Transduction of selective recognition by preorganized ionophores, K+ selectivity of the different 1,3-diethoxycalix[4]arene crown ether conformers

Three different conformers of 1,3-diethoxy-p-tert-butylcalix[4]arene crown ethers have been used to study the effect of the ionophore preorganization on the potentiometric K+-selectivity. Selectivities were measured for chemically modified field effect transistors (CHEMFETs) and membrane ion-selective electrodes (ISEs) by two different methods. The ionophores show decreasing K+/Na+ selectivities in the order: partial cone > 1.3-alternate > cone. As a function of time the cone conformer maintained a constant selectivity whereas a continuous decrease of the selectivity values was observed for the other two conformers. This supports our prediction based on the association constants and our previous 1H NMR studies on conformational stability. \u

ChemInform Abstract: “tert-Amino Effect” in Heterocyclic Synthesis. The Effect of a p-Quinone Moiety on the (1,6)H-Transfer and 1,5-Electrocyclization Reactions.

(Dialkylamino)benzoquinone 15 and (dialkylamino)naphthoquinones 32 and 34-37 undergo a thermal cyclization to the corresponding pyrrolo[1,2-a]indoles 41, 43, and 45-47 and to the pyrido[1,2-a]indole 44, respectively. A corresponding hydroquinone, viz. (E/Z)-2,5-dimethoxy-α-(phenylmethylene)-3,6-di(1-pyrrolidinyl)benzene- acetonitrile (18), cyclizes only slowly to pyrrolo[1,2-a]indole 42. The naphthohydroquinones 38-40 do not undergo a thermal rearrangement. The results demonstrate the accelerating effect of the quinone function on the rate of the reaction, as a result of stabilization of the “negative end” of the intermediate 1,5-dipole. The presence of an electron-donating group at the β-carbon atom of the vinyl moiety lowers the rate of the reaction. Moreover, this influence is demonstrated by oxidation of one of the sulfur atoms in 35 to the ketene dithioacetal S-monooxide 36, which undergoes a fast thermal isomerization to 47. Cyclization of the pyrrolidinylnaphthoquinones 32, 34, and 35 yielded exclusively products in which H-11a and CN have a trans relationship, while in the case of piperidinylnaphthoquinone 37 predominantly trans-1H-benzo[f]pyrido[1,2-a]indole 44a was formed. The trans stereochemistry of 43 was determined by single-crystal X-ray analysis. Heating of (dialkylamino)naphthoquinone 33 afforded the indoline 50 in low yield.</p

Self-assembled monolayers of heptapodant ß-cyclodextrins on gold

A route was developed for the synthesis of three different cyclodextrin adsorbates: heptakis{6-O-[3-(thiomethyl)propionyl)]-2,3-di-O-methyl}-ß\ud -cyclodextrin, heptakis{6-O-[12-(thiododecyl)dodecanoyl)]-2,3-di-O-methyl}-ß\ud -cyclodextrin (a short and long alkyl chain sulfide cyclodextrin adsorbate, respectively), and heptakis[6-deoxy-6-(3-mercaptopropionamidyl)-2,3-di-O-methyl]-ß-cyclodextrin (a short alkyl chain thiol adsorbate). Self-assembled monolayers on gold of these three cyclodextrin adsorbates with seven sulfur moieties were fully characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The electrochemical capacitance measurements show the differences between the thicknesses of the ß-cyclodextrin monolayers, and the XPS-(S2p) measurements show the different effectivenesses of the sulfur moieties of the three monolayers in their binding to the gold surface. Sulfide-based -cyclodextrin monolayers use on average 4.5 of the 7 attachment points whereas the thiol-based cyclodextrin monolayer only uses 3.2 of the 7 sulfurs. These experiments show that, for adsorbates with multiple attachment points, sulfides may be more effective than thiols. TOF-SIMS measurements confirm the robust attachment of these adsorbates on gold obtained by XPS

Host-guest interactions at self-assembled monolayers of cyclodextrins on gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of α-, β-, and γ-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electrochemistry and wettability studies. On average about 70 % of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for β-cyclodextrin monolayers a quasihexagonal lattice with a lattice constant of 20.6 Å, which matches the geometrical size of the adsorbate. The α-cyclodextrin and γ-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1, 8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2, 6-TNS) and the highly ordered monolayers of heptapodant β-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a -cyclodextrin monolayer and 1, 8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (≤5 µM). The association constant for the binding of 1, 8-ANS (K=289 000±13 000 M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the β-cyclodextrin strongly decreases the binding