A new spectrophotometric method for quantitative multicomponent analysis resolution of mixtures of salicylic and salicyluric acids

A new spectrophotometric method for resolving binary mixtures is proposed. The method is based on use of the first derivative of the ratios of spectra. The absorption spectrum of the mixture is obtained and the amplitudes at appropriate wavelengths are divided by the corresponding amplitudes in the absorption spectrum of a standard solution of one of the components, and the first derivative of the ratio spectrum is obtained. The concentration of the other component is then determined from a calibration graph. The method has been applied for resolving binary mixtures of salicylic and salicyluric acids. Calibration graphs for 2.6-52 ppm salicylic acid and for 2.1-42 ppm salicyluric acid were established by measuring the analytical signals at the maximum at 241.5 nm (for salicylic acid) and from the peak at 258 nm to the trough at 247 nm (for salicyluric acid) in the first derivative ratio spectra.     

Investigation of the low-frequency vibrations of crystalline tartaric acid using terahertz spectroscopy and solid-state density functional theory

The room temperature and cryogenic terahertz (THz) spectra (10-95 cm(-1)) of l-tartaric acid and dl-tartaric acid were investigated. At 293 K, the l-tartaric acid spectrum showed four absorption features at 36.4, 61.6, 78.7, and 87.3 cm(-1) in the experimental spectrum. Once cooled to 78 K, these features narrowed and shifted to 35.9, 63.4, 81.1, and 90.1 cm(-1). The THz spectrum of dl-tartaric acid is significantly different, containing only a single absorption at 79.9 cm(-1) at room temperature, which shifts to 82.9 cm(-1) at 78 K. Solid-state density functional theory calculations [B3LYP/6-311G(2d,2p)] were performed to simulate the crystalline structure of both molecular solids and to assign the observed spectral features to specific atomic motions. The THz spectrum of l-tartaric acid is particularly interesting in that it contains a theoretically unaccounted for spectral feature that may arise from second-order phonon processes and also exhibits an anomalous red-shifting absorption feature with cooling that is shown to originate from negative thermal expansion of the crystal.     

The electronic spectrum of (−)-s-(ps)-2,5,3',6'-tetrahydro[2.2]paracyclophane-2-carboxylic acid

A new, efficient route was used in the synthesis of [2,2]paracyclophane-2-carboxylic acid. The chiral acid was then resolved and the Birch reduction performed yielding one enantiomer of tetrahydro[2,2]paracyclophane-2-carboxylic acid. The UV spectrum of tetrahydro[2,2]paracyclophane-2-carboxylic acid in isopentane shows one absorption at 206 nm (?_max=5271). There are three bands observed in the CD spectrum in isopentane at 236 nm ([θ] = 1.8 × 10⁴), 201 nm ([θ]=-16×10⁴) and a positive band indicated below 180 nm but not observed, in ethanol the CD spectrum exhibits a band at 205 nm ([θ]= 1.5×10⁴) and the UV spectrum shows a band at 208 nm (?_max=5915). The bands were assigned and possible reasons for the occurrence of a π→π^* transition at unexpectedly long wavelengths are discussed.     

The IR spectrum of formic acid in an argon matrix

A new method of preparation of matrix-isolated molecules of formic acid at low temperatures has been developed. A set of experimental frequencies and intensities of the IR spectrum of monomer molecules of formic acid isolated in a low temperature argon matrix has been obtained. It is shown on the basis of analysis of the IR spectrum that the new method eliminates association and decomposition of molecules of the acid during preparation of the sample.     

Low-frequency modes of the benzoic acid dimer in chloroform observed by the optical Kerr effect

The low frequency Raman spectral density associated with the intermolecular hydrogen-bonding interaction of benzoic acid in chloroform was investigated through the ultrafast optically-heterodyne-detected optical Kerr effect. The low-frequency solute Raman spectrum was obtained by Fourier transform analysis and subtraction of the solvent spectrum from the solution spectrum. The resulting difference spectrum has a broad band below 150 cm(-1) with a peak at around 80 cm(-1). Previous studies of aromatic liquids suggest that the origin of such a low-frequency band is librational motion, although intermolecular hydrogen-bonding modes in benzoic acid may also contribute. To clarify these contributions to the low-frequency band, methyl benzoate was used to estimate the librational component; its structure is similar to benzoic acid, but it forms no intermolecular hydrogen bonds. Both librational and intermolecular modes were found to contribute to the low-frequency Raman spectrum of the dimer and thus can be separated. These experimental results were compared with the results of density functional theory calculations. In addition, the effect of deuteration on the Raman spectrum was also investigated.     

