Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

Hydrous ferric oxides (HFO) are efficient sorbents for inorganic and organic pollutants and therefore have great potentials in environmental science and engineering applications. Freezing and thawing of HFO suspensions leads to the formation of dense HFO aggregates. It facilitates the handling and increases the drying rate of HFO. In this study, we used a combination of pycnometry, gas adsorption (N(2) gas, water vapor), and small-angle neutron scattering (SANS) to characterize the porosity and pore size distribution of dense HFO aggregates formed by freezing dialyzed HFO suspensions at -25 degrees C and thawing them at room temperature. The crystallinity of the HFO, which was a 2-line ferrihydrite, was not affected by this treatment. Wet sieving and laser diffraction analysis showed that the dense HFO aggregates had a unimodal size distribution with an average diameter of 235+/-35 microm. Increasing the freezing rate by cooling with liquid N(2) (-196 degrees C) resulted in much smaller aggregates with an average diameter of 20 microm. Adding NaNO(3) electrolyte to the HFO suspensions prior to freezing also resulted in the formation of smaller aggregates. The dense HFO aggregates formed at -25 degrees C had a porosity of 0.73+/-0.02 ll(-1). SANS revealed a unimodal size distribution of pores, with an average pore diameter of 2.0 nm. The diameter of the HFO crystallites was estimated by transmission electron microscopy to be 1.9+/-0.5 nm. Geometrical considerations taking into account the unit particle and average pore size suggest that the crystallites retain 1-2 layers of hydration water during the coagulation induced by freezing. Analysis by N(2) gas adsorption showed that drying the dense HFO aggregates induced a reduction in porosity by about 25% and shifted the pore size distribution to smaller diameters. Rewetting during water vapor adsorption did not induce significant changes of the aggregate structure. The specific surface area of the dry HFO aggregates was between 320 and 380 m(2)g(-1).

Acrylamide: increased concentrations in homemade food and first evidence of its variable absorption from food, variable metabolism and placental and breast milk transfer in humans

We have developed a liquid chromatography/mass spectrometry (LC-MS/MS) assay to determine acrylamide in various body fluids. The assay also allows the reliable quantitation of acrylamide in food. In a total of 11 healthy male and female subjects, we were able to show that acrylamide from food given to humans is in fact absorbed from the gut. The half-lives determined in two male subjects were 2.2 and 7 h. Acrylamide was found in human breast milk and penetrated the human placenta (n = 3). The variability of acrylamide concentrations found in this investigation is most likely caused by variable intersubject bioavailability and metabolism. This may be an important indication that the assessment of the risk from acrylamide for the individual may be very difficult without knowing the concentrations of acrylamide in the body. This should be considered in the design of any risk assessment study or post hoc analysis of earlier studies. At this time, we suggest that pregnant women and breast-feeding mothers avoid acrylamide-containing food.

Role of chelate substituents and cis σ-effect on the rate of ligand substitution at Pt(N–N–N) and Pt(N–N–C) centres

Four complexes of the type [Pt(N-N-X)Cl](X = N or C) were tailor synthesized for mechanistic studies in methanol. The terdentate ligands included terpy, 4'-Ph-terpy, 4'-(2"-CF(3)-Ph)-terpy, and 4'-(2"'-CF(3)-Ph)-6-Ph-2,2'-bipy. The rate of substitution of the chloro ligand by thiourea, N,N'-dimethylthiourea, and N,N,N',N'-tetramethylthiourea was studied as a function of nucleophile concentration, temperature and pressure by using a stopped-flow technique. The observed pseudo-first-order rate constants for the substitution reactions obeyed the simple rate law k(obs) = k(2)[Nu]. Second-order kinetics and negative activation entropies and volumes support an associative substitution mechanism. At 298 K, the values of the second-order rate constant show a slight dependence on the nature of the moiety attached to the terpy ligand. Changing from a nitrogen sigma-donor to a carbon sigma-donor in the cis position, results in a deceleration of the substitution rate. The results suggest that the Pt-C bond in the cis position activates the metal centre in a different way than in the trans position.

