Molecular recognition of organic compounds by the data on polymorphic and pseudo-polymorphic transformations of tert-butylthiacalix[4]arene derivative

The receptor properties of metastable polymorphic forms of 5,11,17,23-tetra(tert-butyl)-25,26,27,28-tetrakis[N-(2-ethoxycarbonyl(methyl)carbamoylmethoxy]-2,8,14,20-tetrathiacalix[4]arene in the cone and partial cone configurations obtained by the crystallization of their solutions in an organic solvent were studied. The ability of the studied calixarenes to “remember” the history of interaction with individual vaporous organic guests and their mixtures was discovered. The observed different effects of methanol and ethanol vapors on the phase state of the studied calixarene in the cone configuration can be used for qualitative and quantitative analyses of ethanol in binary mixtures. Calixarene in the partial cone configuration can remember the earlier bound methanol. The “memory” effect appears as a specific polymorphic transition in the receptor phase after bound methanol leaving on heating the clathrate. This effect is not observed for other studied guests.     

Thermal analysis of charge-transfer complex formed by nitrogen dioxide and substituted calix[4]arene

Simultaneous thermal analysis with evolved gas analysis (STA-EGA) was used to study the ability of 1,3-alternate conformer of tert-butylcalix[4]arene with four n-propoxy substituents (1) to be applied for detection of nitrogen dioxide in reversible sensors. Solid calixarene 1 forms an intensively colored charge-transfer complex (CTC) with gaseous NO₂/N₂O₄. Using the STA-EGA method, the nature and conditions of CTC bleaching were characterized, including the conditions of its reversible change of color from white to dark blue and back at CTC formation and decomposition. For this, the thermal stability of CTC and its regeneration products were studied. This, together with the ion thermograms for evolved gases, gives the information on the oxidation of 1 by nitrogen dioxide if present.     

Electrochemical Acetylcholinesterase Biosensor Based on Polylactide–Nanosilver Composite for the Determination of Anti-dementia Drugs

A new acetylcholinesterase biosensor has been developed for the determination of anticholinesterase drugs applied for neurodegenerative disease treatment. For this purpose, silver nanosendrites were deposited by potentiostatic electrolysis on a glassy carbon electrode covered with oligolactides cross-linked with p-tert-butylthiacliax[4]arene core in the cone, partial cone, and 1,3-alternate configurations. The roles of macrocycle configuration and electrolysis conditions on the silver depostion were characterized and optimal conditions selected for the subsequent immobilization of acetylcholinesterase. Silver nanoparticles provide higher response at low working potential (0.05?V) due to the electrostatic accumulation of silver ions and prevention of their leaching after reoxidation. The biosensor allows the determination of 10^?12 – 10^?7 M donepezil, berberine, and huperzine A within 20-30?s by the relative decay of the current related to the oxidation of thiocholine formed in enzymatic reaction. The reversible inhibition of immobilized acetylcholinesterase with huperzine A was quantified for the first time. The developed biosensor was employed for the analysis of spiked urine samples.     

Structure-property relationship for clathrates formed in systems with guest vapor and 1,3-disubstituted <Emphasis Type="Italic">tert</Emphasis>-butylcalix[4]arene

Structure-property relationship was studied for a series of clathrates formed in the systems that model guest-host interactions on the surface of chemical odor sensors of quartz microbalance type. The clathrates of 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis(2-naphthylmethoxy)calix[4]arene (1) obtained by the saturation of its powder with gaseous organic compounds (guests) with the unity thermodynamic activity at 298 K were studied. The stoichiometry and temperature at the starting and ending points of thermal dissociation were determined for all the clathrates and stable intermediates by thermal gravimetric analysis. A sorption isotherm was determined for one guest-host combination; it indicates the formation of a stable clathrate in the system and phase transition of host upon reacting with guest. Decrease in thermal stability of the clathrates of 1 with guests of greater size was observed for studied pairs of homologous guests.     

Guest exchange in dimeric capsules of a tetraurea calix[4]arene in the solid state

A solid powder of hydrogen bonded dimers of a tetraurea calix[4]arene is able to exchange the encapsulated guest in contact with the vapor of a second guest. The molecules of a guest-free powder obtained from a polar solvent cannot rearrange in the solid phase to form new guest-filled capsules under these conditions.     

Metastable tert-butylcalix[6]arene with unusually large tunable free volume for non-threshold enclathration of volatiles

A metastable material with tunable free volume of molecular size, vapor sorption properties of a porous sorbent and variable thermal stability was prepared from tert-butylcalix[6]arene.     

Molecular recognition of chloroform by divergent polymorphic transitions in tert-butylthiacalix[4]arene tetrasubstituted with N-(2-hydroxyethyl)carbamoylmethoxy groups in a lower rim

The genuine molecular recognition of chloroform by a tert-butylthiacalix[4]arene derivative was observed, where the host remembers the guest above its elimination point showing two polymorphic transitions with opposite heat effects.