The fluorescence spectrum of HCN (A≈1 A′' → X≈1 Σ+) using ArF laser excitation

The fluorescence spectrum of HCN A≈(¹A′') → X≈(¹Σ⁺) is reported using a tuned ArF laser as the excitation source. Assignments for the fluorescence spectra from two upper state vibrational levels are given. Franck—Condon factors for the absorption and fluorescence spectra are calculated. A laser-induced fluorescence spectrum is given which agrees with published absorption spectra of HCN.     

Catalytic reaction of methyl diazoacetate with silylated enynes

Factors affecting the regioselectivity of the catalytic reaction of methyl diatoacetate with 1-trimethylsilylalkene-1-ynes have been revealed. Conditions for selective cyclopropanation of the double bond in 1-trimethylsilylbut-3-ene-1-yne and 1-trimethylsilyl-3-methylbut-3-ene-1-yne in the presence of Rh₂(OAc)₄ have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1248–1252, July, 1993.The authors express their gratitude to B. I. Ugrak and D. E. Dmitriev for help in recording and interpreting the NMR spectra, E. G. Baskir and V. A. Korolyov for taking the chromato-IR spectra and A. A. Kutin for recording the chromato-mass spectra.     

Measuring molecular force fields: Terahertz,inelastic neutron scattering,Raman, FTIR,DFT, and BOMD molecular dynamics of solid l-serine

A vibrational analysis of polycrystalline l-serine is provided using experimental terahertz, FTIR, Raman and inelastic neutron scattering (INS) spectra, calculated INS spectra – and Born–Oppenheimer molecular dynamics (BOMD) simulations from which the power spectra for the electronegative elements are compared to the THz spectra. Corrections are made to density functional theory (DFT) calculations for van der Waals interactions. Assignments and potential energy distributions are included for all 3N = 336 normal modes of an eight molecule supercell, including those for 48 non-bonded whole molecule translating and rotating vibrations, of which three are acoustic modes, usually not considered. Calculated and observed frequencies differ by an average 3 cm⁻¹ (s = 4). The INS spectrum of these modes below 100 cm⁻¹, calculated from energy second derivatives, show a remarkable similarity to the experimental 10 K spectra. The calculated low frequency modes are insensitive to small changes in cell parameters and geometry. THz intensities are represented by power spectra and not calculated explicitly. Nevertheless, power spectra of 13 ps BOMD trajectories at classical temperatures of 20 K, 400 K, and 500 K are markedly similar to the experimental terahertz spectra at 77 K and 298 K. Calculations on a serine crystal supercell 2 × 2 × 2 molecules deep appear to include, in a crude but fortuitously accurate way, enough of the principle out of phase dispersion to yield a match with experimental frequencies and intensities.     

Common components and specific weights analysis: a tool for monitoring the molecular structure of semi-hard cheese throughout ripening

Twelve semi-hard (Raclette) cheeses, belonging to four brand products, namely A (n = 3), B (n = 3), C (n = 3) and D (n = 3), were produced during summer period and ripened at an industrial scale. Tryptophan, riboflavin and vitamin A fluorescence spectra were scanned on the 12 cheeses at 2, 30 and 60 days of ripening. The physico-chemical analyses were performed only at the end of the ripening stage (60 days). Common components and specific weights analysis (CCSWA) were applied on the four data tables. CCSWA showed that the common component 1 (q₁), discriminating cheeses labelled A, B and C from those labelled D, expressed 94.4 and 59% of the inertia of vitamin A and tryptophan fluorescence spectra and a less amount for riboflavin fluorescence spectra and physico-chemical data (24.2 and 13.2%, respectively). Common component 3 (q₃), differentiating between cheeses labelled B and those labelled A and C, explained 34.6 and 23.9% of the inertia of the physico-chemical data and tryptophan fluorescence spectra, respectively, and a tiny part of the inertia of riboflavin and vitamin A fluorescence spectra (3.2 and 0.7%, respectively). The CCSWA showed its ability to describe the overall information collected from fluorescence and physico-chemical data tables and to extract relevant information at the molecular level throughout ripening of the investigated semi-hard cheeses.     

