PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “CITRIC ACID”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 325 records · Page 18Linked to original sources
PubMed2002

Photodegradation of a ternary iron(III)-uranium(VI)-citric acid complex.

The mechanisms of photodegradation of binary iron- and uranium-citrate and ternary iron-uranium-citrate complexes were elucidated. Citric acid degradation products were identified by HPLC and GC, and the metal precipitates were identified by XRD and EXAFS. Photodegradation of a binuclear iron-citrate complex occurred as a result of two one-electron oxidations of citric acid with the formation of 3-oxoglutarate and two ferrous ions. The ferrous ions were reoxidized by a photo-Fenton reaction, resulting in the precipitation of iron as two-line ferrihydrite Fe(OH)3. The citric acid in the uranium-citrate complex underwent a two-electron oxidation to acetoacetate with the concomitant reduction of U(VI) to U(IV). The U(IV) was subsequently photooxidized in the presence of dioxygen with precipitation of uranium as the mineral schoepite (UO3 x 2H2O). A two-step electron reduction of two ferric ions to two ferrous ions wasthe primary mechanism for photodegradation of the ternary iron-uranium-citrate complex with oxidation of citric acid to 3-oxoglutarate; reduction of uranium was not observed. The iron precipitated as ferrihydrite and the uranyl ion as a uranyl hydroxide species. These results show the potential application of photochemical treatment of wastewater and decontamination solutions containing binary and ternary iron- and uranium-citrate complexes.

Chromatography, Gas↗
PubMed2005

Effect of EDTA and citric acid solutions on the microhardness and the roughness of human root canal dentin.

The purpose of this study was to evaluate the effect of citric acid and EDTA solutions on the microhardness and the roughness of human root canal dentin. Forty-five human teeth sectioned longitudinally were used. Specimens were randomly divided into three groups of 30 teeth each and were treated as follows: (a) one molar (19%) citric acid (C6H8O7) for 150 s followed by 5.25% NaOCl; (b) 17% EDTA for 150 s and rinsed with 5.25% NaOCl; (c) rinsed with distilled water and served as control. Three groups were then divided into two subgroups of 15 specimens each. The specimens, in first subgroup were subjected to Vicker's testing whereas the second subgroup underwent surface roughness testing. The results were analyzed using one-way ANOVA and Tukey tests. Significant differences were observed in microhardness among the test groups, citric acid group being the least hard (p 0.05). Also, citric acid significantly increased surface roughness.

Adult↗
PubMed1975

Kinetic studies on citric acid production by Aspergillus niger. II. The two-stage process.

A two-stage process of submerged citric acid fermentation with replacement of growth medium by fermentation medium has been worked out. The optimum composition of mineral nutrients and pH of the fermentation medium of the second stage of the process were determined. An addition of 0.5 g/l of NH4NO3 as nitrogen source and 0.1 g/l of MgSO4-7H2O as magnesium source ensured effective conversion of sucrose to citric acid. An addition to KH2PO4, on the other hand, was definitely unfavourable as it considerably reduced the product yield. The medium for the second stage of fermentation should be acidified to about pH 2.2, while the water used for washing the mycelium from the remains of the growth medium should have a pH of 2.5--3.5. Under these conditions, with an initial sucrose concentration of 100 g/l, after 132 hr fermentation at 26 degrees up to 90 g/l of citric acid was obtained, which corresponds to a productivity of over 16 g/l. day. The highest activity for citric acid formation was found in three- or four-day-old mycelium.

Aspergillus↗
PubMed2003

Cough reflex induced by microinjection of citric acid into the larynx of guinea pigs: new coughing model.

We developed a new coughing model that evoked coughs by microinjection of citric acid into the larynx in unanesthetized unrestrained guinea pigs; additionally, we recorded synchronous sounds and waveforms of coughing utilizing built-in microphones and a whole body plethysmograph. The coughing model was able to distinguish a coughing response from other expiratory responses, such as an expiratory reflex or a sigh, by examining the waveform of the expiratory response and the existence of sound. It was not necessary to distinguish a cough from a sneeze, since the administration site was restricted to the larynx. Microinjection of 0.4 M citric acid, total of 20 microl (10 times, 2 microl at 30-s intervals), induced coughs (27.03 +/- 4.03 coughs in 10-min observation) that were stable and independent of the inhalation volume. In the inhalation studies, animals were exposed to citric acid only once, because the number of coughs remarkably decreased with repeated administration at intervals of 24 h (tachyphylaxis). However our coughing model was able to repeatedly challenge the microinjection of citric acid at an interval of 24 h. These results indicated that this coughing model was highly sensitive and correctly assessed the cough response.

Animals↗
PubMed1987

Effects of citric acid and fibronectin and laminin application in treating periodontitis.

