Transformation of hydrogel-based inverse opal photonic sensors from FCC to L1(1) during swelling

The structural evolution of Bragg diffracting inverse opal hydrogel sensors during swelling is directly observed by two-photon laser scanning fluorescence microscopy and compared to predictions from finite element analysis. A fluorescently labeled pH-sensitive hydrogel is UV-polymerized in a dried polystyrene colloidal crystal template, which is etched to yield an inverse opal. Fluorescence imaging of the hydrogel at different pH values reveals an inhomogeneous deformation of the FCC array of aqueous pores. The pores elongate along the sample normal direction and collapse along the sample parallel directions, consistent with the Bragg response, which indicates a 1-D increase in the interlayer distance. Interconnects between the pores serve as anchor points during hydrogel expansion into the pores. Pinning of the hydrogel to the substrate causes a change of the hydrogel lattice symmetry during deformation, from FCC (ABC stacking) to L1(1) (ABCA'B'C' stacking). Reconstructed cross-sections confirm that a 1-D increase in the interlayer distance along the substrate normal direction is responsible for the diffraction response of an inverse opal hydrogel sensor. Comparison with predictions from finite element analysis shows qualitative agreement, although the experimental mesostructure is significantly more deformed than the calculated data, due to buckling in the experimental system that is not captured by the model.     

Screening of amphetamines by gradient microbore liquid chromatography and pre-column technology

Amphetamine-type drugs with a wide polarity range have been screened in both human and horse urine using on-line pre-concentration on pre-columns packed with hydrophobic and cation-exchange sorbents in series and gradient microbore high-performance liquid chromatography. The underivatized amphetamines were identified by UV detection at 210 nm. The method has potential for the automated liquid chromatographic screening of amphetamines in urine, e.g., for doping control.     

Photochemical Reactions. 128th Communication. Isolation of a Thermally Labile 2,8-Dioxabicyclo[3.2.1]oct-3-ene Intermediate on Photolysis of 3,4: 5,6-Diepoxy-5,6-dihydro-β-ionone

Photolysis (λ = 254 mm, THF) of the diepoxyenone (E)- 1 at ?78° leads to the 2,8-dioxabicyclo[3.2.1]oct-3-ene intermediate 3 (51%). At ambient temperature 3 undergoes an unexpectedly rapid electrocyclic opening to the triketone 2 in quantitative yield. Compound 3 seems likely to be the intermediate in the acid-catalyzed rearrangement of (E)- 1 → 18 also.     

Some aspects of room-temperature phosphorescence in liquid solutions

Experimental requirements for room-temperature phosphorescence measurements in liquids (RTPL) are discussed. Phosphorescence quantum yields and triplet lifetimes of some brominated naphthalenes and halogenated biphenyls at 77 K in 2-methyltetrahydrofuran and at room temperature in hexane are reported and compared. Surprisingly the naphthalenes show only little loss in quantum yields in going from 77 K to room temperature. Sensitized phosphorescence is discussed as a means of expanding the analytical potential of RTPL. Results with a model system of benzophenone as a donor (analyte) and 1,4-dibromonaphthalene as an acceptor are presented.     

Photochemical CO2 splitting by metal-to-metal charge-transfer excitation in mesoporous ZrCu(I)-MCM-41 silicate sieve

Binuclear redox sites consisting of a Zr oxo-bridged to a Cu(I) center have been obtained on the pore surface of MCM-41 silicate sieve by a stepwise grafting procedure, along with isolated metal centers. The bimetallic site features a Zr(IV)-O-Cu(I) to Zr(III)-O-Cu(II) metal-to-metal charge-transfer (MMCT) absorption extending from the UV region to about 500 nm. The Zr-O-Cu linkage is revealed by a Cu(I)-O infrared stretch mode at 643 cm-1. Irradiation of the MMCT chromophore of ZrCu(I)-MCM-41 loaded with 1 atm of CO2 gas at room temperature resulted in growth of CO (2150 cm-1) and H2O (1600 cm-1). Photolysis experiments using 13CO2 and C18O2 demonstrate that carbon monoxide and the oxygen atom of the water product originate from CO2. This indicates splitting of the CO2 by the excited MMCT moiety to CO and a surface OH radical, followed by trapping of the products at Cu(I) centers (OH is reduced to H2O). This is the first observation of CO2 photoreduction at a binuclear MMCT site at the gas-solid interface.     

Photochemische Reaktionen 94. Mitteilung. Vinyloge β-Spaltung bei Epoxy-enonen der Jonon-Reihe

