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Large Aggregates (large + aggregate)
Selected AbstractsPhotoactive Protochlorophyllide Regeneration in Cotyledons and Leaves from Higher Plants,,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2000Benoît Schoefs ABSTRACT Chlorophyll accumulation during greening implies the continuous transformation of photoactive protochlorophyllide (Pchlide) to chlorophyllide. Since this reaction is a light-dependent step, the study of regeneration of photoactive Pchlide under a continuous illumination is difficult. Therefore this process is best studied on etiolated plants during a period of darkness following the initial photoreduction of photoactive Pchlide. In this study, the regeneration process has been studied using spinach cotyledons, as well as barley and bean leaves, illuminated by a single saturating flash. The regeneration was characterized using 77 K fluorescence emission and excitation spectra and high-performance liquid chromatography. The fluorescence data indicated that the same spectral forms of photoactive Pchlide are regenerated by different pathways: (1) photoactive Pchlide regeneration starts immediately after the photoreduction through the formation of a nonphotoactive Pchlide form, emitting fluorescence at approximately 651 nm. This form is similar to the large aggregate of photoactive Pchlide present before the illumination, but it contains oxidized form of nicotinamide adenine dinucleotide phosphate, instead of the reduced form (NADPH), in the ternary complexes; and (2) after the dislocation of the large aggregates of chlorophyllide,light-dependent NADPH:Pchlide a photooxidoreductase,NADPH ternary complexes, the regeneration occurs at the expense of the several nonphotoactive Pchlide spectral forms present before the illumination. [source] Histo-cytochemistry and scanning electron microscopy of lavender glandular trichomes following conventional and microwave-assisted hydrodistillation of essential oils: a comparative studyFLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2006Marcello Iriti Abstract The conventional hydrodistillation method (HD) has been compared with three different variants of the microwave-assisted hydrodistillation technique (MADH), on Lavandula angustifolia flowers, both in terms of oil yield and effects on the glandular trichome morpho-structure. The amount and composition of essential oil extracted in 4 h by HD was similar to that obtained in only 20 min by MADH and even lower than that extracted with a steam variant (MASD) of MADH itself. Histo-cytochemical investigations and scanning electron microscopy showed that glandular trichome, after 4 h of HD, appeared swollen, with a deeply wrinkled surface and empty of essential oil, however maintaining the integrity of their cuticle. Many oil droplets were stuck to the outside of the trichome cuticle, sometimes arranged in large aggregates. After 20 min of MADH or MASD, trichomes appeared empty as well, but also particularly disrupted, or at least with holes in their head cuticle. Oil droplets were present outside the glands and in the inter-rib regions of the flower calyx, except in the case of MASD. After this extraction method, neither oil droplets nor other lipid staining were present in the samples, confirming the effectiveness of this particular MADH technique. These investigations suggest that the rapidity of MADH and MASD in extracting essential oil is mainly due to the collapse of trichome structure and the consequent direct release of its content, without which it has to slowly permeate through membranes and cuticle, as in the case of HD. Copyright © 2006 John Wiley & Sons, Ltd. [source] Increased strength of erythrocyte aggregates in blood of patients with inflammatory bowel diseaseINFLAMMATORY BOWEL DISEASES, Issue 5 2009Nitsan Maharshak MD Abstract Background: Increased strength of red blood cell (RBC) aggregates are present during the acute inflammatory response and contribute to erythrocyte aggregation and may lead to microvascular dysfunction. Inflammatory bowel diseases (IBDs) are characterized by damage to the bowel wall. This damage may be at least partially attributed to microvascular ischemia caused by enhanced erythrocyte aggregation. The aim of this study was to evaluate the strength of RBC aggregates in the blood of patients with IBD. Methods: The strengths of RBC aggregates were characterized by integrative RBC aggregation parameters, determined by measuring of RBC aggregation as a function of shear stress. The results are represented as the area under the curve (AUC) of aggregate size plotted against shear stress. For each patient, dynamic aggregation and disaggregation of RBC were recorded and analyzed according to the RBC aggregate size distribution at the different shear stresses. Aggregation indices were correlated with disease activity and inflammatory biomarkers. Results: We examined 53 IBD