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Propane-1,3-diaminium squarate dihydrate, C 3 H 12 N 2 2+ ·C 4 O 4 2- ·2H 2 O, results from the proton-transfer reaction of propane-1,3-di-amine with squaric acid and subsequent crystallization from aqueous medium. The title compound crystallizes in the tetra-gonal crystal system (space group P 4 bm ) with Z = 2. The squarate dianion belongs to the point group D 4 h and contains a crystallographic fourfold axis. The propane-1,3-diaminium dication exhibits a C 2 v -symmetric all- anti conformation and resides on a special position with mm 2 site symmetry. The orientation of the propane-1,3-diaminium ions makes the crystal structure polar in the c- axis direction. The solid-state supra-molecular structure features a triperiodic network of strong hydrogen bonds of the N-H⋯O and O-H⋯O types., (© Seidel and Kolev 2024.)

The crystal structure of 1,2,3,4-tetra-hydro-isoquinolin-2-ium (2 S ,3 S )-3-carb-oxy-2,3-di-hydroxy-propano-ate monohydrate, C 9 H 12 N + ·C 4 H 5 O 6 - ·H 2 O, at 115 K shows ortho-rhom-bic symmetry (space group P 2 1 2 1 2 1 ). The hydrogen tartrate anions and solvent water mol-ecules form an intricate diperiodic O-H⋯O hydrogen-bond network parallel to (001). The tetra-hydro-isoquinolinium cations are tethered to the anionic hydrogen-bonded layers through N-H⋯O hydrogen bonds. The crystal packing in the third direction is achieved through van der Waals contacts between the hydro-carbon tails of the tetra-hydro-isoquinolinium cations, resulting in hydro-phobic and hydro-philic regions in the crystal structure., (© Seidel and Kolev 2024.)

Two previously synthesized styrylquinolinium dyes, namely ( E )-1-butyl-4-(4-(dimethylamino)styryl)quinolinium iodide ( D36 ) and ( E )-1-butyl-4-(4-hydroxystyryl)quinolinium iodide ( D34 ), were compared in terms of their properties by single-crystal X-ray diffraction (XRD), Hirshfeld surface analysis, Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), fluorescence, and ultraviolet-visible (UV-Vis) spectroscopy, and 1 H- and 13 C-NMR methods. Both dyes D36 and D34 crystallized in the triclinic and monoclinic systems in the centrosymmetric space groups P -1 and P 2 1 /n , respectively. The unit cell of D36 contains two molecules of the dye, participating in weak intermolecular interactions, whereas that of D34 contains four formula units. The phenolic hydroxy group of D34 participates in the formation of a hydrogen bond with the iodide anion. The 4-styrylquinolinium moieties of the cationic dye molecules are nearly planar. The dihedral angle between the mean planes through the ten-membered quinolinium system and the benzene ring is 7.5° in D36 and 5.9(1)° in D34 . The structural parameters planarity and bond length alternation (BLA) are discussed, which are important for the evaluation of the first hyperpolarizability β at the molecular level, even in a centrosymmetric crystal. The UV-visible spectra of the dyes in 14 solvents of different polarities were investigated. The reversible solvatochromic behavior of the dyes is demonstrated experimentally and compared with known "binuclear dyes" by evaluating the Rezende model. Dye D36 does not fluoresce, and D34 has a very low emission in the solvents tested., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Pyridin-4-ylmethanaminium perchlorate monohydrate (synonym: 4-picolyl-ammonium perchlorate monohydrate), C 6 H 9 N 2 + ·ClO 4 - ·H 2 O, crystallizes in the monoclinic system (space group P 2 1 / n ) with the asymmetric unit comprising two formula units ( Z ' = 2). All mol-ecular entities are located on general positions. The two crystallographically distinct 4-picolyl-ammonium cations exhibit different conformations. The two unique perchlorate anions are non-disordered, showing an r.m.s. deviation of 0.011 Å from mol-ecular T d symmetry. The supra-molecular structure in the solid state features an intricate tri-periodic network of N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds., (© Seidel and Kolev 2023.)

