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Biomedical subjects

A Beeby

Publications and source records attributed to A Beeby.

12 recordsLinked to original sources
PubMed2001

Photochemistry of the pi-extended 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene system: generation and characterisation of the radical cation, dication, and derived products.

Flash photolysis of bis[4.5-di(methylsulfanyl) 1,3-dithiol-2-ylidene]-9,10(-dihydroanthracene (1) in chloroform leads to formation of the transient radical cation species 1.+ which has a diagnostic broad absorption band at lambdamax approximately 650 nm. This band decays to half its original intensity over a period of about 80 micros. Species 1.+ has also been characterised by resonance Raman spectroscopy. In degassed solution 1.+ disproportionates to give the dication 1(2+), whereas in aerated solutions the photodegradation product is the 10-[4,5-di(methylsulfanyl) 1,3-dithiol-2-ylidene]anthracene-9(10 H)one (2). The dication 1(2+) has been characterised by a spectroelectrochemical study [lambdamax (CH2Cl2) = 377, 392, 419, 479 nm] and by an X-ray crystal structure of the salt 1(2-) (ClO4)2, which was obtained by electrocrystallisation. The planar anthracene and 1,3-dithiolium rings in the dication form a dihedral angle of 77.2 degrees; this conformation is strikingly different from the saddle-shaped structure of neutral 1 reported previously.

Journal Article↗
PubMed2001

What do sentinels stand for?

Sentinel species are biological monitors that accumulate a pollutant in their tissues without significant adverse effects. Primarily used to measure the amount of a pollutant that is biologically available, they may also increase the sensitivity of an analytical procedure or summarise a complex pollution signal. This paper examines the validation of sentinels, referring particularly to the use of invertebrates in monitoring toxic metal pollution in terrestrial ecosystems. Few studies measure the capacity of a sentinel to quantify changes in ambient levels. Definitions of 'bioavailability' also differ between workers and few note that this may be a highly species-specific measure. Validation requires that the temporal and spatial scales over which a sentinel integrates a pollution signal are known. The sentinel has to be calibrated against source concentrations and this relationship shown to be consistent over the normal range of exposure. This requires some consideration of the environmental and biological determinants of pollutant assimilation. Differences between populations can confound simple comparisons between sites based on native populations. Transplanted individuals, matched for age, sex and physiological state, might be used when the aim is not to assess bioavailability to the resident population. A simple measure of their capacity to detect differences in ambient pollutant levels is proposed to evaluate candidate species, to assess their consistency and capacity to equilibrate with their source. A small survey of earthworms from a well-defined gradient of Pb pollution is used to illustrate problems of interpreting tissue concentrations in sentinels.

Animals↗
PubMed2001

Intraspecific competition in populations of Helix aspersa with different histories of exposure to lead.

A range of invertebrates have become adapted to certain toxic metals, such that, in the presence of the contaminant, some measure of their performance, typically growth or reproduction, is superior to that of an unexposed population. Under such a toxic stress, a population with a history of exposure might outperform a naïve population in competition for limited resources. This study compared the shell growth of laboratory-bred juveniles from six populations of Helix aspersa with different histories of exposure to Pb. In 10 trials using various combinations of two populations, the snails competed for a limited supply of food that contained either no Pb or 500 micrograms/g-1 Pb, for 98 days. Each trial consisted of 10 juveniles, five from each population and was replicated four times. Nearly all of the food provided was consumed quickly after presentation. The total amount of shell growth within each replicate (the sum of the mean growth of the two populations) was highly consistent between trials so that the total amount of shell built was limited by food availability. The presence of Pb in the diet caused no measurable depression of shell growth and exposure history did not appear to confer any competitive advantage or disadvantage in any of the trials. One population consistently grew faster than its competitors in every trial of which it was a part. Shell growth tended to be greater in smaller juveniles. Snail activity is known to be inhibited at high densities and this may have contributed to the lower incremental growth in individuals kept at the higher densities. The competitive advantage enjoyed by one population may be primarily determined by their activity or perhaps their Ca metabolism.

Adaptation, Physiological↗
PubMed2001

Protonation of tetrasulfonated zinc phthalocyanine in aqueous acetonitrile solution.

The phenomenon of protonation of phthalocyanines (Pc) and its effect upon their photophysical properties has seen considerable neglect in the literature. The work reported here clearly shows that tetrasulfonated zinc Pc, a known photodynamic therapy (PDT) agent, is strongly susceptible to protonation at the azomethine bridges. Absorption and fluorescence spectra demonstrate the absolute dependence of the redshifted peak on the pH of the solution. The fluorescence spectra and lifetimes of the protonated Pc are reported, and the potential application of this phenomenon to the development of a PDT agent with increased selectivity is discussed.

Journal Article↗
PubMed2000

Luminescence imaging microscopy and lifetime mapping using kinetically stable lanthanide(III) complexes.

The sensitised luminescence from stable lanthanide complexes (1 and 2) bearing a phenanthridine antenna has been used to generate time-resolved images of silica particles. The millisecond order luminescent lifetime of these complexes is utilised to demonstrate time-gated imaging of the sample from a fluorescent background and to facilitate lifetime mapping over the area of the sample.

Europium↗
PubMed2000

The photophysical properties of menthyl anthranilate: a UV-A sunscreen.

