Amino-functionalized Surfaces Research Articles

Atomic Layer Deposition of Amino-Functionalized Silica Surfaces Using N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane as a Silylating Agent

Atomic layer deposition (ALD) technique can be used for the preparation of amino-functionalized silica surfaces and for the study of the gas−solid reactions. In the present study N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPS) was used as a silylating agent. The characterization of aminosilylated silica samples was performed by elemental analyses, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and solid-state 13C NMR. Under saturation conditions, viz. at 180 °C and at a pressure of 20−50 mbar, vaporized AAPS molecules were observed to react with the silanols of silica at the silane end of the molecule forming siloxane bridges. Thus, one surface-saturated molecular layer was deposited on the surface. Under these conditions indication of the gas-phase reaction of terminal amino groups with methoxy groups of other AAPS molecules or silanol groups of silica was observed. The surface density of amino groups on the silica surface could be controlled within 2.0−3.4 amino groups/nm2 silica through the pretreatment temperature of silica, i.e., 200−800 °C. The amino group density on silica could also be controlled through a procedure based on sequential gas-phase reactions of AAPS and water. Thus, a high-density aminopropylsiloxane network was grown on the silica surface. With this procedure a surface density of 3.0−5.4 amino groups/nm2 of silica (pretreated at 450 °C) could be obtained depending on the number of AAPS/water cycles. The surface was observed to be saturated with the precursor molecules after four AAPS/water cycles. The gas−solid reactions of AAPS on silica were also compared with those of single-amino-group precursors, viz. γ-aminopropyltrialkoxysilanes.

Modification of lipid transport through a microporous PTFE membrane wall grafted with poly(ethylene glycol)

Lipid interaction with ePTFE arterial prostheses has been identified in previous studies as being one of the causes leading to graft failure. Our research group has previously proposed a mathematical model of the lipid uptake mechanism in Teflon® prostheses as two first-order reactions based on in vitro experiments. The present study sought to determine whether surface modification with methoxy poly(ethylene glycol) (MPEG) derivatives of various molecular weights modified the kinetics of lipid transport through microporous PTFE membranes. PTFE films and ePTFE tubular microporous membranes were functionalized with amine groups using an ammonia radio frequency glow discharge plasma. MPEGs were conjugated as succinimidyl activated esters on the aminated-PTFE surfaces. In order to maximize the surface coverage by MPEGs, the conjugation reactions were performed under conditions near the cloud point. XPS and contact angle analyses confirmed the ability to covalently graft activated MPEGs to amino-functionalized PTFE surfaces of the films and microporous membranes. Lipid adsorption onto PTFE films monitored by ATR-FTIR spectroscopy demonstrated that the surface coverage by each MPEG resulted in a significant decrease in lipid adsorption regardless of the MPEG molecular weight ( M w). ATR-FTIR spectroscopy and FTIR microscopy were used to characterize lipid adsorption onto the PTFE microporous membrane surface and lipid absorption across the microporous structure, respectively. The surface modification by the MPEG, regardless of its M w, resulted in both decrease of lipid adsorption onto the surface of the modified membrane and delayed lipid uptake kinetics. It was concluded that MPEG anchored to the surface of a PTFE microporous membrane may modify mass transport through the ePTFE porous structure.

FTIR spectroscopic studies of interfacial reactions between amino functionalized silicon surfaces and molten maleic anhydride copolymers

The interactions of two reactive maleic anhydride copolymers, a styrene maleic anhydride copolymer and an alternating copolymer of malic anhydride and α-olefin side chains, with amino-functionalized surfaces were studied by means of FTIR-ATR spectroscopy. The interfacial processes were detected at a planar surface of a thermally oxidized silicon as internal reflecting element. This ATR element can be understood as a model for a glass fiber which is used as reinforcing material in polymer matrices. A typical glass fiber coupling agent, γ-aminopropyltriethoxysilane (γ-APS), was used to functionalize the silicon dioxide layer. It was found that the amino groups of the amino siloxane network layer, which were obtained by a coating procedure with γ-APS, react with the anhydride groups of the copolymer melt to form amic acid structures and imide structures depending on the chemical composition of the copolymers and the temperature.

Influence of Surface Charge on Protein Adsorption at an Amphoteric Surface: Effects of Varying Acid to Base Ratio

Plasma polymerization of 1,2-diaminocyclohexane (DACH) results in an amino functional surface which is not stable under ambient conditions. The aging process has previously been assumed to be an oxidation initiated by residual polymer radicals. We here propose that the surface process is not an oxidation but a carboxylation. Primary amino groups react with atmospheric carbon dioxide to give carbamate groups which are stabilized by salt formation with adjacent ammonium groups. We have used a novel electrokinetic technique to measure electroosmosis and monitor the aging process. While the total number of ionizable surface groups was constant, a gradual change in the ratio of basic to acid sites at the surface was found. This amphoteric surface which spontaneously changed its ratio of basic to acid sites was used as substrate to investigate the effect of surface charge on adsorption of two proteins: human serum albumin (HSA) and lysozyme. It was found that lysozyme adsorbs in much higher amounts than HSA irrespective of the charge at the surface. Whereas adsorption of HSA was not dependent on the change in surface charge, adsorption of lysozyme decreased with aging, i.e., as the ratio of acid to base sites at the surface approached unity. An interesting finding was that more lysozyme was adsorbed the more positively charged the surface, even at pH values where the protein carried a strong net positive charge.

Enhanced stability of urease immobilized onto phospholipid covalently bound to silica, tungsten, and fluoropolymer surfaces

Exceptionally high stability of urease covalently immobilized on silica, tungsten, and poly(tetrafluoroethylene) (Teflon) supports has been observed by using a novel immobilization protocol which links the enzyme via its surface-exposed carboxylic groups (rather than conventionally used amino groups) to phospholipid-coated surfaces. Silanization of each of the three solid supports with [N-[11-(trifluoroacetamido)undecanoyl]amino]propyltriethoxysilane, followed by removal of the trifluoroacetyl protective group, furnished the required amino-functionalized surfaces