Some aspects of the scope and limitations of derivative spectroscopy

Synthesised spectra are used to illustrate discussion of some relationships between recorded absorption profiles and their second and fourth derivative spectra. Limitations arising from the fortuitous overlap of a derivative peak with a neighbouring wing, and the possibilities of resolving spectra into their overlapping bands are also considered. The combined use of second and fourth derivative spectra to ascertain the correct number of bands within an observed profile is described. It is suggested that the practice of computing a least-squares fit of overlapping bands to a spectral profile be changed, because the minimisation achieved often produces a result involving excessive or negative absorbances: the spectral profile should be regarded as a boundary limit and any unaccounted (positive) absorbance then assessed as possible evidence for an additional band. An example is given, concerning the resolution of the spectrum of a thin, single crystal of uranium(IV) oxide at 77 K superimposed on an absorption edge. A comparison of the difference between the observed spectrum and the sum of its resolution into twelve overlapping bands, plus a similar comparison of their fourth derivative spectra, reveals a thirteenth band.     

Shift reagent spectra. The automatic determination of relative bound shifts and the automatic assignment of signals in the parent spectrum. Effects of concentration,temperature and solvent on relative bound shifts

In the use of a shift reagent as an aid in the structural elucidation of organic compounds, it is shown that accurate measurements of the shift reagent and substrate concentrations are not needed to determine the relative bound shifts of the substrate and the chemical shifts of the free substrate spectrum with good precision. This is possible whenever the induced shift ratios of nuclei of a given molecule are independent of the shift reagent concentration. This independence has been verified for all the monofunctional compounds described in this paper. The effect of absolute substrate concentration, solvent, temperature and the presence of water on the relative bound shifts is studied using the eight methyl group signals of β-amyrin. The method is demonstrated by its use for structural determinations in the ketoandrostane series.     

Spectrum shift fitting technique for atomic emission spectrometry

The use of the principle of additivity for the atomic emission spectra registered by a multi-element solid-state detector (SSD) requires to take into account the possible non-controlled spectrum shift. The method of solution for the problem, based on the construction of parabolic model of signal change on pixels under the spectrum shift with respect to detector, is suggested. The algorithm of the model construction depends neither on the spectral line shape nor on the spectrometer apparatus function. The method can be applied with equal success both for the short spectral regions (10–20 pixels) and for the long regions (10 000 and more pixels). The values of relative spectrum shifts can lie in a continuous range from 0.05 to 100 and more pixels. The advantages of this method are shown on the examples of subtraction of spectra in the process of registration on diffraction spectrograph PGS-2 (Carl Zeiss, Jena) with the help of a linear solid state detector (MAES-10, VMK-Optoelectronika, Russia, Novosibirsk).     

A complete 1H and 13C NMR data assignment for 3-phenylmethylene-1H,3H-naphtho-[1,8-c,d]-pyran-1-one

Complete assignments of the 1H and 13C NMR chemical shifts for 3-phenylmethylene-1H,3H-naphtho-[1,8-c,d]-pyran-1-one were done by means of one- and two-dimensional NMR techniques, including 1H-(1)H COSY, HMQC and HMBC spectra. Ab initio quantum chemistry calculations and a shift prediction by an incremental method provided values close to the proposed assignments. All mid-IR spectral bands are given as reference data. The DRIFT FTIR, ATR FTIR and Raman spectra are given as a Supplementary data in JCAMP-DX format, version 4.24. In addition, a method of compound's synthesis, that has the product yield higher as compared to already known data in the literature, is given.     

Influence and correction of peak shift and band broadening observed by rank analysis on vibrational bands from variable-temperature measurements

Variable-temperature infrared (IR) spectra of cyclohexane and IR and Raman spectra of chlorocyclohexane have been investigated by graphic eigenvalue analysis. Thermal effects known as peak shift and band broadening combined with heteroscedastic noise in vibrational bands are found to have severe influence on the interpretation of the outcome of rank analysis. Methods for correction of frequency shifts and band broadening in the spectral profiles due to temperature variation are developed and tested.     

