Predissociation via conformational change: photodissociation of N,N-dimethylnitrosamine in the S(1) state.

We investigated the photodissociation mechanism of N,N-dimethylnitrosamine (CH(3))(2)NNO (DMN) by ab intio quantum chemical methods. Inspired by an earlier study we calculated two-dimensional potential energy surfaces of the S(1) state of DMN in its planar and pyramidal conformations. While the planar molecular geometry appears to possess no direct dissociation channel, the pyramidal configuration is dissociative yielding the products NO + (CH(3))(2)N. Using wave packet dynamics on the planar S(1) potential energy surface the experimental absorption spectrum was well reproduced which gives indirect but strong support for the nondissociative nature of this surface. The transition from the planar to the pyramidal conformation of DMN was then investigated by an ab initio molecular dynamics method which revealed the time evolution of the geometrical parameters of the molecule up to the dissociation of the N-N bond. This occurs about 90 fs after photon excitation. The calculated minimum energy path along the N-N coordinate and the structural changes of the molecule along this coordinate provided a detailed picture of this indirect dissociation or, more specific, predissociation process via conformational change.

Dissociation and recombination in the photochemical decay of carbonyl cyanide CO(CN)2 in cryogenic matrixes.

The photochemistry of CO(CN)2 in cryogenic matrixes has been investigated employing pulsed laser excitation at 193 nm. During irradiation, the parent molecule, the intermediate, and the final photoproducts were monitored by IR spectroscopy. Four new species were identified including the isocyano isomer of the parent NCC(O)NC, cyanogen NCCN, isocyanogen CNCN, and CO according to spectroscopic features and ab initio calculations. After prolonged irradiation, the only remaining species were CO and the two isomers NCCN and CNCN. A reaction scheme is proposed which is in agreement with the first dissociation step being a branching of the decay path into the radical channel to CN+OCCN and the molecular channel to CO+(CN)2. The caged radicals of the former reaction either recombine to the parent molecule and its isomer which are both photolyzed again or they react directly to the stable and final products.

Sorption and degradation characteristics of phosmet in two contrasting Australian soils.

The organophosphate insecticide phosmet [phosphorodithioic acid, s-((1,3-dihydro-1,3-dioxo-2H-isoindol-2yl)methyl), o,o-dimethyl ester] is used to control red-legged earth mites (Halotydeus destructor), lucerne flea (Sminthurus viridis), and Oriental fruit moth (Cydia molesta) in horticulture and vegetable growing. This study was undertaken with two soils of contrasting properties to determine the extent to which sorption and degradation of the insecticide might influence its potential to leach from soil into receiving waters. Two soils were used: a highly organic, oxidic clay soil (Ferrosol) and a sandy soil low in organic matter (Podosol), sampled to 0.3 m depth. The extent of sorption and decomposition rate of a phosmet commercial formulation were measured in laboratory experiments. Sorption followed a Freundlich isotherm at all depths. The Freundlich coefficient K was significantly correlated (p = 0.005) with organic C content in the Podosol, and significantly correlated (p = 0.005) with organic C and clay content in the Ferrosol. K was highest (48.8 L kg-1) in the 0- to 0.05-m depth of the Ferrosol, but lowest (1.0 L kg-1) at this depth in the Podosol. Degradation followed first-order kinetics, with the phosmet half-life ranging from 14 h (0-0.05 m depth) to 187 h (0.2-0.3 m depth) in the Ferrosol. The half-life was much longer in the sandy Podosol, ranging from 462 to 866 h, and did not change significantly with depth. Soil organic C and to a lesser degree clay content influenced phosmet sorption and degradation, but the interaction was complex and possibly affected by co-solvents present in the commercial formulation.

Changes in steroid hormone profiles and ovarian histology during salmon pituitary-induced vitellogenesis and ovulation in female New Zealand longfinned eels, Anguilla dieffenbachii gray.