A new stilbazolium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide monohydrate (DANSQI) having enlarged π-conjugated system was synthesized and characterized by X-ray diffraction, IR, Raman, UV-Vis, Fluorescence, (1)H- and (13)C NMR spectroscopy. Quantum chemical calculations were performed to obtain electronic structure and vibrational data, using DFT. The crystals are monoclinic, space group P21/n, with a=8.0751(14), b=25.839(4), c=10.9031(15) Å, V=2141.4(6) Å(3), and Z=4 (at 300(2) K). The unit cell contains four molecules of the dye, participating in weak intermolecular interactions. The cation is nearly flat with a deviation of the planarity of 5.08 (1)°. The dye investigated is the first stilbazolium iodide containing water molecule in the solid state therefore the N-dimethylamino group declines significantly from planarity, as indicated by C13N1C2C3 torsion angle of 16.08°. The dye studied shows solvatochromism of 84 nm in visible region and very large Stokes shift up to 253 nm. The intensity of fluorescence bands strongly depends on solvent polarity., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The title compound, 2-(phenylethyl)ammonium hydrogensquarate hemihydrate, was synthesized and structurally and spectroscopically characterized by a single crystal X-ray diffraction and solid-state polarized IR spectroscopy of oriented colloids in a nematic host. The crystal structure consists of two crystallographically independent 2-(phenylethyl)ammonium cations, joined in a 2D hydrogen-bonded network with hydrogensquarate anions and solvent water molecules. Surprisingly, the crystallographically non-equivalent cations exhibit differing pseudo T and G trans configurations.

The novel 3-phenylpyridinium hydrogensquarate (1) has been synthesized and its structure and properties are elucidated spectroscopically, thermally and structurally, using single crystal X-ray diffraction, linear-polarized solid-state IR-spectroscopy, UV-spectroscopy, TGA, DSC, DTA and ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectrum. 3-Phenylpyridinium hydrogensquarate, crystallizes in the space group P-1 and the ions in the unit cell are joined into layers by intermolecular NH...O=C((Sq)) bonds with bond lengths of 2.625 and 2.626 A, respectively. Hydrogentartarates form dimers by strong O=COH...OCO interactions (2.499 A)., (Copyright 2009 Elsevier B.V. All rights reserved.)

Method of linear polarized vibrational (both IR- and Raman) spectroscopy of oriented colloids in nematic host is applied on N-acetyl-L-cysteine, L-cysteine, L-cystine and L-ascorbic acid with a view to obtain experimental bands assignment and local structural elucidation in solid-state. Structural results are compared with available crystallographic data for all of the systems studied. Scopes and limitations of the polarized method are shown. Discussion on the correlation between polarized spectroscopic data and the space group type as well as the number of the molecules in the unit cell (Z) is performed. Compounds with monoclinic space group P2(1), containing Z = 1 (N-acetyl-L-cysteine) and 2 (L-cysteine and L-ascorbic acid) are elucidated. One of the rare for organic molecules, hexagonal P6(1)22 space group and Z = 6 (L: -cystine) is also elucidated. Experimental assignment of the characteristics frequencies is obtained, explaining the typical for the crystals Fermi-resonance, Fermy-Davydov and Davydov splitting effects. For first time in the literature we are reported the orientation of the solid-mixture in nematic host, using the trade product ACC (Hexal, Germany), containing mainly N-acetyl-L-cysteine and L-ascorbic acid. Quantitative IR-spectroscopic approach for determination of solid mixtures is presented as well. The intensity ratio between 1,716 cm(-1) (characteristic for N-acetyl-L-cysteine) and 990 cm(-1), (attributed N-acethyl-cysteine and vitamin C) is used. Linear regression analysis between content and the peak ratio data for ten solid-binary mixtures, leads to straight-line plot y = 1.08(2) (+/-0.04(9)) + (-0.11(4) +/- 0.01(1))x, where x = 1/X ( i ). Factor r of 0.9641 and a reliability of 98.85% are obtained. The analysis of ACC 200 (Hexal, Germany) show that the IR measurements leads to standard deviation of 0.010 and 0.011 at P about 0.0500 for the systems and a confidence of >98.77(1)%.

