Timur I. Abdullin

Synthesis and antibacterial activity of novel phosphonium salts on the basis of pyridoxine.

A series of 13 phosphonium salts on the basis of pyridoxine derivatives were synthesized and their antibacterial activity against clinically relevant strains was tested in vitro. All compounds were almost inactive against gram-negative bacteria and exhibited structure-dependent activity against gram-positive bacteria. A crucial role of ketal protection group in phosphonium salts for their antibacterial properties was demonstrated. Among synthesized compounds 5,6-bis[triphenylphosphonio(methyl)]-2,2,8-trimethyl-4H-[1,3]dioxino[4,5-c]pyridine dichloride (compound 20) was found to be the most effective towards Staphylococcus aureus and Staphylococcus epidermidis strains (MIC 5μg/ml). The mechanism of antibacterial activity of this compound probably involves cell penetration and interaction with genomic and plasmid DNA.

Pluronic block copolymer-mediated interactions of organic compounds with noble metal nanoparticles for SERS analysis.

The composite silver and gold nanoparticles (AgNPs and AuNPs) coated with nonionic amphiphilic block copolymers (Pluronics L121, F68, or F127) are prepared by their adsorption under critical micelle concentrations. It is found that Pluronics bind to the surface of metal NPs as a very thin film by the hydrophobic association through poly(propylene oxide) block of the copolymers. The modification increases the colloidal stability of NPs with increasing hydrophilic-lipophilic balance of Pluronics in the order of L121, F127, and F68. In order to investigate the potentials of polymer coated noble metal NPs as surface-enhanced Raman spectroscopy (SERS) probes, fluorescent dyes and doxorubicin are used as model compounds. It is found that Pluronic component promotes the adsorption of these compounds on the composite NPs resulting in a considerable increase of Raman signal. This effect is attributed to increased concentration of the analyte molecules on the composite surface due to the hydrophobic and charge-charge interactions between the analytes and the Pluronic coat, and the stabilization of NPs by poly(ethylene oxide) blocks. The copolymer coated AgNPs show higher SERS activity than the counterparts prepared with AuNPs. Among the prepared composites, the AgNPs modified with Pluronic F127 containing extended poly(propylene oxide) and poly(ethylene oxide) blocks exhibit maximal Raman activity using rhodamine 6G (Rh6G) with a EF of 9.04 x 10(6). The results show that the developed Pluronic-based SERS probes can be used for sensitive and selective analysis of organic analytes.

Binding and purification of plasmid DNA using multi-layered carbon nanotubes

We propose a new method for the separation of nucleic acids using multi-layered carbon nanotubes (CNTs) as an adsorbent. According to agarose gel electrophoresis, oxidized water-stable CNTs adsorb certain forms of nucleic acids, such as high molecular weight RNA, chromosomal DNA, linear and denatured forms of plasmid DNA. However, CNTs do not adsorb supercoiled form of plasmid DNA. Nucleic acids bound to CNTs can be readily removed by centrifugation whereas supercoiled plasmid DNA remains in solution. Upon the addition of divalent metal ions supercoiled plasmid DNA forms relatively stable complexes with CNTs due to chelation. Thus, new details about association of nucleic acids with CNTs were revealed and stoichiometry of the complexes was estimated. Our results can be used for fine purification of supercoiled plasmid DNA for gene therapy applications as well as manipulation of nucleic acids for biosensor design.

Effect of size and protein environment on electrochemical properties of gold nanoparticles on carbon electrodes

We studied the electrochemical properties of gold nanoparticles (GNPs) and their complexes with proteins using square-wave voltammetry. Effect of the nanoparticle size and detection procedure was explored upon the oxidation of GNPs on a glassy carbon electrode (GCE). For pre-characterized GNPs of 13, 35 and 78 nm diameter, the oxidation peak potential was +0.98, +1.03 and +1.06 V vs. Ag/AgCl, respectively. The conjugation of GNPs with four different proteins was verified by UV-Vis spectroscopy and atomic force microscopy indicated the formation of protein shells around GNPs. This process hampered the oxidation of GNPs on bare GCE causing pronounced decrease in the current response by an average factor of 72. GCE modification with carbon nanotubes weakly influenced the sensitivity of GNP detection but resulted in a 14.5-fold signal increase averaged for all GNP-protein complexes. The acidic dissolution and electrodeposition of GNPs or their complexes adsorbed on GCE allowed superior signal amplification directly proportional to nanoparticle size. The results are useful for the optimization of voltammetric analysis of GNP-protein complexes and can be extended to the characterization of other metal nanostructures and their complexes with biological components.

Carbon nanotube-modified electrodes for electrochemical DNA-sensors

Glassy-carbon electrodes (GCEs) are modified with preoxidized multiwalled carbon nanotubes (CNTs). According to the data of atomic force microscopy, the layers of CNTs on GCEs possess a homogeneous nanostructurized surface. The voltammetric properties of a GCE/CNT depend on the modifier load. Guanine and deoxyguanosine monophosphate are strongly adsorbed on GCE/CNT and oxidized at +690 and +930 mV (pH 7.0), respectively. The oxidation current of guanine DNA nucleotides adsorbed on a GCE/CNT is significantly higher for the thermally denaturated biopolymer than for the native one. Our results are of interest for the development of sensors based on the electrochemical properties of nucleic acids.

