Tarmo Tamm

QSPR Studies on Vapor Pressure, Aqueous Solubility, and the Prediction of Water−Air Partition Coefficients

The vapor pressures and the aqueous solubilities of 411 compounds with a large structural diversity were investigated using a quantitative structure−property relationship (QSPR) approach. A five-descriptor equation with the squared correlation coefficient (R2) of 0.949 for vapor pressure and a six-descriptor equation with R2 of 0.879 for aqueous solubility were obtained. All descriptors were derived solely from the chemical structure of the compounds. The QSPR correlation equations for vapor pressure and aqueous solubility allow the reliable prediction of water−air partition coefficients.

In search of better electroactive polymer actuator materials: PPy versus PEDOT versus PEDOT–PPy composites

A comparative study of metal-free air-operated polypyrrole and PEDOT based trilayer actuators is presented. Actuators made of both pure and combined conducting polymers are considered. Trilayer bending actuators, synthesized in similar conditions, are characterized in terms of the structure, electrochemical and electro-chemo-mechanical properties. The characterization was carried out using two popular electrolytes: LiTFSI in propylene carbonate and a room-temperature ionic liquid EMIm TFSI. The results reveal that structure and actuation properties of the synthesized actuators depend on both the polymer chosen for the chemically synthesized electrode layer as well as the electrochemically synthesized working layer.

QSPR Treatment of Solvent Scales

The results of the quantitative structure−property relationship (QSPR) analysis of 45 different solvent scales and 350 solvents using the CODESSA program are presented. The QSPR models for each of the scales are constructed using only theoretical descriptors. The high quality of the models (32 of the 45 give R2 > 0.90, only two have R2 < 0.82) enables direct calculation of predicted values for any scale for any previously unmeasured solvent. The descriptors involved are shown to be in good agreement with the physical concepts invoked by the original authors of the scales.

Ionic electroactive polymer artificial muscles in space applications

A large-scale effort was carried out to test the performance of seven types of ionic electroactive polymer (IEAP) actuators in space-hazardous environmental factors in laboratory conditions. The results substantiate that the IEAP materials are tolerant to long-term freezing and vacuum environments as well as ionizing Gamma-, X-ray, and UV radiation at the levels corresponding to low Earth orbit (LEO) conditions. The main aim of this material behaviour investigation is to understand and predict device service time for prolonged exposure to space environment.

Prediction of Cell-Penetrating Peptides using Artificial Neural Networks

An investigation of cell-penetrating peptides (CPPs) by using combination of Artificial Neural Networks (ANN) and Principle Component Analysis (PCA) revealed that the penetration capability (penetrating/non-penetrating) of 101 examined peptides can be predicted with accuracy of 80%-100%. The inputs of the ANN are the main characteristics classifying the penetration. These molecular characteristics (descriptors) were calculated for each peptide and they provide bio-chemical insights for the criteria of penetration. Deeper analysis of the PCA results also showed clear clusterization of the peptides according to their molecular features.

Study of the Properties of Electrodeposited Polypyrrole Films

Experimental and theoretical methods have been used for characterization of the properties of polypyrrole films. The AFM studies show that the morphology of polypyrrole (PPy) films on polycrystalline gold electrodes at the first stages of synthesis depends on the structure of the metal surface. It was established that mobility of anions depends remarkably on the rate of electrodeposition of the polymer film. If PPy film was deposited at relatively low current density, mobility of ClO-4 anion was not high enough to guarantee electroneutrality during redox cycling and cations take part in this process especially when Li+ cations were replaced by more mobile К+ cations. Semiempirical (AM1 and PM3) quantum-chemical methods were used for theoretical studies. It was established that different size and charge of the anions together with the variation in doping levels give rise to a different optimal conformation of oligopyrrole cations which, in turn, define the resulting polymer to be either all-anti (common linear chains) or all-syn (formation of helical structures) or a combination of the two.

On the unexpected cation exchange behavior, caused by covalent bond formation between PEDOT and Cl- ions: Extending the conception for the polymer-dopant interactions

The ionic motion in connection with the redox transformation of poly(3,4-ethylenedioxythiophene) (PEDOT) conjugated polymer have been studied by both experimental-electrochemical (electrochemical quartz crystal nanobalance, EQCN) and spectroscopic (infrared spectroscopy, IR-ATR)-and theoretical methods. The observations have been completed by direct, semiquantitative analytical data, provided by energy dispersive X-ray (EDX) microanalysis. The EQCN results suggested an anomalous behavior, since only cationic movements have been observed for films deposited from chloride solutions. Chloride ions were proved to be immobile also when bulky tetrabutylammonium (Bu(4)N(+)) cations were substituted with even larger (hexadecyltrimethylammonium) cations. Since PEDOT films synthesized in the presence of other spherical, not too large anions-such as perchlorate and tetrafluoroborate-endowed mixed ion exchange behavior together with the Bu(4)N(+) cation, the possibility of a special interaction between chloride and the polymeric chain has been assumed. Semiempirical and DFT calculations indicated that chloride ions interact with the α carbon atoms of the thiophene rings of the oxidized EDOT oligomers, creating sp(3) type perturbations in the polymer chain. FTIR-ATR spectra evidenced the appearance of C-Cl bonds. Elementary analysis, performed by EDX spectroscopy with eight polymer samples at different doping levels clearly showed the permanent presence of constant amount of chlorine, independently of the oxidation state of the PEDOT layer. Finally, the presented observations call attention to the fact that unique dopant-polymer interactions during the electrochemical polymerization are of prime importance, being able to rule over conventions for the charge compensation of conjugated polymers, often solely based on steric parameters.

Fragment-Based Development of HCV Protease Inhibitors for the Treatment of Hepatitis C

A novel computational technology based on fragmentation of the chemical compounds has been used for the fast and efficient prediction of activities of prospective protease inhibitors of the hepatitis C virus. This study spans over a discovery cycle from the theoretical prediction of new HCV NS3 protease inhibitors to the first cytotoxicity experimental tests of the best candidates. The measured cytotoxicity of the compounds indicated that at least two candidates would be suitable further development of drugs.

Direct chemical synthesis of pristine polypyrrole hydrogels and their derived aerogels for high power density energy storage applications

A direct chemical route for preparing pristine polypyrrole hydrogels and derived aerogels with specific surface areas of up to 425.8 m2 g−1 is presented. The structure of the thick hydrogel electrodes relieves the diffusion limitations of conventional polypyrrole-modified electrodes. The properties can be tuned by altering the synthesis conditions and exchanging the dopant.

Carbide-derived carbon in polypyrrole changing the elastic modulus with a huge impact on actuation

While carbide-derived carbon (CDC)-based materials have shown stable behavior in ionic electro-chemo-mechanical actuators, the displacement and actuation speed have remained low compared to conducting polymer-based actuators. The goal of this research was to obtain more responsive conducting polymer–CDC composite films and to investigate their linear actuation properties, comparing the stress and strain to those of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS−). The PPy–CDC hybrid films were synthesized electrochemically using polyoxometalate (POM) (phosphotungstic acid) to attach charge to the CDC particles for embedding them into the PPy matrix as secondary dopants in addition to DBS−. Cyclic voltammetry and square wave potential steps in electro-chemo-mechanical deformation (ECMD) measurements were performed in aqueous electrolyte solution, showing that the PPy–CDC hybrids had higher strain (12%) and stress (0.6 MPa) than the PPy/DBS films. The new composite was investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy to evaluate the composition of these promising materials.