Increase In Concentration Of Agent Research Articles

Gadolinium-Based MRI Contrast Agents Induce Mitochondrial Toxicity and Cell Death in Human Neurons, and Toxicity Increases With Reduced Kinetic Stability of the Agent

This preclinical study was devised to investigate potential cellular toxicity in human neurons induced by gadolinium-based contrast agents (GBCAs) used for contrast-enhanced magnetic resonance imaging (MRI). Neurons modeling a subset of those in the basal ganglia were tested, because the basal ganglia region is 1 of 2 brain regions that displays the greatest T1-dependent signal hyperintensity changes. Eight GBCAs were tested. Dopaminergic neurons modeling a subset of those in the basal ganglia were differentiated from an established human neuroblastoma cell line and exposed to increasing concentrations of each agent for 7 days. The tested dosages ranged from clinically relevant concentrations measured in some autopsy patients who had received repeated injections of contrast for MRI, to higher concentrations to reveal dose-dependent toxicity trends. Cell death, mitochondrial membrane potential, mitochondrial oxidative capacity, and mitochondrial function measured by oxygen consumption were quantified in cells treated with each GBCA or the osmolality control mannitol and compared to untreated cells which served as a negative control. Mannitol caused no change from negative controls in any of the tests, at any concentration tested. For all GBCAs, cell death increased with exposure dose, with toxicity at clinically relevant doses for agents with lower kinetic stability. Reduction of mitochondrial membrane potential and oxidative respiratory function also generally mirrored the agents' structural kinetic stabilities, with greater impairment at lower concentration for the less stable agents. In human neurons modeling a subset of those in the basal ganglia, these results demonstrate a toxic effect of gadolinium-containing MRI contrast agents on mitochondrial respiratory function and cell viability. Toxicity increases as agent concentration increases and as the kinetic stability of the agent decreases.

ORGANOPHOSPHATE ESTERS REMOVAL BY UV/H2 O2 PROCESS MONITORED BY 31P NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Abstract The present work aims to study the photocatalytic degradation of three organophosphate esters considered environmental emerging contaminants by the UV/H2O2 system with the use of 31P NMR spectroscopy to investigative their removal after the treatment. Results demonstrated the efficiency of the oxidation system in removing the esters tris(2-butoxyethyl) phosphate (TBEP), tris(2-chloroethyl) phosphate (TCEP) and tri-butyl phosphate (TBP) from aqueous solutions when they were individually present and mixed. High levels of degradation of these chemicals were achieved, in addition to the good performance of the analytical technique applied in the study, which represents some advantages in comparison with other techniques reported in the literature. An increase in the 31P NMR signal removal could also be observed when the oxidizing agent concentration increases. Decreases in solution acute toxicity were also verified for both TBP and TBEP treated samples when compared with the samples before the treatment.

Analysis on the crystallization degree inside the cryoprotectant microdroplets during freezing process on the liquid nitrogen surface

Based on the non-isothermal crystallization kinetic model, the temperature distribution and the degree of crystallization inside cryoprotectant (CPA) microdroplets are theoretically investigated when they are frozen on the liquid nitrogen surface. The results show that the ice crystallization degree in surface region is the largest one during the phase transition temperature zone, while the middle region is intermediate, and the center region is the lowest. Also, the higher the concentration of CPA, the more uneven both the temperature and the crystallization inside the droplets. The maximum temperature difference between the surface and the center region of 50% glycerol with a volume of 4 μL is about 8 K, but the crystallization degree of the former is about 41 times larger than that of the latter. For water case, the temperature difference is only 1.1 K, and the degree of ice crystallization on the surface is roughly 6 times higher than that in the center. The volume of microdroplets seems to have few effects on the final crystallization degree for lower concentration solutions, but prolongs the freezing phase transition duration (i.e. 14.48 s for 2 μL and 19.82 s for 8 μL for 20% glycerol case). For the higher concentration solutions, the freezing phase change temperature zone is not obvious, but the final crystallization degree will increase significantly as the volume of microdroplets rising (i.e. 0.29×10−6 for 2 μL, 0.80×10−6 for 8 μL for 50% glycerol case). As CPA agent concentration increases, the phase transition temperature obviously decreases (i.e. 273.15 K for water, 250 K for 20% glycerol, 225 K for 50% glycerol, 158 K for Vs55) and the final crystallization degree also has the same trends (i.e. 1 for both water and 20% glycerol, 5.61×10−7 for 50% glycerol, and 5.7×10−16 for Vs55).

