Assignment Of Bands Research Articles

Deuteration and Vibrational Spectra of Dimethylammonium Paratungstate‐B Hydrates

Infrared and Raman spectra of two solvatomorphs of a new dimethylammonium polytungstate decakis(dimethylammonium) dihydrogendodecatungstate, (Me2NH2)(H2W12O42)·nH2O (n = 10 or 11), were evaluated and discussed. The assignment of bands corresponding to the cationic and anionic components as well as the water of crystallization is presented. Deuteration has been used in the interpretation of the spectra. The dimethylammonium cation and the molecules of water of crystallization form a network of regular and multifurcated hydrogen bonds, thus a fraction of the N–H hydrogen atoms are so strongly bound to the anion, that the compound can only be deuterated with an aggressive procedure. The method for deuteration is described in detail. The deuterated undecahydrate can be obtained from both solvatomorphs.

Raman study of 3.65 Å-phase MgSi(OH)6 under high pressure and the bands assignment

ABSTRACT 3.65 Å-phase (or hydroxide-perovskite), MgSi(OH)6, is a representative of dense hydrous magnesium silicates (DHMS) with maximum water content (up to ∼35 wt.% H2O) and thus is of interest as one of the largest repositories of water among all the known hydrous phases. Sample of 3.65 Å-phase, grown in DIA-type multianvil apparatus, was studied by Raman spectroscopy under pressure up to ∼7 GPa with diamond anvil cell. Interpretation of the Raman spectrum was carried out using lattice-dynamical simulations within ab initio DFT method (CASTEP code). Additionally, OH-stretching bands are analyzed with two phenomenological models: empirical model by Novak and Libowitzky, using correlation between O–O distance and the wavenumber of the OH-stretching band, and theoretical model, using double Morse potentials of hydrogen bond O–H···O. Upon the pressure increase, octahedral and bending δ(ОН) vibrations exhibit linear positive pressure shift, whereas wavenumbers of the ОН-stretching modes show inverse pressure dependence.

Detection of caffeine intake by means of EC-SERS spectroscopy of human saliva.

This work presents the application of EC-SERS spectroscopy for the detection of caffeine consumption from human saliva. Caffeine and paraxanthine as the major metabolite of caffeine were tested. Model samples of saliva spiked with caffeine were investigated, and detection of caffeine in real-life saliva samples was tested in order to ensure the viability of the method for clinical applications. Two doses of caffeine (2 mg/kg and 3.5 mg/kg) were ingested by volunteers, and their saliva samples were taken at different time periods ranging from 1 h to 10 h after the consumption. Density functional theory calculations of caffeine and paraxanthine adsorbed on the silver surface were performed in order to better understand the adsorption of the investigated molecules and to make a correct assignment of the experimental spectral bands of the EC-SERS spectra. It was determined that a low dose caffeine consumption can be detected by the appearance of the SERS spectral marker band of caffeine and paraxanthine at 692 cm-1. The intensity of this band is mostly reasoned by the paraxanthine concentration since the intensity changes of the band over time correlates to the concentration changes of paraxanthine determined by the pharmacokinetic studies of paraxanthine and caffeine in the human saliva. It was found that the limit of detection paraxanthine in saliva by means of EC-SERS is as low as 15 μM and can be further improved.

DFT computational insights into structural, electronic and spectroscopic parameters of 2-(2-Hydrazineyl)thiazole derivatives: a concise theoretical and experimental approach

