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In this study, we developed a method to build Raman calibration models without culture data for cell culture monitoring. First, Raman spectra were collected and then analyzed for the signals of all the mentioned analytes: glucose, lactate, glutamine, glutamate, ammonia, antibody, viable cells, media, and feed agent. Using these spectral data, the specific peak positions and intensities for each factor were detected. Next, according to the design of the experiment method, samples were prepared by mixing the above-mentioned factors. Raman spectra of these samples were collected and were used to build calibration models. Several combinations of spectral pretreatments and wavenumber regions were compared to optimize the calibration model for cell culture monitoring without culture data. The accuracy of the developed calibration model was evaluated by performing actual cell culture and fitting the in-line measured spectra to the developed calibration model. As a result, the calibration model achieved sufficiently good accuracy for the three components, glucose, lactate, and antibody (root mean square errors of prediction, or RMSEP = 0.23, 0.29, and 0.20 g/L, respectively). This study has presented innovative results in developing a culture monitoring method without using culture data, while using a basic conventional method of investigating the Raman spectra of each component in the culture media and then utilizing a design of experiment approach.

Application of the Kolmogorov–Smirnov two-sample test to detect the intrinsic symmetry of the cross peaks contributes to the identification of the correct pattern of the cross peaks from the noisy 2D asynchronous spectrum.

When diffusion coefficients of different components in a mixture are similar, NMR spectra of pure individual components are difficult to be obtained via a diffusion-ordered spectroscopy (DOSY) experiment. Two-dimensional correlation spectroscopy (2D-COS) is used to analyze the data from the DOSY experiment. Through the properties of the systematic absence of cross-peak (SACP) in the 2D asynchronous spectra, spectra of pure components can be obtained even if their diffusion coefficients are similar. However, fluctuations in peak-position and peak-width are often unavoidable in NMR spectra, which makes SACPs unrecognizable. To address the problem, a 2D quotient spectrum is used to identify the masked SACPs. However, undesirable interference peaks due to the fluctuations in peak-position and peak-width are still present when we extract a spectrum of a component by slicing the 2D asynchronous spectrum across the SACP. A genetic algorithm (GA) is used to select a suitable subset of spectra where the diversities of peak-position and peak-width are significantly reduced. Then, we used the selected spectra to construct a refined 2D asynchronous spectrum so that the spectra of pure components with significant attenuated interference can be obtained. The above approach has been proven to be effective on a model system and a real-world example, demonstrating that 2D-COS possesses a bright perspective in the analysis of the bilinear data from DOSY experiments.

Inter- and intramolecular hydrogen bonding and their temperature-dependent changes in a poly(4-vinylphenol)/poly(methyl methacrylate)(PVPh 30%/PMMA 70%) blend were investigated using near-infrared (NIR) and infrared (IR) spectroscopy. Band assignments of the fundamentals and first overtones of the OH stretching mode of a free OH group and OH groups in C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding of PVPh 30%/PMMA 70% were carried out by comparison between its NIR and IR spectra and comparison with NIR and IR spectra of phenol. The comparison of the NIR spectra of the PVPh 30%/PMMA 70% blend (hereafter, we denote it as PVPh30%) with the corresponding IR spectra reveals that to observe bands arising from the free OH and OH···OH dimer, which is a weaker hydrogen bonding, NIR is better while to investigate bands originating from OH groups in the OH···O=C and OH···OH (oligomer) hydrogen bonds, which are stronger hydrogen bonding, IR is better. Thus, a combination of IR and NIR spectroscopy has provided convincing results for the hydrogen bonding of PVPh30%. The relative intensity of the two bands at 7058 and 6921 cm–1 (I7058/I6921) due to the first overtones of the OH stretching modes of the free OH group and the OH group in the dimer, respectively, increases significantly above 90 °C, which is close to Tg of PVPh. In concomitance with the intensity increase in the relative intensity of the free OH band, the intensity of a band at 1706 cm–1 due to the C=O stretching mode of the C=O···HO hydrogen bond of PVPh30% decreases above 90°C. These results suggest that above the Tg of PVPh the C=O···HO hydrogen bond is broken gradually and that the free OH increases. Of note is that below Tg the intensities of NIR bands due to the OH first overtones of free OH group and OH groups in the OH···OH dimer gain intensity in parallel with temperature increase, and above Tg the intensity of the band derived from the OH···OH group increases linearly much slower than that of the band due to the free OH. Moreover, a band due to an OH···OH oligomer decreases linearly. Hence, it is very likely that the OH···OH oligomers dissociate into free OH groups. Anharmonicity of O–H bonds, which is sensitive to a hydrogen bond, was estimated for the free OH and OH bonds in the C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding by comparison between the NIR and IR spectra in the OH stretching band regions.