Field desorption mass spectra of flavonoid acylglycosides. I. Natural acetyl derivatives

The field desorption mass spectra (FD spectra) of 17 natural flavonoid acetylglycosides have been studied. In the spectra of each of the 0-monoglycosides the molecular ion (M or M + H) appears as the main peak and it is accompanied by the ions of the aglycone (A or A + H) and of the acylated anhydrosugar (S). The intensity of the latter peak is largely connected with the structure of the substance. In the FD spectra of flavone 0-biosides, fragment S is absent but its mass can be calculated from the difference (M – A). Useful information for establishing the position of the acetyl group is given by the fragments S₁ and (M – S₁) corresponding to the detachment of the terminal sugar residue. The FD spectra of flavone C-glycosides differ greatly from the spectra of the 0-glycosides: In them the main peak is that of the ion (M), but peaks (A) and (S) are absent and the ions present resemble the fragmentation of the C-glycosides under the action of electron impact.All-Union Scientific-Institute of Medicinal Plants, Moscow. L. Ya. Karpov Scientific-Research Institute of Physical Chemistry, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 573–582, September–October, 1984.     

Sum frequency generation spectroscopic study of the condensation effect of cholesterol on a lipid monolayer

Sum frequency generation (SFG) spectra and surface pressure–molecular area (π–A) isotherms have been obtained for mixed cholesterol–DPPC monolayers with cholesterol mole fractions, x(chol.), from 0 to 1.0, at the air–water interface, under same conditions, at 22 °C. Analysis of the spectra indicated that incorporation of cholesterol into the monolayers at 3 mN m⁻¹ greatly increases the conformational and orientational order of the alkyl chains of DPPC, maximizing these properties at x(chol.)=0.4. Analysis also indicated that order in the mixed monolayers at 15 and 35 mN m⁻¹ is not affected by incorporation of cholesterol. The π–A isotherms measured at 3 mN m⁻¹ for the mixed monolayer with x(chol.)=0.4 have the largest negative deviation of the molecular area relative to those of ideal mixtures (the so-called “condensation effect” of cholesterol), indicating the most thermodynamically stable state. Comparison of results from SFG spectra and π–A isotherms explicitly proved that the condensation effect can be interpreted in terms of conformational and orientational ordering of the alkyl chains of DPPC.     

Sequence Dependent Repair of 1,N6-Ethenoadenine by DNA Repair Enzymes ALKBH2, ALKBH3, and AlkB

Mutation patterns of DNA adducts, such as mutational spectra and signatures, are useful tools for diagnostic and prognostic purposes. Mutational spectra of carcinogens derive from three sources: adduct formation, replication bypass, and repair. Here, we consider the repair aspect of 1,N⁶-ethenoadenine (εA) by the 2-oxoglutarate/Fe(II)-dependent AlkB family enzymes. Specifically, we investigated εA repair across 16 possible sequence contexts (5′/3′ flanking base to εA varied as G/A/T/C). The results revealed that repair efficiency is altered according to sequence, enzyme, and strand context (ss- versus ds-DNA). The methods can be used to study other aspects of mutational spectra or other pathways of repair.     

Vergleich von Bibliothekssuchverfahren für Steroidmassenspektren

Zusammenfassung 29 Bibliothekssuchverfahren wurden mit einer Bibliothek von 524 Steroidmassenspektren geprüft. Mit einer Stichprobe von 100 Spektren wurde die Wiedererkennung verrauschter Spektren in der Bibliothek abgeschätzt. Besonders rasche und erfolgreiche Verfahren sind mit binär codierten Spektren (konstante Intensitätsschwelle von 1–5% des Basispeaks) und mit reduzierten Spektren (1 oder 2 Peaks in Massenintervallen der Länge 7 oder 14) möglich. Mit diesen Verfahren wurden 93–100% der unbekannten Spektren durch das 1. Nachbarspektrum der Bibliothek richtig identifiziert. Die Wiedererkennungsrate verrauschter Spektren steht in engem Zusammenhang mit dem Informationsgehalt (Entropie) der codierten Bilbliothek.

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Comparison of library search methods for steroid mass spectraRecognition of noisy spectra in a library

29 library search methods have been tested with a library of 524 steroid mass spectra. A random sample of 100 spectra was used as unknown to estimate recognition of noisy spectra in the library. Binary encoded spectra with constant thresholds of 1–5% of base peak or reduced spectra with 1 (or 2) peaks in mass ranges of 7 (or 14) mass units enable quick and successful searches. 93–100% of the unknowns were identified correctly by the first neighbour spectra of the library. Recognition of noisy spectra is closely related to information content (entropy) of coded libraries.

