861 resultados para Er3 ion
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A simple and rapid spectrophotometric method for the determination of nevirapine is described. The method is based on the reaction of nevirapine with tetrathiocyanatocobalt(II) ion in buffer of pH 4 to form the corresponding complex. Beer's law is obeyed in the range of 0.2 - 2.0 g mL-1 for nevirapine. The optical parameters such as molar absorptivity, Sandell's sensitivity, detection limit and quantitation limit were found to be 1.16 10(4) Lmol-1cm-1, 2.09 X 10-3 g cm-2, 0.073 g mL-1 and 0.222 g mL-1 respectively. The optimum reaction conditions and other analytical parameters were evaluated. The statistical evaluation of the method was examined by determining intra-day and inter-day precision. The proposed method has been successfully applied for the determination of nevirapine in pharmaceutical formulations.
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I likhet med vanliga plaster r de π-konjugerade polymererna flexibla, lsliga och processbara vid lga temperaturer (< 150 C). Drutver har de egenskapen att leda strm. Konduktivitetsintervallet r brett och omfattar nstintill metallisk ledningsfrmga ena sidan, via halvledarkonduktiva till isolerande andra sidan. Polymererna utgrs av regelbundna kedjor av kolatomer och associeras slunda till organiska material. Sedan de frsta vetenskapliga rapporterna publicerades vid slutet av 1970-talet har π-konjugerade polymerer anvnts och utvecklats i exempelvis solceller, dioder, lysdioder och transistorer. Nobelpriset i kemi tilldelades r 2000 t Hideki Shirakawa, Alan J. Heeger och Alan G. MacDiarmid fr upptckten och utvecklandet av ledande polymerer. I min avhandling har jag arbetat med att utveckla och frst lgspnnings jonmodulerade organiska transistorer. Tv typer av jonmodulerade organiska transistorer studeras: (1) den jonmodulerade organiska flteffekt transistorn (jonmodulerade OFETen), som utgr den centrala transistorn i avhandlingen, samt (2) den elektrokemiska transistorn. Den frsta typen fungerar som en konventionell OFET. Strmmen i halvledaren moduleras av det elektriska fltet ver isolatorn. Med anvndandet av en elektrolyt isolator orsakar polariseringen av jonerna dremot ett hgt elektriskt flt vid elektrolyt/halvledargrnssnittet och man stadkommer modulering av strmmen redan vid ngra volts drivspnningar. I den andra typen utnyttjas elektrokemi fr att medelst reduktion/oxidation modulera strmmen i den π-konjugerade polymeren. Ett viktigt ndaml i avhandlingen har ocks varit att kunna tillverka transistorerna med masstillverkningsmetoder. I avhandlingen presenteras de jonmodulerade organiska transistorernas mjlighet att framstllas med masstillverkningsmetoder. Nya koncept introduceras och svagheter identifieras. Skillnaderna mellan OFETen, jonmodulerade OFETen och den elektrokemiska transistorn klargrs. Arbetet skall dremot inte anses fullbordat utan forskningen fortgr fr att kringg svagheterna, ka p transistorernas stabilitet och framfrallt tillmpa dem i innovativa applikationer.
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Nitrate is the main form of nitrogen associated with water contamination; the high mobility of this species in soil justifies the concern regarding nitrogen management in agricultural soils. Therefore, the objective of this research was to assess the effect of companion cation on nitrate displacement, by analyzing nitrate transport parameters through Breakthrough Curves (BTCs) and their settings made by numerical model (STANMOD). The experiment was carried out in the Soil and Water Quality Laboratory of the Department of Biosystems Engineering, "Luiz de Queiroz" College of Agriculture in Piracicaba (SP), Brazil. It was performed using saturated soil columns in steady-state flow condition, in which two different sources of inorganic nitrate Ca(NO3)2 and NH4NO3 were applied at a concentration of 50 mg L-1 NO3-. Each column was filled with either a Red-Yellow Oxisol (S1) or an Alfisol (S2). Results are indicative that the companion ion had no effect on nitrate displacement. However, nitrate transport was influenced by soil texture, particle aggregation, solution speed in soil and organic matter presence. Nitrate mobility was higher in the Alfisol (S2).