Application of Differential UV Spectroscopy to the Determination of Lignin Substances in Polluted Water

The absorption spectra of Bjorkman lignin, lignin sulfate, lignosulfonates, and humic substances in neutral and alkaline media are considered. It was found that the difference spectra of lignins (an alkaline solution with reference to a neutral solution) exhibited several intense bands, whereas humic substances exhibited equal shifts of the spectra over the entire spectral range. This distinctive property of the difference spectra of lignin substances, as compared to the spectra of humic substances, can be used for determining lignins in polluted water.     

Infrared line collisional parameters of HCl in argon, beyond the impact approximation: measurements and classical path calculations

Measurement of room temperature absorption by HCl-Ar mixtures in the 1-0 and 2-0 bands have been made for pressures between 10 and 50 atm. Fits of these spectra are made for the determination of the width, spectral shift, asymmetry, and intensity of individual lines. The broadening and shifting parameters are in satisfactory agreement with previous determinations but provide the first complete and self-consistent sets covering P(15)-R(14) and P(7)-R(8) in the 1-0 and 2-0 bands, respectively. The asymmetries of the profiles, which have been studied for the first time, are smaller than typically 10(-3) atm(-1) and cannot be determined experimentally. On the other hand, the intensities of the low j lines show a significant linear decrease with increasing Ar pressure. Calculations of all measured quantities are made with a classical path approach and an accurate vibrational-dependent HCl-Ar potential energy surface (PES). Comparisons with experimental values show that widths and shifts are well predicted, confirming the quality of the PES and of the theoretical model, and the calculations confirm that asymmetries are small. The damping factors of the intensities are analyzed by considering three contributions: The first is due to the formation of van der Waals complexes, the second results from the finite duration of collisions, and the last comes from initial correlations. Calculations indicate that the last process has negligible consequences but that the first two processes lead to effects of the same order and explain most of the observed decrease of the intensities, even if some discrepancies persist for the mid R:mmid R:=1 rotational components.     

FT-IR studies on the mechanical response of the crystalline fraction in ultrastrong polyethylene tapes

FT-IR spectra of UHMW-PE tapes with different moduli have been studied in dependence of mechanical deformation and stress. Small spectral variations have been revealed in the difference spectra. Band shifts of the 730/720 cm^–1 doublet have been observed under stress relaxation and upon stretching. A clear correlation between the shift of crystalline bands and the Young's modulus could be determined. Polarized measurements demonstrated variations in the mechanical response of nearly perfectly oriented and non-oriented crystallites. Crosslinking was performed by blending the polyethylene with 10% polysilane and UV-irradiation of the drawn material. The band shift increases as the linkage between oriented crystal blocks is improved with higher draw ratios and chemical crosslinking.     

Prediction of the ~(13)C NMR Chemical Shifts of 9,10-Dihydrophenanthrene Analogues by the GIAO Method

After the geometry optimizations at the B3LYP/6-31+G(d,p) level, the NMR calculations of a series of 9,10-dihydrophenanthrene analogues have been carried out by GIAO method at the HF/6-31+G(d) level. The calculated 13C NMR chemical shifts are in agreement with the observed values. By a series of linear correlation equations (δpred = a + bδcal.c) of the 13C chemical shifts, accurate prediction of 13C chemical shifts was achieved for the new 9,10- dihydrophenanthrene compound, for which the predicted 13C NMR chemical shifts are in quite good agreement with the experimental values. The linear correlation between δpred and δexptl is excellent, and the square of correlation coefficient, r2, is up to 0.9973. The maximum absolute difference between δpred and δexptl, Δδ, is 4.5 ppm, and the rms error between δpred and δexptl is 2.55 ppm. In the meantime, according to the theoretical predicted result, we could confirm that the new 9,10-dihydrophenanthrene analogue is erianthridin (2,7-dihydroxy-3,4-dimethoxy-9,10-dihydro-phenanthrene).     

