SEARCH · Search PubMed

Results for “Buffers”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources

PubMed1976

A search for the best buffer to use in assaying human lactate dehydrogenase with the lactate-to-pyruvate reaction.

Highly purified human lactate dehydrogenases I and V were assayed in 17 different buffers, at a variety of reaction pH's. Diethanolamine and 2-amino-2-methyl-1,3-propanediol provided the best measurements of the enzyme, assayed lactate-to-pyruvate. However, the commercial preparation of 2-amino-2-methyl-1,3-propanediol contained insoluble matter and was relatively expensive. All of the four buffers nowmost commonly used were found to present difficulties. Glycine and pyrophosphate were inhibotory tolactate dehydrogenase activity with increasing buffer concentration. 2-Amino-2-methyl-1-propanol had three major disadvantages: it is chemically unstable during reagent preparation; activity is dependent on buffer concentration; and the pH optima for isoenzymes I and V are vastly different. The pKa of tris(hydroxymethyl)aminomethane is 8.0 at 30 degrees C, whereas to measure total activity the reaction pH should be greater than 8.5; thus tris(hydroxymethyl)aminomethane has limited buffering capacity at the reaction pH.

Buffers↗

PubMed2000

Buffering action of human dentin in vitro.

PURPOSE: The purpose of this study was to determine the relative contributions of the mineral and organic phases of dentin to its total buffering capacity and to compare the buffering abilities of normal and caries-affected dentin for acids used in adhesive dentistry. MATERIALS AND METHODS: Disks of normal and caries-affected human coronal dentin 0.6 mm thick were prepared. Fifty microL of various acids were applied to the surface of mineralized or completely demineralized dentin for varying lengths of time. They were collected from the surface and combined with water rinses to permit titration of the total amount of acid applied, the amount recovered, the total amount that was taken up by the dentin, and the amount that diffused across dentin into 1 mL of water. Equal volumes of acids were applied to mineralized or demineralized dentin powder or hydroxyapatite powder. RESULTS: About 88% to 90% of applied acid was recovered from the surface; only 10% to 12% of the acid was taken up by dentin. Of the H+ that was taken up, only 1% to 2% actually diffused across 0.6 mm of dentin. Increasing the application time of 37% phosphoric acid did not increase the amount of H+ that diffused across dentin. Increasing the concentration of phosphoric acid from 10% to 65% produced only slight increases in H+ diffusion across dentin. There was no difference in the buffering capacity of normal vs caries-affected dentin disks. Almost all of the buffering capacity of dentin is due to its mineral phase. CONCLUSION: The high buffering capacity of dentin and the high reactivity of H+ insure that little H+ diffuses through dentin more than 0.6 mm thick.

Analysis of Variance↗

PubMed2003

Effect of ionic strength of buffer on the measurement of erythrocyte electrophoretic mobility.

BACKGROUND: Measurement of the electrophoretic mobility (EM) of biological cells provides information on the electrical properties of the cell surface. Different research groups have used different electrophoretic techniques. It is well known that the osmolality of the buffer used during an experiment exerts a major impact on EM, particularly in biological cells. In previous experiments either high or low ionic strength electrophoresis buffers were used with an arbitrary preference. The aim of this study is to investigate which buffer is more useful for EM measurements, and hence to give greater insight into the results of such experiments. MATERIAL/METHODS: Blood was drawn from healthy volunteers. Two different buffers were prepared: low ionic and high ionic. Twenty molarity steps were prepared by mixing the buffers in different ratios. Measurements were made using a Zetasizer. RESULTS: Our data confirmed that the EM fell as ionic strength increased. However, the relationship was biphasic: the first ten points were linear with a steep negative slope and the second set also linear but with a much smaller slope. CONCLUSIONS: EM studies usually have one of two extreme aims: either to compare the inherent surface electrical properties of cells from different sources at the same ionic strength, or to study the influence of different ionic environments on the surface electrical properties of cells from the source. Our data suggest that in the first instance it is better to work at high ionic strength. In the second, low ionic strength is preferable.

