Computerized search system based on digitized infrared spectra

Summary A system for the digitization of infrared spectra and subsequent automatic generation, management and search of spectral data files is described. The older version of the search system was further developed and upgraded. In the present version, the user can constantly update not only the spectral files but also the inverted files of peak positions, needed during the search. The system was tested in routine industrial analysis and can be compared favourably with the existing commercialized IR search systems.

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Suchsystem für digitalisierte IR-Spektren mit Hilfe des Computers

Zusammenfassung Ein System wird beschrieben zur Digitalisierung von IR-Spektren und nachfolgender automatischer Aufstellung, Bearbeitung und Durchsuchung von Spektrendateien. Eine ältere Version des Systems wurde weiterentwikkelt und fortgeschrieben. Mit Hilfe der gegenwärtigen Entwicklungsstufe kann der Benutzer sowohl die Spektrendatei als auch die Umkehrdatei der Peakpositionen, die bei der Suche benötigt wird, laufend aktualisieren. Das System wurde in der technischen Routineanalyse getestet und ist den bestehenden kommerziellen IR-Suchsystemen durchaus ebenbürtig.

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A condensed version of the paper was presented in the poster session of the 2nd COBAC Conference, Munich, April     

Combination of analytical spectrometers and spectroscopic data bases

Most search systems receive input data through manual keyboards in remote terminals for searching spectroscopic data bases for candidate compounds corresponding to unknown samples, but manual input systems are slow, subject to human error and mentally fatiguing. This paper records preliminary attempts to transmit spectroscopie data (peak heights and positions) directly to the data base without manual input and to let the central computer retrieve the best-fitting data and transmit them to the ramote terminals. First the spectroscopie data were digitized, exact correspondence between the intensities and peak positions being maintained. Chart data were digitized automatically; tests were made for n.m.r. and i.r. data. Direct connexion of an infrared spectrometer to the data base was also tested. Error corrections were made during the transfer processes to ensure exact spectroscopic information. The data were also concentrated for brevity and minimization of error. Two re-transmission systems were tested. In the final step, peak positions and heights were extracted from the transferred data, and the results were used for the search of the i.r. data base. Performance tests showed a considerable degree of success.     

Computer identification of infrared spectra by correlation-based file searching

A new method for the computerized search and identification of infrared spectra has been developed and evaluated. Based on cross-correlation, the search system utilizes all spectral information in a digitized spectrum when it attempts to match an unknown spectrum to one in a small library of known spectra. To evaluate a spectral match, the search program calculates the cross-correlation function between the unknown and known (library) spectra which indicates their degree of similarity and allows library spectra to be ranked in order of probability of match to the unknown spectrum. In this study, several small infrared spectral libraries of structurally similar compounds were searched under conditions which examined the sensitivity of the search method to chemical and instrumental variations. Because the correlation technique is slower than conventional file-searching methods, it will probably find greatest use in the search of small collections of similar spectra or as a match-ranking procedure following preliminary selection by a faster search method.     

Negative chemical ionization and accurate mass measurement applications for a linked gas chromatography/Fourier transform infrared spectrometer/Fourier transform mass spectrometer

Summary The analytical utility of a linked GC/FTIR/ FTMS system operating in accurate mass and negative CI modes is demonstrated. In addition to the complementary information derived from IR and MS search results, accurate mass measurement data (average error of 4.2 ppm) is employed in the analysis of a seven component mixture. A post search filter uses accurate mass data to eliminate spectral search results with incorrect elemental compositions. An alternate positive ion EI and negative ion CI GC/IR/MS analysis is also performed on a mixture of substituted phenyl aldehydes and ketones. The reagent gas, ammonia, is introduced by pulsed valve thus minimizing crossover spectral contamination while maximizing spectral resolution. Proton abstraction by the amide produces an intense (M-1)^– for all compounds in the mixture. Molecular weight information from the negative CI data is used in a post search filter to improve the reliability of both IR and MS search results.

