IR Band Intensities Research Articles

How Aqueous Solvation Impacts the Frequencies and Intensities of Infrared Absorption Bands in Flavin: The Quest for a Suitable Solvent Model.

FTIR spectroscopy accompanied by quantum chemical simulations can reveal important information about molecular structure and intermolecular interactions in the condensed phase. Simulations typically account for the solvent either through cluster quantum mechanical (QM) models, polarizable continuum models (PCM), or hybrid quantum mechanical/molecular mechanical (QM/MM) models. Recently, we studied the effect of aqueous solvent interactions on the vibrational frequencies of lumiflavin, a minimal flavin model, using cluster QM and PCM models. Those models successfully reproduced the relative frequencies of four prominent stretching modes of flavin's isoalloxazine ring in the diagnostic 1450-1750 cm-1 range but poorly reproduced the relative band intensities. Here, we extend our studies on this system and account for solvation through a series of increasingly sophisticated models. Only by combining elements of QM clusters, QM/MM, and PCM approaches do we obtain an improved agreement with the experiment. The study sheds light more generally on factors that can impact the computed frequencies and intensities of IR bands in solution.

Optimizing energy storage performance of ALD YSZ thin film devices via yttrium concentration variations

In the last decade, research has focused on fabricating new materials to accelerate the development of energy storage devices. In this work, metal-electrolyte-metal (Au-YSZ-Ru) structures were fabricated on silicon substrates using atomic layer deposition, sputtering, and thermal evaporation techniques. The effect of the yttrium concentration in YSZ films on their chemical, structural, optical, and electrical properties were studied. XPS analysis showed yttrium concentrations of 14.6, 10.3, 6.8, and 5.3 at.% for films with ALD cycle ratios Zr:Y of 2:1, 4:1, 6:1, and 8:1. Deconvolution of the oxygen XPS signal demonstrate the yttrium to oxygen vacancies ratio. The band gap was calculated through UV–vis indicating an increase in values with yttrium concentration. In addition, the trend was confirmed by reflection electron energy loss spectroscopy (REELS). The structure was investigated by performing X-ray diffraction (XRD) and infrared attenuated total reflectance spectroscopy (IR-ATR) measurements. Both results indicate a better crystallization of the cubic phase for the samples with lower concentrations, as the intensity of (111) diffraction peaks and IR band increased for lower yttrium concentrations. Impedance spectroscopy revealed an activation energy of 1.69, 1.32, and 1.28 eV for the 10.3, 6.8, and 5.3 at.% film concentration, respectively. According to cyclic voltammetry and charge-discharge tests, a lower yttrium concentration, 5.3 at.%, promotes electrode REDOX reactions improving the energy-storage properties.

An in-situ FTIR-LCR meter technique to study the sensing mechanism of MnO2@ZIF-8/CNPs and a direct relationship between the sensitivity of the sensors and the rate of surface reaction

Diethylamine vapor is harmful to people if inhaled or swallowed, as it results in the oxidation of hemoglobin in the body into unwanted methemoglobin, which is unable to transport oxygen in the blood, resulting in reduced blood oxygenation. Lack of blood oxygenation leads to hypoxemia. MnO2 nanorods, carbon soot, and MnO2@ZIF-8 are sensing materials used to prepare solid-state gas sensors that operate at room temperature. The prepared sensing materials were characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The performance of the MnO2@ZIF-8 based sensor improved significantly when the carbon soot was introduced into the composite. The effect of the amount of CNPs in the composite on the performance of the sensors was studied. The MnO2@ZIF-8/CNPs-based sensor with a 3:1 mass ratio was highly selective towards diethylamine vapor over acetone, methanol, ethanol, and 3-pentanone vapors. An in situ FTIR coupled with LCR meter was used to understand the sensing mechanism of diethylamine vapor and it was found that the sensing mechanism was by deep oxidation of diethylamine to CO2, H2O, and other molecules. The sensing mechanism was studied by monitored by CO2 band intensity which was produced from the reaction between the sensing materials and the analyte vapor. As the sensor's exposure time increased the intensity of the CO2 IR band increased. We observed the direct relationship between the surface reaction rate and the sensor's sensitivity.

