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11.
Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer 总被引:2,自引:0,他引:2
A piezoelectric quartz sensor coated with molecularly imprinted polymer (MIP) for caffeine was developed. The MIP was prepared by co-polymerizing methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of azobis(isobutyronitrile) as initiator, caffeine as template molecule, and chloroform as solvent. The MIP suspension in polyvinyl chloride/tetrahydrofuran (6:2:1 w/w/v) solution was spin coated onto the surface of the electrode of a 10 MHz AT-cut quartz crystal. The sensor exhibited a linear relationship between the frequency shift and caffeine concentration in the range of 1×10–7 mg mL–1 up to 1x10–3 mg mL–1 [correlation coefficient (r)=0.9935] in a stopped flow measurement mode. It has a sensitivity of about 24 Hz/ln(concentration, mg mL–1). A steady-state response was achieved in less than 10 min. The performance characteristic of the sensor shows a promising and inexpensive alternative method of detecting caffeine. Surface studies were carried out for the reagent phase of the sensor using SEM, AFM, and XPS analysis in order to elucidate the imprinting of the caffeine molecule. The SEM micrograph, AFM image, and XPS spectra confirmed the removal of caffeine by Soxhlet extraction in the imprinting process and the rebinding of caffeine to the MIP sensing layer during measurement. 相似文献
12.
J. D. Petke Gerald M. Maggiora‡ Lester Shipman‡ Ralph E. CHRISTOFFERSEN‡ 《Photochemistry and photobiology》1979,30(2):203-223
Abstract— Ab initio configuration interaction wavefunctions and energies are reported for the ground state and many low-lying excited singlet and triplet states of ethyl pheophorbide a (Et-Pheo a) and ethyl chlorophyllide a (Et-Chl a), and are employed in an analysis of the electronic absorption spectra of these systems. In both molecules the visible spectrum is found to consist of transitions to the two lowest-lying 1(π, π*) states, S1 and S2. The configurational compositions of S1 and S2 in both molecules are similar, and are described qualitatively in terms of a four-orbital model. The S1← S0 transition in each case is predicted to be intense, and is largely in-plane y-polarized, while the S2← S0 transition is predicted to be extremely weak and in-plane polarized. The orientation of the S2← S0 transition dipole is not conclusively established in the present calculations. The Soret band in both molecules is composed of transitions to no less than ten states (S3-S12 in Et-Chl a and S3-S7S9-S12. and S14 in Et-Pheo a), which exhibit primarily (π, π*) character. The configurational compositions of these states are generally a complex mixture of excitations from both occupied macrocyclic π molecular orbitals and occupied orbitals with electron density in the cyclopen-tanone ring and the carbomethoxy chain. No clear correspondences are evident between respective Soret states of the two systems. Transitions to these states are generally intense and display a variety of in-plane polarizations. Two additional Soret states of Et-Pheo a, S8 and S13, exhibit primarily (n. π*) character. S8 is characterized by excitations from u and non-bonding regions of the carbomethoxy chain, while S13 is described by n →π* excitations involving the nitrogen atom of ring II. No corresponding (n, π*) states were found for Et-Chl a. In both molecules the lowest two triplet states, T1 and T2, are found to lie lower in energy than S1. while T, and S1 are approximately degenerate. The configurational compositions of T1-T4 of both molecules are nearly identical, and may be described by a four-orbital model. However, the compositions of T1-T4 differ sharply from those of S1 and S2. A number of higher-lying 3(π, π*) states of both molecules (T5-T13 in Et-Chi a and T8-T9, T11-T13 in Et-Pheo a) are found to have energies similar to the singlet Soret states, relative to S0. They are characterized by a complex mixture of configurations which do not include significant contributions involving the four-orbital model. In addition, two 3(n, π*) states of Et-Pheo a, T10 and T14, are found, which are somewhat analogous to S8 and S13. Additional data presented include the charge distributions and molecular dipole moments of the S0. S1, and T1 states of both molecules, as well as energies and oscillator strengths of computed Sn←S1 and Tn←1 transitions. 相似文献
13.
PHOTOINACTIVATION OF CATALASE 总被引:6,自引:0,他引:6
Abstract— Inactivation of catalase with visible light (>400nm) has been studied in purified bovine liver catalase and in peroxisomal catalase in the mitochondrial fraction of rat liver. Light corresponding to that of maximal absorbance of the heme site (405 nm) was most effective in inactivation. Although photoinactivation is O2 dependent, scavengers of OH radical, 1 O2 and O− 2 did not protect against loss of activity in either system. Superoxide dismutase partially protected purified catalase added into the mitochondrial fraction system. However, complete protection of catalase was afforded by low concentrations of substrates such as formic acid or methanol which rapidly convert Compound I to Ferricatalase. 相似文献
14.
Summary A method has been developed for the direct spectrophotometric determination of gold by using the wine coloured complex formed in the interaction of gold with the Woods reagent. The colour reaction follows Beer's law and is stable. The method is sensitive, reproducible and accurate. Of the several anions and cations studied, only a few interfered seriously in the determination of gold. However, the ones that do interfere seriously can be separated by conventional methods. The mole ratio curve for the gold-Woods reagent system shows definite evidence that a 1 to 1 interaction product is produced in the reaction. As the mole ratio of the Woods reagent to gold was varied from 15 to 101, absorbance measurements indicated that reaction products lower or higher than 1 to 1 mole ratio are not formed.
