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Query: UMLS:C0276640 (TEM)
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The strontium ferrite ultrafine particles have been prepared using the microemulsion processing. The mixed hydroxide precursor was obtained via the coprecipitation of Sr(2+) and Fe(3+) in a water-in-oil microemulsion of water/CTAB/n-butanol/isooctane. According to the investigation on the thermochemical properties by TGA/DTA and the phase analysis by XRD, it was shown that the precursor could yield pure strontium ferrite after calcination at 700 degrees C for 5 h while using an appropriate molar ratio of Sr/Fe in microemulsions. From TEM measurement, the diameters of the precursor and calcined particles were 3.8+/-0.7 and 50-100 nm, respectively. The magnetic properties characterized by a SQUID magnetometer showed that the saturation magnetization, remanent magnetization, coercivity, and squareness ratio were 55 emu/g, 28 emu/g, 492 Oe, and 0.51, respectively. The magnetization was also observed to increase with the decrease of temperature at 5-400 K. Compared with those reported earlier, the quite low coercivity implies the potential application of final product in the high-density perpendicular recording media. Copyright 2001 Academic Press.
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PMID:Synthesis of Strontium Ferrite Ultrafine Particles Using Microemulsion Processing. 1125 26

The catalytically competent active-site structure of a true acylenzyme reaction intermediate of TEM-1 beta-lactamase formed with the kinetically specific spin-labeled substrate 6-N-(2,2,5,5-tetramethyl-1-oxypyrrolinyl-3-carboxyl)-penicillanic acid isolated under cryoenzymologic conditions has been determined by angle-selected electron nuclear double resonance (ENDOR) spectroscopy. Cryoenzymologic experiments with use of the chromophoric substrate 6-N-[3-(2-furanyl)-propen-2-oyl]-penicillanic acid showed that the acylenzyme reaction intermediate could be stabilized in the -35 to -75 degrees C range with a half-life suitably long to allow freeze-quenching of the reaction species for ENDOR studies while a noncovalent Michaelis complex could be optically identified at temperatures only below -70 degrees C. The wild-type, Glu166Asn, Glu240Cys, and Met272Cys mutant forms of the mature enzyme were overexpressed in perdeuterated minimal medium to allow detection and assignment of proton resonances specific for the substrate and chemically modified amino acid residues in the active site. From analysis of the dependence of the ENDOR spectra on the setting of the static laboratory magnetic field H0, the dipolar contributions to the principal hyperfine coupling components were estimated to calculate the separations between the unpaired electron of the nitroxyl group and isotopically identified nuclei. These electron-nucleus distances were applied as constraints to assign the conformation of the substrate in the active site and of amino acid side chains by molecular modeling. Of special interest was that the ENDOR spectra revealed a water molecule sequestered in the active site of the acylenzyme of the wild-type protein that was not detected in the deacylation impaired Glu166Asn mutant. On the basis of the X-ray structure of the enzyme, the ENDOR distance constraints placed this water molecule within hydrogen-bonding distance to the carboxylate side chain of glutamate-166 as if it were poised for nucleophilic attack of the scissile ester bond. The ENDOR results provide experimental evidence of glutamate-166 in its functional role as the general base catalyst in the wild-type enzyme for hydrolytic breakdown of the acylenzyme reaction intermediate of TEM-1 beta-lactamase.
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PMID:ENDOR structural characterization of a catalytically competent acylenzyme reaction intermediate of wild-type TEM-1 beta-lactamase confirms glutamate-166 as the base catalyst. 1132 60

The purpose of the present study was to determine whether Octopus vulgaris spermatozoa are activated by progesterone stimulation. Spermatozoa were collected from the spermatophores in the Needham's sac of the male (MS) and from the spermathecae of oviducal glands of the female (FS). We used transmission (TEM) and scanning (SEM) electron microscopy to study the morphology of untreated, Ca2+ ionophore A23187 and progesterone-treated MS spermatozoa, and untreated FS spermatozoa. We showed that ionophore and progesterone stimulation of MS spermatozoa induce breakdown of the membranes overlapping the acrosomal region, exposing the spiralized acrosome. These modifications resemble the acrosome reaction observed in other species. FS stored in the spermathecae did not show the membranes covering the acrosomal region present in the MS spermatozoa. When ionophore and progesterone treatments were performed in Ca2+-free artificial sea water, no changes were observed, suggesting the role of external calcium in modifying membrane morphology. Lectin studies showed a different fluorescence distribution and membrane arrangement of FS-untreated spermatozoa with respect to the MS, suggesting that spermatozoa transferred in the female genital tract after mating, are stored in a pre-activated state. The plasma membrane of the untreated MS and FS spermatozoa was labelled with Progesterone-BSA-FITC, indicating the presence of plasma membrane progesterone receptor. Taken together these data suggest that progesterone induces an acrosome- like reaction in MS spermatozoa similar to that induced by calcium elevation. In addition progesterone may play a role in the pre-activation of spermatozoa stored in the female tract, further supporting the hypothesized parallelism between cephalopods and vertebrates.
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PMID:Progesterone induces activation in Octopus vulgaris spermatozoa. 1133 51

