137,762 research outputs found
Physiological adaptation of two unicellular green algae to pH stress.
No full textTwo marine algae, Dunaliella parva and Chlorococcum submarinum were selected to study the effect of pH stress on single celled algae. D. parva has been well characterised physiologically, but not with regards to pH stress. C submarinum has not been so extensively studied, but is known to grow over a wide pH range from pH 4.5 to 10.5. It was of prime importance that the algal cells were grown at the desired extreme values of external pH. Problems were encountered at high levels of pH but were overcome by growing the algae in a fermenter set up as a batch culture. This method of growth was used for both algae at extreme values of external pH and it allowed the accurate control of the media pH by the automatic addition of acid or alkali. pH 7.5 cells were grown in normal flask batch culture. The cell number, cell volume, and chlorophyll content of both algae were determined over a wide range of pH values, showing that differences in external pH had significant effects on individual cells. Protein concentrations were measured and were shown to increase in pH 9.0 grown cells. Determination of cell volume, internal pH and membrane potential have been carried out using radiolabelled isotopes for algae grown over a wide pH range. Cell volume was shown to increase at both acid and alkaline pH values. The internal pH of both algae was found to be at a more neutral pH than the external pH. For both D. parva and C submarinum, the membrane potential increased with increasing external pH. Enzyme activities in crude extracts were measured to establish the effects of external pH changes on metabolic pathways. The activity of these enzymes, taken from different organelles in the cell, was used to investigate the uniformity of internal pH
Measurement of the D+/- production asymmetry in 7 TeV pp collisions
No full textThe asymmetry in the production cross-section \sigma of D+/- mesons, A_P = (\sigma(D+) - \sigma(D-))/(\sigma(D+) + \sigma(D-)), is measured in bins of pseudorapidity \eta and transverse momentum p_T within the acceptance of the LHCb detector. The result is obtained with a sample of D+ -> K_S pi+ decays corresponding to an integrated luminosity of 1.0 fb^-1, collected in pp collisions at a centre of mass energy of 7 TeV at the Large Hadron Collider. When integrated over the kinematic range 2.0 K_S pi+ decay is negligible. No significant dependence on \eta or p_T is observed
Concept and development of an autonomous wearable micro-fluidic platform for real time pH sweat analysis
No full textIn this work the development of an autonomous, robust and wearable micro-fluidic platform capable of performing on-line analysis of pH in sweat is discussed. Through the means of an optical detection system based on a surface mount light emitting diode (SMD LED) and a light photo sensor as a detector, a wearable system was achieved in which real-time monitoring of sweat pH was performed during 55 minutes of cycling activity. We have shown how through systems engineering, integrating miniaturised electrical components, and by improving the micro-fluidic chip characteristics, the wearability, reliability and performance of the micro-fluidic platform was significantly improved
D-, L- and D,L-Tryptophan-Based Polyamidoamino Acids: pH-Dependent Structuring and Fluorescent Properties
No full textChiral polyamidoamino acids were obtained by polyaddition of N,N’methylenebisacrylamide with D-, D,L- and L-tryptophan (M-D-Trp, M-D,L-Trp and M-L-Trp). L-tryptophan/glycine copolymers, M-G-L-Trp5, M-G-L-Trp10, M-G-L-Trp20 and M-G-L-Trp40, were prepared from L-tryptophan/glycine mixtures. These polymers were amphoteric, with acid-base properties similar to those of the parent amino acids. The L-tryptophan/glycine copolymers with high glycine content were water soluble in the
pH range 2-12. M-G-L-Trp40 showed a solubility gap centred at pH 4.5 and all tryptophan homopolymers were soluble only at pH > 7. Dynamic light scattering measurements performed in their solubility ranges, namely 2-11 M-G-L-Trp5, M-G-L-Trp10 and M-G-L-Trp20 and 7-11 for M-G-L-Trp40, M-D-Trp, M-L-Trp and M-D,L-Trp, showed that the size of all samples did not significantly vary with pH. Both M-L-Trp and M-G-L-Trp copolymers showed pH-dependent circular dichroism spectra in the wavelength interval 200–280 nm, revealing structuring. All samples were fluorescent. Their emission spectra were unstructured and, if normalized for their tryptophan content, almost superimposable at the same pH, providing evidence that only tryptophan governed the photoluminescence properties. Changing pH induced in all cases a slight shift of the emission wavelength maximum ascribed to the modification of the microenvironment surrounding the indole ring induced by different protonation degrees
Control of mineral scaling in power plant recirculating cooling systems using treated municipal wastewater
No full textThe global energy demand is projected to increase by 77% from 2006 to 2030 along with a projected 38% increase in freshwater withdrawal for cooling in power industry. Finding alternative sources of water for cooling has become essential for future energy generation in thermoelectric power plants because of water scarcity in many parts of the US. Treated municipal wastewater is considered as one of the most promising alternative water sources because of its geographic distribution and abundant quantity. However, its impaired water quality makes the cooling tower management more challenging. Therefore, effective approaches are required to prevent scaling, corrosion, and biological growth to promote the reuse of treated municipal wastewater as cooling water in power plants.
