Seung Bin Kim

Enhanced Cr(vi) removal using iron nanoparticle decorated graphene.

Nanoscale iron particles decorated graphene sheets synthesized via sodium borohydride reduction of graphene oxide, showed enhanced magnetic property, surface area and Cr(vi) adsorption capacity compared to bare iron nanoparticles.

Work-Function Engineering of Graphene Electrodes by Self-Assembled Monolayers for High-Performance Organic Field-Effect Transistors

We have devised a method to optimize the performance of organic field-effect transistors (OFETs) by controlling the work functions of graphene electrodes by functionalizing the surface of SiO2 substrates with self-assembled monolayers (SAMs). The electron-donating NH2-terminated SAMs induce strong n-doping in graphene, whereas the CH3-terminated SAMs neutralize the p-doping induced by SiO2 substrates, resulting in considerable changes in the work functions of graphene electrodes. This approach was successfully utilized to optimize electrical properties of graphene field-effect transistors and organic electronic devices using graphene electrodes. Considering the patternability and robustness of SAMs, this method would find numerous applications in graphene-based organic electronics and optoelectronic devices such as organic light-emitting diodes and organic photovoltaic devices.

Selective n-Type Doping of Graphene by Photo-patterned Gold Nanoparticles

Selective n-type doping of graphene is developed by utilizing patternable gold nanoparticles functionalized with photoreactive cinnamate moieties. The gold nanoparticles can be regularly patterned on the graphene by UV-induced cross-linking of cinnamate, which provides a convenient method to control the optical and electrical properties of graphene site-specifically. The strong n-type doping of graphene covered with the patterned gold nanoparticles was confirmed by Raman, X-ray photoelectron spectroscopy, and electron transport measurements. We believe that our method would find numerous applications in the area of graphene-based optoelectronics including light-emitting devices, solar cells, and optical sensors.

New Approach to Generalized Two-Dimensional Correlation Spectroscopy. 1: Combination of Principal Component Analysis and Two-Dimensional Correlation Spectroscopy

The direct combination of chemometrics and two-dimensional (2D) correlation spectroscopy is considered. The use of a reconstructed data matrix based on the significant scores and loading vectors obtained from the principal component analysis (PCA) of raw spectral data is proposed as a method to improve the data quality for 2D correlation analysis. The synthetic noisy spectra were analyzed to explore the novel possibility of the use of PCA-reconstructed spectra, which are highly noise suppressed. 2D correlation analysis of this reconstructed data matrix, instead of the raw data matrix, can significantly reduce the contribution of the noise component to the resulting 2D correlation spectra.

New approach to generalized two-dimensional correlation spectroscopy. II: Eigenvalue manipulation transformation (EMT) for noise suppression.

This paper introduces the concept of eigenvalue manipulating transformation (EMT) of a data matrix for noise suppression in two-dimensional (2D) correlation spectroscopy. The FT-IR spectra of a polystyrene/methyl ethyl ketone/toluene solution mixture during the solvent evaporation process, to which were added a substantial amount of artificial noise, have been analyzed. By uniformly raising the power of a set of eigenvalues, the major eigenvalues become more prominent. As a consequence, minor eigenvectors representing the noise component are no longer strongly represented in the reconstructed data. This EMT operation is similar to the simple truncation of noise-dominated minor factors practiced in standard principal component analysis (PCA), as demonstrated in our preceding paper on PCA-2D correlation spectroscopy. The effect of this new EMT scheme is more gradual, with attractive flexibility to continuously fine-tune the balance between the desired noise reduction effect and the retention of pertinent spectral information.

Host-guest chemistry in the gas phase: selected fragmentations of CB[6]-peptide complexes at lysine residues and its utility to probe the structures of small proteins.

The gas phase host-guest chemistry between cucurbit[6]uril (CB[6]) and peptide is investigated using electrospray ionization mass spectrometry (ESI-MS). CB[6] exhibits a high preference to interacting with a Lys residue in a peptide forming a CB[6]-peptide complex. Collisionally activated CB[6] complexes of peptides yield a common highly selective fragment product at m/z 549.2, corresponding to the doubly charged CB[6] complex of 5-iminiopentylammonium (5IPA). The process involves the formation of an internal iminium ion, which results from further fragments to an a-type ion from a y-type ion, and the resulting 5IPA ion threads through CB[6]. Numerous peptides are investigated to test the generality of the observed unique host-guest chemistry of CB[6]. Its potential utility in probing protein structures is demonstrated using CB[6] complexes of ubiquitin. Low-energy collision induced dissociation yields CB[6] complex fragments, and further MS(n) spectra reveal details of the CB[6] binding sites, which allow us to deduce the protein structure in the solution phase. The mechanisms and energetics of the observed reactions are evaluated using density functional theory calculations.