patients and 63 controls. IBD patients had significantly elevated concentrations of inflammation-sensitive proteins and aggregation parameters. The strength of large aggregates, represented by AUC for large fraction aggregates, among patients (15.2 ± 18.6) was double that of controls (7 ± 10.9) (P = 0.006). The strength of large aggregates correlated with disease activity (r = 0.340; P < 0.001) with concentration of fibrinogen (r = 0.575; P < 0.001) and with concentration of high sensitivity C-reactive protein (r = 0.386; P < 0.001). Conclusions: The strength of RBC aggregates is increased in patients with IBD and correlates with the intensity of the acute phase response. This could contribute to bowel damage in these diseases. (Inflamm Bowel Dis 2009) [source] Involvement of the ,3 E749ATSTFTN756 region in stabilizing integrin ,IIb,3 -ligand interactionJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2003P. E. M. H. Litjens Summary., Platelet integrin ,IIb,3 must be activated via intracellular mechanisms before it binds soluble ligands, and it is thought to be activated at its extracellular site by surface-bound ligands. Integrin activation is associated with rearrangement of the cytoskeleton and phosphorylation of proteins that become localized in focal contacts. In these processes, the cytoplasmic tail of the ,-subunit plays a central role. We introduced peptides homologous to the E749ATSTFTN756 domain (E,N peptide) and the T755NITYRGT762 domain (T,T peptide) of ,3 in streptolysin O-permeabilized platelets and analyzed the initial interaction with soluble fibronectin, fibrinogen and PAC-1 after stimulation with thrombin. E,N peptide left the initial binding of fibronectin intact but interfered with stable receptor occupancy. E,N peptide also inhibited fibrinogen binding, thereby reducing the formation of large aggregates. Strikingly, E,N peptide did not disturb the binding of PAC-1, which is known to reflect activation of the integrin. E,N peptide also inhibited tyrosine phosphorylation of focal adhesion kinase, a response known to be dependent on ,IIb,3. T,T peptide did not affect these processes. In a model for outside-in integrin activation, E,N peptide disrupted the binding of CHO cells expressing ,IIb,3 to surface-bound ligand. Again, T,T peptide had no effect. We conclude that the E749ATSTFTN756 region of the ,3 -tail stabilizes the binding of soluble and surface-bound ligand to integrin ,IIb,3 via a mechanism that involves the phosphorylation of FAK. [source] A novel flow cytometric analysis for platelet activation on immobilized von Willebrand factor or fibrillar collagenJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2003S. Kao Summary., Under flow conditions, platelets adhere singly or in small aggregates on von Willebrand factor (VWF)-coated surfaces, but form large aggregates on immobilized fibrillar collagen. We developed a novel flow cytometric analysis to study the mechanisms underlying these distinct platelet deposition patterns. Flow cytometry was used to measure platelet activation after platelet adherence onto microspheres coated with either VWF or collagen fibrils. Two representative indices were calculated to quantify activated GpIIb,IIIa and P-selectin expression on adherent platelets. The signaling pathways responsible for platelet activation after interacting with fibrillar collagen were elucidated using various inhibitors. An in vitro endothelial cell wound model was also used to study the roles of VWF and fibrillar collagen in platelet deposition onto subendothelial matrixes. The adherent platelets on fibrillar collagen express more activated GpIIb,IIIa and P-selectin than those on VWF. Activation of GpIIb,IIIa and expression of P-selectin after platelet interaction with collagen occur via different intracellular signaling pathways; however, Ca2+ released from intracellular pools is common to both phenomena. Platelets were deposited singly or formed small aggregates on the endothelial cell wounded area, and this deposition pattern was dependent on VWF molecules secreted by endothelial cells and the absence of subendothelial collagen fibrils. As less activated GpIIb,IIIa and P-selectin are expressed after platelets interact with immobilized VWF alone, subsequent flowing platelet recruitment is minimal. Collagen fibrils, however, can activate adherent platelets sufficiently to promote the formation of large platelet aggregates. [source] Microwave-Assisted One-Pot Synthesis of Hyperbranched Epoxide-Amine AdductsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2009Julia Theis Abstract Hyperbranched epoxide-amine adducts were synthesized by a one-pot microwave (MW) assisted reaction. 