Development of Vinyl Sulfone-Based Surface Conjugation Strategies and Their Applications in Biointerface Fabrication

Author:Wang Han Qi

Supervisor:wang qing cheng


Degree Year:2019





One of the essential issues in biointerface fabrication is how to anchor functional molecules onto the surface of biomaterials or devices,which is known as surface conjugation techniques.The commonly used surface conjugation reagents all have some drawbacks,such as low tolerance toward water and low reaction versatility.This dissertation developed the vinyl sulfone-based strategies for surface conjugation,which is advantageous over traditional strategies in the aspects of chemical stability,reaction versatility,reactivity and reaction controllability.This dissertation also demonstrated the nucleophile catalyzed oxa-Michael reaction between hydroxyl group and vinyl sulfone group,facilitating the conjugation of hydroxyl species under mild conditions.Firstly,vinyl sulfone(VS)group terminated disulfide was synthesized to enable the preparation of VS terminated self-assemble monolayers(VS SAMs)on Au substrate.Conj ugation of glutathione(GSH),N-(5-amino-l-carboxypentyl)-iminodiacetic acid(ab-NTA)and mannose onto VS SAMs were achieved by optimizing solution pH values,respectively.Selective conjugation of GSH occurred at pH 6.5-7.5,conjugation condition of ab-NTA and mannose was optimized to be pH 8.5 and 10.5,respectively.Kinetic studies showed the pH dependence of surface conjugation reactions on VS SAMs,in which increase in pH values would accelerate the surface reactions.A half-life of 69 min for GSH at pH 6.5,63 min for ab-NTA at pH 8.5 and 77 min for mannose at pH 10.5 provided the feasibility for the control of ligand density through reaction kinetics.By varying reaction time,surfaces with different mannose densities were fabricated and the ligand density-protein binding relationship was established.Secondly,introduction of VS group on silica surface was achieved through two-step solution reactions and subsequently applied in the conjugation of natural amino acid as anti-fouling coatings.A library of natural amino acids was immobilized on 3-aminopropyltriethoxy-silane(APTES)modified silica surface using divinyl sulfone(DVS)as a crosslinker.Both dynamic lights scattering of silica nanoparticles and biosensing demonstrated that lysine and arginine-bearing surfaces can effectively resist nonspecific protein adsorption due to their zwitterionic structures.Among them,lysine surface exhibits the best anti-fouling performance,which reduces 80%of BSA adsorption,67%of fibrinogen and 67%of serum adsorption compared to bare silica surface.Thirdly,the nucleophile catalyzed oxa-Michael addition of silanol group with VS group was demonstrated,facilitating the one-step functionalization of silica materials.By simply immersing silica materials in vinyl sulfone solutions at 60℃,PEGylation was achieved in hours in the presence of organo catalysts.The stability of resulting Si-O-C bond is tunable by solvents,pH values as well as properties of attached organic moieties.Organic solvents would stabilize the functionalized silica surface while aqueous solution would lead to the degradation of Si-O-C bond in a controllable manner.Using divinyl sulfone as a crosslinker,the silica surface was labeled with fluorescent dye molecule and the release of the dye molecule was tuned by solution pH.Finally,the catalytic reaction of hydroxyl group with VS group was detailed studied in solution.An ylid mediated mechanism was proposed and established in deuterated methanol using 1H NMR measurement.The catalysts and solvent effects on this catalytic reaction were screened for the preparation of VS terminated poly(ethylene)glycol(PEG)derivative.4-Dimethylamino-pyridine(DMAP)showed the best catalytic activity,with a half-time of 13.2 min under a solvent-free condition at room temperature.Preparation of PEG gels was realized by adding glycerol as a crosslinker.Upon hydration,the properties of the hydrogels were easily controlled by changing glycerol molar ratio as well as PEG chain length.The PEG hydrogels showed good antifouling properties,low cytotoxicity,and ability to release drugs at a tunable rate.In summary,this dissertation developed a series of strategies to fabricate VS surfaces on gold and silica materials,which is advantageous over traditional strategies in biointerface fabrication in the aspects of the chemical stability,reaction versatility,reactivity and controllability.The nucleophile catalyzed oxa-Michael addition provides an efficiency strategy for functionalizing hydroxyl-bearing materials and compounds under mild conditions.