ABSTRACT It has been uncovered that compounds containing thiazole moiety display noteworthy biological properties, which have attracted the attention of many researchers in chemical biology as well as in medicinal chemistry. In the current examination, ten 2-(2-hydrazineyl)thiazole derivatives were studied using density functional theory (DFT). The geometry of all ten molecules was optimized by employing the DFT method with the B3LYP/6-311G (d,p) basis set. For the detailed structural and spectroscopic examination, the (E)-4-phenyl-2-(2-(1,2,6,7-tetrahydro-8H-indeno[5,4-b]furan-8-ylidene)hydrazineyl)thiazole (PIFHT) was studied as a representative molecule. The bond lengths and bond angles of the PIFHT molecule were discussed for the detailed understanding of the structural entities. The electronic parameters of all ten molecules were analyzed by computing HOMO and LUMO pictures. Using frontier molecular orbital analysis, spectroscopic and quantum chemical parameters were evaluated and discussed to explore the chemical reactivity of the molecules. Besides, absorption energies, oscillator strength, and electronic transitions of PIFHT molecule were explored using time-dependent density-functional theory (TD-DFT) at the B3LYP/6-311G (d,p) level of theory in the gas phase, dichloromethane, and dimethyl sulfoxide solvents. The TD-DFT computed theoretical UV-Visible spectra of the PIFHT molecule were compared with the experimental UV-Visible spectra. The scaled vibrational frequencies were compared with the experimental frequencies for the assignment of the vibrational bands. The comparisons between computed and experimental UV-Visible and IR spectral results are gratifying. The molecular electrostatic surface potential plots were computed for locating the reactivity sites. Mulliken atomic charges were also studied for acquiring insights into charge density.

A Series of Discrete Dichloride Dihydrates: Characterisation and Symmetry Effects.

A series of three discrete dichloride dihydrates [Cl2 (H2 O)2 ]2- have been isolated with different triaminocyclopropenium (TAC) cations and with different crystallographic symmetries. The cluster exhibits D2h symmetry with the tris(dimethylamino)cyclopropenium cation [C3 (NMe2 )3 ]+ , C2h symmetry with the fluorinated cation [C3 (N(CH2 CF3 )2 )(NBu2 )2 ]+ (containing two 2,2,2-trifluoroethyl substituents) and C2v symmetry with the more fluorinated [C3 (N(CH2 CF3 )2 )2 (NBu2 )]+ cation. The effect of symmetry on the infrared spectra of the dichloride ion-pair clusters, as well as deuterated analogues, has been investigated. The D2h - and C2h -symmetric clusters each exhibit two stretching bands in the infrared at 3427 and 3368 cm-1 for D2h symmetry and 3444 and 3392 cm-1 for C2h symmetry, whereas the C2v -symmetric cluster exhibits three bands at 3475, 3426 and 3373 cm-1 . Computational studies were carried out on a [Cl2 (H2 O)2 ]2- cluster with C2v symmetry to aid the infrared band assignments.

An experimental and theoretical study of the electronic spectra of tetraethylammonium [tris(1,3-dithiole-2-thione-4,5-dithiolato)M] and tetraethylammonium [tris(1,3-dithiole-2-one-4,5-dithiolato)M], for M = Sn(IV) and Sb(V)

Metal-dmit complexes and related compounds have been studied extensively over the last few decades. Experimental reports of its UV-Vis spectra present the main spectroscopic features, although many details of the electronic structure still have to be investigated. This work presents a detailed analysis of the UV-vis spectra of the [NEt4]x[M(L)3] (L = dmit and dmio), for M,x = Sn,2 and Sb,1. The experimental spectrum was deconvoluted and analyzed with B3LYP and CAM-B3LYP DFT methodologies. The results lead to an assignment of several bands involving LMCT, besides confirming the presence of a metal orbital in the HOMO-LUMO boundary, with additional observation performed through the analysis of the dmio complex in order to enhance the results. Several methods such as EDA, NBO, and QTAIM were applied to determine the covalent character of the metal-ligand interaction. Furthermore, the solvent effect was evaluated using the CPCM model to observe the changes in the overall properties.

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.

Near-Infrared Spectroscopy as a Rapid Screening Method for the Determination of Total Anthocyanin Content in Sambucus Fructus.

