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Dinuclear Azide-Bridged Copper(II) Complex as Building Block for the Assembly of a 2D-Supramolecular Array

ALVES, Wendel A.; SANT`ANA, Antonio C.; ABBOTT, Mariana P.; HOMEM-DE-MELLO, Paula; MARTINHO, Herculano; SANTOS, Regina H. A.; FERREIRA, Janaina G.; TEMPERINI, Marcia L. A.; PADUAN-FILHO, Armando; FERREIRA, Ana Maria da Costa
Fonte: AMER SCIENTIFIC PUBLISHERS Publicador: AMER SCIENTIFIC PUBLISHERS
Tipo: Artigo de Revista Científica
ENG
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A novel Schiff base-copper(II) complex [Cu(2)L(2)(N(3))(2)](ClO(4))(2) 1, where L = (4-imidazolyl)ethylene-2-amino-1-ethylpyridine (apyhist), containing azide-bridges between adjacent copper ions in a dinuclear arrangement was isolated and characterized both in the solid state and in solution by X-ray crystallography and different spectroscopic techniques. Azide binding constants were estimated from titrations of the precursor [CuL(H(2)O)(2)](2+) solutions with sodium azide, giving rise to the azido-bridged species, [Cu(2)L(2)(N(3))(2)](2+). Raman spectra showed asymmetric stretching band at 2060 cm(-1), indicating the presence of azido ligands with a symmetric mu(1,) (1) binding geometry. EPA spectra, in frozen methanol/water solutions at 77 K, exhibited characteristic features of copper centers in tetragonal pyramidal coordination geometry, exhibiting magnetic interactions between them. Further, in solid state, two different values for magnetic coupling in this species were obtained, J/k = -(5.14 +/- 0.02) cm(-1) attributed to the mu(1, 1) azide-bridge mode, and J`z`/k = -(2.94 +/- 0.11) cm(-1) for the interaction between dinuclear moieties via water/perchorate bridges. Finally, an attempt was made to correlate structure and magnetic data for this dinuclear asymmetric end-on azido bridged-copper(II) 1 complex with those of another correlated dinuclear system...

A supramolecular proposal of lignin structure and its relation with the wood properties

Abreu,Heber S.; Latorraca,João V.F.; Pereira,Regina P.W.; Monteiro,Maria Beatriz O.; Abreu,Fábio A.; Amparado,Kelysson F.
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2009 EN
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In spite of the great importance of cellulose the lignin is considered the second most abundant substance of the wood. However, little attention has been given it, mainly to wood properties. The lignin as well as other structural compounds (cellulose and hemicelluloses), has obviously an important role on the wood properties, probably due its composition and existent bonds. In general lignins have β-O-4 (Alkyl Aril Ether) as majoritary bond. This bond in a continued structure form big molecules with spiral conformation as virtual model. Based on this idea, lignins that have high/low β-O-4 content may have differentiated spiraled structures,suggesting different behaviors on the wood properties,which shows that the lignins (Guaicyl:Syringyl (GS)) of angiosperms, for example, which have higher β-O-4 content would present higher spiral conformation than gymnosperms lignins(HG). On the other hand HG lignins have chance of being more anchored on the matrix compound than GS lignins. In this context, the β-O-4 bonds of lignins possibly affect the wood properties, therefore, it is considered relevant for wood technology science discussion.

Increasing the Amphiphilicity of an Amyloidogenic Peptide Changes the β-Sheet Structure in the Fibrils from Antiparallel to Parallel