Blood Chemical Analysis↗

PubMed2003

[Effects of Na(+)-HCO3- symport on ischemia/reperfusion injury; Na+/H+ exchanger inhibitor and buffer composition].

We studied the impact of perfusate buffer composition on the relative degree of protection afforded by Na+/H+ exchanger (NHE) inhibition during ischemia as opposed to during reperfusion. Isolated rat hearts were perfused with bicarbonate- or HEPES-buffered medium. There was infusion of HOE 694 immediately before ischemia, during initial reperfusion, or during both of these periods. With bicarbonate-buffered medium, HOE 694 improved the post-ischemic recovery of left ventricular developed pressure (LVDP) when given before ischemia and before ischemia plus during reperfusion. In the presence of HEPES-buffered medium, however, HOE 694 significantly improved recovery of LVDP in all protocols. HOE 694 also provided an almost complete recovery of LVDP (88 +/- 9% vs 30 +/- 7% in controls) when given before ischemia plus during reperfusion. In conclusion, our results suggest that the influence of NHE activity during reperfusion on the extent of functional recovery is modulated significantly by perfusate buffer composition.

Animals↗

PubMed2003

[Influence of the buffer capacity of amine fluoride-containing toothpastes and gels in enamel erosion].

The aim of the study was to evaluate the abrasion resistance of eroded enamel brushed with experimental toothpastes and fluoride gels of varying buffering capacities. 50 Specimens were prepared from extracted human molars and cycled through three alternating de- and remineralizations including brushing abrasion in a brushing machine. Demineralization was accomplished by immersing the samples in 1% citric acid (5 min), remineralization occurred during immersing the samples in artificial saliva (1 min). Groups of ten samples were brushed with either one of the toothpaste (A-C) or one of the fluoridated gels (D-E). Toothpastes and gels were produced on the basis of elmex toothpaste or elmex-gelée (GABA International AG, Switzerland). Amount of titrable acid was defined as amount (mg) of 1 N KOH needed for neutralization of 1 g toothpaste or gel (A: 6 mg, B: 12 mg, C: 24 mg, D: 3.1 mg, E: 10 mg KOH). The following abrasion values (mean + S.D. [micron]) were obtained profilometrically: A: 6.76 +/- 2.05, B: 6.84 +/- 1.19, C: 8.28 +/- 2.89, D: 4.19 +/- 1.09 and E: 0.83 +/- 0.61. No significant difference in abrasion between the toothpastes was found. The fluoride gel with the higher buffering capacity (E) exhibited significantly less abrasion than the gel with the lower buffering capacity (D). It is concluded that in eroded enamel buffering capacity of the tested fluoridated toothpastes has no effect on abrasion, whereas use of fluoride gel with a higher buffering capacity leads to reduced abrasion values.

Amines↗

PubMed1992

Gastric tolerance of single dose unbuffered and buffered acetylsalicylic acid: a randomized comparative endoscopic study in 24 volunteers.

A randomized, three-way crossover study by gastroscopic examination in 24 healthy male volunteers was performed to compare the gastric tolerance of a single dose of buffered or unbuffered acetylsalicylic acid. Gastroscopic assessment was made two hours after administration of the buffered (800 mg ASA) or unbuffered (500 mg ASA) tablets taken with 200 ml of water. Mucosal changes were rare and of a minor nature. Only two volunteers in the unbuffered ASA group presented minor changes (erythema and oedema). No pathological changes were observed after the buffered ASA. Subjective adverse reactions, e.g. epigastric complaints, were reported by four volunteers in the unbuffered group and by two in the buffered group. Based on the limited number and the minor extent of visible changes, statistical tests did not appear to be warranted. The results indicate that buffered ASA is better tolerated.

Adult↗

PubMedDate not supplied

Evaluation of extraction buffers using the current approach of detecting multiple allergenic and nonallergenic proteins in food.

