Kutatás

Recent Research topics of the Department of General and Physical Chemistry:

Weak Molecular Interactions
Electrochemistry


Weak molecular interactions

Weak molecular interactions plays determining role in the nature due to their reversible behavior they are able to control many complex systems including living organizations. Through the background electric field created by the solvent molecules around solutes, in condensed phase the strength of such interactions preferably controlled by the first coordination sphere of the solvation shells of molecules interacted. Therefore these weak interactions are highly controllable by varying the composition and structure of the solvation shell. Our preliminary results show unique properties of the solvation shells formed in binary solutions which composition differs considerably from the composition of the bulk. Furthermore, the composition of the solvation shell shows significant change within a range while the variation of the molar composition of bulk solutions less than about 0.01 of molar fraction. This property means that very slight change in the composition of the bulk molecular environment result in huge change in the structure and composition of the solvation shells raising large change of the complex stabilities and enormously shifts the chemical equilibriums in the system. Further the unexpected thermodynamic behaviors, our previous investigations highlighted solvent-dependent inhomogeneous distribution of the kinetic energy on molecules possessing aromatic moieties. This property affects significantly the kinetics of the chemical reactions driven by weak molecular interactions. Due to the preliminary observations listed above via controlling the environment we are able to control at least a particular family of weak molecular interactions which however plays important role in very wide scale of chemistry and biochemistry.



The following particular fields of the weak molecular interactions have been investigated in our institute during the past few years:

i)  Host - guest interactions of calixarenes towards aromatic neutral guest phenols and benzotrifluoride molecules, interactions of crown ethers with alkali metal ions

ii)  Controlling the folding of Bovin Serum Albumine via slight change in the composition of bulk binary solutions

iii)  Competitive interactions of flavons and flavonols with Ochratoxin A towards Human Serum Albumin

iv)  Interactions of anthocyanines with polyphenols in red wines as model for water-ethanol mixtures

v)  Association of carbon nanotubes and their adsorption onto a nanostructured wide band gap CeO2 semiconductor surfaces.

vi)  Structure of common solvents and solvation shells in solvent mixtures


i) Host - guest interactions of calixarenes towards aromatic neutral guest phenols and benzotrifluoride molecules

In our previous works interactions of a series of phenol derivatives with a family of calixarene derivatives were intensively studied in solvents having high and low permittivity. We have shown that the electron density and also the electron distribution of the aromatic species affects the ordering and movings of solvent molecules in the solvation shells of the interacted species. All of these studies confirmed the earlier observed decrease of the entropy term during such molecular interactions and this was described as a consequence of the reorganization of solvent molecules in the solvation shell during complex formation. This reorganization was supported later experimentally by solvent relaxation measurements.



Selected recent references :

1.  S. Kunsági-Máté, Zs. Csók, K. Iwata, E. Szász, L. Kollár: Role of the Conformational Freedom of the Skeleton in the Complex Formation Ability of Resorcinarene Derivatives toward a Neutral Phenol Guest, J. Physical Chemistry B 115 (2011) 3339-3343.

2.  Y. Li, Zs. Csók, L. Kollár, K. Iwata, E. Szász, S. Kunsági-Máté: The role of the solvation shell decomposition of alkali metal ions in their selective complexation by resorcinarene and its cavitand, Supramolecular Chemistry 24 (2012) 374-378.

3.  Yin Li, P. Huszthy, S. Kunsági-Máté: Effect of molecular vibrations on the selectivity character of pyridino-18-crown-6 derivatives towards potassium ion, Chemical Physics Letters 533 (2012) 45-49.


ii) Controlling the folding of Bovin Serum Albumine via slight change in the composition of bulk binary solutions

Complexation ability of water-soluble tiacalix[4]arene-tetrasulfonate towards three aromatic amino acids (Phenylalanine, Tyrosine and Tryptophane) was studied in water-ethanol mixtures by photoluminescence (PL) method as a function of the ethanol content of the bulk solutions. Job’s method followed by the application of the van’t Hoff theory was used to determine the thermodynamic parameters of the molecular association. Results show quite different thermodynamics of formation of calixarene-amino acid complexes at low and higher ethanol content of the solutions. The considerable stability of the individual calixarene-aromatic amino acids complexes supports their existence also in the case when the amino acids are in a protein. To test this idea the conversion rate, enthalpy and entropy change associated to the structural transition of BSA (Bovine Serum Albumin) were investigated by Differential Scanning Calorimetry (DSC) in the absence and in the presence of calixarene. Results show that presence of calixarene changes significantly both the thermodynamics and the kinetics of the transition of BSA and the information collected for the individual calixarene-amino acid complexes gives insights about the possible processes at molecular level. These properties of solvent effect have been investigated in the case of patulin - BSA and promycin – ergosterol interactions.