Gordon, David J.; Balbach, John J.; Tycko, Robert; Meredith, Stephen C.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /01/2004 EN
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Solid-state NMR measurements have been reported for four peptides derived from β-amyloid peptide Aβ(1–42): Aβ(1–40), Aβ(10–35), Aβ(16–22), and Aβ(34–42). Of these, the first two are predicted to be amphiphilic and were reported to form parallel β-sheets, whereas the latter two peptides appear nonamphiphilic and adopt an antiparallel β-sheet organization. These results suggest that amphiphilicity may be significant in determining fibril structure. Here, we demonstrate that acylation of Aβ(16–22) with octanoic acid increases its amphiphilicity and changes the organization of fibrillar β-sheet from antiparallel to parallel. Electron microscopy, Congo Red binding, and one-dimensional 13C NMR measurements demonstrate that octanoyl-Aβ(16–22) forms typical amyloid fibrils. Based on the stability of monolayers at the air-water interface, octanoyl-Aβ(16–22) is more amphiphilic than Aβ(16–22). Measurements of 13C-13C and 15N-13C nuclear magnetic dipole-dipole couplings in isotopically labeled fibril samples, using the constant-time finite-pulse radiofrequency-driven recoupling (fpRFDR-CT) and rotational echo double resonance (REDOR) solid-state NMR techniques, demonstrate that octanoyl-Aβ(16–22) fibrils are composed of parallel β-sheets...

The Structure of Tip Links and Kinocilial Links in Avian Sensory Hair Bundles

Tsuprun, Vladimir; Goodyear, Richard J.; Richardson, Guy P.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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Recent studies have indicated that the tip links and kinocilial links of sensory hair bundles in the inner ear have similar properties and share a common epitope, and that cadherin 23 may also be a component of each link type. Transmission electron microscopy was therefore used to study and compare the fine structure of the tip links and kinocilial links in avian sensory hair bundles. Tannic acid treatment revealed a thin strand, 150–200 nm long and 8–11 nm thick, present in both link types. Fourier analysis of link images showed that the strand of both link types is formed from two filaments coiled in a helix-like arrangement with an axial period of 20–25 nm, with each filament composed of globular structures that are ∼4 nm in diameter. Differences in the radius and period of the helix-like structure may underlie the observed variation in the length of tip and kinocilial links. The similar helix-like structure of the tip links and kinocilial links is in accord with the presence of a common cell-surface antigen (TLA antigen) and similarities in the physical and chemical properties of the two link types. The spacing of the globular structures comprising each filament of the two link types is similar to the 4.3 nm center-to-center spacing reported for the globular cadherin repeat...

Structure of Core Domain of Fibril-Forming PHF/Tau Fragments

Inouye, Hideyo; Sharma, Deepak; Goux, Warren J.; Kirschner, Daniel A.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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Short peptide sequences within the microtubule binding domain of the protein Tau are proposed to be core nucleation sites for formation of amyloid fibrils displaying the paired helical filament (PHF) morphology characteristic of neurofibrillary tangles. To study the structure of these proposed nucleation sites, we analyzed the x-ray diffraction patterns from the assemblies formed by a variety of PHF/tau-related peptide constructs containing the motifs VQIINK (PHF6*) in the second repeat and VQIVYK (PHF6) in the third repeat of tau. Peptides included: tripeptide acetyl-VYK-amide (AcVYK), tetrapeptide acetyl-IVYK-amide (AcPHF4), hexapeptide acetyl-VQIVYK-amide (AcPHF6), and acetyl-GKVQIINKLDLSNVQKDNIKHGSVQIVYKPVDLSKVT-amide (AcTR4). All diffraction patterns showed reflections at spacings of 4.7 Å, 3.8 Å, and ∼8–10 Å, which are characteristic of an orthogonal unit cell of β-sheets having dimensions a = 9.4 Å, b = 6.6 Å, and c = ∼8–10 Å (where a, b, and c are the lattice constants in the H-bonding, chain, and intersheet directions). The sharp 4.7 Å reflections indicate that the β-crystallites are likely to be elongated along the H-bonding direction and in a cross-β conformation. The assembly of the AcTR4 peptide, which contains both the PHF6 and PHF6* motifs...

