## 3 Experimental Section
### Synthesis of Compounds
#### 3.2.2 \(d_{5}\)-Ethyl Dodecanoate  
This compound was prepared using the procedure described for \(d_{5}\)-ethyl nonanoate, using dodecanoyl chloride (1.85 mL, 8.29 mmol), \(d\)-ethanol (500 \(\mu\)L, 8.64 mmol), pyridine (614 \(\mu\)L, 7.6 mmol), and DMAP (105.6 mg, 864 \(\mu\)mol) in CH\({}_{2}\)Cl\({}_{2}\) (13 mL). Purification by column chromatography on silica (85% hexane/EtOAc, R\({}_{F}\) = 0.59) gave the title compound (1.85 g, 7.93 mmol, 96%) as a colourless oil, which was \(>\)99% pure (GC-MS). \({}^{1}\)H-NMR (MeOH-\(d_{4}\)) \(\delta\) 2.29 (2H, t, \(J\) = 7.6 Hz, Hz); 1.62 (2H, app q, \(J\) = 7.2 Hz, H\({}_{3}\)); 1.35-1.22 (16H, m, H\({}_{4}\)); 0.88 (3H, t, \(J\) = 7.0 Hz, H\({}_{12}\)); \({}^{13}\)C-NMR (MeOH-\(d_{4}\)) \(\delta\) 173.97 (C\({}_{1}\)); 59.39 (\(J\)C-D = 22.2 Hz, CD\({}_{2}\)); 58.88 (C\({}_{13}\)); 34.38 (C\({}_{2}\)); 31.88 (C\({}_{10}\)); 29.58 (C\({}_{4,5}\)); 29.44 (C\({}_{6}\)); 29.32 (C\({}_{7}\)); 29.25 (Cs); 29.13 (C\({}_{9}\)); 24.97 (C\({}_{3}\)); 22.67 (C\({}_{11}\)); 14.11 (C\({}_{12}\)); 13.31 (C\({}_{14}\)); 13.2 (\(J\)C-D = 19.5 Hz, CD\({}_{3}\)). ESI-HRMS (_m/z_): Calc led for C\({}_{4}\)H\({}_{24}\)D\({}_{5}\)O\({}_{2}\)\({}^{+}\) ([M+H]\({}^{+}\)), 234.2467; found, 234.2476. EI-MS (_m/z_) (%) 233 (M\({}^{+}\), 6), 204 (5), 190 (12), 183 (12), 162 (15), 148 (8), 120 (5), 106 (52), 98 (5), 94 (12), 93 (100), 84 (6), 83 (5), 74 (24), 69 (7), 63 (6), 61 (11), 57 (10), 55 (16), 43 (16), 41 (16), 34 (6), 32 (9), 29 (6), 28 (33). 2.3 (2\(R\)/s)-3-Carboxy-2-(nonanoyl)-\(N\),\(N\),\(N\)-trimethylpropan-1-aminium (\(N\)-Nonanoyl carnitine)  
Carnitine derivatives were prepared based on the method of [PERSON] and [PERSON] [44]. To a stirred solution of trifluoroacetic acid (TFA) (500 \(\mu\)L) at room temperature containing (\(\pm\))-carnitine chloride (1.00 g, 5 mmol) was added dropwise nonanoyl chloride (1.77 g, 10 mmol), at which time a white precipitate formed. The reaction was maintained at 50 \({}^{\circ}\)C with stirring overnight. After cooling to room temperature, acetone (5.5 mL) was added, stirring was maintained for 1 hour and the precipitate that formed was removed via centrifugation. Diethyl ether (\(\sim\)3 mL) was added dropwise to incipient cloudiness, followed by cooling to 0 \({}^{\circ}\)C. Additional Et\({}_{2}\)O (10 mL) was added once crystallisation was well underway. Once crystallisation was complete, centrifugation and resuspension in Et\({}_{2}\)O (40 mL) was used to wash the crystals (repeated two more times), followed by isolation and drying. Purification by recrystallisation in MeOH/Et\({}_{2}\)O produced the known [45] title compound (1.16 g, 3.43 mmol, 69%) as a white crystalline solid, which was \(>\)99% pure (HPLC-MS), mp 155.2-157.7 \({}^{\circ}\)C. \({}^{1}\)H-NMR (MeOH-\(d_{4}\)) \(\delta\) 5.63 (1H, app q, \(J\) = 6.9 Hz); 4.92 (1H, bs); 3.49 (1H, dd, \(J\) = 14.4, 8.6 Hz); 3.75 (1H, dd, \(J\) = 14.4, 0.90 Hz); 3.23 (9H, s); 2.79-2.76 (2H, m); 2.39 (2H, m); 1.63 (2H, q, \(J\) = 7.35 Hz); 1.38-1.25 (10H, m); 0.90 (3H, t, \(J\) = 7.1 Hz). \({}^{13}\)C-NMR (MeOH-\(d_{4}\)) \(\delta\) 174.27, 172.54, 69.50, 66.35, 54.68, 37.93, 35.22, 33.11, 30.50, 30.39, 30.31, 25.83, 23.84, 14.60. 2.4 (2\(R\)/s)-3-Carboxy-2-(dodecanoyloxy)-\(N\),\(N\),\(N\)-trimethylpropan-1-aminium (\(N\)-Dodecanoyl carnitine)  
Using the same reaction and isolation procedure as that for \(N\)-nonanoyl carnitine above, \(N\)-dodecanoyl carnitine was prepared using (\(\pm\))-carnitine chloride (1.00 g, 5 mmol) and dodecanoyl chloride (2.19 g, 10 mmol) in (TFA) (500 \(\mu\)L). Purification by recrystallisation in MeOH/Et\({}_{2}\)O produced the known [45] title compound (1.32 g, 3.47 mmol, 69%) as a white crystalline solid, which was 93% pure (HPLC-MS), mp 167.5-175.3 \({}^{\circ}\)C. \({}^{1}\)H-NMR (MeOH-\(d_{4}\)) \(\delta\) 5.63 (1H, app q, \(J\) = 6.9 Hz); 3.89 (1H,dd, \(J\) = 14.3, 8.6 Hz); 3.74 (1H, d, \(J\) = 14.3 Hz); 3.22 (9H, s); 2.79-2.76 (2H, m); 2.39 (2H, app t, \(J\) = 7.5 Hz); 1.63 (2H, q, \(J\) = 7.3 Hz); 1.37-1.24 (16H, m); 0.90 (3H, t, \(J\) = 7.0 Hz).