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Anwendung der negativen chemischen Ionisation und genauer Massenmessungen für ein gekoppeltes GC/FTIR/FTMS-System

Zusammenfassung Die analytische Anwendbarkeit eines gekoppelten GC/FTIR/FTMS-Systems mit akkurater Massenmessung und NCI-Betrieb wird dargestellt. Zusätzlich zu den komplementären Informationen aus IR- und MS- Bibliothekssuchen werden Daten aus akkuraten Massenmessungen (mittlerer Fehler 4.2 ppm) bei der Analyse einer Mischung aus sieben Komponenten mit herangezogen. Im Anschluß an die Bibliothekssuche eliminiert ein Filter mit Hilfe der akkuraten Massen Ergebnisse mit fehlerhafter Elementarzusammensetzung. Von einer Mischung aus substituierten Phenylaldehyden und -ketonen wird eine Analyse mit alternierender Registrierung von positiven EI- und negativen CI-Spektren durch ein GC/IR/-MS-System ausgeführt. Das Reaktandgas Ammoniak wird über ein gepulstes Ventil zugegeben, um bei maximaler spektraler Auflösung minimale Störung durch Verunreinigung zu erhalten. Durch Abstraktion eines Protons von der Amidfunktion werden von allen Komponenten der Mischung intensive (M-1)-Ionen gebildet. Molekulargewichtsinformationen aus dem NCI-Experiment werden als Filter verwendet, mit dem die Zuverlässigkeit des Suchens in IR- und MS-Datenbanken erhöht werden kann.

     

Hose — a novel substructure code

A novel system of substructure codes has been developed to characterize the spherical environment of single atoms and complete ring systems. The codes are generated automatically from topologically represented chemical structures and serve to describe structural entities corresponding to spectral parameters uniquely. Their hierarchical order permits desired substructures and the corresponding chemical shifts to be sought in inverted files generated from a larger data base, thereby facilitating the estimation of unknown spectra.     

The tetrazole–azide tautomerism of some nitrotetrazolo [1,5-a]pyridines studied by NMR, IR spectroscopy and molecular orbital calculations

The 6-nitro- and 8-nitro- groups in the tetrazolo[1,5-a]pyridine molecule exhibit completely different influences on the tetrazole–azide equilibrium. Introduction of the methyl-, nitro-, azido groups or a bromine atom in positions 5, 6, 7 or 8 of the nitrotetrazolopyridine produce changes in the equilibrium constants. Based on the IR spectra taken in the solid state, the tetrazole structure was assigned for almost all the compounds studied. Only one of them, 2,6-diazido-3-nitropyridine, exists in the diazido-form in the solid. The ¹H, ¹³C, ¹⁵N, and ¹⁷O NMR spectral parameters (coupling constants, chemical shifts) as well as ab initio molecular orbital calculations were used to describe the tetrazole–azide tautomerism in solutions. The differences in the NMR parameters between the neutral compound (6,8-dinitrotetrazolo[1,5-a]pyridine) and its σ-adducts are also included as data for distinguishing between both molecules.     

Benzindoles

The previously undescribed tetrahydro[4, 5]- and tetrahydro[6, 7]benzindoles and some of their derivatives were synthesized by Fischer cyclization of pyruvic acid 5- and 6-tetralinylhydrazones. A linear isomer — tetrahydro[5, 6]benzindole^–and its derivatives were obtained only in a mixture with tetrahydro[4, 5]-benzindole. The geometrical isomers of the pyruvic acid hydrazones were isolated and characterized. A method for the separation of the mixtures of 5- and 6-aminotetralins was developed. The structures of the isolated compounds were confirmed by the PMR and IR spectral data.See [1] for communication XIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 634–640, May, 1978.     

Structure of aqueous solutions of group IIIA metals perchlorates by near infrared spectroscopy

The state of water in aqueous solutions of group IIIA metal perchlorates at 25°C was studied by the IR spectroscopy in the range of 5400–7500 cm^?1. The optical density values of the solution measured at different wavelengths were combined in a matrix of experimental data of the uniform dimension. The matrices were chemometrically analyzed. A number, spectra, and concentration profiles of the spectral forms existing in the solution were determined. By the principal component method, the IR spectra of the studied systems are grouped into the mathematical clusters according to the nature of the cation-water interaction in the solution. The combined use of the infrared spectroscopy and chemometric analysis showed that the structural changes in the solution predicted by the generalized phenomenological model are due to the existence and interconversion of the spectral forms.     