This mini review deals with the modern aspects of the spectroscopy and structural elucidation of amino acid derivatives and small biologically active compounds. Free peptide bond rotation in these systems yields various conformers, which possess differing biological activities. Another phenomenon is the intermolecular or intramolecular stacking observed in aromatic small peptides. Specifically, the main aim is to illustrate the successful application of the "complex tool", consisting of a combination of the theoretical approximation methods with experimental linear polarized infrared (IR-LD) and/or Raman spectroscopy of oriented colloid suspensions in a nematic host. The possibilities and limitations of the approach for detailed vibrational assignment and structural elucidation of small peptides are discussed. Having in mind that physical and chemical properties of these systems can be precisely calculated by means of ab initio and DFT methods at Hartee-Fock, MP2 and B3LYP level of theory, varying basis sets, the results obtained allow a precise assignment of many vibrational bands to the corresponding normal modes, electronic structures and conformational state. The validity of the conclusions about the structure or vibrational properties of these systems have been supported, compared and/or additionally proved by the results from independent physical methods. In this respect (1)H and (13)C-NMR, single crystal X-ray diffraction, HPLC tandem mass spectrometry as well as thermal methods are all employed. A well ordered crystal must first be grown in order to determine the molecular structure by the absolute method of single crystal X-ray diffraction. Although the 3D structures of peptides have been determined over the past decades, peptide crystallization is still a major obstacle to X-ray diffraction work, the presence of chiral centre/s makes for this difficulty. For this reason the "complex tool" presented can be regarded as an alternative method for obtaining of structural information in the solid-state. It is obviously that only absolute crystallographic method can yield geometric parameters, bond lengths and angles, but the spectroscopic method presented can provide information about the dihedral angles for cis- and trans-configurated amide groups, mutual disposition of the aromatic fragments in peptides. Its validity is illustrated by comparing the theoretical and spectroscopic results obtained with available crystallographic data. The mini review can serve as a useful source of information not only for specialists in IR spectroscopy but, also, for other scientists, working in the field of structural analysis of amino acid derivatives and other small biologically active systems.

The hydrogensquarate [LeuNH(2)] (HSq) of L-leucinamide has been synthesized and its structure has been determined by single crystal X-ray diffraction. A three dimensional network is formed by hydrogen bonds with participation of the O=C-NH(2) function, the hydrogensquarate ion and the N(+)H(3) group [NH(2)...O=C((Sq)) (2.840 and 2.749 A), ((Sq))OH...O=C(NH(2)) (2.618 A), NH(3) (+)...O=C((Sq)) (3.246, 2.804 and 2.823 A)], respectively. A theoretical approximation of the electronic structure was carried out by means of ab initio UMP2 and MP2 level of theory at the 6-311++G** basis set. The IR-spectroscopic assignment in the solid-phase was obtained by linear-polarized IR-spectroscopy of oriented samples as colloid suspensions in a nematic host and application of the reducing-difference procedure for the interpretation of polarized IR-spectra.

The crystal structure of the title compound, C16H19N3, comprises neutral molecules of a dipolar Schiff base chromophore. A density functional theory (DFT) optimized structure at the B3LYP/6-31G(d) level is compared with the molecular structure in the solid state. The compound crystallizes in the noncentrosymmetric space group Pna2(1) with a herring-bone packing motif and is therefore a potential candidate for nonlinear optical effects in the bulk.

We report the synthesis, spectroscopic and structural elucidation of two prolinamide derivatives of squaric acid, i.e. prolinamide ester amide of squaric acid ethyl ester (1) and prolinamide diamide of squaric acid dihydrate (2). Both compounds crystallize in non-centrosymmetric space groups, monoclinic P2(1) (1) and orthorhombic P2(1)2(1)2(1) (2), respectively. For first time in the literature the crystal structure of homodiamide of amino acid amide of squaric acid is reported. The data for heterodiamides is also absent. Supramolecular zig-zag chains by hydrogen bonds of H(2)N-C=O ..., HNH (3.020 A) and HNH ..., OC((S(q))) (2.972 A) types with the participation of amide and squaric acid (S(q)) fragments, -CO=NH(2) and O=C((S(q))) are refined in (1). A helix supramolecular structure is formed in (2) by moderate intermolecular HNH ... O=C(NH(2)) hydrogen bond with length of 2.947A. The two crystallographical non-equivalent water molecules stabilized the helix by interactions of types HOH...OC((Sq)) (2.917A), HOH...O=C(NH(2)) (2.899A), H(2)O...NH(2)(C=O) (2.972A), respectively. Optical and magnetic properties are investigated with a view to explain the correlation structure-properties of the newly synthesized molecules.

