Electrical properties of diamond surfaces functionalized with molecular monolayers

Recent studies have shown that semiconductor surfaces such as silicon and diamond can be functionalized with organic monolayers, and that these monolayer films can be used to tether biomolecules such as DNA to the surfaces. Electrical measurements of these interfaces show a change in response to DNA hybridization and other biological binding processes, but the fundamental nature of the electrical signal transduction has remained unclear. We have explored the electrical impedance of polycrystalline and single-crystal diamond surfaces modified with an organic monolayer produced by photochemical reaction of diamond with 1-dodecene. Our results show that, by measuring the impedance as a function of frequency and potential, it is possible to dissect the complex interfacial structure into frequency ranges where the total impedance is controlled by the molecular monolayer, by the diamond space-charge region, and by the electrolyte. The results have implications for understanding the ability to use molecularly modified semiconductor surfaces for applications such as chemical and biological sensing.     

High resolution core and valence band XPS spectra of non-conductor pyroxenes

High resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of the non-conductor pyroxene minerals, bronzite ((Mg_0.8,Fe_0.2)₂Si₂O₆) and diopside (Ca(Mg_0.8Fe_0.2)Si₂O₆) have been obtained with the Kratos magnetic confinement charge compensation which minimizes differential charge broadening. Observed Si 2p, O 1s, Mg 2p and Ca 2p total linewidths are all about 1.3 eV, very similar to those observed previously with the same instrument for SiO₂ and olivines ((Mg,Fe)₂SiO₄); and we consider that these widths are within 0.05 eV of the minimum room temperature linewidths for these samples with the experimental resolution of this instrument of 0.35 eV. These linewidths are all determined by vibrational broadening due to the M-O symmetric stretch in the ion states. The Si 2p binding energies (BE) are intermediate between the quartz and olivine Si 2p binding energies; but the O 1s spectra resolve the bridging oxygen (BO) and non-bridging oxygen (NBO) in the unit, with the NBO O 1s very close in BE to the O in olivine, and the BO very close to the BO in SiO_2. Indeed in both diopside and bronzite, it is possible to separate the three structurally inequivalent O atoms in the O 1s spectra: the BO at a BE of about 532.6 eV, a NBO peak from the MgOSi moiety (Mg in the M1 site) at about 531.3 eV, and a NBO peak at 531 eV from the CaOSi or the FeOSi moieties (Ca and Fe in the M2 site). The O 1s BE increases with the increase in the electronegativity Ca < Mg < Fe < Si. Moreover, the linewidths of these peaks increase when Fe and Mg are both present in either M1 (diopside) or M2 (bronzite) sites.The valence band spectra for the two pyroxenes are rather similar, and quite different from the VB spectra of quartz and olivines. The dispersion of the pyroxene VB spectra is intermediate between the VB spectra of quartz and olivines; the valence band spectrum of pyroxenes are more dispersed than in olivines by about 1.5 eV but less dispersed than quartz by about 1.5 eV. These VB spectra can be assigned using the previous olivine VB spectra and high quality pseudopotential density functional theoretical calculations in the generalized gradient (GGA) approximation. As for the olivine VB spectra, the Fe 3d t_2g and e_g orbitals in M1 and M2 sites of the pyroxene are located at the top of the pyroxene valence band, and the BE of the Fe 3d peaks from M1 are about 0.7 eV smaller than the Fe 3d peaks in M2. The theoretical XPS valence band spectra using the theoretical density of states and the Gelius intensity approximation are is in good semi-quantitative agreement with the experimental spectra. This intermediate dispersion of pyroxenes is due to the partial polymerization of the Si-O units in pyroxenes, and the intermediate charge on the Si atoms as indicated by the Si 2p BE.     

Selective oxidation of naphthalene derivatives with ruthenium catalysts using hydrogen peroxide as terminal oxidant

The selective oxidation of naphthalene and its derivatives to give naphthoquinones has been investigated in detail. The reaction can be carried out effectively in the presence of a catalytic amount of Ru complexes (0.2 mol%) and phase transfer catalysts (PTC) using H₂O₂ as the terminal oxidant and water as the solvent. The effect of different ruthenium complexes, phase transfer catalysts, and the concentration of hydrogen peroxide were studied. Compared to previous procedures for this type of reactions, acidic solvents and high concentration of hydrogen peroxide are not necessary, which makes the reaction more environmentally friendly.     

Label-free cell separation and sorting in microfluidic systems

Cell separation and sorting are essential steps in cell biology research and in many diagnostic and therapeutic methods. Recently, there has been interest in methods which avoid the use of biochemical labels; numerous intrinsic biomarkers have been explored to identify cells including size, electrical polarizability, and hydrodynamic properties. This review highlights microfluidic techniques used for label-free discrimination and fractionation of cell populations. Microfluidic systems have been adopted to precisely handle single cells and interface with other tools for biochemical analysis. We analyzed many of these techniques, detailing their mode of separation, while concentrating on recent developments and evaluating their prospects for application. Furthermore, this was done from a perspective where inertial effects are considered important and general performance metrics were proposed which would ease comparison of reported technologies. Lastly, we assess the current state of these technologies and suggest directions which may make them more accessible.     

