Spectra Of Reference Compounds Research Articles

Precision-characterization and quantitative determination of main compounds in Si-Ni-San with UHPLC-MS/MS based targeted-profiling method

Mass spectrometry based precision identification of natural products requires the validation of the reference compounds. This study attempted to develop a LC-QTOF MS combined with LC-TQ MS method to precisely characterize the chemicals of Si-Ni-San (SNS), a classic traditional Chinese medicine formula, which is composed of four medicinal plants, and widely used for the treatments of liver disorders. 74 compounds in SNS were provisionally identified by acquiring MS spectra and MS/MS spectra of the possible chemical features, as well as retrieving small-molecule database. By comparing with the accurate MS/MS spectra of reference compounds, 37 compounds in SNS were precisely identified for the first time. In addition, our effort also successfully assigned the origin of each identified compounds against four medicinal plants. Furthermore, we developed a UHPLC-TQ MS based quantitative-profiling method for simultaneous determination of 37 targeted compounds in the different extracts of the raw SNS and commercial lyophilized powders, enabling to facilitate overall quality control of SNS and associated commercial products. Collectively, our finding precisely characterized the main chemicals in SNS, which also provides a new strategy with LC-MS/MS based chemical profiling to precisely identify a diversity of chemicals in Chinese medicinal plants and associated formulae.

DAFNE-Light DXR1 Soft X-Ray Synchrotron Radiation Beamline: Characteristics and XAFS Applications

X-ray Absorption Fine Structure Spectroscopy (XAFS) is a powerful technique to investigate the local atomic geometry and the chemical state of atoms in different types of materials, especially if lacking a long-range order, such as nanomaterials, liquids, amorphous and highly disordered systems, and polymers containing metallic atoms. The INFN-LNF DAΦNE-Light DXR1 beam line is mainly dedicated to soft X-ray absorption spectroscopy; it collects the radiation of a wiggler insertion device and covers the energy range from 0.9 to 3.0 keV or the range going from the K-edge of Na through to the K-edge of Cl. The characteristics of the beamline are reported here together with the XAFS spectra of reference compounds, in order to show some of the information achievable with this X-ray spectroscopy. Additionally, some examples of XAFS spectroscopy applications are also reported.

Structure, Bonding, and Stability of Mercury Complexes with Thiolate and Thioether Ligands from High-Resolution XANES Spectroscopy and First-Principles Calculations.

We present results obtained from high energy-resolution L3-edge XANES spectroscopy and first-principles calculations for the structure, bonding, and stability of mercury(II) complexes with thiolate and thioether ligands in crystalline compounds, aqueous solution, and macromolecular natural organic matter (NOM). Core-to-valence XANES features that vary in intensity differentiate with unprecedented sensitivity the number and identity of Hg ligands and the geometry of the ligand environment. Post-Hartree-Fock XANES calculations, coupled with natural population analysis, performed on MP2-optimized Hg[(SR)2···(RSR)n] complexes show that the shape, position, and number of electronic transitions observed at high energy-resolution are directly correlated to the Hg and S (l,m)-projected empty densities of states and occupations of the hybridized Hg 6s and 5d valence orbitals. Linear two-coordination, the most common coordination geometry in mercury chemistry, yields a sharp 2p to 6s + 5d electronic transition. This transition varies in intensity for Hg bonded to thiol groups in macromolecular NOM. The intensity variation is explained by contributions from next-nearest, low-charge, thioether-type RSR ligands at 3.0-3.3 Å from Hg. Thus, Hg in NOM has two strong bonds to thiol S and k additional weak Hg···S contacts, or 2 + k coordination. The calculated stabilization energy is -5 kcal/mol per RSR ligand. Detection of distant ligands beyond the first coordination shell requires precise measurement of, and comparison to, spectra of reference compounds as well as accurate calculation of spectra for representative molecular models. The combined experimental and theoretical approaches described here for Hg can be applied to other closed-shell atoms, such as Ag(I) and Au(I). To facilitate further calculation of XANES spectra, experimental data, a new crystallographic structure of a key mercury thioether complex, Cartesian coordinates of the computed models, and examples of input files are provided as Supporting Information .