The detection of food allergens has been a challenge because of the increasing need to ensure the absence of undeclared allergens in foods. The current trend in the detection of some food allergens, like peanuts, is based on the detection of multiple allergenic and nonallergenic proteins, and this is the approach that kit manufacturers have adopted. Because commercial kits differ in their ability to detect allergens, regulatory agencies, the food industry, and kit manufacturers are working together to standardize the detection methods. Three kits for the detection of peanuts have been evaluated for performance by the AOAC Research Institute. For this evaluation, a peanut butter suspension was used as a reference material. Several kit components contribute to between-kit analytical variation, even when the same sample is used. One component of commercial kits, which may be contributing to this variability, is the sample extraction buffer. In this study, differences in extractability of 3 allergenic foods were evaluated by using 4 different extraction buffers. The conclusion is that optimum allergen extractability was buffer-dependent, and no single buffer is appropriate for use as a universal extraction solution for all allergenic foods. Therefore, a thorough evaluation of sample preparation buffers needs to be performed for every individual allergenic food. In light of the results obtained, the current approach used for detection of peanut allergens based on the detection of multiple allergenic and nonallergenic proteins is being analyzed.

Allergens↗

PubMed2005

Capacity buffer of the saliva in children and adolescents with cancer: Variations induced by the administration of metotrexate or cyclophosphamide.

OBJECTIVE: To determine the variations in the levels of capacity buffer of the saliva in children and adolescents with cancer that receiving Metotrexate or cyclophosphamide. MATERIALS AND METHODS: A clinical, random-controlled assay was carried out. The sample was composed by 24 children, ages between 2 and 16 years, with diagnostic of Leukemia and Lymphomas attending to The Autonomous Service of University Hospital of Maracaibo and Hospital of Pediatric Specialties. Two groups were conformed to which a sample of saliva was taken before and after the chemotherapy; twelve patients were randomly placed in the G1: patient receiving Metotrexate and twelve in the G2: patient receiving cyclophosphamide. In order to determine the capacity buffer, the CRT Buffer IVOCLAR VIVADENT was used. RESULTS: The capacity salivary buffer did not show significant differences before and after the administration of the cytostatic agents studied. CONCLUSIONS: In this study, the Metotrexate or cyclophosphamide administration does not modify the salivary buffer capacity in pediatric patient with cancer.

Acid-Base Equilibrium↗

PubMed1991

Control of buffer pH during agarose gel electrophoresis of glyoxylated RNA.

There is a shift in buffer pH routinely encountered during electrophoresis. If one is running glyoxylated RNA on agarose gels, this pH shift can have potentially detrimental effects on experimental objectives if the shift is allowed to proceed unabated; this is due to the fact that the RNA will deglyoxylate if the pH is allowed to rise above 8.0. In order to counteract the shift, the buffer may be continuously recirculated or totally replaced at predetermined intervals. Because constant recirculation may be technically bothersome to achieve and because repeated total buffer replacement may require large amounts of highly purified water, we have studied (a) the time course of the pH change encountered during the electrophoretic process and (b) whether or not simple manual mixing of the buffer system at specific intervals was sufficient to maintain pH within acceptable bounds. We found that, under the given conditions, the cathode pH had nearly reached 8.0 at 25 min and had soared to 10.5 at 40 min. We further found that manual mixing at 20-min intervals not only prevented the cathode pH from rising above 7.8, but also restored the buffer to its initial pH.

Buffers↗

PubMed1978

D(-)-N-Methylglucamine buffer for pH 8.5 to 10.5.

A new amine buffer for the pH range 8.5 to 10.5 based on D(-)-N-methylglucamine and its hydrochloride is described. Important physical and chemical constants characterizing this buffer system have been determined: thermodynamic pKa = 9.52 (25 degrees C), buffer capacity = 0.055, dilution value pH 1/2 = -0.02, temperature coefficient dpKa/dT = 0.023, the heat of ionization delta H degrees = 36.93 kj mol-1. D(-)-N-Methylglucamine, which is available in highly purified form, is highly soluble in water. Thus one can prepare either buffer solutions or stable solid mixtures when combined with D(-)-N-methylglucaminium chloride. D(-)-N-Methylglucamine buffers are suitable for both biochemistry and pH control.

