Propionic acid

p-Toluenesulfonyl
chloride (97%), p-toluenesulfonyl amide (97%), lithium
hydroxide monohydrate, potassium permanganate, calcium chloride, N-methyl-2-pyrrolidone (NMP, anhydrous, 99.8%), pyridine
(anhydrous, 99.8%), lithium aluminum hydride (95%), tetrahydrofuran
(THF, anhydrous, 99.8%), lithium bis(trimethylsilyl) amide solution
(1 M in THF), tributyl phosphate (≥99%), and titanium(IV) isopropoxide
(97%) were purchased from Sigma-Aldrich. Aluminum nitrate (Al(NO₃)₃ × 9H₂O), 3-(aminopropyl)triethoxysilane,
1-propanol, and propionic acid were acquired from Merck. 4,4-(Hexa-fluoroisopropylidene)dianiline
(98%) was obtained from TCI Europe, poly(vinylidene difluoride-co-hexafluoropropylene)
(PVdF-HFP, Kynar FLEX LBG) from Arkema, and lithium
nitrate (LiNO₃ × xH₂O)
from Alfa Aesar. Concentrated hydrochloric acid, methanol, dimethyl
sulfoxide (DMSO), and triphenyl phosphite were acquired from VWR.
Ethylene carbonate, propylene carbonate, and NMC622 were purchased
from BASF. Carbon black (Super C65) was obtained from Imerys Graphite
& Carbon and polyvinylidene difluoride (PVdF, Solef 5130) from
Solvay. Prior to use, calcium chloride was dried at 180 °C under
reduced pressure (10^–3 mbar) for 48 h.

Cesium carbonate (Cs₂CO₃, 99%) and lead(II) bromide (PbBr₂, 99.99%) were purchased
from Fluorochem. Propionic acid (PA, >99.5%) and tetrabutylammonium
bromide (TBAB, >98%) were purchased from Merck. Heptane (Hept,
Gpr
rectapur, 99.8%) and isopropanol (iPrOH, HiPerSolv chromanorm for
HPLC >98%) were purchased from VWR. Oleylamine (OAm, 80%–90%)
was purchased from Acros Organic. Isopropanol was dried over CaH₂ for a week and then distilled before use. All other chemicals
were used without any further purification and stored in a dryer.
Compositions of solvent mixtures are indicated as volume/volume ratios.
A turboemulsifier homogenizer was bought from IKA and is composed
of a motor group T25/T50 digital Ultra Turrax + dispersing tool with
codes S25N-25G and S50N-G45 M for volumes, respectively, up to 2 L
and above 2 L.

Drosophila cultures were reared at 24.5 ± 0.5 °C and 65% humidity on standard cornmeal/sugar/yeast media [6.94 g/L agar (Merck), 41.67 g/L sugar, 16.67 g/L yeast (Merck), 47.23 g/L corn flour, 0.278% propionic acid (Merck), 2.78 g/L nipagin (SDFCL)] under a constant 12 h light: 12 h dark cycle. Expression of human HTT exon 1 transgene containing CAG repeats of either 25Qs (wild-type) or 120Qs (mutant) was carried out by using the bipartite UAS-GAL4 expression system in transgenic Drosophila. These transgenes are inserted at the same chromosomal location^{61 (link)}. Transgenic stocks include w[*]; M{w[+m*] = UAS-HTTex1p Q25}ZH-51D, w[*]; M{w[+m*] = UAS-HTTex1p Q120}ZH-51D^{61 (link)}; kind gifts from J. Lawrence Marsh, UCI, Irvine, California) and fat body specific driver, collagen-GAL4 (Cg-GAL4). Virgins of UAS-HTTex1p Q25 and UAS-HTTex1p Q120 were mated with the males of Cg-GAL4 and the resulting progeny with 25Qs (Cg-GAL4 > UAS-HTTex1p Q25) represented control and with 120Qs (Cg-GAL4 > UAS-HTTex1p Q120) represented experimental flies.

