Joonyeong Kim

Formation, structure, and reactivity of amino-terminated organic films on silicon substrates

Amino-functionalized organic films were prepared by self-assembling 3-aminopropyltriethoxysilane (APTES) on silicon wafers in either anhydrous toluene or phosphate-buffered saline (PBS) for varied deposition times. Fourier transform infrared spectroscopy (FTIR) and ellipsometry have shown that the structure and thickness of APTES films are governed by the deposition time and reaction solution. Deposition from an anhydrous toluene solution produces APTES films ranging from 10 to 144 A in thickness, depending on the reaction time. FTIR spectra indicate that film growth initially proceeds by adsorption of APTES to the silicon surface followed by siloxane condensation, and after an extended period of time APTES molecules accumulate on the underlying APTES film by either covalent or noncovalent interactions. In contrast, spectroscopically indistinguishable APTES films in thickness ranging from 8 to 13 A were formed when deposition was conducted in aqueous solutions. Measured water contact angles indicate that APTES films deposited in aqueous solutions are more hydrophilic compared to those prepared in toluene solutions. Fluorescence measurements revealed that APTES films prepared in toluene solutions contain more reactive surface amino groups by ca. 3 to 10 times than those prepared in aqueous solutions for the identical reaction time.

Investigations of Chemical Modifications of Amino-Terminated Organic Films on Silicon Substrates and Controlled Protein Immobilization

Fourier transform infrared spectroscopy by grazing-angle attenuated total reflection (FTIR-GATR), ellipsometry, atomic force microscopy (AFM), UV-visible spectroscopy, and fluorescence microscopy were employed to investigate chemical modifications of amino-terminated organic thin films on silicon substrates, protein immobilization, and the biological activity and hydrolytic stability of immobilized proteins. Amino-terminated organic films were prepared on silicon wafers by self-assembling 3-aminopropyltriethoxysilane (APTES) in anhydrous toluene. Surface amino groups were derivatized into three different linkers: N-hydroxysuccinimide (NHS) ester, hydrazide, and maleimide ester groups. UV-visible absorption measurements and fluorescence microscopy revealed that more than 40% of surface amino groups were chemically modified. Protein immobilization was carried out on modified APTES films containing these linkers via coupling with primary amines (-NH(2)) in intact monoclonal rabbit immunoglobulin G (IgG), the aldehyde (-CHO) of an oxidized carbohydrate residue in IgG, or the sulfhydryl (-SH) of fragmented half-IgG, respectively. FTIR spectra contain vibrational signatures of these functional groups present in modified APTES films and immobilized IgGs. Changes in the APTES film thickness after chemical modifications and protein immobilization were also observed by ellipsometric measurements. The biological activity and long-term hydrolytic stability of immobilized IgGs on modified APTES films were estimated by fluorescence measurements of an adsorbed antigen, fluorescein isothiocyanate (FITC)-labeled goat anti-rabbit IgG (FITC-Ab). Our results indicate that the FITC-Ab binding capacity of half-IgG immobilized via maleimide groups is greater than that of the oxidized IgG and the intact IgG immobilized via hydrazide and NHS ester groups, respectively. In addition, IgGs immobilized using all coupling chemistries were hydrolytically stable in phosphate-buffered saline (PBS).

Elucidating changes in interfacial water structure upon protein adsorption

A coat to fit the body: Although protein adsorption onto surfaces is a complicated process, sum-frequency generation (SFG) spectroscopy probes the interfacial water structure around a silica surface as a model protein (bovine serum albumin, BSA) adsorbs onto it from solution. At pH 8.0, the attenuated SFG intensity after BSA adsorption indicates that interfacial water molecules are less ordered due to a reduction in surface ξ-potential. The SFG spectrum shows the C-O stretching vibrations subject to stronger ([symbol: see text]≈3200 cm(-1)) and weaker (3200 cm(-1)) hydrogen bonds.

Curing induced structural reorganization and enhanced reactivity of amino-terminated organic thin films on solid substrates: observations of two types of chemically and structurally unique amino groups on the surface.