Supported liquid extraction in combination with LC‐MS/MS for high‐throughput quantitative analysis of hydrocortisone in mouse serum

A high‐throughput LC–MS/MS bioanalytical method was developed and validated for the determination of hydrocortisone in mouse serum via supported liquid extraction (SLE) in a 96‐well plate format. Although sample extracts from SLE result in similar matrix effects compared with conventional liquid–liquid extraction (LLE), greater analyte extraction recovery and much higher analysis throughput for the quantitative analysis of hydrocortisone in mouse serum were obtained. The current LC‐MS/MS method was validated for a concentration range of 2.00–2000 ng/mL for hydrocortisone using a 0.100 mL volume of mouse serum. The intra‐ and inter‐day precision and accuracy of the quality control samples at low, medium and high concentration levels showed ≤12.9% CV and ?3.4–6.2% bias for the analyte in mouse serum. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of rhynchophylline and hirsutine in rat plasma by UPLC‐MS/MS after oral administration of Uncaria rhynchophylla extract

An ultra‐performance liquid chromatography with tandem mass spectrometry (UPLC–MS/MS) method was developed and validated to concurrently determine rhynchophylline and hirsutine in rat plasma. The sample preparation of rat plasma was achieved by alkalization and liquid–liquid extraction. The mass transition of precursor ion → product ion pairs were monitored at m/z 385.2 → 160.0 for rhynchophylline, m/z 369.3 → 144.0 for hirsutine and m/z 414.0 → 220.0 for noscapine (internal standard). This method revealed linear relationships from 2.5 to 50 ng/mL (r² > 0.997) for rhynchophylline and from 2.5 to 50 ng/mL (r² > 0.998) for hirsutine. The limit of quantification values for rhynchophylline and hirsutine in rat plasma were both 2.5 ng/mL. Intra‐day and inter‐day precisions were within 10.6% and 12.5%, respectively, for rhynchophylline and hirsutine, and the accuracy (bias) was <10%. Liquid–liquid extraction of rat plasma samples resulted in insignificant matrix effect, and the extraction recoveries were >83.6% for rhynchophylline, 73.4% for hirsutine and 90.7% for the internal standard. This method was applied successfully to a pharmacokinetic study of rhynchophylline and hirsutine in rats after oral administration. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of Soller slits to remove reference foil fluorescence from transmission spectra

Measurement of X‐ray absorption spectroscopy (XAS) in transmission is the method of choice for strong or concentrated samples. In a typical XAS experiment above 5 keV the sample is placed between the first (I₀) and second (I₁) ion chambers and a standard foil is placed between the second (I₁) and third (I₂) ion chambers for simultaneous calibration of energy during sample analysis. However, some fluorescence from the foil may be registered in I₁, causing anomalies in the transmission signal of the sample, especially when the sample edge jump is relatively small. To remedy this, Soller slits were constructed and placed between the foil and I₁ to minimize back‐fluorescence from the foil. A comparison of blank and standard samples, measured with or without Soller slits or under a worst‐case scenario, demonstrates the advantages of Soller slits when analyzing weak signal samples via transmission XAS.     

Time-dependent density functional calculations of optical rotatory dispersion including resonance wavelengths as a potentially useful tool for determining absolute configurations of chiral molecules

The optical rotations for six organic molecules (verbenone, fenchone, camphor, nopinone, Tr?ger's base, dimethyl-cyclopropane) and the transition metal complex [Co(en)(3)](3+) were calculated as a function of wavelength using time-dependent density functional theory (TDDFT). In the calculations, a realistic behavior of the optical rotation in the vicinity of an electronic transition was obtained by using a phenomenological damping parameter of the order of 0.2 eV (0.007 au). In comparison with experiment, for the molecules studied here the sign and order of magnitude of the optical rotation as well as the excitation energies were reasonably well reproduced in most computations. These findings apply to the investigated wavelength ranges typically between about 200 and 650 nm even when using comparatively small basis sets. Such calculations might therefore routinely be applied to help assigning the absolute configurations of chiral molecules. Supplementary calculations of the circular dichroism (CD) and comparison with experimental CD were used for further assessment of the optical rotation calculations. In particular, a combined study of optical rotation and CD turned out to be useful in cases where the optical rotatory dispersion in a specific energy range exhibits a considerable blue or red shift or where it is difficult to reproduce because of an interplay of several competing Cotton effects. The influence of basis set, density functional, and the damping parameter was also investigated.     

First-principles investigation on the geometry and electronic structure of the three-dimensional cuboidal C(60) polymer

The structural stability and electronic properties of the recently characterized three-dimensional (3D) cuboid-shaped C(60) polymer are studied using periodic ab initio density functional methods. It is shown that the experimentally observed structure is metastable and not fully relaxed from the high pressure state. A second polymorph, which is more stable than the experimental structure, is identified from the calculations. This new structure differs from the observed structure in the number of fourfold-coordinated atoms per C(60) molecule. Both structures are found to be metallic with bulk moduli only about one-third that of diamond. The cuboidal C(60) is not the long sought after superhard 3D carbon polymer; however, the two polymorphs studied here reveal unusual electronic band structures that might suggest interesting electronic properties.