Light-induced multistep oxidation of dinuclear manganese complexes for artificial photosynthesis

Two dinuclear manganese complexes, [Mn(2)BPMP(mu-OAc)(2)].ClO(4) (1, where BPMP is the anion of 2,6-bis([N,N-di(2-pyridinemethyl)amino]methyl)-4-methylphenol) and [Mn(2)L(mu-OAc)(2)].ClO(4) (2, where L is the trianion of 2,6-bis([N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2-pyridinemethyl)amino]methyl)-4-methylphenol), undergo several oxidations by laser flash photolysis, using ruthenium(II)-tris-bipyridine (tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate) as photo-sensitizer and penta-amminechlorocobalt(III) chloride as external electron acceptor. In both complexes stepwise electron transfer was observed. In 1, four Mn-valence states from the initial Mn(2)(II,II) to the Mn(2)(III,IV) state are available. In 2, three oxidation steps are possible from the initial Mn(2)(III,III)state. The last step is accomplished in the Mn(2)(IV,IV) state, which results in a phenolate radical. For the first time we provide firm spectral evidence for formation of the first intermediate state, Mn(2)(II,III), in 1 during the stepwise light-induced oxidation. Observation of Mn(2)(II,III) is dependent on conditions that sustain the mu-acetato bridges in the complex, i.e., by forming Mn(2)(II,III) in dry acetonitrile, or by addition of high concentrations of acetate in aqueous solutions. We maintain that the presence of water is necessary for the transition to higher oxidation states, e.g., Mn(2)(III,III) and Mn(2)(III,IV) in 1, due to a bridging ligand exchange reaction which takes place in the Mn(2)(II,III) state in water solution. Water is also found to be necessary for reaching the Mn(2)(IV,IV) state in 2, which explains why this state was not reached by electrolysis in our earlier work (Eur. J. Inorg. Chem (2002) 2965). In 2, the extra coordinating oxygen atoms facilitate the stabilization of higher Mn valence states than in 1, resulting in formation of a stable Mn(2)(IV,IV) without disintegration of 2. In addition, further oxidation of 2, led to the formation of a phenolate radical (g = 2.0046) due to ligand oxidation. Its spectral width (8 mT) and very fast relaxation at 15 K indicates that this radical is magnetically coupled to the Mn(2)(IV,IV) center.     

d-matrix – database exploration,visualization and analysis

Background  

Motivated by a biomedical database set up by our group, we aimed to develop a generic database front-end with embedded knowledge discovery and analysis features. A major focus was the human-oriented representation of the data and the enabling of a closed circle of data query, exploration, visualization and analysis.     

Head development in the onychophoran Euperipatoides kanangrensis with particular reference to the central nervous system

The neuroectoderm of the Euperipatoides kanangrensis embryo becomes distinguishable during germ band formation when the antennal segment is evident externally. During later stages of development, the neuroectoderm proliferates extensively and, at the anterior part of the head, newly-formed neuron precursor cells occupy most of the volume. The antenna forms from the dorsolateral side of the anterior somite. The antenna has no neuroectoderm of its own at the onset of its formation, but instead, neurons migrate out to the appendage from the nearby region of the developing brain. When the antennal tract is formed it is positioned horizontally in the brain, in line with the antennal commissure. Only later, and coincidentally with the anterior repositioning of the antenna, is the tract's distal part bent anteriorly and positioned laterally. The eye starts to develop posteriorly to the antenna and the antennal commissure. This suggests that the segment(s) associated with the onychophoran eye and antenna are not serially homologous with segments carrying equivalent structures within the Euarthropoda. Evidence is presented to further support the presence of a terminal mouth in the ground plan of the Onychophora and, hence, an acron may not exist in the arthropod clade.     

Temporal variation in feeding morphology and size-structured population dynamics in fishes

Considerable variation in morphology associated with resource use is a classic example of local adaptation to the environment. We demonstrate that a temporal change in feeding morphology might occur within a population. In a 5-year natural field experiment, we estimated gill raker morphology, resource density and population dynamics of the roach and its competitor, the perch. Despite a variation in density of zooplankton resources and perch across years, no change in roach density was observed. However, gill raker morphology in roach covaried with size structure of the zooplankton resource across years. A laboratory experiment confirmed that gill raker morphology has a great effect on roach foraging efficiency on zooplankton and that there is a functional trade-off with regard to zooplankton foraging. We suggest that the response in gill raker structure is an adaptation to deal with the rapid population dynamics of zooplankton, which are in turn mediated by changes in the size structure of the competing perch.     

The refining influence of ethics committees on animal experimentation in Sweden

Mandatory scrutiny of projects by animal ethics committees was introduced in Sweden in 1979. The present study investigated the minutes of meetings held between 1989 and 2000 at which consideration of applications for experimental work in animals resulted in requests for modification (n = 3607). 18.1% of the applications received were approved only after modifications. The majority of the changes requested may be classified as 'Refinement'. The most common requests were for improvement of project design, euthanasia method and housing and husbandry. There was a relative increase in modifications requested by the committees related to anaesthesia, choice of licensed supervisor and the need for licenses or informed consent from animal owners during the period investigated. There was a relative decrease in modifications related to euthanasia, housing and husbandry, and general endpoint assertions. The results suggest that the work of the committees may be perceived as an ongoing process, since several of the applications for which modification was requested were projects that had been approved on a previous occasion but were now up for renewal. In order to have maximal influence on the refinement of scientific protocols it is important that the scientists in the committees are continuously updated on developments in laboratory animal science.     

