Measurements of single-molecule electromechanical properties

The electromechanical properties of a single molecule covalently attached to two gold electrodes are studied by simultaneously measuring the conductance and the force during the stretching of the molecule. The conductance, the spring constant of the molecular junction, and the dependence of the conductance on the stretching force are determined. Like the conductance, the spring constant of a molecule depends also on the molecule-electrode contacts. The forces required to break the molecule-gold contacts are 1.5 nN for alkanedithiols and 0.8 nN for 4,4' bipyridine, indicating that the breakdowns take place at the Au-Au bond and at the N-Au bond, respectively.     

Molecularly imprinted macroporous monolithic materials for protein recognition

Synthetic materials that can specifically recognize proteins will find wide application in many fields.In this report,bovine serum albumin was chosen as the template protein.Acrylamide and N,N’-methylenebisacrylamide were employed as the functional and cross-linker monomers,respectively.Molecularly imprinted macroporous monolithic materials that can preferentially bind the template protein in an aqueous environment were prepared by combination of molecular imprinting technique and freezing/thawing preparation method.The resulted imprinted macroporous monolithic columns were evaluated by utilizing as stationary phase in high performance liquid chromatography and solid-phase extraction materials.The experimental results indicated that the imprinted macroporous monolithic column exhibited good recognition for template protein,as compared with the control protein(hemoglobin),whereas the non-imprinted polymer(prepared under the same conditions except without addition template protein) had no selective properties.     

The analysis of time resolved protein fluorescence in multi-tryptophan proteins

In the last decades, considerable progress has been made in the analysis of the fluorescence decay of proteins with more than one tryptophan. The construction of single tryptophan containing proteins has shown that the lifetimes of the wild type proteins are often the linear combinations of the family lifetimes of the contributing tryptophan residues. Additivity is not followed when energy transfer takes place among tryptophan residues or when the structure of the remaining protein is altered upon the modification. Progress has also been made in the interpretation of the value of the lifetime and the linkage with the immediate environment. Probably all the irreversible processes leading to return to the ground state have been catalogued and their rate constants are documented. Also, the process of electron transfer to the peptide carbonyl is becoming more and more documented and is linked to the rotameric state of tryptophan. Reversible excited state processes are also being considered, including reversible interconversions between rotamers. Interesting information about tryptophan and its environment comes also from anisotropy measurements for proteins in the native, the denatured and the molten globule states. Alterations of protein fluorescence due to the effects of ligand binding or side chain modifications can be analyzed via the ratio of the quantum yields of the modified protein and the reference state. Using the ratio of quantum yields and the (amplitude weighted) average lifetime, three factors can be identified: (1) a change in the apparent radiative rate constant reflecting either static quenching or an intrinsic change in the radiative properties; (2) a change in dynamic quenching; and (3) a change in the balance of the populations of the microstates or local static quenching.     

Role of electromechanical and mechanoelectric effects in protein hydration under hydrostatic pressure

Recent measurements of lysozyme hydration water density under non-denaturing pressure show that it is higher than that of bulk water in the same conditions. High protein hydration layer density has earlier been observed at ambient conditions and ascribed to electrostriction. We calculate the pressure-induced protein mean surface charge density increment Δσ. Within the hydration layer, the higher fields due to Δσ lead to an additional water compression via electrostriction. The increment Δσ is considered as due to a mechanoelectric effect in protein molecules. The mean value of the effective mechanoelectric coefficient d is calculated and compared with piezoelectric coefficients of amino acids and their compounds.     

Photophysical properties of DASPMI as revealed by spectrally resolved fluorescence decays

Photophysical properties of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) in various solvents were investigated using time- and space-correlated single photon counting. DASPMI is known to selectively stain mitochondria in living cells.1,2 The uptake and fluorescence intensity of DASPMI in mitochondria is a dynamic measure of membrane potential. Hence, an endeavor has been made to elucidate the mechanism of DASPMI fluorescence by obtaining spectrally resolved fluorescence decays in different solvents. A biexponential decay model was sufficient to globally describe the wavelength-dependent fluorescence in ethanol and chloroform. While in glycerol, a three-exponential decay model was necessary for global analysis. In the polar low-viscous solvent water, a monoexponential decay model fitted the decay data. The sensitivity of DASPMI to solvent viscosity was analyzed using various proportions of glycerol-ethanol mixtures. The lifetimes were found to increase with increasing solvent viscosity. The negative amplitudes of the short lifetime component found in chloroform and glycerol at the longer wavelengths validated the formation of new excited-state species from the initially excited state. Time-resolved emission spectra in chloroform and glycerol showed a biphasic increase of spectral width and emission maxima. The spectral width had an initial fast increase within 150 ps and a near constant thereafter. A three-state model of generalized scheme, on the basis of successive formation of locally excited state (LE), intramolecular charge transfer state (ICT), and twisted intramolecular charge transfer (TICT) state, has been proposed to explain the excited-state kinetics. The presumed role of solvation dynamics of ICT and TICT states leading to the asymmetrical broadening and structureless fluorescence has been substantiated by the decomposition of time-resolved emission spectra in chloroform, glycerol, and ethanol/glycerol mixtures.     

