Biomedical subjects

T Hianik

Publications and source records attributed to T Hianik.

At least 19 recordsLinked to original sources

PubMed2006

Study of calix[4]resorcinarene-dopamine complexation in mixed phospholipid monolayers formed at the air-water interface.

We have studied the physical properties of monolayers formed by calix[4]resorcinarene and in mixtures with dipalmitoyl phosphatidylcholine (DPPC) in various molar ratios formed at the air-water interface and at presence of dopamine in water subphase by means of measurements of surface pressure and dipole potential. We showed that both calix[4]resorcinarene as well as its mixture with DPPC form stable monolayers at the water subphase. The presence of dopamine resulted in an increase of the mean molecular area and in a decrease of the compressibility modulus of the monolayers. For mixed monolayers at higher content of calix[4]resorcinarene (> 0.2 molar fraction) a deviation from ideal miscibility took place especially for monolayers in a solid state. This can be connected with formation of aggregates of calix[4] resorcinarene. Lowest miscibility and weakest interaction of dopamine with a monolayer was observed for calix[4]resorcinarene molar fraction of 0.33 in the monolayer.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

DNA-duplexes containing abasic sites: correlation between thermostability and acoustic wave properties.

Aldehydic apurinic or apyrimidinic sites that lack a nucleobase moiety are one of the most common forms of toxic lesions in DNA. In the present study, a close structural analog of such a site, the 2-(hydroxymethyl) tetrahydrofuranyl residue, was synthesized in order to act as a model for damaged nucleic acid probes. Prepared oligodeoxyribonucleotides containing one, two or three abasic sites were hybridized to complementary sequences immobilized on a gold surface using the neutravidin-biotin interaction for study by thickness shear mode acoustic wave detector. Measurement of the complex electrical impedance of an AT-cut quartz device with immobilized biotinylated nucleotide allowed the detection of changes of series resonance frequency, Deltafs, and motional resistance, Rm, associated with duplex formation. The changes as detected by the acoustic wave method correlated well with the thermostability of DNA duplexes in solution. With respect to the latter, UV-monitored melting curves indicate that both the number of sites and their localization in the double-stranded structure influence the amount by which a 19 b.p. duplex is destabilized. The presence of 3 abasic sites completely destabilized the DNA duplex.

Acoustics↗

PubMed2005

The detection of DNA deamination by electrocatalysis at DNA-modified electrodes.

The method of electrocatalysis based on using a methylene blue (MB) as an electrochemical indicator and ferricyanide ions [Fe(CN)6]3- as an electron acceptor was applied in screening DNA for lesions caused by deamination of nucleobases. The damaged DNA was modeled by short 18-mer oligonucleotides containing the different number of mismatched target bases (uracil instead of cytosine residues). The hybridization capacity of these oligomers with complementary probes (immobilized on gold electrodes or free) was investigated by both electrochemical methods and UV spectroscopy. We have shown that the amplitude of the reduction signal corresponding to ferricyanide ions considerably increases in the presence of MB. This electrocatalytic effect allowed us to detect the changes in electrochemical properties of DNA caused by dU.dG mismatches. Using differential pulse voltammetry and cyclic voltammetry, we showed that the electron transport from the electrode through the double-stranded DNA to MB and then to ferricyanide ions is suppressed by the mismatches in duplex structure. According to UV-monitored melting data, single or multiple wobble dU.dG base pairs destabilize 18-mer DNA duplex by 9-27 degrees C.

Catalysis↗

PubMed2004

Properties of mixed alkanethiol-dendrimer layers and their applications in biosensing.

We studied the properties of mixed alkanethiol-dendrimer layers on a gold support and their application in biosensing. We showed that properties of glucose sensor can be modified using a different ratio of 1-hexadecanethiol (HDT) and poly(amidoamine) dendrimer of first generation (G1). The cyclic voltammetry in the presence of the redox couple, Fe(CN)(6)(3-)/Fe(CN)(6)(4-), was used for estimating how effectively the layer blocks the redox probe's access to the electrode surface. A scanning electrochemical microscope (SECM) was used to image the resulting distribution of the organic compounds. We found that with increasing content of dendrimers, the integrity of the layers was improved.

Biosensing Techniques↗

PubMed2004

The study of the interaction of a model alpha-helical peptide with lipid bilayers and monolayers.