Computational analysis of the vibrational spectra and structure of aqueous cytosine.

The recently developed efficient protocol for the explicit quantum mechanical modeling of the structure and IR spectra of liquids and solutions [Katsyuba et al., J. Phys. Chem. B, 2020, 124, 6664-6670] is used to describe aqueous solutions of cytosine. The same cluster model of a solute surrounded by the first solvation shell of solvent molecules was shown to be sufficient to reproduce experimental vibrational frequencies and relative IR and Raman intensities. An equally good quality of Raman spectra was provided by B3LYP-D3/def2-TZVP and B3LYP-D3/aug-cc-pVDZ simulations. Computations using the PBE functional were sufficient for modeling of the IR spectra but failed in the simulations of Raman scattering. It is shown that strong changes of frequencies and relative intensities of Raman and IR bands of cytosine, caused by its hydration, cannot be completely assigned to the influence of hydrogen bonds (HBs) with 7 or 8 closest water molecules. They are rather ascribed to the combined effect of solute-solute and solute-solvent HBs with the participation of at least 30 water molecules separating cytosine from the bulk solvent. This suggests that the vibrational modes and derivatives of the polarizability and dipole moment of the solute are mainly locally influenced by its first hydration shell, while the influence of bulk water is rather modest.

Lyα irradiation of solid-state formamide

Context. Formamide (NH2CHO) has been proposed as a potential prebiotic precursor in the scientific discourse on the origin of life. It has been observed in different environments in space, including protostellar regions and comets. The abundance and stability of NH2CHO in the early stages of star formation can be better understood by incorporating the formation and destruction data in astrochemical models. Aims. We carried out an experimental investigation to study the destruction of pure NH2CHO ice at 12 K as a result of the interaction with Lyα (121.6 nm) photons. Methods. We studied UV photo destruction of NH2CHO using Fourier-transform infrared spectroscopy. Results. After UV processing, the intensity of NH2CHO IR bands decreased and new bands corresponding to HCN, CO, NH4+ OCN−, HNCO, and CO2 appeared in the spectrum. We then derived the destruction and cumulative product formation cross-sections. Conclusions. A comparison of destruction rates derived from the cross-section in a cold and dense molecular cloud for different energetic processing agents reveals that UV photons induce NH2CHO destruction at a level that is one order of magnitude greater than that affected by cosmic rays; however, it is three orders of magnitude lower than that of H atoms.

Chemical composition of labile carbon fractions in Hungarian forest soils: Insight into biogeochemical coupling between DOM and POM

Understanding how the chemical composition of dissolved and particulate organic matter (DOM and POM) is affected by environment factors is critical because these labile pools of carbon are involved in an array of biological, chemical and physical processes. In this study, the chemical composition of DOM and POM was measured in 13 forest soils using UV–Vis spectroscopy, fluorescence spectroscopy with parallel factor analysis (PARAFAC modelling) and FT-IR spectroscopy.There were significant differences between the soils for the SUVA indexes, PARAFAC components and relative intensities of different IR bands. Redundancy analysis (RDA) revealed that soil parameters had a strong influence on the chemical composition of DOM and POM with high constrained variability (77.9 and 77.1 %, respectively). The pH of the soils proved to be an important controlling factor for both DOM and POM, regulating the concentration of the C3 PARAFAC component (low-molecular-weight compounds associated with biological activity) and the aromatic compounds of POM (aromaticity, rA1630 and rA1515). The silt content was the other main regulating factor controlling the chemical characteristics of the labile pool, having a strong negative correlation with the specific UV absorbance (SUVA) values of DOM due to the preferential adsorption of hydrophobic moieties. RDA analysis also revealed that there is a strong correlation between the chemical composition of POM and DOM: the relative amount of aromatic compounds (rA1515, rA1630 for aromatic rings and rA1270 for phenolic compounds) in the POM fraction was closely correlated with the SUVA values of the DOM. This clearly indicates a strong biogeochemical link between the two labile organic carbon fractions; the high molecular weight compounds of the DOM fraction may be derived from lignin-like structures of the POM fraction.

