Probing chiral interfaces by infrared spectroscopic methods

Biological homochirality on earth and its tremendous consequences for pharmaceutical science and technology has led to an ever increasing interest in the selective production, the resolution and the detection of enantiomers of a chiral compound. Chiral surfaces and interfaces that can distinguish between enantiomers play a key role in this respect as enantioselective catalysts as well as for separation purposes. Despite the impressive progress in these areas in the last decade, molecular-level understanding of the interactions that are at the origin of enantiodiscrimination are lagging behind due to the lack of powerful experimental techniques to spot these interactions selectively with high sensitivity. In this article, techniques based on infrared spectroscopy are highlighted that are able to selectively target the chiral properties of interfaces. In particular, these methods are the combination of Attenuated Total Reflection InfraRed (ATR-IR) with Modulation Excitation Spectroscopy (MES) to probe enantiodiscriminating interactions at chiral solid-liquid interfaces and Vibrational Circular Dichroism (VCD), which is used to probe the structure of chirally-modified metal nanoparticles. The former technique aims at suppressing signals arising from non-selective interactions, which may completely hide the signals of interest due to enantiodiscriminating interactions. Recently, this method was successfully applied to investigate enantiodiscrimination at self-assembled monolayers of chiral thiols on gold surfaces. The nanometer size analogues of the latter--gold nanoparticles protected by a monolayer of a chiral thiol--are amenable to VCD spectroscopy. It is shown that this technique yields detailed structural information on the adsorption mode and the conformation of the adsorbed thiol. This may also turn out to be useful to clarify how chirality can be bestowed onto the metal core itself and the nature of the chirality of the latter, which is manifested in the metal-based circular dichroism activity of these nanoparticles.

Comparison of performance and patient satisfaction of two types of ERG electrodes

BACKGROUND: An age-controlled comparison concerning patient satisfaction and electrical performance of microfibres (DTL) and rigid contact lens (Henkes) corneal ERG electrodes was carried out. METHODS: 36 test persons underwent complete ophthalmological examination and were equally distributed into 3 age groups. Electroretinograms were recorded according to ISCEV standards. Randomly, in one eye a Henkes electrode was used and in the other eye a DTL electrode. Amplitudes of a- and b-waves and implicit times were measured and compared for the two electrode types. RESULTS: 34 of 36 test persons preferred DTL electrodes. Electrical performance concerning b-wave amplitudes was comparable. Statistically significant differences were detected only for scotopic combined cone-rod stimulation in the age groups 20 - 40 and 41 - 60 years between the different electrodes. Other recordings did not show differences. A statistically significant reduction of signal amplitudes with age was detected for scotopic isolated rod signals and combined cone-rod signals. Significance level was p < 0.05. No conjunctival or corneal erosions were found after ERG recordings for either electrode. CONCLUSIONS: Electrical performance is comparable between electrodes. For scotopic stimulations age was a significant influencing factor for signal amplitude and should be respected for normative values. DTL electrodes were preferred by the vast majority of patients. No adverse clinical effects were observed for either electrode. DTL electrodes should be preferred due to hygienic reasons (single use) and patient comfort.