Effects of in vitro production on horse embryo morphology,cytoskeletal characteristics,and blastocyst capsule formation

Blastocyst formation rates during horse embryo in vitro production (IVP) are disappointing, and embryos that blastulate in culture fail to produce the characteristic and vital glycoprotein capsule. The aim of this study was to evaluate the impact of IVP on horse embryo development and capsule formation. IVP embryos were produced by intracytoplasmic sperm injection of in vitro matured oocytes and either culture in synthetic oviduct fluid (SOF) or temporary transfer to the oviduct of a ewe. Control embryos were flushed from the uterus of mares 6-9 days after ovulation. Embryo morphology was evaluated with light microscopy, and multiphoton scanning confocal microscopy was used to examine the distribution of microfilaments (AlexaFluor-Phalloidin stained) and the rate of apoptosis (cells with fragmented or terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive nuclei). To examine the influence of culture on capsule formation, conceptuses were stained with a monoclonal antibody specific for capsular glycoproteins (OC-1). The blastocyst rate was higher for zygotes transferred to a sheep's oviduct (16%) than for those cultured in SOF (6.3%). Day 7 IVP embryos were small and compact with relatively few cells, little or no blastocoele, and an indistinct inner cell mass. IVP embryos had high percentages of apoptotic cells (10% versus 0.3% for in vivo embryos) and irregularly distributed microfilaments. Although they secreted capsular glycoproteins, the latter did not form a normal capsule but instead permeated into the zona pellucida or remained in patches on the trophectodermal surface. These results demonstrate that the initial layer of capsule is composed of OC-1-reactive glycoproteins and that embryo development ex vivo is retarded and aberrant, with capsule formation failing as a result of failed glycoprotein aggregation.     

Embryo production by ovum pick up from live donors

Embryo production by in vitro techniques has increased steadily over the years. For cattle where this technology is more advanced and is applied more, the number of in vitro produced embryos transferred to final recipients was over 30,000 in 1998. An increasing proportion of in vitro produced embryos are coming from oocytes collected from live donors by ultrasound-guided follicular aspiration (ovum pick up, OPU). This procedure allows the repeated production of embryos from live donors of particular value and is a serious alternative to superovulation. Ovum pick up is a very flexible technique. It can be performed twice a week for many weeks without side effects on the donor's reproductive career. The donor can be in almost any physiological status and still be suitable for oocyte recovery. A scanner with a sectorial or convex probe and a vacuum pump are required. Collection is performed with minimal stress to the donor. An average of 8 to 10 oocytes are collected per OPU with an average production of 2 transferable embryos. The laboratory production of embryos from such oocytes does not differ from that of oocytes harvested at slaughter as the results after transfer to final recipients. For other species such as buffalo and horses OPU has been attempted similarly to cattle and data will be presented and reviewed. For small ruminants, laparotomy or laparoscopy seems the only reliable route so far to collect oocytes from live donors.     

Regulation of the production of polygalacturonase by Aspergillus niger

Synthesis of ethylene in static cultures as well as the effect of endogenous and exogenous ethylene on the synthesis of polygalacturonase byAspergillus niger were determined. This strain produced maximum ethylene amounts when cultured at 30 °C for 3 d. The effect of adding ethylene precursors (citrate-cycle intermediates) on ethylene production was investigated. Best intracellular and extracellular polygalacturonase production was obtained with 2-oxoglutaric, pyruvic and fumaric acids, and with glutamic acid too. Addition of ethylene to the culture medium also increased the synthesis of polygalacturonase, although to a lower degree than when glutamic acid was added.     

Kinetics of oocyte maturation and subsequent development of IVF,parthenogenetic, and NT bovine embryos after meiotic inhibition with roscovitine

The developmental competence of bovine oocytes meiotically arrested with specific cdk2 inhibitor roscovitine was studied. After removal of the 32-h block with roscovitine, 82.7 +/- 5.4% reached the metaphase II stage at the end of maturation, which was lower than in controls (96.3 +/- 1.3%, p < 0.001). The process of polar body formation started at 11 h of maturation in the roscovitine group, that is 4 h earlier than in controls and its kinetics was quite similar to controls up to 16 h of maturation, when nearly 70% of oocytes extruded their polar bodies. The rate of blastocyst formation of roscovitine oocytes and their cell number after IVF, parthenogenetic activation, and nuclear transfer (NT) were equal to controls, which demonstrates the possibility of artificially maintaining bovine oocytes in the GV stage for 32 h without altering their preimplantation developmental competence. This approach can be very useful for the management of an NT program where enucleated oocytes are required at specific times or locations.