RESUMO
Deprotonation of the methyl-ene group in bis-(3,5-diiso-propyl-pyrazol-1-yl)methane with nBuLi and reaction with carbon dioxide yields lithium bis-(3,5-diiso-propyl-pyrazol-1-yl)acetate (1). Treatment of 1 with ZnCl2 results in the com-pound bis-[bis-(3,5-diiso-propyl-pyrazol-1-yl)acetato]-zinc(II), [Zn(C20H31N4O2)2] (2), whose structure has monoclinic (P21/c) symmetry. The ZnII ion resides on an inversion center and is coordinated by two bis-(3,5-diiso-propyl-pyrazol-1-yl)acetate (bdippza) ligands. Each ligand facially coordinates the zinc center via κ3N,N',O coordination modes to form a distorted octa-hedral complex with four pyrazole N atoms in the basal plane and two carboxyl-ate O atoms in the axial sites.
RESUMO
Here we report a general method for engineering three-way junction DNA aptamers into split aptamers. Split aptamers show significant potential for use as recognition elements in biosensing applications, but reliable methods for generating these sequences are currently lacking. We hypothesize that the three-way junction is a "privileged architecture" for the elaboration of aptamers into split aptamers, as it provides two potential splitting sites that are distal from the target binding pocket. We propose a general method for split aptamer engineering that involves removing one loop region, then systematically modifying the number of base pairs in the remaining stem regions in order to achieve selective assembly only in the presence of the target small molecule. We screen putative split aptamer sequence pairs using split aptamer proximity ligation (StAPL) technology developed by our laboratory, but we validate that the results obtained using StAPL translate directly to systems in which the aptamer fragments are assembling noncovalently. We introduce four new split aptamer sequences, which triples the number of small-molecule-binding DNA split aptamers reported to date, and the methods described herein provide a reliable route for the engineering of additional split aptamers, dramatically advancing the potential substrate scope of DNA assembly based biosensors.
Assuntos
Aptâmeros de Nucleotídeos/metabolismo , Técnica de Seleção de Aptâmeros/métodos , Aptâmeros de Nucleotídeos/genética , Sequência de Bases , Ligantes , Esteroides/metabolismoRESUMO
Here we describe the first example of selective reductive amination in biological fluids using split aptamer proximity ligation (StAPL). Utilizing the cocaine split aptamer, we demonstrate small-molecule-dependent ligation that is dose-dependent over a wide range of target concentrations in buffer, human blood serum and artificial urine medium. We explore the substrate binding preferences of the split aptamer and find that the cinchona alkaloids quinine and quinidine bind to the aptamer with higher affinity than cocaine. This increased affinity leads to improved detection limits for these small-molecule targets. We also demonstrate that linker length and hydrophobicity impact the efficiency of split aptamer ligation. The ability to carry out selective chemical transformations using non-bioorthogonal chemistry in media where competing reactive groups are present highlights the power of the increased effective molarity provided by DNA assembly. Obviating the need for bioorthogonal chemistry would dramatically expand the repertoire of chemical transformations available for use in templated reactions such as proximity ligation assays, in turn enabling the development of novel methods for biomolecule detection.