This review article for the Karl Norris Award Special Issue consists of four parts. First, the unique history of NIR spectroscopy is described briefly. Then, I discuss the main topic, “what a wonderful world – uniqueness and versatility of NIR spectroscopy.” Next, I introduce our NIR studies for the last 35 years – When did serendipity work in our minds? – a long way of NIR research in the Ozaki group. The investigations on spectral analysis, applications of NIR spectroscopy to physical chemistry, those to life science and NIR imaging studies are reported. Finally, the perspective of NIR spectroscopy is discussed briefly. Through this review, I emphasize on the importance of serendipity in the research.

A supramolecular complex may be formed by two solutes via a weak intermolecular interaction in a solution. The spectrum of the complex is often inundated by the spectra of the solutes that are not involved in the intermolecular interaction. Herein, a novel spectral analysis approach is proposed to retrieve the spectrum of the supramolecular complex. First, a two-dimensional (2D) asynchronous spectrum is constructed. Then, a genetic algorithm is used to obtain a heuristic spectrum of the supramolecular complex. The heuristic spectrum is a linear combination of the spectrum of the complex and the spectrum of a solute. The coefficients of the linear combination are then obtained, according to which the equilibrium constants are invariant among the sample solutions used to construct the 2D asynchronous spectrum. We have applied the approach to a supramolecular system formed by benzene and I

Intracellular H2O2 in single living cells was visualized by SERS technology using label-free bifunctional Fe3O4@Ag nanoparticles with ultra-sensitivity.

The interfacial charge transfer (CT) that plays an important role in enhancing the photoelectric conversion efficiency of dye-sensitized solar cells (DSSCs) has not always been fully explored. Here, TiO2@N719@Ag DSSCs system was constructed, and the CT processes have been monitored by surface-enhanced Raman scattering (SERS) spectra. Meanwhile, it is well known that as one of the most common external stimulis, high pressure can increase the free carrier density of TiO2 NPs and cause the band gap to narrow. In the high pressure SERS experiment, we observed a significant enhancement of N719 dye in the TiO2@N719@Ag system up to 2.48 GPa, which is consistent with the variation trend of charge transfer degree (ρCT). It is indicated that band gap changes will strongly affect the CT process, further influence the SERS signal intensity (or ρCT), and thus increase the CT probability of DSSCs. Futhermore, the decoration of Ag NPs in the TiO2@N719@Ag DSSCs system can introduce localized surface plasmon resonance (LSPR), enhance the light trapping ability and offer additional CT pathways. Importantly, it is possible to improve the photoelectric conversion performance of DSSCs via high pressure method and the introducing of Ag NPs. Finally, in order to observe the CT process of DSSCs more clearly, the models describing the CT mechanism have been proposed. SERS spectroscopy is expected to be a promising technique for the exploration of the interfacial CT behavior in DSSCs devices, which may further broaden the thoughts of improvement of efficiency of cells.

In this work, we attempt to determine the influence of the oxidation state of copper [Cu(I) vs Cu(II)], the nature of the interface (solid/aqueous vs solid/air), the incubation time, and the structure of N-substituted phenylboronic acids (PBAs) functionalizing the surface of copper oxide nanostructures (NSs) on the mode of adsorption. For this purpose, 4-[(N-anilino)(phosphono)-S-methyl]phenylboronic acid (1-PBA) and its two analogues (2-PBA and bis{1-PBA}) and the copper oxide NSs were synthesized in a surfactant-/ion-free solution via a synthetic route that allows controlling the size and morphology of NSs. The NSs were characterized by scanning electron microscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, and X-ray diffraction, which confirmed the formation of spherical Cu2O nanoparticles (Cu2ONPs) with a size of 1.5 μm to 600 nm crystallized in a cubic cuprite structure and leaf-like CuO nanostructures (CuONSs) with dimensions of 80–180 nm in width and 400–700 nm in length and crystallized in a monoclinic structure. PBA analogues were deposited on the surface of the copper oxide NSs, and adsorption was investigated using surface-enhanced Raman spectroscopy (SERS). The changes in the orientation of the molecule relative to the substrate surface caused by the abovementioned factors were described, and the signal enhancement on the copper oxide NSs was determined. This is the first study using vibrational spectroscopy for these compounds.

