Growth substrate induced functional changes elucidated by FTIR and Raman spectroscopy in in–vitro cultured human keratinocytes

Non-invasive measurements of cellular function in in vitro cultured cell lines using vibrational spectroscopy require the use of spectroscopic substrates such as quartz, ZnSe and MirrIR etc. These substrates are generally dissimilar to the original in vivo extracellular environment of a given cell line and are often tolerated poorly by cultured cell lines resulting in morphological and functional changes in the cell. The present study demonstrates various correlations between vibrational spectroscopic analyses and biochemical analyses in the evaluation of the interaction of a normal human epithelial keratinocyte cell line (HaCaT) with MirrIR and quartz substrates coated with fibronectin, laminin and gelatin. The findings of this study suggest that there is a correlation between quantitative measurements of cellular proliferative capacity and viability and peak area ratios in FTIR spectra, with replicated differences in similar areas of the observed Raman spectra. Differences in the physiology of cells were observed between the two spectroscopic substrates coated in fibronectin and laminin, but little differences were observed when the cells were attached to gelatin-coated quartz and MirrIR slides. The correlations demonstrate the sensitivity of the spectroscopic techniques to evaluate the physiology of the system. Furthermore the study suggests that gelatin is a suitable coating for use in spectroscopic measurements of cellular function in human keratinocytes, as it provides a material that normalises the effect of substrate attachment on cellular physiology. This effect is likely to be cell-line dependent, and it is recommended that similar evaluations of this effect are performed for those combinations of spectroscopic substrate and cell lines that are to be used in individual experiments.     

Two crystalline modifications of 2‐­hydroxy­cyclo­pent‐2‐enone

The orthorhombic form of 2‐hydroxy­cyclo­pent‐2‐enone, C₅H₆O₂, consists of chains of hydrogen‐bonded mol­ecules aligned along a twofold screw axis. The monoclinic form contains two independent mol­ecules, which have different orientations of the hydroxyl proton, and which assemble into ribbons along a twofold screw axis.     

Quantitative portfolio selection: Using density forecasting to find consistent portfolios

In the knowledge that the ex-post performance of Markowitz efficient portfolios is inferior to that implied ex-ante, we make two contributions to the portfolio selection literature. Firstly, we propose a methodology to identify the region of risk-expected return space where ex-post performance matches ex-ante estimates. Secondly, we extend ex-post efficient set mathematics to overcome the biases in the estimation of the ex-ante efficient frontier. A density forecasting approach is used to measure the accuracy of ex-ante estimates using the Berkowitz statistic, we develop this statistic to increase its sensitivity to changes in the data generating process. The area of risk-expected return space where the density forecasts are accurate, where ex-post performance matches ex-ante estimates, is termed the consistency region. Under the 'laboratory' conditions of a simulated multivariate normal data set, we compute the consistency region and the estimated ex-post frontier. Over different sample sizes used for estimation, the behaviour of the consistency region is shown to be both intuitively reasonable and to enclose the estimated ex-post frontier. Using actual data from the constituents of the US Dow Jones 30 index, we show that the size of the consistency region is time dependent and, in volatile conditions, may disappear. Using our development of the Berkowitz statistic, we demonstrate the superior performance of an investment strategy based on consistent rather than efficient portfolios.     

Electrochemistry of redox-active self-assembled monolayers

Redox-active self-assembled monolayers (SAMs) provide an excellent platform for investigating electron transfer kinetics. Using a well-defined bridge, a redox center can be positioned at a fixed distance from the electrode and electron transfer kinetics probed using a variety of electrochemical techniques. Cyclic voltammetry, AC voltammetry, electrochemical impedance spectroscopy, and chronoamperometry are most commonly used to determine the rate of electron transfer of redox-activated SAMs. A variety of redox species have been attached to SAMs, and include transition metal complexes (e.g., ferrocene, ruthenium pentaammine, osmium bisbipyridine, metal clusters) and organic molecules (e.g., galvinol, C₆₀). SAMs offer an ideal environment to study the outer-sphere interactions of redox species. The composition and integrity of the monolayer and the electrode material influence the electron transfer kinetics and can be investigated using electrochemical methods. Theoretical models have been developed for investigating SAM structure. This review discusses methods and monolayer compositions for electrochemical measurements of redox-active SAMs.     

Using copulas to model repeat purchase behaviour – An exploratory analysis via a case study

We develop a model of the evolution of inter-purchase times for a consumer-packaged product. After the introduction of the product, a consumer waits to make the initial purchase, then either waits to repurchase or decides not to. A repurchasing consumer repeats this decision process. The components of the model are the repurchase probability and the density function of the time to repurchase at each stage of the purchasing cycle. Issues of interest are: the strength of the dependency between successive repurchase times; the number of repeat purchases before stability occurs; the effects of consumer characteristics on inter-purchase times. The model of individual purchasing behaviour can be transformed via simulation to produce sales time series for a given population. As an example, the model is estimated for a product using Australian panel data. The accuracy of the model’s prediction is compared with an existing model.     

In vitro analysis of immersed human tissues by Raman microspectroscopy

Raman microspectroscopy is a powerful tool for the analysis of tissue sections, providing a molecular map of the investigated samples. Nevertheless, data pre‐processing and, particularly, the removal of the broad background to the spectra remain problematic. Indeed, the physical origin of the background has not been satisfactorily determined. Using 785 nm as source in a confocal geometry, it is demonstrated for the example of the protein kappa‐elastin that the background and resulting quality of the recorded spectrum are dependent on the morphology of the sample. Whereas a fine powder yields a dominant broad background, compressed pellets and solution‐cast thin films produce, respectively, improved quality spectra and significantly reduced spectral background. As the chemical composition of the samples is identical, the background is ascribed to stray light due to diffuse scattering rather than an intrinsic photoluminescence. The recorded spectra from a tissue sample exhibit a large and spatially variable background, resulting in poorly defined spectral features. A significant reduction of the background signal as well as improvement of the spectral quality is achieved by immersion of the sample in water and measurement with an immersion objective. The significant improvement in signal to background is attributed to a reduction of the diffuse scattering due to a change in the effective morphology as a result of an improved index matching at the water/tissue interface compared to the air/tissue interface. Compared to sections measured in air, the background is reduced to that of the water, and pre‐processing is reduced to the subtraction of the substrate and water signal and correction for the instrument response, both of which are highly reproducible. Data pre‐processing is thus greatly simplified and the results significantly more reliable. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel redox active bifunctional crosslinkers from unsymmetrical 1,1′-disubstituted ferrocenes

The synthesis and electrochemistry of novel redox active bifunctional crosslinkers bearing pendant amine and maleimide groups from unsymmetrical 1,1′-disubstituted ferrocene precursors are reported.     

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