Infrared-visible sum frequency generation vibrational spectroscopy (SFG) was used to characterize the structure of 3-aminopropyltriethoxysilane (APTES) films deposited on solid substrates under controlled experimental conditions for the first time. Our SFG spectra in combination with complementary analytical data showed that APTES films undergo structural changes when cured at an elevated temperature. Before the films are cured, well-ordered hydrophobic ethoxy groups are dominantly present on the surface. A majority of hydrophilic surface amino groups are protonated, and they are either buried or randomly oriented at the interface. After the films are cured, chemically and structurally different neutral amino groups are detected on the surface. Unlike the protonated amino groups, a new class of neutral amino groups is ordered at the interface and shows enhanced reactivity.

Characterization of polymer surface structure and surface mechanical behaviour by sum frequency generation surface vibrational spectroscopy and atomic force microscopy

Sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM) have been used to study polymer surface structure and surface mechanical behaviour, specifically to study the relationships between the surface properties of polymers and their bulk compositions and the environment to which the polymer is exposed. The combination of SFG surface vibrational spectroscopy and AFM has been used to study surface segregation behaviour of polyolefin blends at the polymer/air and polymer/solid interfaces. SFG surface vibrational spectroscopy and AFM experiments have also been performed to characterize the properties of polymer/liquid and polymer/polymer interfaces, focusing on hydrogel materials. A method was developed to study the surface properties of hydrogel contact lens materials at various hydration conditions. Finally, the effect of mechanical stretching on the surface composition and surface mechanical behaviour of phase-separated polyurethanes, used in biomedical implant devices, has been studied by both SFG surface vibrational spectroscopy and AFM.

Molecular composition and mechanical properties of biopolymer interfaces studied by sum frequency generation vibrational spectroscopy and atomic force microscopy.

Sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM) have been used to study the surface structure and surface mechanical behavior of biologically-relevant polymer systems. These techniques have emerged as powerful surface analytical tools to deduce structure/property relationships in situ, at both air/solid and air/liquid interfaces. SFG and AFM studies have been performed to understand how the surface properties of polymers are linked to polymer bulk compositions, changes in the ambient environment, or the degree of mechanical strain. Specifically, this review discusses (1) the macroscopic- and molecular-level tracking of small end groups attached to polyurethane blends, engineered to reduce blood clotting; (2) the role of ambient humidity on the surface mechanics of soft contact lenses possessing different water content in the bulk; (3) the affect of cyclic stretch on the molecular surface structure of polyurethane films, designed to mimic the mechanical deformation caused by heartbeat; and (4) the molecular ordering of functional groups at the polystyrene-protein interface. The correlation of spectroscopic and mechanical data by SFG and AFM is a powerful methodology to study and design materials with tailored surface properties.

Direct and indirect preparation of layered quaternary manganese tellurides; AMnxMyTe2 (A=Li, Na; M=Cu, Ag; x+y≤2)

Abstract A series of layered quaternary tellurides with AMnxMyTe2 (A=Li, Na; M=Cu, Ag; x+y≤2) compositions were prepared in two different ways; direct synthesis from elemental starting materials and reaction of coinage metals (Cu or Ag) with ternary tellurides, AMnTe2 (A=Li, Na) with partially empty tetrahedral sites. Products were characterized by single crystal and powder X-ray diffraction, atomic absorption (AA) measurements, and wavelength dispersive spectrometry (WDS). These compounds adopt the CaAl2Si2 structure type (space group Pm 3 1, No. 164), in which Te atoms are arrayed by hexagonal closed packing with random distribution of Mn and M (Cu or Ag) atoms in the tetrahedral sites. Alkali metals reside in octahedral sites between two layers to complete the structure. Resistivity measurements showed that these compounds are either insulators or semiconductors.

Synthesis and Structure of Novel Ternary Manganese Tellurides: MMnTe 2 (M = Li, Na), Na 3 Mn 4 Te 6 , and Na 3 Mn 4 . 7 Te 6

The synthesis and structure of four ternary manganese tellurides are reported. All the title compounds form layered structures wherein MnTe 4 tetrahedra are the fundamental building blocks. In two compounds MMnTe 2 (M = Li, Na), MnTe 4 tetrahedra share three corners in the formation of [MnTe 3/3 Te] 1− layers, the fourth Te is bound to only one Mn and formally bears a negative charge. MnTe 4 tetrahedra share both corners and edges in the formation of [Mn 4 Te 6 ] 3− and [Mn 4.7 Te 6 ] 3− layers in Na 3 Mn 4 Te 6 and Na 3 Mn 4.7 Te 6 , respectively. Structural relationships between these ternary tellurides and oxides will be discussed.