Zusammenfassung Es wird eine Methode zur direkten spektrophotometrischen Goldbestimmung beschrieben, die auf der Bildung des weinrot gefärbten Komplexes mit Woods' Reagens beruht. Die Färbung ist beständig und befolgt das Beersche Gesetz. Das Verfahren ist empfindlich und liefert reproduzierbare und genaue Ergebnisse. Die wenigen Ionen, die beträchtliche Störungen verursachen, können nach üblichen Methoden abgetrennt werden. Es wurde festgestellt, daß das Molverhältnis Au: Reagens in dem gebildeten Komplex 11 beträgt.相似文献
15.
Reaction of laser-ablated Zr with CH(4) ((13)CH(4), CD(4), and CH(2)D(2)) in excess neon during condensation at 5 K forms CH(2)=ZrH(2), the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm(-)(1). Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C(1) symmetry structure with agostic C-H- - -Zr bonding and distance of 2.300 A. Identification of the agostic CH(2)=ZrH(2) methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHD=ZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH(2)=ZrH(2). Finally, methane activation by CH(2)=ZrH(2) gives the new (CH(3))(2)ZrH(2) molecule. 相似文献
16.
Fluorescence-dip infrared spectroscopy and predissociation dynamics of OH A 2Sigma+ (v = 4) radicals
Derro EL Pollack IB Dempsey LP Greenslade ME Lei Y Radenović DC Lester MI 《The Journal of chemical physics》2005,122(24):244313
Fluorescence-dip infrared spectroscopy, an UV-IR double-resonance technique, is employed to characterize the line positions, linewidths, and corresponding lifetimes of highly predissociative rovibrational levels of the excited A (2)Sigma(+) electronic state of the OH radical. Various lines of the 4 <--2 overtone transition in the excited A (2)Sigma(+) state are observed, from which the rotational, centrifugal distortion, and spin-rotation constants for the A (2)Sigma(+) (v = 4) state are determined, along with the vibrational frequency for the overtone transition. Homogeneous linewidths of 0.23-0.31 cm(-1) full width at half maximum are extracted from the line profiles, demonstrating that the N = 0 to 7 rotational levels of the OH A (2)Sigma(+) (v = 4) state undergo rapid predissociation with lifetimes of < or =23 ps. The experimental linewidths are in near quantitative agreement with first-principles theoretical predictions. 相似文献
17.
The mass spectra of aluminum isopropoxide show that polymers, [Al(OC3H7)3]x where x = 1 to 7, can be present in the vapor and are, therefore, probably present in the bulk sample. The polymeric composition of the vapor depends on the previous history of the sample. Exact mass measurements on many of the ions along with data on a number of metastable peaks support the proposed fragmentation mechanisms. Loss of 102 mass units between intense peaks in the mass range above 500 a.m.u. leads to the suggestion that the higher polymers may be used as high mass marking substances. 相似文献
18.
Kenji Maeda Ross A. Miller Ali Shafiee Joseph D. Armstrong III 《Tetrahedron letters》2005,46(9):1545-1549
Highly diastereoselective (>20:1) bromo-lactonization of N-sulfonyl-2-allyl-2-phenylglycine methyl ester (11) was observed. Successive treatment of the chiral lactone with MeONa gave the desired (2S,4R)-4-hydroxy-2-phenylproline derivative in high yield without erosion of the diastereoselectivity. The starting chiral non-racemic compound (5) was prepared from the racemic 2-phenylglycine using a classical kinetic resolution (crystallization), an asymmetric phase transfer alkylation, and an enzyme-catalyzed kinetic resolution. 相似文献
19.
C. E. Aalseth F. T. Avignone III R. L. Brodzinski H. S. Miley J. H. Reeves 《Journal of Radioanalytical and Nuclear Chemistry》1998,233(1-2):119-125
A fast digital oscilloscope based pulse shape discrimination (PSD) system has been tested with intrinsic germanium detectors
large enough to allow ionizing events which generate localized electron-hole pairs at a single site to be segregated from
those depositing energy at several different sites in the crystal. Drift velocities of the electrons and holes result in pulses
several hundred nanoseconds long. Since the electric field varies by almost a factor of 10 between the outer and inner surfaces,
collection of electrons and holes can frequently be dinstinguished, and pulses due to multi-site events can be distinguished
from single site events. 相似文献
20.
Oscar H. Will III Natalie A. Newland Kaylan L. Blelville 《Photochemistry and photobiology》1985,41(3):283-287
Abstract— Exposure of variously pigmented strains of Ustilago violacea to high intensity incandescent radiation resulted in the generation of three types of survival curves. High carotene, low cytochrome c containing strains of U. violacea were generally characterized by linear type I survival curves with slopes approximately equal to zero. Strains which lacked carotenes were characterized by exponential decay type II survival curves. A third survival curve, type III was observed with carotene accumulating strains which also contained large amounts of cytochrome c. The type III curves are characterized by an initial loss of viability, similar to the type II curves, followed by a recovery period, with eventual stability in survival. The survival curve type appears to be dependent on the relative mg quantities of cytochrome c and carotenes in the cells. Strains with carotene/cytochromec ratios of0–1 × 10-1 ,3–15× 10-1 and l6 × 10-1 and above had type II, type III and type I survival curves, respectively. 相似文献