Nanoscale IR Near-Field Imaging of the SEI Layer on an HOPG Electrode

The solid electrolyte interphase (SEI) layer [1] is essential to Li-ion battery functionality as it ideally forms an ionically conductive passivation layer, which protects the electrolyte from further reduction at the electrode surface. Although the SEI has been studied extensively in a number of electrode/electrolyte systems, its chemical composition, structure, and operation mechanism still remain a subject of considerable debate. Among the principal obstacles to detailed SEI characterization is the fact that the signal spatial resolution of traditional optical techniques such as Fourier transform infrared (FTIR) and Raman spectroscopy/microscopy is limited by the diffraction limit c.a. 500 nm. The standard optical response signal from the SEI layer convolves spectral features from many different compounds, which makes characterization of the inherently nanoscale chemical building blocks of the SEI layer nearly impossible. Infrared apertureless near-field scanning optical microscopy (IR aNSOM) [2] can easily overcome the diffraction limit. In aNSOM, light is focused onto a metal-coated atomic force microscope (AFM) tip, which causes a strongly enhanced field at the tip apex. Since the tip is held in close proximity to the sample surface, the microscope is capable of imaging at a resolution only limited by the tip’s radius of curvature (~20 nm). The scattering from the tip is modulated by the dielectric function of the sample surface, allowing for a direct surface-selective measurement of local absorption at the nanoscale. This capability is valuable in characterization of Li-ion electrode materials [3]. In this work we apply IR aNSOM to image the surface film on highly oriented pyrolitic graphite (HOPG). Linear sweep voltammetry (LSV) was conducted on ZYH-grade HOPG electrode in 1 M LiPF6 in EC:DEC 1:2 (w:w) electrolyte from open-circuit potential (OCP ~ 2.9 V vs. Li/Li+) to several potentials that correspond to the SEI layer formation. The HOPG electrodes were removed from the cells and imaged ex situ under a dry nitrogen atmosphere with the IR aNSOM at a variety of wavelengths within the IR laser tuning range 927-1094 cm-1. IR aNSOM images of the HOPG electrode are shown in Figure 1. The image intensity Asinϕis proportional to the IR absorption at the tip location. The variation in IR contrast with wavenumber demonstrates the nanoscale chemical inhomogeneity of the layer. Variation in wavenumber produces near-complete contrast reversal, highlighting the locations of different compounds with non-overlapping absorption bands within the laser tuning range. These results show the capability of near-field microscopy to explore the composition and structure of interfaces in electrochemical systems. Correlating near-field absorption data with spectra of reference compounds will enable full identification of the SEI’s chemical constituents at the nanoscale. Acknowledgement This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 under the Batteries for Advanced Transportation Technologies (BATT) Program. References E. Peled, J. Electrochem. Soc., 126, 2047 (1979).L. Novotny and B. Hecht, Principles of Nano-Optics, Cambridge University Press, Cambridge (2006).I. Lucas et al. Nano Lett., DOI: 10.1021/nl5010898. Figure 1: Ex situ IR aNSOM images of the HOPG electrode at (a) 1.36 V, 940 cm-1, (b) 1.36 V, 1070 cm-1, (c) 0.9 V, 1030 cm-1 (d) 0.9 V, 1088 cm-1 Figure 1

Determination of oxidation state of iron in normal and pathologically altered human aortic valves

