NMR detects molecular interactions of graphene with aromatic and aliphatic hydrocarbons in water

Abstract

IntroductionThe non-covalent interactions between polyaromatic carbon and the hydrocarbon-based structure of organic molecules are both of fundamental interest and a promising means of modifying graphene-based electronics [1][2][3][4][5][6][7], spintronics [8][9][10], optoelectronics and sensors [11][12][13][14]. The high relative surface area of graphene is attractive for the sequestration of xenobiotics in environmental [15][16][17] AbstractPolyaromatic carbon is widely held to be strongly diamagnetic and hydrophobic, with textbook van der Waals and 'π-stacked' binding of hydrocarbons, which disrupt their self-assembled supramolecular structures. The NMR of organic molecules sequestered by polyaromatic carbon is expected to be dominated by shielding from the orbital diamagnetism of π electrons. We report the first evidence of very different polar and magnetic behavior in water, wherein graphene remained well-dispersed after extensive dialysis and behaved as a 1 H-NMR-silent ghost. Magnetic effects dominated the NMR of organic structures which interacted with graphene, with changes in spinspin coupling, vast increase in relaxation, line broadening and decrease in NMR peak heights when bound to graphene. However, the interactions were weak, reversible and did not disrupt organic self-assemblies reliant on hydrophobic 'π-stacking', even when substantially sequestered on the surface of graphene by the high surface area available. Interacting assemblies of aromatic molecules retained their strongly-shielded NMR signals and remained within self-assembled structures, with slower rates of diffusion from association with graphene, but with no further shielding from graphene. Binding to graphene was selective for positively-charged organic assemblies, weaker for non-aromatic and negligible for strongly-negatively-charged molecules, presumably repelled by a negative zeta potential of graphene in water. Stronger binders, or considerable excess of weaker binders readily reversed physisorption, with no evidence of structural changes from chemisorption. The fundamental nature of these different electronic interactions between organic and polyaromatic carbon is considered with relevance to electronics, charge storage, sensor, medical, pharmaceutical and environmental research.

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RNA knockdown by synthetic peptidyl-oligonucleotide ribonucleases: behavior of recognition and cleavage elements under physiological conditions

“…1 H DOSY experiments (Bichenkova et al, 2017;Valentini et al, 2004) were carried out on the 400 MHz Bruker Avance þ II spectrometer, using 5 mm MIC Z121725/0001DOSY z-diffusion probe with fixed 1 H/X configuration and 2 H lock to generate a gradient strenghth of 30 Gauss/cm/A. The combination of the DIFF30L probe with the 40 Amp gradient current amplifier (GREAT 40) allowed to produce a field strength upto maximum of 1200 Gauss/cm.…”

“…The diffusion coefficient D of the conjugate was measured by 1 H DOSY (Bichenkova et al, 2017;Provencher, 1982aProvencher, , 1982bValentini et al, 2004) from the ratio between the intensity of the attenuated NMR signal I and the initial signal I 0 (as described in the 'Material & Methods' section) using the Stejskal-Tanner equation (Kerssebaum & Salnikov, 2006):…”

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