A Study of Urea-dependent Denaturation of β-Lactoglobulin by Principal Component Analysis and Two-dimensional Correlation Spectroscopy

The water-urea-beta-lactoglobulin interaction was studied by means of principal component analysis (PCA) and two-dimensional correlation spectroscopy applied to the urea concentration-dependent FTIR spectra of aqueous urea-protein solutions. The two nu(CO) and nu(as)(CN) bands coming from ureas absorbance, instead of the amide bands arising from protein, were employed in the analysis. To get a precise view of the changes induced by the urea concentration-controlled unfolding process, the absorbance variations developed in the ternary water-urea-protein system were compared with those observed in a binary water-urea system [Y.M. Jung et al., J. Phys. Chem. B 2004, 108, 13008]. The comparative studies enabled to detect apparent differences between the absorbance changes caused solely by ureas concentration increase and by the urea-dependent unfolding process. Ureas ability to unfold protein was discussed in context of the indirect and the direct mechanism depending on ureas concentration. It was shown that both mechanisms are relevant, that is, the indirect for solutions below 3 M and the direct for solutions above 3 M concentration. The character of the mechanism is strictly correlated with the association level of urea molecules.

Characterization of the Structures of Size-Selected TiO2 Nanoparticles Using X-Ray Absorption Spectroscopy

To investigate the relationship between the size and structure of TiO2 nanoparticles, three size-selected samples of TiO2 nanoparticles were prepared via a hydrolysis method that uses Ti[OCH(CH3)2]4 as the starting material. The structures of the nanoparticles were characterized using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). Analysis of the XRD patterns and of the TEM images showed that the samples were dispersed, with an average particle size of ∼30 nm (sample A), ∼12 nm (sample B), and ∼7 nm (sample C). Their X-ray absorption spectra indicate that samples A and B have an anatase structure, whereas sample C has a structure very similar to that of the TiO2 II phase, which generally arises only under high-pressure conditions. This difference can be attributed to size-induced radial pressure within the smaller nanoparticles, which plays an important role in the phase of TiO2 nanoparticles in sample C.

Characterization of Transition Temperatures of a Langmuir-Blodgett Film of Poly( tert -butyl methacrylate) by Two-Dimensional Correlation Spectroscopy and Principal Component Analysis

External reflection FT-IR spectra of a Langmuir–Blodgett (LB) film of poly(tert-butyl methacrylate) (PtBMA) were measured at temperatures ranging from 26 to 136 °C. The glass transition temperature (Tg) was determined from a two-dimensional (2D) mapping of the first derivative spectra of absorbance values against temperature over the wavenumber range 1100–1300 cm−1, which contains spectral features that are very sensitive to conformational changes. This mapping provides a surprisingly simple and direct method for detecting the value of Tg. The glass transition temperature determined from the 2D map was approximately 84 °C. Another transition at 103 °C, corresponding to the glass transition temperature of bulk PtBMA, was also detected from the 2D map. Principal component analysis (PCA) was employed to analyze the temperature-dependent FT-IR spectra. The glass transition temperatures (80 °C; 100 °C) of the PtBMA LB film determined by the score plot of PCA are consistent with those determined by the 2D map. Additionally, the loading vectors of PCA were found to give valuable insight into the molecular-level phenomena associated with the glass transition process. To gain more details about the polymer chain mobility, two-dimensional (2D) correlation analysis was performed on two sets of FT-IR spectra collected above and below Tg. In the synchronous 2D correlation spectrum obtained below the glass transition temperature (26–66 °C), the observation that the strongest intensity change occurs at 1137 cm−1 indicates that the reorganization of the bending mode of the bbC–C–O and bbC–C=O bonds connected to the backbone (bb) chain and coupled to the C–O stretching mode of the tert-butoxy group is potentially the mechanism underlying the β-transition. This result is in good agreement with the presence of a transition (β-transition) at approximately 43 °C obtained from the band around at 1137 cm−1 in the 2D mapping data.

New Approach to Generalized Two-Dimensional Correlation Spectroscopy. III: Eigenvalue Manipulation Transformation (EMT) for Spectral Selectivity Enhancement

This paper demonstrates the potential of eigenvalue manipulating transformation (EMT) of a data matrix for spectral selectivity enhancement, especially useful in 2D correlation analysis. The EMT operation aims at the accentuation of select features of the information content of the original data matrix. For example, by uniformly lowering the power of a set of eigenvalues associated with the original data, the smaller eigenvalues become more prominent and the contributions of secondary loadings become amplified. As a direct consequence of the minor factor accentuation by such EMT operations, 2D correlation spectra gain much stronger discriminating power. The selectivity enhancement effect of such manipulation of eigenvalues is much more noticeable on the synchronous 2D correlation spectrum. This improvement for the spectral selectivity of synchronous 2D correlation spectra is potentially very important, as we usually put more emphasis on the interpretation of asynchronous 2D spectra in 2D correlation analysis due to overlaps of synchronous peaks. Such EMT operations tend to exaggerate the information content of minor PCs and reduce that of major PCs. Thus, much more subtle difference of spectral behavior for each component is now highlighted. Surprisingly, asynchronous 2D correlation spectra are found to be much less sensitive to such EMT operations. The result indicates that the distinction of different band responses has already been accomplished effectively by the original asynchronous 2D correlation analysis.