Buffers↗

PubMed1975

Effects of buffers on aspartate aminotransferase activity and association of the enzyme with pyridoxal phosphate.

Using purified enzymes of human origin and patients' sera, we examined factors influencing the in vitro association of pyridoxal phosphate with aspartate aminotransferase (EC 2.6.1.1). The rate of association was markedly retarded by phosphate buffer in comparison with tris(hydroxymethyl)aminomethane or six other buffers. Pyridoxal phosphate at an incubation concentration of 130 mumol/liter reactivated the entire apoenzyme portion of an apoenzyme/holoenzyme mixture within 5 min in tris(hydroxymethyl)aminomethane; in contrast, less than 20% was associated during 15 min in phosphate. Activity measured in tris(hydroxymethyl)aminomethane-buffer without exogenous pyridoxal phosphate was 4% greater than that in phosphate and was slightly increased by increasing the pH of the assay mixture from 7.5 to 8.0. Aspartate in the incubation medium did not retard the stimulation in tris(hydroxymethyl)aminomethane buffer. While the magnitude of stimulation varied greatly among sera, a consistent mean stimulation of 30% for groups of sera with normal activities was found when asparate at 125 mmol/liter, 2-oxoglutarate at 6.7 mmol/liter and tris(hydroxymethyl)aminomethane at 90 mmol/liter were used, an increase over the 16% with phosphate buffer [Clin. Chem. 19, 92 (1973)]. Absorbance spectra suggest pyridoxal phosphate exists as the Schiff base of tris(hydroxymethyl)aminomethane or aspartate, or both, under conditions of assay incubation (without addition of 2-oxoglutarate). Nonenzymatic catalysis of the reaction by pyridoxal phosphate alone or a formation of a protein/pyridoxal phosphate adduct was discounted with use of a D-asparate substrates.

Animals↗

PubMed1989

Electrically stimulated Krebs-Henseleit buffer does not relax precontracted human bronchi in vitro.

Electric field stimulation (EFS) causes a non-adrenergic relaxation of precontracted human airways. Only 10-20% of this response can be blocked with the nervous conductance blocker tetrodotoxin (TTX). Therefore, 80-90% of the non-adrenergic relaxation is not neurally mediated. The mechanism of this non-neural component is unclear. We examined whether EFS induces the generation of muscle relaxing substances in oxygenated Krebs-Henseleit buffer. Strips of central airways of 6 patients were precontracted with methacholine (10(-5) M) and exposed to Krebs buffer that had previously been stimulated with EFS (50 V, 0.3 ms, 30 s, 1-50 Hz). Results were compared to those obtained with unstimulated buffer. The contractile state of the airways did not change significantly with either EFS-stimulated or unstimulated buffer. We conclude that in oxygenated Krebs buffer EFS does not cause generation of substances that change the contractile state of prestimulated human airways.

Bronchi↗

PubMed1979

The solubility of sickle and non-sickle hemoglobins in concentrated phosphate buffer.

A new turbidimetric method for the direct measurement of the solubility of oxy- and deoxyhemoglobins (Hb) in concentrated phosphate buffer has been established. The principle of the method is the formation of a homogeneous emulsion when hemoglobin is introduced in concentrated phosphate buffer. The solubility of the oxy and deoxy forms of Hb A, Hb S, Hb C, Hb F, and Hb CHarlem (beta 6Glu leads to Val, beta 73Asp leads to Asn) has been studied. The solubility of deoxy-Hb S was the lowest and the solubility curve was broader than those of the other hemoglobins indicating that the aggregates of deoxy Hb S require more water to be dissolved. The solubility of oxy- and deoxyhemoglobins depends on temperature and pH. The solubility of hemoglobins is increased as the temperature is lowered and the pH is raised. The pH dependency of the solubility of deoxy-Hb S in high phosphate buffer was opposite to that of the minimum gelling concentration of deoxy-Hb S. The order of the solubility of Hb CHarlem, Hb FS, Hb AS, Hb CS, and Hb S in concentrated phosphate buffer corresponds to the order of minimum gelling concentration of these hemoglobins or hemoglobin mixtures. Solubility studies of a 1:1 mixture of deoxy-Hb A and deoxy-Hb S show that deoxy-Hb A aggregates in 2.42 M phosphate buffer in which pure deoxy-Hb A is totally soluble. This result indicates that deoxy-Hb S interacts with deoxy-Hb A and decreases its solubility.