To determine the effect on new connective tissue attachment of citric acid conditioning and fibronectin-laminin application in treating naturally occurring periodontitis, all 4 quadrants in each of 2 Beagle dogs were used. Each quadrant included: P2, P3, P4, and M1 teeth. 2 treatment modalities were employed and comparatively analyzed for differences in histological healing respponses at 120 days after surgery. The treatments were: (1) surgery (mucoperiosteal flaps) plus citric acid; (2) surgery plus citric acid followed by fibronectin-laminin application. After scaling and root planing, coronal and root surface reference notches were placed for histometric measurements. Following each of the randomly assigned treatments, flaps were sutured. After sacrifice, tissue blocks of treated areas were decalcified and serially cut, obtaining bucco-lingual and mesiodistal sections. Using a Filar micrometer, 5 distances were masured on the buccal aspect: (1) from root surface notch to alveolar bone crest; (2) from root surface notch to coronal extent of the cementum; (3) from root surface notch to apical extent of the junctional epithelium; 84) from free gingival margin to apical extent of junctional epithelium; (5) from the coronal notch to the alveolar bone crest. Results showed no differences among the 5 measurements between the 2 treatments tested. On mesio-distal sections, surface area determinations were made in the furcations, evaluating the space occupied by new connective tissue, with or without bone, or by epithelium. For this, images were digitized using a Zeiss IBAS Image analysis system with a 4mB of array processor memory coupled to a Newvicon TV camera and a microcomputer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

Healing after treatment of periodontal intraosseous defects. II. Effect of citric acid conditioning of the root surface.

Citric acid conditioning of the root surface as a supplement to replaced flap surgery of intraosseous periodontal defects was evaluated. Thirteen patients and a total of 45 proximal defects with residual probing pocket depth greater than or equal to 6 mm after initial preparation were used. The effect of treatment was studied in matched subsamples of the total material including one acid-treated and one nonacid-treated defect from each subject. The results demonstrated that an average gain of probing attachment level amounting to 2.l0 mm was obtained following acid treatment as compared to 1.1-1.2 mm for the nonacid-treated controls. Corresponding figures for gain or probing bone level were 1.2-1.3 mm for acid treatment and 0.8-0.9 mm for controls. The clinical significance of these findings was discussed.

Adult↗
PubMed1991

Mechanism of aluminum tolerance in snapbeans : root exudation of citric Acid.

One proposed mechanism of aluminum (Al) tolerance in plants is the release of an Al-chelating compound into the rhizosphere. In this experiment, two cultivars of snapbeans (Phaseolus vulgaris L. "Romano" and "Dade") that differ in Al tolerance were grown hydroponically with and without Al under aseptic conditions. After growth in nutrient solutions for 8 days, aliphatic and phenolic organic acids were analyzed in the culture solutions with an ion chromatograph and a high pressure liquid chromatograph. The tolerant snapbean, "Dade", when exposed to Al, exuded citric acid into the rhizosphere in a concentration that was 70 times as great as that of "Dade" grown without Al, and 10 times as great as that of "Romano" grown with or without Al. The sensitive cultivar, "Romano", exuded only slightly more citric acid into the growing medium under Al-stress, compared to nonstressed conditions. Citric acid is known to chelate Al strongly and to reverse its phytotoxic effects. Also, citric acid has been shown previously to enhance the availability of phosphorus (P) from insoluble Al phosphates. Thus, one mechanism of Al-tolerance in snapbeans appears to be the exudation of citric acid into the rhizosphere, induced either by toxic levels of Al or by low P due to the precipitation of insoluble Al phosphates. Our experiment was not able to distinguish between these two factors; however, tolerance to both primary and secondary Al-stress injuries are important for plants growing in Al-toxic soils.

Journal Article↗
PubMed2002

Development of calcium phosphate cement using chitosan and citric acid for bone substitute materials.

We developed a calcium phosphate cement that could be molded into any desired shape due to its chewing-gum-like consistency after mixing. The powder component of the cement consists of alpha-tricalcium phosphate and tetracalcium phosphate, which were made by decomposition of hydroxyapatite ceramic blocks. The liquid component consists of citric acid, chitosan and glucose solution. In this study, we used 20% citric acid (group 20) and 45% citric acid (group 45). The mechanical properties and biocompatibility of this new cement were investigated. The setting times of cements were 5.5 min, in group 20 and 6.4 min, in group 45. When incubated in physiological saline, the cements were transformed to hydroxyapatite at 3, and 6 weeks, the compressive strengths were 15.6 and 20.7 MPa, in group 45 and group 20, respectively. The inflammatory response around the cement implanted on the bone and in the subcutaneous tissue in rats was more prominent in group 45 than in group 20 at 1 week after surgery. After 4 weeks, the inflammation disappeared and the cement had bound to bone in both groups. These results indicate that this new calcium phosphate cement is a suitable bone substitute material and that the concentration of citric acid in the liquid component affects its mechanical properties and biocompatibility.

Animals↗
PubMed2002

Kinetic study of citric acid influence on calcium phosphate bone cements as water-reducing agent.

