Formation of giant liposomes promoted by divalent cations: critical role of electrostatic repulsion

Spontaneous formation of giant unilamellar liposomes in a gentle hydration process, as well as the adhesion energy between liposomal membranes, has been found to be dependent on the concentration of divalent alkali cations, Ca2+ or Mg2+, in the medium. With electrically neutral phosphatidylcholine (PC), Ca2+ or Mg2+ at 1-30 mM greatly promoted liposome formation compared to low yields in nonelectrolyte or potassium chloride solutions. When negatively charged phosphatidylglycerol (PG) was mixed at 10%, the yield was high in nonelectrolytes but liposomes did not form at 3-10 mM CaCl2. In the adhesion test with micropipette manipulation, liposomal membranes adhered to each other only in a certain range of CaCl2 concentrations, which agreed with the range where liposome did not form. The adhesion range shifted to higher Ca2+ concentrations as the amount of PG was increased. These results indicate that the divalent cations bind to and add positive charges to the lipids, and that membranes are separated and stabilized in the form of unilamellar liposomes when net charges on the membranes produce large enough electrostatic repulsion. Under the assumption that the maximum of adhesion energy within an adhesive range corresponds to exact charge neutralization by added Ca2+, association constants of PC and PG for Ca2+ were estimated at 7.3 M(-1) and 86 M(-1), respectively, in good agreement with literature values.     

Simultaneous determination of inorganic anions and cations in waters by capillary electrophoresis

A simple and rapid assay method for three stimulant drugs (amphetamine, methamphetamine, and dimethamphetamine) in human urine using solid-phase microextraction was developed. In solid-phase microextraction, the drugs were equilibrated between the adsorbent coated-fiber and aqueous sample matrix. After adsorption of the analytes, the fiber was directly transferred to the injector of a gas chromatograph, where the analytes were thermally desorbed and subsequently separated by the gas chromatograph and detected by mass spectrometer. The solid-phase microextraction method, which did not require solvents, was found to be a fast and simple analytical method. We optimized the solid-phase microextraction technique, for factors such as the NaCl salt effect (30%), pH effect (pH=12.4), equilibration time (30 min), desorption time (1 min) and coated-fiber type (100 microm poly(dimethylsiloxane)) and detected the stimulants in human urine, obtained from human subjects. The detection limits of each drug were below 1-10 ng/ml. The developed method can be applied to the abused drug test.     

Osmotic effectors and DNA structure: effect of glycine on precipitation of DNA by multivalent cations

We have investigated the effect of glycine (an organic osmolyte) on DNA precipitation induced by spermine4+, spermidine3+ and Tb3+ addition, using circular dichroism (CD), UV spectroscopy (UV), and electric linear dichroism (ELD) techniques. DNA precipitation by the three compounds is perturbed by glycine: more spermine4+, spermidine3+ and Tb3+ must be added to obtain the same extent of precipitation as compared to the behaviour in absence of this organic osmolyte. It seems that glycine has a general effect on the DNA environment. Calculations based on experimental results and Manning's counterion condensation theory show that glycine could modify the electrostatic environment of DNA as a consequence of a change in dielectric constant.     

Stabilization of the purine.purine.pyrimidine DNA base triplets by divalent metal cations

An extensive search of aphasia-treatment literature yielded 55 reports of clinical outcomes satisfying the essential criteria for inclusion in a meta-analysis. The results confirmed those of an earlier meta-analysis in demonstrating the utility of aphasia treatments, generally considered, for bringing about desirable clinical outcomes. Beyond the general case, the new findings address clinical utility in finer detail than was previously possible. Effects of treatment for aphasia are synthesized and assessed for each of four important dimensions: amount of treatment, type of treatment, severity of aphasia, and type of aphasia.     

Structure and mechanical properties of iron subjected to surface severe plastic deformation by friction: I. Structure formation

Depth-sensing indentation is used to study the effect of grain refinement to submicro- and nanograins on the mechanical properties (hardness, plasticity, Young’s modulus) of armco iron subjected to severe plastic deformation by attrition in argon. In contrast to fcc metals, where the hardness increases and the plasticity decreases as the grain size decreases to 20 nm, the hardness of bcc iron decreases from 5.8 to 3.7 GPa and plasticity δ _A increases from 0.82 to 0.87 as the grain size decreases from 50 to 20 nm.     

Divalent cations stabilize unstacked conformations of DNA and RNA by interacting with base pi systems

Nucleic acid structure, stability, and reactivity are governed substantially by cations. We propose that magnesium and other biological inorganic ions unstack bases of DNA and RNA. This unstacking function of cations opposes their previously accepted role in stabilizing DNA and RNA duplexes and higher assemblies. We show that cations interact favorably with pi-systems of nucleic acid bases. These cation-pi interactions require access of cations or their first hydration shells to faces of nucleic acid bases. We observe that hydrated magnesium ions located in the major groove of B-DNA pull cytosine bases partially out from the helical stack, exposing pi-systems to positive charge. A series of critical cation-pi interactions contribute to the stability of the anticodon arm of yeast-tRNAphe, and to the magnesium core of the Tetrahymena group I intron P4-P6 domain. The structural consequences of divalent cation-pi interactions are clearly distinct from, and some cases in opposition to, cation-electron lone pair interactions. These observations of cation-pi interactions suggest a number of new mechanistic roles for cations in DNA bending, DNA-protein recognition, base-flipping, RNA folding, and catalysis.     