This study focuses on understanding mineral scale formation and developing effective mitigation methods when using tertiary treated municipal wastewater as power plant cooling makeup. Two types of tertiary-treated municipal wastewater that were evaluated included secondary-treated water with pH adjustment (MWW_pH) and water from secondary-treatment followed by nitrification and sand filtration (MWW_NF). Laboratory-scale studies and pilot-scale cooling systems were used to evaluate mineral scaling formation and inhibition on non-heated surfaces (e.g., pipelines, tower packing, etc.) under conditions relevant to full-scale cooling systems. Results showed that pH adjustment to 7.8 plus the addition of 5 ppm polymaleic acid (PMA) could reduce the scaling significantly with MWW_pH. MWW_NF exhibited little scaling potential, which is related in part to the lower pH and alkalinity in this water. Amorphous calcium phosphate (ACP) was the primary form of mineral scale on non-heated surface with the above two-types of tertiary-treated municipal wastewater.
A bench-scale experimental system was designed to simulate the condenser surface to study the impacts of mineral scaling on the heated surfaces and the effectiveness of proposed scaling control strategies under these conditions. Heated surface favored the formation of hydroxyapatite (HAP), the most thermodynamically stable calcium phosphate, was the main reason for the crystalline fouling with MWW_pH at pH 7.8. 10 ppm PMA addition could suppress the crystalline fouling of MWW_pH at 7.8 to a low level by inhibiting the transformation of amorphous calcium phosphate to hydroxyapatite during the test period. Significant crystalline fouling was identified with MWW_NF at pH 7.2 while pH adjustment to 7.8 resulted in negligible fouling.
The impact of flow velocity on particle deposition was analyzed in a quantitative model, showing positive deposition potential for bulk precipitates at flow velocity of 0.5 and 0.4 m/s while little particulate fouling was theoretically predicted at 0.6 m/s in the test situation. Bench-scale studies were consistent the model prediction, confirming that the model could be used to identify optimal hydrodynamic conditions to control depositions of bulk precipitates.
The mechanism of calcium phosphate scale control by common antiscalants included PMA and 1-hydroxyethane 1,1-diphosphonic acid (HEDP) was elucidated to provide scientific background for the effective scaling mitigation when treated municipal wastewater is used as make-up in thermoelectric power plant cooling systems. Both PMA and HEDP inhibited the transformation of ACP to HAP by preventing the aggregation of ACP particles. However, PMA dispersed the ACP particles mainly through electrostatic repulsive force while hydration force was hypothesized to be the reason for the function of HEDP in dispersion.
The key findings of this study indicate that it is possible to control mineral scaling through direct chemical addition at proper operating conditions when treated municipal wastewater is used as makeup water in the recirculating cooling system. This study not only evaluated scaling control methods in cooling systems, but also revealed the fundamentals of scaling formation and inhibition
Photonic porous silicon as a pH sensor
No full textChronic wounds do not heal within 3 months, and during the lengthy healing process, the wound is invariably exposed to bacteria, which can colonize the wound bed and form biofilms. This alters the wound metabolism and brings about a change of pH. In this work, porous silicon photonic films were coated with the pH-responsive polymer poly(2-diethylaminoethyl acrylate). We demonstrated that the pH-responsive polymer deposited on the surface of the photonic film acts as a barrier to prevent water from penetrating inside the porous matrix at neutral pH. Moreover, the device demonstrated optical pH sensing capability visible by the unaided eye
The effect of dietary calcium inclusion on broiler gastrointestinal pH: quantification and method optimization
No full textThere is little consensus as to the most appropriate methodology for the measurement of gastrointestinal pH in chickens. An experiment was conducted to establish the optimum sampling method for the determination of broiler digesta pH in birds fed differing levels of dietary calcium. Ross 308 broilers (n = 60) were fed one of two experimental diets, one containing 0.8% monocalcium phosphate and 2% limestone and one containing 0.4% monocalcium phosphate and 1% limestone. Four factors were investigated to determine the most appropriate method of measuring broiler gastrointestinal digesta pH: removal from the tract, prolonged air exposure, altering the temperature of the assay, and controlling the water content of the digesta. The conditions were assessed at bird ages from 7 to 42 d post hatch. Dietary Ca content had no significant effect on in situ pH, but it contributed towards variance in ex situ pH of both gizzard and duodenum digesta