Photoinduced Vinylogous β-Cleavage of Epoxy-enones of the Ionone Series The photochemistry of the α,β-unsaturated γ,δ-epoxy-enones 1–3 is determined by: (i) C(γ)-O-scission of the epoxide (vinylogous β-cleavage of Type A); (ii) C(γ)-C(δ)-cleavage of the oxirane (vinylogous β-cleavage of Type B); (iii) (E/Z)-isomerization of the enone chromophore. In contrast, 4 with tertiary C(β) shows no Type B cleavage. Type A cleavage is induced both by n,π*- and π,π*-excitation and arises probably from the T₁-state, but Type B cleavage is observed only on π,π*-excitation and represents presumably a S₂-reaction. On Type A cleavage 1–4 undergo 1,2-alkyl-shifts to 1,5-dicarbonyl compounds ( 15–18, 25–28, 34 and 35 ) or rearrange to dihydrofuranes ( 7 and 30 ). The isomerization 1→7 proceeds by a stereoselective [1,3]-sigmatropic shift. On Type B cleavage 1–3 isomerize to a bicyclic enol-ether ( 8, 29 ) or to a monocyclic enol-ether ( 9 ; product of a homosigmatropic [1,5]-shift) or undergo fragmentation to isomers such as allenes 10, 22 and 31 or cyclopropenes 11 and 21 . The non-isolated, unstable (Z)-epoxy-enones 14, 19, 24 and 38 isomerize by fragmentation to the furanes 12, 23, 33 and 39 respectively, on contact with traces of acid or by heating. However, for 19 and 4 , Type B cleavage may lead to the furanes 23 and 39 . On UV. irradiation of the epoxy-enone 4 the initially formed (E/Z)-isomers 34 and 35 yield on π,π*-excitation the enones 37 and 40 by a vinylogous β-fragmentation. In addition, on n,π*-excitation 34 isomerizes to 35 , which decarbonylates exclusively to the enone 37 . The reactions of 1–4 with BF₃ · O(C₂H₅)₂ were also studied (see appendix). The epoxy-enones 1 and 2 isomerize by an 1,2-alkyl shift in good yield to the 1,4-dicarbonyl compounds 79 and 81 , whereas 3 gives the 1,4-diketone 83 , and in small amounts the 1,5-diketone 84 . On the other hand, 4 is converted to the fluorohydroxy-enone 85 and to the 1,5-dicarbonyl product 34 , the only isomer in this series which is identical with one of the photoproducts.     

Quenched peroxyoxalate chemiluminescence detection in aqueous liquid chromatographic separations

Several analytes, such as bromide, iodide, sulphite, nitrite, substituted anilines and organosulphur compounds cause quenching of peroxyoxalate chemiluminescence. This phenomenon, quenched peroxyoxalate chemiluminescence, can be used as a method of detection for liquid chromatography. The potential of quenched chemiluminescence is discussed, with special attention give to its compatibility with aqueous separation systems. An immobilized fluorophore, 3-aminofluoranthene on controlled pore glass, is packed in the detector cell. Liquid-state studies show that the influence of both the nature and concentration of the fluorophore is small, which indicates a more complicated mechanism of the chemiluminescence reaction than previously assumed. It is shown that bis(2-nitrophenyl)oxalat is a more suitable oxalate for quenched chemiluminescence detection than bis(2,4,6-trichlorophenyl) oxalate. This is demostrated for ion-chromatography of bromide and iodide and the aqueous reversed-phase separation of organosulphur compounds. Detection limits in the low nanogram and sub-nanogram region are reported for the above compounds. When an electronic inverter was used, calibration curves were linear over a concentration range of 2–3 decades. The method is quite selective and can be applied to relatively complex matrices without sample pretreatment.     

Synthesis and Configuration of Some Hydroxymilbemycin Derivatives Including 22,23-Dihydroavermectin B1b Aglycone

The synthesis of several configurationally defined hydroxymilbemycin derivatives is described. One of these allylic alcohols is the known 5-O-[(tert-butyl)dimethylsilyl]-13α-hydroxymilbemycin D (= 5-O-[(tert-butyl)-dimethylsilyl]-22,23-dihydroavermectin B _1b, aglycone; 15D ), the synthesis of which represents LI conversion of the milbemycin to the avermectin series of natural products. The configurations at C(13), C(14), and C(15) of the new milbemycin derivatives were determined by NMR experiments and force-field calculations.     

Photochemical Reactions 151st Communication. Photo-oxygenation of (E)- and (Z)-7-Methyl-β-ionone

Photo-oxygenation of (E)-7-methyl-β-ionone ((E)? 1 ) and (E)-8-methyl-β-ionone ((E)? 2 ) gave rise to the formation of the hydroperoxy-enones (E)? 10 and (E)? 15 , respectively, which, in part, underwent intramolecular epoxidation to the hydroxy-epoxy-ketones 11 and 16 , respectively, The product distribution of the photo-oxidation of (Z)? 1 shows a marked influence of the skewed ground-state conformation of the dienone chromophore. Thus, singlet oxygen (¹O₂) was added to C(γ) of the dienone chromophore leading to the spirocyclic peroxy-hemiacetal 12 and to the endoperoxide 13 . In addition, the tricyclic peroxide 14 was formed as a new type of product via primary addition of ¹O₂ to C(γ) of the dienone chromophore. The structure of 14 was established by X-ray crystal-structure analysis of the hemiacetal 22 .     

Photochemical reaction detectors in continuous-flow systems — applications to pharmaceuticals

Several basic parameters of a photochemical reactor coupled to a high-performance liquid Chromatographie system are discussed. The non-fluorescent clobazam and desmethylclobazam and three phenothiazines, which exhibit native fluorescence, are used as model compounds. On irradiation with ultra-violet light, the reaction products formed display fluorescence (clobazam, desmethylclobazam) or unproved fluorescence characteristics (phenothiazines). The effects of carrier stream (mobile-phase) composition, time of irradiation and band broadening in the reactor on the fluorescence signal are described. The polarity of the organic solvents used (methanol, ethanol, acetonitrile) appears to have an important effect on the fluorescence intensity. For clobazam and desmethylclobazam, detection limits of 70 and 120 pg, respectively, were calculated after an irradiation time of 28 s with methanol—0.01 M (pH 5) acetate buffer (1:1) as mobile phase. The method is applied to the determination of both compounds in serum and urine samples.