The IR-spectroscopic properties of three esters of 1-coumarinylbenzylphosphonic acid are elucidated both in solution and in solid-state. Linear-polarized IR-spectroscopy of oriented colloid suspensions in nematic host is used for experimental IR-characteristic band assignment in solid-state. Theoretical quantum chemical DFT calculations at B3LYP level of theory and 6-31++G** basis set are carried. Theoretical electronic structure and vibrational properties of compounds studied are discussed.

Synthesis, isolation, spectroscopic and structural elucidation of tyrosinamide hydrogensquarate monohydrate (I) is reported on the basis of quantum chemical DFT calculations, vibrational analysis and experimental linear-polarized IR-spectroscopy in solid state. These data are compared with those obtained using single crystal X-ray diffraction, which show that the molecules of (I) in the unit cell formed 3D network through moderate intermolecular (Tyr)OH...O = C(Sq) (2.727 A), O=C-NH2...OH(Tyr) (2.991 A), O=C-NH2...OH(Sq) (2.988 A), O=C-NH2...O=C-NH2 (3.068 A), N+H3...O=C(Sq) (2.737, 2.953, 2.954 A), OH2...O=C(Sq) (2.839 A) and (Sq)OH...OH2 (2.607 A) hydrogen bonds. The relationship between the structure and spectroscopic properties is studied.

The synthesis, isolation, spectroscopic and structural elucidation of sympathomimetic amine, tyramine dihydrogenphosphate are of interest due to its biological activity and the establishing correlation between spectroscopic properties and structure. The complex approach for investigation included single crystal X-ray diffraction, new technique in linear-polarized IR-spectroscopy in solid state and quantum chemical calculations with a view to predict the electronic structure and vibrational data of interacting species in entitled compound, the correlation structure-spectroscopic properties as well as the influence of intermolecular interaction on IR-characteristic bands are carried out.

Structure, magnetic and optical properties of tetraphenylborate salts of 2,5-[1-methyl-4-[2-(4-hydroxyphenyl)ethenyl]piridinium]-propane and butane are performed in gas and condense phase by means of solution and solid-state conventional and linear-polarized IR-spectroscopy of oriented colloids in nematic liquid crystal suspension, UV-vis and fluorescence methods, HPLC tandem ESI mess spectrometry (MS/MS), (1)H, (13)C and (1)H-(1)H COSY NMR, TGV and DSC methods. Quantum chemical DFT calculations are used for performing of the structures, optical and nonlinear optical properties of the studied compounds.

Spectroscopic and structural elucidation of the peptides L-Valyl-L-Prolyl-L-Proline (1) and L-Isoleucyl-L-Prolyl-L-Proline (2) are reported on the basis of experimental linear-polarized IR-spectroscopy in solid-state, 1H-NMR data and DFT. Curiously, the experimental data shown that both peptides stabilized in solution and in solid-state neutral H2N-R-COOH form. Conformational analysis made, shown two strong intramolecular NH2-O=C-N(Amide) and O=C-OH-NH2 hydrogen bonds with lengths of 2.979 A and 2.475 A in (1) and 2.599 A and 2.507 A in (2) respectively. The presence of the Pro-Pro fold resulted to strong steric effect leading to the stabilization of free COOH and NH2 groups. The Erel values of zwitterion form are significant higher than the neutral forms with a difference of 1.2 and 0.9 kJ/mol. The manner of interaction of the peptides with angiotensin-I converting enzyme is proposed.