In order to investigate changes in chemical state of iron in normal and pathologically altered human aortic valves X-ray absorption spectroscopy was applied. Since Fe is suspected to play detrimental role in aortic valve stenosis pathogenesis the oxidation state of this element has been determined. The experimental material consisted of 10μm sections of valves excised during routine surgery and from autopsies. The experiment was performed at the MicroXAS beamline of the SLS synchrotron facility in Villigen (Switzerland). The Fe K-edge XANES spectra obtained from tissue samples were carefully analyzed and compared with the spectra of reference compounds containing iron in various chemical structures. The analysis of absorption edge position and shape of the spectra revealed that both chemical forms of iron are presented in valve tissue but Fe3+ is the predominant form. Small shift of the absorption edge toward higher energy in the spectra from stenotic valve samples indicates higher content of the Fe3+ form in pathological tissue. Such a phenomenon suggests the role of Fenton reaction and reactive oxygen species in the etiology of aortic valve stenosis. The comparison of pre-edge regions of XANES spectra for control and stenotic valve tissue confirmed no differences in local symmetry or spin state of iron in analyzed samples.

Quantitative assessment of the degree of lipid unsaturation in intact Mortierella by Raman microspectroscopy.

Fungi of the genus Mortierella can accumulate large amounts of unusual lipids depending on species, strain, and growth conditions. Fast and easy determination of key parameters of lipid quality for these samples is required. In this contribution, we apply Raman microspectroscopy to determine the degree of unsaturation for fungal lipids directly inside intact hyphae without elaborate sample handling. Six Mortierella species were grown under varying conditions, and Raman spectra of single lipid vesicles were acquired. From the spectra, we calculate a peak intensity ratio I(1270cm(-1))/I(1445cm(-1)) from the signals of =CH and -CH2/-CH3 groups, respectively. This ratio is linked to the iodine value (IV) using spectra of reference compounds with known IV. IVs of fungal samples are compared to gas chromatography results. Values from both methods are in good accordance. Lipid composition is found to vary between the investigated species, with Mortierella alpina having the most unsaturated lipid (IV up to 280) and Mortierella exigua the least unsaturated (IV as low as 70). We find Raman microspectroscopy a suitable tool to determine the IV reliably, fast, and easily inside intact hyphae without extensive sample handling or treatment. The method can also be transferred to other microscopic samples.

Study of bioaccumulation and biotransformation by microanalytical X-ray techniques: investigation of distribution and speciation of Cu and Cr in the body of the plant-feeding nematode, Xiphinema vuittenezi

Free-living nematodes, due to their microscopic size and quite complex life processes can be widely applied as biological model organisms to study the effect of soil pollutants. The modern X-ray spectrometric methods enable the individual analysis of microscopic biological samples, hereby expanding the scope of environmental and toxicological sciences. In order to study the uptake and bioaccumulation of Cu and Cr by nematodes (Xiphinema vuittenezi), the worms were starved in tap water for five days, and then treated with solutions of CuSO4, Cu(NO3)2, KCr(SO4)2 or K2CrO4 for 1–120h. The effect of two soil-polluting elements, Cu, which is often applied in herbicides, and Cr, which is essential in the form of Cr(III), but toxic if it occurs as Cr(VI), on soil-inhabiting nematodes was studied. The uptake of these toxicants and their bioaccumulation was investigated by TXRF, following a two-step sample digestion method (digestion with HNO3 and using cold O plasma). Their effect on the essential element content of nematodes was also studied. Differences were found between the uptake of Cr(III) and Cr(VI). The Cr(III) causes decreased Zn content comparing with untreated nematodes, for Cr(VI) it was not observed. Elemental maps in the cross-sections of the worms prepared by focused gallium ion beam, following a special sample preparation method (quick-freezing in liquid nitrogen for 2min and lyophilization for 72h) were collected by scanning electron microscope equipped with energy dispersive X-ray detector. The distribution of Cr-P and Cu-P showed a similar pattern, however, the distribution of S deviated from these ones. According to these findings, the role of P-containing ligands in the binding of Cu and Cr is more characteristic than of S-containing ones. With the purpose of studying the speciation of the Cu and Cr in the worm, X-ray absorption near edge structure spectrometry was applied. The sample preparation method was the same as in the case of the elemental mapping. For Cu, the sample spectrum was fitted by the spectra of reference compounds, and Cu3(PO4)2, was found to be the main component, which harmonized with the results of the elemental distribution measurements. However, the role of S-containing ligands in Cu detoxification cannot be excluded, since the spectrum of Cu-cysteine complex was a minor component of the fit. It was also established that in the chromate treated nematodes a considerable part of Cr(VI) was reduced to Cr(III).

