Sodium chloride (nacl)

FeCl₂·4H₂O, FeCl₃·6H₂O, KMnO₄, NaNO₃, concentrated H₂SO₄, 25 wt% NH₃ and 30 wt% H₂O₂ solution were of analytical grade (Molar Chemicals Ltd., Halásztelek, Hungary) and used without further purification. Reduction was carried out by NaBH₄ and L-ascorbic acid (Spektrum 3D, Debrecen, Hungary). Constant electrolyte concentration and pH were set and maintained using NaOH, HCl and NaCl in analytical purity (Reanal, Budapest, Hungary). Hydroxylamine, ammonium acetate, glacial acetic acid, FeSO₄·7H₂O and 1,10-phenantroline used for spectrophotometric determination of dissolved iron were purchased from Sigma-Aldrich. Ultrapure water produced by a Zeener Power RO&UP system was used as dispersion medium and the experiments were carried out mainly at room temperature (25 °C). Magnetic nanoparticles were synthesized by a traditional co-precipitation method using Fe(II) and Fe(III) salts under strongly alkaline conditions and purified by dialysis against dilute (0.001 M) HCl, as was described in detail elsewhere [4 (link),33 (link)]. Graphite oxide was prepared by the Hummers–Offeman method, using KMnO₄, and NaNO₃ for oxidation of graphite flakes (SGA20 graphite powder, Kropfmühl GmbH, Germany) under highly acidic circumstances (cc. H₂SO₄) [33 (link),43 (link)]. The product was purified by dialysis against water to eliminate the excess of salts originating from synthesis.

HPLC grade acetic and formic acid, myricetin-3-O-rhamnoside, quercetin-3-O-rhamnoside, hirsutenone, oregonin, caffeine and rutin standards, dimethyl sulfoxide-d₆ (99.8 atom% D with 0.03 vol.% TMS) and methanol-d₄ (99.8 atom% D), phosphatidylcholine, cholesterol and the porcine polar brain lipid extract were purchased from Merck (Darmstadt, Germany). Ethyl acetate, n-hexane and methanol of reagent grade, HPLC-MS grade acetonitrile, methanol, n-dodecane, dimethyl sulfoxide, NaCl, HCl, Na₂HPO₄·7H₂O and NaH₂PO₄·H₂O were obtained from Reanal-Ker (Budapest, Hungary). HPLC-grade water was prepared with a Millipore Direct Q5 water purification system (Bedford, MA, USA). All aqueous eluents for HPLC were filtered through MF-Millipore membrane filters (0.45 μm, mixed cellulose esters) (Billerica, MA, USA) and degassed in an ultrasonic bath before use.

Pfu (Pyrococcus furiosus) polymerase, dNTP (deoxyribonucleotide), T4 DNA ligase, and DNA ladder were purchased from Thermo Scientific. Restriction enzymes were purchased from Thermo Scientific and New England Biolabs. NaCl was purchased from Reanal, Tripton from Fluka, Bacto-agar from Biolab, and Agarose from Lonza.
The synthesis of the oligonucleotides used and the sequencing of the DNA constructs were carried out by Microsynth AG (http://microsynth.ch/).