     

Chemical-ionization mass spectra of diterpene alkaloids

The chemical-ionization spectra of diterpene alkaloids have been investigated for the first time with the recording of positive and negative ions [Cl(+) and (–)). A comparison has been made of the CI(+) spectra with the EI and SIMS spectra. It has been shown that the nature of the CI(+) and (–) spectra depends greatly on the type and position of substituents in the lycoctonine skeleton.Deceased.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 114–122, January-February, 1995. Original article submitted October 31, 1994.     

Resonant raman scattering from heme proteins: Polarization dispersion and α band splitting

A new polarization phenomenon, a dip in ρ_l for excitation in the α band, is reported for heme protein resonance Raman spectra. Interference between nearly-degenerate excited electronic states can explain this effect.     

The vibrational spectra and rotational isomerism of 1,1,1-Trimethoxyethane

The liquid, vapour and solid-state infrared spectra of 1,1,1-trimethoxy-ethane were recorded in the region 250–4000 cm⁻¹. The laser-Raman spectrum with qualitative depolarization data was obtained for liquid only. The spectra show that there are at least two rotational isomers present in the liquid phase. The solution spectra reveal that the less polar form is the more stable in the liquid phase. The form playing an important role has GGG configuration. A vibrational assignment has been attempted for the observed infrared and Raman bands.     

Comparison of electron ionization mass spectra of some organic compounds (MW < 200 Da) recorded on mass spectrometers of various types

Low-resolution electron ionization mass spectra recorded on various types of mass spectrometers (time-of-flight, quadrupole, and three-dimensional ion trap) were compared. A model mixture of 10 organic compounds (MW < 200 Da) was analyzed by gas chromatography-mass spectrometry. Pure mass spectra of analytes were extracted using the AMDIS software. The best repeatability was achieved for the time-of-flight mass spectrometer. The mass spectra recorded by a quadrupole and a time-of-flight mass spectrometer were quite similar. In the case of these instruments, library search using a commercial mass spectral data base (NIST’05) gave satisfactory result for each analyte (rank 1 or 2 in the “hit list”; Match > 900). In some cases, the mass spectra of model compounds recorded by the ion trap mass spectrometer differed in intensity of certain mass spectral peaks (but not in the set of peaks) from the mass spectra presented in the library and from the experimental mass spectra recorded by the time-of-flight and quadrupole instruments.     

Substitution in barbituric acids

Aromatic and aliphatic aldehydes readily condense with thiobarbituric acid to form 5-arylidenethiobarbituric acids or 5-arylidenebis(thiobarbituric acid)s. A longer time is required for condensation with ketones. The UV spectra of the arylidene derivatives have two absorption bands, with maxima at 240–275 and 280–405 nm, while the spectra of the alkylidene derivatives only one absorption band, with a maximum at 280–295 nm.For part I, see [1].     

Analysis of the hyperfine structures and

From the theories of the nuclear hyperfine structure (HFS) and Λ doubling of diatomic molecules, several brief algebraic equations for interpretation of HFS and Λ doubling of transitions of diatomic molecule have been developed. A few important parameters of HFS and Λ doubling of¹⁵N¹⁶O have been efficiently and accurately obtained from the analysis of the high resolution spectra of¹⁵N¹⁶O (X²∏) observed in our experiments with these equations. This method can provide an effective approach to obtain important hyperfine parameters of novel radicals from their high resolution laser magnetic resonance spectra. Liu Yu-yan, Guo Yuan-qing, Assignments of FIR-LMR spectra of CF X²∏(υ= 1) and MIR-LMR spectra of NO X²∏ (υ =1←0), Spectroscopy and Spectral Analysis (in press).     

Vibrational spectra of 2-biphenylmethanol. Spectrum simulation and molecular structure

The vibrational spectra of a solid crystalline sample of 2-biphenylmethanol have been measured at room temperature. The IR absorption spectra were recorded in the range 400 cm^–1–3600 cm^–1; Raman spectra were measured in the range 10 cm^–1–1640 cm^–1. The direct mechanical and optoelectronic problems were solved using the fragment method realized as Lev-100 software; the intensity distribution in the IR spectrum of 2-biphenylmethanol was obtained by the same method. The experimental Raman and IR absorption spectra were interpreted by analyzing the calculated data on the frequencies and forms of normal vibrations and their intensities in the IR spectra. IR absorption spectra were simulated for several models of 2-biphenylmethanol conformers that differ in the mutual orientation of fragments. Based on the results of simulation and comparison of the calculated and experimental spectra of conformers we suggested a model for the conformer realized in the solid phase under normal conditions.Original Russian Text Copyright © 2004 by L. M. Babkov, J. Baran, N. A. Davydova, J. I. Kukielskii, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 624–631, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Front face fluorescence spectroscopy as a tool for the assessment of egg freshness during storage at a temperature of 12.2 degrees C and 87% relative humidity