ESR spectra of poly(methacrylic acid) and poly(methyl methacrylate): Reinterpretation of the 9-line spectrum

The temperature dependence of the ESR spectra of poly(methacrylic acid) and poly-(methyl methacrylate) γ-irradiated at room temperature was studied between ?196°C and +25°C. The conventional 9-line spectrum was observed throughout this range with no significant spectral change, in contrast to the propagating radical ··· CH₂? °C(CH₃)COOR found in methacrylic acid monomer or barium methacrylate dihydrate irradiated at ?196°C. In addition, the irradiation of methacrylic acid monomer with a low dose at 0°C gave the same 13-line spectrum as that of the propagating radical obtained by the irradiation at ?196°C, while prolonged irradiation at 0°C gave the same conventional 9-line spectrum as that of poly(methacrylic acid) or poly(methyl methacrylate). The conventional 9-line spectrum has a much weaker 4-line component than that of the propagating radical. The difference comes from the surrounding matrix, and the conventional 9-line spectrum is well interpreted by introducing the concept of the distribution of the conformational angle in the irregular polymer matrix. From simulation of the ESR spectrum, it was found that the intensity of the 4-line component is very sensitive to the distribution, and that the observed 9-line spectrum is well reproduced assuming a Gaussian distribution (half-height width of 5–6°) around the most probable conformation which is nearly the same as that of the propagating radical, where the conformational angles of the two C? H_β bonds to the half-filled p-orbital are 55° and 65°.     

Infrared spectroscopic studies of the effect of elevated temperature on the association of pyroglutamic acid with clay and other minerals

Fourier transform i.r. measurements of L-pyroglutamic acid dispersed in a matrix of a clay, silica or alumina have been obtained at various temperatures between 25 and 220 degrees C. The i.r. spectrum of L-pyroglutamic acid varies in a manner dependent upon the matrix material and shows considerable change as the temperature of the mixtures is increased. The differences in the spectrum at elevated temperatures are explained in terms of a chemical reaction between hydroxyl groups in the matrix and the carboxylic acid. The i.r. spectra of trimethylsilyl derivatives of L-pyroglutamic acid and aluminum pyroglutamate were also measured to assist the understanding of spectra and interpretation of the spectral changes dependent upon increasing temperature.     

The role of tautomers in the UV absorption of urocanic acid

Tautomeric effects in the UV-absorption of trans-urocanic acid in the gas phase are investigated by means of quantum chemical calculations of sixteen tautomers at different levels, followed by absorption cross section simulations. It is shown that several trans tautomers give significant contributions to the total spectrum and that cis tautomers should not contribute to the spectrum at room temperature. The spectra of tautomers protonated at the N1 site of the imidazole ring are strongly red shifted in comparison to the spectra of tautomers protonated at the N3 site. As a consequence, excitation of the first absorption band at different wavelengths produces very different tautomeric populations. This effect helps to explain specific features observed in dispersion emission spectroscopy as well as the anomalous photophysics of urocanic acid.     

尖晶石LiMn2O4前驱体的低热固相反应法合成机理及其结构与热分解过程研究

以氢氧化锂、醋酸锰和柠檬酸为原料,采用低热固相反应法制备了Li+与Mn2+摩尔比为1∶2的前驱体化合物LiMn2L(Ac)2.通过元素分析、红外光谱、质谱和热重/差热等测试方法对前驱体的组成、结构、合成反应机理及热分解过程进行了研究.结果表明,可在全固相条件下通过低热固相反应得到锂离子与锰离子达到分子级混合水平的前驱体,该前驱体在350℃下焙烧4h即可出现明显的尖晶石相LiMn2O4产物.     