We studied the interaction of the alpha-helical peptide acetyl-Lys(2)-Leu(24)-Lys(2)-amide (L(24)) with tethered bilayer lipid membranes (tBLM) and lipid monolayers formed at an air-water interface. The interaction of L(24) with tBLM resulted in adsorption of the peptide to the surface of the bilayer, characterized by a binding constant K(c)=2.4+/-0.6 microM(-1). The peptide L(24) an induced decrease of the elasticity modulus of the tBLM in a direction perpendicular to the membrane surface, E(radial). The decrease of E(radial) with increasing peptide concentration can be connected with a disordering effect of the peptide to the tBLM structure. The pure peptide formed a stable monolayer at the air/water interface. The pressure-area isotherms were characterized by a transition of the peptide monolayer, which probably corresponds of the partial intercalation of the alpha-helixes at higher surface pressure. Interaction of the peptide molecules with lipid monolayers resulted in an increase of the mean molecular area of phospholipids both in the gel and liquid crystalline states. With increasing peptide concentration, the temperature of the phase transition of the monolayer shifted toward lower temperatures. The analysis showed that the peptide-lipid monolayer is not an ideally miscible system and that the peptide molecules form aggregates in the monolayer.

Adsorption↗

PubMed2003

Hybridization of DNA at the surface of phospholipid monolayers. Effect of orientation of oligonucleotide chains.

We studied the properties of lipid monolayers formed at the air-water interface composed of dioleoylphosphatidylcholine (DOPC) with incorporated short (19-mer) oligonucleotides. These oligonucleotides were modified by oleylamine at both (3' and 5') terminals or only at one (3') terminal. Interaction of single-stranded (19-mer) oligonucleotides without oleylamine with DOPC monolayers resulted only in slight increase of surface pressure and the area per phospholipid molecule, while more substantial and significant increase of these values were observed following incorporation of oligonucelotides modified by oleylamine. This influence is similar for both types of oligonucleotide modifications. However, considerable differences in changes of monolayer properties took place after hybridization with complementary oligonucleotides. The hybridization of oligonucleotides with the DNA modified by oleic acid at both 3' and 5' terminals at the surface of lipid monolayer resulted in further increase of surface pressure and in the increase of the area per phospholipid molecule, while decrease of both the surface pressure and the area per phospholipid molecules were observed for hybridization with DNA modified by oleic acid at 3' terminal. It is possible that in latter case, the hybridization caused the loss of hybridized molecules from monolayers. Interaction of noncomplementary chains with DOPC monolayers with incorporated oleyl acid-modified DNA also influenced the properties of monolayers, but the effect was weaker in comparison with that observed for complementary chains.

DNA↗

PubMed2003

Changes of compressibility of low density lipoproteins following copper mediated oxidation.

The methods of measuring the ultrasound velocity and density were used for study the adiabatic compressibility of low density lipoproteins (LDL) during their oxidation. We showed, that copper-mediated oxidation of LDL resulted in a decrease of apparent specific compressibility, phi(k)/beta0, of lipoproteins. The changes of ultrasound velocity and phi(k)/beta0 value started much earlier than the beginning of propagation phase corresponding to the fast increase in concentration of conjugated dienes, measured by absorption at 230 nm. It was assumed that the changes of compressibility could be in particularly due to increase in ordering of the phospholipids during reductive activation of Cu2+.

Copper↗

PubMed2003

Effects of oxidation on changes of compressibility of bovine serum albumin.

The methods of ultrasound velocity and density measurements were used to study the adiabatic compressibility of bovine serum albumin (BSA) during its oxidation by the prooxidants Cu2+ and 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH). We did not find changes of compressibility of BSA in the presence of copper ions at rather high molar ratio Cu2+/BSA = 0.66 mol/mol. This can be explained by binding of the Cu2+ to the binding site of BSA and thus protecting the prooxidant action of the copper. However, AAPH-mediated oxidation of BSA resulted in an increase of its apparent specific compressibility (psik/beta0). These changes could be caused by the fragmentation of the protein.

Amidines↗

PubMed2002

Properties of glucose biosensors based on dendrimer layers. Effect of enzyme immobilization.

The properties of glucose biosensors based on dendrimer layers on a gold support, which depend on the method of immobilization of glucose oxidase (GOX), were studied by amperometry. The kinetic parameters of enzymatic reactions, response time, sensitivity, detection limit, linear range, and enzyme turnover were determined. We showed that a more stable and sensitive sensor was obtained when GOX was immobilized on the dendrimer by crosslinking with glutaraldehyde in vacuum. This biosensor was stable for at least eight weeks. The response time was approximately 1.3 min, the detection limit of glucose was 25 micro M, and the apparent Michaelis-Menten constant was relative low ( K(m)=1.1+/-0.1 mM) in comparison with that for GOX in solution. The reason for these differences is discussed. The example of the application of the developed biosensors for the detection of mercury is also presented. The inhibitory effect of mercury on GOX activity was observed at mercury concentration of 100 nM.