Novel dendritic polyphenylazomethines (DPAs), which consist of a pi-conjugated backbone, were synthesized up to the fourth generation by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of titanium(IV) tetrachloride. The obtained dendrimers, DPA G1-4 (designated as GX, where X is the generation number), show high thermostability (Td(10%) 521 degrees C in DPA G4) and high solubility for the common solvents such as chloroform, THF, and DMSO unlike the conventional linear polyphenylazomethines, which have very low solubilities. The DPA G4 molecule was confirmed to have a spherelike structure by GPC measurement and a molecular model based on the crystal structure of DPA G2. Crystal data for DPA G2: monoclinic space group P2(1)/a, a = 25.352(4) A, b = 8.577(2) A, c = 16.151(2) A, beta = 106.25(1) degrees, V = 3371.6(10) A(3), Z = 2, D(calc) = 1.168 g/cm(3), mu(Cu Kalpha) = 0.536 cm(-1), final R = 0.089, and R(w) = 0.287. The molecular modeling reveals that a DPA G4 molecule has a spherelike structure, in which the height, width, and depth are 2.3, 2.9, and 2.5 nm, respectively. The TEM and AFM pictures show the DPA G4 molecules to have a spherelike structure (the diameter: 2.3 nm) and are regularly assembled on a plate by casting. The occupied area of one DPA G4 molecule in a monolayer on water was estimated by pi-A measurements to be 3.8-4.2 nm(2) (the calculated diameter 2.2-2.3 nm, which agreed with the TEM result). NMR studies (1H NMR at 130 degrees C and T(1) measurements) supported a conformational rigidity of DPA G4 in solution.
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PMID:First synthesis of phenylazomethine dendrimer ligands and structural studies. 1145 26

Recently published results confirm the positive effect of regional hyperthermia combined with external radiotherapy on pelvic tumours. Several studies have been published on the improvement of RF annular array applicator systems with dipoles and a closed water bolus. This study investigates the performance of a next-generation applicator system for regional hyperthermia with a multi-ring annular array of antennas and an open water bolus. A cavity slot antenna is introduced to enhance the directivity and reduce mutual coupling between the antennas. Several design parameters, i.e. dimensions, number of antennas and operating frequency, have been evaluated using several patient models. Performance indices have been defined to evaluate the effect of parameter variation on the specific absorption rate (SAR) distribution. The performance of the new applicator type is compared with the Coaxial TEM. Operating frequency appears to be the main parameter with a positive influence on the performance. A SAR increase in tumour of 1.7 relative to the Coaxial TEM system can be obtained with a three-ring, six-antenna per ring cavity slot applicator operating at 150 MHz.
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PMID:Regional hyperthermia applicator design using FDTD modelling. 1147 34

This review explores the robustness of the assumptions underpinning the two- (fat mass [FM], fat-free mass [FFM]), three- (FM; total body water [TBW], fat free dry solid), and four- (FM; TBW; bone mineral [BM], residual) compartment models of body composition. The measurement of body density (BD) via underwater weighing (UWW) and TBW via isotopic dilution are the two most frequently used two-compartment techniques. The former assumes that the FM and FFM have densities of 0.9007 g/cm(3) and 1.1000 g/cm(3), respectively, while the latter uses a FFM hydration constant. Although both techniques can estimate body composition precisely (technical error of measurement [TEM]: UWW = 0.4 %BF; TBW = 0.6 %BF), the validity of these estimates is adversely affected by biological variability in the assumed percentages for the FFM components (TBW = 73.72%; protein = 19.41%; BM = 5.63%; non-BM = 1.24%). The three-compartment model, which incorporates measures of BD and TBW, greatly increases validity by removing errors relating to variability in TBW, which comprises the largest percentage of the FFM and is furthermore acutely variable. The four-compartment model marginally improves on the three-compartment model by additionally controlling for BM, which displays less variability than the TBW component of the FFM. The three- and four-compartment models therefore provide more valid estimates of body composition than the two-compartment model, and this increased accuracy is not offset by propagation of errors (TEM = 0.7 %BF for both models) from the combinations of multiple measurements (BD, TBW, BM). Am. J. Hum. Biol. 11:175-185, 1999. Copyright 1999 Wiley-Liss, Inc.
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PMID:Critical appraisal of the estimation of body composition via two-, three-, and four-compartment models. 1153 41

