Tethered bilayer lipid membranes (tBLMs) are designed on mixed self-assembled monolayers (SAMs) of a novel synthetic anchoring thiol, 2,3-di-o-palmitoylglycerol-1-tetraethylene glycol ...mercaptopropanoic acid ester (TEG-DP), and a new short dilution thiol molecule, tetraethylene glycol mercaptopropanoic acid ester (TEG). tBLM formation was accomplished by self-directed fusion of small unilamellar vesicles of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. The influence of the dilution of the anchoring thiol molecule in the SAM on the vesicle fusion process and on the properties of the resulting tBLMs is studied. It is observed by quartz crystal microbalance that vesicle fusion is a one-step process for a pure TEG-DP SAM as well as for mixed SAMs containing a high concentration of the anchoring thiol. However, upon dilution of the anchoring thiol to moderate concentrations, this process is decelerated and possibly follows a pathway different from that observed on a pure TEG-DP SAM. Electrochemical impedance spectroscopy is used to qualitatively correlate the composition of the SAM to the electrical properties of the tBLM. In this paper we also delineate the necessity of a critical concentration of this anchoring TEG-DP thiol as a requisite for inducing the fusion of vesicles to form a tBLM.
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Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) was used to investigate the mucoadhesive properties of nanoparticles decorated with low, medium and high molar mass chitosan (CS). ...Uncoated and chitosan-coated polycaprolactone (PCL) nanoparticles loaded with curcumin were prepared by nanoprecipitation method and characterized in terms of size, surface charge and drug content. The interactions between nanoparticles and mucin layer were monitored after the treatment of SAM-functionalized gold-coated quartz crystals with bovine submaxillary gland mucin (BSM). The results show that all investigated chitosan-coated nanoparticles adsorb onto the BSM layer, and the mass uptake was found to be independent of the chitosan molar mass. Uncoated nanoparticles showed, however, no affinity with BSM layer, confirming that the adsorption of colloidal systems occurs due to their decoration with chitosan. The adhesion is mainly attributed to electrostatic interactions between protonated amino groups of mucoadhesive chitosan and negatively charged groups of mucin. The results suggest that chitosan-coated nanoparticles are promising carriers for hydrophobic drugs delivery in the buccal mucosa.
This paper starts with reviewing the basis of civil and mechanical engineering practices, focusing on the need for engineers to know the maximum effects induced by applied loads, including seismic ...loads. In this context, the response spectrum appeared historically as the most convenient tool for representing the seismic input motion; especially in design standards. Pro and cons of this model are discussed, with an emphasis on industrial facilities, for which two major difficulties appear, for transferring the input motion through the supporting structure towards the equipment and generating realistic input motions when necessary for the analysis of cases with inherent non-linear response. Another option advocated in this paper is that a power spectral density format is used for seismic input motion modelling. Outlines of the approach are presented as well as candidate input motion; its pro and cons are discussed. Compared to the response spectrum, the method simplifies dramatically the generation of compatible time series and the calculation/computation of seismic motion transferred to equipment. It makes easy the calculation of seismically induced fatigue type damage. Calculation of the maximum of the response is less straightforward than with the response spectrum, but the case is resolved by using peak factors.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We have investigated the structure of (3-mercaptopropyl)sulfonate (MPS) monolayer self-assembled onto gold surfaces by quartz crystal microbalance with energy dissipation monitoring (QCM-D) and ...various electrochemical methods. QCM-D experiments show that the MPS monolayer behaves as a thin rigid film with a surfacic mass of 166 ng cm-2. Interfacial capacitance measurements demonstrate that the MPS monolayer is a rather open structure that can be penetrated by the ionic species of the phosphate buffer electrolyte. From MPS reductive desorption experiments, MPS surface concentration corresponds to 4.6 × 10-10 mol cm-2, which represents 60% of the coverage reported for a densely packed thiol monolayer. Despite this low packing density, oxidation of catechol is strongly inhibited leading to voltammograms that are free of diffusional contribution. This unique behavior has been exploited to show that the MPS monolayer covers the entire gold surface with a surface coverage at least equal to θ = 0.9981, which means a very low number of MPS-free pinholes and/or defects. Kinetics of electron transfer toward soluble redox species has been studied using catechol as a neutral hydrophilic probe, but also ferrocyanide as hydrophilic anion and ferrocenemethanol as neutral hydrophobic molecule. It is proposed that the MPS monolayer provides a high kinetic barrier toward permeation of these species and that electron transfer mainly occurs by electron tunneling through the MPS monolayer.
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Surface plasmon resonance (SPR) is a powerful technique for label-free and real-time characterization of molecular interactions at interfaces. However, the detection of small molecules still remains ...a challenge. Here, we report on the direct detection of a low-molecular-weight compound by its receptor presented as a monolayer. Moreover, the signal observed is more than twice the expected mass-weighted response. To establish the origin of the signal enhancement, we present herein a theoretical model that simulates the maximal SPR response by taking into account the aptamer conformational change. We demonstrated that the variation of layer thickness is not the only parameter to be considered. We highlighted that the conformational transition of the aptamer also induces a deviation of the refractive index increment (RII) of the target/aptamer complex from the sum of the RII of individual entities. This nonadditivity of the RII significantly contributes to the magnitude of the signal. We also propose the prediction of the maximal SPR response as a function of the penetration depth, the ratio of the mass-weighted RII of the partners, the sensing layer thickness, and the correction of the complex RII. This model provides new insights into parameters to be considered for the analysis of SPR signals.
