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C. A. Parker

Bio: C. A. Parker is an academic researcher. The author has contributed to research in topics: Phosphorescence & Fluorescence. The author has an hindex of 1, co-authored 1 publications receiving 191 citations.

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Journal ArticleDOI
01 Feb 1967
TL;DR: Parker et al. as discussed by the authors outline the principles of all these techniques and draw attention to some unusual results obtained with them, including the observation of delayed fluorescence, which was until recently of interest only to the photochemist, but it has now been shown to have potential value as an analytical technique also.
Abstract: From its first analytical applications (Bowman et al, 1955: Parker, et al, 1957) the technique of fluorescence photoelectric spectrometry developed within a decade to become a standard technique for trace organic and inorganic analysis. Reviews and text-books (Bartholomew, 1958: Parker, et al, 1962: Hercules, 1966) deal with the principles of its analytical application and the excellent text book of Udenfriend (1962) covers the applications in the biochemical field. The possibility of using phosphorescence measurement for analytical purposes was first suggested by Lewis and Kasha (1944) and was subsequently taken up by Freed and Salmre (1958) and by Parker and Hatchard (1962). It now promises to rival fluorescence measurement as a method for the trace analysis of organic materials. The observation of delayed fluorescence was until recently of interest only to the photo-chemist, but it has now been shown to have potential value as an analytical technique also (Parker et al, 1965). The object of this paper is to outline briefly the principles of all these techniques and to draw attention to some unusual results obtained with them.

191 citations


Cited by
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Journal ArticleDOI
TL;DR: Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells.

2,424 citations

Journal ArticleDOI
TL;DR: Several, but not all, results support the raft concept, but further definition of the structure, dynamics and function of lipid domains in various biological contexts is urgently required.

412 citations

Journal ArticleDOI
TL;DR: In this paper, a system of first-order linear differential equations containing as only parameters the rate of fluorescence emission and rate of transport of the excitation from one orthogonal component of the emission to another is described.
Abstract: The depolarization of the fluorescence of solutions by either Brownian rotations or intermolecular energy transfer may be simply described by a system of first‐order linear differential equations containing as only parameters the rate of fluorescence emission and the rate of transport of the excitation from one orthogonal component of the emission to another. The steady‐state solution has the form of Perrin's equation describing the depolarization by Brownian rotations, and the time‐dependent depolarization following a unit light impulse is that originally described by Jablonski. The solution for sinusoidal excitation is novel in that: 1. It shows the difference in lifetime between the polarized components of the emission to be a sensitive function of the ratio of the modulation frequency ω to the emission rate λ. For ω/λ > 1 the difference between the polarized lifetimes may become many times greater than that observed after a unit light impulse. 2. It permits the determination of both the rate of transport of the excitation and the limiting polarization of the fluorescence from observations at one fixed temperature and viscosity. 3. It allows the definition of conditions under which the true or exponential decay of the fluorescence may be measured. Experimental tests of the theory by phase fluorometry are described: These include observations upon dilute solutions in media of limited viscosity where Brownian motion is the only cause of depolarization and observations upon concentrated frozen solutions where depolarization is due to energy transfer alone.

345 citations

Journal ArticleDOI
TL;DR: Substitution of 5-bromodeoxyuridine for thymidine in synthetic polynucleotides, DNA, or unfixed chromatin quenches the fluorescence of bound dye, and suppression of dye fluorescence permits optical detection of BrdU incorporation associated with DNA synthesis in cytological chromosome preparations.
Abstract: The interaction of the bisbenzimidazole dye 33258 Hoechst with DNA and chromatin is characterized by changes in absorption, fluorescence, and circular dichroism measurements. At low dye/phosphate ratios, dye binding is accompanied by intense fluorescence and circular dichroism and exhibits little sensitivity to ionic strength. At higher dye/phosphate ratios, additional dye binding can be detected by further changes in absorptivity. This secondary binding is suppressed by increasing the ionic strength. A-T rich DNA sequences enhance both dye binding and fluorescence quantum yield, while chromosomal proteins apparently exclude the dye from approximately half of the sites available with DNA. Fluorescence of the free dye is sensitive to pH and, below pH 8, to quenching by iodide ion. Substitution of 5-bromodeoxyuridine (BrdU) for thymidine in synthetic polynucleotides, DNA, or unfixed chromatin quenches the fluorescence of bound dye. This suppression of dye fluorescence permits optical detection of BrdU incorporation associated with DNA synthesis in cytological chromosome preparations. Quenching of 33258 Hoechst fluorescence by BrdU can be abolished by appropriate alterations in solvent conditions, thereby revealing changes in dye fluorescence of microscopic specimens specifically due to BrdU incorporation.

336 citations

Journal ArticleDOI
TL;DR: A novel fluorescence polarization (FP) method that measures the capacity of a competitor chemical to displace a high affinity fluorescent ligand from purified, recombinant human ER-[alpha] at room temperature shows promise as a high throughput screening method for large-scale testing of environmental and industrial chemicals for ER binding interactions.
Abstract: Over the last few years, an increased awareness of endocrine disrupting chemicals (EDCs) and their potential to affect wildlife and humans has produced a demand for practical screening methods to identify endocrine activity in a wide range of environmental and industrial chemicals. While it is clear that in vivo methods will be required to identify adverse effects produced by these chemicals, in vitro assays can define particular mechanisms of action and have the potential to be employed as rapid and low-cost screens for use in large scale EDC screening programs. Traditional estrogen receptor (ER) binding assays are useful for characterizing a chemical's potential to be an estrogen-acting EDC, but they involve displacement of a radioactive ligand from crude receptor preparations at low temperatures. The usefulness of these assays for realistically determining the ER binding interactions of weakly estrogenic environmental and industrial compounds that have low aqueous solubility is unclear. In this report, we present a novel fluorescence polarization (FP) method that measures the capacity of a competitor chemical to displace a high affinity fluorescent ligand from purified, recombinant human ER-[alpha] at room temperature. The ER-[alpha] binding interactions generated for 15 natural and synthetic compounds were found to be similar to those determined with traditional receptor binding assays. We also discuss the potential to employ this FP technology to binding studies involving ER-ss and other receptors. Thus, the assay introduced in this study is a nonradioactive receptor binding method that shows promise as a high throughput screening method for large-scale testing of environmental and industrial chemicals for ER binding interactions.

311 citations