[Psychotherapeutic treatment of traumatic stress with the EMDR (Eye Movement Desensitization and Reprocessing) method]

EMDR (Eye Movement Desensitization and Reprocessing) is a method, developed at the end of the nineteen-eighties, for the treatment of the post-traumatic stress disorder (PTSD). The patient is asked to concentrate on certain aspect of the traumatic memory while keeping his eyes fixed on the movements of the therapist's finger. Apparently, this triggers information processing that results in appreciable relief for the patient. The method has proven to be equally as effective as behavioral-therapeutic techniques, and, has in the meantime, been included in national and international guidelines for the treatment of PTSD. The indications for EMDR treatment include not only PTSD, but, increasingly, also other, sometimes more severely chronic, it trauma sequelae. Within the framework of basic care, EMDR must be embedded within a treatment plan and should, where applicable, be combined with other methods.

Bioengineered human bone tissue using autogenous osteoblasts cultured on different biomatrices

Surgical treatment of critical-size posttraumatic bone defects is still a challenging problem, even in modern bone and joint surgery. Progress in cellular and molecular biology during the last decade now permits novel approaches in bone engineering. Recent conceptual and technical advances have enabled the use of mitotically expanded, bone-derived cells as a therapeutic approach for tissue repair. Using three different tissue carrier systems, we successfully cultivated human osteoblasts in a newly developed perfusion chamber. We studied cell proliferation and the expression of osteocalcin, osteopontin, bone morphogenetic protein-2A, alkaline phosphatase, and vascular endothelial growth factor as parameters for osteoblast function and viability. Adherence of highly enriched human osteoblasts had already started after 1 h and resulted in completely overgrown human bone pieces after 10 days. Expression analysis of bone-specific alkaline phosphatase indicated differentiating osteoblasts, whereas the high mRNA expression of osteocalcin and osteopontin revealed terminally differentiated osteoblasts and the process of mineralization. Additionally, gene expression was significantly higher when demineralized bone was used as biomatrix, compared to autoclaved bone and hydroxyapatite ceramics. We conclude that with our newly developed perfusion culture system, vital autogenous bone implants of clinically applicable size can be generated within 17 days in order to manage critical-size bone defects.

[Uremic patients--late referral, early death]

BACKGROUND AND OBJECTIVE

A number of reports from various countries document that patients with renal failure who are referred late to renal units, have more complications e. g. lack of vascular access when dialysis has to be started as well as longer hospitalisation and have also a higher risk of early death. No data on these points are available from Germany.

PATIENTS AND METHODS

In a retrospective analysis the timing of referral to the nephrologists was studied in two Departments of Medicine, e. g. Heidelberg and Vienna, for all patients who started renal replacement therapy. For patients in Heidelberg the relation between timing of referral and survival on dialysis was analysed using the Kaplan-Maier-technique.

RESULTS

In Heidelberg 280 patients were analysed, 174 men, 106 women, age 61.8 +/- 14.5 years; 136 diabetic patients (9 type 1). They had been referred from GPs (n = 131), specialists (diabetologists, cardiologists; n = 20), emergency departments (n = 33), other hospitals (n = 90) or other institutions (n = 16). The measured median creatinine clearance at the time of referral was 14 ml/min (5-34). The median interval between referral and start of dialysis was 17 weeks. 137 patients had been referred < 17 weeks and 143 patients > or = 17 weeks prior to the start of dialysis. 97 of the 111 patients referred < or = 4 weeks prior to dialysis and 59 of the 169 patients referred > 4 weeks had to be dialysed with a central catheter. There were clear differences in patient survival. In patients referred < 17 weeks before the start of dialysis, the actuarial risk of death during the first 12 month was 34.2 % compared to 5.5 % (p < 0.0001) in patients referred > or = 17 weeks. Even the mortality in the interval between 12 and 24 months after the start of dialysis was clearly higher (15.3 %) in patients with late compared to early referral (11.4 %).

CONCLUSION

Late referral of patients with impaired renal function to renal units causes more frequent problems of vascular access, longer hospitalisation, more medical complications, higher costs and higher mortality. Early referral of patients with renal failure is indispensable to improve dialysis outcomes.

