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Vibrational spectroscopy is a widely used technique for chemical characterizations across various analytical sciences. Its applications are increasingly extending to the analysis of complex samples such as biofluids, providing high‐throughput molecular profiling. While powerful, the technique suffers from an inherent limitation: The overlap of absorption information across different spectral domains hinders the capacity to identify individual molecular substances contributing to measured signals. Despite the awareness of this challenge, the difficulty of analyzing multi‐molecular spectra is often underestimated, leading to unsubstantiated molecular interpretations. Here, we examine the prevalent overreliance on spectral band assignment and illuminate the pitfalls of correlating spectral signals to discrete molecular entities or physiological states without rigorous validation. Focusing on blood‐based infrared spectroscopy, we provide examples illustrating how peak overlap among different substances, relative substance concentrations, and preprocessing steps can lead to erroneous interpretations. We advocate for a viewpoint shift towards a more careful understanding of complex spectra, which shall lead to either accepting their fingerprinting nature and leveraging machine learning analysis – or involving additional measurement modalities for robust molecular interpretations. Aiming to help translate and improve analytical practices within the field, we highlight the limitations of molecular interpretations and feature their viable applications. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) spectroscopy is one of the most powerful tools in analytical chemistry. An important step in the analysis of NMR data is the assignment of resonance frequencies to the corresponding atoms in the molecule being investigated. The traditional approach considers the spectrum's characteristic parameters: chemical shift values, internuclear couplings, and peak intensities. In this paper, we show how to support the process of assigning a series of spectra of similar organic compounds by using temperature coefficients, that is, the rates of change in chemical shift values associated with given changes in temperature. [ABSTRACT FROM AUTHOR]

In this study, an NMR spectral analysis of the mixture of diastereomeric acetals, synthesized from 2,3-dihydrofurane and a racemic mixture of citronellol, was performed. 1H-NMR full spin analysis was achieved by manually adjusting δH and J values (previously calculated using the Spartan software) to fit the experimentally available values, followed by further optimization using MestreNova software. The simulated 1H- and 13C-NMR spectra of individual diastereomers, as well as their superimposed and summed spectra, were compared with the obtained experimental spectra. Spin simulation of proton signals was particularly useful for the assignment of the diastereotopic protons of tetrahydrofuranyl moiety and diastereomer discrimination. The NMR spectral data of individual diastereomers – chemical shifts, coupling constants, HMBC and NOESY interactions were systematized in appropriate tables and schemes. To the best of our knowledge, this is for the first time that the complete assignment of tetrahydrofuranyl moiety was performed, and the data obtained herein may be of great importance for the utilization of this protecting group in the future.

Terahertz spectroscopy has proven to be a powerful tool for the study of condensed phase materials, opening research directions in a number of fields ranging from the pharmaceutical to semiconducting industries. Recent developments in terahertz technology have made this technique more accessible than ever before, and an increasing number of researchers are turning to terahertz spectroscopy for analysis and characterization of advanced materials. However, unlike mid-IR techniques, there do not exist any functional group specific transitions at terahertz frequencies, making the interpretation and assignment of terahertz spectral data more complex than complementary techniques. Through the aid of computational tools, incredible insights into the atomic-level dynamics occurring at terahertz frequencies have been uncovered, yet such highly accurate simulations require more care than traditional simulation methods in order to obtain such results. This review aims to highlight the recent advances in the computational assignment of terahertz spectral data, as well as showcasing common pitfalls to avoid, in order to demonstrate the utility of simulation methods for terahertz spectral assignment. Finally, cutting edge techniques and applications will be discussed, opening the door for future work in this exciting area of terahertz science. [ABSTRACT FROM AUTHOR]

Here we present the XIPP (eXtensible Interactive Peak Picker) NMR software for analyzing multidimensional NMR data of proteins, DNA, RNA and protein-nucleic acid complexes. XIPP organizes experiments into pre-defined studies and replaces our original PIPP software suite which is no longer supported. Default study types exist for backbone assignment, sidechain assignment, NOE assignment and several relaxation series experiments, used in solution NMR studies. XIPP is written in Java and Jython. The default study types are defined in Jython which can be modified and extended to create new types of studies. [ABSTRACT FROM AUTHOR]