Poly(amidoamine)s (PAAs) are water-soluble polymers that display pH-dependent membrane activity. PAAs have the potential to act as a synthetic alternative to fusogenic peptides and thus promote endosomal escape. The purpose of this study was to investigate for the first time whether PAA have the ability to complex DNA, protect it from nuclease degradation and to promote transfection in vitro. PAAs ISA 1 (Mn 6900) and ISA 23 (Mn 10,500) and their 2-phenylethylamine containing analogues ISA 4 and ISA 22 (Mn approximately 8000) were studied. All PAAs retarded the electrophoretic mobility of lambda Hind III DNA demonstrating interpolyelectrolyte complex (IPEC) formation and toroids of 80-150 nm in diameter (10:1 polymer excess) were visible using TEM. DNase II inhibition was observed. At a polymer:DNA ratio of 10:1, this was ISA 1(89.6 +/- 6.1%), ISA 4 (92.2 +/- 11.2%), ISA 22 (69.4 +/- 3.7%), and ISA 23 (58.0 +/- 10.0%). PAAs demonstrated the ability to mediate pSV beta-galactosidase transfection of HepG2 cells. At a vector:DNA mass ratio of 5:1, ISA 23 showed equivalent transfection ability compared with polyethylenimine and LipofectIN and was more effective than LipofectACE. These properties suggest that PAAs warrant further development as endosomolytic vectors.
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PMID:Poly(amidoamine)s as potential nonviral vectors: ability to form interpolyelectrolyte complexes and to mediate transfection in vitro. 1171 5

The microvasculature of the water buffalo (Bubalus bubalis) epididymis was investigated using light (LM), scanning electron (SEM), and transmission electron (TEM) microscopy techniques. SEM analysis of the buffalo epididymis showed fenestrations that occupied ovoid inside the endothelium of the postcapillary venules located in the caput, corpus, and cauda. They varied in shape and dimension, but more importantly, they connected the venules of the blood vascular system to the capillaries of the peripheral lymphatic vascular system. Morphofunctional analysis of these connections suggests that the microvasculature of the buffalo epididymis plays a role in facilitating the circulation of biologically active substances, and the absorption and secretion processes necessary for the survival and maturation of spermatozoa. The lymphatic capillaries at the connection points formed a network of variously sized polygonal links. These capillaries then converged to form the precollector lymphatic vessels, which in turn converged with the larger vessels originating from the testis. It was further noted that in the capillary endothelium there were no fenestrations, and in the large veins there were many diverticula. These diverticula appear to play a role in the regulation of the seasonal variations of the blood reflux. In general, the microvascular architecture of the buffalo epididymis, particularly its connection to the lymphatic vascular system, appears to play an important role in the absorption and secretion processes of the epididymal epithelium.
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PMID:Microvasculature of the buffalo epididymis. 1174 72

Polyterephthalamide microcapsules containing a poly(acrylic acid) gel as a macromolecular ligand (PAA-CAPS) were prepared using an original two step polymerization process in a water-in-oil inverse emulsion system. A polyamide microcapsule containing acrylic acid, initiator and cross-linking agent, is formed by interfacial polycondensation of terephthaloyl dichloride with hexamethylenediamine. In situ radical polymerization of the microcapsule core acrylic acid is initiated to obtain encapsulated poly(acrylic acid) gel. Reference polyamide microcapsules, i.e. without ligand (CAPS), were also synthesized. The mean diameter of synthesized microcapsules was 210 microm, and the microcapsule wall thickness was evaluated by SEM and TEM observations of microcapsule cross-section cuts. The microcapsule water content was determined by thermogravimetric experiments. The extractabilities of Cu(II), Ni(II), Co(II) and Zn(II) into PAA-CAPS were examined. The stripping of the various cations can be promoted in diluted hydrochloric acid solutions.
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PMID:Extraction of metal cations by polyterephthalamide microcapsules containing a poly(acrylic acid) gel. 1181 55

A new species of naked amoeba, Platyamoeba pseudovannellida n.sp., is described on the basis of light microscopic and fine structural features. The amoeba was isolated from the Salton Sea, California, from water at a salinity of ca. 44%. Locomotive amoebae occasionally had a spatulate outline and floating cells had radiating pseudopodia, sometimes with pointed tips. Both these features are reminiscent of the genus Vannella. However, the surface coat (glycocalyx) as revealed by TEM indicates that this is a species of Platyamoeba. Although salinity was not used as a diagnostic feature, this species was found to have remarkable tolerance to fluctuating salinity levels, even when changes were rapid. Amoebae survived over the range 0 per thousand to 150 per thousand salt and grew within the range 0 per thousand to 138 per thousand salt. The generation time of cells averaged 29 h and was not markedly affected by salt concentration. This is longer than expected for an amoeba of this size and suggests a high energetic cost of coping with salinity changes. The morphology of cells changed with increasing salinity: at 0 per thousand cells were flattened and active and at the other extreme (138 per thousand) amoebae were wrinkled and domed and cell movement was very slow. At the ultrastructural level, the cytoplasm of cells grown at high salinity (98 per thousand was considerably denser than that of cells reared at 0 per thousand.
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PMID:Platyamoeba pseudovannellida n. sp., a naked amoeba with wide salt tolerance isolated from the Salton Sea, California. 1183 75


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