Elderberry (Sambucus nigra L., fructus) is a very potent herbal drug, deriving from traditional European medicine (TEM). Ripe elderberries are rich in anthocyanins, flavonols, flavonol esters, flavonol glycosides, lectins, essential oils, unsaturated fatty acids and vitamins. Nevertheless, unripe elderflower fruits contain a certain amount of sambunigrin, a toxic cyanogenic glycoside, whose concentration decreases in the ripening process. Therefore, quality assurance must be carried out. The standard method described in literature is the photometric determination (pH-differential method) of the total anthocyanin content (TAC) that is the highest when the berries are ripe. The drawback of the pH-differential method is the extensive sample preparation and the low accuracy of the method. Therefore, the goal of this publication was to develop a fast non invasive near-infrared (NIR) method for the determination of TAC in whole berries. TAC of elderberries was measured using pH-differentiation method where TAC values of 632.87 mg/kg to 4342.01 mg/kg were measured. Additionally, cyanidin-3-O-glucoside, cyanidin-3-O-sambubioside and cyanidin-3-O-sambubioside-5-O-glucoside which represent more than 98% of TAC in elderberry were quantified using ultra high performance liquid chromatography-multiple wavelength detection—ultra high resolution-quadrupole-time of flight-mass spectrometry (UHPLC-MWD-UHR-Q-TOF-MS) and their sum parameter was determined, ranging between 499.43 mg/kg and 8199.07 mg/kg. Using those two methods as reference, whole elderberries were investigated by NIR spectroscopy with the Büchi NIRFlex N-500 benchtop spectrometer. According to the constructed partial least squares regression (PLSR) models the performance was as follows: a relative standard deviation (RSDPLSR) of 13.5% and root mean square error of calibration (RMSECV/RMSEC) of 1.31 for pH-differentiation reference and a RSDPLSR of 12.9% and RMSECV/RMSEC of 1.28 for the HPLC reference method. In this study, we confirm that it is possible to perform a NIR screening for TAC in whole elderberries. Using quantum chemical calculations, we obtained detailed NIR band assignments of the analyzed compounds and interpreted the wavenumber regions established in PLSR models as meaningful for anthocyanin content. The NIR measurement turned out to be a fast and cost-efficient alternative for the determination of TAC compared to pH-differential method and UHPLC-MWD-UHR-Q-TOF-MS. Due to the benefit of no sample preparation and extraction the technology can be considered as sustainable green technology. With the above mentioned inversely proportional ratio of TAC to total amount of toxic cyanogenic glycosides, NIR proves to be a reliable screening method for the ideal harvest time with maximal content of TAC and lowest content of cyanogenic glycosides in elderberry.

Scrutinizing "Ligand Bands" via Polarized Single-Crystal X-ray Absorption Spectra of Copper(I) and Copper(II) Bis-2,2'-bipyridine Species.

High-energy resolution fluorescence-detected Cu K-edge X-ray absorption spectroscopy (XAS) and single-crystal polarized XAS data are presented toward refining the assignments of bands assigned as excitations from Cu 1s to ligand-localized molecular orbitals. These have been previously dubbed "XAS-metal-ligand charge transfer" (XAS-MLCT) bands. Data are presented for a series of [Cu(xbpy)2]n+ complexes (xbpy = 2,2'-bipyridine (1n+), 4,4'-bisamino-2,2'-bipyridine (2n+), and 4,4'-dimethoxy-2,2'-bipyridine (3n+); n = 1 and 2). Dipolar dependencies of these "XAS-MLCT" bands in both Cu1+ and Cu2+ species lead to reassignment of these features as owing their intensities primarily to Cu 1s → Cu 4p excitations. The transition densities are Cu-localized, highlighting that XAS-MLCT features in Cu XAS spectra are not "charge transfer" transitions but rather quasi-atomic transitions. Although scrutiny of the acceptor orbitals supports assignment as Cu 1s → ligand π* transitions, it ultimately appears that while the ligand orbital energetics govern the positions of these bands the intensity is conferred through a small degree of metal 4p mixing into otherwise ligand-dominated acceptor molecular orbitals.

Anomalous high-infrared reflectance of extruded polyoxymethylene

Polarized infrared (IR) reflectance measurements were performed on polyoxymethylene (POM) prepared by the extrusion method, and an abnormally high reflectance of ∼90% was observed along the extruded direction in the 1000 cm−1–900 cm−1 region. High reflectivity was found in samples made by the conventional injection molding. However, the response of the extrusion sample was higher than that of the injection sample, which can be attributed to the Reststrahlen band. The relative permittivity calculated from the polarized reflection spectrum of the extruded direction shows a notably deep negative region in this high reflectance frequency. Using x rays, by differential scanning calorimetry, and by field emission scanning electron microscopy characterization, the difference in crystallinity and morphology from the extrusion and the injection molding plate was investigated, and the difference in IR optical response was discussed. The conventional IR band assignment of POM was also discussed.

