Understanding the enzymatic inhibition of intestinal alkaline phosphatase by aminophenazone-derived aryl thioureas with aided computational molecular dynamics simulations: synthesis, characterization, SAR and kinetic profiling.

The work presented in this paper aims toward the synthesis of aryl thiourea derivatives 4a-l of pyrazole based nonsteroidal anti-inflammatory drug named 4-aminophenazone, as potential inhibitors of intestinal alkaline phosphatase enzyme. The screening of synthesized target compounds 4a-l for unraveling the anti-inflammatory potential against calf intestinal alkaline phosphatase gives rise to lead member 4c possessing IC50 value 0.420 ± 0.012 µM, many folds better than reference standard used (KH2PO4 IC50 = 2.8 ± 0.06 µM and L-phenylalanine IC50 = 100 ± 3.1 µM). SAR for unfolding the active site binding pocket interaction along with the mode of enzyme inhibition based on kinetic studies is carried out which showed non-competitive binding mode. The enzyme inhibition studies were further supplemented by molecular dynamic simulations for predicting the protein behavior against active inhibitors 4c and 4g during docking analysis. The preliminary toxicity of the synthesized compounds was determined by using brine shrimp assay. This work also includes detailed biochemical analysis along with RO5 parameters for all the newly synthesized drug derivatives 4a-l.

In Silico Identification of Chemicals Capable of Binding to the Ecdysone Receptor.

The process of molting, known alternatively as ecdysis, is a feature integral in the life cycles of species across the arthropod phylum. Regulation occurs as a function of the interaction of ecdysteroid hormones with the arthropod nuclear ecdysone receptor-a process preceding the triggering of a series of downstream events constituting an endocrine signaling pathway highly conserved throughout environmentally prevalent insect, crustacean, and myriapod organisms. Inappropriate ecdysone receptor binding and activation forms the essential molecular initiating event within possible adverse outcome pathways relating abnormal molting to mortality in arthropods. Definition of the characteristics of chemicals liable to stimulate such activity has the potential to be of great utility in mitigation of hazards posed toward vulnerable species. Thus the aim of the present study was to develop a series of rule-sets, derived from the key structural and physicochemical features associated with identified ecdysone receptor ligands, enabling construction of Konstanz Information Miner (KNIME) workflows permitting the flagging of compounds predisposed to binding at the site. Data describing the activities of 555 distinct chemicals were recovered from a variety of assays across 10 insect species, allowing for formulation of KNIME screens for potential binding activity at the molecular initiating event and adverse outcome level of biological organization. Environ Toxicol Chem 2020;39:1438-1450. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Non-immunological toxicological mechanisms of metamizole-associated neutropenia in HL60 cells.

Metamizole is an analgesic and antipyretic, but can cause neutropenia and agranulocytosis. We investigated the toxicity of the metabolites N-methyl-4-aminoantipyrine (MAA), 4-aminoantipyrine (AA), N-formyl-4-aminoantipyrine (FAA) and N-acetyl-4-aminoantipyrine (AAA) on neutrophil granulocytes and on HL60 cells (granulocyte precursor cell line). MAA, FAA, AA, and AAA (up to 100 µM) alone were not toxic for HL60 cells or granulocytes. In the presence of the myeloperoxidase substrate H2O2, MAA reduced cytotoxicity for HL60 cells at low concentrations (<50 µM), but increased cytotoxicity at 100 µM H2O2. Neutrophil granulocytes were resistant to H2O2 and MAA. Fe2+ and Fe3+ were not toxic to HL60 cells, irrespective of the presence of H2O2 and MAA. Similarly, MAA did not increase the toxicity of lactoferrin, hemoglobin or methemoglobin for HL60 cells. Hemin (hemoglobin degradation product containing a porphyrin ring and Fe3+) was toxic on HL60 cells and cytotoxicity was increased by MAA. EDTA, N-acetylcystein and glutathione prevented the toxicity of hemin and hemin/MAA. The absorption spectrum of hemin changed concentration-dependently after addition of MAA, suggesting an interaction between Fe3+ and MAA. NMR revealed the formation of a stable MAA reaction product with a reaction pathway involving the formation of an electrophilic intermediate. In conclusion, MAA, the principle metabolite of metamizole, increased cytotoxicity of hemin by a reaction involving the formation of an electrophilic metabolite. Accordingly, cytotoxicity of MAA/hemin could be prevented by the iron chelator EDTA and by the electron donors NAC and glutathione. Situations with increased production of hemin may represent a risk factor for metamizole-associated granulocytopenia.