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Att vervaka frekomsten av giftiga komponenter i naturliga vattendrag r ndvndigt fr mnniskans vlmende. Eftersom halten av froreningar i naturens ekosystem br hllas mjligast lg, pgr en stndig jakt efter kemiska analysmetoder med allt lgre detektionsgrnser. I dagens lge grs miljanalyser med dyr och sofistikerad instrumentering som krver mycket underhll. Jonselektiva elektroder har flera goda egenskaper som t.ex. brbarhet, lg energifrbrukning, och dessutom r de relativt kostnadseffektiva. Att anvnda jonselektiva elektroder vid miljanalyser r mjligt om deras knslighetsomrde kan utvidgas genom att snka deras detektionsgrnser. Fr att snka detektionsgrnsen fr Pb(II)-selektiva elektroder undersktes olika typer av jonselektiva membran som baserades p polyakrylat-kopolymerer, PVC och PbS/Ag2S. Fast-fas elektroder med membran av PbS/Ag2S r i allmnhet enklare och mer robusta n konventionella elektroder vid sprmnesanalys av joniska froreningar. Fast-fas elektrodernas detektionsgrns snktes i detta arbete med en nyutvecklad galvanostatisk polariseringsmetod och de kunde sedan framgngsrikt anvndas fr kvantitativa bestmningar av bly(II)-halter i miljprov som hade samlats in i den finska skrgrden nra tidigare industriomrden. Analysresultaten som erhlls med jonselektiva elektroder bekrftades med andra analytiska metoder. Att snka detektionsgrnsen m.hj.a. den nyutvecklade polariseringsmetoden mjliggr bestmning av lga och ultra-lga blyhalter som inte kunde ns med klassisk potentiometri. Den verkliga frdelen med att anvnda dessa blyselektiva elektroder r mjligheten att utfra mtningar i obehandlade miljprov trots nrvaron av fasta partiklar vilket inte r mjligt att gra med andra analysmetoder. Jag vntar mig att den nyutvecklade polariseringsmetoden kommer att stta en trend i sprmnesanalys med jonselektiva elektroder.
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Ion exchange membranes are indispensable for the separation of ionic species. They can discriminate between anions and cations depending on the type of fixed ionic group present in the membrane. These conventional ion exchange membranes (CIX) have exceptional ionic conductivity, which is advantageous in various electromembrane separation processes such as electrodialysis, electrodeionisation and electrochemical ion exchange. The main disadvantage of CIX membranes is their high electrical resistance owing to the fact that the membranes are electronically non conductive. An alternative can be electroactive ion exchange membranes, which are ionically and electronically conducting. Polypyrrole (PPy) is a type of electroactive ion exchange material as well as a commonly known conducting polymer. When PPy membranes are repeatedly reduced and oxidised, ions are pumped through the membrane. The main aim of this thesis was to develop electroactive cation transport membranes based on PPy for the selective transport of divalent cations. Membranes developed composed of PPy films deposited on commercially available support materials. To carry out this study, cation exchange membranes based on PPy doped with immobile anions were prepared. Two types of dopant anions known to interact with divalent metal ions were considered, namely 4-sulphonic calix[6]arene (C6S) and carboxylated multiwalled carbon nanotubes (CNT). The transport of ions across membranes containing PPy doped with polystyrene sulphonate (PSS) and PPy doped with para-toluene sulphonate (pTS) was also studied in order to understand the nature of ion transport and permeability across PPy(CNT) and PPy(C6S) membranes. In the course of these studies, membrane characterisation was performed using electrochemical quartz crystal microbalance (EQCM) and scanning electron microscopy (SEM). Permeability of the membranes towards divalent cations was explored using a two compartment transport cell. EQCM results demonstrated that the ion exchange behaviour of polypyrrole is dependent on a number of factors including the type of dopant anion present, the type of ions present in the surrounding medium, the scan rate used during the experiment and the previous history of the polymer film. The morphology of PPy films was found to change when the dopant anion was varied and even when the thickness of the film was altered in some cases. In nearly all cases the permeability of the membranes towards metal ions followed the order K+ > Ca2+ > Mn2+. The one exception was PPy(C6S), for which the permeability followed the order Ca2+ K+ > Mn2+ > Co2+ > Cr3+. The above permeability sequences show a strong dependence on the size of the metal ions with metal ions having the smallest hydrated radii exhibiting the highest flux. Another factor that affected the permeability towards metal ions was the thickness of the PPy films. Films with the least thickness showed higher metal ion fluxes. Electrochemical control over ion transport across PPy(CNT) membrane was obtained when films composed of the latter were deposited on track-etched Nucleopore membranes as support material. In contrast, the flux of ions across the same film was concentration gradient dependent when the polymer was deposited on polyvinylidene difluoride membranes as support material. However, electrochemical control over metal ion transport was achieved with a bilayer type of PPy film consisting of PPy(pTS)/PPy(CNT), irrespective of the type of support material. In the course of studying macroscopic charge balance during transport experiments performed using a two compartment transport cell, it was observed that PPy films were non-permselective. A clear correlation between the change in pH in the receiving solution and the ions transported across the membrane was observed. A decrease in solution pH was detected when the polymer membrane acted primarily as an anion exchanger, while an increase in pH occurred when it functioned as a cation exchanger. When there was an approximately equal flux of anions and cations across the polymer membrane, the pH in the receiving solution was in the range 6 - 8. These observations suggest that macroscopic charge balance during the transport of cations and anions across polypyrrole membranes was maintained by introduction of anions (OH-) and cations (H+) produced via electrolysis of water.