Estimations of OH·N hydrogen bond length from positions and intensities of IR bands

In this computational work applicability of IR spectral parameters for evaluations of OH···N hydrogen bond length is discussed. For a set of 124 complexes with OH···N hydrogen bond formed by combinations of methanol/acetic acid and pyridine (and their fluorine substituted versions) geometries, energies and IR parameters were calculated at MP2/def2-TZVP level of theory. For a number of IR parameters (the shift of proton donor group stretching vibration Δνs, increase of its intensity I, the low-frequency hydrogen bond stretching vibration νσ, bending in-plane δ and out-of-plane γ vibrations) equations linking them with interatomic distances are proposed, the robustness and accuracy of such equations are discussed. The enthalpy of OH···N hydrogen bond formation ΔH was also linked with electron density parameters in (3; –1) critical point.

Designing a novel 3D nanofibrous scaffold based on nanoalloy AuAg NPs (AuAg@ PAN NFs) for osteogenic differentiation of human adipose derived mesenchymal stem cells (hADMSCs)

The present study applied a new strategy to modify the surface properties of a polymeric matrix with the aim of forming an osteogenic scaffold with a stable structure and better osteo-inductive potential. To this purpose, we applied appropriate electrospinning conditions to design the nanofibrous scaffold of AuAg@ polyacrylonitrile (P) nanofibers (AAP NFs), based on incorporation of the AuAg nanoparticles (AA NPs) which were prepared by ultrasound irradiation, with an electrospinning solution of polyacrylonitrile. This study has combined structural properties (crystalline, morphology, roughness) and surficial properties (mechanical and wettability) of fibrous samples, in order to elucidate the role of surface modification and formation of a stable fibrous scaffold in osteogenic differentiation. The XRD and FT-IR findings showed that the all crystalline properties of hexagonal system and the intensity of related IR-bands were changed. This modification caused the removal a smooth outer fiber layer of the P NFs and the creation of chunky shapes of AA NPs on the surface of the corresponding fibrous sample, which were confirmed by enhancing Ra values. The nanofibrous scaffold with 2% AA NPs disclosed the best mechanical performance and wettability. Finally, we showed that AAP NFs, not only improved cell adhesion, but also induced osteogenic differentiation of human adipose derived mesenchymal stem cells(hADMSCs) more efficiently than P NFs and tissue culture plates (TCPs).

Hirshfeld surfaces analysis and DFT study of the structure and IR spectrum of N-ethyl-2-amino-1-(4-chlorophenyl)propan-1-one (4-CEC) hydrochloride

This paper represents a Hirshfeld surfaces analysis of crystalline 4-chloroethylcathinone (4-CEC) hydrochloride and a quantum chemical study of the IR spectrum of 4-CEC dimer, which models the crystalline structure of 4-CEC within the framework of density functional theory (DFT) with B3LYP functional and 6-31G(d,p) basis set. The Hirshfeld surfaces analysis of 4-CEC X-ray crystal structure reveals that NH∙∙∙Cl, CH∙∙∙Cl and π∙∙∙π interactions play a major role in the cooperative way of crystal architecture securing and approves the formation of the NH2+–Cl– salt fragment in the 4-CEC crystal. The same structural trends are supported by the Bader’s QTAIM analysis of density gradients and critical points. The DFT calculated infrared spectrum of the investigated psychotropic substance contains absorption features, which correspond to the frequency and relative intensity of the experimental IR bands of the 4-CEC standard sample. All IR bands being assigned and interpreted in the experimental spectrum of the 4-CEC standard crystal sample represent an important aspect of analytical chemistry in the forensic problems. It is shown that the presence of the ionized form of the 4-CEC compound, which contains the NH2+Cl– fragment, is a key condition for the correct reproduction of the IR spectrum when calculating the dimer structure as a model of a crystalline sample. The unravel of the complicated nature of the IR bands associated with vibration of the NH2+Cl– fragment is an important achievement of the present study.

