Measuring the metabolome: current analytical technologies

The post-genomics era has brought with it ever increasing demands to observe and characterise variation within biological systems. This variation has been studied at the genomic (gene function), proteomic (protein regulation) and the metabolomic (small molecular weight metabolite) levels. Whilst genomics and proteomics are generally studied using microarrays (genomics) and 2D-gels or mass spectrometry (proteomics), the technique of choice is less obvious in the area of metabolomics. Much work has been published employing mass spectrometry, NMR spectroscopy and vibrational spectroscopic techniques, amongst others, for the study of variations within the metabolome in many animal, plant and microbial systems. This review discusses the advantages and disadvantages of each technique, putting the current status of the field of metabolomics in context, and providing examples of applications for each technique employed.     

MALDI-MS of drugs: Profiling,imaging, and steps towards quantitative analysis

Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique which can be used in mass spectrometry to produce ions from biomolecules without inducing the fragmentation associated with traditional methods of ionization. When used with small molecules, the lack of fragmentation allows identification of specific molecules against a background of alternative signals; thus, for example, the presence of drug molecules and metabolites can be distinguished from a range of alternative biomolecules present within a tissue sample. Using highly collimated lasers in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) allows imaging of a tissue sample whereby the laser is rastered across the sample and individual mass spectra are collected in a serial manner. Thus, the distribution of the molecules within the tissue sample can be presented in the form of a 2D image. While the detection of specific drug molecules and metabolites within biological samples has its uses, quantification of those same molecules would be of greater benefit in a clinical setting. However, accurate quantification presents additional challenges. We present an overview of the MALDI-MS technique followed by recent progress in profiling drugs and their metabolites through imaging drug distributions within tissues and finish with recent developments in the quantification of drugs in tissues by MALDI-MSI.     

Investigation of the doping efficiency of poly(styrene sulfonic acid) in poly(3,4‐ethylenedioxythiophene)/poly(styrene sulfonic acid) dispersions by capillary electrophoresis

CE can efficiently separate poly(3,4‐ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT/PSS) complexes and free PSS in dispersions and can be used to estimate the degree of PSS doping. We investigated the doping efficiency of PSS on PEDOT in dispersions using CE and its effect on the conductivity of the resulting PEDOT/PSS films. Results of this study indicate that dispersions containing 1:2.5–3 EDOT:PSS feed ratio (by weight) exhibiting 72–73% PSS doping generate highly processable and highly conductive films. Conductivity can be optimized by limiting the time of reaction to 12 h. At this point of the reaction, the PEDOT/PSS segments, appearing as broad band in the electropherogram, could still exist in an extended coil conformation favoring charge transport resulting in high conductivity. Above a threshold PEDOT length formed at reaction times longer than 12 h, the PEDOT/PSS complex, appearing as spikes in the electropherogram, most likely have undergone a conformational change to coiled core‐shell structure restricting charge transport resulting in low conductivity. The optimal conductivity (5.2 S/cm) of films from dispersions synthesized for 12 h is significantly higher than those from its commercial equivalent Clevios P and other reported values obtained under similar conditions without the addition of codopants.     

Anion sensing 'venus flytrap' hosts: a modular approach

A series of podands based on three hydrogen bonding 'arms' have been prepared and their affinities for simple inorganic anions measured.     

Nuclear disintegration in relativistic heavy ion collisions

The breakdown of the participant spectator model for central relativistic nuclear collisions is discussed and a different picture of a hot spot followed by a target explosion is suggested to be more consistent with the data.     

On the range of influences in back-circulant Latin squares

In this note we obtain a large lower bound for the index of a certain critical set in the back-circulant Latin squares of odd order. This resolves in the negative a conjecture of Fitina, Seberry and Chaudhry [Back-circulant Latin square and the influence of a set, Austral. J. Combin. 20 (1999) 163-180].     

Automorphisms of higher‐dimensional Hadamard matrices

This article derives from first principles a definition of equivalence for higher‐dimensional Hadamard matrices and thereby a definition of the automorphism group for higher‐dimensional Hadamard matrices. Our procedure is quite general and could be applied to other kinds of designs for which there are no established definitions for equivalence or automorphism. Given a two‐dimensional Hadamard matrix H of order ν, there is a Product Construction which gives an order ν proper n‐dimensional Hadamard matrix P⁽ⁿ⁾(H). We apply our ideas to the matrices P⁽ⁿ⁾(H). We prove that there is a constant c > 1 such that any Hadamard matrix H of order ν > 2 gives rise via the Product Construction to cν inequivalent proper three‐dimensional Hadamard matrices of order ν. This corrects an erroneous assertion made in the literature that ”P⁽ⁿ⁾(H) is equivalent to “P⁽ⁿ⁾(H′) whenever H is equivalent to H′.” We also show how the automorphism group of P⁽ⁿ⁾(H) depends on the structure of the automorphism group of H. As an application of the above ideas, we determine the automorphism group of P⁽ⁿ⁾(Hk) when Hk is a Sylvester Hadamard matrix of order 2^k. For ν = 4, we exhibit three distinct families of inequivalent Product Construction matrices P⁽ⁿ⁾(H) where H is equivalent to H₂. These matrices each have large but non‐isomorphic automorphism groups. © 2008 Wiley Periodicals, Inc. J Combin Designs 16: 507–544, 2008     

Liquid scintillation counters calibration stability over long timescales

Liquid scintillation spectrometry is widely used for the analysis of alpha and beta emitting radionuclides. Robust calibration of liquid scintillation (LS) spectrometers is fundamental to accurate LS measurement but at the same time is time consuming and costly, particularly if a wide range of radionuclides are analysed by the laboratory. The frequency of the calibration varies in different laboratories and is based on many practical and operational factors. This work summarizes the observations regarding variations in 1220 Quantulus spectrometers efficiency calibrations performed annually using various radionuclides: ³H ⁶³Ni, ⁵⁵Fe, ³⁶Cl, ⁴⁵Ca, ¹⁴⁷Pm, ²⁴¹Pu, ⁹⁹Tc for a period of 9 years and discusses the implication to calibration frequency.

     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.