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Chlorophenols have been classified as possible carcinogens for humans. Chlorophenols have been used as pesticides and wood preservatives. In Finland, during 1930 1980s, saw mills used KY-5 wood preservative that contained 2,4,6-TCP, 2,3,4,6-TeCP and PCP. Especially in Finland chlorophenols have entered the environment by leaking from contaminated grounds of old saw mills. Although chlorophenol concentrations found in environment do not cause acute concern, long term exposure can increase the risk of cancer. SPME is relatively cheap and simple sampling method, in which the sample extraction and concentration are performed in a single step. Solvents are not required in SPME. IMS is based on the detection of sample ion drift times. Based on the drift times, reduced mobilities are calculated, which are comparable despite the measurement conditions. SPME-IMS coupling has not been used earlier in the determination of chlorophenols from water samples. The scope of this work was to study, if SPME-IMS system is suitable for detecting chloro-phenols from water samples. The aim was to determine the most optimal extraction condi-tions, which were then applied to real water samples. Following detection limits were deter-mined: 2,4,6-TCP: 0.33 mg/l; 2,3,4,6-TeCP: 0.63 mg/l and PCP: 1.63 mg/l. Detection limits were high compared to the highest possible chlorophenol concentration that is allowed in Finnish drinking water, 10 g/l. Detected concentrations from water sample differed from verified concentrations in the case of 2,3,4,6-TeCP by 4.6 % and in the case of 2,4,6-TCP by 48.4 %. Based on the results it can be said that SPME-IMS setup is suitable for preliminary analysis of mg/l chlorophenol concentrations from water samples.
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In this thesis, the DFMA is presented and used for the purpose of having a design for a vertical transfer line that can be easily manufactured and assembled. The design of the transfer line, the major components and drawings are presented. The ease of assembly, the costs of manufacturing and differences between the use of steel structure and aluminum are compared. The ALARA principle is followed to minimize the risk of radiation exposure by the means of locating the test ion sources outside the radioactive area.
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Potentiometric ion sensors are a very important subgroup of electrochemical sensors, very attractive for practical applications due to their small size, portability, low-energy consumption, relatively low cost and not changing the sample composition. They are investigated by the researchers from many fields of science. The continuous development of this field creates the necessity for a detailed description of sensor response and the electrochemical processes important in the practical applications of ion sensors. The aim of this thesis is to present the existing models available for the description of potentiometric ion sensors as well as their applicability and limitations. This includes the description of the diffusion potential occurring at the reference electrodes. The wide range of existing models, from most idealised phase boundary models to most general models, including migration, is discussed. This work concentrates on the advanced modelling of ion sensors, namely the Nernst-Planck-Poisson (NPP) model, which is the most general of the presented models, therefore the most widely applicable. It allows the modelling of the transport processes occurring in ion sensors and generating the potentiometric response. Details of the solution of the NPP model (including the numerical methods used) are shown. The comparisons between NPP and the more idealized models are presented. The applicability of the model to describe the formation of diffusion potential in reference electrode, the lower detection limit of both ion-exchanger and neutral carrier electrodes and the effect of the complexation in the membrane are discussed. The model was applied for the description of both types of electrodes, i.e. with the inner filling solution and solidcontact electrodes. The NPP model allows the electrochemical methods other than potentiometry to be described. Application of this model in Electrochemical Impedance Spectroscopy is discussed and a possible use in chrono-potentiometry is indicated. By combining the NPP model with evolutionary algorithms, namely Hierarchical Genetic Strategy (HGS), a novel method allowing the facilitation of the design of ion sensors was created. It is described in detail in this thesis and its possible applications in the field of ion sensors are indicated. Finally, some interesting effects occurring in the ion sensors (i.e. overshot response and influence of anionic sites) as well as the possible applications of NPP in biochemistry are described.
