Xcalibur 2 0 7 sp1

UV-Vis spectra were recorded on an Agilent (Santa Clara, CA, USA) 8453 diode array spectrophotometer equipped with a magnetically stirred quartz optical cell of 1 cm path length. Peptide purification was performed on a Shimadzu HPLC instrument equipped with two LC-20AD pumps and an SPDM20A diode array detector (working range: 190–800 nm) using a Phenomenex Jupiter 4U Proteo semipreparative column (4 μm, 250 × 10 mm). Mass spectrometry analysis was performed on an LCQ ADV MAX ion-trap mass spectrometer with an ESI ion source. The ESI conditions were as follows: capillary temperature 210 °C, tube lens voltage −25 V, and source voltage +4.9 kV. The system was run in automated LC-MS/MS mode, using a surveyor HPLC system (Thermo Finnigan, San Jose, CA, USA) equipped with a Phenomenex Jupiter 4U Proteo column (4 μm, 150 × 2.0 mm). For the analysis of peptide fragments, Bioworks 3.1 and Xcalibur 2.0.7 SP1 software were used (Thermo Finnigan, San Jose, CA, USA).

All reagents for the peptide synthesis, including protected amino acids and rink amide resin, were purchased from Novabiochem, while other chemical compounds were reagent grade from Sigma-Aldrich. Purification of tau peptides was performed on a Shimadzu HPLC instrument equipped with two LC-20AD pumps and a SPD-M20A diode array detector, using a Phenomenex Jupiter 4µ Proteo semipreparative column (4 μm, 250 × 10 mm). Mass analysis and LC-MS/MS chromatograms were acquired with a LCQ ADV MAX ion-trap mass spectrometer, with an ESI ion source. The instrument works in automated LC-MS/MS mode through a surveyor HPLC system (Thermo Finnigan, San Jose, CA, USA) equipped with a Phenomenex Jupiter 4µ Proteo column (4 µm, 150 × 2.0 mm). In order to identify the oxidative modifications of peptide fragments, Bioworks 3.1 and Xcalibur 2.0.7 SP1 software were used (Thermo Finnigan, San Jose, CA, USA). UV-visible absorption spectra were collected with a Thermo Evolution 260 Bio spectrophotometer, provided with a Peltier thermostat. Circular dichroism spectra were acquired with a Jasco J715 spectropolarimeter, equipped with a Peltier thermostat. UV-visible kinetic profiles were obtained through an Agilent 8453 diode array spectrophotometer, equipped with a thermostated, magnetically stirred optical cell.

The HPLC-ESI-MS/MS analyses for photoproducts identification were performed by using a surveyor HPLC system (Thermo Finnigan, San Jose, CA, USA), equipped with a 150 × 2.0 mm, 4 µm Jupiter 4U Proteo column (Phenomenex). The mobile phase consisted of ultrapure water (0.1% v/v formic acid) (A) and ACN (0.1% v/v formic acid) (B). The starting concentration of eluent B was 2%, increased to 100% by 40 min with a linear gradient. This concentration was maintained for 5 min to wash the column. The flow rate was 0.2 mL min⁻¹. The MS/MS system consisted of an LCQ ADV MAX ion-trap mass spectrometer with an ESI ion source operating in ion-positive mode with the following instrument conditions: source voltage 5.0 kV; capillary voltage 46 V; capillary temperature 210 °C; tube lens voltage 55 V. The Xcalibur 2.0.7 SP1 software (Thermo Finnigan, San Jose, CA, USA) was used for spectra processing.