Secondary Structure and Pd(II) Coordination in S-Layer Proteins from Bacillus sphaericus Studied by Infrared and X-Ray Absorption Spectroscopy

Fahmy, Karim; Merroun, Mohamed; Pollmann, Katrin; Raff, Johannes; Savchuk, Olesya; Hennig, Christoph; Selenska-Pobell, Sonja
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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The S-layer of Bacillus sphaericus strain JG-A12, isolated from a uranium-mining site, exhibits a high metal-binding capacity, indicating that it may provide a protective function by preventing the cellular uptake of heavy metals and radionuclides. This property has allowed the use of this and other S-layers as self-assembling organic templates for the synthesis of nanosized heavy metal cluster arrays. However, little is known about the molecular basis of the metal-protein interactions and their impact on secondary structure. We have studied the secondary structure, protein stability, and Pd(II) coordination in S-layers from the B. sphaericus strains JG-A12 and NCTC 9602 to elucidate the molecular basis of their biological function and of the metal nanocluster growth. Fourier transform infrared spectroscopy reveals similar secondary structures, containing ∼35% β-sheets and little helical structure. pH-induced infrared absorption changes of the side-chain carboxylates evidence a remarkably low pK < 3 in both strains and a structural stabilization when Pd(II) is bound. The COO−-stretching absorptions reveal a predominant Pd(II) coordination by chelation/bridging by Asp and Glu residues. This agrees with XANES and EXAFS data revealing oxygens as coordinating atoms to Pd(II). The additional participation of nitrogen is assigned to side chains rather than to the peptide backbone. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate heavy metal binding to the large number of Asp and Glu in both S-layers at particularly low pH as an adaptation to the environment from which the strain JG-A12 has been isolated. These side chains are thus prime targets for the design of engineered S-layer-based nanoclusters.

A Model Structure for the Heterodimer apoA-IMilano–apoA-II Supports Its Peculiar Susceptibility to Proteolysis

Rocco, Alessandro Guerini; Mollica, Luca; Gianazza, Elisabetta; Calabresi, Laura; Franceschini, Guido; Sirtori, Cesare R.; Eberini, Ivano
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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In this study, we propose a structure for the heterodimer between apolipoprotein A-IMilano and apolipoprotein A-II (apoA-IM–apoA-II) in a synthetic high-density lipoprotein (HDL) containing L-α-palmitoyloleoyl phosphatidylcholine. We applied bioinformatics/computational tools and procedures, such as molecular docking, molecular and essential dynamics, starting from published crystal structures for apolipoprotein A-I and apolipoprotein A-II. Structural and energetic analyses onto the simulated system showed that the molecular dynamics produced a stabilized synthetic HDL. The essential dynamic analysis showed a deviation from the starting belt structure. Our structural results were validated by limited proteolysis experiments on HDL from apoA-IM carriers in comparison with control HDL. The high sensitivity of apoA-IM–apoA-II to proteases was in agreement with the high root mean-square fluctuation values and the reduction in secondary structure content from molecular dynamics data. Circular dichroism on synthetic HDL containing apoA-IM–apoA-II was consistent with the α-helix content computed on the proposed model.

Effect of Calcium Concentration on the Structure of Casein Micelles in Thin Films

Müller-Buschbaum, P.; Gebhardt, R.; Roth, S. V.; Metwalli, E.; Doster, W.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
EN
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The structure of thin casein films prepared with spin-coating is investigated as a function of the calcium concentration. Grazing incidence small-angle x-ray scattering and atomic force microscopy are used to probe the micelle structure. For comparison, the corresponding casein solutions are investigated with dynamic light-scattering experiments. In the thin films with added calcium three types of casein structures, aggregates, micelles, and mini-micelles, are observed in coexistence with atomic force microscopy and grazing incidence small-angle x-ray scattering. With increasing calcium concentration, the size of the aggregates strongly increases, while the size of micelles slightly decreases and the size of the mini-micelles increases. This effect is explained in the framework of the particle-stabilizing properties of the hairy layer of κ-casein surrounding the casein micelles.

Early steps in reovirus infection are associated with dramatic changes in supramolecular structure and protein conformation: analysis of virions and subviral particles by cryoelectron microscopy and image reconstruction