Selected recent references :

1.  S. Kunsági-Máté, S. Lecomte, E. Ortmann, É. Kunsági-Máté, B. Desbat: The environment controlled effect of thiacalix[4]arene on the transition thermodynamics and kinetics of bovine serum albumin, J. Inclusion Phenomena and Macrocyclic Chemistry, 66(1-2) (2010) 147-151.

2.  E. Virág, M. Pesti, S. Kunsági-Máté: Competitive hydrogen bonds associated with the effect of primycin antibiotic on oleic acid as a building block of plasma membranes, The Journal of Antibiotics 63 (2010) 113-117.

3.  E. Virág, M. Pesti, S. Kunsági-Máté: Complex formation between primycin and ergosterol: entropy–driven initiation of modification of the fungal plasma membrane structure, The Journal of Antibiotics 65 (2012) 193–196.


iii) Competitive interactions of flavons and flavonols with Ochratoxin A towards Human Serum Albumin

The mycotoxin Ochratoxin A (OTA) appears worldwide in cereals, plant products, different foods and drinks. Ochratoxin A binds to plasma albumin with a very high affinity. However, it is well known that natural flavonoids can also bind to human serum albumin (HSA) at the same binding site as OTA does (site I, subdomain IIA). A few experimental literature data suggest that reducing the bound fraction of OTA speeds up its elimination rate with a potential decrease in its toxicity. In our experimental model competitive binding properties of flavonoid aglycones were examined with a fluorescence polarization based approach. Our data show that some of the flavonoids are able to remove the toxin from HSA. We conclude that among the thirteen studied flavonoid aglycones galangin and quercetin were the most effective competitors for OTA.



Selected recent references :

1.  M. Poór, S. Kunsági-Máté, T. Bencsik, J. Petrik, S. Vladimir-Knežević, T. Kőszegi: Flavonoid aglycones can compete with Ochratoxin A for human serum albumin: A new possible mode of action, Int. J. of Biological Macromolecules 51 (2012) 279-283.


iv) Interactions of anthocyanines with polyphenols in red wines as model for water-ethanol mixtures

The interaction of malvidin-3-O-glucoside with ellagic acid molecules was studied in aqueous solutions in dependence of the ethanol content of the samples. Results show significant changes of the thermodynamic parameters when the ethanol content exceeds the 8%vol. The quantum chemical calculations and the solvent relaxation measurements validate that the solvatation shell of the malvidin – ellagic acid complexes changes from water to ethanol around this critical alcoholic concentration. The effect of the change of the solvation shell is accompanied by increasing copigmentation, i.e. higher ‘multi-sandwich’ complexes are formed. According to the considerable role of this interaction (namely copigmentation) in the formation of color in red wines, our results have several consequences for the winemaking process with regard to the stabilization of wine color.



Selected recent references :

1.  S. Kunsági-Máté, A. Kumar, P. Sharma, L. Kollár, M.P. Nikfardjam: Effect of Molecular Environment on the Formation Kinetics of Complexes of Malvidin-3-O-glucoside with Caffeic Acid and Catechin, J. Physical Chemistry B 113 (2009) 7468-7473.

2.  S. Kunsági-Máté, B. May, C. Tshiersch, D. Fetzer, I. Horváth, L. Kollár, M.P. Nikfardjam: Transformation of stacked pi-pi-stabilized malvidin-3-O-glucoside - Catechin complexes towards polymeric structures followed by anisotropy decay study, Food Research International 44 (2011) 23-27.

3.  Zs. Czibulya, I. Horváth, L. Kollár, S. Kunsági-Máté: Unexpected Effect of Potassium Ions on the Copigmentation in Red Wines, Food Research International 45 (2012) 272-276.

4.  Zs. Czibulya, L. Kollár, M. P. Nikfardjam, S. Kunsági-Máté: The Effect of Temperature on the Color of Red Wines, J. Food Science 77(8) (2012) 880-885.


v) Association of carbon nanotubes and their adsorption onto a nanostructured wide band gap CeO2 semiconductor surfaces

Multiwalled carbon nanotubes (MWCNTs) were deposited from solution phase onto the nanostructured CeO2 films grown on sapphire substrate. High resolution images by scanning electron microscopy showed that MWCNTs laid on the top of CeO2 islands. Raman shifts of these combinatorial materials showed considerable dependence on the morphology of the underlay CeO2 nanostructures. Quantum chemical calculations validated the resonant nanotube vibrations, especially for the stationary longitudinal wave at typical surface morphology, as the origin of this unexpected property of the Raman signal. Considering that the CeO2 surface morphology is fully controlled by the experimental setup of growth, properties of the CNT layers are tunable towards the requirements of practical applications.