Tyrammonium 4-nitrophthalate has been synthesized and its structural and spectroscopic properties elucidated by single-crystal X-ray diffraction, solid-state polarized IR-spectroscopy of oriented colloids in a nematic host, HPLC with tandem mass spectrometry (HPLC ESI-MSMS), and TGV and DSC methods. The compound crystallizes in the monoclinic P2(1)/c space group and its structure consists of a 3D network of molecules joined by intermolecular interactions with the participation of cations, anions and two solvent molecules. The tyrammonium cation adopts a T trans configuration with corresponding angles of phi (1) = 76.0(4) degrees, phi (2 )= 54.8(1) degrees and phi (3) = 63.4(1) degrees, respectively. In the 4-nitrophthalate anion, the COO(-) and COOH groups are turned off the plane of the benzene ring at angles of tau (1) = 88.1(5) degrees and tau (2)= 22.1(7) degrees, respectively.

Structural and spectroscopic elucidation of merocyanine dye, 2,5-[1-metyl-4-[2-(4-hydroxyphenyl)ethenyl)]piridinium]-hexane tetraphenylborate, is performed in gas and condense phase by means of solution and solid-state conventional and linear-polarized IR-spectroscopy of oriented colloids in nematic liquid crystal suspension, UV-vis and fluorescence methods, HPLC MS/MS tandem and ESI mass spectrometry, (1)H, (13)C and (1)H-(1)H COSY NMR, TGV and DSC methods. Quantum chemical DFT calculations are performed for structural optimization and spectroscopic properties prediction.

The linear-dichroic infrared (IR-LD) spectroscopy of oriented solid samples as suspension in nematic liquid crystal have been carried out for experimental IR-band assignment and structural information of 2-{5,5-dimethyl-3-[2-(2,4,6-trimethoxyphenyl)vinyl]cyclohex-2-enylidene} malononitrile polymorphs. The last data have been compared with known crystallographic ones, thus determining the validity of IR-LD spectral conclusions as well as its possibility to determination of Davydov's splitting effect and separation of pairs of maxima corresponding to non-equivalent molecules included in the unit cell of given compound. The experimental structural and spectroscopic data in our case are supported with theoretical DFT ones, obtaining both the electronic structure and vibrational frequencies in gas phase.

A distortion of the aromatic character and stabilization of the imino-form as a result of the protonation of 4-dimethylaminopyridine was established by IR-, UV- and 1H NMR-spectral analysis of 4-diaminopyridinium hydrogensquarate. Quantum chemical calculations were carried out at MP2 and B3LYP levels of theory and a 6-311++G** basis set with a view to determining the changes in geometrical parameters and IR-spectroscopic characteristics resulting from Npy protonation. Linear-dichroic IR-spectroscopy coupled with the orientation techniques of solid samples as liquid crystal suspensions and melted solid polycrystalline films was applied for the identification of the IR-bands, characteristic for the structural fragments of the neutral and imino-form of the pyridine derivative. The spectral results were compared with the structure, obtained by a single crystal X-ray analysis. The salt contains dimmers of hydrogensquarate anions and Npy protonated cations of which the former are stabilized by strong intermolecular OH...O interactions (2.552 angstroms and 143.1(2) degrees). The 4-diaminopyridinium cation interacts with the anion through moderate NH...O bonds (2.729 angstroms and 165.0(0) degrees ). Individual cations are pi-pi stacked with their neighbors at a distance of 3.406 angstroms.

Counterions affect on the substructures formation in the case of the merocyanine dye, 1-methyl-4-[2-(4-hydroxyphenyl)ethenyl)]piridinium] hydrogensquarate both in gas and condense phase. Spectroscopically and structural elucidation of these aggregates have been performed, using solid-state conventional and linear-polarized IR-spectroscopy of oriented colloids as a nematic liquid crystal suspension, UV-vis spectroscopy, HPLC tandem ESI mass spectrometry, 1H and 13C NMR, TGV and DSC. Quantum chemical DFT calculations have been carried out as well. Experimental and theoretical data are compared with analogous ones of corresponding iodide salt of dye studied.