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/09/1993 EN
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Three structural forms of type 1 Lang reovirus (virions, intermediate subviral particles [ISVPs], and cores) have been examined by cryoelectron microscopy (cryoEM) and image reconstruction at 27 to 32-A resolution. Analysis of the three-dimensional maps and known biochemical composition allows determination of capsid protein location, globular shape, stoichiometry, quaternary organization, and interactions with adjacent capsid proteins. Comparisons of the virion, ISVP and core structures and examination of difference maps reveal dramatic changes in supra-molecular structure and protein conformation that are related to the early steps of reovirus infection. The intact virion (approximately 850-A diam) is designed for environmental stability in which the dsRNA genome is protected not only by tight sigma 3-mu 1, lambda 2-sigma 3, and lambda 2-mu 1 interactions in the outer capsid but also by a densely packed core shell formed primarily by lambda 1 and sigma 2. The segmented genome appears to be packed in a liquid crystalline fashion at radii < 240 A. Depending on viral growth conditions, virions undergo cleavage by enteric or endosomal/lysosomal proteases, to generate the activated ISVP (approximately 800-A diam). This transition involves the release of an outer capsid layer spanning radii from 360 to 427 A that is formed by 60 tetrameric and 60 hexameric clusters of ellipsoidal subunits of sigma 3. The vertex- associated cell attachment protein...

Design of 11-Residue Peptides with Unusual Biophysical Properties: Induced Secondary Structure in the Absence of Water☆

Mo, Xiaoqun; Hiromasa, Yasuaki; Warner, Matt; Al-Rawi, Ahlam N.; Iwamoto, Takeo; Rahman, Talat S.; Sun, Xiuzhi; Tomich, John M.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 01/03/2008 EN
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A series of oligopeptides with β-forming and adhesive properties, were synthesized and analyzed for adhesion shear strength, secondary structure, and association properties. The sequences contained related hydrophobic core segments varying in length from 5 to 12 residues and flanked by di- or tri-lysine segments. Three remarkable peptides consisting of just 11 residues with hydrophobic core sequences of FLIVI, IGSII, and IVIGS flanked by three lysine residues gave the highest dry adhesion shear strength and displayed unusual biophysical properties in the presence and absence of water. KKKFLIVIKKK had its highest adhesion strength at 2% (w/v) at pH 12.0 and showed the highest adhesion strength after exposure to water (water resistance). Both KKKIGSIIKKK and KKKIVIGSKKK, at 4% (w/v) at pH 12.0, displayed nearly identical dry shear strength values to that with the FLIVI core sequence. The peptide with IGSII core, however, displayed a lower water resistance and the latter, IVIGS, showed no water resistance, completely delaminating upon soaking in water. These are the smallest peptides with adhesive properties reported to date and show remarkable adhesion strength even at lower concentrations of 0.2% (w/v), which corresponds to 1.6 mM. The FLIVI containing peptide adopted a β-sheet secondary structure in water while the IGSII- and IVIGS-containing sequences folded similarly only in the absence of water. Analytical ultracentrifugation studies showed that when the FLIVI sequence adopts β-structure in aqueous solution...

Rheology and Confocal Reflectance Microscopy as Probes of Mechanical Properties and Structure during Collagen and Collagen/Hyaluronan Self-Assembly

Yang, Ya-li; Kaufman, Laura J.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 18/02/2009 EN
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In this work, the gelation of three-dimensional collagen and collagen/hyaluronan (HA) composites is studied by time sweep rheology and time lapse confocal reflectance microscopy (CRM). To investigate the complementary nature of these techniques, first collagen gel formation is investigated at concentrations of 0.5, 1.0, and 1.5 mg/mL at 37°C and 32°C. The following parameters are used to describe the self-assembly process in all gels: the crossover time (tc), the slope of the growth phase (kg), and the arrest time (ta). The first two measures are determined by rheology, and the third by CRM. A frequency-independent rheological measure of gelation, tg, is also measured at 37°C. However, this quantity cannot be straightforwardly determined for gels formed at 32°C, indicating that percolation theory does not fully capture the dynamics of collagen network formation. The effects of collagen concentration and gelation temperature on kg, tc, and ta as well as on the mechanical properties and structure of these gels both during gelation and at equilibrium are elucidated. Composite collagen/HA gels are also prepared, and their properties are monitored at equilibrium and during gelation at 37°C and 32°C. We show that addition of HA subtly alters mechanical properties and structure of these systems both during the gelation process and at equilibrium. This occurs in a temperature-dependent manner...