Strategy for the vibrational circular dichroism study of a glycosylflavonoid evaluated as its peracetate. The case of bioactive 7-O-β-D-glucopyranosylchrysin

As it is difficult to study polyhydroxylated natural products by vibrational circular dichroism (VCD) due to their very limited solubility in infrared transparent solvents, 7-O-β-D-glucopyranosylchrysin (1), isolated from Mimosa rosei, was acetylated to provide 7-O-(2ʹʹ,3ʹʹ,4ʹʹ,6ʹʹ-tetraacetyl-β-D-glucopyranosyl)-5-acetylchrysin (2). Density functional theory (DFT) VCD spectra of 2 were calculated using the B3LYP, B3PW91, and PBEPBE functionals and the DGDZVP basis set to ascertain a good level of theory for calculating this kind of compounds. Statistical comparison of the experimental and calculated VCD spectra revealed that the frequently employed B3LYP and B3PW91 functionals provided good confidence levels with similar statistical results, allowing band assignments for the pyranoside portion of 2. This is the first report on a satisfactory statistical validation of a VCD measurement for such a glycopyranoside. In addition, in vitro cytotoxicity studies of 1 and 2 against the human colon cell line HT-29 and the human melanoma cell line UACC-62 by the MTT method were assayed. Moreover, the immunomodulatory response of 1 and 2 was evaluated by measuring TNF-α, IL-1β, and IL-10 levels by the ELISA technique. The results revealed low cytotoxicity of both compounds against cancer cells. However, flavonoid 1 upregulated the IL-1β production in lipopolysaccharide (LPS)-induced THP-1 macrophage, thus suggesting the potential of this molecule as an immunostimulant for cancer treatment.

Fourier transform infrared spectroscopy of BH3 with the first identification of the ν4 band

High-resolution Fourier transform infrared spectra of the ν4 bands of 11BH3 and 10BH3 have been analyzed by taking into account Coriolis interaction between the ν4 = 1 and ν2 = 1 states in the 900–1300 cm−1 region. The main parameters thus obtained are the band origin ν4 = 1196.022(1), the rotational constant B4 = 7.9759(2), C4 = 3.84033(9), the first-order Coriolis coupling constant Cζ4 = -0.3255(2), the Coriolis interaction constant D24(~(2)1/2Bζ24) = 7.7065(3) cm−1 for 11BH3, and ν4 = 1201.805(7) B4 = 7.9662(7), C4 = 3.8466(3), Cζ4 = -0.3282(8), D24 = 7.631(1) cm−1 for 10BH3 with one standard deviation in parentheses. The ν2 band of 10BH was analyzed for the first time to determine ν2 = 1159.409(2), B2 = 7.8259(8), C2 = 3.8887(2) cm−1 and other constants. The observed absorption line intensities of the ν4 and ν2 bands were explained by using the ratio of the transition moments μ4/μ2 = 0.4. Assignments in the ν3 bands of 11BH3 and 10BH3 were extended with a set of newly determined ground state constants.

Structural, optical, FT-IR and SHG studies of L-Isoleucine D-Valine: A spectroscopic and DFT approach

Organic nonlinear optical single crystal of L-Isoleucine D-Valine (LIDV) with dimensions 3 X 3 X 4 mm3 was successfully grown by the slow evaporation solution growth technique (SEST). The structural analysis of the grown crystals has been analyzed by Powder X-ray diffraction which revealed that grown (LIDV) crystal belongs to monoclinic crystal system with P21 space group. The structure of LIDV is optimized using Density Functional Theory (DFT) method. The vibrational band assignments were performed at B3LYP/6-31G + (d, p) theory level. The theoretical IR frequencies are found to be in good agreement with the experimental IR frequencies. Nonlinear optical (NLO) behavior of LIDV is examined by the theoretically predicted values of first hyper polarizability. The cut-off wavelength and the optical band gap value of the grown crystal is found using Optical studies. The SHG efficiency of the grown material is found to be 2.5 times the reference material.