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Ion mobility spectrometry (IMS) is a straightforward, low cost method for fast and sensitive determination of organic and inorganic analytes. Originally this portable technique was applied to the determination of gas phase compounds in security and military use. Nowadays, IMS has received increasing attention in environmental and biological analysis, and in food quality determination. This thesis consists of literature review of suitable sample preparation and introduction methods for liquid matrices applicable to IMS from its early development stages to date. Thermal desorption, solid phase microextraction (SPME) and membrane extraction were examined in experimental investigations of hazardous aquatic pollutants and potential pollutants. Also the effect of different natural waters on the extraction efficiency was studied, and the utilised IMS data processing methods are discussed. Parameters such as extraction and desorption temperatures, extraction time, SPME fibre depth, SPME fibre type and salt addition were examined for the studied sample preparation and introduction methods. The observed critical parameters were extracting material and temperature. The extraction methods showed time and cost effectiveness because sampling could be performed in single step procedures and from different natural water matrices within a few minutes. Based on these experimental and theoretical studies, the most suitable method to test in the automated monitoring system is membrane extraction. In future an IMS based early warning system for monitoring water pollutants could ensure the safe supply of drinking water. IMS can also be utilised for monitoring natural waters in cases of environmental leakage or chemical accidents. When combined with sophisticated sample introduction methods, IMS possesses the potential for both on-line and on-site identification of analytes in different water matrices.
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Ribonucleic acid (RNA) has many biological roles in cells: it takes part in coding, decoding, regulating and expressing of the genes as well as has the capacity to work as a catalyst in numerous biological reactions. These qualities make RNA an interesting object of various studies. Development of useful tools with which to investigate RNA is a prerequisite for more advanced research in the field. One of such tools may be the artificial ribonucleases, which are oligonucleotide conjugates that sequence-selectively cleave complementary RNA targets. This thesis is aimed at developing new efficient metal-ion-based artificial ribonucleases. On one hand, to solve the challenges related to solid-supported synthesis of metal-ion-binding conjugates of oligonucleotides, and on the other hand, to quantify their ability to cleave various oligoribonucleotide targets in a pre-designed sequence selective manner. In this study several artificial ribonucleases based on cleaving capability of metal ion chelated azacrown moiety were designed and synthesized successfully. The most efficient ribonucleases were the ones with two azacrowns close to the 3- end of the oligonucleotide strand. Different transition metal ions were introduced into the azacrown moiety and among them, the Zn2+ ion was found to be better than Cu2+ and Ni2+ ions.
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Ischemic pain occurs when there is insufficient blood flow for the metabolic needs of an organ. The pain of a heart attack is the prototypical example. Multiple compounds released from ischemic muscle likely contribute to this pain by acting on sensory neurons that innervate muscle. One such compound is lactic acid. Here, we show that ASIC3 (acid-sensing ion channel #3) has the appropriate expression pattern and physical properties to be the detector of this lactic acid. In rats, it is expressed only in sensory neurons and then only on a minority (~40%) of these. Nevertheless, it is expressed at extremely high levels on virtually all dorsal root ganglion sensory neurons that innervate the heart. It is extraordinarily sensitive to protons (Hill slope 4, half-activating pH 6.7), allowing it to readily respond to the small changes in extracellular pH (from 7.4 to 7.0) that occur during muscle ischemia. Moreover, both extracellular lactate and extracellular ATP increase the sensitivity of ASIC3 to protons. This final property makes ASIC3 a "coincidence detector" of three molecules that appear during ischemia, thereby allowing it to better detect acidosis caused by ischemia than other forms of systemic acidosis such as hypercapnia.
