In this paper, a novel solid state Nitric Oxide (NO) sensor made of a spin trap (iron(II)-diethyldithiocarbamate complex, FeDETC) encapsulated in a siloxane-poly(oxypropylene) (PPO) matrix was developed. Nitric oxide (NO), a free radical molecule, has numerous roles in various physiological functions, such as the regulation of blood pressure, immune response to bacterial infection, and nervous systems. Siloxane-polyether hybrid materials, for example siloxane-poly(oxypropylene) (PPO), are easy to prepare, transparent and flexible. The combination of all these characteristics in a unique material allows it to be used in several scientific and technological areas, including human health. NO radical is trapped in FeDETC, which allows its detection by electron paramagnetic resonance (EPR). FeDETC was added while PPO was a sol, which was then left in air for gelation. The novel sensor was dived directly into a solution of NO, when the NO-FeDETC complex was formed. Our results show that the novel sensor responds to NO, with similar sensitivity as previously published sensors. PPO sensors present a strong EPR signal and a high stability, keeping its signal for 45 days. We have studied ways to accelerate the NO release from the sensor, in order to study its potential as a drug delivery system. We observed an acceleration in NO release by using a modulated magnetic field of 40 G at 100 kHz; as well as by UV irradiation. Thermal induced NO release was also tested by heating NO-FeDETC PPO up to 50°C, with good results.
Nitric oxide (NO) is a free radical with multiples physiological functions [1-3], and few decades ago, NO was just another toxic molecule, one of a lengthy list of environmental pollutants such as cigarette smoke and smog. Over the past few years, diverse lines of evidence have converged to show that this sometime toxic pollutant gas plays a fundamental role in numerous biological processes in the body [
In one of these matrixes, a NO sensor was made encapsulating FeDETC in a sol-gel matrix [
In another work [12,13], natural rubber latex (NRL) was used as a matrix for the sustained and controlled delivery of NO. NRL is an important inductor of the healing process of wounds, being used in various biomedical applications like prosthetics and bone grafts [15-18]. Results showed that one can have sustained delivery of NO from NRL matrix for up to 350 hours. FTIR spectroscopy showed that NO/FeDETC when encapsulated in NRL has its properties and structure preserved [
In this work, we present a novel EPR NO sensor based on a siloxane-poly(oxypropylene) (PPO) matrix. The sensor was obtained by the spin trap iron(II)-diethyldithiocarbamate complex (FeDETC) encapsulated in a siloxane-poly(oxypropylene) PPO matrix. This same system is used for the sustained and controlled delivery of NO. This material is flexible, transparent and easily manipulated. We have tested different ways to do accelerated and controlled release of NO. The PPO-FeDETC system was exposed to ambient atmosphere (humidity 60%, 25˚C), ultraviolet, temperature at 50˚C, dark room, and magnetic field (amplitude modulation) of 40 G. The EPR signal of NO in the matrix was monitored as function of time.
First The PPO used in this work was obtained by sol-gel. All chemical reagents used are commercially available (Fluka, Aldrich). Succinctly, 3-isocyanatopropyltriethoxysilane (IsoTrEOS) and O,O’Bis(2-aminopropyl(polyoxypropylene)) in the molar ratio 2:1 were stirred together in tetrahydrofuran (THF) under reflux at 80˚C for 6 h to form the hybrid precursor 3(EtO)Si-(PPO)- Si(OEt)3 [20,21].
The sol was obtained by mixing the precursor with the spin trap FeDETC in an ethanol solution containing HCl or NH4F. Hydrolysis was promoted by water addition followed by polycondensations reactions. This process was adopted for PPO polymers with molecular weight (MW) of 300 and 2000 g/mol (labeled as PPO300 and PPO2000).
