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The novel saturated tetraaza macrocycle isocyclam (2) has been synthesized and the behavior of its nickel(II) complexes, which contain a 5,5,6,6 sequence of chelate rings, is compared with that of corresponding complexes of cyclam (1) (sequence: 5,6,5,6). These complexes exist in solution as a mixture of blue, octahedral, high-spin and yellow, planar, low-spin species; the thermodynamic parameters for the blue-to-yellow conversion depend upon the cyclic nature of the ligand. In analogy with Ni (cyclam)2"1", Ni(isocyclam)2+ undergoes one-electron oxidation and reduction processes at a platinum electrode in acetonitrile. The easier reduction and more difficult oxidation of both blue and yellow 5,5,6,6 complexes with respect to the 5,6,5,6 analogues have been related to the differences in the in-plane NUN interaction parameters, as inferred from electronic spectra. General redox behavior of Ni(II) complexes with tetraaza macrocycles has been reconsidered and a linear correlation between oxidation and reduction potentials is presented.

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The presence of Aeromonas spp. in water can represent a risk for human health. Therefore, it is important to know the physiological status of these bacteria and their survival in the environment. We studied the behavior of a strain of Aeromonas hydrophila in river water, spring water, brackish water, mineral water, and chlorinated drinking water, which had different physical and chemical characteristics. The bacterial content was evaluated by spectrophotometric and plate count techniques. Flow cytometric determination of viability was carried out using a dual-staining technique that enabled us to distinguish viable bacteria from damaged and membrane-compromised bacteria. The traditional methods showed that the bacterial content was variable and dependent on the type of water. The results obtained from the plate count analysis correlated with the absorbance data. In contrast, the flow cytometric analysis results did not correlate with the results obtained by traditional methods; in fact, this technique showed that there were viable cells even when the optical density was low or no longer detectable and there was no plate count value. According to our results, flow cytometry is a suitable method for assessing the viability of bacteria in water samples. Furthermore, it permits fast detection of bacteria that are in a viable but nonculturable state, which are not detectable by conventional methods.During the last decade scientific interest has turned to members of the genus Aeromonas as human and animal pathogens. Many Aeromonas species have been associated with human diseases, including gastroenteritis, hemolytic-uremic syndrome, septicemia, etc. (21, 30, 48).Aeromonas spp. are common aquatic microorganisms that occur in seawater, irrigation water, river water, brackish water, freshwater, groundwater, spring water, sewage-contaminated water, and activated sludge (4,7,9,14,15,23,24,37,43).The wide distribution of aeromonads in different aquatic ecosystems underlines their capacity to adapt to environments with different trophic levels. Several studies have shown that the phenospecies Aeromonas hydrophila is prevalent in cleaner water, whereas Aeromonas caviae is prevalent in water with a high level of fecal pollution; the frequencies of the other phenospecies appear to be unrelated to environmental conditions (3,15,17,23).These bacteria have also been isolated from chlorinated and unchlorinated drinking water and from bottled mineral water, which shows that they are able to withstand long periods of nutrient limitation (6,16,19,20,29,31,46,50). The survival of aeromonads in these ecosystems can be correlated with their capacity to produce and live within biofilms on the surfaces of pipes and bottles (26); on the other hand, it is known that Aeromonas spp. can cope with nutrient limitation conditions by entering into a starvation survival state (33).The growing interest in these organisms addresses aquatic environments, because these environments represent an important reservoir of aeromonads. It is assumed that huma...