Conjugation of succinic acid to non-ionogenic amphiphilic polymers modulates their interaction with cell plasma membrane and reduces cytotoxic activity.

Pluronic block copolymers L61 and L121 were reacted with succinic anhydride to produce, respectively, their mono- and bisderivatives with succinic acid. The critical micelle concentration of Pluronics decreased after modification. The modification of Pluronic L61 promoted its association with the plasma membrane of human cells and increased membrane damage, while the membranotropic activity of modified Pluronic L121 reduced compared to the initial copolymer. Modified Pluronics interfered with the viability, apoptosis induction and metabolism of A549 cells and skin fibroblasts to a much lesser extent presumably due to the introduction of succinic acid residue inhibited intracellular penetration of copolymers. Modified Pluronic L121 promoted the cellular uptake of doxorubicin and rhodamine 123 in A549 cells attributed to the inhibition of membrane P-glycoprotein. Our study provides an approach to assessing the mechanism of interaction of amphiphilic polymers with living cells and demonstrates that Pluronic-succinic acid conjugates can be used as safe and efficient modulators of intracellular drug delivery.

Lipid-like trifunctional block copolymers of ethylene oxide and propylene oxide: effective and cytocompatible modulators of intracellular drug delivery.

A new glycerol-based trifunctional block copolymer (TBC) of propylene oxide and ethylene oxide and its conjugate with succinic acid (TBC-SA) were studied as a drug delivery system and compared with Pluronic L61. TBCs have multiple effects on the plasma membrane of human cells, e.g. increasing its fluidity and ion permeability, inhibiting ATPase activity of efflux transporter P-glycoprotein through reversible membrane destabilization. Such membrane-modulating properties attributed to the unimer form of copolymers increase in the order Pluronic L61≪TBC<TBC-SA and correlate with an ability of TBCs to promote the accumulation of P-glycoprotein substrates in lung cancer A549 cells. Furthermore, TBC, and especially TBC-SA, exhibit substantially lower hemolytic, cytotoxic and proapoptotic activities in comparison with Pluronic L61. Our results demonstrate that TBCs are promising analogs of bifunctional Pluronics in anticancer drug delivery.

Electrochemical sensor for blood deoxyribonucleases: design and application to the diagnosis of autoimmune thyroiditis

We designed an electrochemical sensor based on a carbon nanotube modified electrode (ME) to analyze DNA-cleaving activity. The cleavage of high molecular weight DNA resulted in an increase in the oxidation current from DNA guanine nucleotides due to a change in DNA adsorptive behavior on the surface of the ME. DNA digestion with DNAse I was accompanied by a linear increase in the DNA signal in proportion to the enzyme activity. We then proposed an assay based on the sensor for the direct assessment of the total deoxyribonuclease activity of blood serum as well as the separate detection of DNAse I and DNA abzymes. The assay was applied to analyze deoxyribonucleases in sera from 21 healthy donors and 17 patients with autoimmune thyroiditis. Our results show that the response of the sensor to DNA cleavage by blood deoxyribonucleases is a promising diagnostic criterion for autoimmune thyroiditis. This sensor can be implemented in a disposable screen-printed electrode format for application in clinical laboratories.

Carbon nanotube-based biosensors for DNA structure characterization

The possibility of DNA detection using electrodes modified with carbon nanotubes (CNTs) was studied. CNTs facilitate the electrochemical oxidation of DNA guanine nucleotide, which allows direct detection of DNA on a modified electrode. Electrochemical properties of DNA depend on its secondary structure and molecular weight. Denaturation of native DNA improves the adsorption of biopolymer on CNTs and results in an increase in DNA oxidation current on the modified electrode. A similar effect is observed after ultrasonic shearing of DNA or its treatment with Fenton’s reagent due to the fragmentation of biopolymer. Our results demonstrate the feasibility of biosensors based on CNT-modified electrodes for the direct detection and characterization of DNA and DNA damaging factors.

Detection of DNA depurination with the use of an electrode modified with carbon nanotubes

The possibility of detecting DNA depurination products on a glassy carbon electrode modified with carbon nanotubes (CNTs) was revealed. Adenine and a guanine DNA nucleotide were oxidized at similar potentials of about +1.1 V against Ag/AgCl; this fact did not allow us to detect adenine in the presence of DNA. DNA components did not interfere with the detection of guanine, which was oxidized at +0.9 V. Guanine was strongly adsorbed on the CNT-modified glassy carbon electrode; the oxidation current of guanine was a linear function of the concentration described by the equation i (10−6 A) = 3.21 + 0.44 c (10−6 M), r = 0.963. The results were suitable for the determination of guanine liberated from DNA on the CNT-modified glassy carbon electrode. The procedure developed was applied to evaluate the rates of DNA depurination under various conditions.