4-(2,3-epoxypropyl-1-oxy)benzonitrile was hydrogenated using Pd/C under microwave conditions, forming the AB2 monomer 1-aminomethyl-4-(2,3-epoxypropyl-1-oxy)benzene. Depending on the reaction temperature this monomer immediately reacts to give hyperbranched epoxide-amine adducts. Mass spectrometric investigations proved the formation of a homologous series of oligomers containing up to six repeating units. Due to the complexing properties of the poly(amino alcohol) moieties in the presence of Cu2+ ions, large aggregates were formed. [source] Gd(III)-EPTPAC16, a new self-assembling potential liver MRI contrast agent: in vitro characterization and in vivo animal imaging studies,NMR IN BIOMEDICINE, Issue 4 2008Suzana Torres Abstract The recently reported amphiphilic chelate, [Gd(EPTPAC16)(H2O)]2,, forms supramolecular aggregates in aqueous solution by self-assembly of the monomers with a relaxometrically determined critical micellar concentration (CMC) of 0.34,mM. The effect of sonication on the aggregate size was characterized by dynamic light scattering and relaxometry, indicating the presence of premicellar aggregates and an overall decrease in aggregate size and polydispersity upon sonication, slightly below the CMC. {[153Sm](EPTPAC16)(H2O)}2, radiotracer was evaluated in vivo from , scintigraphy and biodistribution in Wistar rats. It was found to depend strongly on the sample concentration, below or above the CMC, and its sonication, in a way that correlates with the effect of the same factors on the size of the aggregates formed in solution. Below CMC, the very large aggregates of the [153Sm]3+ -labeled chelate were persistently and mainly taken up by the lungs, and also by the macrophage-rich liver and spleen. Sonication of this solution led to loss of the lung uptake. Above CMC, the metal chelate was mainly taken up by the liver, with very little uptake by the spleen and lungs. In vivo, dynamic contrast-enhanced (DCE)-MRI evaluation of the micellar [Gd(EPTPAC16)(H2O)]2, compound in Wistar rats showed a persistent hepatic positive-contrast effect in T1 -weighted images, qualitatively similar to the clinically established GdIII -based hepatobiliary-selective agents. No enhancement effect was observed in the lungs because of the scarcity of mobile protons in this organ, despite the scintigraphic evidence of significant lung retention of the [153Sm]3+ -labeled chelate at concentrations below the CMC. Copyright © 2007 John Wiley & Sons, Ltd. [source] Effect of Digitonin on the Rhodopsin Meta I-Meta II Equilibrium,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2005Istvan Szundi ABSTRACT Absorbance difference spectra were recorded from 10 ,s to 540 ms after photoexcitation of sonicated suspensions of hypotonically washed bovine rod outer segments with varying amounts of the detergent digitonin added (0 to 2%) at 20°C. Metarhodopsin I480 and metarhodopsin II displayed the expected anomalous pH dependence at pH 6 and 8 (i.e. opposite to that expected from direct protonation of the chromophore Schiff base). However, increasing levels of digitonin eliminated the pH dependence of the equilibrium, and at 2% digitonin the pH 6 and pH 8 data were both similar to the data collected at pH 8 without digitonin. Addition of 0.5% azolectin restored approximately 50% of the anomalous pH dependence at pH 6 in the 2% digitonin sample. The possibility that digitonin induced large-scale aggregation of rhodopsin in the disk membrane that could be reversed by azolectin was tested using time-resolved linear dichroism. Those results showed that even 0.3% digitonin disrupted the membrane, and no large aggregates were detectable under any conditions. Thus, digitonin reduces the activity of a component of the disk membrane required for metarhodopsin II formation, and that deficiency can be compensated for by azolectin. [source] Photoactive Protochlorophyllide Regeneration in Cotyledons and Leaves from Higher Plants,,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2000Benoît Schoefs ABSTRACT Chlorophyll accumulation during greening implies the continuous transformation of photoactive protochlorophyllide (Pchlide) to chlorophyllide. Since this reaction is a light-dependent step, the study of regeneration of photoactive Pchlide under a continuous illumination is difficult. Therefore this process is best studied on etiolated plants during a period of darkness following the initial photoreduction of photoactive Pchlide. In this study, the regeneration process has been studied using spinach cotyledons, as well as barley and bean leaves, illuminated by a single saturating flash. The regeneration was characterized using 77 K fluorescence emission and excitation spectra and high-performance liquid chromatography. The fluorescence data indicated that the same spectral forms of photoactive Pchlide are regenerated by different pathways: (1) photoactive Pchlide regeneration starts immediately after the photoreduction through the formation of a nonphotoactive Pchlide form, emitting fluorescence at approximately 651 nm. This form is similar to the large aggregate of photoactive Pchlide present before the illumination, but it contains oxidized