Luminescence line shapes of band to deep centre and donor–acceptor transitions in AlN

Energy structure and electron coupling with local lattice vibrations have been investigated for deep centres in AlN using hybrid functional density functional theory. Local phonon energies and Huang–Rhys parameters have been calculated for defects and defect complexes containing most common unintentional impurities of carbon, oxygen and silicon, and for intrinsic vacancies, nitrogen split-interstitial defect, and complexes of Al and N vacancies in AlN. Luminescence line shapes of band to deep centre transitions in AlN have been calculated in dependence on temperature for most abundant defects in AlN. Donor–acceptor luminescence line shapes for shallow donor to deep acceptor and deep donor to deep acceptor transitions have been considered theoretically. Configuration diagrams of oxygen and silicon DX centres have been calculated by density functional theory with hybrid functional, and peak energies of optical transitions of an electron from the DX-centres to deep acceptors have been estimated. Possible assignments of the experimental luminescence bands in AlN based on the calculations have been discussed.

Vibrational spectroscopic investigation and antibacterial activity studies on Trichloroisocyanuric acid

In the present work, a quantum chemical approach is followed to study the molecular geometry, vibrational spectra, thermodynamic and molecular electrostatic potential of the title compound. Experimental techniques of FTIR, FT-Raman and UV–Visible were used to study the vibrational and electronic spectrum. The complete vibrational band assignment has been made on the basis of PED distribution and the values are proposed. The thermodynamic properties were calculated at different temperatures and corresponding relations between the properties and temperature were also studied. The antibacterial activity of the title compound was examined against E. coli and other gram positive and gram negative bacteria’s by micro dilution method.

Experimental (Raman and IR) and computational (DFT, MP2) studies of conformational diversity of 1-chloromethyl-1-fluorosilacyclohexane

Since 1-chloromethyl-1-fluorosilacyclohexane is a newly synthesized molecular compound its structural parameters and conformational stability is unknown. Raman and infrared vibrational spectroscopy methods were employed for analysis of this molecule. IR spectra were recorded for both gas phase and liquid sample, whereas the Raman experiments were performed in the liquid state. Additionally, low temperature matrix isolation infrared spectra were recorded after isolating the molecule in argon and nitrogen matrices. For the assignment of the experimental spectral bands, theoretical DFT/B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ calculations were performed. From the calculations it was found that 1-chloromethyl-1-fluorosilacyclohexane may exist in twelve different conformational forms out of which the chair axial trans conformer is the most stable form. However, there are three more chair type conformers – equatorial trans, equatorial gauche and axial gauche that are stable enough to be observed in the experimental spectra.

Machine learning‐oriented resource allocation in C + L + S bands extended SDM–EONs

The enormous growth in the number of smartphones, internet usage, and internet of things applications require high data-rate transport platforms. Therefore, spectrally and spatially scalable core optical networks are essential. Moreover, the current generation, field existing networks, consume the conventional (C) band of the single-mode single-core fibres. The recent studies evidence that the increased traffic occupies the complete C band. To overcome this, the spectral and spatial expansion employing multicore (MC), multimode (MM), and multiband (MB, C + L + S) fibre-based spatial division multiplexing (SDM)–elastic optical network (EON) is a promising solution. However, dynamic traffic, complex networking with MC–MM–MB–SDM–EON requires dynamic network solutions. To accomplish this, the authors propose the machine learning (ML) oriented route, core, mode, band, and modulation format aware spectrum assignment. Such resource allocation (RA) reduces the impact of the physical layer impairments, inter core cross-talk, differential mode delay, and mode dependent losses. As per the author's best knowledge, ML-oriented RA for SDM–EON considering the aforementioned parameters is the first investigation. They propose several RA algorithms to reduce the total network cost with increased fibre capacity. Among all, priority-based RA comes out as an optimal solution.

