1,346 research outputs found
Vibrational nonequilibrium effects in the conductance of single-molecules with multiple electronic states
Vibrational nonequilibrium effects in charge transport through
single-molecule junctions are investigated. Focusing on molecular bridges with
multiple electronic states, it is shown that electronic-vibrational coupling
triggers a variety of vibronic emission and absorption processes, which
influence the conductance properties and mechanical stability of
single-molecule junctions profoundly. Employing a master equation and a
nonequilibrium Green's function approach, these processes are analyzed in
detail for a generic model of a molecular junction and for
benzenedibutanethiolate bound to gold electrodes.Comment: 5 pages, 4 figure
Two decades of studying non-covalent biomolecular assemblies by means of electrospray ionization mass spectrometry
Mass spectrometry (MS) is a recognized approach for characterizing proteins and the complexes they assemble into. This application of a long-established physico-chemical tool to the frontiers of structural biology has stemmed from experiments performed in the early 1990s. While initial studies focused on the elucidation of stoichiometry by means of simple mass determination, developments in MS technology and methodology now allow researchers to address questions of shape, inter-subunit connectivity and protein dynamics. Here, we chart the remarkable rise of MS and its application to biomolecular complexes over the last two decades
Analysing protein competition on self-assembled mono-layers studied with quartz crystal microbalance
The mechanisms by which proteins adsorb to surfaces of biomaterials have long been of interest. The
present work started with the premise that small/hard and large/soft proteins will yield different sets
of normalized frequency shift and dissipation signals when studied with a quartz crystal microbalance.
The aim was to evaluate the usefulness of these raw data to study protein competition using protein incubations
in sequence and from mixtures of albumin (BSA) and gamma-globulin (BGG) at various ratios.
Increasing the concentration of BSA decreases the adsorption of subsequently incubated BGG. For BSA/
BGG mixtures the dissipation is similar for all logarithmic molar ratios BGG/BSA below 1 but soon
decreases when the molar ratio of BSA/BGG (and opposite for the normalized frequency shift) is above
1, indicating preferential binding of BGG. Modelling indicated that differences in the film shear modulus
and viscosity depend more on the properties of the self-assembling mono-layers (SAMs) than on the proteins.
Films high in BSA tentatively differ in film shear modulus and viscosity from that of films high in
BGG but only on the hydrophobic surfaces. The results were encouraging as the raw data were deemed to
be able to point at protein adsorption competition.The authors thank the Portuguese National Science and Technology Foundation (FCT) for the Project Grants PTDC/FIS/68517/2006 and PTDC/FIS/68209/2006, and personal Grant BPD/39331/2007 for J.B
Fluorescence probe techniques to monitor protein adsorption-induced conformation changes on biodegradable polymers
The study of protein adsorption and any associated conformational changes on interaction with biomaterials is of great importance in the area of implants and tissue constructs. This study aimed to evaluate some fluorescent techniques to probe protein conformation on a selection of biodegradable polymers currently under investigation for biomedical applications. Because of the fluorescence emanating from the polymers, the use of monitoring intrinsic protein fluorescence was precluded. A highly solvatochromic fluorescent dye, Nile red, and a well-known protein label, fluorescein isothiocyanate, were employed to study the adsorption of serum albumin to polycaprolactone and to some extent also to two starch-containing polymer blends (SPCL and SEVA-C). A variety of fluorescence techniques, steady state, time resolved, and imaging were employed. Nile red was found to leach from the protein, while fluorescein isothiocyanate proved useful in elucidating a conformational change in the protein and the observation of protein aggregates adsorbed to the polymer surface. These effects were seen by making use of the phenomenon of energy migration between the fluorescent tags to monitor interprobe distance and the use of fluorescence lifetime imaging to ascertain the surface packing of the protein on polymer
Morphology and miscibility of chitosan/soy protein blended membranes
A physico-chemical characterization of blended membranes composed by chitosan and soy protein has been carried out in order to
probe the interactions that allow membranes to be formed from these biopolymer mixtures. These membranes are developed aiming at
applications in wound healing and skin tissue engineering scaffolding. The structural features of chitosan/soy blended membranes were
investigated by means of solid state carbon nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), contact angle, and atomic
force microscopy. FTIR investigations suggested that chitosan and soy may have participated in a specific intermolecular interaction.
