Chirality sensing with pores: Reactive signal amplifiers for otherwise undetectable small molecules

Abstract

Recently, we have introduced a concept to determine enantiomeric excess (ee) with synthetic multifunctional pores (Tanaka and Matile, Chirality 2008;20:307-312). The reported approach is, however, limited to macromolecules and not applicable to small molecules. The problem is that the ability of synthetic pores to respond to chemical stimulation decreases with the size and the charge of the analyte. Here we demonstrate that this problem can be overcome with reactive signal amplifiers that covalently capture elusive analytes for sensitive recognition by the pore. For proof of principle, we use L-lactate and D-lactate as representative pair of enantiomers, L-lactate oxidase as stereospecific signal generator, and cascade blue hydrazide as reactive signal amplifier to capture the produced pyruvate. After stereospecific signal generation and reactive signal amplification, L-lactate was detectable quantitatively and without further optimization in the presence of at least 99% ee of D-lactate. Attempts to sense the traces of impurity in commercial samples of D-lactate gave values in the expected range (99.6% ee expected, 99.3 +/- 0.1% ee found).

Sensing applications of synthetic transport systems

“…Studies with mixtures of L-and D-lactate demonstrated detectability of enantiopurities up to at least 99.6% ee. 16 This high sensitivity was in agreement with earlier results concerning the detection of extreme ee's up to 99.9975% with synthetic transport systems. 11 These results were obtained for protein biosensing a Enzymes confirmed as operational signal generators.…”

“…45 Lactate sensing was realized with lactate oxidase as a signal generator, catalase for peroxide removal, hydrazide 50 as a signal amplifier and b-barrel pore 52 (2,4 = K,H) or polyguanidino-oxanorbornene transporters as signal transducers (Table 1, entry 16). 10,15,16 In excellent agreement with the literature, concentrations from 54 to 72 mM were determined in sour milk. 10,15 The stereoselectivity of the enzymatic signal generator provided access to chirality sensing with synthetic transport system 52 (2,4 = K,H) and amplifier 50.…”

“…This account summarizes the development of sensors that operate with synthetic transport systems comprehensively, covering 18 original papers published over one decade. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Since the beginning, more than three decades ago, the field of synthetic transport systems, particularly ion channels and pores that act in lipid bilayer membranes, has reached remarkable maturity. Most classical motifs of supramolecular chemistry can be found in many elegant variations, including cyclodextrins, calixarenes, calixpyrroles, crown ethers, G quartets, peptidomimetics, steroids, particularly cholates, porphyrins, organometallic architectures, and so on.…”

Recent synthetic transport systems

“…1,2 Progress made during the current period concerns modifications of staves, 131 termini 132 and internal active sites 133,134 as well as covalent capture approaches for signal amplification in sensing applications. [135][136][137][138][139][140][141] As far as the stave are concerned, replacement of the 1 3 ,2 3 ,3 2 ,4 3 ,5 2 ,6 3 ,7 2 ,8 3 -pattern in 220 with a regioisomeric 1 2 ,2 2 ,3 3 ,4 2 ,5 3 ,6 2 ,7 3 ,8 2 -motif in 221 did not disturb the formation of multifunctional b-barrel pores. 131 Attachment of tetralysine (K 4 ) tails in 222 improved pore delivery to the membrane.…”

“…137 Enantiomer discrimination was explored for a-helices and lactate with pore 219 and the aid of proteases and lactate oxidase as enantioselective signal generators. 138,139 Signal amplification of analytes other than ketones or aldehydes was exemplified with the reaction of hydrazides such as 241 with aldehydes 246-249. 140 Inactivation of pore 223 with the resulting boronic acids could be reversed by covalent capture of catechols such as catechin 250 or epigallocatechin gallate.…”