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A nanometer scale redox active biomolecular architecture has been successfully synthesized through an efficient chemoselective oxime based coupling between ferrocenyl groups and a regioselectively ...addressable cyclodecapeptide. This molecular tool exhibits electronic, structural, and chemical properties driven by the biomimetic recognition activity of the polypeptide skeleton associated to the well-defined electrochemical activity of metallocenyl probes. Biomolecular materials obtained by confinement of the redox cyclopeptide in self-assembled monolayers on gold surfaces shows efficient through-bond electron transfer from the ferrocenes to the electrode surface via the peptidic backbone, as well as markedly improved sensing properties toward anionic species in organic electrolyte, as compared to those observed in homogeneous solution.
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•Combination of two equivalence criteria: secant stiffness and maximum displacement.•New equivalent damping derived from a systematic numerical analysis.•Key parameter of equivalent damping: ...non-dimensional frequency of oscillator f0fc.•Wide range of considered oscillator stiffness from f0fc = 0.1 to f0fc = 2.•Validation of new equivalent damping with real signals from the database RESORCE.•Ductile range of validation is up to 20.
The Nonlinear Static Procedure, also known in the literature as Pushover Analysis procedure or Capacity Spectrum Method (CSM), is mainly developed in the report of Applied Technology Council entitled “Seismic evaluation and retrofit of concrete buildings” ATC (1996). This is a widely practical engineering method to calculate the seismically induced ductility demand of a System, Structure or Component (SSC) without performing nonlinear transient analyses. Many authors have improved this method by introducing different equivalent linear concepts. However, discrepancy between predictive results by CSM and references obtained by transient nonlinear analyses remains quite important. In this paper, we present a new equivalent linear concept, in which the conventional equivalent frequency corresponding to the secant stiffness is adopted, and new equivalent damping value is calibrated so that the maximum displacement of equivalent linear oscillator is the same as the one of nonlinear oscillator. The new proposed damping values are derived from systematic analysis of the response of a series of nonlinear single degree of freedom (SDOF) oscillators to seismic type input motions. Oscillators have a bilinear elastic–plastic constitutive relationship with a hardening slope equal to 10% or 20% of the initial stiffness. Their natural frequency (f0) is such that f0/fc varies between 0.1 and 2.0, where fc is the central frequency of the input signal and their damping in elastic regime remained at 5%. Input motion is a set of one thousand synthetic filtered white noise signals. The novelty of the proposed approach is that new equivalent damping values exhibit strong frequency dependence on the f0/fc ratio, which has not been discussed so far. In order to validate the proposed equivalent linear concept, predictive results for nonlinear SDOF oscillators undergoing one hundred natural signals are performed by CSM with the new equivalent damping values and compared to reference results obtained from nonlinear transient analyses. It is concluded that the CSM using the new proposed equivalent damping values can determine the seismically induced ductility demand of SDOF oscillators with a better accuracy than methods used at the moment as a routine.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Aptamers have emerged as promising biorecognition elements in the development of biosensors. The present work focuses on the application of quartz crystal microbalance with dissipation monitoring ...(QCM-D) for the enantioselective detection of a low molecular weight target molecule (less than 200 Da) by aptamer-based sensors. While QCM-D is a powerful technique for label-free, real-time characterization and quantification of molecular interactions at interfaces, the detection of small molecules interacting with immobilized receptors still remains a challenge. In the present study, we take advantage of the aptamer conformational changes upon the target binding that induces displacement of water acoustically coupled to the sensing layer. As a consequence, this phenomenon leads to a significant enhancement of the detection signal. The methodology is exemplified with the enantioselective recognition of a low molecular weight model compound, L-tyrosinamide (L-Tym). QCM-D monitoring of L-Tym interaction with the aptamer monolayer leads to an appreciable signal that can be further exploited for analytical purposes or thermodynamics studies. Furthermore, in situ combination of QCM-D with spectroscopic ellipsometry unambiguously demonstrates that the conformational change induces a nanometric decrease of the aptamer monolayer thickness. Since QCM-D is sensitive to the whole mass of the sensing layer including water that is acoustically coupled, a decrease in thickness of the highly hydrated aptamer layer induces a sizable release of water that can be easily detected by QCM-D.
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Nucleic acid aptamers are involved in a broad field of applications ranging from therapeutics to analytics. Deciphering the binding mechanisms between aptamers and small ligands is therefore crucial ...to improve and optimize existing applications and to develop new ones. Particularly interesting is the enantiospecific binding mechanism involving small molecules with nonprestructured aptamers. One archetypal example is the chiral binding between l-tyrosinamide and its 49-mer aptamer for which neither structural nor mechanistic information is available. In the present work, we have taken advantage of a multiple analytical characterization strategy (i.e., using electroanalytical techniques such as kinetic rotating droplet electrochemistry, fluorescence polarization, isothermal titration calorimetry, and quartz crystal microbalance) for interpreting the nature of binding process. Screening of the binding thermodynamics and kinetics with a wide range of aptamer sequences revealed the lack of symmetry between the two ends of the 23-mer minimal binding sequence, showing an unprecedented influence of the 5′ aptamer modification on the bimolecular binding rate constant k on and no significant effect on the dissociation rate constant k off. The results we have obtained lead us to conclude that the enantiospecific binding reaction occurs through an induced-fit mechanism, wherein the ligand promotes a primary nucleation binding step near the 5′-end of the aptamer followed by a directional folding of the aptamer around its target from 5′-end to 3′-end. Functionalization of the 5′-end position by a chemical label, a polydA tail, a protein, or a surface influences the kinetic/thermodynamic constants up to 2 orders of magnitude in the extreme case of a surface immobilized aptamer, while significantly weaker effect is observed for a 3′-end modification. The reason is that steric hindrance must be overcome to nucleate the binding complex in the presence of a modification near the nucleation site.
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