Structure of polycrystalline Al-Ni-Fe-La alloys after quenching and plastic deformation by shear under pressure

The structure and phase composition of aluminum-based polycrystalline alloys (85 at % Al) containing transition (Fe, Ni) and rare-earth (La) metals are studied by metallography, differential scanning calorimetry, X-ray diffraction, and electron-microscopic analysis after melt quenching and subsequent severe plastic deformation (SPD) by shear under pressure. The melt-quenched alloys are shown to have a four-phase structure consisting of an aluminum-based solid solution, intermetallics Al₃Ni and Al₁₁La₃, and iron intermetallics. SPD results in the fragmentation and spheroidization of all phase constituents of the alloys and in the dissolution of the iron intermetallics. A multiphase nanostructured state forms in the alloys. The nanocrystallite sizes after SPD at various deformation parameters are determined. The microhardness is maximal after deformation corresponding to six anvil revolutions at a pressure of 8 or 10 GPa. The structural parameters and the microhardnesses are compared after SPD by shear under pressure of the alloys having the same compositions and different structural states (namely, amorphous and polycrystalline) before deformation. An amorphous-nanocrystalline structure with the minimum nanograin sizes and the maximum microhardnesses forms in the alloys having an initial amorphous structure and subjected to SPD.     

Fields of strains around the inclusion of second phase in a uniform matrix undergoing plastic deformation

This paper focuses on the problem of the evaluation of strains around the inclusions of various shapes and properties located in the uniform matrix undergoing large plastic deformations. The analysis is performed using the rigid-plastic finite-element approach. The uniform plane-strain deformation field is simulated by an introduction of zero friction forces into the program for the compression process. An assumption that the die is wider than the sample allows to simulate ideally uniform flow of metal. Several shapes of the inclusions are investigated, but the results for three most common shapes of the particle's cross-section are presented in the paper. They are: square with the sides parallel to the main directions, square with the sides inclined under an angle of 45° to the main directions and round.     

On the causes of collapse and sudden death by Avicenna

Avicenna's views on the causes of collapse and sudden death are presented from a literal translation of the mediaeval Arabic text. Medical knowledge based on observation mixed with pure abstract reasoning forms the essence of Avicenna's medical writings.     

Effects of the Health Structure Regulation on the form of documentation in clinics

The requirements of the German Health Structure Law (GSG) are not matchable without the help of electronic data processing, especially regarding medical documentation in combination with the documentation for financial and calculation reasons. As a wide number of different and partly parallel keys are used, the electronic documentation has to be integrated in the clinical routine. Data have to be documented where they arise, by whom they are produced and unproductive double-documentation have to be avoided by any means. Investments in electronic data processing have to take into consideration the direct benefit for the user. This is a key to motivation and rises the validity of data.     

Changes in expression site control and DNA modification in Trypanosoma brucei during differentiation of the bloodstream form to the procyclic form

The 2 x 2 table is an invaluable tool for displaying bivariate binary data. It is easy to find examples of correlated binary response in biopharmaceutical experiments and clinical research and analysis of these data is a current research topic. The most common hypothesis tested for 2 x 2 tables of correlated proportions is that of homogeneity of the marginal proportions or, equivalently, the hypothesis of table symmetry. The 2 x 2 table of correlated proportions is rich with information and we present a survey of some of the analyses relevant for these data. Using asymptotic theory, we develop estimators of relevant parameters and associated test statistics that are of interest. We discuss interval estimation using arguments proposed by Quesenberry and Hurst (1) and Goodman (2). These interval estimators do not rely on estimation of the covariance matrix and are not necessarily equivalent to those obtained using modified chi-square statistics.     

DNA loop domains in a 1.4-Mb region around the human hprt gene mapped by cleavage mediated by nuclear matrix-associated topoisomerase II

The aim of the study was the definition of the clinical features and survival of 27 resected cases of distal bile duct carcinoma. This neoplasm accounted for 14% of all periampullary malignancies treated by pancreaticoduodenectomy between 1990 and 1996. Jaundice was present in 96% of patients, but was the first symptom only in 78%. Preoperative investigations allowed to recognize distal bile duct cancer in a minority of patients (41%). Operative mortality and morbidity were 3.7 and 44%, respectively. Most patients (88%) were assigned to UICC stage IV-A. Postoperative survival was not significantly better than survival of 101 patients undergoing pancreaticoduodenectomy for pancreatic ductal carcinoma; median survival was 22 months, with a 13% 5-year survival rate. Determinants of a better prognosis were UICC stage 相似文献   

Structure and magnetic properties of bulk nanocrystalline Nd-Fe-B permanent magnets prepared by hot pressing and hot deformation

Structure and magnetic properties were studied for bulk nanocrystalline Nd-Fe-B permanent magnets that were prepared at 650 °C for 3 min under 300 MPa using the SPS-3.20-MK-V sintering machine and the hot pressed magnets were then submitted to hot deformation with height reduction of 50%,60%,70%,80%,and 85%.Effects of height reduction(HR) and deformation temperature on the structure and magnetic properties of the magnets were investigated.The crystal structure was evaluated by means of X-ray diffraction(XRD) and the microstructure was observed by transmission electron microscopy(TEM).The magnetic properties of the magnets were investigated by vibrating sample magnetometer(VSM).As the height reduction increased,the remanence(B r) of the magnets increased first,peaks at 1.3 T with HR=60%,then decreased again,and the coercivity(H ci) of the magnets decreased monotonically.On the other hand,as the deformation temperature increased,the B r of the magnets increased first,peaks at 1.36 T with HR=60%,then decreased again,and the H ci of the magnets decreased monotonically.Under optimal conditions,the hot deformed magnet possessed excellent magnetic properties as B r =1.36 T,H ci =1143 kA/m,and(BH) max =370 kJ/m 3,suggesting the good potential of the magnets in practical applications.