Selected recent references :

1.  S. Kunsági-Máté and Jia Cai Nie: Entropy-driven adsorption of carbon nanotubes on (001) and (111) surfaces of CeO2 islands grown on sapphire substrate, Surface Science 604 (2010) 654-659.

2.  Heng Li, Jia Cai Nie, S. Kunsági-Máté: Modified dispersion of functionalized multi-walled carbon nanotubes in acetonitrile, Chemical Physics Letters 492 (2010) 258-262.

3.  B. Peles-Lemli, G. Matisz, A-M. Kelterer, W.M.F. Fabian, S. Kunsági-Máté: Noncovalent Interaction between Aniline and Carbon Nanotubes: Effect of Nanotube Diameter and the Hydrogen-Bonded Solvent Methanol on the Adsorption Energy and the Photophysics, J. Physical Chemistry C, 114 (2010) 5898-5905.

4.  H. Li, A. Petz, H. Yan, J. C. Nie, S. Kunsági-Máté: Morphology Dependence of Raman Properties of Carbon Nanotube Layers Formed on Nanostructured CeO2 Films, J. Physical Chemistry C 115 (2011) 1480-1483.

5.  Heng Li, Jia Cai Nie, S. Kunsági-Máté: EtOH induced formation of nanographite fractions and their reorganization on nanostructured CeO2 films, Chemical Physics Letters 531 (2012) 183-187.


vi) Structure of common solvents and solvation shells in solvent mixturess

To get experimental evidence about the structure of the sovation shells mixtures of primary alcohols were studied. The formation of the solvatation shell of anthracene molecule was investigated in binary mixtures of protic alcoholic solvents by solvent relaxation measurements, anisotropy decay studies and quantum-chemical modeling. Results show significant change of the solvatation shell of anthracene dissolved in binary solutions of methanol, ethanol or n-propanol with n-butanol when the molar fraction of n-butanol in the bulk solution exceeds a critical value. Both the solvent relaxation and anisotropy decay data suggest clusterization process in the solvatation shell of the anthracene probe. Quantum chemical calculation support formation of energetically preferred heteromolecular (X2(BuOH)2, X=MeOH, EtOH or PrOH) clusters around the solute.



Benzene – methanol cluster structures were investigated with theoretical chemistry methods to describe the microsolvation of benzene and the benzene-methanol azeotrope. Benzene – methanol (MeOH) clusters containing up to 6 methanol molecules have been calculated by ab initio [MP2/6-311++G(d,p)//MP2/6-31+G(d,p) + BSSE correction] method. The BSSE was found quite large with this basis set, hence, different extrapolation schemes in combination with the aug-cc-pVxZ basis sets have been used to estimate the complete basis set limit of the MP2 interaction energy [ΔE(MP2/CBS)]. For smaller clusters, n ≤ 3, DFT procedures (DFTB+, MPWB1K, M06-2X) have also been applied. Geometries obtained for these clusters by M06-2X and MP2 calculations are quite similar. Based on the MP2/CBS results, the most stable C6H6(MeOH)3 cluster is characterized by a hydrogen bonded MeOH trimer chain interacting with benzene via pi…H-O and O…H-C(benzene) hydrogen bonds. Larger benzene - MeOH clusters with n ≥ 4 consist of cyclic (MeOH)n subclusters interacting with benzene by dispersive forces, to be denoted by C6H6 + (MeOH)n. Interaction energies and cooperativity effects are discussed in comparison with methanol clusters. Besides MP2/CBS calculations, for selected larger clusters the M06-2X/6-311++G(d,p)//M06-2X/6-31+G(d,p) procedure including the BSSE correction was also used. Interaction energies obtained thereby are usually close to the MP2/CBS limit. To model the benzene – MeOH azeotrope, several structures for (C6H6)2(MeOH)3 clusters have been calculated. The most stable structures contain a tilted T-shaped benzene dimer interacting by pi...H-O and O...H-C (benzene) hydrogen bonds with a (MeOH)3 chain. A slightly less negative interaction energy results for a parallel displaced benzene sandwich dimer with a (MeOH)3 chain atop of one of the benzene molecules.



Selected recent references :

1.  S. Kunsági-Máté, K. Iwata: Effect of cluster formation of solvent molecules on the preferential solvatation of anthracene in binary alcoholic solutions, Chemical Physics Letters 473 (2009) 284-287.