This work provides new insight into assembling of phenol in various solvents and competition between different kinds of interactions. To examine both weak and strong interactions, we selected a series of non-aromatic and aromatic solvents. Infrared spectra were measured at low (0.05 M) and high (2 M) phenol content. In addition, we performed density functional theory calculations of the structures and harmonic vibrational spectra of 1:1 complexes of phenol with the solvents and the associates of phenol from dimer to tetramer. Based on these results, we divided the solvents into three groups. The first group consists of non-aromatic solvents weakly interacting with phenol. Depending on the concentration, molecules of phenol in these solvents remain non-bonded or self-associated. In diluted solutions of phenol in chlorinated non-aromatic solvents do not appear free OH groups, since they are involved in a weak OH···Cl interaction. It is of note that in diluted solutions of phenol in tetramethyl ethylene both the non-bonded and bonded OH coexists due to solvent–solvent interactions. The second group consists of aromatic solvents with methyl or chlorine substituents. At low concentration, the molecules of phenol are involved in the phenol–solvent OH···π interaction and the strength of these interactions depends on the solvent properties. At a higher phenol content an equilibrium exists between phenol–solvent OH···π and phenol–phenol OH···OH interactions. Finally, the third group includes the aromatic and non-aromatic solvents with highly polar group (C≡N). In these solvents, regardless of the concentration all molecules of phenol are involved in the solute–solvent OH···NC interaction. Comparison of the experimental and theoretical band parameters reveals that molecules of phenol in non-aromatic solvents prefer the cyclic associates, while in the aromatic solvents they tend to form the linear associates.

Far-ultraviolet (FUV) spectra were measured for cyclohexane, methyl cyclohexane, six isomers of dimethyl cyclohexane, and cis- and trans-decalin. Attenuated total reflection-FUV (ATR-FUV) spectroscopy, which we originally proposed, provides systematic information about the excitation states of saturated organic molecules and the hyperconjugation of σ bonds. The FUV spectra of cyclohexane and methyl cyclohexane in neat liquids showed a band with central wavelengths near 155 and 162 nm. The simulation spectrum of cyclohexane calculated by time-dependent density-functional theory (TD-DFT) (CAM-B3LYP/aug-cc-pVTZ) gives two bands at 146 and 152 nm owing to the transition from HOMO-2 to Rydberg 3pz (Tb) and those from HOMO and HOMO-1 to Rydberg 3px/3py (Ta), respectively. The simulation spectrum of methyl cyclohexane with the equatorial substituent has peaks at approximately the same positions as cyclohexane. The calculated molar absorption coefficient is larger than that of cyclohexane, estimating the observed FUV spectra very well. The FUV spectra of dimethyl cyclohexane with two methyl substituents at the equatorial positions (trans-1,2-, cis-1,3-, and trans-1,4-) and trans-decalin had similar features to those of cyclohexane and methylcyclohexane. The TD-DFT calculations revealed that the shoulders at the shorter- and longer-wavelength sides of the band center of dimethyl cyclohexane (with methyl substituents at equatorial positions) and trans-decalin are assigned to Tb and Ta, respectively. In the case of dimethyl cyclohexane with one methyl substituent in the axial position (cis-1,2-, trans-1,3-, and cis-1,4-) and cis-decalin, the band caused by Tb decreased compared to those of the other compounds. The decrease in intensity and the longer-wavelength shift of the Tb band for dimethyl cyclohexane (with one methyl group at the axial position) and cis-decalin revealed that the band on the longer-wavelength side was assigned to the overlap band of Ta and Tb. The reason for such a large spectral alternation for the axial substitution may be the increase in the orbital energy of HOMO-2, which has its electron density concentrated at the axial C-H bond. Regarding the effect of the hyperconjugation of C-C and C-H σ orbitals, the second perturbation energies of the interaction between Cα-Hax and Cβ-Hax were estimated for molecules by natural bond orbital (NBO) analysis. There is a correlation between the orbital energies of HOMO-2 and the changes in vicinal interaction by axial substitution.

Estimation of the stoichiometric ratio of a supramolecular aggregate formed by different compounds is very important in elucidating the structure and function of the aggregate. Many spectroscopic methods used to estimate the stoichiometric ratios of coordination complexes become invalid when characteristic peaks of the aggregate overlap with peaks of compounds that form the aggregate. Previously, we combined the asynchronous orthogonal sample design with Job's method to address the abovementioned problem. However, the interference of noise may lead to incorrect results. Herein, a new method has been developed. In the generation of corresponding Job's curve, the intensity of a cross peak at a single apex is replaced by the volume of the cross peak. Since most noise is canceled in the calculation of the volume of the cross peak, resultant Job's curve is robust to noise. Moreover, the Jonckheere-Terpstra statistical test, a famous nonparametric method to detect whether the data has an upward or downward trend, could further reduce the risk of yielding incorrect results caused by noise. We have applied this approach to two real-world examples (resveratrol/β-Cyclodextrin (β-CD) andiN, N/i-diethyl-iN/i'-benzoylthiourea (DEBT)/Cusup2+/sup) with satisfactory results. The method described in this paper provides a robust way to measure the stoichiometric ratio in supramolecular systems.

We aimed to develop an amino acid sequence-dependent analytical method using near-infrared (NIR) spectroscopy. The detailed analysis of the NIR spectra of eight different amino acid aqueous solutions (glycine, alanine, serine, glutamine, lysine, phenylalanine, tyrosine, and proline) revealed different spectral patterns characteristic of different amino acid residues in the 6200-5700 and 5000-4200 cm