocrystals prepared by the reduction of tetrachloroauric acid by tetrakis(hydroxymethyl)phosphonium chloride, which allows slow reduction, is investigated by small-angle X-ray scattering and isothermal titration calorimetry in combination with transmission electron microscopy. The growth of the nanocrystals does not follow the diffusion-limited Ostwald ripening but instead follows a sigmoidal rate curve. The activation energy obtained from the temperature-dependent growth study is very small. The heat change associated with the growth is determined for the first time as approximately 10 kcal mol(-1) per 1 nm increase in the nanocrystals' diameter.
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