Biosensing Techniques↗

PubMed2002

A novel method of introducing hydrophobic moieties into oligonucleotides for covalent and non-covalent immobilization on electrode surfaces.

An effective method for the introduction of oleylamine-modified cytidine units into predetermined position(s) of the oligodeoxyribonucleotide (ON) chain during automated ON synthesis has been developed. The high yields of the condensation products upon the introduction of the modified units allow the methods suggested to be used for the synthesis of ONs with two hydrophobic substituents. We also suggest a simple method for obtaining ONs with 5'-terminal hydrophobic linker with free thiol group. The functionality of synthesized ON modified by thiol group and that with hydrophobic spacer for the detection DNA hybridization has been approved in conductometric experiments.

Base Sequence↗

PubMed2002

Affinity interactions on a liposome surface detected by ultrasound velocimetry.

In this work, we performed targeted immobilization of immunoglobulins by means of bacterial S-layer proteins from Bacillus coagulans E38-66/V1 recrystallized on liposomes, which were exploited as immobilization matrix for antibody (Ab)-human IgG. The study of interaction of rabbit or swine anti-human IgG as antigens (Ag) was performed by means of measuring changes of ultrasound velocity. We showed that at a temperature of 25 degrees C, the increment of ultrasound velocity [u] linearly decreased following an increase of concentration of Ag. The decrease of [u] was presumably due to changes of hydration of the membrane due to the binding process. Approximately 10 times lower changes of [u] were observed at 45 degrees C for Ag-Ab interaction as well as for nonspecific interaction of Ag with liposomes covered by S-layer without Ab. No substantial differences in the behaviour of [u] were observed for interactions of human IgG with rabbit or swine anti-human IgG.

Bacterial Proteins↗

PubMed2002

Reagentless biosensing using electrochemical impedance spectroscopy.

The use of electrochemical impedance spectroscopy (EIS) and the conducting polymer, poly (pyrrole), as an integrated recognition and transduction system for reagentless biosensor systems was demonstrated with two different systems. The first system being an immunoassay for detection of luteinising hormone (LH) with the antibody being entrapped with in the poly (pyrrole) matrix and the second, a construct for DNA hybridisation discrimination able to differentiate single- and double-stranded DNA based on the interaction of the DNA with poly (pyrrole).

Biosensing Techniques↗

PubMed2002

Electrostriction of supported lipid films at presence of cationic surfactants, surfactant-DNA and DNA-Mg(2+) complexes.

The method of electrostriction has been applied to study the physical properties of supported lipid membranes (sBLM) during membrane formation at application of negative potential. Application of negative potential -350 mV to the sBLM during its formation resulted in more compact membrane structure as revealed by higher elastic modulus in comparison with sBLM formed without application of this potential. We also studied interaction with sBLM cationic surfactant hexadecylamine (HDA), HDA-DNA and DNA-Mg(2+) complexes. Interaction of HDA with sBLM resulted in decrease of membrane capacitance and two-directional effect on elasticity modulus (increase or decrease), which can be caused by different aggregation state of surfactant at the surface of sBLM. In contrast with effect of HDA, the complexes of HDA-DNA resulted, in most cases, increase of elasticity modulus and increase of membrane capacitance, which can be caused by incorporation of these complexes into the hydrophobic interior of the membrane. Certain part of these complexes can, however, be adsorbed on the sBLM surface. DNA itself does not cause substantial changes of physical properties of sBLM; however, addition of bivalent cations Mg(2+) to the electrolyte-contained DNA caused substantial increase of elasticity modulus and surface potential. These changes are, however, much slower than that observed for HDA-DNA complexes, which can be caused by slow competitive exchange between Na(+) and Mg(2+) ions.

Amines↗

PubMed2001

Interaction of the antimicrobial peptide gramicidin S with dimyristoyl--phosphatidylcholine bilayer membranes: a densitometry and sound velocimetry study.