Chemical species of sulfur in prostate cancer cells studied by XANES spectroscopy

The role of sulfur in prostate cancer progression may be significant for understanding the process of carcinogenesis. This work, based on X-ray Absorption Near Edge Structure (XANES) spectroscopy, is focused on determination of sulfur chemical species occurring in prostate cancer cell lines. The experimental material consisted of four commercially available cell lines: three from metastasized prostate cancer (PC3, LNCaP, and DU145) and one, used as a control, from the non-tumourigenic peripheral zone of the prostate (PZ-HPV-7). The experiment was performed at the SUL-X beamline of the synchrotron radiation source ANKA, Karlsruhe (Germany). The K-edge XANES spectra of sulfur were analyzed by deconvolution in order to establish sulfur species that occur in prostate cancer cells and to find out whether there are any differences in their content between various cell lines. Experimental spectra were fitted in two ways: with two Gaussian peaks and one arctangent step function, and additionally by a Linear Combination Fit with spectra of reference compounds in order to obtain quantitative chemical information. All fitting procedures were performed with the Athena code (Ravel and Newville, 2005) and the results of deconvolution were used to determine the fraction of each sulfur form. The results of data analysis showed that cell lines from different metastasis had different ratio of reduced to oxidized sulfur species. The LCF analysis demonstrated that the highest content of GSH, one of the most important sulfur-bearing compounds in cells, was observed in DU145 cells. These findings may confirm the hypothesis of changes in redox balance in case of cancer initiation and progression.

An efficient spectra processing method for metabolite identification from 1H-NMR metabolomics data

The spectra processing step is crucial in metabolomics approaches, especially for proton NMR metabolomics profiling. During this step, noise reduction, baseline correction, peak alignment and reduction of the 1D (1)H-NMR spectral data are required in order to allow biological information to be highlighted through further statistical analyses. Above all, data reduction (binning or bucketing) strongly impacts subsequent statistical data analysis and potential biomarker discovery. Here, we propose an efficient spectra processing method which also provides helpful support for compound identification using a new data reduction algorithm that produces relevant variables, called buckets. These buckets are the result of the extraction of all relevant peaks contained in the complex mixture spectra, rid of any non-significant signal. Taking advantage of the concentration variability of each compound in a series of samples and based on significant correlations that link these buckets together into clusters, the method further proposes automatic assignment of metabolites by matching these clusters with the spectra of reference compounds from the Human Metabolome Database or a home-made database. This new method is applied to a set of simulated (1)H-NMR spectra to determine the effect of some processing parameters and, as a proof of concept, to a tomato (1)H-NMR dataset to test its ability to recover the fruit extract compositions. The implementation code for both clustering and matching steps is available upon request to the corresponding author.

Identification of Pavinane Alkaloids in the Genera Argemone and Eschscholzia by GC-MS

The genera Eschscholtzia and Argemone (Papaveraceae) represent a rich source of pavinane alkaloids, the identification of which in alkaloid extracts is generally problematic without standards. The alkaloid extracts of three Argemone and four Eschscholtzia species were analyzed using GC-MS. The alkaloids were identified based on comparison of their mass spectra with commercial libraries, with reported data in the literature and with spectra of reference compounds. A total of 23 alkaloids of six structural types (pavinane, protopine, benzylisoquinoline, benzophenanthridine, aporphine and protoberberine) were identified. The fragmentation pathway of pavinane alkaloids was used for their identification. O-Methylneocaryachine has been reported for the first time from a natural sources and the alkaloid pattern of Eschscholzia pulchella has been analyzed and described for the first time.

