Jujiro Nishijo

Separation of Raman spectra from fluorescence emission background by principal component analysis

Abstract A novel aspect of principal component analysis (PCA) which was recently revealed has been applied to the separation of a Raman signal from a strong fluorescence emission background. A Raman spectrum of indene with weak intensity that was almost hidden in the high background was readily resolved by PCA only. The resolved spectrum closely resembled the pure Raman spectrum without disturbance by the background. Another resolved spectrum by use of target testing was also very similar to the resolved spectrum by PCA alone. These results preliminarily suggest that PCA is useful to obtain Raman spectra from a collection of replicated raw spectra that are dominated by strong background signal.

Metal Complexation with Langmuir Monolayers of Histidyl Peptide Lipids

Langmuir monolayers made from peptide-lipid molecules represent a novel direction in the research areas of biomimetic interfaces and two-dimensional supramolecular chemistry. Peptide structures and molecular recognition activities toward other guest molecules have been the focus of previous study. This study reports the investigation of metal complexation to histidine-containing peptide lipids in the organized Langmuir, Langmuir-Schaefer, or Langmuir-Blodgett films. Three peptide lipids PEP1-PEP3, with a histidine amino acid incorporated in the middle of the peptide, were designed and synthesized. The monolayer structures and metal-binding activities of each peptide lipid and their 1:1:1 molar ratio mixture were studied by thermodynamic and spectroscopic techniques. It was found that hard Lewis acid type metal cations such as K+ and Mg2+, and borderline or soft metal cations such as Zn2+, Cu2+, and Cd2+ exhibit clearly different binding activity toward peptide-lipid monolayers. The conformational changes of peptides upon binding with Cu2+ and Zn2+ were partially revealed by FT-IR spectroscopic studies. Furthermore, by adding a fluorescent-probe lipid to the peptide monolayer, dramatic fluorescence change was observed when Cu2+ or Zn2+ bound to the Langmuir and Langmuir-Schaefer films of peptide-lipid monolayers. Metal-protein complexation plays a crucial role in the function and activity of proteins and enzymes. Investigation of metal complexation to organized peptide Langmuir monolayers may provide an alternative approach for the development of artificial metalloproteins and novel supramolecular systems or materials.

Spectroscopic evaluation of glucose concentration in phosphate-buffered saline solution using principal component analysis

Principal component analysis (PCA) has been used for quantitative analysis of infrared attenuated total reflection (ATR) spectra of chemical mixtures, so that the minute concentration of glucose in the chemical mixture would be evaluated. Spectroscopic calibration of chemical concentration has been, thus far, believed to require multidimensional least-squares methods, such as classical least squares (CLS) and partial least-squares (PLS) regression techniques. In the present study, however, the analysis of the infrared ATR spectra only by PCA has been found to be useful for the evaluation of concentration of specific minute species in a chemical mixture. The prediction accuracy by PCA only has proved to be comparable to that of PLS. The novel technique would enable us to measure the concentration of glucose in human blood with no invasion.

Infrared studies of mixed Langmuir–Blodgett monolayers of octadecyldimethylamine oxide and dioctadecyldimethylammonium chloride with arachidic acid and poly(acrylic acid)

Infrared reflection–absorption spectra (IRAS) have been measured for monolayers of octadecyldimethylamine oxide (C18DAO), dioctadecyldimethylammonium chloride (2C18DAC) and their mixtures with arachidic acid and poly(acrylic acid) prepared by Langmuir–Blodgett (LB) technique on gold-evaporated glass slides. The spectra show that arachidic acid and C18DAO or 2C18DAC molecules form well-ordered monolayers with trans zigzag conformations. The order of the alkyl chain in C18DAO is greatly increased upon the formation of the mixed LB film. The relative intensities of infrared bands due to CH2 and CH3 stretching modes of the hydrocarbon chains indicate that they are tilted with respect to the surface normal in the mixed LB films of arachidic acid and C18DAO or 2C18DAC. The hydrocarbon chains of C18DAO and 2C18DAC are disordered in the mixed LB films of poly(acrylic acid) and C18DAO or 2C18DAC.

THE EFFECT OF SURFACE ROUGHNESS ON INFRARED EXTERNAL REFLECTION SPECTROSCOPY

Abstract The effect of surface roughness of the back-side of a film-supporting material on Fourier transform infrared (FTIR) external reflection (ER) spectra was studied by using 9-monolayer cadmium stearate Langmuir–Blodgett (LB) films. The LB films are prepared on two infrared-transparent ZnSe substrates whose top surfaces are optically polished and bottom surfaces have controlled surface roughness with 1.2 and 0.1 μm of protrusions. Although the roughness of 0.1 μm is smaller than the wave-length of the infrared ray, both LB films show typical ER spectra qualitatively. On closer inspection, however, the LB film on the substrate with 0.1 μm protrusions is irregular and the LB film on 1.2 μm protrusions is better. These results indicate that the surface roughness of the backside of substrate is necessary for ER analyses.