The proton spin–lattice relaxation experiments in the rotating frame on blended membranes indicated that independently of the preparation
conditions, the blend components are not completely miscible possibly due to a weak polymer–protein interaction. It was also
shown that the blended systems showed a rougher surface morphology which was dependent of soy content in the blend system
Hybrid biodegradable membranes of silane-treated chitosan/soy protein for biomedical applications
In recent years, progress in the field of hybrid materials has been accelerated through use of the sol–gel process for creating materials and devices, which benefit from the incorporation of both inorganic and organic components. In this work, organic–inorganic hybrid membranes were prepared from tetraethoxysilane and a blend system composed of chitosan and soy protein. By introducing a small amount of siloxane bond into the chitosan/soy protein system, the chitosan/soy protein hybrid membranes were improved in terms of structure, topography and mechanical properties. It appears that the chitosan/soy protein hybrid membranes were formed by discrete inorganic moieties entrapped in the chitosan/soy protein blend, which improved the stability and mechanical performance assessed by the dynamic mechanical analysis as compared to chitosan/soy protein membrane. Also, in vitro cell culture studies evidenced that the chitosan/soy protein hybrid membranes are non-cytotoxic over a mouse fibroblast-like cell line. The hybrid membranes of silane-treated chitosan/soy protein developed in this work have potential in biomedical applications, including tissue engineering.This work was financially supported by the Portuguese Foundation for Science and Technology - FCT (Grant SFRH/BPD/45307/2008, SFRH/BPD/21786/2009, SFRH/BPD/39331/2007 and SFRH/BD/64601/2009), 'Fundo Social Europeu' - FSE and 'Programa Diferencial de Potencial Humano - POPH' and was partially supported by the FEDER through POCTEP 0330_IBEROMARE_1_P
Application of fluorescence techniques to the study of protein adsorption and packing on biomaterial surfaces
[Excerpt] The ways proteins compete for the surface of biomaterials and
change conformation are believed to be important for the host response
to implants. It is possible to elucidate information on
packing and any induced conformational change by making use of
different fluorescence techniques on fluorescently labelled proteins.
Employing probe-probe resonance energy transfer (RET) allows
inter and intra protein interactions to be distinguished. Homo resonance
energy transfer (hRET) avoids many problems with having
two different probes and means that labelling and subsequent purification
can be done in one step. [...]Portuguese Foundation for Science and
Technology, project PROTEOLIGHT (PTDC/FIS/68517/2006)
and J.B. grant SFRH/BPD/17584/2004. European Union NoE
EXPERTISSUES (NMP3-CT-2004-500283) and European Union
FP6 STREP project HIPPOCRATES (NMP3-CT-2003-505758).info:eu-repo/semantics/publishedVersio
Unraveling the molecular basis of subunit specificity in P pilus assembly by mass spectrometry
P pili are multisubunit fibers essential for the attachment of uropathogenic Escherichia coli to the kidney. These fibers are formed by the noncovalent assembly of six different homologous subunit types in an array that is strictly defined in terms of both the number and order of each subunit type. Assembly occurs through a mechanism termed “donor-strand exchange (DSE)” in which an N-terminal extension (Nte) of one subunit donates a β-strand to an adjacent subunit, completing its Ig fold. Despite structural determination of the different subunits, the mechanism determining specificity of subunit ordering in pilus assembly remained unclear. Here, we have used noncovalent mass spectrometry to monitor DSE between all 30 possible pairs of P pilus subunits and their Ntes. We demonstrate a striking correlation between the natural order of subunits in pili and their ability to undergo DSE in vitro. The results reveal insights into the molecular mechanism by which subunit ordering during the assembly of this complex is achieved
Redesign of the Jefferson Lab -300 kV DC Photo-Gun for High Bunch Charge Operations
Production of high bunch charge beams for the ElectronIon Collider (EIC) is a challenging task. High bunch charge (a few nC) electron beam studies at Jefferson Lab using an inverted insulator DC high voltage photo-gun showed evidence of space charge limitations starting at 0.3 nC, limiting the maximum delivered bunch charge to 0.7 nC for beam at -225 kV, 75 ps (FWHM) pulse width, and 1.64 mm (rms) laser spot size. The low extracted charge is due to the modest longitudinal electric field (Ez) at the photocathode leading to beam loss at the anode and downstream beam pipe. To reach the few nC high bunch charge goal, and to correct the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun the existing photo-gun was modified. This contribution discusses the electrostatic design of the modified photo-gun obtained using CST Studio Suite’s electromagnetic field solver. Beam dynamics simulations performed using General Particle Tracer (GPT) with the resulting electrostatic field map obtained from the modified electrodes confirmed the validity of the new design
Surface engineered carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles for intracellular targeting
Novel highly branched biodegradable macromolecular systems have been developed by grafting carboxymethylchitosan
(CMCht) onto low generation poly(amidoamine) (PAMAM) dendrimers. Such structures organize into sphere-like nanoparticles
that are proposed to be used as carriers to deliver bioactive molecules aimed at controlling the behavior of stem cells,
namely their proliferation and differentiation. The nanoparticles did not exhibit significant cytotoxicity in the range of
concentrations below 1 mg mL"1, and fluorescent probe labeled nanoparticles were found to be internalized with highly
efficiency by both human osteoblast-like cells and rat bone marrow stromal cells, under fluorescence-activated cell sorting and
fluorescence microscopy analyses. Dexamethasone (Dex) has been incorporated into CMCht/PAMAM dendrimer nanoparticles
and release rates were determined by high performance liquid chromatography. Moreover, the biochemical data demonstrates
that the Dex-loaded CMCht/PAMAM dendrimer nanoparticles promote the osteogenic differentiation of rat bone marrow
stromal cells, in vitro. The nanoparticles exhibit interesting physicochemical and biological properties and have great potential to
be used in fundamental cell biology studies as well as in a variety of biomedical applications, including tissue engineering and
regenerative medicine
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