form of nicotinamide adenine dinucleotide phosphate, instead of the reduced form (NADPH), in the ternary complexes; and (2) after the dislocation of the large aggregates of chlorophyllide,light-dependent NADPH:Pchlide a photooxidoreductase,NADPH ternary complexes, the regeneration occurs at the expense of the several nonphotoactive Pchlide spectral forms present before the illumination. [source] Chlorophyll a Self-assembly in Polar Solvent,Water Mixtures ,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000Radka Vladkova ABSTRACT The conversion of chlorophyll a (Chl a) monomers into large aggregates in six polar solvents upon addition of water has been studied by means of absorption, fluorescence spectroscopy and fluorescence lifetime measurements for the purpose of elucidating the various environmental factors promoting Chl a self-assembly and determining the type of its organization. Two empirical solvent parameter scales were used for quantitative characterization of the different solvation properties of the solvents and their mixtures with water. The mole fractions of water f1/2 giving rise to the midpoint values of the relative fluorescence quantum yield were determined for each solvent, and then various solvent,water mixture parameters for the f1/2 values were compared. On the basis of their comparison, it is concluded that the hydrogen-bonding ability and the dipole,dipole interactions (function of the dielectric constant) of the solvent,water mixtures are those that promote Chl a self-assembly. The influence of the different nature of the nonaqueous solvents on the Chl aggregation is manifested by both the different water contents required to induce Chl monomer , aggregate transition and the formation of two types of aggregates at the completion of the transition: species absorbing at 740,760 nm (in methanol, ethanol, acetonitrile, acetone) and at 667,670 nm (in pyridine and tetrahydrofuran). It is concluded that the type of Chl organization depends on the coordination ability and the polarizability (function of the index of refraction) of the organic solvent. The ordering of the solvents with respect to the f1/2 values,methanol < ethanol < acetonitrile < acetone < pyridine < tetrahydrofuran,yielded a typical lyotropic (Hofmeister) series. On the basis of this solvent ordering and the disparate effects of the two groups of solvents on the Chl a aggregate organization, it is pointed out that the mechanism of Chl a self-assembly in aqueous media can be considered a manifestation of the Hofmeister effect, as displayed in the lipid-phase behavior (Koynova et al., Eur. J. Biophys. 25, 261,274, 1997). It relates to the solvent ability to modify the bulk structure and to distribute unevenly between the Chl,water interface and bulk liquid. [source] Polyolefins,biofibre composites: A new way for an industrial productionPOLYMER ENGINEERING & SCIENCE, Issue 4 2007J. Soulestin Low density polyethylene (LDPE) composites based on cellulose fibres have been processed by high shear extrusion with water injection to help dispersion of fibres and release nanofibres from cellulose. Influence of extrusion parameters as shear, residence time, storage conditions of the matrix, and effect of water injection on the morphological properties of the composites have been studied using microscopy. Optimization of the extrusion parameters is necessary to reach a dispersion of the fibres. Increasing shearing forces and residence time allows limiting the presence of large aggregates of cellulose fibres. Use of powdered LDPE, even for short residence time and low shear, is efficient to produce well-dispersed composites. Injection of water during the extrusion also improves the quality of the dispersion. However, no nanofibres are observed. The main effect is a spectacular decrease of the discoloration (yellowing) due to cellulose degradation. Mechanical properties of the composites have been investigated. Young modulus increases with cellulose content and reinforcing effect is more important above 10% by weight. For well-dispersed composites, the extrusion parameters have no significant influence on the stiffness of the composites. However, due to the weakness of the interface, the ductility of composites is reduced compared with LDPE. POLYM. ENG. SCI., 47:467,476, 2007. © 2007 Society of Plastics Engineers. [source] The relationship between synovial lymphocyte aggregates and the clinical response to infliximab in rheumatoid arthritis: A prospective study,,ARTHRITIS & RHEUMATISM, Issue 11 2009Ruth Klaasen Objective Some patients with rheumatoid arthritis (RA) exhibit lymphocyte aggregates in the synovium. This study was undertaken to address whether the presence of lymphocyte aggregates before treatment could serve as a biomarker for the clinical response to tumor necrosis factor (TNF) blockade, and to confirm whether the aggregation of synovial lymphocytes is reversible after anti-TNF