To assess whether induced vitellogenesis in longfinned eels mimics that in naturally maturing conspecifics, female eels were artificially matured and steroid hormone status and oocyte cytology during oogenesis were evaluated. Successful induction of vitellogenesis was evident from the presence of yolk granules in the ooplasm of salmon pituitary homogenate (SPH)-injected, but not saline-, 17-hydroxyprogesterone-, and/or gonadotropin-releasing hormone-treated fish. In SPH-treated females, the migratory nucleus stage was reached after 33-53 days, followed by ovulation around 30 hours after induction of final maturation and ovulation. Only a portion of the germ cells matured, although resumption of vitellogenesis was seen in the majority of oocytes. In contrast, in ovaries of saline-injected controls, the most advanced oocytes were early vitellogenic. Atretic follicles were observed in ovaries of all eels, but abundance was greater in controls than in SPH-treated fish. SPH injections elevated plasma levels of estradiol-17beta and androgens, but not pregnenes, from within three days of treatment. Our results indicate that sex steroid levels in midvitellogenic hormone-treated females are similar to those in wild midvitellogenic females. In contrast, differences in yolk morphology of midvitellogenic follicles were seen between SPH-treated and wild females, especially in the second crop of midvitellogenic-sized oocytes measuring 300-400 microm in diameter. We discuss whether the observed differences affect egg quality, and perhaps explain the short life span of captive-bred eel larvae. J. Exp. Zool. 289:119-129, 2001.

Frequency of sensitization to 13 common preservatives in Switzerland. Swiss Contact Dermatitis Research Group.

From February 1989 to January 1990, the Swiss Contact Dermatitis Research Group conducted a 1-year study to examine the frequency of sensitization to a series of 13 common preservatives. A group of 2295 consecutive outpatients with suspected allergic contact dermatitis (age range 7-90 years, with a mean age of 42; 911 males, 1384 females) was tested. The %s of positive reactions to the preservatives studied are as follows, in descending order: formaldehyde 5.7%, benzalkonium chloride 5.5%, Kathon CG 5.5%, thimerosal 4.2%, chlorhexidine digluconate 2.0%, DMDM hydantoin 1.7%, paraben mix 1.7%, chloroacetamide 1.5%, Bronopol 1.2%, imidazolidinyl urea 1.0%, quaternium 15 1.0%, triclosan 0.8%, 2,4-dichlorobenzyl alcohol 0.4%. These relatively high values suggest a heavy exposure of the Swiss population to topical preservatives. Compared to previous studies, the sensitization rate to Kathon CG has stabilized in Switzerland over the last 2 years. Sensitization to formaldehyde portrayed impressive geographical variation, with sensitization rates up to 9% in western and only 3% in eastern Switzerland. The low sensitization rate to parabens argues for their inclusion in a medicament or preservative series, rather than in the standard series.

Primary structure of two P-type ATPases involved in copper homeostasis in Enterococcus hirae.

We cloned an operon, copAB, from Enterococcus hirae encoding two P-type ATPases of 727 and 745 amino acids, respectively. Both enzymes display heavy metal ion binding motifs in their polar N-terminal region. With an antibody against CopB, we showed on Western blots that expression of the operon is induced by either low or high ambient copper concentrations. Disruption of the copA gene renders the cells dependent, whereas copper disruption of copB results in a copper-sensitive phenotype. CopA exhibits 35% sequence similarity to CopB and 43% similarity to the ATPase encoded by the recently cloned human Mc1 gene, a gene responsible for the Menkes inborn error of copper metabolism. Our results imply that CopA and CopB are heavy metal ion ATPases that regulate the cytoplasmic copper activity, with CopA serving in the uptake and CopB in the extrusion of copper.

Sensitization to the isothiazolinone biocide. Report of the Swiss Contact Dermatitis Research Group 1988-1990.

The rate of sensitization to isothiazolinones (Kathon CG) detected in Switzerland rose from 3.5% (out of 2,491 patients) in 1987 to 6.3% (out of 982 patients) in 1988 and 5.6% (out of 2,295 patients) in 1989-90. This rate of sensitization appears to be related to the more and more widespread use of isothiazolinone biocide in cosmetics, domestic products and in industry.