Synthesis and molecular interaction of tung oil‐based anionic waterborne polyurethane dispersion

AbstractIn the present work, four types of anionic waterborne polyurethane dispersions (APUD) based on polytetramethylene ether glycol (PTMG) and two aliphatic diisocyanates, dicyclohexylmethane diisocyanate (HMDI) or isophorone diisocyanate (IPDI), were prepared by polymerization methods which for the first time controlled the location (soft or hard segment) of hydroxylated tung oil (HTO) incorporation into the final APUD. The resulting HTO‐containing APUD polymers (HTO‐APUDs) with postpolymerization crosslinking capability were characterized using FTIR, DMA, AFM and water imbibition methods, and compared to model compounds synthesized to have the same parts of chemical structural linkages for band assignment. A common PUD sample, as well as polypropylene oxide (PPG) with molecular weight similar to HTO (Mn = 400), was used to replace it for preparing control samples to highlight the role of long branched chains and conjugated double bonds in HTO. Based on the analysis of multiple H‐bond interactions, the relationship of HTO location in the APUD polymer structure to the soft/hard segment compatibility and the diisocyanate structure was further studied. This work is expected to provide basic data for properties regulation in practical applications by adjusting the chain and phase structure, as well as the intermolecular interactions, in these APUDs.

Spectral observation of agarwood by infrared spectroscopy: The differences of infected and normal Aquilaria microcarpa

Abstract. Adi DS, Hwang SW, Pramasari DA, Amin Y, Widyaningrum BA, Darmawan T, Septiana E, Dwianto W, Sugiyama J. 2020. Spectral observation of agarwood by infrared spectroscopy: The differences of infected and normal Aquilaria microcarpa. Biodiversitas 21: 2893-2899. This study was conducted to evaluate and to determine the potential spectral band assignments that influenced the differentiation of normal and infected agarwood of Aquilaria microcarpa using Fourier Transform Infrared Spectroscopy (FTIR) and Fourier Transform Near-Infrared Spectroscopy (FTNIR). The results showed that the differences in band intensity on FTIR were identified as C=O stretching (lignin), COO-stretching (hemicellulose), aromatic skeletal vibration (lignin), and C-H bending vibration. The increasing absorbances of infected agarwood were supposed as the change on the wood tissues due to the releasing resinous compound. The C-O bond (aromatic alkane) and stretching (ether), C-C stretching (aromatic alkane), and C-H bond (aromatic ring) which related to the scented fragrance of agarwood have appeared on the FTIR spectra. Multivariate analysis with principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA) of the second derivative NIR spectra at the wavenumber 8,000-4,000 cm-1 showed that normal and infected agarwood was successful to be separated. Discriminant model one-on-one classification exhibited good performances as the R2 performance (R2P) values was 0.99. There were eight major wood components which contributed to the separation based on NIR spectra, where lignin, hemicellulose, and xylans were the most valuable chemical compound.

Electronic structure and characterization of the spectra of trans/cis tautomers of urocanic acid isomers: A diagnostic tool

The gas-phase information of ionization on the fundamental properties of biological molecules is essential for understanding numerous biological phenomena, as it provides insight into the physicochemical origin of molecular properties. In this work, conformational and tautomerism analysis of urocanic acid (UA) were performed by two methods of B3LYP and M062X at 6-311++g (d,p) basis set for all structures in two isomers of cis/trans in the gas phase. Then, stable structures were selected to calculate the ionization potential. The symmetry-adapted-cluster configuration interaction (SAC-CI General-R) method was used for calculating ionization energies and the photoelectron spectra. The NBO calculations were performed to determine the contribution of different natural bonding orbitals to the canonical molecular orbitals involved in ionization processes, which was required for spectral band assignment. The results of NBO calculation indicated that the ionization bands corresponding to ionizations from orbitals localized the imidazole ring had a larger contribution to the ionization process than the CC and CO bands. The most important point about the ionization of all tautomers is the removal of an electron from the imidazole ring. Koopmans’ approximation is only applicable for describing the first lowest-energy orbital ionization (photoelectron band), and others may make a linear combination of HF determinations.