Quantifiable correlation of ToF-SIMS and XPS data from polymer surfaces with controlled amino acid and peptide content

Peptide-coated surfaces are widely employed in biomaterial design, but quantifiable correlation between surface composition and biological response is challenging due to, for example, instrumental limitations, a lack of suitable model surfaces or limitations in quantitatively correlating data from different surface analytical techniques. Here, we first establish a reference material that allows control over amino acid content. Reversible addition-fragmentation chain-transfer (RAFT) polymerisation is used to prepare a copolymer containing alkyne and furan units with well-defined chain length and composition. Huisgen Cu(I)-catalysed azide-alkyne cycloaddition reaction is used to attach the model azido-polyethyleneglycol-amide-modified pentafluoro-l -phenylalanine to the polymer. Different compositional ratios of the polymer provide a surface with varying amino acid content that is analysed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Nitrogen-related signals are compared with fluorine signals from both techniques. Fluorine and nitrogen signals from both techniques are found to be related to the copolymer compositions, but the homopolymer data deviate from this trend. The approach is then translated to a heparin-binding peptide that supports cell adhesion. Human embryonic stem cells cultured on copolymer surfaces presenting different amounts of heparin-binding peptide show strong cell growth while maintaining pluripotency after 72 h of culture. The early cell adhesion at 24 h can be correlated to the logarithm of the normalised CH₄N⁺ ion intensity from ToF-SIMS data, which is established as a suitable and generalisable marker ion for amino acids and peptides. This work contributes to the ability to use ToF-SIMS in a more quantitative manner for the analysis of amino acid and peptide surfaces.     

High-temperature stable gratings in germanosilicate planar waveguides

Negative index gratings in planar germanosilicate waveguides were found to be stable up to 500 degrees C. The annealing properties are similar to those of negative index fiber gratings.     

Quantitative analysis of chromium(V) by EPR spectroscopy

A procedure to accurately quantitate chromium(V) in environmental and medicinal chemistry samples was developed using electron paramagnetic resonance spectroscopy (EPRS) as the method of detection. It was found to have an error in the order of +/-10% and a detection limit of 0.010 mM (0.5 mg l(-1)) chromium(V). The method has been used to quantitate the formation of chromium(V) in the interaction of chromium(VI) with fulvic acid and a simple model of this acid, viz, 1.2-dihydroxybenzene. Analysis of solutions obtained from the reaction of 1,2-dihydroxybenzene with chromium(VI) demonstrated that even when the organic substrate was present in a 182-fold excess, the maximum chromium(V) concentration attained represented just 1.44% of the initial chromium(VI). Reactions between chromium(VI) and fulvic acid yielded similar results. It was therefore concluded that at background environmental concentrations of chromium and fulvic acid, the production of chromium(V) is insignificant, however, its possible importance in contaminated systems cannot be disregarded on this basis alone. The method for quantitative analysis reported in this paper should be an invaluable tool for investigations into the significance of chromium(V) in the toxicological mechanism of chromium(VI) and its role as a mutagenic agent.     

Propagation in air by field superposition of scattered light within a Fresnel fiber

Propagation of light at 1.5 microm with peak intensity in an air hole is achieved within an air-silica-structured Fresnel waveguide. Thus a simpler fiber design alternative to photonic crystal fibers is possible for high-peak-power propagation with reduced nonlinear interactions. Multiple foci are observed in the far field.     

Ultraviolet-induced absorption losses in hydrogen-loaded optical fibers and in presensitized optical fibers

Reduced hydroxyl formation in presensitized fibers exposed to cw 244-nm light after hydrogen outdiffusion is reported. The OH band in the presensitized fiber shifts toward 1390 nm. In the fully hydrogen-loaded fiber the OH band is centered at 1397 nm and does not shift with fluence.     

Auger spectra of carbon monoxide chemisorbed on Pt(111) and Cu(111)

The Auger spectra of carbon monoxide adsorbed on Pt(111) and Cu(111) are compared. The characteristic features now regarded as a fingerprint of this adsorbed species are observed, even for the weakly adsorbed CO on copper which gives complex X-ray photoelectron spectra. No coverage dependence of the spectra was observed on either substrate. The C lsVV spectrum of CO/Cu(111) is dominated by transitions involving the “screening” electron in the 2π orbital.     

Equilibration of ortho- and para-hydrogen by homogeneous hydrogenation catalysts in solution; A test for the reversibility of hydrogen addition using Raman spectroscopy

para-Enriched hydrogen is converted into the ortho-para equilibrium mixture by tris(triphenylphosphine)rhodium chloride in toluene solution. The rotational Raman effect can be used to show that this equilibration occurs during the course of hydrogenation of cyclohexene by the above catalyst. The methanol solvate formed by reduction of 1,4-bis(diphenylphosphino)butanebicyclo[2.2.1] heptadienerhodium tetrafluoroborate also catalyses the ortho-para equilibration of hydrogen, in common with related cationic rhodium complexes. No equilibration occurs, however, during the course of hydrogenation of (Z)-α-benzamidocinnamic acid by cationic chelate rhodium complexes, including that derived from the chiral ligand (R,R)-1,2-bis(o-methoxyphenylphenyl)ethane (DIPAMP), thus demonstrating that addition of hydrogen to rhodium is irreversible.     

Characterization of titanium nitride films and sputter target material by 14 MeV neutron activation analysis

Titanium nitride films /3.0 and 3.8 microns/ deposited by the magnetron sputtering technique on silicon substrates and the commercially procured compound sputter target material are characterized for their bulk compositions by non-destructive 14 MeV neutron activation analysis /NAA/. The practical sensitivity and precision obtained under the present experimental conditions are 0.7 mg and 5% in the case of titanium and 0.1 mg and 8% in the case of nitrogen, respectively. The bulk composition of the films seems to conform to stoichiometric nitride, TiN, while the presence of oxygen could not be precluded in the compound target material.     

Modal interferometer for in situ measurements of induced core index change in optical fibers

A simple interferometer based on modal interference is described. Without compromising interferometer stability it is possible to measure index changes of less than 1 x 10(-6).