treatment. Methods Synovial tissue biopsy samples were obtained from 97 patients with active RA before the initiation of infliximab treatment. Lymphocyte aggregates in the synovial tissue were counted and also graded for size. Logistic regression analysis was performed to identify whether the presence of lymphocyte aggregates could be a predictor of the clinical response at week 16. Furthermore, the effects of TNF blockade on lymphocyte aggregates were compared between patients with RA and patients with psoriatic arthritis (PsA). Results Fifty-seven percent of RA synovial tissue samples contained lymphocyte aggregates, and 32% of the patients had large aggregates. Aggregates were found in 67% of clinical responders compared with 38% of nonresponders. The presence of aggregates at baseline was a highly significant predictor of the clinical response to anti-TNF treatment (R2 = 0.10, P = 0.008). Positivity for lymphocyte aggregates increased the power to predict the clinical response (R2 = 0.29), when analyzed in a prediction model that included baseline disease activity evaluated by the Disease Activity Score in 28 joints, anti,cyclic citrullinated peptide antibody positivity, and synovial TNF, expression. There was a reduction in lymphocyte aggregates after anti-TNF antibody therapy in both RA and PsA. Conclusion RA patients with synovial lymphocyte aggregates have, on average, a better response to infliximab treatment than those with only diffuse leukocyte infiltration. Moreover, the aggregation of synovial lymphocytes is reversible after anti-TNF antibody treatment. [source] Hepatocyte Function in a Radial-flow Bioreactor Using a Perfluorocarbon Oxygen CarrierARTIFICIAL ORGANS, Issue 11 2005Martin J. Nieuwoudt Abstract:, The aims of this study were, first, to indicate the metabolic activity of hepatocytes in a radial-flow polyurethane foam matrix bioreactor relative to monocultures, and second, to evaluate the effect on the hepatocytes of including a synthetic perfluorocarbon (PFC) oxygen carrier to the recirculating medium. The efficient O2 -carrying ability of PFCs may be beneficial to bioreactors employed in stressed cellular environments. Thus, they may also be useful in the treatment of an acute liver failure patient with a bioartificial liver support system (BALSS). Data on the function of three-dimensional (3-D) hepatocyte cultures exposed to emulsified PFCs are lacking. Results: the metabolic functions of the 3-D hepatocyte cultures were improved relative to monocultures. Three-dimensional cultures with and without PFC behaved similarly, and no adverse effects could be detected when PFC was included in the recirculating medium. The addition of PFC significantly improved lidocaine clearance possibly due to the presence of higher O2 tension in the medium. Imaging indicated that large aggregates formed and that seeding had followed flow through the matrix. Simulations indicated first, that the cell numbers used in this study had been insufficient to challenge the bioreactor O2 supply explaining the similarity in performance of the 3-D cultures, and second, that the benefit of adding PFC would be more pronounced at the cell densities likely to be used in a BALSS bioreactor. [source] Self-Association of Bis-Dendritic Organogelators: The Effect of Dendritic Architecture on Multivalent Cooperative InteractionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Myungeun Seo Dr. Abstract A series of bis-dendritic gelators consisting of a benzamide dendron and an alkyl dendron were synthesized to investigate the dendritic effect on self-assembly. The gelators with a first-generation benzamide (benzamide- G1) dendron or a first-generation alkyl (alkyl- G1) dendron formed stable gels in most aromatic solvents, and their self-assembled fibrillar networks were imaged by electron microscopy. The unbranched molecule (G0 - G0) or the molecule possessing a second-generation benzamide (benzamide- G2) dendron did not form gels. Differential scanning calorimetry, powder X-ray diffraction, and Fourier transform IR studies revealed that introduction of a dendritic branch strongly affected the molecular packing as well as the strength of intermolecular interactions. Furthermore, concentration-dependent diffusion coefficient measurements and the evaluation of association constants by 1H NMR spectroscopy indicated that bis-dendritic gelators with a benzamide- G1 dendron possessed high association constants and formed large aggregates, whereas molecules with a single benzamide formed dimers in chloroform. The formation of self-assembled fibrillar networks was driven by the multivalent and cooperative hydrogen bonding observed in the benzamide- G1 dendrons. ,,, stacking of aromatic groups and van der Waals interactions between alkyl chains also played roles in the self-assembly process, thus indicating that a spatial balance between two dendrons is important. [source] | ||||||||||||||||