Peña-Luengas, Sandra L.

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2007 - 200912010 - 20151
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    SPME-HPLC methodology for detection of nitroexplosives
    (2007) Peña-Luengas, Sandra L.; Hernández-Rivera, Samuel P.; College of Arts and Sciencies - Sciences; Roman, Félix; Rivera, Luis; Department of Chemistry; Sundaram, Paul A.
    Solid Phase Microextraction (SPME) has been coupled with liquid chromatography to widen its range of application to nonvolatile and thermally unstable compounds, generally limited to SPME-gas chromatography. A method for analysis of nitroaromatic explosives and its degradations products was developed using SPME and high performance liquid chromatography with ultraviolet detection (HPLC/UV), introducing a modified interface that ensure accuracy, precision, reproducibility, high efficiency, unique selectivity and high sensitivity to detection and quantification of explosives from surface soil samples and increased chromatographic efficiency. A pretreatment step was introduced for the soil samples which extracted the target compounds into an aqueous phase. Several parameters that affect the microextraction were evaluated, such as: fiber coating, adsorption and desorption time, desorption mode, stirring rate, the effect of NaCl (salting out) concentration on analyte extraction and the role of various solvents on SPME fiber. Carbowax-templated resin (CW/TPR) and polydimethilsiloxane-divinilbenzene (PDMS-DVB) fibers were used to extract the analytes from the aqueous samples. Explosives were detected at 330 pg concentrations. Effects of daylight and UV radiation were analyzed over soil samples during 1 month and degradations products found were: 1,3,5-TNB, nitrobenzene, 4-ADNT and 2-ADNT. This study demonstrated that SPME-HPLC is a very promising method of analysis of explosives from aqueous samples and has been successfully applied to the determination of nitroaromatic compounds, such as TNT.
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    Enhanced singlet oxygen from Zno quantum dots nanoparticles derivatives for Photodynamic Therapy (PDT) and cytotoxic activity in chronic lymphocytic leukemia (CLL) tumor cells
    (2015) Peña-Luengas, Sandra L.; Rivera-Montalvo, Luis; College of Arts and Sciences - Sciences; Perales-Pérez, Oscar; Roman, Felix; Ríos Steiner, Jorge L.; Department of Chemistry; Nieto, Dra Miriam
    The generation of singlet oxygen (SO) in presence of specific photosensitizers (PS) or semiconductor quantum dots and its application in photodynamic therapy is of great interest to develop cancer therapies with no need of surgery, chemotherapy or radiotherapy. The present work is focused on the identification of the main factors leading to the enhancement of SO production using rose bengal (RB), and methylene blue(MB) as PS species in organic and aqueous medium , subsequent the capacity of ZnO, ZnS and ZnO/ZnS core-shell quantum dots (QDs) and manganese-doped ZnO and ZnS nanoparticles (NPs) to generate SO as potential photosensitizers, was determined. The presence of the Mn+2 dopant ion alters the electronic properties of QDs increasing surface defects also affecting the optical, structural and morphological properties of NPs, enhancing the generation of SO, which is very important in photodynamic therapy (PDT). The Mn+2 dopant atomic percentages for ZnO were 0.5, 1.0, 1.5 and 2.0% and for ZnS NPs was 1.0%. ZnO/ZnS water soluble core-shell QDs were obtained by slow decomposition of aqueous Zn+2 - MPA complexes at pH 10.3 over a ZnO QDs water suspension under reflux. Colloidal ZnS nanocrystals with Mn+2 ion as dopant were prepared using poly-vinylpyrrolidine (PVP) as capping agent. Mn-doped ZnO were synthesized by a precipitation method based in a wet chemical process using highly pure zinc acetate dihydrate as a precursor with sodium hydroxide solution. As part of the research work, a comparative study was performed evaluating different parameters as type and concentration of the quencher, NPs and PSs, light source, excitation wavelength, irradiation time, distance from light source, and nature of solvent. In this research four quenchers were studied: 1,3-diphenylisobenzofuran, 2,5- diphenylfuran, the system n,n-dimethyl-4-nitrosoaniline (RNO) coexisting with imidazole or L-histidine. Concentrations of the photosensitizers (PS), NPs and chemical quenchers were optimized for photooxidation reactions. The kinetics of the quenchers degradation by generated SO species and the corresponding quantum yield (QY), was determined by photo-oxidation of the chemical quencher by monitoring the disappearance of the quencher by fluorescence and spectrophotometry and analysis of a fluorescent probe Singlet Oxygen Sensor Green (SOSG) in the presence of NPs. These biologically synthesized NPs were found to be highly cytotoxic against multi drug resistant B-Chronic Lymphocytic Leukemia (B-CLL) cells in vitro. This disease usually follows an adverse, relentless clinical course by slowly developing drug resistance to fludarabine and other chemo-therapeutic agents, as well as by acquiring new different genetic abnormalities. As these cells spontaneously produce high amounts of Reactive Oxygen Species (ROS) having an altered redox state in relation to that of normal B lymphocytes, we decided to also probe our different metal ZnNPs, quantifying the levels SO and see if little variations of its intracellular concentrations could execute and accelerate deadly programs in these leukemic cells when applied with PDT, producing almost no significant damage on normal B lymphocytes. In this way, when testing our different metal Zn NPs, one made of 0.5% Mn Doped Zn Oxide (MnZnO) was finally selected for further probes as it had the best killing activity in fludarabine resistant B-CLL cells, specially when combined with PDT. An interesting and rapidly dying process of B-CLL cells, known as autophagy, was seen under Transmission Electronic Microscopy (TEM) when incubated with these 0.5% Mn doped ZnO NPs. This phenomenon correlated well with those intracellular increases of SO when PDT was administered, and measured by a novel method first described by us. As this therapy seems to be very specific to fludarabine resistant B-CLL cells, without much harm to normal lymphocytes, it could contribute in the near future as a new innovative targeted strategy to be delivered in the clinical setting, for the definitive benefit of these bad prognostic patients. SO is believed to be the major cytotoxic agent involved in PDT. Measurement of SO in biological environments is a major task specially when intracellular values, without interferences from the external medium, are required. Our intracellular SO measurement method proved to be good enough, reproducible, un-expensive and quite simple to perform and may be, it will easily be introduced soon as a useful routine diagnostic tool. PDT is a clinically tested promising technique to treat cancer and can be associated therapeutically with NPs. We could be in front of a new promising treatment not only for B-CLL and other lymphomas but maybe also to all types of cancer.