Valery V. Gorbatchuk

Molecular recognition of organic vapors by adamantylcalix[4]arene in QCM sensor using partial binding reversibility.

The parameters of stability, guest binding reversibility, and Gibbs energy of guest inclusion were determined for clathrates of adamantylcalix[4]arene (1). These data provide a new insight into the structure-property relationships in vapor sensor applications of clathrate-forming hosts. A thin layer of 1, used in the quartz microbalance (QCM) sensor, demonstrates a selectivity for organic vapors, which depends on the regeneration technique after the guest binding. Complete regeneration of 1 on the sensor surface was reached through the exchange of bound guest with ethanol vapor, which forms an unstable clathrate with 1. The efficiency of the used regeneration technique was proved by comparing the QCM data with the isotherms of guest vapor sorption by guest-free host 1 and with the data of simultaneous thermogravimetry and differential scanning calorimetry for the saturated clathrates of 1. In sensor, the extent of host regeneration without guest exchange depends on the guest molecular structure. This extent, or guest-binding reversibility parameter, being determined in a combination with the sensor responses of completely regenerated 1 to guest vapors, increases the recognition capability of single sensor device. Using this technique, 13 of 15 studied guests were discriminated. The structural hints on the suitable sensor properties of 1 were found in the determined X-ray monocrystal data for clathrate of this host with toluene.

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.

Unusually high selectivity of guest exchange in tert-butylthiacalix[4]arene clathrate producing more thermostable inclusion and memory of guest.

New properties, earlier unknown for calixarenes, were found for tert-butylthiacalix[4]arene (1) clathrate with 1,2-dichloroethane (DCE). Guest exchange in 1·1.90DCE for vapors of some organic compounds gives clathrates, which are more thermostable at 34-59 °C than those prepared by direct saturation of guest-free 1 with pure guests. Besides, guest exchange may produce clathrates that cannot be formed by direct saturation in binary host-guest systems. Some compounds, like water, toluene, and trichloroethylene, expel DCE from its clathrate with 1 but are not included above the trace level. Residual contents of DCE in clathrate may be controlled by variation of water and 1·1.90DCE ratio in the studied system. Host 1 can remember methanol after its elimination from the guest exchange product. This memory can be read as an exoeffect by differential scanning calorimetry. Only methanol and only after guest exchange is remembered giving an example of a genuine molecular recognition.

The effect of substrate and air humidity on morphology of films of L-leucyl-L-leucine dipeptide

The effect of a substrate and air humidity on the morphology of a thin film of L-leucyl-L-leucine dipeptide was studied. For this purpose, conditions for obtaining a thin film of the dipeptide were determined by thermal analysis. The morphology of L-leucyl-L-leucine film deposited on the surface of highly oriented pyrolytic graphite (HOPG) and mica at different humidities was studied by atomic force microscopy. It was established that film was formed on the surface of HOPG and uniformly coated with nanostructures, the sizes and shapes of which depended on the film thickness. Crystallization of the dipeptide with the formation of complex crystalline nanosized objects occurs on the surface of mica. An increase in air humidity results in a decrease in the geometric dimensions of nanostructures on the surface of the dipeptide film in the case of HOPG and complication of crystal agglomerate structure when mica was used as a substrate.

Interaction of l‐leucyl‐l‐leucyl‐l‐leucine thin film with water and organic vapors: receptor properties and related morphology

The ability of highly ordered tripeptide structures to keep or change their morphology in contact with organic vapors was studied. A thin film of tripeptide l‐leucyl‐l‐leucyl‐l‐leucine (LLL) was prepared having microcrystals and nanocrystals on its surface, which are stable upon vacuum drying but become objects of selective morphology change after a contact with vapors of organic solvents. Fine separate LLL crystals and their agglomerates of submicron and larger dimensions were observed by atomic force microscopy and scanning electron microscopy. After saturation with guest vapors, these crystals can remain intact or change their morphology with the increase in size or complete destruction depending on the guest molecular structure. The crystals completely lose their shape after the binding of pyridine vapors. The other studied guests produce much smaller transformations or have no effect on crystal morphology despite being sorbed by solid LLL, which was shown using quartz crystal microbalance sensor. The observed size‐exclusion effect for guest sorption by LLL was found to be broken by the same guests that can change the initial crystal shape. This helps to explain the morphology changes of LLL crystals after the guest sorption and release. Copyright

Specific vapor sorption properties of phosphorus-containing dendrimers.