Centrally acting .alpha.1-adrenoceptor agonists based on hexahydronaphth[2,3-b]-1,4-oxazines and octahydrobenzo[g]quinolines

Centrally acting alpha 1-agonists may be of therapeutic value in dementias and other CNS disorders characterized by symptoms of noradrenergic insufficiency. Therefore, on the basis of known peripherally acting alpha 1-agonists two new groups of centrally acting alpha 1-agonists with improved lipophilicity, the hexahydronaphth[2,3-b]-1,4-oxazines type A and the octahydrobenzo[g]quinolines type B were designed. The N-methylated derivatives 14 and 33 demonstrate potent, direct agonistic activity at postjunctional alpha 1-receptors. Ring substituent alterations in compounds of type A and B change the potency of compounds on the rabbit ear artery by over 3 orders of magnitude (pD2 = 5.35-8.40). The efficacy of these compounds varies from 42 to 110%. Those alpha 1-agonists which were selective in the pithed rat increase vigilance in rats. Compound 14 was found to be a centrally acting alpha 1-agonist with good tolerability in different animal species and in healthy volunteers. Furthermore, 14 selectively stimulates the breakdown of phosphatidylinositol in rat cerebral cortex slices. In vivo, the compound reverses behavioral deficits in animals which received noradrenergic lesions following DDC or DPS4 treatment. Oxazine 14 and its close derivatives are by far more lipophilic than commonly known alpha 1-agonists. This is demonstrated in a ClogP-PROBIS plot.

PCSB--a program collection for structural biology and biophysical chemistry

We present the first package of Java classes specifically aimed at the handling of structural and biophysical problems. To enable object-oriented programming a basis of fundamental Java classes is required which deals with basic operations of vectors, matrices, amino acid sequences, crystal symmetries and PDB files. Five classes, which carry out these basic operations, were constructed and bundled together with several utility functions in the PCSB package. Furthermore, to demonstrate their applicability and to obtain programs handling common tasks in structural laboratories, we present the first six applications of PCSB. All applications are portable to different platforms and require only the Java Runtime Environment to be installed on the system. available as PDF file.

[Post-traumatic kyphosis of the truncal vertebrae]

Assessing the initial post-traumatic situation is of imminent importance in choosing the most suitable approach for primary treatment of thoracic and lumbar spine fractures. Misjudging the static situation of the injured spine is a common reason for selecting an inadequate therapeutic procedure. The consequence is a defective spinal position with the corresponding symptoms, which usually requires a complicated surgical procedure. Our experience is based on 34 patients with a post-traumatic defective position of the thoracic and lumbar spine: 12 patients underwent primary surgical and 22 primary conservative treatment. The aim of our study was to demonstrate the initial situation and primary management as well as subsequent problems and the respective surgical procedure applied in our department for correcting and stabilizing the areas involved and to present intermediate results.

Crystal structure of paprika ferredoxin-NADP+ reductase. Implications for the electron transfer pathway

cDNA of Capsicum annuum Yolo Wonder (paprika) has been prepared from total cellular RNA, and the complete gene encoding paprika ferredoxin-NADP(+) reductase (pFNR) precursor was sequenced and cloned from this cDNA. Fusion to a T7 promoter allowed expression in Escherichia coli. Both native and recombinant pFNR were purified to homogeneity and crystallized. The crystal structure of pFNR has been solved by Patterson search techniques using the structure of spinach ferredoxin-NADP(+) reductase as search model. The structure was refined at 2.5-A resolution to a crystallographic R-factor of 19.8% (R(free) = 26.5%). The overall structure of pFNR is similar to other members of the ferredoxin-NADP(+) reductase family, the major differences concern a long loop (residues 167-177) that forms part of the FAD binding site and some of the variable loops in surface regions. The different orientation of the FAD binding loop leads to a tighter interaction between pFNR and the adenine moiety of FAD. The physiological redox partners [2Fe-2S]-ferredoxin I and NADP(+) were modeled into the native structure of pFNR. The complexes reveal a protein-protein interaction site that is consistent with existing biochemical data and imply possible orientations for the side chain of tyrosine 362, which has to be displaced by the nicotinamide moiety of NADP(+) upon binding. A reasonable electron transfer pathway could be deduced from the modeled structures of the complexes.