Analysis of Thermal Phase Transition via Time-Resolved Infrared Spectra Using Partial Least-Squares Regression Modeling Parameters

The thermal phase transition of dl-norleucine (crystalline) has been analyzed via time-resolved Fourier transform infrared (FT-IR) spectroscopy by using a double-scores plot calculated from partial least-squares regression (PLSR). In a previous study, the temperature-dependent spectra collected by time-resolved infrared spectroscopy suggested that another minor thermal phase transition would be present prior to the well-known major transition at ∼118 °C. Eigenvalue analysis by principal component analysis (PCA) suggested, however, that there were four distinguishable signal components, which was not consistent with the evaluation by the absorbance-change plot. In the present study, it has been noticed that a non-systematic response to the temperature increase is involved in the systematic spectral changes. To discriminate the temperature-independent (non-systematic) change from the temperature-related (systematic) changes, two scores of X- and Y-variables in the PLSR modeling have been comparatively used. The new evaluation has readily discriminated a non-systematic factor from basis factors, and the non-systematic factor has been attributed to fringes due to the optical setup used for the measurements.

Analysis of monolayer formation of α-mycolic acid derived from Mycobacterium bovis BCG pasteur strain by infrared reflection-absorption spectrometry with two-dimensional correlation analysis

Monolayer formation mechanism of α-mycolic acid (α-MA) isolated from Mycobacterium bovis BCG Pasteur strain was investigated by infrared reflection-absorption (IRRA) spectrometry with two-dimensional (2D) correlation analysis. The raw IRRA spectra did not characterize the precise feature of the MA monolayer. 2D correlation analysis, however, clearly revealed that the longer or the major chain of the MA stood up earlier than the shorter chain or the α-alkyl group when the monolayer was compressed, and that the upright chains were in the form of ordered conformation.

Quantitative analysis of molecular orientation of structurally heterogeneous Langmuir-Blodgett films by infrared reflection-absorption spectra

Infrared reflection-absorption (RA) spectra were measured for Langmuir-Blodgett (LB) films of octadecyl-dimethylamine oxide (C18DAO) and dioctadecyl-dimethylammonium chloride (2C18DAC) on gold-evaporated slide glasses. The RA spectra showed unique relations between the reflection-absorbance and the number of layers of the LB films. Since the RA spectrum of the monolayer LB film showed different properties from the upper layers especially for the C18DAO LB film, this layer was separated from other layers in the molecular orientation analysis. We then proposed a new schematic model comprising a four-phase architecture (IR//air/LB2/LB1/gold) to explain the RA spectra (LB1 refers to the first monolayer only). The results by the new model indicated that the first monolayer directly on the substrate had different film structure from that of the upper layers. These relations could not be figured out by a simple three-phase model (IR//air/LB/gold) that ignored the heterogeneous architecture in the film phase. The...

Quantitative Estimation of Molecular Orientation in Langmuir-Blodgett Films of Octadecyldimethylamine Oxide and Dioctadecyl-dimethylammonium Chloride

Abstract The molecular orientation in the Langmuir-Blodgett (LB) films of octadecyl-dimethylamine oxide (C18DAO) and dioctadecyldimethylammonium chloride (2C18DAC) was estimated by a newly proposed calculation method for the infrared reflection-absorption (RA) spectral data. The Y- and X-type multilayer LB films of both compounds were prepared respectively as LB (Y) and LB(X) for the RA measurements. There found a large difference in thermal stability between the LB(Y) and LB(X) films for both compounds. Above all, the 9-monolayer LB(Y) films showed a structurally heterogeneous property. The molecular orientation in the heterogeneous structure was explored by introducing a new analyzing method. The method revealed that the first monolayer directly deposited on a gold surface had a specific molecular structure arising from the interaction with the substrate. The structure is different from that in the rest layers. The LB(X) films were found to be thermally very stable; the thermal recovery was notably good...

Photocyclodimerization of cinnamic acid in a Langmuir-Blodgett film investigated by infrared spectroscopy

Abstract Monolayer Langmuir-Blodgett (LB) films of octadecyldimethylamine oxide (C18DAO), dioctadecyldimethylammonuim chloride (2C18DAC) and their mixtures with cinnamic acid were prepared on gold evaporated glass slides by use of the LB technique and their structures were investigated by infrared spectroscopy. The infrared study indicates that cinnamic acid exists as a monomer and its C═O group is nearly perpendicular to the substrate surface in the LB film of 2C18DAC mixed with cinnamic acid, while the C═O group is nearly parallel the substrate surface in the case of mixed film with C18DAO. The irradiation of UV light causes a marked change in the C═O stretching band of the film of 2C18DAC mixed with cinnamic acid, indicating that the acid is changed into the dimeric form.