Coordination-driven self-assembly of ruthenium(ii) architectures: synthesis, characterization and cytotoxicity studies.

Coordination-driven self-assembly of organometallic η6-arene ruthenium(ii) supramolecular architectures (MA1-MA4) was carried out by employing dinuclear ruthenium acceptors [Ru2(µ-η4-C2O4)(CH3OH)2(η6-p-cymene)2](CF3SO3)2 (Rua), [Ru2(µ-η4-C6H2O4)(CH3OH)2(η6-p-cymene)2](CF3SO3)2 (Rub), [Ru2(dhnq)(H2O)2(η6-p-cymene)2](CF3SO3)2 (Ruc) and [Ru2(dhtq)(H2O)2(η6-p-cymene)2](CF3SO3)2 (Rud) separately with a new tetratopic donor (TD) in methanol at room temperature [TD = N,N,N',N'-tetra(pyridin-4-yl)-[1,1'-biphenyl]-4,4'-diamine]. All the coordination architectures were characterized by using spectroscopic techniques. The potency of these self-assembled architectures against human cervical cancer HeLa and human lung adenocarcinoma A549 cell lines is explored in vitro using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), annexin V-FITC/PI and 2',7'-dichlorofluorescein-diacetate assays.

Transformation of aminopyrine in the presence of free available chlorine: Kinetics, products, and reaction pathways.

Aminopyrine (AMP) has been frequently detected in the aquatic environment. In this study, the transformation mechanism of AMP by free available chlorine (FAC) oxidation was investigated. The results showed that FAC reacted with AMP rapidly, and a 74% elimination was achieved for 1.30 µM AMP after 2 min at 14.08 µM FAC dose. AMP chlorination was strongly pH-dependent, and its reaction included second- and third-order kinetic processes. Three active FAC species, including chlorine monoxide (Cl2O), molecular chlorine (Cl2), and hypochlorous acid (HOCl), were observed to contribute to AMP degradation. The intrinsic rate constants of each FAC species with neutral (AMP0) and cation (AMP+) species were obtained by kinetic fitting. Cl2O exhibited the highest reactivity with AMP0 (kAMP0, Cl2O = (4.33 ± 1.4) × 109 M-1s-1). In addition, Cl2 showed high reactivity (106-107 M-1s-1) in the presence of chloride, compared with HOCl (kAMP+, HOCl = (5.73 ± 0.23) × 102 M-1s-1, kAMP0, HOCl = (9.68 ± 0.96) × 102 M-1s-1). At pH 6.15 and 14.08 µM FAC dose without chloride addition, the contribution of Cl2O reached to the maximum (33.3%), but in the whole pH range, HOCl was the main contributor (>66.6%) for AMP degradation. The significance of Cl2 was noticeable in water containing chloride. Moreover, 11 transformation products were identified, and the main transformation pathways included pyrazole ring breakage, hydroxylation, dehydrogenation, and halogenation.

Effect of Esters on the Permeation of Chemicals with Different Polarities through Synthetic Artificial Membranes Using a High-Throughput Diffusion Cell Array.

This study investigated the effects of 25 kinds of esters that are used in cosmetics on the permeation of four model compounds with different polarities (caffeine [CF], aminopyrine [AMP], benzoic acid [BA], and flurbiprofen [FP]). The amount of each model compound that permeated through two types of artificial membrane (silicone and Strat-M®) was measured and correlated with the physicochemical properties of the esters, including their solubility, viscosity, wettability, surface tension, and uptake. The amount of each model compound that permeated through the silicone membrane was not significantly correlated with the solubility of the esters but was significantly correlated with all other measured physical properties of the esters. Similar correlations were observed for the amounts of AMP, BA, and FP that passed through the Strat-M® membrane. However, the amount of CF that permeated through the Strat-M® membrane also correlated with the solubility of the esters. There was a highly significant correlation between the amount permeating through the silicone and Strat-M® membranes because the model compounds had high lipophilicity. These findings demonstrated that to control the permeation of various chemicals through artificial membranes, it is important to consider the uptake of the esters and that the solubility of the esters is also an important consideration when using a more complex membrane.