Structural and vibrational study of molecular interaction in a ternary liquid mixture of benzylamine, ethanol and benzene

The structural study of the non-covalent interactions in the ternary mixture of benzylamine (BA), ethanol and benzene has been attempted through Density Functional Theory (DFT) calculation. The optimized structure of monomers (BA, ethanol and benzene), BA dimer and their complexes (BA-benzene, BA-ethanol, BA-ethanol-benzene) and their interaction energies are used to describe the intermolecular interaction. In addition to conventional H-bonding, the stability of the system is found to depend on several other interactions such as CH/π, NH/π, OH/π interactions. The Fourier Transform InfraRed (FTIR) spectroscopy technique is also used to study the molecular interaction. An interpretation of the IR stretching bands based on the interaction is also provided. The variation in IR band position and intensity of spectra with change in concentration of the mixture shows that different kinds of interactions are present in the mixture. The strength of these interactions varies with concentration. At lower concentration of benzylamine, weak OH/π interaction between benzene and ethanol takes place, while at other mole fractions, N-H-----O, O-H------N or NH/π interaction are present between the molecules.

Crystal structure, computational study, optical and vibrational properties of a new luminescent material based on bismuth(III): (C10H28N4)[Bi2Cl10

Development of new Bi-based perovskites with various structures offers considerable potential for lead-free solar cells and other optoelectronic devices as they retain the high-performing properties of halide perovskites with high power conversion efficiency and improved long-term and environmental device stability. This work addresses the study of a new chlorobismuthate(III) hybrid compound with the chemical formula (C10H28N4)[Bi2Cl10], prepared at room temperature by the slow evaporation method. The resulting crystals were investigated using Single Crystal X-ray diffraction, which gave an accurate crystal structure determination that allows searching the role played by intermolecular contacts in the self-assembly of the crystal structure using Hirshfeld surface analysis. The compound was additionally characterized using FTIR and Raman spectroscopies correlated by Ab-initio calculations at different levels of theory. The optical study supports the strong absorption of the compound in the visible region showing its luminescent character with emission peaks falling in the blue and near green regions. Natural bond orbital (NBO) calculations suggest a high stability of the new hybrid material attributed to energetically electronic transitions of [Bi2Cl10]4- anion that probably support its interesting optical properties. The shifting of stretching modes assigned to N–H groups belonging to the piperazine ring of the compound toward lower wavenumbers confirms well the interactions observed by NBO calculations between Cl atoms of the anion with these groups. The Raman bands detected below 300 cm−1 were found in perfect agreement with the characteristic of isolated Bi2Cl10 anion, made up of two [BiCl52−] units. The TG-DTA analysis revealed the high stability of the compound and its decomposition at 280°С. Frontier orbital studies showed the gap values of the new hybrid and its low reactivity. Probably, the inert mapped molecular electrostatic potential (MEP) surface predicted on the new material could support its high stability and low reactivity. The complete assignments for this compound in comparison with the organic and inorganic species are also presented. HF/Lanl2dz calculations in n-hexane solution have evidenced an increase in the reactivity of the hybrid and changes of positions and intensities of IR bands, attributed to NH3, NH and CH2 stretching modes, as a consequence of interactions of the anion with those groups belonging to the cation.

