Aromatic protonation—4: On the 1H-2H exchange of three 9-n-alkylanthracenes on reaction with CF3CO2[2H] and FSO3[2H]

The reactions of 9-methyl-, 9-ethyl- and 9-propyl-anthracene with CF₃CO₂[²H] in C[²H]Cl₃ and with FSO₃[²H] in SO₂ClF have been investigated. Using 4 equivalents of CF₃CO₂[²H] at 50° ¹H-²H exchange was observed only for the 10-H and the side-chain α-hydrogens, and on using 8 and 12 equivalents at 50° also for the aromatic α-hydrogens. Treatment of the substrates with FSO₃[²H] at -60° leads to the stable 9-alkyl-[10-²H]-10-anthracenium ions. On warming up to ?25° a slow ¹H-²H exchange of only the 10-¹H of these anthracenium ions is observed. A mechanism for the ¹H-²H exchange of the aromatic and the side-chain α-hydrogens of the 9-alkylanthracenes is presented.     

Shpol''skii fluorimetric determination of polycyclic aromatic hydrocarbons in complex environmental samples

Summary High-resolution fluorimetry in low-temperature n-alkane Shpol'skii matrices is a powerful technique for the analysis of rigid, non-polar compounds like polycyclic aromatic hydrocarbons. Because of the method's sensitivity and selectivity, sample clean-up, preconcentration and even chromatographic separation can often be left out. The Shpol'skii analysis of pyrene in crude extracts from marine sediments and from bird meat is demonstrated. Special attention is focussed on the extra possibilities acquired when a laser is used as excitation source (Laser Excited Shpol'skii Spectroscopy, LESS).     

Sequential energy and electron transfer in aggregates of tetrakis[oligo(p-phenylene vinylene)] porphyrins and C60 in water

Chiral aggregation of oligo(p-phenylene vinylene)-functionalized Zn and free-base porphyrins is observed in water. The formation of mixed assemblies containing both porphyrins results in sequential energy transfer from OPV via zinc porphyrin to free-base porphyrin. Furthermore, the incorporation of C60 as electron acceptor yields a charge separated state by ultimate electron transfer.     

Flavonoids in Leguminosae: analysis of extracts of T. pratense L., T. dubium L., T. repens L., and L. corniculatus L. leaves using liquid chromatography with UV, mass spectrometric and fluorescence detection

Reversed-phase LC on C-18 bonded silica with a methanol–ammonium formate gradient was used to determine the main flavonoids in leaves of four species of the Leguminosae family. The detection modes were diode-array UV absorbance, fluorescence, and (tandem) mass spectrometry. LC–UV was used for a general screening, sub-classification, and the calculation of total flavonoid contents. LC–FLU was included to identify isoflavones on the basis of their native fluorescence. Most structural information regarding aglycons, sugar moieties, and acidic groups was derived from LC–MS in both the full-scan and extracted-ion mode, using negative-ion atmospheric pressure chemical ionization. MS/MS did not provide much additional information, because the same fragments were observed as in full-scan MS.In T. pratense and T. repens, the main constituents were flavonoid glucoside–(di)malonates, while T. dubium and L. corniculatus mainly contained flavonoid (di)glycosides. Satellite sets comprising an aglycon, the glucoside and glucoside–malonates or –acetates, were abundantly present only in T. pratense. Generally speaking, the main aglycons and sugars in the four plant species are surprisingly different. In addition, while the results for T. pratense are similar to those reported in the literature, there is little agreement in the case of the other species. Finally, total flavonoid contents ranged from 50–65 mg/g for L. corniculatus and T. dubium, to 15 mg/g for T. pratense and only 1 mg/g for T. repens.     

Applicability of surface-enhanced resonance Raman scattering for the direct discrimination of ballpoint pen inks

In situ surface-enhanced resonance Raman spectroscopy (SERRS) with excitation at 685 nm is suitable for the direct discrimination of blue and black ballpoint pen inks on paper. For black inks, shorter excitation wavelengths can also be used. For blue inks, SERRS at 514.5 and 457.9 nm does not provide adequate discriminative power. At these excitation wavelengths, the SERRS signals of the Methyl Violet derivatives present in inks easily dominate the overall spectrum because of resonance enhancement and preferential interaction with silver sol particles. At 685 nm, this problem is not encountered as the Methyl Violet derivatives do not show resonance enhancement, while other components may still exhibit resonance. Thirteen blue and thirteen black ink lines were examined. For the blue and black inks, on the basis of the 685 nm SERR spectra, eight and six groups of spectra, respectively, could be distinguished. This discrimination largely agrees with information from thin layer chromatography (TLC) experiments, although some differences in group compositions are found. The in situ SERR spectra show good repeatability with regard to the Raman frequencies, band shapes and relative intensities of the spectral bands. However, absolute intensities cannot be used for discrimination purposes.     

Hyphenation of column liquid chromatography and Raman spectroscopy via a liquid-core waveguide: chemometrical elimination of spectral eluent background

In column liquid chromatography (LC) coupled to conventional Raman spectroscopy (RS) removal of the spectral background of the eluent is often demanding, because of the strong signals of the organic modifier. A new chemometrical method is proposed, called the eluent background subtraction (EBS) method, which can correct for small shape and intensity differences of the eluent spectra. The variations in the eluent spectra are modelled using principal component analysis (PCA). The PCA loading vectors are subsequently used for eluent background correction of the elution spectra of the analyte. The loading vectors are fitted under these spectra by an asymmetric least-squares method. This method was successfully applied under various experimental conditions and performed much better than conventional background correction methods. Analyte detectability was improved by (weighted) averaging of all elution spectra and smoothing via a p-spline function.     

SULFONATION OF 9-ALKYLANTHRACENES

Abstract

The reaction of anthracene, 9-phenylanthracene and some 9-alkylanthracenes with dioxan-SO₃ has been studied. Anthracene yields the 1-, 2- and 9-sulfonic acid in a ratio of 24 : 6 : 70. 9-Phenyl- and 9-neopentyl-anthracene both yield a mixture of the 4- and 10-sulfonic acids in a ratio of 33 : 67 and 15 : 85 respectively. Unexpectedly, 9-methylanthracene yields, in a more rapid reaction, exclusively 9-anthrylmethanesulfonic acid (1, R[dbnd]H) 9-Alkylanthracenes of which the alkyl group contains at least one α-H yield as main product (s) the α-sulfonic acids 1 and/or (depending on the further structure of the alkyl group) the sulfonic acids 2–4.     

Structural Effects in Visible‐Light‐Responsive Metal–Organic Frameworks Incorporating ortho‐Fluoroazobenzenes

The ability to control the interplay of materials with low‐energy photons is important as visible light offers several appealing features compared to ultraviolet radiation (less damaging, more selective, predominant in the solar spectrum, possibility to increase the penetration depth). Two different metal–organic frameworks (MOFs) were synthesized from the same linker bearing all‐visible ortho‐fluoroazobenzene photoswitches as pendant groups. The MOFs exhibit different architectures that strongly influence the ability of the azobenzenes to isomerize inside the voids. The framework built with Al‐based nodes has congested 1D channels that preclude efficient isomerization. As a result, local light–heat conversion can be used to alter the CO₂ adsorption capacity of the material on exposure to green light. The second framework, built with Zr nodes, provides enough room for the photoswitches to isomerize, which leads to a unique bistable photochromic MOF that readily responds to blue and green light. The superiority of green over UV irradiation was additionally demonstrated by reflectance spectroscopy and analysis of digested samples. This material offers promising perspectives for liquid‐phase applications such as light‐controlled catalysis and adsorptive separation.