Biomedical subjects
Publications and source records attributed to P A Christensen.
This paper describes a novel, composite device, based not on optical excitation but on the transfer of holes from Si to the TiO(2)/air or TiO(2)/water interface, for the disinfection and detoxification of fluid streams.
A new technology for remediation of halogenated organics-oil systems, which can cause serious environmental problems, has been demonstrated using the electrochemical hydrodehalogenation of 2,4-dibromophenol (DBP) in paraffin oil in a solid polymer electrolyte reactor. The reactor has been evaluated in terms of cathode materials and structure and the ratio of the cathode surface area to the solution volume. A cathode of titanium minimesh with a palladium electrocatalyst produced by electrodeposition was particularly effective. Current efficiencies of up to 85% and percentage of DBP removal of up to 62%, space-time yields of up to 7.6 kg DBP m(-3) h(-1), and energy consumption as low as 1.6 kW h (kg of DBP)(-1) were achieved. The reactor showed stable operation for periods of up to 170 h. The results demonstrated that electroreduction could be an alternative technology to electrooxidation forthe treatment of wastes and toxic halogenated compounds, making the process simpler in comparison to electrooxidation.
We have undertaken simple proof of principle experiments to find out if electric field enhanced photo-oxidation using immobilised titanium dioxide will damage Cryptosporidium oocysts. Using a simple Petri dish reactor and two forms of immobilised titanium catalyst (sol-gel and thermal-film) we have tested the ability of this technology to affect Cryptosporidium oocysts permeability assessed by propidium iodide exclusion. Test and control reactor runs were significantly different (P = 0.007). The thermal-film reactor had the greatest effect (approximately 27% of the seed) and was statistically distinguishable from the sol-gel reactor and the controls. The sol-gel reactor showed an increase in oocyst permeability, but was not statistically distinguishable from one of the controls. The enhanced performance of the thermal film reactor is attributed to the superior conversion of photochemical holes to hydroxyl radicals at the surface of this catalyst.
The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(000 1) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials < 900 mV vs. Ag/AgCl, and at all three temperatures employed, 10, 25 and 50 degrees C. However, both formaldehyde and formic acid did undergo dissociative adsorption, even at -200 mV, to form linear (CO(L)) and 3-fold-hollow (COH) binding CO adsorbates. In contrast to the adsorption of CO, it was found that increasing the temperature to 50 degrees C markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of both formaldehyde and formic acid. On increasing the potential, the electro-oxidation of the CO adsorbates to CO2 took place via reaction with the active (1 x 1)-O oxide. Formic acid was detected as a partial oxidation product during formaldehyde electro-oxidation. At all three temperatures employed, it was found that adsorbed CO species were formed from the adsorption of both formic acid and formaldehyde, and were oxidised to CO2 faster than was observed in the experiments involving CO adsorbed from CO(g), suggesting a higher mobility of the CO adsorbates formed from the adsorption of the HCOOH and HCHO. At potentials > 1000 mV, both the oxidation of formic acid to CO2 and the oxidation of formaldehyde to both CO2 and formic acid were significantly increased, and the oxidation of methanol to CO2 and methyl formate was observed, all of which were attributed to the formation of an active RuO2 phase on the Ru(0001) surface.
Electrogenerated polymers based on the nickel(II) complex 2,3-dimethyl-N,N'-bis(salicylidene)butane-2,3-diaminatonickel(II), poly[Ni(saltMe)], were characterised by in situ FTIR and UV/Vis spectroscopy and ex-situ EPR spectroscopy in order to gain insights into film structure, electronic states and charge conduction. The role of the nickel ions during film oxidation was probed by using EPR to study naturally abundant Ni and 61Ni-enriched polymers. The data from all the spectroscopic techniques are consistent, and clearly indicate that polymerisation and redox switching are associated with oxidative ligand based processes; coulometry suggests that one positive charge was delocalised through each monomer unit. EPR provided evidence for the non-direct involvement of the metal in polymer oxidation: the polymer is best described as a polyphenylene-type compound (conducting polymer), rather than an aggregation of nickel complexes (redox polymer), and the main charge carriers are identified as polarons. An explanation for the high electrochemical stability and conductivity of poly[Ni(saltMe)] with respect to that of poly[Ni(salen)] is proposed. based on stereochemical repulsion between monomeric units; this can impose a less compact supramolecular structure on polymers with bulkier substituents.