We determined changes in the volume and adiabatic compressibility of large multi- and unilamellar vesicles composed of dimyristoylphosphatidylcholine containing various concentrations of the antimicrobial peptide gramicidin S (GS) by applying densitometry and sound velocimetry. Gramicidin S incorporation was found to progressively decrease the phase transition temperature of DMPC vesicles as well as to decrease the degree of cooperativity of the main phase transition and to increase the volume compressibility of the vesicles. GS probably enhanced thermal fluctuations at the region of main phase transition and provide more freedom of rotational movement for the phospholipid hydrocarbon chains. The ability of GS to increase the membrane compressibility and to decrease the phase transition temperature is evidence for regions of distorted membrane structure around incorporated gramicidin S molecules. At relatively high GS concentration (10 mol%), more significant changes of specific volume and compressibility appear. This might suggest changes in the integrity of the lipid bilayer upon interaction with high concentrations of GS.

Anti-Bacterial Agents↗

PubMed2001

Amperometric detection of DNA hybridization on a gold surface depends on the orientation of oligonucleotide chains.

We tested the possibility of amperometric detection of DNA hybridization on a gold surface influenced by the immobilization of oligonucleotide giving different orientations of single stranded DNA relative to the gold surface. The DNA sensor was fabricated by chemisorption of 18-mer oligonucleotide modified by a phosphorothioate group either at its 3' or both 3' and 5' terminal. After immobilization of oligonucleotide to the gold support, the sensor was immersed in 11-mercaptoundecanoic acid (MUA) solution. Further chemisorption of MUA resulted in approximately 10-fold increase of resistance of the organic layer. Addition of complementary oligonucleotide resulted in an increase of conductivity for DNA sensor oriented perpendicular to the gold support (DNA with one thiol group), while the conductance decreased for DNA sensor with single stranded DNA oriented parallel to the gold support (with DNA modified by thiol groups at both 3' and 5' terminals). Addition of non-complementary chain resulted a slight decrease or no change of sensor conductivity. The hybridization process at both types of DNA orientations is not cooperative and can be described by Langmuir isotherms. The hybridization event on gold support has been confirmed by mass detection using the quartz crystal microbalance technique.

Base Sequence↗

PubMed2001

Liposome aggregation in presence of the sweeteners cyclamate and saccharine.

The interaction of the sweeteners saccharine and cyclamate with large unilamellar liposomes and planar bilayer lipid membranes (BLM) was studied. Application of the methods of light scattering and sound velocimetry showed that saccharine induces aggregation of liposomes, while cyclamate probably caused increase of the hydration of liposome surface. The sweeteners induced changes of BLM compressibility in a direction perpendicular to the membrane plane. The cyclamate induced considerably larger decreases in the elasticity module than saccharine. The obtained results show that both saccharine and cyclamate interacts with the surface of lipid bilayer and could modify the physical properties of lipid membranes.

Cyclamates↗

PubMed2000

Adiabatic compressibility of red blood cell membrane: influence of skeleton.

Measurements of ultrasound velocity and density were used for determination of the adiabatic compressibility of red blood cells (RBC) during detachment of the membrane skeleton. Skeleton detachment was induced by addition of nystatin into a low ionic strength RBC suspension resulting in an increase (10%) of the ultrasound velocity concentration increment, [u], while the specific volume of cells, phi(v) did not change significantly. Changes of the concentration increment had rather long kinetics and were not completed even after 60 min. Both [u] and phiV values were used for calculation of the specific apparent adiabatic compressibility of RBC, phiK/beta0. The value of the specific apparent compressibility decreases following addition of nystatin. This corresponds to an increase in the volume elastic modulus of RBC membranes during detachment of the membrane skeleton. Control experiments with large unilamellar liposomes at conditions similar to that performed with the RBC did not reveal significant changes of [u] after the addition of nystatin. Our results show that the role of the membrane skeleton probably consists in maintaining higher compressibility of the RBC membranes. This may partly provide conditions for conformational changes of RBC membrane proteins.

Cell Size↗

PubMed2000

Electrostriction and dynamics of solid supported lipid films.

This review reports the significance of bilayer lipid membranes on a solid support (sBLM) for the construction of biosensors. The methods of formation of lipid membranes on different solid supports including different metals (silver, gold, stainless steel), agar and conducting polymers are presented. Several examples of the application of electrostriction and dielectric relaxation methods for the study of mechanical properties and dynamics of solid supported bilayers have been shown. We demonstrated that these methods are useful for determination of the binding of enzymes and antibodies to sBLM, for the study of hybridization of nucleic acids on membrane surfaces and for the study of physical properties of modified supported membranes.

Antigen-Antibody Reactions↗