Vehicle identification from automotive paints transferred in road accidents

Introduction Paint chips and smears represent the most common types of trace evidence resulting from vehicle-related incidents [1,2]. Analysis of these traces would ideally lead to the identification of the paint producer and ultimately of the vehicle in question [2]. Despite the chemical complexity of automotive paints, several reports showed this identification to be possible through the use Py-GC/MS, SEM-EDX, WDXRF, Raman and FTIR spectroscopy [1,3–5]. However, these studies were focussed on the analysis of each of the individual layers that compose the painting, making the analysis more complex, time consuming and dependent on highly specialised equipment. In the present work, we evaluated the discriminative potential of ATR-FTIR for the identification of paint producers, based on the analysis of the paint as a whole. Materials and methods Fragments of 6 different car paints obtained from the hood and lateral panels were milled and analysed through ATR-FTIR, both individually and as mixtures between pairs of paint Figure 1. Spectra were obtained between 450 and 4000 cm−1, with a resolution of 4 cm−1 and 16 accumulations. Figure 1. ATR-FTIR spectra of the isolated paints (top and bottom spectra), and of the mixtures at different ratios (middle spectra), where A) corresponds to a blue Volvo (A) and a red Renault (B); (B) to a blue Citröen (A) and a grey Skoda (B); (C) to a black Peugeot (A) and a grey Seat (B). Results The obtained results show the paint spectra to have considerable differences both in the number and intensity of IR bands. Furthermore, the mixtures’ spectra clearly show bands of both individual paints that are proportional, in intensity, to the ratio of each individual paint. Discussion and conclusions: These preliminary results show considerable differences between the FTIR spectra of the individual paints that propagate throughout the paint mixtures. This suggests that there are features in the ATR-FTIR spectra of automotive paints, as a whole that might be suitable predictors for the development of highly accurate predictive models.

High-Electric-Field-Induced Hierarchical Structure Change of Poly(vinylidene fluoride) as Studied by the Simultaneous Time-Resolved WAXD/SAXS/FTIR Measurements and Computer Simulations

A high electric field was applied cyclically to poly(vinylidene fluoride) films, during which the simultaneous and time-resolved measurements of the two-dimensional wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and transmission-type Fourier transform infrared (FTIR) spectra were performed using a synchrotron X-ray radiation system. The inversion of the CF2 dipole moments caused by the alternate change of the electric field vector direction was detected to occur around ±80–100 MV/m as estimated by the electric-field-strength dependence of the IR band intensity. On the other hand, the WAXD peaks were found to show the maximal intensities at 0 and ±250–300 MV/m. In these regions, the 001 reflection of the β form and the 002 reflection of the δ form changed the intensities remarkably and periodically. These experimental data were interpreted, not by the idea of a simple inversion motion of the rigid polar chains (the planar zigzag chains of the form β and the TGTG̅ chains of the α and δ forms) but by the more complicated couplings between the rotation and tilting motions of the chain segments, the cooperative T-G conformational exchanges, and the associated inversion motion of the CF2 dipoles. The idea of the cooperative chain motions was supported by the density functional theory calculations performed under the external electric field. Different from the remarkable changes of the WAXD and FTIR data, the SAXS patterns did not show the detectable changes in these processes, indicating that the above-mentioned cooperative structural changes should occur in the crystalline regions with the stacked lamellar structure kept unchanged.

Shift of CO2-I absorption bands in diamond: A pressure or compositional effect? A FTIR mapping study

Infra-red maps and profiles with high spatial resolution were obtained for two single crystal diamonds with pronounced CO2 IR absorption peaks. Detailed examination allows unambiguous assignment of the spectral features to solid CO2-I phase. It is shown that the distribution of IR band positions, intensities and widths in the sample follows regular patterns and is not chaotic as was suggested in previous works where spectra of a few individual spots were analysed. Consequently, pressure effects alone fail to explain all observed features and shifts of the CO2 bands. Experimental data can be explained by presence of impurities (such as water, N2, etc.) in the trapped CO2. This implies that spectroscopic barometry of CO2 microinclusions in diamond may be subject to poorly controlled bias. However, barometry is still possible if Davydov splitting of the CO2-I ν2 band is unequivocally observed, as this indicates high purity of the CO2 ice.