Effect of cyclic compression and curing agent concentration on the stabilization of mechanical properties of PDMS elastomer

Under repeated deformation, the mechanical properties of polydimethylsiloxane (PDMS) elastomer evolve. This paper aims to investigate the effect of curing agent concentration on the mechanical response of PDMS elastomer under cyclic compressive loading. PDMS elastomer samples containing various curing agent concentrations were prepared following ASTM D575 standard. Three different curing agent concentrations were investigated: 6.25, 9.09 and 16.67wt%. Monotonic compressive test up to failure and 100cycles of cyclic compressive test were performed using Instron 3369 50kN dual column testing machine at a constant crosshead displacement rate of 12mm/min. It was found that the compressive modulus increases with the curing agent concentration. The effects of cyclic compression on strain hardening, compressive modulus, and creep were also investigated. Results showed that cyclic compression contributes to the stabilization of the materials. Moreover, the number of cycles required to reach strain hardening stabilization decreases as the curing agent concentration increases.

Optical investigations of blue shift in ZnS quantum dots

ZnS quantum dots were synthesized using sulfur source of sodium sulphide and mercaptoethanol via chemical bath deposition technique. The synthesized ZnS QDs were analyzed and characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and UV–visible (UV–vis) spectrophotometry. The average particle size goes down to 1.9 nm as capping agent concentration increases and corresponding absorption coefficient peak goes down to 265 nm. The blue shift within absorption-wavelength was elaborated. The refractive index and optical dielectric constant are calculated. A correlation between energy gap and absorption coefficient aside and particle size another side is discussed.

Preparation, Characterization and Electroluminescence Studies of Cadmium Selenide Nanocrystals

Nanoparticles of CdSe were prepared using chemical method by reacting cadmium acetate and sodium selenosulfite in presence of capping agent mercaptoacetic acid (MAA). Two-propanol was added to this mixture, drop wise, till it becomes turbid. The precipitate was separated through centrifugation to get dry powder. TEM shows that the most particles are spherical with particle size of the order of few nanometres. The XRD pattern indicates the hexagonal phase with wurtzite structure. The broadening of peaks tends to increase with increasing capping agent concentration showing decrease in particle size in range of 3 nm to 4 nm. Absorption spectra of CdSe nanoparticles indicated that the position of absorption peak shift to smaller wavelength as the capping agent concentration increases. Considering this as band-to-band absorption, their effective band gap was calculated and particle size was estimated using effective mass approximation, which is nearly same as obtained by XRD. The electroluminescence (EL) cells were prepared by placing CdSe nanoparticles between SnO2 coated conducting glass plate and aluminum foil. Alternating voltage of various frequencies was applied and EL brightness at different voltages was measured and corresponding current was also recorded. It is seen that emission starts at a threshold voltage and then increases rapidly with increasing voltage. The lower threshold and higher brightness have been observed for smaller nanoparticles. Linear relation between voltage and current indicates ohmic nature. Voltage vs brightness curve shows that EL is produced by acceleration-collision mechanism.

Oligomerization of ribonuclease A under reducing conditions

By lyophilization from 40% acetic acid solutions, bovine ribonuclease A forms well characterized, three-dimensional domain-swapped oligomers: dimers, trimers, tetramers, and higher order multimers. Each oligomeric species consists of at least two conformers. Identical oligomers also form by thermally-inducing the oligomerization of highly concentrated RNase A dissolved in fluids endowed with various denaturing power. Now, our question is: which might the influence of a reducing agent be on RNase A oligomerization, i.e., of conditions that decrease the stability of the protein and increase the mobility of its swapping domains? To address this question, we carried out experiments of RNase A oligomerization in the presence of increasing concentrations of dithiothreitol (DTT) under the two experimental conditions mentioned above. Results indicate that RNase A oligomers similar to those previously known form anyhow, but with a change of their relative proportions. The amounts of dimers and trimers decrease by increasing the concentration of DTT, while the yields of two tetramers remarkably increase. Moreover, in the presence of DTT RNase A forms labile and probably unstructured aggregates that can possibly drive the protein towards precipitation when the reducing agent's concentration increases. Taken together, these results point out once again (i) the important role of the 3D domain swapping mechanism in protein oligomerization, and (ii) the importance of the native structure of RNase A (and of proteins in general) in preventing an uncontrolled aggregation and precipitation in a reducing and highly crowded environment like that existing in a living cell.

RAFT synthesis of poly(N‐isopropylacrylamide) and poly(methacrylic acid) homopolymers and block copolymers: Kinetics and characterization

AbstractReversible addition‐fragmentation chain transfer (RAFT) polymerization was used successfully to synthesize temperature‐responsive poly(N‐isopropylacrylamide) (PNIPAAm), poly(methacrylic acid) (PMAA), and their temperature‐responsive block copolymers. Detailed RAFT polymerization kinetics of the homopolymers was studied. PNIPAAm and PMAA homopolymerization showed living characteristics that include a linear relationship between Mn and conversion, controlled molecular weights, and relatively narrow molecular weight distribution (PDI < 1.3). Furthermore, the homopolymers can be reactivated to produce block copolymers. The RAFT agent, carboxymethyl dithiobenzoate (CMDB), proved to control molecular weight and PDI. As the RAFT agent concentration increases, molecular weight and PDI decreased. However, CMDB showed evidence of having a relatively low chain transfer constant as well as degradation during polymerization. Solution of the block copolymers in phosphate buffered saline displayed temperature reversible characteristics at a lower critical solution temperature (LCST) transition of 31°C. A 5 wt % solution of the block copolymers form thermoreversible gels by a self‐assembly mechanism above the LCST. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1191–1201, 2006