Hydrogen bond stabilization in 1,3-dimethylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate probed by high pressure: the role of charge-enhanced C-H...O interactions in the room-temperature ionic liquid

The hydrogen bonding structures of room-temperature ionic liquids 1,3-dimethylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate have been studied by infrared spectroscopy. High-pressure infrared spectral profiles and theoretical calculations allow us to make a vibrational assignment of these compounds. The imidazolium C-H bands of 1,3-dimethylimidazolium methyl sulfate display anomalous non-monotonic pressure-induced frequency shifts. This discontinuity in frequency shift is related to enhanced C-H...O hydrogen bonding. This behavior is in contrast with the trend of blue shifts in frequency for the methyl C-H stretching mode at ca. 2960 cm(-1). Our results indicated that the imidazolium C-H groups are more favorable sites for hydrogen bonding than the methyl C-H groups in the pure 1,3-dimethylimidazolium methyl sulfate. Nevertheless, both methyl C-H and imidazolium C-H groups are favorable sites for C-H...O hydrogen bonding in a dilute 1,3-dimethylimidazolium methyl sulfate/D(2)O mixture. Hydrogen bond-like C-H...F interactions were observed between PF(6)(-) and H atoms on the alkyl side chains and imidazolium ring for 1-butyl-3-methylimidazolium hexafluorophosphate.     

Scaled absorbance difference spectroscopy for the analysis of solutions — What residuals can be expected?

The analysis of compounds by IR spectrometry frequently involves the use of solvents. For dilute solutions in particular, the compensation of the solvent spectrum is required. The residual spectra of liquids obtained by scaled absorbance difference spectroscopy are calculated for various effects. These include wavenumber shifts of the absorption bands, the influence of a wedge shaped cell and limited spectral resolution. Further effects resulting from a change in the refractive index of a solution compared to the corresponding solvent have been studied. Magnitude and wavenumber position of the residual maxima are discussed.     

Use of the 13C-NMR chemical shift/charge density linear relationship for recognition and ranking of chemical structures

A novel scheme for computer-aided recognition of chemical structures based on the ¹³C-NMR chemical shift/charge density linear relationship is described. The spectral signals are uniquely assigned to the carbon atoms of each of the compared structures via an automatic assignment procedure. On the basis of this assignment, a factor reflecting the agreement between the spectrum and the molecular structure is defined. This factor has different values for different structures, similar values for similar structures, equal values for equivalent (isomorphic in the graph-theoretical sense) structures, and the lowest value for the structure best corresponding to the ¹³C-NMR spectrum. The potential of this approach for retrieval and ranking of chemical structures is discussed with examples.     

Interpretation of the IR spectrum of methyl-β-D-glucopyranoside based on the theoretical calculation of frequencies and intensities of normal vibrations

For the first time the detailed interpretation of the IR spectrum of methyl-β-D-glucopyranoside is presented based on the complete calculation of frequencies of normal vibrations and absolute intensities of IR absorption bands and on their comparison with the corresponding experimental values. The characteristic spectral features of oxymethyl substitution for the hydroxyl group are detected. The regularities in the formation of the complex band structure in a frequency range from 1150 cm^?1 to 950 cm^?1 is determined.     

Spinodal dewetting of thin films with large interfacial slip: implications from the dispersion relation

We compare the dispersion relations for spinodally dewetting thin liquid films for increasing magnitude of interfacial slip length in the lubrication limit. While the shape of the dispersion relation, in particular the position of the maximum, are equal for no-slip up to moderate-slip lengths, the position of the maximum shifts to much larger wavelengths for large slip lengths. Here, we discuss the implications of this fact for recently developed methods to assess the disjoining pressure in spinodally unstable thin films by measuring the shape of the roughness power spectrum. For polystyrene (PS) films on octadecyltrichlorosilane (OTS) covered Si wafers (with slip length b approximately 1 microm), we predict a 20% shift of the position of the maximum of the power spectrum which should be detectable in experiments.     

Maximum value of the chemical shift in the 1H NMR spectrum of a hydrogen-bonded complex

The values of chemical shifts in the ¹H NMR spectra of complexes with the strongest quasisymmetrical hydrogen bond A^δ?...H...B^δ+ with a minimal A...B distance were analyzed theoretically. According to the calculations, the maximum of the chemical shift is somewhat displaced from the shift of this structure toward that of limiting structure (free acid or protonated base) in which the proton is less shielded, but the value of this displacement is insignificant and does not correlate directly with the difference between the chemical shifts of the limiting structures.     