Acetic acid (Carl Roth GmbH + Co. KG, Karlsruhe, Germany), propionic acid (Merck KGaA, Darmstadt, Germany), d/l-lactic acid (d/l: equal volume units, Carl Roth GmbH + Co. KG, Karlsruhe, Germany) and n-butyric acid (Sigma-Aldrich, Chemie GmbH, Darmstadt, Germany) were added to double concentrated Mueller Hinton 2 Broth. The pH was adjusted to pH 7.5 using 5 M sodium hydroxide (NaOH) (Carl Roth GmbH + Co. KG, Karlsruhe, Germany). The dilutions were sterile-filtered (0.2 µm) and the concentrations were confirmed by gas chromatography (Agilent 6890N, Agilent Technologies Deutschland GmbH, Waldbronn, Germany). Four different concentrations were prepared by 1:2 serial dilutions in Mueller Hinton 2 Broth (acetate, propionate, n-butyrate: 0, 18.75, 37.50, 75.00, 150.00 mM; lactate: 0, 13.75, 27.50, 55.00, 110.00 mM) and the exact concentrations obtained by gas chromatography. The impact on donor and recipient growth was studied prior to the conjugation experiment ). The control medium was nonsupplemented Mueller Hinton 2 Broth.

Drosophila melanogaster wild-type Canton-S line was obtained from the Drosophila Stock Center at Indiana University (Bloomington, IN, USA). To accelerate the aging, the flies were kept at a temperature of 29 °C, which is a common approach in Drosophila studies [162 (link)]. To maintain constant conditions, Binder KT 115 incubator (Binder, Tuttlingen, Germany) was used. Control end experimental flies were kept on food medium consisting of corn flour—92 g/L, dry yeast—32.1 g/L, agar-agar—5.2 g/L, glucose—136.9 g/L, 8 mL/L—10% solution of Nipagin (methyl 4-hydroxybenzoate, #H5501, Merck, Rahway, NJ, USA) in ethanol, and 5 mL/L of propionic acid (#49685, Merck, Rahway, NJ, USA).

All reagents, either analytical or HPLC grade, were purchased from Merck (Darmstadt, Germany). The phenol standards (3-hydroxytyrosol, 2-(4-hydroxyphenyl) ethanol (tyrosol), p-coumaric acid, vanillic acid, vanillin, luteolin, apigenin, pinoresinol, p-hydroxyphenylacetic acid (internal standard 1), o-coumaric acid (internal standard 2) oleuropein and caffeic acid), Trolox, fluorescein, and 2,2′-Azobis(2-amidinopropane) dihydrochloride (AAPH) were obtained from Sigma-Aldrich (St. Louis, MO, USA). Volatile standards 4-methyl-2-pentanol (internal standard), ethanol, ethyl propionate, 4-methyl-2 pentanone, butyl acetate, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-octanone, acetic acid, propionic acid, 1-octanol, butyric acid, heptanoic acid, nonanoic acid, (E)-2-hexenal, hexanal, hexanol, (E)-2-nonenal were purchased from Merck. Tocopherols standards were purchased from Calbiochem (Merck). All standards had a purity of 98% or higher.

Anisaldehyde was acquired from Roth (Karlsruhe Rheinhafen, Germany) while propionic acid and propionic anhydride were obtained from Merck (Darmstadt, Germany). Chloroauric acid tetrahydrate was purchased from Roth (Karlsruhe, Germany) while sodium citrate and THF were acquired from Merck (Darmstadt, Germany). The phosphate buffer (HI 70007 with pH = 7.01) was acquired from Hanna Instruments Inc. (Highland Industrial Park, Woonsocket, RI, USA).
The I₃⁻ complex anion was prepared by mixing solutions of potassium iodide and molecular iodine. Solutions with a known concentration of I₃⁻ were obtained by selecting the concentrations of I₂ and I⁻ to enable the shift to the right of the reaction (Equation (3)) [9 (link)].
The porphyrin base, 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin, was obtained in our laboratory by Adler method [46 (link)].