Effect of Cu(2+)-ions on semiconductor properties of synthetic DOPA melanin polymer.

The purpose of the present study was to examine semiconductor properties of synthetic DOPA melanin, which are basic for future biological applications. DC conductivity, electron spin resonance (ESR), and atomic absorption spectroscopy (AAS) measurements have been performed to investigate the effect of Cu(2+)-ions on the semiconductor properties of melanin polymer synthesized from DOPA (3,4-dihydroxyphenylalanine). DOPA melanin - Cu2+ complexes examined show the decrease of both thermal activation energy delta Ea and pre-exponential factor sigma o values upon doping. At the same time no substantial changes in conductivity at 293 K have been observed. Formation of bipolaron states due to chelation of copper ions by melanin orthosemiquinones has been postulated. The Meyer-Neldel rule with a characteristic temperature T0 equal to 298 K and possible physiological implication of this fact are discussed. These data suggest, that DOPA melanin polymer could be useful as a type of culture substratum.

Electrical conductivity of synthetic DOPA-melanin polymer for different hydration states and temperatures.

The dependence of the d.c. conductivity on the hydration and temperature (293-343 K) for synthetic DOPA-melanin polymer is presented. The hydration state of the melanin has been changed by varying the humidity conditions around the sample. It has been shown, that in the range of relative humidity values (0-100%), changes in the hydration state of melanin have predominant influence on electrical conductivity (10(-13)-10(-5)S cm-1) in comparison to temperature. The influence of the two forms of water on the conductivity--the first form adsorbed mainly on the melanin surface and easily removed by drying, and the second one incorporated into the inner structure of the polymer, has been investigated. The temperature dependence of the conductivity in vacuum (0.8 and 0.04 mb) and thermal activation energy values (0.49-0.76 eV) for cooling and heating curves have been determined. The relationship between thermal activation energy and preexponential factor sigma 0 (compensation effect) and possible charge transport mechanisms are discussed.

Mammography screening for breast cancer: first year results from Helsinki and surroundings.

11,789 women aged 50-59 years were invited for screening by the mammography screening centre of the Cancer Society of Finland in Helsinki. 9829 women (83.37%) attended and 3.85% of those were recalled for further studies. After complete examination seventy-one women (0.72%) were referred for surgical biopsy and breast cancer was histologically detected in 44 (0.45%) of those screened. The proportion of Stage I + TIS breast cancers detected was 75%, and of Stage II or more advanced, 25%. With modern mammography techniques and proper training of technicians and radiologists, with double reading of all the films, it is possible to minimise both the recall rate and the number of women who are referred for surgical biopsy, and still find cancers in their early stages.

Bile salt-associated electrolyte secretion and the effect of sodium taurocholate on bile flow.

Sodium taurocholate has a remarkably varied effect on bile flow. Preisig et al. showed that a portion of electrolyte secretion is related to bile salt secretion, and other studies have suggested that this fraction of electrolyte secretion is important in bile salt--dependent flow. In the present study in the baboon and the dog, it was found that the magnitude of bile salt-associated electrolyte secretion was closely correlated to the effect of sodium taurocholate on bile flow. Theophylline, an agent widely used to alter cellular electrolyte transport, simultaneously reduced the fraction of biliary electrolyte secretion related to bile salts and the effect of the bile salt on flow. The study suggests an important role for electrolyte secretion in the modulation of the effect of bile salts on bile flow.