分子印迹技术

分子印迹是国外近几十年才发展起来的一种新的研究方法,它主要是利用所合成的印迹高分子内含有的特殊结构对所使用的印迹分子的高选择性来进行各方面研究。目前,在手性分离,催化,传感器方面分子印迹的研究已取得了突破性进展。     

The effect of dye sorption on electromechanical properties in sodium poly(L-glutamate)

Piezoelectric constant, Young's elastic modulus, and dielectric constant of undyed and dyed films of poly(L -glutamate) were measured at 10 H_z over the temperature range ?120 to 120°C. The temperature of the maximum in ?d″₁₄ shifts toward higher temperature up to 0.6 mg/g polymer of dye uptake and then shifts toward lower temperature by further dye sorption. The variation of the piezoelectric modulus was interpreted by the change of mobility of impurity ions in the sample.     

Proton diffusion reaction in a protein polyelectrolyte membrane and the kinetics of electromechanical forces

A theoretical model is developed for proton transport in a charged, protein polyelectrolyte membrane. Protons bind to fixed charge groups of the membrane. This binding process also modulates electromechanical tensile forces in the membrane, due to the change in the electrostatic interactions between the charged membrane molecules. We used this force as an experimental measure of the space—time evolution of proton transport inside the membrane. A step change in the bath pH produced a measurable change in the isometric tensile force of the membrane. H⁺ ion transport was modelled by a diffusion reaction theory. The kinetics of the measured force were compared to the H⁺ diffusion reaction dynamics predicted by the theory. Experimental and theoretical time constants were in good agreement for reasonable values of the H⁺ diffusivity, the equilibrium dissociation reaction constant and the number of available binding sites. This suggests that the diffusion reaction of H⁺ into the membrane is rate-limiting in force generation. Other nonequilibrium processes, including molecular reconformation and osmotic swelling, must be proceeding at least as rapidly as H⁺ transport. The combination of theory and experiment provides a useful, non-destructive technique for characterizing the kinetics of binding, and other transport processes, in charged polymers and in certain biological tissues.     

Molecularly imprinted hydrogel displaying reduced non‐specific binding and improved protein recognition

A novel approach for enhancing protein recognition in molecularly imprinted hydrogel (MIH) is presented. This approach was developed based on the hypothesis that the number of specific binding sites created in the previously described MIH is very small, thus attempts to enhance the capacity result in most cases in additional non‐specific binding and loss of selectivity. Thus, blocking the non‐specific binding sites could lead to higher capacities and better selectivity. To test this hypothesis, MIH interpenetrating networks designed to block non‐specific binding sites were synthesized using two separate stages of polymerization. Re‐binding of the template protein (lysozyme) and a competitor protein (cytochrome C) was measured, and the results were compared with the similar experiment performed using a control non‐imprinted hydrogel and a “conventional” MIH. The imprinting efficacy of the MIH interpenetrating network was found to be much higher than that of the controls. Furthermore, competitive adsorption assays have demonstrated the superiority of the new formulation.     

Electron capture dissociation of electrosprayed protein ions for spatially resolved hydrogen exchange measurements

Mass spectrometry (MS) methods involving gas-phase fragmentation hold considerable promise for analyzing regioselective deuteration patterns of proteins following solution-phase amide hydrogen exchange (HX). However, the general viability of such an approach is questionable due to the possible occurrence of intramolecular hydrogen migration ("scrambling"), which tends to randomize or distort the spatial isotope distribution. Rand et al. (J. Am. Chem. Soc. 2008, 130, 1341-1349) have recently reported the application of electron capture dissociation (ECD) for measuring deuteration patterns of short peptides with very little scrambling by FT-MS. The current work shows that even much larger systems such as the 76-residue protein ubiquitin can be successfully analyzed by ECD following solution-phase HX. The resulting c and z. ion deuteration levels are in remarkable agreement with previous NMR data, demonstrating that the extent of scrambling and/or other gas-phase artifacts is negligible. These results open the door to future experiments on the folding, structure, and dynamics of proteins by HX/ECD-FT-MS.     

Molecularly Imprinted Electrochemical Sensors

In this review, the applications of molecularly imprinted polymer (MIP) materials in the area of electrochemical sensors have been explored. The designs of the MIPs containing different polymers, their preparation and their immobilization on the transducer surface have been discussed. Further, the employment of various transducers containing the MIPs based on different electrochemical techniques for determining analytes has been assessed. In addition, the general protocols for getting the electrochemical signal based on the binding ability of analyte with the MIPs have been given. The review ends with describing scope and limitations of the above electrochemical based MIP sensors.     