The Mineral Phase of Calcified Cartilage: Its Molecular Structure and Interface with the Organic Matrix

Duer, Melinda J.; Friščić, Tomislav; Murray, Rachel C.; Reid, David G.; Wise, Erica R.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 22/04/2009 EN
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We have studied the atomic level structure of mineralized articular cartilage with heteronuclear solid-state NMR, our aims being to identify the inorganic species present at the surfaces of the mineral crystals which may interact with the surrounding organic matrix and to determine which components of the organic matrix are most closely involved with the mineral crystals. One-dimensional 1H and 31P and two-dimensional 1H-31P heteronuclear correlation NMR experiments show that the mineral component is very similar to that in bone with regard to its surface structure. 13C{31P} rotational echo double resonance experiments identify the organic molecules at the mineral surface as glycosaminoglycans, which concurs with our recent finding in bone. There is also evidence of γ-carboxyglutamic acid residues interacting with the mineral. However, other matrix components appear more distant from the mineral compared with bone. This may be due to a larger hydration layer on the mineral crystal surfaces in calcified cartilage.

Conserved and Variable Features of Gag Structure and Arrangement in Immature Retrovirus Particles▿ †

de Marco, Alex; Davey, Norman E.; Ulbrich, Pavel; Phillips, Judith M.; Lux, Vanda; Riches, James D.; Fuzik, Tibor; Ruml, Tomas; Kräusslich, Hans-Georg; Vogt, Volker M.; Briggs, John A. G.
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
EN
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The assembly of retroviruses is driven by oligomerization of the Gag polyprotein. We have used cryo-electron tomography together with subtomogram averaging to describe the three-dimensional structure of in vitro-assembled Gag particles from human immunodeficiency virus, Mason-Pfizer monkey virus, and Rous sarcoma virus. These represent three different retroviral genera: the lentiviruses, betaretroviruses and alpharetroviruses. Comparison of the three structures reveals the features of the supramolecular organization of Gag that are conserved between genera and therefore reflect general principles of Gag-Gag interactions and the features that are specific to certain genera. All three Gag proteins assemble to form approximately spherical hexameric lattices with irregular defects. In all three genera, the N-terminal domain of CA is arranged in hexameric rings around large holes. Where the rings meet, 2-fold densities, assigned to the C-terminal domain of CA, extend between adjacent rings, and link together at the 6-fold symmetry axis with a density, which extends toward the center of the particle into the nucleic acid layer. Although this general arrangement is conserved, differences can be seen throughout the CA and spacer peptide regions. These differences can be related to sequence differences among the genera. We conclude that the arrangement of the structural domains of CA is well conserved across genera...

Blending Gelators to Tune Gel Structure and Probe Anion-Induced Disassembly

Foster, Jonathan A; Edkins, Robert M; Cameron, Gary J; Colgin, Neil; Fucke, Katharina; Ridgeway, Sam; Crawford, Andrew G; Marder, Todd B; Beeby, Andrew; Cobb, Steven L; Steed, Jonathan W
Fonte: Wiley-VCH Verlag GmbH & Co Publicador: Wiley-VCH Verlag GmbH & Co
Tipo: Artigo de Revista Científica
EN
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Blending different low molecular weight gelators (LMWGs) provides a convenient route to tune the properties of a gel and incorporate functionalities such as fluorescence. Blending a series of gelators having a common bis-urea motif, and functionalised with different amino acid-derived end-groups and differing length alkylene spacers is reported. Fluorescent gelators incorporating 1-and 2-pyrenyl moieties provide a probe of the mixed systems alongside structural and morphological data from powder diffraction and electron microscopy. Characterisation of the individual gelators reveals that although the expected α-urea tape motif is preserved, there is considerable variation in the gelation properties, molecular packing, fibre morphology and rheological behaviour. Mixing of the gelators revealed examples in which: 1) the gels formed separate, orthogonal networks maintaining their own packing and morphology, 2) the gels blended together into a single network, either adopting the packing and morphology of one gelator, or 3) a new structure not seen for either of the gelators individually was created. The strong binding of the urea functionalities to anions was exploited as a means of breaking down the gel structure, and the use of fluorescent gel blends provides new insights into anion-mediated gel dissolution.