A Description of Vibrational Modes in Hexaphyrins: Understanding the Aromaticity Reversal in the Lowest Triplet State

Aromaticity reversal in the lowest triplet state, or Baird's rule, has been postulated for the past few decades. Despite numerous theoretical works on aromaticity reversal, experimental study is still at a rudimentary stage. Herein, we investigate the aromaticity reversal in the lowest excited triplet state using a comparable set of [26]‐ and [28]hexaphyrins by femtosecond time‐resolved infrared (IR) spectroscopy. Compared to the relatively simple IR spectra of [26]bis(rhodium) hexaphyrin ( R26H ), those of [28]bis(rhodium) hexaphyrin ( R28H ) show complex IR spectra the region for the stretching modes of conjugated rings. Whereas time‐resolved IR spectra of R26H in the excited triplet state are dominated by excited state IR absorption peaks, while those of R28H largely show ground state IR bleaching peaks, reflecting the aromaticity reversal in the lowest triplet state. These contrasting IR spectral features serve as new experimental aromaticity indices for Baird's rule.     

Theoretical prediction of gas-phase infrared spectra of imidazo[1,2-a]pyrazinediones and imidazo[1,2-a]imidazo[1,2-d]pyrazinediones derived from glycine

Imidazo[1,2-a]pyrazine-3,6-diones and imidazo[1,2-a]imidazo[1,2-d]pyrazine-3,8-diones can be produced by pyrolysis of simple amino acids. While such bicyclic and tricyclic amidines were detected and characterized by IR spectroscopy for some alpha-substituted amino acids, the parent systems composed of glycine fragments are unknown up to now. IR spectra for five amidines derived from glycine were calculated by using different semi-empirical (PM3, AM1, MNDO and MINDO/3), HF, and hybrid DFT (B3LYP, B3P86 and B3PW91) methods in conjunction with 6-31G(d) basis set (for HF and DFT). Vibration frequencies in the experimental IR spectra were predicted based upon the B3LYP data, by correcting the calculated wavenumbers by a scaling factor of 0.959. The behavior of most characteristic bands (nu(CX), nu(NH), etc.) and their shifts with respect to such bands in the spectra of alanine and alpha-aminoisobutyric acid derivatives studied before, are discussed. Performance of the semi-empirical methods was tested, bearing in mind possible future needs for IR spectra predictions for larger molecular systems of similar chemical nature; the use of MINDO/3 and MNDO is recommended. A basis set effect on the B3LYP fundamental vibration frequencies for hexahydroimidazo[1,2-a]pyrazine-3,6-dione was studied by varying Pople basis sets from minimal STO-3G to 6-311++G(d, p). No significant improvements were found beyond the 6-31G(d) basis set, which thus can be recommended to predict IR spectra for the amidines and similar molecules.     

Structural characterization of flavonol di-O-glycosides from Farsetia aegyptia by electrospray ionization and collision-induced dissociation mass spectrometry

This study reports the application of mass spectrometric methods to characterize unknown flavonoids of the herb Farsetia aegyptia Turra (Crucifereae). High-performance liquid chromatography was performed in combination with UV-photodiode array detection (LC/UV-DAD) and electrospray ionization mass spectrometry (LC/ESI-MS) in both positive and negative ion modes. Collision-induced dissociation (CID) mass spectral data were obtained off-line by nanospray (nano-ESI) analysis, which provided a wealth of information and led to the structural proposal of the flavonol di-O-glycosides present in the herb extract. In addition to the mass spectral data, we also report NMR data for the major compound which allowed the completion of its structural elucidation. The Farsetia aegyptia Turra herb extract was found to contain three flavonol di-O-glycosides containing a monosaccharidic residue linked to the 3-O position and a disaccharidic residue linked to the 7-O position; the major compound was characterized as the new flavonoid, isorhamnetin 3-O-alpha-L-arabinoside 7-O-[beta-D-glucosyl-1 --> 2]-alpha(L)rhamnoside. Different types of CID spectra, i.e., low-energy [M+H]+, [M+Na]+ and [M--H]- spectra as well as high-energy [M+Na]+ spectra, were evaluated with respect to their utility to locate the O-linked saccharidic residues in flavonol di-O-glycosides and to determine the sequence in the disaccharidic part. In agreement with previously published data, the 3-O-glycosyl residue was more readily lost from the protonated molecule than the 7-O-glycosyl residue. The opposite behavior was noted for the fragmentation of the deprotonated and sodiated molecules. Radical ions were observed in the high-energy [M+Na]+ CID spectra which provided supporting information on the glycosylation positions.     

