title: Active transport of amino acids by a guanidiniocarbonyl-pyrrole receptor.
abstract: Herein we report the synthesis and characterization of a transporter 9 for N-acetylated amino acids. Transporter 9 is a conjugate of a guanidiniocarbonyl pyrrole cation, one of the most efficient carboxylate binding motifs reported so far, and a hydrophobic tris(dodecylbenzyl) group, which ensures solubility in organic solvents. In its protonated form, 9 binds N-acetylated amino acid carboxylates in wet organic solvents with association constants in the range of 10(4) M(-1) as estimated by extraction experiments. Aromatic amino acids are preferred due to additional cation-pi-interactions of the amino acid side chain with the guanidiniocarbonyl pyrrole moiety. U-tube experiments established efficient transport across a bulk liquid chloroform phase with fluxes approaching 10(-6) mol m(-2) s(-1). In experiments with single substrates, the release rate of the amino acid from the receptor-substrate complex at the interface with the receiving phase is rate determining. In contrast to this, in competition experiments with several substrates, the thermodynamic affinity to 9 becomes decisive. As 9 can only transport anions in its protonated form and has a pK(a) value of approximately 7, pH-driven active transport of amino acids is also possible. Transport occurs as a symport of the amino acid carboxylate and a proton.
authors.affiliation: Universität Duisburg-Essen, Institut für Organische Chemie, Universitätsstrasse 7, 45141 Essen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Urban
authors.forename: Carsten
authors.initials: C
authors.lastname: Schmuck
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D000838:Anions / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D001693:Biological Transport, Active / Q000502:physiology*; D002412:Cations / Q000737:chemistry / Q000378:metabolism*; D019791:Guanidine / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D011758:Pyrroles / Q000737:chemistry / Q000378:metabolism*; D012997:Solvents / Q000737:chemistry
chemical_list: D000596:Amino Acids; D000838:Anions; D002412:Cations; D011758:Pyrroles; D012997:Solvents; D019791:Guanidine