Quantitative IR- and Raman spectroscopic determinations of four cephalosporin antibiotics in six solid binary mixtures have been conducted. This is a new approach for spectroscopic determination of these antibiotics, since the corresponding quantitative analysis in solution only has been reported so far. The correlation coefficient r2 was found to be in the confidence intervals within 99.32-99.88% and 99.90-95.54% for the systems under study by using the absorption ratios of the characteristic bands at 800 cm(-1) and 721 cm(-1) present in the IR- and Raman spectra of the antibiotic compounds cephalexin, cephalotin, cephaloglycin and cephamandole, respectively. Solid-state linear dichroic infrared (IR-LD) spectral analysis of the solid mixtures was carried out in order to obtain experimental IR-spectroscopic assignment of the compounds studied. Independent high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis was performed for the validation of the vibrational spectroscopic data. The application of this instrumental analytical tool for the analysis of 10 tablets of the commercial products Cefamandole and Cefalotin (Actavis) was also studied.

In the title compound, C(18)H(22)N(2)O(4), the dihedral angle between the pyrrolyl and quinolinyl fragments is 68.97 (2)°. Two non-classical intra-molecular C-H⋯O hydrogen bonds stabilize the mol-ecular geometry. In the crystal structure, mol-ecules form infinite chains via moderate inter-molecular N-H⋯O(CH(3)) hydrogen bonds.

The novel hydrogensquarate salt of 4-cyanopyridine was synthesized, and its structure and properties were elucidated in detail spectroscopically, thermally, and structurally, using single-crystal X-ray diffraction, linear-polarized solid-state IR spectroscopy, UV spectroscopy, TGA, DSC, DTA, and positive and negative ESI MS as well as 1H and 13C NMR methods. Quantum chemical methods were used to calculate the electronic structure, vibrational data, and electronic spectra. 4-Cyanopyridinium hydrogensquarate monohydrate crystallizes in the space group P and exhibits a layered structure with molecules linked by intermolecular NH...O(HSq-) (2.651 A) and HOH...O(HSq-) (2.792 and 2.563 A) hydrogen bonds with participation of cations, anions, and the solvent molecule. The formation of stable layers of the type (2HSq-.2H2O)n and the observation of a red color in the solid state is discussed. The optical and magnetic properties were elucidated in comparison to the data for neutral 4-cyanopyridine as well as its four known salts.

3-Ethylamino-2-(4-nitro-benzoyl)-but-2-enoic acid phenylamide is synthesized, isolated, spectroscopical and structural characterized by means of linear-polarized IR-spectroscopy (IR-LD) of oriented solids as a colloidal suspension in nematic liquid crystal. The experimental IR-band assignment and structural information are supported by quantum chemical calculations at MP2 and B3LYP level of theory and 6-311++G** basis set. The geometry is characterized by two inramolecular hydrogen bonds of NH...O=C with bond lengths of 2.589 and 3.449 angstroms. The NHO angles are 142.1(3) degrees and 125.8(4) degrees , respectively. A transoide configuration of amide fragments is predicted with a torsion NH-C=O angle of 150.6 degrees . Phenyl fragments are mutually perpendicular oriented closing an angle of 92.6 degrees .

Quantitative infrared (IR) and Raman spectroscopic approach for determination of phenacetin (Phen) and salophen (Salo) in binary solid mixtures with caffeine: phenacetin/caffeine (System 1) and salophen/caffeine (System 2) is presented. Absorbance ratios of 746 cm(-1) or 721 cm(-1) peaks (characteristic for each of determined compounds in the Systems 1 and 2) to 1509 cm(-1) and 1616 cm(-1) (attributed to Phen and Salo, respectively) were used. The IR spectroscopy gives confidence of 98.9% (System 1) and 98.3% (System 2), while the Raman spectroscopic data are with slightly higher confidence of 99.1% for both systems. The limits of detection for the compounds studied were 0.013 and 0.012 mole fraction for IR and Raman methods, respectively. Solid-state linear dichroic infrared (IR-LD) spectral analysis of solid mixtures was carried out with a view to obtaining experimental IR spectroscopic assignment of the characteristic IR bands of both determined compounds. The orientation technique as a nematic liquid crystal suspension was used, combined with the so-called reducing-difference procedure for polarized spectra interpretation. The possibility for obtaining supramolecular stereo structural information for Phen and Salo by comparing spectroscopic and crystallographic data has also been shown. An independent high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis was performed for comparison and validation of vibrational spectroscopy data. Applications to 10 tablets of commercial products APC and Sedalgin are given.