Substrate Specificity of Human Cytochrome P450 (CYP) 2C Subfamily and Effect of Azole Antifungal Agents on CYP2C8.

PURPOSE: The metabolic activities of aminopyrine N-demethylation and tolbutamide methylhydroxylation by the human hepatic cytochrome P450 (P450 or CYP) 2C subfamily were compared and the effects of azole antifungal agent on the drug-metabolizing activity of CYP2C8 were investigated. METHODS: Aminopyrine N-demethylation and tolbutamide methylhydroxylation by CYP2C8, CYP2C9, and CYP2C19 were determined by the previous reported methods. The effects of five azole antifungal agents, fluconazole, itraconazole, ketoconazole, miconazole, and voriconazole, on the aminopyrine N-demethylation activity by CYP2C8 were investigated. RESULTS: With regard to aminopyrine N-demethylation, CYP2C19 had the lowest Michaelis constant (Km) and CYP2C8 had the highest maximal velocity (Vmax) among the CYP2C subfamily members. The Vmax/Km values for CYP2C8 were the highest, followed by CYP2C19. For tolbutamide methylhydroxylation, the Km and Vmax for CYP2C19 were three and six times higher than the corresponding values for CYP2C9, and the Vmax/Km value for CYP2C19 was twice that for CYP2C9, whereas hydroxylated tolbutamide formed by CYP2C8 was not detected. Fluconazole, itraconazole, and voriconazole at a concentration of 2 or 10 µM neither inhibited nor stimulated CYP2C8-mediated aminopyrine N-demethylation activity at substrate concentrations around the Km (5 mM). However, ketoconazole and miconazole noncompetitively inhibited CYP2C8-mediated aminopyrine N-demethylation with the inhibitory constant values of 1.98 and 0.86 µM, respectively. CONCLUSION: These results suggest that ketoconazole and miconazole might inhibit CYP2C8 clinically. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Critical appraisal of 13C breath tests for microsomal liver function: aminopyrine revisited.

As liver diseases are a major health problem and especially the incidence of metabolic liver diseases like non-alcoholic fatty liver disease (NAFLD) is rising, the demand for non-invasive tests is growing to replace liver biopsy. Non-invasive tests such as carbon-labelled breath tests can provide a valuable contribution to the evaluation of metabolic liver function. This review aims to critically appraise the value of the (13) C-labelled microsomal breath tests for the evaluation of metabolic liver function, and to discuss the role of cytochrome P450 enzymes in the metabolism of the different probe drugs, especially of aminopyrine. Although a number of different probe drugs have been used in breath tests, the perfect drug to assess the functional metabolic capacity of the liver has not been found. Data suggest that both the (13) C(2) -aminopyrine and the (13) C-methacetin breath test can play a role in assessing the capacity of the microsomal liver function and may be useful in the follow-up of patients with chronic liver diseases. Furthermore, CYP2C19 seems to be an important enzyme in the N-demethylation of aminopyrine, and polymorphisms in this gene may influence breath test values, which should be kept in mind when performing the (13) C(2) -aminopyrine breath test in clinical practice.

Novel sample preparation method for surfactant containing suppositories: effect of micelle formation on drug recovery.

