The use of graphene-based nanomaterials is being explored in the context of various biomedical applications. Here, we performed a molecular dynamics simulation of individual amino acids on graphene utilizing an empirical force field potential (Amber03). The accuracy of our force field method was verified by modeling the adsorption of amino acids on graphene in vacuum. These results are in excellent agreement with those calculated using ab initio methods. Our study shows that graphene exhibits bioactive properties in spite of the fact that the interaction between graphene and amino acids in a water environment is significantly weaker as compared to that in vacuum. Furthermore, the adsorption characteristics of capped and uncapped amino acids are significantly different from each other due to the desolvation effect. Finally, we conclude that when assessing protein-surface interactions based on adsorption of single amino acids, the minimum requirement is to use capped amino acids as they mimic residues as part of a peptide chain.

Preparation and characterization of the disjoint diradical 4,4'-bis(1,2,3,5-dithiadiazolyl) [S2N2C-CN2S2] and its iodine charge transfer salt [S2N2C-CN2S2] Bryan, C.D.; Cordes, A.W.; Goddard, J.D.; Haddon, R.C.; Hicks, R.G.; MacKinnon, C.D.; Mawhinney, R.C.; Oakley, R.T.; Palstra, T.T.M.; Perel, A.S.

The condensation of diaminobenzenedithiol with sulfur monochloride leads to the chloride salt of the radical cation of 3,6-dichlorobenzo[1,2-d:4,5-d‘]bis(1,2,3-dithiazole), dichloro-[BB-123-DTA][Cl], which can be reduced to neutral dichloro-[BB-123-DTA] with triphenylantimony. A similar condensation with selenium tetrachloride leads, upon reduction, to the corresponding bis(1,2,3-thiaselenazole) dichloro-[BB-123-TSA]. The crystal and molecular structures of both compounds have been determined by X-ray diffraction. Both compounds, which are formally antiaromatic 16π-systems, exhibit internal bond lengths consistent with a quinoid formulation. The radical cations of both rings have been characterized by ESR spectroscopy; for dichloro-[BB-123-DTA]+ g = 2.0114 and a N = 0.201 mT, while for dichloro-[BB-123-TSA]+ g = 2.021 and a N = 0.44 mT. Further oxidation of both rings affords the corresponding dications, both of which have been characterized crystallographically as their AlCl4 - salts. The structural features of these compounds are consistent with those expected for dithiazolylium (or thiaselenazolylium) derivatives. The structure and redox chemistry of the benzo[1,2-d:4,5-d‘]bis(1,2,3-dithiazole) framework is discussed in the light of the results of ab initio calculations.

Forty four stationary points have been located on the lowest singlet and triplet potential energy surfaces of S(2)N(2). Ten minima and ten saddle points on the lowest singlet surface and eleven minima and thirteen saddle points on the lowest triplet surface were found. All saddle points were connected to minima or lower-order saddle points by following the intrinsic reaction coordinate. Renner-Teller effects in the linear isomers were studied by examining their bending curves. The S(2)N(2) polymerization mechanism was investigated by first locating the transition state corresponding to ring opening and then considering all species connected to it that are close in energy. The commonly accepted mechanism is problematic due to the number of species that would lead to dissociation to SN + SN. Other possible isomers that are consistent with the experimental evidence but do not connect to SN radicals in the dissociation limit were examined. A mechanism of polymerization to (SN)(x)() is proposed that involves excitation of the square planar singlet molecule to the triplet surface. The triplet species then undergoes a puckering, and polymerization occurs in a direction approximately perpendicular to the S(2)N(2) plane. Consideration of the predicted vibrational frequencies suggests the structure of the second isomer of S(2)N(2). This isomer has a trans-NSSN structure with a long SS bond. The energetics of trans-NSSN are consistent with the observed temperature effects in the dimerization of SN. Analysis of the bending curves of linear NSSN and NSNS indicates that trans-NSSN is the only isomer which has a small yet significant barrier to that dimerization.