The IR-spectroscopic and structural elucidation of tetrapeptide glycyl-(L)-prolyl-glycyl-glycine and its hydrogensquarate was performed by employing linear-polarized IR-spectroscopy of oriented colloid suspensions in nematic host as well as mass spectrometry. Quantum-chemical ab initio calculations were carried out in order to evaluate both the electronic structure and optical properties of the compound studied.

L-Tyrosine-containing dipeptides valyl-tyrosine (H-Val-Tyr-OH) and tyrosyl-alanine (H-Tyr-Ala-OH) are characterized structurally by means of quantum chemical ab initio calculations and solid-state linear-dichroic infrared (IR-LD) spectroscopy. The IR-characteristic bands are assigned by application of reducing-difference procedure for polarized IR-spectra interpretation. Infrared data obtained are supported as well by the made vibrational analysis. The structures of both peptides are predicted on the basis of conformational analysis and structural information, obtained by the shown IR-spectroscopic tool.

2-amino-4-nitroaniline crystallizes in a noncentrosymmetric space group, which gives it significant potential for second-order nonlinear optical properties (NLO) in the bulk. Crystallographic and linear-polarized IR-spectrocopic data in the solid state unambiguously confirm a quinoide-like structure in the ground state in contrast to UV and theoretical data, which indicate an aromatic one for the excited state. UV-vis spectral elucidations in solutions with different polarities indicate a significant charge-transfer band with shifts of up to 100 nm, corresponding to a large value for the molecular first hyperpolarizability. Calculations of the UV- and IR-spectroscopic properties confirm the stabilization of the quinoide-like structure in the ground state, as well as the theoretically predicted NLO properties at the molecular level and provide a value of beta(tot), which is some 3.6 times higher than the analogous parameter for p-nitroaniline, a classical compound with experimentally confirmed NLO properties.

By means of IR-LD spectroscopy of oriented as suspension in nematic liquid crystal solids, a detailed IR-bands assignment and a stereo-structural prediction of codeine, codeinone and N-norcodeine have been carried out. The data are compared with known crystallographic ones of codeine and codeinone obtained by single crystal X-ray diffraction.

The hydrogensquarates of glycine-containing tripeptides glycylglycylglycine (H-Gly-Gly-Gly-OH), glycylglycylmethionine (H-Gly-Gly-Met-OH), and methionylglycylglycine (H-Met-Gly-Gly-OH) have been characterized structurally. Quantum chemical ab initio calculations, solid-state linear-dichroic infrared (IR-LD) spectroscopy, 1H and 13C NMR data, ESI-MS, HPLC-MS/MS, TGV, and DSC methods were employed. The structures consist in a positively charged peptide moiety and a negative hydrogensquarate anion (HSq), stabilized by strong intermolecular hydrogen bonds., ((c) 2006 Wiley Periodicals, Inc.)

Structural prediction and IR-characteristic bands assignment of arginine-containing tri- and tetrapeptides glycyl-glycyl-arginine (GGArg) and glycyl-glycyl-arginyl-alanine (GGArgAla) have been carried out, using linear-dichroic infrared (IR-LD) spectroscopy of oriented solid-samples in a nematic liquid crystal suspension. Spectroscopic data have been supported with ab initio analysis (Hartree-Fock level of theory and 6-31++G** basis set). Predicted geometry parameters have been compared with known crystallographic ones of similar peptides, indicating a good correlation., (Copyright 2006 Wiley Periodicals, Inc.)

As part of an investigation on the coordination ability of peptides, structural analyses of the solid di-, tri, and tetrapeptides glycyl-glycine (GG), glycyl-glycyl-glycine (GGG), glycyl-glycyl-glycyl-glycine (GGGG), and their protonated hydrochlorides glycyl-glycine.HCl (GGH), glycyl-glycyl-glycine.HCl (GGGH), and glycyl-glycyl-glycyl-glycine.HCl (GGGGH) have been carried out. The quantum chemical calculations (Hartree-Fock/6-31++G**) and linear-dichroic infrared (IR-LD) spectroscopy predict a near to linear structure of the pure ligands, but the experimental IR-LD data are in accordance with a cross-linked disposition of amide fragments in the protonated forms., (Copyright 2006 Wiley Periodicals, Inc.)