Buffers↗

PubMed1986

Preparation of protein colloidal gold complexes in the presence of commonly used buffers.

In the presence of various commonly used buffers, phosphate-buffered saline (PBS), tris-buffered saline (TBS), Na-cacodylate, bovine serum albumin and a wide range of cytochemically active proteins (monoclonal and polyclonal IgG, concanavalin A, Ricinus communis lectin I, Helix pomatia lectin, protein A) were complexed to colloidal gold of different particle sizes (6 nm, 9 nm, 22 nm). The resulting complexes were active in cytochemical labelling. Complex-formation in the presence of electrolyte opens the possibilities of: maintenance of ionic environment during complexing of proteins sensitive to low ionic strength, pH control by addition of buffers to the protein solution or to the gold sol, direct coupling of protein supplied in PBS or saline avoiding dialysis against low ionic strength buffers. Using the electron microscope to estimate the protein amounts needed for stabilization provided a sensitive and economical method to obtain aggregate-free protein-gold complexes.

Adsorption↗

PubMed1984

Dehydration and delayed proton equilibria of red blood cells suspended in isosmotic phosphate buffers. Implications for studies of sickled cells.

PO4 buffers isosmotic with plasma or phosphate-buffered saline solution with a substantial proportion of PO4 are often used to wash and suspend red blood cells in studies of respiratory or sickling behavior. Measurements of sequential changes in mean cell hemoglobin concentration, pH, and ion content of red blood cells suspended in 295 mOsm Na-phosphate, pH 7.4, at 23 degrees or 37 degrees C, showed (1) rapid, persistent cell dehydration (mean cell hemoglobin concentration greater than 40 gm/dl) caused initially by Cl- efflux and later by replacement of monovalent Cl- by divalent HPO=4; and (2) temporary reversal of membrane pH gradients with normalization time (30 to 120 minutes) dependent on factors controlling the rate of phosphate-chloride exchange. Sequential equilibration of red blood cells in isosmotic citrate (impermeable) followed by PO4 demonstrated the two stages of the observed shifts in PO4 alone, and red blood cells suspended in 0.15 mol/L 32PO4 at 37 degrees C showed PO4 influx consistent with pH equilibrium kinetics. Sickle trait red blood cells deoxygenated at 37 degrees C, pH 7.4, in plasma or 10 mmol/L HEPES-buffered saline solution showed only 6% to 20% sickling. In isosmotic PO4, mean cell hemoglobin concentration was 40 to 41 gm/dl with approximately 80% sickling. In phosphate-buffered saline solution containing 70 mmol/L PO4, red blood cells showed smaller, similar changes (mean cell hemoglobin concentration approximately 38 gm/dl) with a longer equilibration period and deoxygenated sickle trait cells showed 40% sickling. The altered properties of red blood cells suspended in PO4 or phosphate-buffered saline solution were neither intended nor appropriate for many studies using these media, particularly with hemoglobin S-containing red blood cells, and interpretations of reported results must be reassessed in light of these findings.

Anemia, Sickle Cell↗

PubMed1982

Effect of multidose cardioplegia and cardioplegic solution buffering on myocardial tissue acidosis.