Change with temperature of the ESR spectra of methacrylic acid radicals

In order to elucidate the structure of methacrylic acid radicals, the change with observation temperature of the ESR spectrum of free radicals trapped in solid methacrylic acid γ-irradiated at ?196°C was studied. Below ?80°C, we found a 9-line spectrum, which is similar to the ordinary 9-line spectrum observed in irradiated poly(methacrylic acid) or poly(methyl methacrylate), but which differs in the stronger intensity of the so-called 4-line component. Our 9-line spectrum changes reversibly into a 13-line spectrum above ?80°C. With broad-line NMR measurements of methacrylic acid, it was found that there is such an unusual crystalline transition around ?30°C that the line width is narrower in the lower-temperature region (phase II) than that in the higher-temperature region (phase I). The change of the ESR spectrum can be interpreted in terms of the exchange of the two β-protons due to the hindered oscillation around the C_α? C_β bond of the single radical ···C_βH₂C_α(CH₃)COOH if one assumes the gradual change of the hindering potential barrier caused by the crystalline transition and the lower barrier in phase II. The modified Bloch treatment gave the hindering potential barrier to be 7.2 kcal/mole in phase I and 1.5 kcal/mole in phase II. The difference between our 9-line spectrum and the ordinary one with the very weak 4-line component comes from the difference of the surrounding matrix.     

INACTIVATION OF A RHIZOBIUM BACTERIO-PHAGE BY ULTRAVIOLET RADIATION OF DIFFERENT WAVE-LENGTHS

Abstract— The action spectrum for inactivation of a Rhizobiurn bacteriophage by U.V. radiation follows the shape of the absorption spectrum of DNA between the wave-lengths of 240 and 290 mμ (where inactivation probably reflects damage to the nucleic acid only), and deviates sharply upwards at wave-lengths shorter than 240 mμ (where inactivation may depend on damage to both the nucleic acid, and protein of the phage). The rate of inactivation follows first order kinetics approximately at all wave-lengths tested. Infectivity of the phage is halved when each mg of the phage nucleic acid has absorbed about 0 08 J of radiation energy at any wave-length between 240 and 290 mμ.
The bacteriopharge can be photoreactivated after inactivation at any wave-length between 230 and 290 mμ, but less so after inactivation at 230 mμ than at any wave-length above 240 mμ. No evidence was found to suggest that dimerization of thymine residues of the phage-DNA plays any part in the mechanism of inactivation of the bacteriophage by U.V. radiation.     

Single peptide bonds exhibit poly(pro)II ("random coil") circular dichroism spectra

The far-UV circular dichroism spectra of a series of amino acid derivatives containing single peptide bonds have been measured. The N-acetyl-alanine displays a polyproline (PP) II-like spectrum, but alaninamide shows a very weak positive signal. Similarly Gly-Ala shows a PPII spectrum, but Ala-Gly does not. On heating, the spectrum shows a two-state transition also shown by long PPII polypeptides. Thus the characteristic PPII negative maximum at <200 nm results from the coupling of a peptide bond N-terminal to the chiral alpha-carbon, and therefore the simplest peptide bonds have a preferred conformation that defines the spectrum of disordered proteins of any size.     

新型阳离子光固化剂双[(4-二苯硫鎓)苯]硫醚-双-六氟磷酸盐的合成

以二苯硫醚为主要原料,以过氧化氢为氧化剂,在室温条件下氧化得到了二苯亚砜.然后,二苯亚砜与二苯硫醚在硫酸的作用下,进行缩合反应制备了双[(4-二苯硫)苯]硫醚-双-六氟磷酸盐,收率由文献报道的39%提高到75%;对其结构进行了UV、IR、H NMR和元素分析.     

Ratiometric fluorescence response of N-methylacridone for methanesulfonic acid.

A new method for the sensitive and selective determination of stronger acids, such as methanesulfonic acid, based on an acid-base interaction with N-methylacridone fluorophore (1), is proposed. The fluorescence spectrum of 1 was changed drastically by the addition of methanesulfonic acid in methanol. A ratiometric analysis of methanesulfonic acid by measuring the fluorescence intensities of 1 both at 426 nm and 473 nm showed good linearity with a correlation coefficient of 0.9995.     