Molecularly imprinted polymer grafted on polysaccharide microsphere surface by the sol-gel process for protein recognition

An interfacial organic–inorganic hybridization concept was applied to the preparation of a new spherical imprinted material for protein recognition. The functional biopolymer chitosan (CS), shaped as microsphere and high-density cross-linked, constituted of the polysaccharide core for surface imprinting. After the model template protein, bovine serum albumin, was covalently immobilized by forming imine bonds with the functional amine groups of CS, two kinds of organic siloxane (3-aminopropyltrimethoxysiloxane: APTMS, and tetraethoxysiloxane: TEOS) assembled and polymerized on the polysaccharide–protein surface via sol–gel process in aqueous solution at room temperature. After template removal, the protein-imprinted sol–gel surface exhibited a prevalent preference for the template protein in adsorption experiments, as compared with four contrastive proteins. Bioinformatics methods were also employed to investigate the imprinting process and the recognition effect. The influence of siloxane type, pH, siloxane/water ratio on template removal and recognition selectivity was assessed. Under optimized imprinting conditions, a large quantity of well-distributed pores was observed on the immobilized-template imprinted surface. The surface-imprinted adsorbent offered a fast kinetics for template re-adsorption and could be reused. Compared with the imprinted material prepared with free-template, material prepared with immobilized-template possessed higher adsorption capacity towards template protein. Easy preparation of the described imprinted material, high affinity and good reusability make this approach attractive and broadly applicable in biotechnology for down-stream processing and biosensor.     

Molecularly Regulated Reversible DNA Polymerization

Natural polymers are synthesized and decomposed under physiological conditions. However, it is challenging to develop synthetic polymers whose formation and reversibility can be both controlled under physiological conditions. Here we show that both linear and branched DNA polymers can be synthesized via molecular hybridization in aqueous solutions, on the particle surface, and in the extracellular matrix (ECM) without the involvement of any harsh conditions. More importantly, these polymers can be effectively reversed to dissociate under the control of molecular triggers. Since nucleic acids can be conjugated with various molecules or materials, we anticipate that molecularly regulated reversible DNA polymerization holds potential for broad biological and biomedical applications.     

Molecularly imprinted polymer sensor arrays

An eight channel molecularly imprinted polymer sensor array was prepared that was able to differentiate six different aryl amine analytes, including diastereomers with 94% accuracy.     

分子印迹电化学传感器

分子印迹电化学传感器能够选择性识别并检测特定目标化合物,因其设计简单、灵敏度高、价格低廉、携带方便、易于微型化和自动化等优点,在临床诊断、环境监测、食品分析等方面越来越受到人们的关注.本文作者主要论述分子印迹技术与电化学技术相结合构建分子印迹电化学传感器,包括分子印迹电化学传感器的种类,以及电化学方法制备分子印迹聚合物膜的常用单体等.对分子印迹电化学传感器领域新出现的分子印迹聚合物-纳米材料复合物以及纳米结构分子印迹聚合物也一并做了评述.     

High-performance graphene oxide electromechanical actuators

Having demonstrated unparalleled actuation stresses and strains, covalently bonded carbon-based nanomaterials are emerging as the actuators of the future. To exploit their full potential, further investigations into the optimum configurations of these new materials are essential. Using first-principle density functional calculations, we examine so-called clamped and unzipped graphene oxide (GO) as potential electromechanical actuator materials. Very high strains are predicted for hole injection into GO, with reversible and irreversible values of up to 6.3% and 28.2%, respectively. The huge 28% irreversible strain is shown to be the result of a change in the atomic structure of GO from a metastable clamped to more stable unzipped configuration. Significantly, this strain generation mechanism makes it possible to hold a constant strain of 23.8% upon removal of the input power, making this material ideal for long-term, low-power switching applications. A unique contraction of unzipped GO upon electron injection is also observed. It is shown that the origin of this unique behavior is the modulation of the structural rippling effect, which is a characteristic feature of GO. With reversible strains and stresses in excess of 5% and 100 GPa, respectively, GO is poised to be an extremely useful material for micro/nanoelectromechanical system actuators.     

A Molecularly Imprinted Nicotine-Selective Polymer

Abstract

A (-)-nicotine-selective polymer was prepared by molecular imprinting technique using methacrylic acid as a functional monomer. Liquid-chromatographic tests, using the polymers as a stationary phase, exhibited that the basicity of the functional group of (-)-nicotine is crucial for rebinding by the molecularly imprinted polymer. Scatchard analysis implied that the binding sites generated within the polymer are heterogeneous in terms of affinity, and the apparent dissociation constant of the highest affinity binding sites was estimated as 3.7 μM.