Rectal drug delivery is currently at the focus of attention. Surfactants promote drug release from the suppository bases and enhance the formulation properties. The aim of our work was to develop a sample preparation method for HPLC analysis for a suppository base containing 95% hard fat, 2.5% Tween 20 and 2.5% Tween 60. A conventional sample preparation method did not provide successful results as the recovery of the drug failed to fulfil the validation criterion 95-105%. This was caused by the non-ionic surfactants in the suppository base incorporating some of the drug, preventing its release. As guidance for the formulation from an analytical aspect, we suggest a well defined surfactant content based on the turbidimetric determination of the CMC (critical micelle formation concentration) in the applied methanol-water solvent. Our CMC data correlate well with the results of previous studies. As regards the sample preparation procedure, a study was performed of the effects of ionic strength and pH on the drug recovery with the avoidance of degradation of the drug during the procedure. Aminophenazone and paracetamol were used as model drugs. The optimum conditions for drug release from the molten suppository base were found to be 100 mM NaCl, 20-40 mM NaOH and a 30 min ultrasonic treatment of the final sample solution. As these conditions could cause the degradation of the drugs in the solution, this was followed by NMR spectroscopy, and the results indicated that degradation did not take place. The determined CMCs were 0.08 mM for Tween 20, 0.06 mM for Tween 60 and 0.04 mM for a combined Tween 20, Tween 60 system.

Physico-chemical solid-state characterization of pharmaceutical pyrazolones: an unexpected thermal behaviour.

In this work, the thermal behaviour of three active substances (phenazone, aminophenazone, phenylbutazone) was studied by drawing up the TG/DTG/DTA curves in air/nitrogen atmosphere at 10 °C min(-1) heating rate. The information on the thermal-induced events was corroborated with the IR spectra of the solid samples (pharmaceutical compounds and the remaining chars after heating treatment), respectively with the ones obtained by evolved gases analysis (EGA). The data on a possible drug-excipient interaction were obtained from the thermoanalytical study of mixtures of these active compounds with talc, magnesium stearate, starch and microcrystalline cellulose. No changes were observed by TG/DTG/DTA curves of mixtures in comparison with the pure compound. Even if the three active substances contain the same heterocyclic ring, having similar molecular structures, their thermal behaviour is not similar. According to thermal and evolved gas analysis, it was proved that formation of CO2 does not involve atmospheric oxygen. By stoichiometric means, the molecular breakdown of aminophenazone can generate only carbon monoxide, which undergoes disproportionation, generating CO2.

High-performance liquid chromatographic assay for metamizol metabolites in rat plasma: application to pharmacokinetic studies.

In order to evaluate the pharmacokinetics of metamizol in the presence of morphine in arthritic rats, after subcutaneous administration of the drugs, an easy, rapid, sensitive and selective analytical method was proposed and validated. The four main metamizol metabolites (4-methylaminoantipyrine, 4-aminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoantipyrine) were extracted from plasma samples (50-100µl) by a single solid-phase extraction method prior to reverse-phase high performance liquid chromatography with diode-array detection. Standard calibration graphs for all metabolites were linear within a range of 1-100µg/ml (r(2)≥0.99). The intra-day coefficients of variation (CV) were in the range of 1.3-8.4% and the inter-day CV ranged from 1.5 to 8.4%. The intra-day assay accuracy was in the range of 0.6-9.6% and the inter-day assay accuracy ranged from 0.9 to 7.5% of relative error. The lower limit of quantification was 1µg/ml for all metabolites using a plasma sample of 100µl. Plasma samples were stable at least for 4 weeks at -20°C. This method was found to be suitable for studying metamizol metabolites pharmacokinetics in arthritic rats, after simultaneous administration of metamizol and morphine, in single dose.

Lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene: synthesis, characterization, and selective recognition of Hg2+ and its sensitivity toward pyrimidine bases.

The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg(2+) among other biologically important metal ions, viz., Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+) as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg(2+) by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg(2+) is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg(2+) is bound through an N(2)O(2) extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg(2+) complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest.

Pillar height dependent formation of unprecedented Pd8 molecular swing and Pd6 molecular boat via multicomponent self-assembly.

Three-component self-assembly of a cis-blocked 90° Pd(II) acceptor with a mixture of a tetraimidazole and a linear dipyridyl donor self-discriminated into unusual Pd(8) molecular swing (1) and Pd(6) molecular boat (2), which are characterized by single-crystal X-ray diffraction analysis; their ability to bind C(60) in solution is established by fluorescence titration.

A comparison of the reproducibility of the parameters of the ¹³C-aminopyrine breath test for the assessment of hepatic function.