The results of a comprehensive investigation of the photophysical properties of the sunscreen agent menthyl anthranilate in various solvent systems are reported. Luminescence studies reveal that this ester is highly fluorescent (phi f = 0.64 +/- 0.06 in ethanol) and has a solvent-dependent emission maximum in the range of 390-405 nm. Phosphorescence has also been detected in low-temperature glasses with an emission maximum at 445 nm and a lifetime of 2.5 s. Kinetic UV-visible absorption measurements revealed a transient species with absorption maxima at 480 nm and solvent-dependent lifetimes of 26-200 microseconds that are attributed to the triplet state. The triplet state is efficiently quenched by oxygen, leading to the formation of singlet oxygen in all of the solvent systems studied. The singlet-oxygen quantum yields (phi delta) determined by time-resolved near-infrared luminescence measurements were determined to be in the range 0.09-0.12 for all systems.

Humans↗
PubMed1997

Excited triplet state photophysics of the sulphonated aluminium phthalocyanines bound to human serum albumin.

The binding of the sulphonated aluminum phthalocyanines to human serum albumin (HSA) in aqueous phosphate buffer solution at 25 degrees C has been studied by measuring the properties of the triplet excited states of these dyes. The triplet lifetimes were measured by triplet-triplet absorption flash photolysis. The triplet lifetime of the disulphonated AlS2Pc (2.5 microM) varies from 500 +/- 30 microseconds in the absence of protein to 1.100 microseconds and longer with HSA concentrations above 100 microM. Under identical conditions, the maximum triplet lifetimes of the mono-, tri- and tetrasulphonated compounds bound to HSA are shorter than those for the disulphonated species. The increase in the triplet state lifetimes is attributed to the ability of the bulk aqueous phase to interact with the sensitizer at the site of binding; the site of binding being dependent on the degree of sulphonation. For AlS2Pc and AlS3Pc at all HSA concentrations, and regardless of the degree of sulphonation, all the triplet state decay profiles follow simple pseudo-first-order kinetics. The exponential decay of the triplet phthalocyanine at all HSA concentrations is ascribed to the rapid association and dissociation of the phthalocyanine-HSA complex on the time-scales of the triplet state lifetimes. A simplified one-step binding model is utilized to describe the results. The association of AlS1Pc with HSA results in substantial quenching of the triplet state quantum yield, and a more complex model is required to analyze the results. The tetrasulphonated compound (AlS4Pc) binds to the protein at a site where it experiences some protection from the aqueous phase.

Aluminum↗
PubMed1993

Characterisation of the photochemotherapeutic agent disulphonated aluminium phthalocyanine and its high-performance liquid chromatographic separated components.

Disulphonated aluminium phthalocyanine (AlPcS2), a potential clinical photosensitiser, has been synthesised in a reproducible form and shown by reversed-phase HPLC to consist of at least eight components which are believed to be individual AlPcS2 regioisomers. These components have been isolated either as single bands or mixtures of two using preparative reversed-phase HPLC methods. The number and position of sulphonate groups per phthalocyanine macromolecule for each component has been determined using a chemical degradation and HPLC assay. Results suggest that the bulk AlPcS2 material consists mostly (> 60%) of an amphiphilic alpha-, alpha-disubstituted regioisomer, with both sulphonate groups substituted to the same side of the molecule (adjacent form). Possible structures for some of the other separated components of AlPcS2 are also presented.

Chromatography, High Pressure Liquid↗
PubMed1991

Preparative, analytical and fluorescence spectroscopic studies of sulphonated aluminium phthalocyanine photosensitizers.

Fluorescence spectroscopic studies were carried out on aluminium phthalocyanine with defined numbers (mono, di, tri and tetra) of sulphonate groups. Selective sulphonation was achieved using one of two synthetic methods to prepare a mixture of components which were separated using reverse-phase liquid chromatography. Fluorescence lifetimes were measured in methanol and buffer solution using time-correlated single-photon counting with picosecond laser excitation; the lifetime shows little variation with the number of sulphonate groups. Using steady state excitation, fluorescence quantum yields were determined for the tetrasulphonated component (phi F = 0.51) and, for comparison, unsulphonated aluminium phthalocyanine.

Indoles↗
PubMed1987

Synthesis and binding affinities of analogues of cholecystokinin-(30-33) as probes for central nervous system cholecystokinin receptors.

CCK-30-33 has been identified as the minimum fragment of CCK with nanomolar affinity for the central CCK receptors, as assayed by displacement of [3H]-Boc-beta-alanyl-CCK-30-33 (pentagastrin) in homogenized mouse cerebral cortex. Examination of binding using this assay in the two series Boc-Trp-X-Phe-NH2 when X = Met-Asp (Boc-CCK-30-33), Gly-Asp, Met-Gly, and Gly-Gly and when X = (CH2)n (n = 0-4) reveals that modification of the tetrapeptide reduces affinity to a maximum of micromolar affinity (Boc-Trp-Gly-Asp-Phe-NH2; Ki = 2 X 10(-6) M), whereas in the series when n = 0 and 2 pentamolar affinity is still retained (Boc-Trp-Phe-NH2, Ki = 7 X 10(-5) M; Boc-Trp NH CH2-CH2-CO-Phe-NH2, Ki = 3 X 10(-5) M). Modification of the tetrapeptide CCK-30-33 reduces affinity 1000-fold, whereas di- and tripeptide fragments are identified that reduce affinity only a further 10-fold. This structure-activity relationship establishes a basis to design "peptoid" analogues of CCK that have therapeutic potential.

Amino Acid Sequence↗