Stimulation of Na<sup>+</sup>/H<sup>+</sup> Exchanger Isoform 1 Promotes Microglial Migration
No full textRegulation of microglial migration is not well understood. In this study, we proposed that Na+/H+ exchanger isoform 1 (NHE-1) is important in microglial migration. NHE-1 protein was co-localized with cytoskeletal protein ezrin in lamellipodia of microglia and maintained its more alkaline intracellular pH (pHi). Chemoattractant bradykinin (BK) stimulated microglial migration by increasing lamellipodial area and protrusion rate, but reducing lamellipodial persistence time. Interestingly, blocking NHE-1 activity with its potent inhibitor HOE 642 not only acidified microglia, abolished the BK-triggered dynamic changes of lamellipodia, but also reduced microglial motility and microchemotaxis in response to BK. In addition, NHE-1 activation resulted in intracellular Na+ loading as well as intracellular Ca2+ elevation mediated by stimulating reverse mode operation of Na+/Ca2+ exchange (NCXrev). Taken together, our study shows that NHE-1 protein is abundantly expressed in microglial lamellipodia and maintains alkaline pHi in response to BK stimulation. In addition, NHE-1 and NCXrev play a concerted role in BK-induced microglial migration via Na+ and Ca2+ signaling. © 2013 Shi et al
Molecular probes for the evaluation of three isomerase enzyme mechanisms in secondary metabolism
No full textThis thesis is focused on an investigation of the mechanisms of three enzymatically mediated carbon skeleton isomerisation reactions.
Chapter 1 provides an overview of some representative examples of the carbon skeleton rearrangement reactions in enzymology.
Chapter 2 describes the preparation and use of fluorolittorines to explore the mechanism of the rearrangement of the tropane alkaloid littorine to hyoscyamine which is a reaction mediated by the cytochrome P450 enzyme.
Chapter 3 describes the synthesis of D-ribose-1-phosphonates and the cyclic phosphonates (phostone) that are candidate inhibitors of the enzymatic isomerisation of 5-fluoro-5-deoxy-ribose-1-phosphate (5-FDRP) to 5-fluoro-5-deoxy-ribulose-1-phosphate (5-FDRulP), an important step in fluorometabolite biosynthesis pathway in Streptomyces cattleya.
Chapter 4 describes the synthesis of 5-hydroxy-3,4-dioxohexylphosphonate and [5-13C]-5-hydroxy-3,4-dioxohexylphosphonate. These compounds are proposed as candidates for the transition state of the retro-aldol/aldol mechanism of the enzymatic isomerisation of 1-deoxy-D-xylulose-5-phosphate (DXP) to 2-C-methylerythitol-phophate-2-phosphate (MEP) in the biosynthesis of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). The influence of pH on tautomerisation of [5-13C]-5-hydroxy-3,4-dioxohexylphosphonate is also described.
Chapter 5 describes the general chemical and biochemical methodologies utilised in this research project
Studies Towards a pH-Sensitive Anticancer Prodrug Model
No full textTumour-activated prodrug (TAP) is designed to aim at increasing the prodrug selectivity to kill cancer cells. One strategy to is to design a TAP containing an amine cytotoxin, present as an amide function, which could be released more rapidly in the low pH environment of tumour tissues when amide undergoes hydrolysis.
The prodrug model (1) was the subject of the current study. At lower pH its un-ionised carboxylic acid group provides neighbouring catalysis of hydrolysis of the adjacent amide. It was synthesised via ring-opening of the imide (2) which itself was directly synthesised from endo-bicyclo[2.2.2]octa-5-ene-2,3-dicarboxylic anhydride and p-methoxyaniline.
The pH-rate profile of (1) was established over the pH range of 3-10, covering rapid hydrolysis of un-ionised acid-amide at lower pH but slower imide formation above pH 8 from the ionised acid-amide. From the kinetic data were calculated the dissociation constant for (1) (pKa: 5.1 at 30 C) and limiting lower pH rate constant for hydrolysis of (1) in its fully neutral form (klim: 0.44 min-1 at 30 C). The data in the pH range of 8-10 provided klow (0.067 min-1) representing formation of (2) from fully ionised (1).
The following equilibrium reaction was also investigated at high pH, at which (1) was in its fully ionised amide carboxylate form, by kinetic studies on (2) in hydroxide solutions.
Imide + OH- Amide carboxylate
The second order rate constant for the forward reaction, kf, was 74 L mol-1 min-1 which with klow for the reverse reaction gave K as 1100 L mol-1
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