Search

Carbohydrates are extremely importantbiomolecules and their immobilizationonto solid surfaces is of interest for the development of new biomimeticmaterials and of new methods for understanding processes in glycobiology.We have developed an efficient surface modification methodology forthe functionalization of a range of materials with biologically activecarbohydrates based on aryldiazonium chemistry. We describe the synthesisand characterization of carbohydrate reagents, which were subsequentlyemployed for the one-step, solution-based modification of carbon,metals, and alloys with monosaccharides. We used a combination ofspectroscopic and nanogravimetric methods to characterize the structureof the carbohydrate layers; we report an average surface coverageof 7.8 × 10–10mol cm–2underour experimental conditions. Concanavalin A, a mannose-binding lectin,and Peanut Agglutinin, a galactose-binding lectin, were found to bindfrom solution to their respective monosaccharide binding partnersimmobilized at the surface. This result suggests that the spontaneouschemisorption of aryldiazonium monosaccharide precursors leads tothe formation of monosaccharide layers that retain the biologicalrecognition specificity of the parent carbohydrate molecule. Finally,we carried out measurements using fluorescently labeled Bovine SerumAlbumin (BSA) and found that these carbohydrate coatings reduce unspecificadsorption of this protein at carbon surfaces. These results suggestthat aryldiazonium-derived carbohydrate coatings may offer a promisingstrategy for preventing undesirable protein accumulation onto surfaces. [ABSTRACT FROM AUTHOR]

Aryldiazoniumcations are widely used to covalently functionalize carbon substratesthat display a wide range of composition, from 100% sp2such as graphite or graphene to 100% sp3such as diamondand nanodiamond. In this work we investigated the effect that changesin carbon composition have on aryldiazonium adsorption rates and surfacereaction mechanism. Quartz crystal microbalance (QCM) was used toinvestigate the rates of adsorption in situ and in real time at twoamorphous carbon substrates, one with high sp2content(a-C) and one with high sp3content (a-C:H). A reversibleLangmuir adsorption model was found to satisfactorily describe adsorptionat a-C:H, yielding an adsorption rate coefficient ka= 3.1 M–1s–1anda free energy of adsorption ΔGa=−20.1 kJ mol–1. This model, on the otherhand, could not be applied for the interpretation of adsorption curvesat a-C. Using electrochemical methods and X-ray photoelectron spectroscopy(XPS), we found that adlayers formed at a-C:H and a-C surfaces differconsiderably in composition; in particular, a-C surfaces were foundto display higher rates of dediazoniation with respect to a-C:H surfaces.Our findings are interpreted and discussed in the context of currentproposed mechanisms for aryldiazonium reactions at surfaces that consistof an adsorption/desorption step followed by a chemisorption via dediazoniationstep. Our observations are consistent with proposed mechanisms andstrongly suggest that differences in carbon composition result indifferences in the relative magnitude of adsorption and chemisorptionsrate coefficients. [ABSTRACT FROM AUTHOR]

Amorphous carbon materials find numerous applicationsin diverseareas ranging from implantable biodevices to electronics and catalysis.The spontaneous grafting of aryldiazonium salts is an important strategyfor the modification of these materials, and it is widely used todisplay a range of functionalities or to provide anchoring groupsfor further functionalization. We have investigated the spontaneousattachment of 4-nitrobenzenediazonium salts from aqueous solutionsonto amorphous carbon materials that differ in their sp2content, with the aim of understanding to what extent bulk compositionaffects rates and yields of aryldiazonium adsorption at the carbon/solutioninterface. Amorphous carbons were deposited in the form of thin filmsvia reactive magnetron sputtering and were characterized using a combinationof Raman, infrared, UV–vis, and X-ray photoelectron spectroscopyto determine their sp2content. Attenuated total internalreflection Fourier transform infrared spectroscopy (ATR-FTIR) wasused to monitor in situ and in real time the aryldiazonium adsorptionprocess at the carbon/solution interface. These measurements demonstratethat rates and yields of adsorption for the same aryldiazonium saltincrease nonlinearly vs sp2concentration. Studies of aryldiazoniumsalt grafting as a function of time carried out ex situ via cyclicvoltammetry showed that the amorphous carbon film with highest sp2content displays significantly lower grafting yields thanglassy carbon, a material with 100% sp2content. Intercalationexperiments using 4-nitrobenzylamine suggest that the difference inrelative density of graphitic edge planes exposed at the carbon surfaceis in excellent agreement with the observed relative grafting yields.We discuss the implications of these results for the development ofstructure/reactivity relationships that can be leveraged for understandingthe surface chemistry of disordered carbon materials. [ABSTRACT FROM AUTHOR]