Hierarchically structured computer systems for analytical chemistry

For the Max-Planck-Institutes in Mülheim (Germany) a new centralized computer system has been designed and brought into operation in 1981. The system is built from two VAX 11/780 computers sharing peripheral resources. Experimental data from remote analytical instruments are gathered in real-time via satellite processors connected with coaxial cables and DMA-interfaces to the central computers. Several other small computer systems are transferring completed data files via asynchroneous serial lines.This centralized system is used for all kind of computer applications of the two institutes: for quantum chemical calculations, X-ray structure determinations, spectrometry and chromatography as well as for chemical literature search, text processing, administrative tasks, etc. The essential criteria for designing and using this or similar structured systems are discussed.

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Hierarchisch aufgebaute Rechnersysteme für die Analytik

     

Synthesis of Some Novel Thiazolo[3,2‐a]pyrimidine and Pyrimido[2,1‐b][1,3]thiazine Derivatives and their Antimicrobial Evaluation

A 2‐(2‐Mercapto‐4‐(4‐phenoxyphenyl)‐6‐(thiophen‐2‐yl)‐1,6‐dihydropyrimidin‐5‐yl) acetic acid was used as a reactive key precursor to design various pyrimidine derivatives such as thiazolo[3,2‐a]pyrimidines and pyrimido[2,1‐b][1,3]thiazines. The chemical structures of the newly synthesized products were confirmed by their elemental analyses and spectral data (IR, ¹H NMR, ¹³C NMR, and mass spectra). The antibacterial and antifungal activities of some of the synthesized products were also evaluated, and it was found that compounds 3, 5, 9 , and 11 exhibited potent activity against tested microorganisms in comparison with standard drugs.     

Dual-frequency 2D IR on interaction of weak and strong IR modes

Dual-frequency 2D IR heterodyne photon-echo spectroscopy of C[triple bond]N and C=O stretching vibrational modes in 2-cyanocoumarin is reported. We have shown that the interaction among these modes provides convenient and useful structural constraints for molecules. Implementation of two pulse sequences, 4, 4, and 6 microm and 6, 6, and 4 microm, allowed the clear determination of contributions caused by vibrational relaxation. Positive correlation between C[triple bond]N and C=O frequency distributions was observed in 2-cyanocoumarin. Because C[triple bond]N modes are highly localized and have frequencies in a spectral region with minimal water absorption, the C[triple bond]N/C=O interactions have a strong potential for use as structural reporters in proteins. In addition to CN/CO peaks, the cross-peaks responsible for the C[triple bond]N/C=C interaction are also observed in the 2D IR spectra, where C=C is a coumarin ring stretching mode. We have demonstrated that 2D IR spectroscopy can utilize interactions of strong IR modes with weak local modes as structural reporters.     

FT-IR and FT-Raman study of hydrogen bonding in p-alkylcalix[8]arenes

The FTIR and FT Raman spectra of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) were recorded. Analysis of IR spectra showed that the cyclic cooperative intramolecular hydrogen bond is realized in calix[8]arene. It was found that the strength of the cyclic cooperative intramolecular hydrogen bond in the series of alkyl derivatives of calix[8]arenes depends very little on the replacement of the p-tert-butyl groups by the more bulky isononyl group. From our data follows that the orientation of aromatic fragments in calixarene molecules depends on the type of alkyl substituent.An analysis of the changes in the IR spectra with heating and dissolution shows that the conformation of the “pleated-loop” is retained in p-tert-butylcalix[8]arene. It turned out that the intramolecular hydrogen bond is a “probe” of the conformation of calixarene molecules and IR spectroscopy is a unique method that allows one to follow the slightest nuances of changes in the H-bound system of these supermolecules.     

Storage, retrieval and analysis of infrared spectra

Summary A system for computer-aided storage, retrieval and analysis of fully digitized IR spectra is presented. The on-line spectra acquisition and the procedures of data reduction are described. The additional storage of the chemical structure and the corresponding substructure codes allows a direct evaluation of structural features on the basis of the identity of spectral behaviour. The analysis of the substructure codes is used to optimize the parameters of the matching factor. In several examples the applications of the system with respect to identification, structure and substructure elucidation as well as the different output possibilities are demonstrated.