For the FeDETC solution, iron(III) chloride hexahydrate (FeCl3∙6H2O), dimethylformamide (DMF, C3H7ON) and sodium dietyldithiocarbamate (DETC, C5H10NNaS2∙3H2O) were used. DMF and DETC were obtained from Acrós Organics (Belgium). The solution was prepared using 12 mg of iron chloride and 20 mg of DETC in 3 mL of DMF under magnetic agitation during 10 minutes. The entrapment of FeDETC in the matrix was obtained by mixing the PPO solution with FeDETC solution. After this, the solution was left in air for 2 day to complete the polymerization process resulting in a solid matrix. NO was generated in an aqueous solution by mixing NaNO2 10 mM (250 μL), deionized water (750 μL) and Na2S2O4 (145 mg) in an eppendorf tube of 1.5 mL. In the presence of sodium dithionite (Na2S2O4) nitrite is reduced to NO. The saturated concentration of NO in this solution is 2.2 mM.
Electron Paramagnetic Resonance (EPR) experiments were done in a computer interfaced Varian E-4 X-band spectrometer at room temperature. For EPR measurements, the films were removed from the solution, dried and inserted in a quartz tube. For all samples the only signal observed was of the NO-FeDETC complex. To maximize signal to noise ratio various spectra were summed up, typically at least 10. To avoid sample repositioning induced errors for the measurements following the EPR signal with time, the sample was kept inside the resonant cavity. A reference sample with a known and stable amount of spins was used before each measurement.
In recent years, the study of organic-inorganic nanocomposites became a mushrooming field of investigation due to the promising applications of these materials in optics, electronics, electrochemistry and biology [22-26]. These hybrids are considered as biphasic materials, the organic and inorganic phases being mixed at a nanometric scale. A family of hybrids, which recently attracted interest, consists of siloxane-polyether nanometer scale composites (
synthesized to be used in photochromic devices [
Gradzielski et al. [
We shall start by comparing the EPR signal of FeDETC:NO in different matrixes. [11-13]. In
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ture and UV.
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In Figures 4 and 5, we observed that EPR signal amplitudes (PPO300 and PPO2000) increase with the FeDETC quantify, but non-linearly. We demonstrated that diethyldithiocarbamates is presence in PPO support. FeDETC:NO signal amplitudes are essentially dependent of FeDETC concentration [12,14]. In addition, the PPO sensors present a stronger EPR signal and highest stability, keeping the NO signal intensity for more than 40 days. The ultraviolet radiation induces an increase in EPR signal in both matrixes. Moreover, modulated magnetic field of 40 G at 100 kHz, as well exposing the PPO2000 sensor to a temperature at 50˚C, accelerated the NO release from the sensor, i.e.; field magnetic induced release of NO has potential application as a drug delivery system. The acceleration in the NO release is due the hyperthermia magnetic.
Kumar & Mohammad [
Lien & Wu [
nanocomposites. The magnetic properties of SiO2/Fe3O4 nanoparticles show superparamagnetic behavior. They observed that for thermosensitivity analysis, the phase transition temperatures of multifunctional nanoparticles measured using DSC was at around 34˚C - 36˚C.
Kim et al. [
Already, others works have shown the magnetic field influence in drug delivery. Souza et al. [
Chen et al. [
Souza et al. [
PPOs associated to FeDETC-NO are easy to manipulate, allow species detection and concentrations measurements with few sample contamination. These characteristics indicate that PPO matrix may be a good choice for a NO delivery system, with superior mechanical properties [11-13]. The samples are very stable: the signal amplitude of NO could be detected even after 40 days exposed to ambient atmosphere. As NO is an early mediator of the inflammatory process associated to tissue regeneration presented interesting biological properties.
We propose a novel NO delivery system made of a spin trap (iron(II)-diethyldithiocarbamate complex, FeDETC) encapsulated in a PPO matrix. The rate release of NO in this system was observed by EPR, exposing the sample to ambient atmosphere. The results indicate that it is possible NO release for 40 days. Moreover, a system with modulated magnetic field of 40 G at 100 kHz in PPO sensor to a temperature at 50˚C, accelerated the NO release from the sensor, i.e. field magnetic, and induced release of NO, has potential application as a drug delivery system. The acceleration in the NO release is due to the hyperthermia magnetic. In addition, the matrix is flexible, transparent and easily manipulated.
We are grateful to J. L. Aziani for technical support. This work received financial support from FAPESP, CNPq and CAPES.