The low-density lipoprotein receptor-related protein (LRP) is a large surface receptor that mediates binding and internalization of a large number of structurally and functionally unrelated ligands. The ligand binding sites are located in clusters of complement-type repeats (CR), where the general absence of mutual binding competition suggests that different ligands map to distinct sites. Binding of alpha(2)-macroglobulin-protease complexes to the LRP is mediated by the receptor binding domain (RBD) of alpha(2)-macroglobulin (alpha(2)M). To determine the major binding epitope(s) in the LRP, we generated a complete set of tandem CR proteins spanning the second cluster of CR domains, and identified a binding site for alpha(2)M in the N-terminal part of the cluster comprising CR3-CR6, using ligand blotting and surface plasmon resonance (SPR) analysis. The specific site involved in alpha(2)M recognition resides in the fourth CR domain, CR4, whereas another site is identified in CR5. An acidic epitope in CR4 is identified as important for binding alpha(2)M by mutagenesis and SPR analysis. The formation of the complex between the rat alpha(1)-macroglobulin RBD and CR domain pairs is characterized by analytical size-exclusion chromatography, which demonstrates a sufficiently strong interaction between the alpha(1)M RBD and CR34 or CR45 for the isolation of a complex.
The low density lipoprotein receptor-related protein (LRP), a member of the low density lipoprotein receptor family, mediates the internalization of a diverse set of ligands. The ligand binding sites are located in different regions of clusters consisting of approximately 40 residues, cysteine-rich complement-type repeats (CRs). The 39-40-kDa receptor-associated protein, a folding chaperone/escort protein required for efficient transport of functional LRP to the cell surface, is an antagonist of all identified ligands. To analyze the multisite inhibition by RAP in ligand binding of LRP, we have used an Escherichia coli expression system to produce fragments of the entire second ligand binding cluster of LRP (CR3-10). By ligand affinity chromatography and surface plasmon resonance analysis, we show that RAP binds to all two-repeat modules except CR910. CR10 differs from other repeats in cluster II by not containing a surface-exposed conserved acidic residue between Cys(IV) and Cys(V). By site-directed mutagenesis and ligand competition analysis, we provide evidence for a crucial importance of this conserved residue for RAP binding. We provide experimental evidence showing that two adjacent complement-type repeats, both containing a conserved acidic residue, represent a minimal unit required for efficient binding to RAP.
A case of Behçet's syndrome is described presenting with several peripheral arterial aneurysms. The diagnostic criteria are discussed and the need for increased vigilance of this disease is stressed due to an increasing number of immigrants.
We have studied the effects of electroacupuncture at classical acupuncture points, applied before and during surgery in patients undergoing hysterectomy, on postoperative pain and metabolic stress responses in a prospective, randomized and patient-blinded manner. Fifty otherwise healthy women were allocated randomly to receive or not receive electroacupuncture. Electroacupuncture was begun 20 min before skin incision and continued to the end of surgery. All patients received similar general anaesthesia and all received patient-controlled analgesia (PCA) after operation. Postoperative pain in the two groups was evaluated by recording analgesic requirements by PCA and by pain-rating performed by patients and nursing staff. There were no significant differences between the two groups in postoperative analgesic requirements, pain-rating or metabolic stress responses.
Two monomeric neurotoxic phospholipases A2 have been crystallized and their diffraction properties characterized. Crystals of caudoxin (from the venom of Bitis caudalis) and notexin (from the venom of Notechis scutatus scutatus) were grown at neutral pH, in the absence of calcium ion, and diffract to a resolution of 2.3 and 1.6 A, respectively.
Thirty children scheduled for elective orchiopexy or herniotomy were consecutively assigned at random to premedication with methohexital 80 mg/ml, 20 mg/kg rectally, 15 min before transportation to the operating room, or pentobarbital 28 mg/ml, 7 mg/kg rectally, 45 min before transportation. The quality of premedication was recorded at induction with halothane 1-2% and 60% N2O in O2 by mask. All patients received a caudal injection of bupivacaine 1.9 mg/ml, 1.25 ml/kg before surgery. Following completion of anaesthesia, the postoperative wake-up time and the duration of stay in the post-operative recovery room were recorded. The degree and quality of recovery were assessed using the Aldrete score every 30 min until discharge from the recovery room. The group of children receiving methohexital showed a highly significantly shorter awakening time, and a highly significantly shorter stay in the recovery room compared to the pentobarbital group. The children in both groups had a quiet, easy recovery without significant signs of confusion or agitation, and no difference in quality of recovery could be shown. Emergence delirium or agitation in connection with pentobarbital premedication and a possible relation to postoperative pain is discussed.
We studied 20 otherwise healthy women undergoing lower abdominal surgery. Immediately after wound closure, while still anaesthetized, they received either electroacupuncture (EA) or no further treatment. They were allowed pethidine for postoperative analgesia by patient-controlled infusion pump. Signs of postoperative distress (pain, nausea, drowsiness) were evaluated after 2 and 6 h by visual analogue scale scores. The group receiving EA consumed half the quantity of pethidine as that used used by the no treatment group. Two patients in the EA group had no postoperative analgesia in the first 2 h. There was no difference in the assessments of postoperative distress between groups. No patient was aware of having received EA or not.
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