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Speicherung, Wiederauffindung und Analyse von Infrarotspektren

Zusammenfassung Ein rechnerunterstütztes IR-Spektren-Suchsystem mit vollständig digitalisierten IR-Spektren wird vorgestellt. Die on-line Datenerfassung, die Übertragung der Spektren zum Großrechner und die verschiedenen Möglichkeiten der Datenreduktion für die weitere Verarbeitung werden beschrieben. Die zusätzliche Speicherung der chemischen Struktur sowie der entsprechenden Teilstrukturcodierungen ermöglicht eine direkte Ermittlung von strukturellen Eigenschaften aufgrund spektroskopischer Übereinstimmung. Die Auswertung der Häufigkeit der relevanten Teilstrukturen im Anschluß an einen Spektrensuchlauf mit bekannten Substanzen wird zur Optimierung der Parameter des Vergleichsfaktors benutzt. In verschiedenen Beispielen werden die Ergebnisse bei der Spektrenidentifizierung, der Struktur- und der Teilstrukturermittlung sowie die verschiedenen Möglichkeiten bei der Darstellung der Suchergebnisse aufgezeigt.

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Dedicated to Prof. Dr. Otto Westphal on occasion of his 70th birthday     

Structures and properties of 1,8,15,22-tetrasubstituted phthalocyaninato-lead complexes: the substitutional effect study based on density functional theory calculations

Density functional theory (DFT) and time-dependent DFT calculations were carried out to comparatively describe the molecular structures, molecular orbital energy gaps, atomic charges, infrared (IR) and Raman spectra, and UV-vis spectra of PbPc (1), PbPc(alpha-OC2H5)4 (2), and PbPc(alpha-OC5H11)4 (3) {Pc2- = dianion of phthalocyanine; [Pc(alpha-OC2H5)4]2- = dianion of 1,8,15,22-tetra-ethoxyphthalocyanine; [Pc(alpha-OC5H11)4]2- = dianion of 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine}. The calculated structural data of compounds 1 and 3 and the simulated IR and UV-vis spectra of 3 are compared with X-ray crystallography molecular structures and the experimental absorption spectra respectively to verify the performance of the B3LYP method and the LANL2DZ basis set. Substitution of bulky alkoxy groups at the nonperipheral positions of the phthalocyanine ring adds obvious effect to the molecular structure of phthalocyaninato lead compounds by deflecting the isoindole units in the direction that the isoindole units extends and distorting them in the C4 axis direction due to the steric hindrance. Both the calculated IR and UV-vis absorption spectra of 3 correspond well with the experimental results.     

A new derivative of 1,5-dihydropyrazolo[4,3-c][1,2,5]benzotriazepine

A new compound, 1,5-dihydro-3-methyl-7-nitro-propylpyrazolo[4,3-c][1,2,5]benzotriazepine, was synthesized by intramolecular cyclization of 5-amino-4-[(2-bromo-5-nitrophenyl) azo]-3-methyl-1-isopropylpyrazole, and it was established on the basis of the spectral data that the triazepine ring in the synthesized compound exists in two tautomeric forms — amino-azo- and hydrazone. The structure of the compound synthesized was confirmed by the data of the PMR, IR, electronic, and mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1136–1139, August, 1984.     

Synthesis and Antimicrobial Evaluation of Some New Spiroindolinone Derivatives

In an attempt to find a new class of antimicrobial agents, a series of spiroindolinone compounds containing pyridine, pyrimidine, benzopyrans, pyrido, naphtodiazepines, pyrazole, and isoxazole ring systems were prepared via the reaction of 3‐(2‐oxo‐2‐(3‐oxo‐3H‐benzo[f]chromen‐2‐yl)ethylidene)indolin‐2‐one ( 4 ) with an appropriate nucleophilic reagent. Newly synthesized compounds were characterized by elemental analysis and spectral data (IR, ¹H‐NMR, ¹³C‐NMR, and mass spectra). Representative compounds were tested and evaluated as antimicrobial agents.     

Information theory applied to feature selection of binary-coded infrared spectra for automated interpretation by retrieval of reference data

A method is described for feature selection from infrared spectra, intended for identification of organic compounds by computer-aided retrieval of reference data contained in small files. Complete discrimination of the binary-coded spectra is achieved by selecting a minimum number of spectral features; the information content is used as the selection criterion. The selection procedure is applied to five data sets (saturated and unsaturated hydrocarbons, alcohols, ethers and aldehydes/ketones) involving some 400 spectra. Each spectrum is uniquely coded by using about 10% of the 140 spectral features (binary-coded peak positions) available originally. For the intensity, a threshold of 50% appears to be applicable in some cases. For coding the frequency or wavelength parameter, wavenumbers (cm^-1) are preferred to wavelengths (mm). The method takes into account the a priori probabilities of spectral features and their correlations. Results of a retrieval program for a few “unknown” spectra are given.