A Single‐Molecule Perspective on the Role of Solvent Hydrogen Bonds in Protein Folding and Chemical Reactions

We present an array of force spectroscopy experiments that aim to identify the role of solvent hydrogen bonds in protein folding and chemical reactions at the single‐molecule level. In our experiments we control the strength of hydrogen bonds in the solvent environment by substituting water (H₂O) with deuterium oxide (D₂O). Using a combination of force protocols, we demonstrate that protein unfolding, protein collapse, protein folding and a chemical reaction are affected in different ways by substituting H₂O with D₂O. We find that D₂O molecules form an integral part of the unfolding transition structure of the immunoglobulin module of human cardiac titin, I27. Strikingly, we find that D₂O is a worse solvent than H₂O for the protein I27, in direct contrast with the behaviour of simple hydrocarbons. We measure the effect of substituting H₂O with D₂O on the force dependent rate of reduction of a disulphide bond engineered within a single protein. Altogether, these experiments provide new information on the nature of the underlying interactions in protein folding and chemical reactions and demonstrate the power of single‐molecule techniques to identify the changes induced by a small change in hydrogen bond strength.     

Cross-sections for deuteron photo-disintegration from 74 to 241 MeV

Recent measurements of the differential cross-sections for deuteron photo-disintegration have been extended to lower photon energies at selected c.m. angles. The new results agree with earlier values from this laboratory and confirm the large discrepancy with data from Bonn and Orsay noted in the 100–250 MeV energy-range. They are in good agreement with the results of theoretical calculations including isobar configurations and meson-exchange currents below 150 MeV.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Surface enhanced Raman scattering for multiplexed detection

The multiplexed detection of biological analytes from complex mixtures is of crucial importance for the future of intelligent management and detection of disease. This review focuses on recent advances in the use of surface enhanced Raman scattering (SERS) spectroscopy as an analytical technique that can deliver multiplexed detection for a variety of biological target in increasingly complex media. The use of SERS has developed from the multipelxed detection of custom dye molecules to biomolecules such as DNA and proteins. Recent work has also shown the capability of SERS multiplexing for in vivo as well as in vitro applications.     

DNA detection using enzymatic signal production and SERS

A novel DNA assay is demonstrated which relies on the production of a surface enhanced resonance Raman scattering (SERS) signal following sequence specific hybridisation and enzyme hydrolysis. This method achieves high sensitivity and specificity that can be applied to the detection of unlabelled duplex DNA and is the first step towards a SERS based signal amplification approach.     

Segregation in aqueous methanol enhanced by cooling and compression

Molecular segregation in methanol-water mixtures is studied across a wide concentration range as a function of temperature and pressure. Cluster distributions obtained from both neutron diffraction and molecular dynamics simulations point to significantly enhanced segregation as the mixtures are cooled or compressed. This evolution toward greater molecular heterogenity in the mixture accounts for the observed changes in the water-water radial distribution function and there are indications also of a change in the topology of the water clusters. The observed behavior is consistent with an approach to an upper critical solution point. Such a point would appear to be "hidden" below the freezing line, thereby precluding observation of the two-fluid region.     

Cross-sections for the photo-production of π0-mesons from hydrogen from 238 to 922 MeV

The results of a comprehensive series of measurements of the cross-sections for the photo-production of ⁰-mesons from hydrogen at pion c.m. angles from 47 to 145 degrees are presented. The minimum and maximum photon energies have been 238 and 922 MeV respectively.     

Methanol-water solutions: a bi-percolating liquid mixture

An extensive series of neutron diffraction experiments and molecular dynamics simulations has shown that mixtures of methanol and water exhibit extended structures in solution despite the components being fully miscible in all proportions. Of particular interest is a concentration region (methanol mole fraction between 0.27 and 0.54) where both methanol and water appear to form separate, percolating networks. This is the concentration range where many transport properties and thermodynamic excess functions reach extremal values. The observed concentration dependence of several of these material properties of the solution may therefore have a structural origin.     

电感耦合等离子体原子发射光谱法测定钛酸钡纳米粉体中7种杂质元素

钛酸钡纳米粉体样品用盐酸溶解,在所得样品溶液中用电感耦合等离子体原子发射光谱法测定了以氧化物存在于样品中的7种杂质元素(包括镁、锶、钾、钠、铝、硅及铁),对测定的光谱条件进行了试验并优化达到上述各元素的测定上限为0.1%(质量分数).测得方法的检出限(3S/b)为(单位μg·L-1):2.0(铝),1.0(铁),20.0(钾),0.2(镁),4.0(钠),3.0(硅)及0.5(锶).应用此方法分析了两件实样,所得结果的相对标准偏差(n=6)小于等于2.0%,对其中4种杂质元素(镁、钾、钠和锶)同时用HG/T 3587-1999标准中的方法作分析校核,所得结果与此方法结果一致.