XAFS spectroscopy study of Eu(III) sorption on γ-Alumina: effect of pH

LIII edge X-ray Absorption Fine Structure (XAFS) spectroscopic study of Eu(III) sorbed on γ-alumina from aqueous solutions of different pH (values ranging from 6 to 8) has been carried out at XAFS beam line of Elettra Synchrotron facility, Italy, in transmission mode. Extended X-ray Absorption Fine Structure spectra of reference compounds, namely, Eu2O3, Eu(OH)3 and Eu-aquo complex in solution, were also measured. The data were analyzed using the IFEFFIT suite of code. XAFS spectra of the sorption samples is dominated by the Eu–O near neighbor co-ordination at distance 2.4 ± 0.1 A. 8–9 oxygen atoms, coming from both coordinating water molecule and oxygen atoms from alumina surface, surround the Eu(III) in the surface complex. Next near neighbor atoms in all the sorption samples consist of Al at distance ~3.6 and 3.8 A, which on comparison with literature data indicates towards Eu(III) bidentate binding to apical oxygen of two different alumina octahedra on γ-alumina surface.

NEXAFS studies of La0.8Bi0.2Fe1−xMnxO3(0.0 ⩽ x ⩽ 0.4) multiferroic system using x-ray absorption spectroscopy

We report the electronic structure studies of well-characterized La0.8Bi0.2Fe1−xMnxO3 (LBFM, 0.0 ⩽ x ⩽ 0.4) multiferroic samples investigated by soft x-ray absorption spectroscopy at O K-, Mn L3,2-, Mn K-, Fe L3,2- and La M4,5-edges along with the spectra of reference compounds. The investigations are performed to find out the chemical states and crystal field symmetry of ions present in the LBFM multiferroic samples after the substitution of Mn ions at Fe sites. Studies reveal a slight shift in the peak positions of O K-edge spectra along with growth in intensities of low-energy features. An analysis of the Mn L3,2- and K-edge, in addition to the comparison with the spectra of reference compounds, indicates that the Mn ions are present in mixed valence states. It is found that the Mn ions are mainly in +3 states along with a small contribution of +2 and +4 ones. The study of Fe L3,2-edge confirms the trivalent state of Fe ion. M4,5-edges of La corroborate the +3 state of La in the system. Atomic multiplet calculations are also performed on Fe L3,2-, Mn L3,2- and La M4,5-edges to further verify the valency, symmetry and the crystal field splitting.

Molybdenum Speciation in Uranium Mine Tailings Using X-Ray Absorption Spectroscopy

Uranium (U) mill tailings in northern Saskatchewan, Canada, contain elevated concentrations of molybdenum (Mo). The potential for long-term (>10,000 years) mobilization of Mo from the tailings management facilities to regional groundwater systems is an environmental concern. To assist in characterizing long-term stability, X-ray absorption spectroscopy was used to define the chemical (redox and molecular) speciation of Mo in tailings samples from the Deilmann Tailings Management Facility (DTMF) at the Key Lake operations of Cameco Corporation. Comparison of Mo K near-edge X-ray absorption spectra of tailings samples and reference compounds of known oxidation states indicates Mo exists mainly as molybdate (+6 oxidation state). Principal component analysis of tailings samples spectra followed by linear combination fitting using spectra of reference compounds indicates that various proportions of NiMoO(4) and CaMoO(4) complexes, as well as molybdate adsorbed onto ferrihydrite, are the Mo species present in the U mine tailings. Tailings samples with low Fe/Mo (<708) and high Ni/Mo (>113) molar ratios are dominated by NiMoO(4), whereas those with high Fe/Mo (>708) and low Ni/Mo (<113) molar ratios are dominated by molybdate adsorbed onto ferrihydrite. This suggests that the speciation of Mo in the tailings is dependent in part on the chemistry of the original ore.