2.  G. Matisz, W.M.F. Fabian, A-M. Kelterer, S. Kunsági-Máté: Weinhold's QCE model - A modified parameter fit. Model study of liquid methanol based on MP2 cluster geometries, J.Mol.Struct. (THEOCHEM) 956 (2010) 103-109.

3.  G. Matisz, A-M. Kelterer, W.M.F. Fabian, S. Kunsági-Máté: Application of the Quantum Cluster Equilibrium (QCE) Model for the Liquid Phase of Primary Alcohols Using B3LYP and B3LYP-D DFT Methods, J. Physical Chemistry B 115 (2011) 3936-3941.

4.  G. Matisz, A-M. Kelterer, W.M.F. Fabian, S. Kunsági-Máté: Coordination of Methanol Clusters to Benzene: A Computational Study, J. Physical Chemistry A 115 (2011) 10556–10564.




Electrochemistry

The main research activity of the Electrochemical Research Group is directed toward developing selective chemical sensors, using them in solving special problems and working out new measuring methods.

Developing SECM apparatus and using them in different studies

The group intensively takes part in the research work dealing development and application of scanning electrochemical microscopy (SECM). This powerful measuring technique has been pioneered by Bard and Engström. It is a version of the so called probe microscopy methods. It is based on combined application of ultramicro electrochemical sensors, precision positioning device and computer controlled measurement, and evaluated programs.
Our group successfully constructed SECM instruments, worked out their working programs and applied the technique solving different problems.



Development of new microsensors for application in SECM

In practice of SECM the overwhelming part of the measurements are done with amperometric micro tip sensors . However, potentiometric sensors can provide higher selectivity, good spatial resolution. Unfortunately earlier developed ion selective electrodes of the size needed for effective SECM application are fragile sensors with high electric resistance and short life time. Their high resistance is a draw back considering application in scanning electrochemical microscopy (SECM) and in life sciences. In our work ion selective mictropipettes with lowered resistance and extended life times have been developed. It proved well applicable in SECM, and in vivo biologic experiments. Up till now new type NH4+, K+, Mg2+ and Zn2+ micropipettes were prepared and tested. Several reports have been published about their properties and applications.



Electrochemical cell for in vivo H2S measurement

Recently the involvements of H2S in numerous physiological processes have been proved. This generated a rapidly increasing interest in studying its interaction with enzymes, with hemoproteins. Its role as a signaling molecule of the inflammatory and nervous systems, and in cardiovascular system has been proved. It regulates vascular tone. It is considered as member of the group of physiological signaling gases together with the NO and CO. The H2S in living tissues takes place in different redox processes and interacts with several endogenous species. Therefore its local concentration is changing rapidly. Furthermore the concentration is very small, it stays in the micromolar range.
Some of the hydrogen sulfide containing thermal mineral waters proved very effective in balneotherapy of different diseases. Question arose about extent of trans dermal absorption of the H2S content of this waters during balneotherapic treatments.
In our laboratory a new type of amperometric microcell was developed for investigation of transdermal H2S transport. The microcell was implanted into subdermal area of anesthetized experimental mice. Our experiments proved that considerable amount of the hydrogen sulfide absorbs through dermal membrane of the experimental animal upon bathing in hydrogen sulfide containing natural waters. Further work with employing and further developing the sensor is in progress.



Time of flight (TOF) method for measuring diffusion coefficient

Taking advantage on the special feature of the scanning electrochemical microscope a simple and fast method for measuring diffusion coefficient of different molecules in different media has been worked out. The advantage of the method has been proved experimentally. A few reports have been published about the results obtained with this technique. The technique is used in studying effect of different parameters on diffusion properties.



Periodically interrupted amperometry (PIA) for enhancing sensitivity of membrane coated electrodes

In case of amperometric biosensors a quiescent reaction layer coats the electrode surface. The amperometric base sensing element detects the change of the species involved in enzyme catalyzed reaction. In conventional amperometry the detector continuously operates. Since the detected species are taking part continuously in the electrode process, their concentration is small at the electrode surface. In the method – developed in our work – the electrolysis is periodically interrupted, allowing time for reloading the surface layer with the electroactive species. The signal, according to this is substantially increased resulting in higher sensitivity of the amperometric biosensor.
The applicability of the method has been proved experimentally.
The biosensors prepared with native enzyme sources owing to the low enzyme activity possess small sensitivity. This limits their applicability in analyzing real samples. In our work the sensitivity of a native tyrosinase based enzyme sensor was enhanced using periodically interrupted amperometric detection and optimized reaction layer thickness. Research work are in progress with applications of PIA technique.