Spectral characterization of the bioactive principles and antibacterial properties of cold methanolic extract of Olea europaea from the Hail region of Saudi Arabia

This work aimed to identify the bioactive constituents and antibacterial activity of a cold methanolic extract of Olea europaea leaves. GC–MS analysis of the cold methanolic extract of the leaves of O. europaea L. revealed several unique bioactive compounds, including 9,12-octadecadienoic acid (Z,Z)-, n-hexadecanoic acid, 9-octadecenamide, (Z)-, hexadecanoic acid, 2-hydroxy-1-(hydroxymethyl)ethyl ester, squalene, 2-(2-Hydroxy-2-phenylethyl)-3,5,6-trimethylpyrazine, Benzoic acid, 4-formyl-, methyl ester, 2-Methoxy-4-vinylphenol, Vitamin E etc. The FT-IR spectrum revealed distinct fingerprint regions at 3313, 2943, 2831, 1662, 1590, 1449, 1300, 1111, and 1020 cm^?1. The fingerprinting region is associated with the presence of several bioactive chemicals as determined by GC–MS analyses. The methanolic extract of O. europaea leaves revealed a broader spectrum of antibacterial activity. On the other hand, the spectrum of activity was substantially narrower than that of standard ciprofloxacin discs.     

Integration of polyaniline/poly(acrylic acid) films and redox enzymes on electrode supports: an in situ electrochemical/surface plasmon resonance study of the bioelectrocatalyzed oxidation of glucose or lactate in the integrated bioelectrocatalytic systems

Electropolymerization of aniline in the presence of poly(acrylic acid) on Au electrodes yields a polyaniline/poly(acrylic acid) composite film, exhibiting reversible redox functions in aqueous solutions at pH = 7.0. In situ electrochemical-SPR measurements are used to identify the dynamics of swelling and shrinking of the polymer film upon the oxidation of the polyaniline (PAn) to its oxidized state (PAn(2+)) and the reduction of the oxidized polymer (PAn(2+)) back to its reduced state (PAn), respectively. Covalent attachment of N(6)-(2-aminoethyl)-flavin adenin dinucleotide (amino-FAD, 1) to the carboxylic groups of the composite polyaniline/poly(acrylic acid) film followed by the reconstitution of apoglucose oxidase on the functional polymer yields an electrically contacted glucose oxidase of unprecedented electrical communication efficiency with the electrode: electron-transfer turnover rate approximately 1000 s(-1) at 30 degrees C. In situ electrochemical-SPR analyses are used to characterize the bioelectrocatalytic functions of the biomaterial-polymer interface. The current responses of the bioelectrocatalytic system increase as the glucose concentrations are elevated. Similarly, the SPR spectra of the system are controlled by the concentration of glucose. The glucose concentration controls the steady-state concentration ratio of PAn/PAn(2+) in the film composition. Therefore, the SPR spectrum of the film measured upon its electrochemical oxidation is shifted from the spectrum typical for the oxidized PAn(2+) at low glucose concentration to the spectrum characteristic of the reduced PAn at high glucose concentration. Similarly, the polyaniline/poly(acrylic acid) film acts as an electrocatalyst for the oxidation of NADH. Accordingly, an integrated bioelectrocatalytic assembly was constructed on the electrode by the covalent attachment of N(6)-(2-aminoethyl)-beta-nicotinamide adenine dinucleotide (amino-NAD(+), 2) to the polymer film, and the two-dimensional cross-linking of an affinity complex formed between lactate dehydrogenase and the NAD(+)-cofactor units associated with the polymer using glutaric dialdehyde as a cross-linker. In situ electrochemical-SPR measurements are used to characterize the bioelectrocatalytic functions of the system. The amperometric responses of the system increase as the concentrations of lactate are elevated, and an electron-transfer turnover rate of 350 s(-1) between the biocatalyst and the electrode is estimated. As the PAn(2+) oxidizes the NADH units generated by the biocatalyzed oxidation of lactate, the PAn/PAn(2+) steady-state ratio in the film is controlled by the concentration of lactate. Accordingly, the SPR spectrum measured upon electrochemical oxidation of the film is similar to the spectrum of PAn(2+) at low lactate concentration, whereas the SPR spectrum resembles that of PAn at high concentrations of lactate.     