Internal Structure of Layer-by-Layer Adsorbed Polyelectrolyte Films: A Neutron and X-Ray Reflectivity Study

Schmitt, Johannes; Gruenewald, Torsten; Decher, Gero; Pershan, Peter S.; Kjaer, Kristian; Loesche, Mathias
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
EN_US
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The internal structure of ultrathin polymer films physisorbed to surface-modified Si wafers by electrostatic deposition of polyelectrolytes from aqueous solutions has been investigated by measuring the X-ray and neutron reflectivity from partially deuterated samples. For the first time it has been demonstrated that the preparation procedure, which involves repeated dipping of the substrate into solutions of polycations and polyanions in an alternating sequence, leads to the deposition of continuous molecular layers that form a polymer fii with a well-defined supramolecular structure. Thus, the structure of a polymer film deposited from solutions with high ionic strength (2 M NaCl) and comprising 48 molecular strata, which were organized in a superlattice of 5 perprotonated layers and 1 perdeuterated layer in 8 repeat units, has been resolved in full detail: the overall layer thickness was found to be 1205 (pm) 20 Å, the layers deposited close to the substrate had a thickness significantly smaller than their equilibrium thickness far from the substrate, and the equilibrium thickness of an individual polycation layer was (sim)20 Å and that of the polyanion layer (sim)35 Å. The surface roughnesses at the substratelfilm and the film/air interface were significantly different...

Fluorescence Characteristics of Size-Fractionated Dissolved Organic Matter: Implications for a Molecular Assembly Based Structure?

Romera-Castillo, Cristina; Chen, Meilian; Yamashita, Youhei; Jaffe´, Rudolf
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
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Surface freshwater samples from Everglades National Park, Florida, were used to investigate the size distributions of natural dissolved organic matter (DOM) and associated fluorescence characteristics along the molecular weight continuum. Samples were fractionated using size exclusion chromatography (SEC) and characterized by spectroscopic means, in particular Excitation-Emission Matrix fluorescence modeled with parallel factor analysis (EEM-PARAFAC). Most of the eight components obtained from PARAFAC modeling were broadly distributed across the DOM molecular weight range, and the optical properties of the eight size fractions for all samples studied were quite consistent among each other. Humic-like components presented a similar distribution in all the samples, with enrichment in the middle molecular weight range. Some variability in the relative distribution of the different humic-like components was observed among the different size fractions and among samples. The protein like fluorescence, although also generally present in all fractions, was more variable but generally enriched in the highest and lowest molecular weight fractions. These observations are in agreement with the hypothesis of a supramolecular structure for DOM, and suggest that DOM fluorescence characteristics may be controlled by molecular assemblies with similar optical properties...

Fluorescence Characteristics of Size-Fractionated Dissolved Organic Matter: Implications for a Molecular Assembly Based Structure?

Romero-Castillo, Cristina; Chen, Meilian; Yamashita, Youhei; Jaffe´, Rudolf
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
359.25152%
Surface freshwater samples from Everglades National Park, Florida, were used to investigate the size distributions of natural dissolved organic matter (DOM) and associated fluorescence characteristics along the molecular weight continuum. Samples were fractionated using size exclusion chromatography (SEC) and characterized by spectroscopic means, in particular Excitation-Emission Matrix fluorescence modeled with parallel factor analysis (EEM-PARAFAC). Most of the eight components obtained from PARAFAC modeling were broadly distributed across the DOM molecular weight range, and the optical properties of the eight size fractions for all samples studied were quite consistent among each other. Humic-like components presented a similar distribution in all the samples, with enrichment in the middle molecular weight range. Some variability in the relative distribution of the different humic-like components was observed among the different size fractions and among samples. The protein like fluorescence, although also generally present in all fractions, was more variable but generally enriched in the highest and lowest molecular weight fractions. These observations are in agreement with the hypothesis of a supramolecular structure for DOM, and suggest that DOM fluorescence characteristics may be controlled by molecular assemblies with similar optical properties...