Characterization of oxide-supported Cu by infrared measurements on adsorbed CO

Infrared spectroscopy on CO chemisorbed on Raney Cu and materials with Cu dispersed as nanoparticles on oxide supports was used to evaluate support effects on the Cu surface properties. The C-O frequency (νC-O) is sensitive to the charge on the adsorption site with νC-O being high on Cu+, intermediate on Cu0, and low on Cu−, whereby this method can probe the charging state of the Cu surface. The Raney Cu reference demonstrates the complex analysis of the IR band intensity, which can be susceptible to dipole coupling. This means that the most intense IR bands may be higher frequency bands strengthened by such coupling effects rather than the bands arising from the most abundant sites. The νC-O of the major band attributable to CO adsorbed on the metallic surface follows the order: Cu/SiO2 > Raney Cu > Cu/Al2O3 > Cu/TiO2. Given the charge-frequency relationship these support-dependent frequency shifts are attributed to changes in the charging of the Cu surface caused by support effects. The Cu surface is more electron deficient for Cu/SiO2 and electron enriched for Cu/TiO2. For the Cu/ZnO(/Al2O3) samples, which are important as industrial methanol synthesis catalysts, band assignments are complicated by a low νC-O on Cu+ sites connected to the ZnO matrix. However, Cu/ZnO(/Al2O3) has a spectral feature at 2065-68 cm−1, which is a lower frequency than observed in the Cu single crystal studies in the literature and thus indicative of a negative charging of the Cu surface in such systems. Experiments with co-adsorption of CO and electron-withdrawing formate on Cu/ZnO and Cu/SiO2 show that νC-O in the adsorbed CO shifts upwards with increasing HCOO coverage. This illustrates that the surface charge is donated to the electron-withdrawing formate adsorbate, and as a result co-adsorbed CO experiences a more charge depleted Cu surface that yields higher νC-O. The support-dependent surface charging may thus affect the interaction with adsorbates on the metal surface and thereby impact the catalytic properties of the Cu surface. Dilution of the samples in KBr, which has been used in many studies in the literature, had pronounced effects on the spectra. The presence of KBr leads to an increase in νC-O indicative of an electron depleted surface attributed to transfer of electron-withdrawing bromine species from KBr to the sample.

Theoretical and matrix isolation studies of infrared spectra of the H2CO∙∙∙HF hydrogen-bonded complex

The equilibrium geometry, the binding energy, and harmonic and anharmonic spectral parameters of H2CO and HF monomers and the H2CO∙∙∙HF complex are calculated in the MP2/6-311++G(3df,3pd) approximation with the basis set superposition error taken into account. Anharmonic calculations are carried out using the second-order vibrational perturbation theory. The changes in transition frequencies and intensities of monomeric IR bands upon formation of the 1:1 complex are analyzed. A high intensity value (53 km mol–1) is predicted for the overtone band of the out-of-plane HF libration. The variational method was used to solve anharmonic vibrational problems in 1D–4D subspaces involving the H–F stretch. The influence of anharmonicity on spectral and structural parameters was studied. The variational calculation confirmed the high intensity value for the overtone of the HF librational mode from the perturbative calculation. Matrix-isolation experiments were performed in N2 at T = 8 K to record the absorption spectra of pure H2CO and HF and H2CO/HF mixtures in the IR region. The spectral features related to the H–F, C=O, and C–H stretches and the in-plane HF librational motion were reliably identified. The predictions of our perturbative calculations for isolated compounds, especially for the band shifts upon complexation, are in satisfactory agreement with the experimental matrix-isolation findings. The only exception is the H–F stretching mode in the complex because of the high anharmonicity of HF and strong interaction of free HF molecules with a matrix environment. Of particular interest is the observation of a rather strong band at 1069 cm–1, which is close to 1072 cm–1 predicted for the overtone of HF out-of-plane librational mode.

IR Cavity Ringdown Spectroscopy and Density Functional Theory for Jet-Cooled Pyrrole-Cyclopentanone Binary Clusters: Effect of Pseudorotation on N-H···O═C Hydrogen Bonds.