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Potentiometric sensors are very attractive tools for chemical analysis because of their simplicity, low power consumption and low cost. They are extensively used in clinical diagnostics and in environmental monitoring. Modern applications of both fields require improvements in the conventional construction and in the performance of the potentiometric sensors, as the trends are towards portable, on-site diagnostics and autonomous sensing in remote locations. The aim of this PhD work was to improve some of the sensor properties that currently hamper the implementation of the potentiometric sensors in modern applications. The first part of the work was concentrated on the development of a solid-state reference electrode (RE) compatible with already existing solid-contact ion-selective electrodes (ISE), both of which are needed for all-solid-state potentiometric sensing systems. A poly(vinyl chloride) membrane doped with a moderately lipophilic salt, tetrabutylammonium-tetrabutylborate (TBA-TBB), was found to show a satisfactory stability of potential in sample solutions with different concentrations. Its response time was nevertheless slow, as it required several minutes to reach the equilibrium. The TBA-TBB membrane RE worked well together with solid-state ISEs in several different situations and on different substrates enabling a miniature design. Solid contacts (SC) that mediate the ion-to-electron transduction are crucial components of well-functioning potentiometric sensors. This transduction process converting the ionic conduction of an ion-selective membrane to the electronic conduction in the circuit was studied with the help of electrochemical impedance spectroscopy (EIS). The solid contacts studied were (i) the conducting polymer (CP) poly(3,4-ethylienedioxythiophene) (PEDOT) and (ii) a carbon cloth having a high surface area. The PEDOT films were doped with a large immobile anion poly(styrene sulfonate) (PSS-) or with a small mobile anion Cl-. As could be expected, the studied PEDOT solid-contact mediated the ion-toelectron transduction more efficiently than the bare glassy carbon substrate, onto which they were electropolymerized, while the impedance of the PEDOT films depended on the mobility of the doping ion and on the ions in the electrolyte. The carbon cloth was found to be an even more effective ion-to-electron transducer than the PEDOT films and it also proved to work as a combined electrical conductor and solid contact when covered with an ion-selective membrane or with a TBA-TBB-based reference membrane. The last part of the work was focused on improving the reproducibility and the potential stability of the SC-ISEs, a problem that culminates to the stability of the standard potential E. It was proven that the E of a SC-ISE with a conducting polymer as a solid contact could be adjusted by reducing or oxidizing the CP solid contact by applying current pulses or a potential to it, as the redox state of the CP solid-contact influences the overall potential of the ISE. The slope and thus the analytical performance of the SC-ISEs were retained despite the adjustment of the E. The shortcircuiting of the SC-ISE with a conventional large-capacitance RE was found to be a feasible instrument-free method to control the E. With this method, the driving force for the oxidation/reduction of the CP was the potential difference between the RE and the SC-ISE, and the position of the adjusted potential could be controlled by choosing a suitable concentration for the short-circuiting electrolyte. The piece-to-piece reproducibility of the adjusted potential was promising, and the day-today reproducibility for a specific sensor was excellent. The instrumentfree approach to control the E is very attractive considering practical applications.
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Avhandlingen handlar om pappers- och membranbaserad jonmodulerad elektronik. Mlet med forskningen har varit att utveckla billig, miljvnlig och brnnbar elektronik, som kan anvndas i vardagliga engngsprodukter. Baskomponenterna som utvecklas och presenteras i avhandlingen r transistorer och kondensatorer. Mer komplicerad logisk kretselektronik demonstreras ocks med hjlp av dessa komponenter. Substraten som utnyttjas vid framstllningen av dessa elektroniska komponenter r papper och membran. Dessa substrat r flexibla, hllbara, billiga, miljvnliga, etc. och drfr vl anpassade fr befintliga tryckteknologier. Sjlva baskomponenterna framstlls sedan p dessa substrat genom att trycka flera skikt p varandra, dr varje enskilt skikt r ett individuellt material. Detta