Flexible biphenyl chromophore as a circular dichroism probe for assignment of the absolute configuration of carboxylic acids

A general and nonempirical approach to determine the absolute configuration (AC) of 2-substituted chiral carboxylic acids by circular dichroism (CD) spectroscopy has been developed. In this protocol, the chiral acids are converted to the corresponding biphenyl amides, in which a flexible biphenyl probe gives rise to a Cotton effect at 250 nm (A band) in the CD spectrum, the sign of which is related to the acid AC. Two different mechanisms of transfer of chirality from the acid stereogenic center to the biphenyl moiety are operative in amides derived from 2-alkyl- and 2-aryl-substituted acids, respectively. For both classes of compounds, a model has been defined which allows one to predict, for a given acid AC, the preferred twist of the biphenyl moiety and thus the sign of the A band in the CD spectrum, related to the biphenyl torsion. Interestingly, while in alkyl-substituted substrates the preferred biphenyl twist is determined only by steric interactions, in the aryl-substituted ones the structure of the prevalent conformer and thus the biphenyl twist are dictated by arene-arene edge-to-face stabilizing interactions. Following this protocol, the AC of a 2-substituted chiral acid can be established simply by preparing its biphenyl amides, recording the CD spectrum, and looking at the sign of the A band. From the sign of such a band, the torsion of the biphenyl can be deduced and then the acid AC. Substrates having different structures and functionalities have been investigated, always obtaining reliable AC assignments by this simple protocol.     

X-ray photoelectron spectra of dinitrogen chelating ligands with some transition metals

The complexes of two chelating agents, CDTA (trans-1,2-cyclohexanediaminetetraacetic acid) and EDTA (ethylenediaminetetraacetic acid), with Ni(II), Co(II) and Cu(II) are studied by means of X-ray photoelectron spectroscopy (XPS). The N1s spectrum of CDTA has two components at 398.5 (±0.2 eV) and 400.9 (±0.2 eV) while only one signal is found after coordination at 400.0±0.2 eV. EDTA shows a N1s spectrum with one component at 400.9±0.2eV. A negative shift of about -1.3eV is observed in its complexes. The results are compared with the literature data on the complexes in the solid state.     

EPR, optical and infrared absorption studies of Mn2+ ions doped in zinc malate trihydrate single crystal

Electron paramagnetic resonance (EPR) studies have been carried out on Mn2+ ions doped in zinc malate trihydrate single crystals in the temperature range 123-413 K on X-band frequency. The EPR spectrum at room temperature exhibits a group of five fine structure transitions each splits into six hyperfine components. Angular variation studies reveal that Mn2+ ions enter the lattice substitutionally. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The variation of zero-field splitting parameter (D) with temperature is measured. From the optical absorption spectrum, the crystal field splitting parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The infrared spectrum exhibits bands characteristic of the carboxylic acid salts.     

Photoelectron spectroscopic studies of the interfacial reaction between glass and commercial adhesive

The valence band and core‐level photoelectron spectroscopy [using X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS)] were used to probe the interfacial reaction between glass and a commercial adhesive (Loctite). The interaction was investigated by comparing experimental valence band spectra with spectra calculated for various possible interaction schemes. The valence band spectrum for the interfacial region between the glass and the adhesive was obtained using difference spectra on a thin film of adhesive on glass. This film was sufficiently thin that the adhesion interphase could be directly probed. Chemical interaction occurs at the interface as evidenced by the fact that the spectrum for the interfacial region could not be represented by the addition of the spectrum of the glass alone and the adhesive alone. The XPS valence band spectrum and the UPS spectrum showed that the shallow top surface layer is very much enriched in acrylic acid, which is a minor component in the adhesive. When the Loctite adhesive was coated on glass, the C1s and O1s regions of the adhesion interface region showed evidences of new chemistry at the adhesive–glass interface. The possible reactions were evaluated by comparison of the experimental spectra with calculated ones based on different models using ab initio molecular orbital calculations. The experimental spectra are well represented by models where the acrylic acid of the surface region of the adhesive reacts with the glass, suggesting chemical interaction occurred at the adhesion interphase. Copyright © 2009 John Wiley & Sons, Ltd.