1100b atomic absorption spectrophotometer

The intracellular pool of potassium upon treatment with various concentrations of selected bile salts was quantified by atomic absorption spectroscopy as described previously (Ioannou et al., 2007 (link)) except that experiments were performed in 5 mM HEPES buffer (pH 7) at a cell density of 10⁸ CFU/ml. Samples from each of the test (bile salts) and control groups (4 μM valinomycin and 100 μg/ml lysostaphin) were collected over a time-course of 20 min and filtered using a 0.22 μm pore size membrane filter. The potassium ion concentration in the filtrate samples was determined using a PerkinElmer 1100B atomic absorption spectrophotometer in flame emission mode.

All reagents and chemicals were purchased from Sigma Aldrich Chemical Company Ltd. and Alfa Aesar. Unless stated otherwise, the materials were used without further purification. The dimeric [Mo₂S₂O₂]²⁺ unit was synthesized according to the modified published procedure by E. Cadot et al.19 and the [Mo₂O₂S₂(H₂O)₆]²⁺ solution obtained was stored under Ar. The [N(CH₃)₄]_1.5K_5.5Na₂[I₃ ⊂ (MoV2O₂S₂)₈(OH)₈(Se^IVO₃)₈]·25H₂O (3) cluster was prepared according to the previously reported procedure.7a Flame atomic absorption spectroscopy (FAAS) and CHN elemental analyses were performed at the Environmental Chemistry Section and microanalysis services within the School of Chemistry, on a Perkin-Elmer 1100B Atomic Absorption Spectrophotometer and an EA 1110 CHN, CE-440 Elemental Analyser, respectively. Thermogravimetric analysis was performed on a TA Instruments Q 500 Thermogravimetric Analyzer under nitrogen flow at a typical heating rate of 5 °C min^–1. UV-Vis spectra were collected using a Shimadzu PharmaSpec UV-1700 UV-Vis spectrophotometer in transmission mode using quartz cuvettes with 1.0 cm optical path length. Infrared spectra (4000–400 cm^–1) of all samples were recorded on JASCO FTIR-410 spectrometer or a JASCO FT-IR 4100 spectrometer. Characteristic IR bands are shown in cm^–1; intensities denoted as s = strong, m = medium, w = weak, sh = sharp.