The cognitive radio networks are an alternative to mitigate the saturation of the radio spectrum in some frequency bands, through a dynamic spectral assignment, where the secondary user opportunistically takes advantage of the free frequency channels of the licensed band of the primary user. In the present article an algorithm is developed to select free frequency channels or spectral opportunities in a cognitive radio network, based on the Artificial Bee Colony method. The evaluation of the proposed algorithm is carried out through simulations that incorporate the real behavior of the primary user, using real spectral occupancy traces, obtained through the spectrum monitoring with the energy detection technique, and having as evaluation criteria, the execution time and the number of failed handoffs. The results show a reduction of 62% in the execution times and 36% in the number of failed handoffs, when going from a bee colony population of 50 to 450. [ABSTRACT FROM AUTHOR]

The Doppler limited non-saturated rotationally resolved infrared spectra of the symmetric and asymmetric CH-stretch bands of CH 2 Br 2 have been measured. A continuous wave cavity ringdown setup with a widely tunable Mid-IR-OPO laser light source yielded a single-shot minimum absorption of 4.9 × 10 −8 cm −1 . In contrast to the heavily congested ν 1 band, the ν 6 band showed partially resolved rotational features that may serve as suitable absorption targets in future environmental detection schemes for CH 2 Br 2 . A straightforward, VPT2 (second-order vibrational perturbation theory) assisted quantum-chemical approach for assigning the rotational structure has been tested using different model chemistries. The molecular structures, anharmonic frequencies and the structural changes upon vibrational excitation of CH 2 Br 2 have been investigated. The predicted changes of the anharmonic rotational constants have been used together with available spectroscopic ground state constants to simulate the rovibrational structures of the ν 1 and ν 6 bands of CH 2 Br 2 . A refined analysis of the ν 6 band is presented yielding accurate values for the band origin and the rotational constants. A fit of the line positions of 312 prominent transitions of the three isotopologues revealed a low standard error of 0.00056 cm −1 , hence within the absolute 0.0009 cm −1 wavelength accuracy of the used spectrometer setup. A combined analysis of the predicted line strengths and positions of the strong Q sub-branches of the ν 6 band has been performed to test the ability of the different density functionals for VPT2 prediction of anharmonic molecular constants. The M06/6-311++G(d,p) model chemistry turned out to yield reliable state-dependent rotational constants that are accurate enough to reproduce the overall rotational structure even without fitting. [ABSTRACT FROM AUTHOR]

All transitions in the experimentally designated and numbered Q, B, and N bands (< 4.8 eV) of the electronic absorption spectrum of zinc phthalocyanine (ZnPc) are assigned on the basis of one-to-one agreement between calculated and experimentally observed transition energies and oscillator strengths. Each band in this range of the spectrum represents a ligand-based transition that originates from a combination of occupied orbitals and terminates in the lowest unoccupied molecular orbital (LUMO [ABSTRACT FROM AUTHOR]

Near infrared (NIR) assignment of Isopsoralen was performed using deuterated chloroform solvent and two-dimensional correlation spectroscopy (2D-COS) technology. Yunkang Oral Liquid was applied to study Isopsoralen, the characteristic bands by spectral assignment as well as the bands by interval partial least squares (iPLS) and synergy interval partial least squares (siPLS) were used to establish partial least squares (PLS) model. The coefficient of determination in calibration $(R_{\rm cal}^{2})$ were 0.9987, 0.9970 and 0.9982. The coefficient of determination in cross validation $(R_{\rm val}^{2})$ were 0.9985, 0.9921 and 0.9982. The coefficient of determination in prediction $(R_{\rm pre}^{2})$ were 0.9987, 0.9955 and 0.9988. The root mean square error of calibration (RMSEC) were 0.27, 0.40 and 0.31 ppm. The root mean square error of cross validation (RMSECV) were 0.30, 0.67 and 0.32 ppm. The root mean square error of prediction (RMSEP) were 0.23, 0.43 and 0.22 ppm. The residual predictive deviation (RPD) were 31.00, 16.58 and 32.41. It turned out that the characteristic bands by spectral assignment had the same results with the chemometrics methods in PLS model. It provided guidance for NIR spectral assignment of chemical compositions in Chinese Materia Medica (CMM).

