Recognition Of Isomers Research Articles

Screening of π-Basic Naphthalene and Anthracene Amplifiers for π-Acidic Synthetic Pore Sensors

Synthetic ion channels and pores attract current attention as multicomponent sensors in complex matrixes. This application requires the availability of reactive signal amplifiers that covalently capture analytes and drag them into the pore. pi-Basic 1,5-dialkoxynaphthalenes (1,5-DAN) are attractive amplifiers because aromatic electron donor-acceptor (AEDA) interactions account for their recognition within pi-acidic naphthalenediimide (NDI) rich synthetic pores. Focusing on amplifier design, we report here the synthesis of a complete collection of DAN and dialkoxyanthracene amplifiers, determine their oxidation potentials by cyclic voltammetry, and calculate their quadrupole moments. Blockage experiments reveal that subtle structural changes in regioisomeric DAN amplifiers can be registered within NDI pores. Frontier orbital overlap in AEDA complexes, oxidation potentials, and, to a lesser extent, quadrupole moments are shown to contribute to isomer recognition by synthetic pores. Particularly important with regard to practical applications of synthetic pores as multianalyte sensors, we further demonstrate that application of the lessons learned with DAN regioisomers to the expansion to dialkoxyanthracenes provides access to privileged amplifiers with submicromolar activity.

Langmuir–Blodgett films of azocrown ethers on electrodes — voltammetric recognition of isomers

Abstract Monolayers of amphiphilic derivatives of crown ethers bearing electroactive azo groups in the macrocycle were transferred from the air ∣ water interface onto indium–tin oxide (ITO) or thin mercury film electrodes (TMFE) using the Langmuir–Blodgett technique. Differences in the electrochemical reversibility of the systems observed on these two electrodes were explained by different orientation of the azocrown molecules on the hydrophobic (TMFE) and hydrophilic (ITO) electrode surfaces. The electrochemical studies of the monolayer modified electrodes proved that the organization of the monolayer and the redox properties of the azocrown molecules depend on the geometry around the NN moiety. Voltammetry allowed Z - and E -isomers of the azocrowns to be recognized and their isomerization processes in monolayers to be followed. The effects of pH and of the alkali metal cations on the stability of the isomers were studied. Isomerization to the more stable E -isomer was hindered in alkaline solutions and under these conditions well separated reduction peaks of the E - and Z -isomers were obtained.

Voltammetric Recognition of Cis (Z) and Trans (E) Isomers of Azobenzene and Azocrown Ethers

An electroanalytical approach allowing the recognition of isomers of azo compounds and the determination of their ratio in the solution is introduced. Adsorptive preaccumulation of the title compounds at the electrode surface retains on the electrode the ratio of isomers present in the solution. Voltammetric reduction of the adsorbed species allows recognition of the cis (Z) and trans (E) forms of the azo-crowns because their reduction potentials in alkaline solutions are different. In the region below pH 10 fast isomerization follows the first electron transfer, hence both forms appear to be reduced at the same potential. At pH>10 interactions of the large crown radical anion with alkali metal cations slow down the isomerization reaction at the electrode surface and a separate reduction peak for each isomer is seen on the voltammogram. The adsorptive voltammetric method provides a simple and useful way of monitoring the progress of isomerization reactions in the solution. Comparison of azobenzenes, azodibenzo- and azotribenzo-crown ethers revealed the largest stability of the latter against Z-to-E isomerization in aqueous solutions.

Computer graphics determination and display of stereoisomers in coordination compounds

An interactive computer program has been written to determine and display stereoisomers of coordination compounds, which include one trigonal bipyramid or one octahedral stereocenter, and up to six tetrahedral centers. Recognition of isomers is made via a stereodescriptor calculated by means of a naming algorithm.