Using SECM in corrosion studies

Ion-selective microelectrodes can be employed as tips in scanning electrochemical microscopy (SECM) for chemical imaging of corrosion processes. They present higher chemical selectivity than conventional amperometric microdisks, and may be the only effective option to visualize the dissolution of metals with negative redox potentials in aqueous environments when the use of Pt microelectrodes is limited by the onset of oxygen reduction and hydrogen evolution reactions. In international cooperation studies about detailed examination of corrosion processes have been carried out. In this work SECM measurements are done using measuring tips developed in our work. The local pH, oxygen concentration and the ionic fluxes are followed over corroding metal surfaces. Effects of different treatments and coatings on the corrosion intensity are studied. Up till now local ionic current density measurements were done by scanning electrochemical microscopy over the surface of an iron-magnesium and iron-zinc galvanic pairs immersed in aqueous chloride-containing solution.



SECM measurements with gas phase scanning

In most of the SECM measurements the tip is scanned in liquid or in gel phases. However, in certain cases gases are evolved over the surface layer of different samples like microorganism colonies or heterogenic surface bound catalysts. Therefore gas phase scanning can gain application in practice of SECM. In our laboratory experiments are in progress with gas phase SECM studies.
Miniaturized version of Severinghaus type carbon dioxide cell was prepared and was used as measuring tip in scanning electrochemical microscopy. While the conventional Severinghause cells contain gas permeable membrane for providing selectivity, the microcell presented here is prepared without membrane. It is an air gap type carbon dioxide sensor. This structure substantially decreases response time. Horizontal line scans were made in gas phase at different vertical distances over a small size, surface confined yeast colony without disturbing it. The collected data were used for preparing CO2 concentration – distance plots. Two methods were employed for estimating the carbon dioxide flux from experimental yeast colony. In practice of substrate generating – tip detecting (SG/TD) mode of SECM the delayed response, that is the long response time can bring in distortions. The air gap construction with shorter response time can provide more realistic concentration profile with higher scanning rate than a slower membrane coated tip.
The results already presented proves that potentiometric SECM can be done scanning in the gas phase over a target without disturbing its conditions. Estimating fluxes of gases from undisturbed surface confined microbial colonies can be a fruitful application of SECM in the future.



Investigation of electrochemical effects of host- guest interaction

The analytical signal generating function of certain chemical sensors is based on host –guest interaction between the sensing (host) species and the analyte (guest ) species. The interaction can change transport properties, electrode potential, electrocatalytic activity, or other voltammetric behavior. The group investigates the effects of interactions on the electrochemical properties. Properties of molecules newly synthesized by partners are studied. Membrane potential response, cyclic voltammetric behavior, electrocatalytic and biocatalytic activities, and transport rate are detected in this work.



Development and application of chemically modified electrodes, among them biosensors
The group has been working successfully in developing and application of chemically modified electrodes. In this line:
 -  Putrescine measuring amperometric enzyme sensor with improved selectivity and sensitivity, micro size glucose sensor, improved dopamine measuring enzyme electrode has been developed.
 -  Carbon nanowire containing screen printed electrodes with enhanced sensitivity were successfully used in analyzing dopamine in biological samples
 -  Voltammetric microcell has been developed and applied for enzyme activity measurements
 -  Electrocatalytic oxide film coated copper electrode based analytical methods and HPLC detector cell have been worked out and applied in analyzing real samples

Developing and using electrochemical sensors and methods for detecting local concentration of reactive oxidizing species (ROS)

Cooperating with research groups working in the field of experimental life sciences and in the field of biosensor developments, efforts are done for working out microsensors and methods applicable for detecting ROS species like hydrogen peroxide, nitrogen oxide, peroxide nitrite, superoxide and following their concentration changes in different media.



Working out ion selective electrodes for applications in biotechnology

Micro algal culturing techniques represent a fast growing branch of biotechnology. It is successfully used in producing fine chemicals as well as just growing algae as source of renewable fuels. The ionic composition of he media is a crucial factor influencing the yield in micro algal culturing techniques. Therefore continuous in situ measurement of concentration and control of different ionic species in the media is highly beneficial. Application of ion selective electrodes as transducer for the analysis is an obvious choice, however their adaptation for this can be a challenging task because of the highly variable concentrations of interfering chemical species in biotechnologic media. Cooperating with groups involved in biotechnology research, the group takes part in working out electrochemical sensors well applicable in the complex media of biotechnology.