Near infrared (NIR) assignment of Isopsoralen was performed using deuterated chloroform solvent and two-dimensional correlation spectroscopy (2D-COS) technology. Yunkang Oral Liquid was applied to study Isopsoralen, the characteristic bands by spectral assignment as well as the bands by interval partial least squares (iPLS) and synergy interval partial least squares (siPLS) were used to establish partial least squares (PLS) model. The coefficient of determination in calibration were 0.9987, 0.9970 and 0.9982. The coefficient of determination in cross validation were 0.9985, 0.9921 and 0.9982. The coefficient of determination in prediction were 0.9987, 0.9955 and 0.9988. The root mean square error of calibration (RMSEC) were 0.27, 0.40 and 0.31 ppm. The root mean square error of cross validation (RMSECV) were 0.30, 0.67 and 0.32 ppm. The root mean square error of prediction (RMSEP) were 0.23, 0.43 and 0.22 ppm. The residual predictive deviation (RPD) were 31.00, 16.58 and 32.41. It turned out that the characteristic bands by spectral assignment had the same results with the chemometrics methods in PLS model. It provided guidance for NIR spectral assignment of chemical compositions in Chinese Materia Medica (CMM). [ABSTRACT FROM AUTHOR]

The vibrational spectra of gaseous and liquid 2-propanol in the C-H stretching region of 2800 ~ 3100 cm−1 were investigated by polarized photoacoustic Raman spectroscopy and conventional Raman spectroscopy, respectively. Using two deuterated samples, that is, CH3CDOHCH3 and CD3CHOHCD3, the overlapping spectral features between the CH and CH3 groups were identified. With the aid of depolarization ratio measurements and density functional theory calculations, a new spectral assignment was presented. In the gas phase, the band at 2884 cm−1 was assigned to the overlapping of one CH3 Fermi resonance mode and a CH stretching of gauche conformer. The bands at 2917 and 2933 cm−1 were assigned to another two CH3 Fermi resonance modes, but the latter includes weak contribution from CH stretching of trans conformer. The bands at 2950 and 2983 cm−1 were assigned to CH3 symmetric and antisymmetric stretching, respectively. The spectral features of liquid 2-propanol are similar to those in the gas phase except for the blue shift of CH and the red shift of CH3 band positions, which can be attributed to the intermolecular interaction in the liquid state. The new assignments not only clarify the confusions in previous studies from different spectral methods but also provide the reliable groundwork on spectral application of 2-propanol in the futures. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The vibronically resolved spectra of an intermediate and a product involved in the photoreaction of α-santonin have been explored by the density functional theory and the post-SCF methodologies, and a detailed comparison of theory with experiment was conducted to obtain reliable assignments to the observed spectra. The predicted emission energies of photosantonic acid and a topochemical product are found to match with the experimental values reasonably. The further calculations manifest that the absorption spectrum of photosantonic acid exhibits vibrationally resolved features, while the absorption band of topochemical product without vibrational resolution is opposite to the experimental observation. These new computational findings lead to a revised assignment to the observed bands and provide a basis for experimentalists to draw a convinced reaction mechanism for the α-santonin photorearrangement. [Copyright &y& Elsevier]

Abstract: Recently, we reported an analysis of carbon lineshapes in high resolution solid-state NMR spectra of uniformly 13C-enriched amino acids. Application of a 13C J-decoupling protocol during the carbon chemical shift evolution period allowed us to separate the contribution of the second-order dipolar shift from that of the 13C–13C J-coupling interactions to carbon linewidths. In this work, we have extended this approach to microcrystalline proteins. We describe the performance of the J-decoupling sequence applied to remove homo-nuclear 13C J-couplings in the 13C spectra of ubiquitin. Analysis of the J-decoupling efficiency for Cα and carbonyl protein sites showed that a significant gain in resolution can be achieved. [Copyright &y& Elsevier]

