Fundamental and applied research in chemistry and biology benefits from opportunities provided by droplet-based microfluidic systems. These systems enable the miniaturization of reactions by compartmentalizing reactions in droplets of femoliter to microliter volumes. Compartmentalization in droplets provides rapid mixing of reagents, control of the timing of reactions on timescales from milliseconds to months, control of interfacial properties, and the ability to synthesize and transport solid reagents and products. Droplet-based microfluidics can help to enhance and accelerate chemical and biochemical screening, protein crystallization, enzymatic kinetics, and assays. Moreover, the control provided by droplets in microfluidic devices can lead to new scientific methods and insights. 相似文献
Neutron activation analysis (NAA) is a very sensitive and accurate multielement analytical method that is widely applied to the investigation of environmental and archaeological problems. The first part of this paper is a review of pollution studies of toxic trace elements in sediments, seawater and marine organisms of Saronikos Gulf, Greece by NAA. The second part of this paper is a review of provenance studies based on minor and trace element research in ancient ceramics, obsidian, flint, limestone, marble and lead by Instrumental NAA, performed at the NCSR Demokritos. 相似文献
In situ generation of reactive species within confined geometries, such as nanopores or nanochannels is of significant interest in overcoming mass transport limitations in chemical reactivity. Solvent electrolysis is a simple process that can readily be coupled to nanochannels for the electrochemical generation of reactive species, such as H(2). Here the production of hydrogen-rich liquid volumes within nanofluidic structures, without bubble nucleation or nanochannel occlusion, is explored both experimentally and by modeling. Devices comprised of multiple horizontal nanochannels intersecting planar working and quasi-reference electrodes were constructed and used to study the effects of confinement and reduced working volume on the electrochemical reduction of H(2)O to H(2) and OH(-). H(2) production in the nanochannel-embedded electrode reactor output was monitored by fluorescence emission of fluorescein, which exhibits a pH-dependent emission intensity. Initially, the fluorescein solution was buffered to pH 6.0 prior to stepping the potential cathodic of E(0)' for the generation of OH(-) and H(2). Because the electrochemical products are obtained in a 2:1 stoichiometry, local measurements of pH during and after the cathodic potential steps can be converted into H(2) production rates. Independent experimental estimates of the local H(2) concentration were then obtained from the spatiotemporal fluorescence behavior and current measurements, and these were compared with finite element simulations accounting for electrolysis and subsequent convection and diffusion within the confined geometry. Local dissolved H(2) concentrations were correlated to partial pressures through Henry's Law and values as large as 8.3 atm were obtained at the most negative potential steps. The downstream availability of electrolytically produced H(2) in nanochannels is evaluated in terms of its possible use as a downstream reducing reagent. The results obtained here indicate that H(2) can easily reach saturation concentrations at modest overpotentials. 相似文献
Electrochemistry is one of the most advanced techniques for monitoring neurochemical activities in the living brain because electrochemical approaches bear the advantageous features of high spatial and temporal resolutions, which facilitate its tremendous potential in investigating the highly spatially heterogeneous brain system and the fast dynamics of neurochemical activities. On the other hand, since brain is the most complicated organ in the sense of its numerous kinds of neurochemical species, high selectivity is always required for any analytical methods that approach the brain. In this review, we will discuss various electrochemical methodologies to achieve selective detection of neurochemicals in mammalian brain and the strategies developed mainly by our group towards selective monitoring of both electrochemically active and inactive neurochemicals. At the end, we will discuss possible solutions towards brain mapping of neurochemical species and combination of neurochemical detection strategy with electrophysiology as the direction of future development of electroanalysis in living brain. 相似文献
The toxicity of inorganic trivalent arsenic for living organisms is reduced by in vivo methylation of the element. In man, this biotransformation leads to the synthesis of monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are efficiently eliminated in urine along with the unchanged form (Asi). In order to document the methylation process in humans, the kinetics of Asi, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of Asi. The arsenic methylation efficiency was also assessed in subjects acutely intoxicated with arsenic trioxide (As2O3) and in patients with liver diseases. Several observations in humans can be explained by the properties of the enzymic systems involved in the methylation process which we have characterized in vitro and in vivo in rats as follows: (1) production of Asi metabolites is catalyzed by an enzymic system whose activity is highest in liver cytosol; (2) different enzymic activities, using the same methyl group donor (S-adenosylmethionine), lead to the production of mono- and di-methylated derivatives which are excreted in urine as MMA and DMA; (3) dimethylating activity is highly sensitive to inhibition by excess of inorganic arsenic; (4) reduced glutathione concentration in liver moderates the arsenic methylation process through several mechanisms, e.g. stimulation of the first methylation reaction leading to MMA, facilitation of Asi uptake by hepatocytes, stimulation of the biliary excretion of the element, reduction of pentavalent forms before methylation, and protection of a reducing environment in the cells necessary to maintain the activity of the enzymic systems. 相似文献