Synthesis, Structure, and Host-Guest Investigations on Self-Assembled Nonwater-Soluble and Water-Soluble Multiple Bridged Platinacyclophanes; Synthese, Struktur und Wirt-Gast-Untersuchungen an selbstorganisierten, wasserlöslichen und wasserunlöslichen mehrfach verbrückten Platinacyclophanen

Khanfar, Monther Abdel Jabbar Fares
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
DE_DE
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The synthesis of the 1,3,5-tris[(diphenylphosphoryl)alkyl]benzenes 7 - 10 succeeds by reaction of the corresponding 1,3,5-tris(bromoalkyl)benzenes 3 - 6 with ethyl diphenylphosphinite in an Arbusov-type reaction. Reduction of these phosphine oxides leads to the trifunctional phosphine ligands 11 - 14. Their potency of self-assembly was examined by the employment of platinum(II) complex fragments. A five-component self-assembly consisting of three equivalents of the platinum complex PtCl2(PhCN)2 and two equivalents of the ligands 11 - 14 under high dilution conditions led to the formation of the triplatinacyclophanes 1 and 15 - 17. In contrast to the reaction between 11 - 13 and PtCl2(PhCN)2 in which polymers were formed as by-products, in the case of 14 three other platinacyles 18 - 20 with a chain-like structure were formed. Trifunctional primary phosphines of the type 1,3,5-[PH2(CH2)n]3C6H3 (26 - 28) were obtained via an Arbusov reaction between the 1,3,5-tris(bromoalkyl)benzenes 3 - 6 and P(OEt)3 followed by a reaction of the trisphosphonates 1,3,5-[(EtO)2P(O)(CH2)n]3C6H3 (21 - 24) with LiAlH4. A straightforward conversion of these sensitive key phosphines 26 - 28 to the corresponding water-soluble ligands 1,3,5-tris-[bis(hydroxymethyl)phosphinylalkyl]benzenes 29 - 31 and 1...

Structure of Functional Staphylococcus aureus α-Hemolysin Channels in Tethered Bilayer Lipid Membranes

McGillivray, Duncan J.; Valincius, Gintaras; Heinrich, Frank; Robertson, Joseph W.F.; Vanderah, David J.; Febo-Ayala, Wilma; Ignatjev, Ilja; Lösche, Mathias; Kasianowicz, John J.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 18/02/2009 EN
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We demonstrate a method for simultaneous structure and function determination of integral membrane proteins. Electrical impedance spectroscopy shows that Staphylococcus aureus α-hemolysin channels in membranes tethered to gold have the same properties as those formed in free-standing bilayer lipid membranes. Neutron reflectometry provides high-resolution structural information on the interaction between the channel and the disordered membrane, validating predictions based on the channel's x-ray crystal structure. The robust nature of the membrane enabled the precise localization of the protein within 1.1 Å. The channel's extramembranous cap domain affects the lipid headgroup region and the alkyl chains in the outer membrane leaflet and significantly dehydrates the headgroups. The results suggest that this technique could be used to elucidate molecular details of the association of other proteins with membranes and may provide structural information on domain organization and stimuli-responsive reorganization for transmembrane proteins in membrane mimics.

Supramolecular Structure and Nuclear targeting efficiency Determine the Enhancement of Transfection by Modified Polylysines

Chan, Chee Kai; Senden, Timothy; Jans, David A
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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Polylysine (ply) has been used as a DNA carrier in nonviral gene delivery systems because it forms complexes with plasmid DNA via charge interaction, and condenses it into a compact structure. We have recently shown that cross-linking nuclear localization sequences (NLSs) to ply can enhance transfection by conferring specific recognition by the cellular nuclear import 'receptor', the NLS-binding importin α/β heterodimer. The present study examines and correlates for the first time the effect of the lysine/nucleotide (Ly/Nu) ratio on transfection, recognition by importin α/β, and structure as determined using electron microscopy (EM) and atomic force microscopy (AFM), for ply-DNA complexes with and without NLSs or mutant versions thereof. Intriguingly, we observed two distinct peaks of transfection enhancement at Ly/Nu ratios of 0.4 and 4.0, attributable to specific NLS recognition by importins and DNA compaction, respectively. The results indicate a clear correlation between the ply-DNA structure, importin α/β recognition, and gene transfer efficiency, thus underlining the importance of using ply-DNA at the optimal Ly/Nu ratio.