Specific combination of guest sorption properties was observed for phosphorus-containing dendrimers, which distinguish them from ordinary polymers and clathrate-forming hosts. The sorption capacity for 30 volatile guests, binding reversibility, guest desorption kinetics and guest exchange, glass transition behavior and ability to be plasticized with guest were studied for phosphorus dendrimers of different generations (G(1)-G(4) and G(9)) using quartz crystal microbalance sensor, FTIR microspectroscopy, atomic force microscopy, simultaneous thermogravimetry and differential scanning calorimetry combined with mass-spectrometry of evolved vapors. The dendrimers were found to have a different selectivity for different homological series of guests, high glass transition points without plasticization with guest even at high temperatures and saturation levels, moderate guest-binding irreversibility and ability both for effective guest exchange and independent guest sorption. These properties constitute an advantage of the studied dendrimers as receptor materials in various applications.

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.

Unusually High Efficiency of β-Cyclodextrin Clathrate Preparation by Water-Free Solid-Phase Guest Exchange

An effective preparation procedure is offered for β-cyclodextrin (bCD) clathrates with volatile guests of moderate hydrophilicity, which otherwise require a finely tuned optimization of the bCD/water/guest ratio. The proposed procedure includes guest exchange in a water-free bCD matrix. As a result, more stable clathrates with a higher inclusion capacity can be prepared than by direct saturation of dried or hydrated bCD. To find an optimal preparation method, the structure-property relationships were studied for four different ways of bCD clathrate formation with guests of varying molecular structure. The study was much simplified by used procedures excluding direct contact of guest and water liquids with bCD. Besides, in clathrate preparation experiments, the thermodynamic activities of water and guest were varied independently, which makes explicit the role of water in this process. Hydration of bCD reduces its inclusion threshold for hydrophobic guests by their activity (relative vapor pressure), giving favorable hydration effect for their inclusion. Besides, water competes with hydrophilic guests for binding sites in bCD at high water activities. Together with bCD dehydration by excess of hydrophilic guests, these observations give a complete thermodynamic picture, which may be fruitful for elaboration of guest encapsulation techniques by cyclodextrins.

Molecular recognition of organic guest vapor by solid adamantylcalix[4]arene

A series of inclusion compounds prepared by saturation of the solid adamantyl[4]calixarene (host 1) with vaporous organic guests at 298 K was studied by thermal gravimetry and static headspace GC analyses. The sorption isotherms of guests by host 1, the stoichiometry of the guest—host inclusion compounds, and the Gibbs energies of their formation were determined. The data obtained give evidence of the molecular recognition of the guest shape by host 1. Hence, compound 1 can be used in sensors for recognizing volatile organic compounds with no strong hydrogen or donor-acceptor bonds involved.

Thermodynamic comparison of molecular recognition of vaporous guests by solid calixarene and diol hosts

Molecular recognition of vaporous guests by the solid hosts 2,2′-bis(9-hydroxyfluoren-9-yl)biphenyl (1) and tert-butylcalix[4]arene (2) was studied. For this purpose the vapour sorption isotherms of 15 organic compounds with various molecular size and group composition with the solid hosts 1 and 2 were determined by static gas chromatographic headspace analysis. Most of the isotherms obtained show a definite inclusion threshold at a specific guest activity and a saturation part corresponding to the formation of stoichiometric supramolecular compounds. The stoichiometry of the host–guest compounds and free energies of their formation based on different standard states were determined. The free energy of guest transfer from the standard state of an infinitely dilute guest solution in toluene to the solid inclusion compound was assumed to be a molecular recognition parameter in the systems studied. For host 1 this transfer free energy exhibits a reasonably good 2-parameter correlation with guest molar refraction and free energy of H-bonding between guest and alcohols. Bad correlation was obtained for solid host 2. The effect of the guest structural parameters on molecular recognition by hosts 1 and 2 is discussed in terms of the different size of potential cavities in the host crystals and different ability of the hosts to H-bond with guests.