[Disease (Lyme disease) in pediatric patients in Switzerland caused by spirochetes (Borrelia burgdorferi) of Ixodes ricinus]. / Durch Ixodes-ricinus-Spirochäten (Borrelia burgdorferi) verursachte Krankheitsbilder (Lyme-Krankheit) bei pädiatrischen Patienten in der Schweiz.

Lyme disease in children is studied in the light of questionnaires sent out twice to departments and divisions of pediatrics in Switzerland. Thirty-six serologically proven cases were collected. The 48 clinical signs attributed to Lyme disease involved the skin in 40%, the nervous system in 40%, and the joints in 20%. They were erythema chronicum migrans (13), lymphocytoma (4), acrodermatitis chronica atrophicans (2), peripheral facial palsy (14), sensomotor radiculoneuritis (2), meningoencephalitis (3) and arthritis (10, 7 of which were monoarthritic). Only half the patients had a history of tick-bite. Antibiotic therapy, usually with penicillin, reduced both the duration of symptoms and frequency of secondary disease. Cardiac involvement and chronic stages with residua were not observed in this series.

Postnatal development of young rats following the treatment of the dams with sodium salicylate during late periods of pregnancy.

Female albino rats were treated with sodium salicylate dissolved in tap water orally by intubation. The first group received daily doses of 25, 75 or 150 mg/kg from day 15 through day 20 of pregnancy. The second group received daily doses of 4.2, 12.5 or 25 mg/kg on day 20 and on day 21, i.e. the day of parturition. Administration of the intermediate and high doses caused a marked increase in the mortality rates of the young animals. However, the development of the surviving young rats was similar to the controls and no change in behaviour was noted.

Prenatal and postnatal development of rats following the maternal treatment with testosterone during the late period of embryogenesis.

Sprague-Dawley derived female albino rats were administered subcutaneously 0.5, 1.5, or 3.0 mg/kg of testosterone acetate in sesame oil at single daily doses, from day 13 until day 16 of pregnancy (day 0 = spermatozoa). The pregnant females were either killed shortly before term or allowed to litter and raise their offspring. Increased rates of prenatal death were observed in the three experimental groups of both these experiments. Reduced body weight of foetuses and, respectively, young rats after weaning was recorded for the intermediate and high dose groups. Embryo-lethality and delay of either foetal or postnatal development occurred at some dose-relationship and in association with slight to moderate loss of maternal body weight during the period of treatment. No teratogenic potency of testosterone was found and no changes of the female sexual organs were observed in the foetuses or young rats.

The regulation of 5-hydroxytryptamine release from superfused synaptosomes by 5-hydroxytryptamine and its immediate precursors.

The effect of L-tryptophan, 5-hydroxy-L-tryptophan (5-HTP), and 5-hydroxytryptamine (5-HT) on the K+-evoked release of [3H]5-HT from superfused rat brain synaptosomes was studied. 5-HT at concentrations above 10 nM significantly inhibited the K+-evoked release of [3H]5-HT. A slight enhancement of [3H]5-HT release was observed at a concentration of 5nM. In contrast tryptophan at a concentration of 10 nM significantly enhanced [3H]5-HT release with little effect at higher concentrations. 5-HTP did not significantly effect [3H]5-HT release. The results confirm previous findings that 5-HT inhibits its own release from nerve endings, and demonstrate that low concentrations of tryptophan in the synaptic region may act as a positive feedback regulator of 5-HT release.

The stimulus-induced release of 5-hydroxytryptamine and tryptophan from superfused rat brain synaptosomes.

The synthesis of 5-hydroxytryptamine (5-HT) from 3H-tryptophan in rat forebrain synaptosomes was studied. Synaptosomes which had been preincubated with 3H-tryptophan were perfused with Krebs solution and the release of tryptophan, 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) was determined. K+ depolarization induced a Ca2+ -dependent release of 5-HT and tryptophan but had no effect on 5-HIAA efflux. This finding suggests that the release of tryptophan is unlikely to be a non-specific effect of depolarization.