Vibrational study of cytotoxic bis(1-ethylimidazole)l(−)malatoplatinum(II)

In this work, we present the FT-Raman and FT-IR spectra (4000–100cm−1) of the newly synthesized cytotoxic platinum complex, bis(1-ethylimidazole)l(−)malatoplatinum(II), (abbr.: I) and reference substances: l(−)malic acid, silver l(−)malate and 1-ethylimidazole. Assignment of the bands was done on the basis of characteristic group vibrations, in comparison with the spectra of I with reference compounds as well as using the literature and our previous data. Using water solution and deuterated samples of I and of l-malic acid was helpful in making an assignment. The spectral analysis confirmed the chelated structure of I and indicated that in contrast to references containing l(−)malate ion, the l(−)malatoplatinum complex I does not form intramolecular hydrogen-bonded cyclic structures in solid state. The intermolecular hydrogen bonding is, however, possible. The characteristic vibrations at the Pt2+ centre was observed below 600cm−1, the ν(Pt–N) and ν(Pt–O) in the range 600–430cm–1, whereas the δ skeletal, δ(N–Pt–N), δ(N–Pt–O) and δ(O–Pt–O), appeared in the lowest part of the observed spectra. In the spectra of reference compounds, the most important are assignments of the band at 323cm−1 of silver malate as ν(Ag–O), as well as the bands at 743cm−1 of l-malic acid and at 801cm−1 of silver malate, as intramolecular hydrogen bonded cyclic structures. Both bands are the most intense in their Raman spectra and might be used as analytical bands.

Control of the NiII/Surface Interaction in the First Steps of Supported Catalyst Preparation: The Interfacial Coordination Chemistry of [Ni(en)2(H2O)2]2+

Model supported nickel catalysts were prepared by deposition of the [Ni(en)2(H2O)2]2+ complex from aqueous solutions onto silica, zeolite Y, two kinds of alumina, a clay, and a pillared clay. UV−visible spectroscopy was used to monitor the d−d transitions of Ni(II) in the solution, upon contact with the support oxide, and upon drying. In comparison with the spectra of reference compounds, and with the help of data provided by other techniques (elemental analysis, thermogravimetry, IR spectroscopy), this allowed us to follow the reactions occurring in the coordination sphere of the nickel ion during the initial stages of catalyst preparation. For the alumina, zeolite, silica, and pillared clay supports, exchange of two (H2O) ligands for support surface groups was evidenced (nickel grafting). On the other hand, deposition/intercalation into clay caused the formation of square-planar [Ni(en)2]2+upon drying. Therefore, these systems allow a precise study of transition metal interfacial coordination chemistry,...

X-ray emission spectra and structural models of BCN materials

The results of measurements of BK α, NK α and CK α (ultra-soft X-ray emission spectra of boron carbonitride phases synthesized by nitridation of boron carbide at 1200, 1800 and 24 000°C) are presented. The obtained results are compared with spectra of reference compounds (a-B, B 4C, BN and graphite). It was found that BK α and NK α spectra of carbonitride phases were identical to that of BN. On the other hand, CK α spectra of the BCN system were very similar to that of graphite. No trace of B-C chemical bonding was found for BCN compounds. The obtained results confirm the structural model of the ternary compound according to which separate boron nitride and graphite layers are in random intercalation.

1H NMR Characterization of Methacrylamide Polymer Conjugates with the AntiCancer Drug Doxorubicin