Direct measurement of water availability in gelled plant tissue culture media

Water constitutes nearly 100% of the volume and 95% of the mass of gelled plant tissue culture media. Even so, plant growth and development responses observed to occur with relatively small changes in gelling agent concentration (0.1% of media total mass) have been attributed to changes in media water availability. Measurements with three alternative direct techniques, specific for measuring physiochemical water availability indicated the effects of a change of this magnitude in gelling agent concentration negligibly affected the media water potential and water conductivity. Sensitive pressure membrane measurements indicated that incremental gelling agent concentration increases of 0.1% (of media total mass) within the range normally used for plant tissue culture media, depressed water matric potential only 1–2cm H2O (1–2×10−4 MPa (mega pascal.)); these values were confirmed with equally sensitive tensiometer measurements. Moreover, no effect of concentration on water movement could be detected with a precise constant-head permeameter over a broader range of gelling agent concentrations. These results indicate that eitherin vitro plants are extremely sensitive to subtle shifts in water status, or other physiochemical factors that also change with gelling agent concentration are contributing to the reported effects on plant growth and development.

Mobilization of heavy metals from river sediments of Northern Greece by complexing agents

The influence of NTA, EDTA, STPP, Triton X100, PO inf4 sup3 and NO inf3 sup− on the mobilization of Pb, Cd, Cu, Cr and Mn from sediments of two rivers located in Northern Greece was studied. The release caused by all examined complexing agents was higher in deionized water than either Axios or Aliakmon river water due to the lack of competition of Ca and Mg cations with the heavy metals for the studied complexing agents, and the decrease of ionic strength. From all examined agents NTA and EDTA showed the greater mobilization ability. Copper showed the greater tendency for remobilization by all examined agents, (according to the order: EDTA≅NTA, Triton X1004 PO inf4 sup3− > NO inf3 sup3− ≅STPP) while Cr and Mn the smallest following the orders: NTA, PO inf4 sup3− >> NO inf3 sup− , Triton X1004 EDTA, STPP and STPP > EDTA > NTA > Triton X 100 ≅ PO inf4 sup3− NO3, respectively. An increase in mobilization was noticed with an increase of agent concentration and time of shaking.

Further elements of structural specificity in potentiation and blockade of excitable tissue preparations by aryl esters of tropine and ψ-tropine. III

The diphenylacetate, o-chlorophenylacetate, m-chlorophenylacetate, p-chlorophenylacetate, and p-tolylacetate esters of tropine and pseudo tropine have been studied in assorted roles as in vitro inhibitors of the acetylcholinesterase-acetylcholine system, as blocking agents on the single node of Ranvier in frog sciatic nerve and on the phrenic nerve-diaphragm preparation from the rat, and as intravenously administered toxins in the mouse. Considerable evidence for stereospecificity in the drug-tissue receptor interactions produced by any isomeric pair of esters (tropine vs. ψ-tropine derivatives) has been amassed. Specific findings of interest include: 1. 1. The entire series of esters functions in the weak-to-moderate category of AChE inhibitors, with no striking instances of isolated potency. 2. 2. These esters are very potent blocking agents on the single node of Ranvier, producing powerful depression of the action current amplitude and elevation of the threshold voltage requirement at bathing concentrations of 1 m M and below. A striking exception to this behavior is afforded by the p-chlorophenylacetate esters III and III-ψ which display no blocking potencies at low concentrations, but instead produce tiny increases in action current at high (20 m M) concentrations. 3. 3. On the rat phrenic nerve-diaphragm, the esters generally evoke striking potentiation of the muscle twitch response via either the direct or indirect stimulation pathways, at low (10 −5 to 10 −4 M) concentrations, followed by an overriding blockade of twitch response as the concentration level is raised. Again, the p-chloro ester III is unique in the series in displaying no potentiating action, and a twitch blockade response (direct stimulation pathway) which is partially alleviated by further increase in concentration of agent. Compound III-ψ shares in the latter behavior. 4. 4. In the intact mouse and cat via the intravenous route of administration, these agents are potent convulsants with additional peripheral involvement. The tropine analogs III and IV are respectively more potent than their pseudo isomers, and in a further demonstration of ordered specificity with the chlorophenylacetate esters in both the tropine and ψ-tropine series, the positional isomerism of the chloro group on the ring furnishes the potency sequence para > meta > ortho. These findings are discussed in terms of possible modes of drug-chemoreceptor interaction in the biologic preparations studied.