Cations and anions of the title compound {systematic name: 1-[4-(aminocarbonyl)butyl]guanidinium bis(hydrogensquarate)}, C6H17N5O2+.2C4HO4(-), are connected into a three-dimensional network by intermolecular N-H...O hydrogen bonds between the L-argininamidium ammonium, amide and guanidinium functions and the hydrogensquarate carbonyl O atoms. The independent hydrogensquarate monoanions are linked into dimers by pairs of O-H...O' hydrogen bonds.

The title compound, C16H9NO4, also known as the 3-benzoylpyridinium betaine of squaric acid, exhibits a dipolar electronic ground-state structure with a positively charged pyridinium fragment and a negatively charged squarate moiety. In the molecule, the two aromatic rings are twisted by 56.03 (2) degrees relative to one another. The three-dimensional packing of the molecules is stabilized by C-H...O short contacts.

Infrared (4000-100 cm(-1)) spectra of aminomethyl-dimethyl-phosphine oxide and 15N-aminomethyl-dimethyl-phosphine oxide have been measured. Geometric parameters (bond distances and angles), net electronic charges and vibrational spectroscopic data of both compounds calculated at various levels of theory (B3LYP/6-31G* and Moeller-Plesset perturbational theory (MP2)/6-31G*) are reported. The theoretical spectral results are discussed mainly in terms of comparison with infrared (4000-100 cm(-1)) spectral data. Better coincidence was achieved with the frequencies calculated at the MP2/6-31G* level: the standard deviation is 16 cm(-1). The calculated isotopic frequency shifts, induced by the 15N labeling, are in good accordance with the measured ones. Complete vibrational assignment is made with the help of MP2 force field calculations. Data obtained here are used to reassign some of the vibrational frequencies.

The FTIR spectra (4000-100 cm(-1)) and Raman spectra (3500-30 cm(-1)) of 2-[5,5-dimethyl-3-(2-phenyl-vinil)-cyclohex-2-enylidene]-malononitrile in solid state were measured. In addition, the structure and harmonic vibrational frequencies of this molecule were theoretically evaluated using B3LYP density functional methods. The computed vibrational frequencies are used to determine the types of molecular motions associated with each of the experimental bands observed. Bond length alternation (BLA) was established. Comparison with the experimental spectra provides important information about the ability of this computational method to describe the vibrational modes in this type of "push-pull" systems with potential non-linear optical applications.

The FTIR spectra of pyridinium-betaine of squaric acid in 4000-100 cm(-1) frequency region in solid state were measured. In addition, the structure and harmonic vibrational frequencies of this molecule were theoretically evaluated using restricted Hartree-Fock and B3LYP density functional methods. The computed vibrational frequencies are used to determine the types of molecular motions associated with each of the experimental bands observed. Comparison with the experimental spectra provides important information about the ability of these computational methods to describe the vibrational modes in these highly polar strained ring compounds.

Geometry and vibrational spectroscopic data of benzil-d0 benzil-d10 and benzil-18O calculated at various levels of theory (RHF/6-31G*, B3LYP/6-31G*, BLYP/6-31G*) are reported. The theoretical results are discussed mainly in terms of the comparisons with infrared (4000-100 cm(-1)) and Raman (4000-50 cm(-1)) spectral data. The calculated isotopic frequency shifts, induced by the 18O- and d10-labeling, are in a good agreement with the measured values. A complete vibrational assignment was made with the help of ab initio force field calculations. The data thus obtained were used for reassigning some vibrational frequencies. The results of the optimized molecular structure obtained on the basis of RHF and the DFT calculations are presented and compared with the experimental X-ray diffraction for the benzil-d0 single crystal. It turns out that the best structural parameters are predicted by the B3LYP/6-31G* method.