Daytime variations in central nervous system activation measured by a pupillographic sleepiness test

Pupil size is regulated exclusively by the autonomic nervous system, and in darkness is proportional to the level of central sympathetic tone. Spontaneous pupillary movements, while at rest in darkness and quiet, were recorded for a period of 11 min, using infrared video pupillography. Thirteen young adults took part in a 30-h experiment lasting from 08.00 h to 14.00 h on the following day. Pupillographic testing and completion of a self-rated scale for the estimate of sleepiness were repeated every two hours. Pupillary unrest index (PUI), as a measure of pupil size instability associated with daytime sleepiness, showed the lowest values at 09.00 h, when pupil size was found to be maximal, and 23.00 h. During the course of the day, amplitude spectrum < or = 0.8 Hz and PUI showed increasing values during the afternoon hours, followed by a decrease during the evening. Daytime variations in the pupillary unrest index in healthy normal subjects were found to be positively correlated with the level of alertness. These findings are similar to the daytime variations found by the MSLT (multiple sleep latency test) in young adults.

Reaction Paths in Concurrence: The Electrochemical Hydrogen Reaction on GaAs(111)A- and GaAs(110)-Surfaces A Quantumchemical Approach

We have performed quantumchemical investigations towards a further explanation of the reaction mechanism of the hydrogen evolution reaction on semiconductor electrodes (continuation of Z. Phys. Chem. 210 (1999) 95). Details of the two-step-mechanism via H

S100A1 and S100B interactions with annexins

Members of the annexin protein family interact with members of the S100 protein family thereby forming heterotetramers in which an S100 homodimer crossbridges two copies of the pertinent annexin. Previous work has shown that S100A1 and S100B bind annexin VI in a Ca(2+)-dependent manner and that annexin VI, but not annexin V, blocks the inhibitory effect of S100A1 and S100B on intermediate filament assembly. We show here that both halves of annexin VI (i.e., the N-terminal half or annexin VI-a and the C-terminal half or annexin VI-b) bind individual S100s on unique sites and that annexin VI-b, but not annexin VI-a, blocks the ability of S100A1 and S100B to inhibit intermediate filament assembly. We also show that the C-terminal extension of S100A1 (and, by analogy, S100B), that was previously demonstrated to be critical for S100A1 and S100B binding to several target proteins including intermediate filament subunits, is not part of the S100 surface implicated in the recognition of annexin VI, annexin VI-a, or annexin VI-b. Evaluation of functional properties with a liposome stability and a calcium influx assay reveals the ability of both S100 proteins to permeabilize the membrane bilayer in a similar fashion like annexins. When tested in combinations with different annexin proteins both S100 proteins mostly lead to a decrease in the calcium influx activity although not all annexin/S100 combinations behave in the same manner. Latter observation supports the hypothesis that the S100-annexin interactions differ mechanistically depending on the particular protein partners.

Structure and mechanism of activity of the cyclic phosphodiesterase of Appr>p, a product of the tRNA splicing reaction

The crystal structure of the cyclic phosphodiesterase (CPDase) from Arabidopsis thaliana, an enzyme involved in the tRNA splicing pathway, was determined at 2.5 A resolution. CPDase hydrolyzes ADP-ribose 1",2"-cyclic phosphate (Appr>p), a product of the tRNA splicing reaction, to the monoester ADP-ribose 1"-phosphate (Appr-1"p). The 181 amino acid protein shows a novel, bilobal arrangement of two alphabeta modules. Each lobe consists of two alpha-helices on the outer side of the molecule, framing a three- or four-stranded antiparallel beta-sheet in the core of the protein. The active site is formed at the interface of the two beta-sheets in a water-filled cavity involving residues from two H-X-T/S-X motifs. This previously noticed motif participates in coordination of a sulfate ion. A solvent-exposed surface loop (residues 100-115) is very likely to play a flap-like role, opening and closing the active site. Based on the crystal structure and on recent mutagenesis studies of a homologous CPDase from Saccharomyces cerevisiae, we propose an enzymatic mechanism that employs the nucleophilic attack of a water molecule activated by one of the active site histidines.