The objective of this study was to investigate intrinsic fluorophores of thick albumen and egg yolk in order to assess egg freshness during storage at a temperature of 12.2 °C and 87% relative humidity (RH). A total of 126 intact brown-shelled eggs of the same flock (29 weeks of age) were stored for 1, 6, 8, 12, 15, 20, 22, 26, 29, 33, 40, 47 and 55 days. The emission fluorescence spectra of aromatic amino acids and nucleic acids (AAA + NA) (excitation: 250 nm; emission: 280-450 nm), fluorescent Maillard reaction products (FMRP) (excitation: 360 nm; emission: 380-580 nm) and the excitation spectra of vitamin A (emission: 410 nm; excitation: 270-350 nm) were scanned on thick albumen and egg yolk. Among the intrinsic fluorophores, only the principal component analysis (PCA) applied on the vitamin A fluorescence spectra allowed a good identification of eggs as a function of their storage time. Factorial discriminant analysis (FDA) was then applied on the first five principal components (PCs) of the PCA applied on each spectral data set. Regarding AAA + NA recorded on thick albumen, correct classification of 69.4% and 63.9% was observed for the calibration and validation sets, respectively. Quite similar results were obtained on AAA + NA scanned on egg yolks. The best results were obtained with vitamin A fluorescence spectra since 97.7% and 85.7% of the calibration and validation sets was obtained, respectively. These results showed that vitamin A fluorescence spectra provide useful fingerprints, mainly allow the identification of eggs during storage and could be considered as a powerful intrinsic probe for the evaluation of egg freshness.     

The low-frequency Raman and IR spectra of nitric acid hydrates

The low-frequency region of the infrared and Raman spectra of nitric acid hydrates is analyzed. Theoretical calculations of the vibrational normal modes of the crystals of nitric acid monohydrate and the β-phases of the dihydrate and trihydrate are carried out, focusing the results in the regions below 175 cm⁻¹ and near the symmetric stretch of the nitrate ion NO₃⁻, around 1000–1100 cm⁻¹. A prediction of the corresponding infrared spectra is presented. A joint study is performed of the calculated normal modes, the predicted IR spectra, and the recently published Raman spectra of these compounds, based on symmetry considerations and using the atomic displacements associated to each normal mode as a further source of information. Although most of the modes present a strong mixture of atomic motions, assignments can be proposed for some of the vibrations.     

Alkaloids of a new type fromSophora alopecuroides L.

Summary The structures of aloperine and allylaloperine (fromSophora alopecuroides L.) — alkaloids of a new structural type for the genusSophora — have been established by chemical and spectral methods. A number of parameters, NMR spectra, and mass spectra characterizing this class of compounds has been obtained. The partial synthesis of allylaloperine has been performed.All-Union Scientific-Research Institute of Medicinal Plants. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 30–37, January–February, 1975.     

Composition and experience in operation of library of molecular structures as software for large-scale calculations of infrared spectra of organic compounds

In this article we describe the composition of a library of molecular structures and evaluate its capabilities for modeling IR spectra of complicated compounds. A predictive calculation of an IR spectrum is performed for the molecule of 1-phenyl-4-(p-tolyl)-1,3-butadiene on the basis of the library of molecular structures, and the theoretical and experimental spectra of this molecule are compared.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 197–201, January–February, 1993.     

On-line gradient liquid chromatography-Fourier transform infrared spectrometry determination of sugars in beverages using chemometric background correction

An on-line gradient reversed phase liquid chromatography-Fourier transform infrared spectrometry (LC-FTIR) method was developed for the determination of fructose, glucose, sucrose and maltose in beverages. Improved chromatographic resolution was obtained using a linear gradient from 75 to 55% (v/v) acetonitrile in water in 15 min. Changes in the background spectra were corrected employing “univariate background correction based on the use of a reference spectra matrix” (UBC-RSM) and using the ratio of absorbance (AR) at 2256 and 2253 cm⁻¹ for the identification of the eluent spectra within the RSM. The method provided limits of detection in the order of 0.75 mg ml⁻¹. The precision (as relative standard deviation) ranged between 3.3 and 4.1% for glucose and fructose, respectively at a concentration level of 3.0 mg ml⁻¹. Quantitative recovery values on spiked samples confirmed the accuracy of the method. A set of samples from the Spanish market were analysed to test the suitability of the procedure.