r mjligt eftersom de organiska materialen som anvnds i dessa komponenter r upplsta i ett lsningsmedel och kan drmed tryckas p samma stt som ett vanligt blck. Ett tredimensionellt objekt kan p detta stt framstllas. I avhandlingen presenteras flera olika typer av transistorer, men den gemensamma nmnaren bland dessa r att isolatorn r en jonledare. Denna, ganska ovanliga, transistormodellen har den stora frdelen att lgspnningskomponenter kan relativt enkelt framstllas. Det som r speciellt med vra transistorer r att vi har anvnt miljvnliga jonledare. Detta, bl.a., leder till att vra komponenter visar bde god prestanda, tillika som de r miljvnliga. I avhandlingen demonstrerar vi ven tryckta superkondensatorer, en motsvarighet till laddningsbara batterier, konstruerade p papper med aktiverat kol och miljvnliga jonledare. De mest komplicerade logiska kretsar som demonstreras i denna avhandling r ring-oscillatorer och 1-bits-minnen konstruerade p papper. --------------------------------------------- Vitskirja ksittelee paperille ja polymeerikalvolle tulostettua ionimoduloitua elektroniikkaa. Tutkimuksen tavoitteena oli kehitt edullista, ympristystvllist ja polttokelpoista elektroniikkaa, jota voidaan kytt esim. tavanomaisissa kertakytttuotteissa. Vitskirjassa esitelln erilaisia transistoreita ja kondensaattoreita. Nit elektronisia peruskomponentteja kytten demonstroidaan mys monimutkaisempia loogisia piirej. Komponenttien valmistuksessa alustana kytettiin paperia ja polymeerikalvoa. Valitut alustat ovat joustavia ja kestvi, ja ovat siksi hyvin yhteensopivia olemassa olevien tulostusmenetelmien kanssa. Peruskomponentit valmistettiin tulostamalla eri materiaaleja pllekkin. Komponenteissa kytettvt orgaaniset aineet ovat liuenneessa muodossa musteessa, joka voidaan tulostaa samalla periaatteella kuin mik tahansa normaali muste. Tll menetelmll voidaan valmistaa mys kolmiulotteisia tuotteita. Vitskirjassa esitelln useita erityyppisi transistoreita, joissa yhdistvn tekijn on ionisesti johtava eriste. Tllaista suhteellisen harvinaista transistorityyppi kyttmll voidaan mahdollistaa matala-jnnitteisten komponenttien yksinkertainen valmistus. Valmistettujen transistoreiden etu on ionisten nesteiden ympristystvllisyys. Elektroniset komponentit ovat tten hyvi suorituskyvyltn, mutteivt haitallisia ympristlle. Vitskirjassa demonstroidaan mys tulostettujen superkondensaattoreiden, eli ladattavien paristojen vastineiden, valmistus paperille aktiivihiilt ja ionisia nesteit kytten. Kaikkein monimutkaisimmat loogiset piirit, jotka tss vitskirjassa esitelln, ovat rengasoskillaattorit sek 1-bittinen paperille valmistettu muisti.
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Small non-coding RNAs have numerous biological functions in cell and are divided into different classes such as: microRNA, snoRNA, snRNA and siRNA. MicroRNA (miRNA) is the most studied non-coding RNA to date and is found in plants, animals and some viruses. miRNA with short sequences is involved in suppressing translation of target genes by binding to their mRNA post-transcriptionally and silencing it. Their function besides silencing of the viral gene, can be oncogenic and therefore the cause of cancer. Hence, their roles are highlighted in human diseases, which increases the interest in using them as biomarkers and drug targets. One of the major problems to overcome is recognition of miRNA. Owing to a stable hairpin structure, chain invasion by conventional Watson-Crick base-pairing is difficult. One way to enhance the hybridization is exploitation of metal-ion mediated base-pairing, i. e. oligonucleotide probes that tightly bind a metal ions and are able to form a coordinative bonds between modified and natural nucleobases. This kind of metallo basepairs containing short modified oligonucleotides can also be useful for recognition of other RNA sequences containing hairpin-like structural motives, such as the TAR sequence of HIV. In addition, metal-ion-binding oligonucleotides will undoubtedly find applications in DNA-based nanotechnology. In this study, the 3,5-dimethylpyrazol-1-yl substituted purine derivatives were successfully incorporated within oligonucleotides, into either a terminal or non-terminal position. Among all of the modified oligonucleotides studied, a 2-(3,5-dimethylpyrazol-1-yl)-6-oxopurine base containing oligonucleotide was observed to bind most efficiently to their unmodified complementary sequences in the presence of both Cu2+ or Zn2+. The oligonucleotide incorporating 2,6-bis(3,5-dimethylpyrazol-1-yl)purine base also markedly increased the stability of duplexes in the presence of Cu2+ without losing the selectivity.