Comparison of experimental and DFT‐calculated NMR chemical shifts of 2‐amino and 2‐hydroxyl substituted phenyl benzimidazoles,benzoxazoles and benzothiazoles in four solvents using the IEF‐PCM solvation model

A comparative study of experimental and calculated NMR chemical shifts of six compounds comprising 2‐amino and 2‐hydroxy phenyl benzoxazoles/benzothiazoles/benzimidazoles in four solvents is reported. The benzimidazoles showed interesting spectral characteristics, which are discussed. The proton and carbon chemical shifts were similar for all solvents. The largest chemical shift deviations were observed in benzene. The chemical shifts were calculated with density functional theory using a suite of four functionals and basis set combinations. The calculated chemical shifts revealed a good match to the experimentally observed values in most of the solvents. The mean absolute error was used as the primary metric. The use of an additional metric is suggested, which is based on the order of chemical shifts. The DP4 probability measures were also used to compare the experimental and calculated chemical shifts for each compound in the four solvents. Copyright © 2015 John Wiley & Sons, Ltd.     

THE BEHAVIOR OF DYE-MUCOPOLYSACCHARIDE COMPLEXES—I. SPECTROSCOPIC STUDIES OF THE SYSTEM CHONDROITIN SULFATE A-ACRIDINE ORANGE

Abstract —Absorption, fluorescence, and circular dichroism (CD) spectra have been obtained for a mucopolysaccharide—cationic dye complex. The dye acridine orange exhibits a blue shift in its absorption maximum and a red shift in its fluorescence maximum when mixed with chondroitin sulfate A in aqueous solution. The spectral shifts of the dye appear to be reversed by addition of salt, divalent cations being more effective than monovalent cations. The complex exhibits induced optical activity in the visible absorption spectrum of acridine orange. The biphasic nature of the CD curve is compatible with interpretations involving chromophore coupling.     

Solvent effects on the S0(1(1)Ag-) --> S2(1(1)Bu+) transition of beta-carotene, echinenone, canthaxanthin, and astaxanthin in supercritical CO2 and CF3H

Solvent-induced spectral shifts of the four C40 carotenoids, beta-carotene, echinenone, canthaxantin, and astaxanthin, have been studied in supercritical CO2 and CF3H. In situ absorption spectroscopic analysis was used to determine the maximum peak position of the electronic transitions from the ground state (1(1)Ag-) to the S2 state (1(1)Bu+) of the carotenoids. The medium polarizability function, R(n) = (n2 - 1)/(n2 + 2) of the refractive index of the solvent was varied over the range R(n) = 0.08-0.14, by changing the pressure of CO2 or CF3H between 90 and 300 bar at the temperature 308 K. For all the carotenoids studied here, a significant hypsochromic shift of ca. 20-30 nm was observed in supercritical fluids as compared to that in nonpolar liquids. The spectral shifts in supercritical fluids were compared with those in liquids and showed a clear linear dependence on the medium polarizability. The temperature-dependent shift of the absorption maxima was less significant. Interestingly, there was almost no difference in the energetic position of the absorption maxima in supercritical CO2 and CF3H at a given R(n) value. This is in contrast to previous extrapolations from studies in liquids at larger R(n) values, which yielded different slopes of the R(n)-dependent spectral shifts for polar and nonpolar solvents toward the gas-phase limit of R(n) = 0. The current experimental results in the gas-to-liquid range show that the polarity of the solvent has only a minor influence on the 1(1)Ag- --> 1(1)Bu+ transition energy in the region of low R(n). We also obtain more reliable extrapolations of this 0-0 transition energy to the gas-phase limit nu(0-0)(gas-phase) approximately (23,000 +/- 120) cm(-1) for beta-carotene.     

A new algorithm of piecewise automated beam search for peak alignment of chromatographic fingerprints

The alignment of chromatographic signals is an important preprocessing step before further multivariate analysis. This paper presents a method, automated peak alignment by beam search (Auto-PABS), to solve the problem of peak shift in chemical chromatographic fingerprints by piecewise shifting and linearly interpolating. It is characterized by searching an adaptive range for the values of shifting and linearly interpolating of each segment. This search range is estimated by the calculation of fast Fourier transform cross correlation between the sample segment and its corresponding reference segment. Thus, arbitrary peak alignment is avoided when the real peak shifts are unknown in a large data set. Since the maximum of search range is close to the real shift, more accurate beam search is adopted to accomplish the optimization process. Simulated data and herbal medicine fingerprints of HPLC and GC are selected for evaluation. The output matrix of aligned chromatographic profiles is used directly for principal components analysis, yielding satisfactory results on real samples.