Dl 2 aminobutyric acid

d-2-aminobutyric acid, d-norvaline, d-norleucine, l-2-aminoheptanoic acid, d-2-amino-octanoic acid, l-2-aminooctanoic acid, d-methionine, dl-2-aminobutyric acid, dl-norvaline, dl-norleucine, dl-2-aminoheptanoic acid, dl-2-amino-octanoic acid and dl-methionine were purchased from Sigma–Aldrich and used without further purification. The racemic amino acids mentioned here were recrystallized by solvent evaporation of an aqueous solution or hanging drop crystallisation as described by Smets et al. (2015 ▸ ), and subsequently measured using DSC. Liquid-assisted grinding was performed on a Retsch Mixer Mill MM 400 at 30 Hz to form co-crystals for the following quasi-racemates in a 1:1 molar ratio (100 mg in total); d-Abu:l-Nva, d-Abu:l-Hep, d-Nva:l-Hep, d-Nle:l-Hep, d-Met:l-Hep, d-Oct:l-Hep, d-Abu:l-Oct, d-Nva:l-Oct, d-Nle:l-Oct and d-Met:l-Oct. The samples were ground in a 2.0 ml Eppendorf SafeLock microcentrifuge tube with a 0.9 mm ball for 25 min using 10 µl ethanol, and a second time for 25 min after adding another 10 µl ethanol, and subsequently measured using DSC.

The following reagents were purchased from Sigma (St. Louis, USA): trifluoroacetic acid (TFA, HPLC grade), acetonitrile (HPLC grade), 12 N hydrochloric acid (HCL), naphthalene-2,3-dicarboxyaldehyde (NDA), potassium cyanide (KCN), potassium hydroxide (KOH), dl-2-aminobutyric acid (internal standard for the amino acid analysis), amino acid standards, boric acid, methanol (HPLC grade), 3-[4-(bromomethyl)phenyl]-7-(diethylamino)coumarin (MPAC-Br), 18-crown-6 ether, potassium bicarbonate (KHCO₃), tris(hydroxymethyl)aminomethane (TRIS), acetic acid, n-hexane, fatty acid standards including octanoic acid (C8:0), decanoic acid (C10:0), dodecanoic acid (C12:0), tridecanoic acid (C13:0 – internal standard for the fatty acid analysis), myristic acid (C14:0), palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) linoleic acid (C18:2), linolenic acid (C18:3), arachidic acid (C20:0) and erucic acid (C22:1). The enzyme Lipozyme TL IM was kindly provided by Novozymes Latin America (Araucária, PR, Brazil). Cellulose cartridges 33 × 80 mm from the Unifil brand (Brazil) were purchased from LAS (Porto Alegre, Brazil).