This study determined the within-subject and between-subject variability of different ways of expressing the results of the (13)C-aminopyrine breath test ((13)C-ABT) and the effect of shortening the test duration. The (13)C-ABT was conducted on three separate occasions in 10 healthy volunteers and on a single occasion in 22 patients with established liver cirrhosis. The within-subject variability of cumulative percentage dose recovered (cPDR), using measured CO(2) production rate (VCO(2)), in the reference group over three trials was 15% over 120 min. Higher within-subject variability in cPDR would have been evident if the test was terminated at either 30 or 60 min. Substitution of predicted VCO(2) to calculate cPDR yielded comparable values at all time points. Significant differences between cirrhotics and reference group were evident after just 10 min using PDR/h, cPDR or enrichment (all P<0.05). The ABT demonstrates clinically acceptable reproducibility. Shortening of the duration may make the test more acceptable clinically, but it is associated with increasing imprecision.

Synthesis and anti-bacterial activities of some novel Schiff bases derived from aminophenazone.

A series of 1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one-containing Schiff bases were synthesized, characterized and screened for their antibacterial activities. The structures of the synthesized compounds were established by spectroscopic (FT-IR, ¹H-NMR, ¹³C-NMR, MS) and elemental analyses. The anti-bacterial activities (with MIC values) of compounds were evaluated. The anti-bacterial screening results reveal that among the six compounds screened, four compounds showed moderate to good anti-bacterial activity. Among the tested compounds, the most effective compounds against four bacterial strains, viz. Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and Streptococcus pyogenes, are [(2-chlorobenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one (4) and [(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-ylimino)methyl]benzonitrile (5) with MIC values of 6.25 µg/mL.

Phospho-regulated ACAP4-Ezrin interaction is essential for histamine-stimulated parietal cell secretion.

The ezrin-radixin-moesin proteins provide a regulated linkage between membrane proteins and the cortical cytoskeleton and also participate in signal transduction pathways. Ezrin is localized to the apical membrane of parietal cells and couples the protein kinase A activation cascade to the regulated HCl secretion. Our recent proteomic study revealed a protein complex of ezrin-ACAP4-ARF6 essential for volatile membrane remodeling (Fang, Z., Miao, Y., Ding, X., Deng, H., Liu, S., Wang, F., Zhou, R., Watson, C., Fu, C., Hu, Q., Lillard, J. W., Jr., Powell, M., Chen, Y., Forte, J. G., and Yao, X. (2006) Mol. Cell Proteomics 5, 1437-1449). However, knowledge of whether ACAP4 physically interacts with ezrin and how their interaction is integrated into membrane-cytoskeletal remodeling has remained elusive. Here we provide the first evidence that ezrin interacts with ACAP4 in a protein kinase A-mediated phosphorylation-dependent manner through the N-terminal 400 amino acids of ACAP4. ACAP4 locates in the cytoplasmic membrane in resting parietal cells but translocates to the apical plasma membrane upon histamine stimulation. ACAP4 was precipitated with ezrin from secreting but not resting parietal cell lysates, suggesting a phospho-regulated interaction. Indeed, this interaction is abolished by phosphatase treatment and validated by an in vitro reconstitution assay using phospho-mimicking ezrin(S66D). Importantly, ezrin specifies the apical distribution of ACAP4 in secreting parietal cells because either suppression of ezrin or overexpression of non-phosphorylatable ezrin prevents the apical localization of ACAP4. In addition, overexpressing GTPase-activating protein-deficient ACAP4 results in an inhibition of apical membrane-cytoskeletal remodeling and gastric acid secretion. Taken together, these results define a novel molecular mechanism linking ACAP4-ezrin interaction to polarized epithelial secretion.

The study of aminophenazone radical cation and its interaction with some antioxidants.