The geometry and energetics of the N-H···O═C hydrogen bond (H-bond) are important to understand the stability and flexibility of biomolecules, such as protein and DNA. Jet-cooled pyrrole-cyclopentanone (Py-Cp) binary clusters are appropriate models to investigate the N-H···O═C H-bond from a microscopic point of view. In this study, NH stretching vibrations of the Py-Cp binary clusters were observed by IR cavity ringdown spectroscopy. Furthermore, density functional theory calculations revealed geometric structures, harmonic vibrations, intermolecular energies, and donor-acceptor interactions for various sizes of binary clusters. The IR spectra of the Py-Cp binary clusters were measured under various conditions of the vapor pressures of Py and Cp in He buffer gas for a supersonic expansion. The dependence of the IR band intensities on the vapor pressure provides vibrational assignments of the NH stretching vibrations, which were reproduced by calculated frequencies of Py1-Cp1, Py1-Cp2, and Py2-Cp1. An admixture of Ar in He buffer gas for a supersonic expansion was also applied to produce Py1-Cp2 in order to differentiate several NH stretches of isomeric structures due to the pseudorotation of Cp molecules. Py1-Cp1 is formed by the N-H···O═C H-bond. Py1-Cp2 has a cyclic structure that is formed by the N-H···O═C H-bond and stacking interactions among Py and two Cp molecules. Py2-Cp1 also has a cyclic structure that is formed by not only the N-H···O═C H-bond but also a N-H···π H-bond between two Py molecules and a stacking interaction between Py and Cp. A comparison of the H-bond geometries between Py2-Cp1 and the corresponding pyrrole-acetone binary cluster reveals that the stacking interaction between Py and Cp strengthens the N-H···O═C H-bond through a cooperative effect.

Calculation and Comparative Analysis of Ir Spectra of Homobrassinolide and (22S,23S)-24-Epibrassinolide

Normal vibrational frequencies and absolute IR band intensities of the biologically active steroid phytohormones homobrassinolide and (22S,23S)-homobrassinolide were calculated in the framework of an original approach that combined classical analysis of normal modes using molecular mechanics with quantum-chemical estimation of the absolute intensities. IR absorption bands were interpreted based on a comparison of the experimental and theoretical absorption spectra. The impact of structural differences in the side chains of these molecules on the formation of their IR spectra in the region 1500–950 cm −1 was estimated.

Surface-enhanced infrared attenuated total reflection spectroscopy via carbon nanodots for small molecules in aqueous solution.

In this study, carbon nanodots (CNDs) with excellent aqueous dispersibility, narrow size distribution, and oxygen-rich functional groups have been prepared via a green electrochemical method. Graphite electrodes were directly electrolyzed at ambient temperatures to form uniform CNDs in deionized water, which is free from additional oxidant/reductant. As-synthesized CNDs have been applied to coat an attenuated total reflection (ATR) waveguide enabling surface-enhanced infrared absorption (SEIRA) spectroscopic studies for detecting a variety of analytes in aqueous phase with remarkably enhanced IR band intensities. Finally, the proposed ATR-SEIRA strategy enabled quantitatively analyzing adenine in aqueous solution after optimizing the amount of CNDs, the solution pH, and potential CND aggregation. Graphical abstract.

Theory of Vibrational Spectra of Excited Quadrupolar Molecules with Broken Symmetry

Quadrupolar molecules of the structure AL–D–AR, where D is an electron donor and AL and AR are identical acceptors, are investigated. A general theory of vibrational spectra of such molecules undergoing symmetry breaking after photoexcitation is developed. The approach is based on the expansion of the electron–vibrational interaction in a series in powers of the displacements of the vibrational modes and the dissymmetry parameter. The theory provides a possibility to calculate the intensities of the IR bands and the splitting of the frequencies of local vibrations associated with vibrations of small groups of atoms symmetrically located in the left and right arms of the molecule. The theory explains the regularities of influence of symmetry breaking on the IR band intensities and the splitting of the frequencies observed recently using time-resolved infrared spectroscopy.