Two poly-2-hydroxypropylmethacrylamide conjugates with the anti-cancer drug doxorubicin were investigated by 1H NMR spectroscopy. In both polymers (FCE 28068 and FCE 28069) the drug is connected to a polymethacrylamide backbone via a tetrapeptidyl spacer (Gly-L,D-Phe–L-Leu–Gly) and, in addition, FCE 28069 contains similarly bound D-galactosamine molecules as liver-targeting moieties. Signals of the drug and galactosamine protons were fully assigned in the spectra of the polymers by means of NOESY and TOCSY experiments and by comparison with the spectra of reference compounds. The integrity of doxorubicin and the connectivity between the drug and peptidyl chain was successfully confirmed in spite of the comparatively low abundance (<5%) of the corresponding monomeric units and of signal spreading due to the diastereomeric mixture of peptidyl chains. Polymer-bound galactosamine molecules were found to be distributed among four isomeric forms (α- and β-anomers of pyranose and furanose forms, with predominance of the α-pyranose form). Diagnostic signals for possible alternative peptidyl chain endings (2-hydroxypropylamide or free carboxyl groups) were identified with the help of model polymers and the first, but not the second, were detected in the spectra of the two FCEs. In addition to the above results, high-field NMR is a rapid and sensitive method for the qualitative identification of low molecular weight contaminants in production batches of polymer–drug conjugates. © 1997 by John Wiley & Sons, Ltd.

1H NMR Characterization of Methacrylamide Polymer Conjugates with the Anti-Cancer Drug Doxorubicin

Two poly-2-hydroxypropylmethacrylamide conjugates with the anti-cancer drug doxorubicin were investigated by1H NMR spectroscopy. In both polymers (FCE 28068 and FCE 28069) the drug is connected to a polymethacrylamide backbone via a tetrapeptidyl spacer (Gly-L,D-Phe–L-Leu–Gly) and, in addition, FCE 28069 contains similarly bound D-galactosamine molecules as liver-targeting moieties. Signals of the drug and galactosamine protons were fully assigned in the spectra of the polymers by means of NOESY and TOCSY experiments and by comparison with the spectra of reference compounds. The integrity of doxorubicin and the connectivity between the drug and peptidyl chain was successfully confirmed in spite of the comparatively low abundance (<5%) of the corresponding monomeric units and of signal spreading due to the diastereomeric mixture of peptidyl chains. Polymer-bound galactosamine molecules were found to be distributed among four isomeric forms (α- and β-anomers of pyranose and furanose forms, with predominance of the α-pyranose form). Diagnostic signals for possible alternative peptidyl chain endings (2-hydroxypropylamide or free carboxyl groups) were identified with the help of model polymers and the first, but not the second, were detected in the spectra of the two FCEs. In addition to the above results, high-field NMR is a rapid and sensitive method for the qualitative identification of low molecular weight contaminants in production batches of polymer–drug conjugates. © 1997 by John Wiley & Sons, Ltd.

Intramolecular hydrogen bonds involving polar carbon–hydrogen bonds: infrared and1H nuclear magnetic resonance spectra of some cyanomethyl and benzyl sulphones

Two series of sulphones, containing respectively the cyanomethylsulphonyl and the benzylsulphonyl groups, have been prepared, in which a polar methylene group is allowed on steric grounds to interact intramolecularly with a nearby donor atom. The i.r. and 1H n.m.r. spectra of these sulphones are compared with spectra of reference compounds in which no such interaction is possible. No conclusive evidence for intramolecular hydrogen bonds is found: possible causes for the observed spectral shifts are discussed.

Photoelektronenspektren organischer verbindungen

Abstract The high resolution He I photoelectron spectra of vinylacetylene, cyclopropylacetylene, cyclobutylacetylene and cyclohexylacetylene are reported and ionization potentials in the low-binding region are assigned by correlating the spectra with spectra of reference compounds, by using the information supplied by vibrational analysis and by comparing the assignment with the results of MINDO/2 calculations. The resonance integrals βRS between the π type orbitals of the acetylene moiety (R) and the π and Walsh type orbitals of the substituents (S) are determined by means of a LCMO model, parametrized with spectra of known assignment. The interaction terms HRs of cyclopropylacetylene, which are 1.3 eV in the bisected conformation and 0.7 eV in the perpendicular conformation, can be considered as experimental verification of the correlation diagram for vinylcyclopropane given by Hoffmann et al. and provide an explanation of the stability of the gauche conformation of vinylcyclopropane. In the case of cyclobutylacetylene, only estimated values of the interaction term HRS can be obtained from the spectrum.