A novel method to accomplish 13C NMR spectral assignments for nematic liquid crystals is proposed. The two-dimensional (2D) isotropic/anisotropic chemical shift correlation spectrum is observed in which the anisotropic shift parameters are represented as sharp lines by γ-encoding. The 13C spectral assignments can be made from the 2D spectrum with the aid of the 13C isotropic shift assignments for the same compound in the isotropic liquid state. The experiments were performed on p-methoxybenzilidene-p-n-butylaniline. [Copyright &y& Elsevier]

Honeysuckle flower is a common edible-medicinal food with significant anti-inflammatory efficacy. Process quality control of its ethanol precipitation is a topical issue in the pharmaceutical field. Near infrared (NIR) spectroscopy is commonly used for process quality analysis. However, establishing a robust and reliable quantitative model of complex process remains a challenge in industrial applications of NIR. In this paper, modeling design based on quality by design concept (QbD) was implemented for the ethanol precipitation process quality control of Honeysuckle flower. According to the 56 models' performances and 25 contour plots, quadratic model was the best with R adj 2 increasing from 0.1395 to 0.9085, indicating the strong interaction among spectral pre-processing methods, variable selection methods, and latent factors. SG9 and CARS was an appropriate combination for modeling. Furthermore, spectral assignment method was creatively introduced for variable selection. Another 56 models' performances and 25 contour plots were established. Compared with the chemometric variable selection method, spectral assignment combined with QbD concept made a higher R pre 2 and a lower RMSEP. When the latent factors of PLS was small, R pre 2 of the model by spectral assignment increased from 0.9605 to 0.9916 and RMSEP decreased from 0.1555 mg/mL to 0.07134 mg/mL. This result suggests that the variable selected by spectral assignment is more representative and precise. This provided a novel modeling guideline for process quality control in PAT. Unlabelled Image • Quality by Design concept was conducted for NIR model design. • Strong synergic interactions among model parameters were discovered by QbD. • Spectral assignment was used to select variable instead of chemometric method. • A more robust model was established by spectral assignment combined with D-optimal. [ABSTRACT FROM AUTHOR]

The section presents abstracts of studies on polymers which appeared in the volume 62, number 4, 2005 issue of Kobunshi Ronbunshu journal. Synthesis of Biodegradable Polymers Utilizing Sugar Diols As One of Their Components reviews the chemical synthesis of biodegradable polymers based on three stereoisomeric sugar diols. Fixation of Carbon Dioxide and Its Application to Reactive Polymer Synthesis examines fixation of carbon dioxide by amidines or oxiranes. Asymmetric Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide reports on asymmetric alternating copolymerization of cyclohexene oxide and carbon dioxide.

Asymmetric alternating copolymerization of cyclohexene oxide and carbon dioxide is reported. The asymmetric alternating copolymerization has been achieved using a dimeric zinc complex initiator, which was synthesized by the reaction of diethylzinc with chiral amino alcohol. The degree of asymmetric induction could be unambiguously evaluated based on the enantiomeric excess of trans-cyclohexane-1,2-diol which was yielded by hydrolysis of the copolymer. The chain-end analysis of the copolymer by MALDI-TOF mass spectrometry showed that the initiation reaction should be CO2 insertion into Zn-O bond. The addition of ethanol to the dimeric zinc complex improved the yield and enantioselectivity to give the copolymer of 80% ee, which is the highest selectivity ever reported. A plausible bimetallic enchainment mechanism is proposed. The asymmetric amplification that is shown to operate in this copolymerization system, is the first such example in the asymmetric synthesis polymerization. The `3C NMR spectral assignments of the copolymer are also demonstrated by synthesizing model oligomers. [ABSTRACT FROM AUTHOR]