Surprisingly, 2,4,6-THB was transported at comparable rates to the 2,4-DHB and 4-HB analogues (Figure ). These results reveal that the distribution of the -OH groups might be more decisive than the number of -OH groups in the transport of small aromatic carboxylates. However, it is important to note that higher number of -OH groups in carboxylates could increase their polarity and, therefore, hinder their transport, as observed in multi-substituted aliphatic carboxylates, such as D-glucuronate and gluconate (Figure ). We hypothesise that the differences in transporting DHB isomers are caused by the formation of interand intramolecular interactions that may occur between the anion and the surrounding media, lipids, and transporter. To shed some light on this, we analysed the H-bonds present in the crystalline arrangement of 2,5-dihydroxybenzoic acid (2,5-DHBA), 2,4-dihydroxybenzoic acid (2,4-DHBA), 3,4dihydroxybenzoic acid (3,4-DHBA), 34 and 3,5-dihydroxybenzoic acid (3,5-DHBA) (Figure and Figure ). The crystal structure of 2,6-dihydroxybenzoic acid (2,6-DHBA) has not been reported. We compared the number of inter-and intramolecular H-bond interactions in each molecule and found that 2,5-DHBA and 2,4-DHBA have a crystalline arrangement where the ortho-hydroxyl participates in a strong intramolecular interaction with the RCOO -group and does not interact significantly with neighbour molecules. In contrast, 3,4-DHBA and 3,5-DHBA have hydroxyl groups in a position that facilitates the formation of three and four hydrogen bonds, respectively. As a result, we hypothesise that -OH groups in DHB isomers could form similar inter-and intramolecular interactions to their DHBA analogues. Consequently, the higher number of H-bonds observed in 3,4-DHB and 3,5-DHB could disfavour the transport of these carboxylates.