Fluorescence energy transfer efficiency in labeled yeast cytochrome c: a rapid screen for ion biocompatibility in aqueous ionic liquids

A fluorescence energy transfer "de-quenching" assay was implemented to follow the equilibrium unfolding behaviour of site-specific tetramethylrhodamine-labelled yeast cytochrome c in aqueous ionic liquid solutions; additionally, this approach offers the prospect of naked eye screening for biocompatible ion combinations in hydrated ionic liquids.     

Maturation of auditory temporal integration and inhibition assessed with event-related potentials (ERPs)

Background

We examined development of auditory temporal integration and inhibition by assessing electrophysiological responses to tone pairs separated by interstimulus intervals (ISIs) of 25, 50, 100, 200, 400, and 800 ms in 28 children aged 7 to 9 years, and 15 adults.

Results

In adults a distinct neural response was elicited to tones presented at ISIs of 25 ms or longer, whereas in children this was only seen in response to tones presented at ISIs above 100 ms. In adults, late N1 amplitude was larger for the second tone of the tone pair when separated by ISIs as short as 100 ms, consistent with the perceptual integration of successive stimuli within the temporal window of integration. In contrast, children showed enhanced negativity only when tone pairs were separated by ISIs of 200 ms. In children, the amplitude of the P1 component was attenuated at ISIs below 200 ms, consistent with a refractory process.

Conclusions

These results indicate that adults integrate sequential auditory information into smaller temporal segments than children. These results suggest that there are marked maturational changes from childhood to adulthood in the perceptual processes underpinning the grouping of incoming auditory sensory information, and that electrophysiological measures provide a sensitive, non-invasive method allowing further examination of these changes.     

pH-Dependent Spectroscopy of Tetracycline and Its Analogs

Tetracyclines (TCs), broad spectrum antibiotics widely used in the prevention and treatment of infectious diseases, are amphoteric molecules containing several ionizable functional groups that exist predominantly as zwitterions at a given pH value. TCs are reported to undergo a wide variety of reactions at different pH values i.e. TCs form to anhydrotetracyclines at low pH, 4-epitetracyclines at pH 3–5 and isotetracyclines at high pH values. The pH-dependent absorbance and emission properties of tetracycline and its 10 analogs (4-epitetracycline, doxycyline, oxytetracycline, chlortetracycline, 4-epichlortetracycline, isochlortetracycline, methacycline, rolitetracycline, minocycline, and demeclocycline) were investigated and reported in this paper. The main focus of the study was on the pH dependent transformation of epichlortetracycline, chlortetracycline and isotetracycline at basic pH. Absorption, emission and time resolved spectroscopy were used to determine the behavior of the three TC derivatives at this condition. Increasing the buffer’s ionic concentration leads to faster transformation to iCTC. A pH dependent transformation of CTC to iCTC was observed and the lifetimes of CTC and iCTC were determined to be 3.0 and 5.89 ns respectively. The distribution factor of CTC to iCTC at basic pH was also reported for the first time.     

On the Origin of the Heterogeneous Emission from Pyrene Sequestered Within Tetramethylorthosilicate-Based Xerogels: A Decay-Associated Spectra and O2 Quenching Study

Steady-state and time-resolved fluorescence spectroscopy are used to determine the local microheterogeneity surrounding pyrene molecules sequestered within tetramethylorthosilicate-derived xerogels. After compensation for the intrinsic background emission from the xerogel, we find that the pyrene intensity decay kinetics are best described by a two-term rate law. This is consistent with the pyrene molecules distributing primarily into two microenvironments. Under ambient conditions, the individual pyrene microenvironments exhibit excited-state fluorescence lifetimes that differ by 100 ns. However, the pyrene I₁ to I₃ band ratios that are associated with each microenvironment are statistically equivalent to one another. These results show that the local dipolarity surrounding these pyrene microenvironments are similar, but the decay rates associated with each microenvironment are very different. The longer-lived pyrene species (Environment #1) constitutes 1/2 of the total fluorescence and it exhibits an O₂ quenching sensitivity (K_sv1) of (5.19 ± 0.52 × 10^–3 %O₂ ^–1 and a bimolecular quenching constant (k_q1) of (2.30 ± 0.23) × 10⁴ %O₂ ^–1 s^–1. Environment #2, associated with the shorter-lived pyrene species, exhibits an O₂ quenching sensitivity (K_sv2) of (2.31 ± 0.16) × 10^–2 %O₂ ^–1 and a bimolecular quenching constant (k_q2) of (2.11 ± 0.23) × 10⁵ %O₂ ^–1 s^–1. These results are interpreted as follows: Environment #1 consists of pyrene molecules sequestered within a relatively rigid siloxane network wherein non-radiative decay pathways are lessened, but these pyrene molecules are not quenched readily by O₂. Environment #2 consists of pyrene molecules adsorbed onto surface silanols within the xerogel. These pyrene molecules are quenched by the silanols and they are simultaneously more accessible to O₂ compared to Environment #1.     

Elimination of bilirubin interference in fluorimetric determination of fluorescein by phase-resolved fluorescence spectrometry

Phase-resolved fluorescence spectrometry is used to eliminate bilirubin interference in the fluorimetric quantitation of fluorescein, despite extensive excitation and emission spectral overlap of the two species. In this method, it is the difference in fluorescence lifetimes of the two species that provides the selectivity parameter. Results are given for a nulling approach and for a multiple phase-angle approach. In the nulling approach, intensity is measured at a detector phase angle at which the intensity for bilirubin is zero. In the multiple phase-angle approach, intensities at several phase angles are used to generate a matrix which is solved for the concentrations of fluorescein and bilirubin. Although a steady-state method yielded low results for fluorescein concentration in the presence of bilirubin concentration about 3 μM, the phase-resolved methods yielded correct values for fluorescein concentration with bilirubin concentration up to 10 μM.     

Holographic chemical vapor sensor

A holographic interferometer senses vapor-induced optical path length changes in polymer or other chemically sensitive films. The interferometer is inherently sensitive to changes in chemical vapor content, self-compensates for drifts, and accommodates a large array of sensor elements. A sniff-locked-loop synchronous detection method takes advantage of the interferometer's rapid response to achieve vapor concentration sensitivity in the parts-per-billion (ppb, parts in 10(9)) range. We demonstrate, for example, 40 ppb sensitivity to ethyl alcohol using poly(N-vinyl pyrrolidone) with a measurement time of 5 s.     

Ma?analytische Methoden

Ohne Zusammenfassung