Multidose administration of cardioplegic solution during cardiac operation is intended to maintain both electromechanical arrest of the heart and myocardial hypothermia as well as to remove accumulated metabolites of anaerobic glycolysis. This study was conducted to assess the effect of multidose infusion of three different types of cardioplegic solution on tissue acidosis during global myocardial ischemia. Three groups of five dogs each were placed on cardiopulmonary bypass and the aorta was cross-clamped for 3 hours. The hearts were maintained at a constant temperature (20 degrees C) and cardioplegic solution was infused at an initial dose of 500 ml and five supplementary doses of 250 ml administered every 30 minutes. Group 1 received a crystalloid solution weakly buffered with sodium bicarbonate, Group 2 received a blood-based solution, and Group 3 received a crystalloid solution strongly buffered with histidine (Bretschneider's solution). The buffering capacities of the solutions used in Groups 2 and 3 were 40 and 60 times, respectively, that of the solution used in Group 1. The average myocardial tissue pH at the end of 3 hours of ischemia was 6.54 +/- 0.07 in Group 1, 7.23 +/- 0.05 in Group 2, and 7.19 +/- 0.06 in Group 3 (Group 1 significantly lower than Groups 2 and 3). Multidose infusion of a cardioplegic solution with low buffering capacity was unable to prevent the progressive development of tissue acidosis during 3 hours of ischemia. However, the multidose infusion of either blood-based or crystalloid solutions with high buffering capacity completely prevented any further reduction of tissue pH after the first 30 minutes of ischemia.

Acidosis↗

PubMedDate not supplied

[Study of DNA-interaction with protons of the medium by means of buffer capacity method].

pH-dependences of buffer capacity of native and denaturated DNA have been obtained. These dependences were expanded into basic functions each corresponding to ionised groups of equal pK. The pH dependence of buffer capacity of native DNA have two narrow g- and s-peaks and are shifted (relatively to nucleosides mixture) to acidic pH values, whereas those of heat denaturated DNA have only one wide assymmetric peak shifted to neutral pH. It was shown that s-and g-peaks of pH dependences of buffer capacity correspond to polymorphic transformation of the double helix (h leads to s transition) and to its disordering (s leads to g transition) respectively. From our data it follows that h leads to s transition at mu = 0.01 M NaCl is observed at temperatures T less than 50 degrees C. The independence of DNA protonation degrees, at which h leads to s leads to g transitions occur, on ionic strength of the solution is, apparently, related to linear dependence of the positions of g- and s-peaks maxima on (lg mu). This points to an important role of protonated bases in double helix destabilisation upon salt elimination. High sensitivity of the buffer capacity method allows us to reveal some differences between states of heat and acid denaturated DNA. Analysing pH dependences of buffer capacity of denaturated DNA it was shown that at neutral pH it contained some double or triple helix regions formed by H-linked bases holding unshared proton. Simms' method was shown to be inapplicable to determine base ionization constants both in native and denaturated DNA.

Animals↗

PubMed1981

Affinity labelling of liver alcohol dehydrogenase. Effects of pH and buffers on affinity labelling with iodoacetic acid and (R, S)-2-bromo-3-(5-imidazolyl)propionic acid.

Both iodoacetic acid and (R,S)-2-bromo-3-(5-imidazolyl)propionic acid (BrImPpOH) react with liver alcohol dehydrogenase in an affinity labelling mechanism between pH 6.1 and 10.5. The buffer-independent dissociation constants and the first-order rate constants have been determined as a function of pH. With BrImPpOH a pKa close to 9 for the free enzyme is assigned to the zinc-water ionization. The buffers used exerted a protective effect upon the inactivation of the enzyme by iodoacetic acid and BrImPpOH. Phosphate buffer showed a high degree of protection especially at lower pH, while zwitterionic buffers like Mes (4-morpholineethanesulfonic acid), Pipes (1,4-piperazinediethanesulfonic acid), Epps [4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid] and Bicine [N,N-bis(2-hydroxyethyl)glycine] gave less protection to various degrees. An exception was Ches (cyclohexylaminoethanesulfonic acid) which had an anomalously high affinity for the iodoacetate binding site. The dissociation constants of the buffers were calculated for the case of inactivation by both iodoacetic acid and BrImPpOH.

Affinity Labels↗