UNLABELLED: The purpose of this study was to identify both the possibilities of in vitro generation of 1-phenyl-2,3-dimethyl-4-dimethylamino-5-pyrazolone (aminophenazone) radical cation (abbreviated APH*+) and the mechanisms of interaction with different antioxidants. MATERIAL AND METHOD: The chromophore radical cation APH*+ was obtained by oxidizing APH with ammonium persulfate. The stages of the oxidation reaction and the production of the intermediate compounds were studied by spectrophotometrical and potentiometric titration. As standard antioxidant there was used a catechin solution in distilled water with concentrations ranging between 50-250 microg/mL, in weak alkaline environment. RESULTS: The oxidation of APH with ammonium persulfate developed in four stages, involving the production of some intermediate compounds with different colorations. A mechanism for this reaction has been proposed. The radical cation forms to an APH - ammonium persulfate molar ratio of 2 : 1. In the presence of an antioxidant (catechin) the radical cation APH*+ forms to a molar ratio APH-ammonium persulfate of 1:1, in weak alkaline environment. It has an absorbtion maxima at lambda = 540 nm. The molar extinction coefficient of APH*+ at lambda = 540 nm has been calculated. Its absorbance was proportional with catechin concentration in the range 50-250 microg/mL (r2 = 0.9988). CONCLUSION: The APH-ammonium persulfate system can be used for spectrophotometric determination of total polyphenols in different systems.

Aminopyridinecarboxamide-based inhibitors: Structure-activity relationship.

Series of aminopyridinecarboxamide-based inhibitors were synthesized and tested against human recombinant IKK-2 and in IL-1beta stimulated synovial fibroblasts. The 2-amino-5-chloropyridine-4-carboxamides were identified as the most potent inhibitors with improved cellular activity.

Photosynthetic antenna-reaction center mimicry: sequential energy- and electron transfer in a self-assembled supramolecular triad composed of boron dipyrrin, zinc porphyrin and fullerene.

A self-assembled supramolecular triad, a model to mimic the photochemical events of photosynthetic antenna-reaction center, viz., sequential energy and electron transfer, has been newly constructed and studied. Boron dipyrrin, zinc porphyrin, and fullerene respectively constitute the energy donor, electron donor, and electron acceptor segments of the antenna-reaction center mimicry. For the construction, first, boron dipyrrin was covalently attached to a zinc porphyrin entity bearing a benzo-18-crown-6 host segment at the opposite end of the porphyrin ring. Next, an alkyl ammonium functionalized fullerene was used to self-assemble the crown ether entity via ion-dipole interactions. The newly formed supramolecular triad was fully characterized by spectroscopic, computational, and electrochemical methods. Selective excitation of the boron dipyrrin moiety in the dyad resulted in energy transfer over 97% efficiency creating singlet excited zinc porphyrin. The rate of energy transfer from the decay measurements of time-correlated singlet photon counting (TCSPC) and up-conversion techniques agreed well with that obtained by the pump-probe technique and revealed efficient photoinduced energy transfer in the dyad (time constant in the order of 10-60 ps depending upon the conformer). Upon forming the supramolecular triad by self-assembling fullerene, the excited zinc porphyrin resulted in electron transfer to the coordinated fullerene yielding a charge-separated state, thus mimicking the antenna-reaction center functionalities of photosynthesis. Nanosecond transient absorption studies yielded a lifetime of the charge-separated state to be 23 micros indicating charge stabilization in the supramolecular triad. The present supramolecular system represents a successful model to mimic the rather complex "combined antenna-reaction center" events of photosynthesis.

[The influence of aminoglycoside antibiotics on the conformation of the unpairing loop adenine of avian leukosis virus RNA as revealed with 2-aminopurine fluorescence].

Fluorescent properties of 2-aminopurine included in the sequence RNA, are now used for the study of structural dynamics and local changes of structure retroviral RNA. We used 2-aminopurine for studying the conformational states of unpaired loop adenine of avian leukosis virus RNA upon the interaction with the aminoglycoside antibiotics. It was shown, that intensity of 2-aminopurine fluorescence for monomer hairpin RNA has greater value in comparison with both RNA dimers. Comparing the 2-aminopurine fluorescence of RNA dimers, it has found out that the intensity of fluorescence for extended dimer significantly lower than the kissing loop dimer RNA. This can be explained by the fact that the stacking contacts forms more compact structure of a loop in extended dimer concerning those in structure of kissing loop dimer. When the binding of aminogycoside antibiotics with kissing loop dimer RNA it was observed that only the tobramycin increases nearly three times the intensity of 2-aminopurine fluorescence. Results of work testify that it is possible to detect local changes in the complexes of retroviral RNA with ligands, using the fluorescence 2-aminopurine.