To consider the past, present and future of in situ spectroelectrochemistry, a review on the recent state of modern spectroelectrochemistry and trends in the development of spectroelectrochemcial techniques is presented for the combined application of different in situ spectroelectrochemcial methods like ESR spectroelectrochemistry, NMR spectroelectrochemistry, Raman spectroelectrochemistry or IR spectroelectrochemistry to electrode systems. Starting with a discussion of the first steps in spectroelectrochemistry in the past, the main part of this review is focused on the advantages of the combined application of spectroelectrochemical techniques in the analysis of electrode reactions. The spectroelectrochemical methods are demonstrated to be successful in electrode reactions both for solid structures like polymers or carbon nanotubes and for molecular structures like fullerenes and oligothiophenes. The final outlook is attributed to future developments in spectroelectrochemistry. 相似文献
The electrochemical treatment of cancer (EChT) consists in the passage of a direct electric current through two or more electrodes inserted locally in the tumor tissue. The extreme pH changes induced have been proposed as the main tumor destruction mechanism. Here, we study ion transport during EChT through a combined modeling methodology: in vivo modeling with BALB/c mice bearing a subcutaneous tumor, in vitro modeling with agar and collagen gels, and in silico modeling using the one-dimensional Nernst-Planck and Poisson equations for ion transport in a four-ion electrolyte. This combined modeling approach reveals that, under EChT modeling, an initial condition with almost neutral pH evolves between electrodes into extreme cathodic alkaline and anodic acidic fronts moving towards each other, leaving the possible existence of a biological pH region between them; towards the periphery, the pH decays to its neutral values. pH front tracking unveils a time scaling close to t(1/2), signature of a diffusion-controlled process. These results could have significant implications in EChT optimal operative conditions and dose planning, in particular, in the way in which the evolving EChT pH region covers the active cancer cells spherical casket. 相似文献
The aim of this study was to explore the protective effects of Trichosanthes kirilowii ethanol extract (TKE) against cisplatin-induced acute renal failure (ARF). In the in vitro study, TKE-pretreated porcine kidney cells (PK15) exhibited enhanced cell viability after cisplatin (15 μg mL? 1) treatment in both MTT and crystal violet assays. PK15 cells pretreated with TKE (50 μg mL? 1) exhibited increased glutathione content, decreased reactive oxygen species production and ameliorated p53 expression. In vivo study, rats were administered with TKE for 4 weeks before cisplatin (5 mg kg? 1) injection. TKE (100 mg kg? 1) decreased blood urea nitrogen and creatinine levels by 24% and 47%, respectively, in comparison with cisplatin-alone group. In addition, TKE pretreatment ameliorated cisplatin-induced oxidative stress, as evidenced by increased antioxidative enzyme levels and decreased lipid peroxidation levels. Moreover, TKE pretreatment reduced histopathological alterations in the kidney with decreased apoptotic cells. Taken together, TKE might be beneficial in treating cisplatin-induced ARF. 相似文献
Summary At the session of the WPAC of Fechem on education in analytical chemistry it was concluded that it is now essential to include chemometrics and basic knowledge of computers in all courses on analytical chemistry.
Tendenzen in der analytisch-chemischen Ausbildung
Zusammenfassung Bei einer Tagung der WPAC über die Lehre auf dem Gebiet der analytischen Chemie wurde bei der Betrachtung neuer Aspekte festgestellt, daß vor allem Chemometrie und Grundkenntnisse in Computertechnik in die Ausbildung aufgenommen werden sollten.
The data on lipid-nucleic interactions and their role in vitro and in vivo are presented. The results of study of DNA-lipid complexes in absence and in presence of divalent metal cations (triple complexes) are discussed. The triple complexes represent the generation of cellular structures such as pore complexes of eucaryotes and "Bayer's junctions" of procaryotes. The participation of triple complexes in the formation of structure of bacterial and eucaryotic nucleoid and nuclear matrix is analysed. A model of formation of triple complexes and cellular structures and their role in DNA-lipid interactions are discussed. 相似文献
Summary: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(II ) 2‐ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight = 14 000 g · mol−1 and a low polydispersity ( = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi‐logarithmic kinetics, which leads to polystyrene with an of 13 400 g · mol−1 and a low polydispersity index ( = 1.14).
Appearance of miniemulsion before and after the reducing agent ascorbic acid was added (left); and GPC traces representing molecular weights during the AGET ATRP of BA in miniemulsion in the presence of air (right). 相似文献
Displacement reactions between calcium sulfates (gypsum and anhydrite) and aqueous solutions of Ba−, Sr− and Pb-salts were investigated by means of TG, DSC,microscopy and x-ray. The reactions can be followed directly by microscopy when cleavage plates of gypsum crystals are used. The first steps of crystallization are in some cases of a topotactical nature. The results presented in this paper deal mainly with the formation of barite, celestite and anglesite by displacement reactions at different temperatures. 相似文献
Biocatalytic electrodes made of buckypaper were modified with PQQ‐dependent glucose dehydrogenase on the anode and with laccase on the cathode. The enzyme modified electrodes were assembled in a biofuel cell which was first characterized in human serum solution and then the electrodes were placed onto exposed rat cremaster tissue. Glucose and oxygen dissolved in blood were used as the fuel and oxidizer, respectively, for the implanted biofuel cell operation. The steady‐state open circuitry voltage of 140±30 mV and short circuitry current of 10±3 µA (current density ca. 5 µA cm?2 based on the geometrical electrode area of 2 cm2) were achieved in the in vivo operating biofuel cell. Future applications of implanted biofuel cells for powering of biomedical and sensor devices are discussed. 相似文献