Most of the research performed on calcium phosphate bone cements (CPBCs) has dealt with the improvement of bone cement formulations for new, demanding bone-filling applications. In particular, the development of injectable bone cements is of real interest for the biomedical community. The aim of this work was to study the effect of citric acid on the injectability and the setting properties of alpha-tricalcium phosphate-based cements. A comparative kinetic study was performed on cements with and without citric acid relating the hardening curves and the hydration rates using a mathematical approach. Citric acid behaved as a fluidificant during the first stages of the cement mixing. The dissolution-precipitation reactions of the alpha-tricalcium phosphate were retarded with the addition of citric acid and the compressive strength at saturation increased. In conclusion, citric acid can behave as a water-reducing admixture.

Bone Cements↗
PubMed2001

[Study of the adsorption properties in chromatographic separation of the citric acid].

A new method studying the change of thermodynamic properties at different temperatures to screen suitable stationary phases for chromatographic separation of the citric acid (CA) on an analytical column has been developed. The applied method is mainly based on using CA with a series of solute concentrations (0 g/L-250 g/L) as mobile phase to seriously overpass the unloaded stationary phase to find the breakthrough curves of CA. The adsorption isotherms were calculated from the retention times of breakthrough curve. The bed porosity of column was calculated from the elution time of a peak of the blue dextran as non-adsorbed tracer. The stationary phase, which has been selected through this method, for the separation of CA from fermentation broth, showed a very high adsorption capacity for CA, even under very low concentrations, so it can even be used in the separation and purification process of minute amounts of CA. The separation effect of this stationary phase for citric acid can be greatly enhanced through the technique of change of temperature. This new separation process can shorten the old process path, improve the yield of finished products more than 10%, and reduce the cost more than 10%. At the same time, the pollution of the production of citric acid can be reduced. It turned out that this method will play an important role in the synthesis of stationary phase for the separation of citric acid and the study of its structure.

Adsorption↗
PubMed1990

Biphasic calcium phosphate ceramic combined with fibrillar collagen with and without citric acid conditioning in the treatment of periodontal osseous defects.

The purpose of this study is to determine whether the combination of biphasic calcium phosphate ceramic (BCP) and collagen and citric acid root conditioning would promote accelerated new attachment of periodontal tissue to the root surface in dogs. Intrabony defects were surgically produced for each animal and were made chronic for 16 weeks. These defects were assigned to two study treatment and one control group: ceramic-collagen without citric acid (CO-CE); ceramic-collagen with citric acid (CO-CE-CA); and control (surgical debridement and root planing only). Results showed that all groups gained new attachment level as demonstrated both clinically and histometrically. The treatment groups showed a significant mean gain greater than the control (P less than .005), but no significant difference was found between treatment groups. Small areas of ankylosis was also found in both treatments but there was no evidence of active root resorption. It is concluded that the use of combined BCP and fibrillar collagen is beneficial in promoting new attachment of periodontal tissues to the root surface in dogs. Although citric acid root conditioning did as well or better than ceramic and collagen alone, its benefits are still speculative and need further experimentation.

Animals↗
PubMed1995

Effects of citric acid treatment on the Ca, P and Mg contents of human dental roots.

An electron microprobe analyser associated with a scanning electronic microscope was used to measure Ca, P and Mg contents of the human dental root hard tissues, before and after a citric acid treatment (pH = 1). The measurements were made on transverse sections through the cervical 1/3 of the molar roots. The measurements were performed at the following 8 levels: the internal cementum, the cementum-dentine junction, cementum-related dentine, 4 external dentine levels located at 220 microns, 420 microns, 620 microns and 820 microns from the cementum-dentine junction, and finally the juxta-pulpal dentine. After the citric acid treatment, the losses in Ca and P, but not in Mg, varied significantly with the level; an acid-resistant dentine layer of approximately 600 microns was found under the cementum-dentine junction. An increase in the Ca/P ratio was also observed in this layer. Since this external dentine zone is less demineralized by the citric acid than the underlying dentine, the collagen matrix in this region may also be less exposed. These differences in the response to citric acid that depend on the distance from the root surface may explain the unpredictability of periodontal healing after citric acid treatment of diseased root surfaces, because the amount of tissue removed during root planing is not constant.

Calcium↗
PubMed1993

Capsaicin-desensitization to the human nasal mucosa selectively reduces pain evoked by citric acid.

1. Kallidin (5-500 nmol), hypertonic saline (0.9-20% NaCl) or low pH medium (citric acid: pH 2.5-1) applied (50 microliters) to the human nasal mucosa produced a pain response (evaluated by a visual analogue scale) that was related to the concentration of the peptide, NaCl or hydrogen ions, respectively. 2. Application (50 microliters) of capsaicin (50 nmol) to the human nasal mucosa produced overt pain. After repeated administrations (once a day for 5-7 days) to one nostril this effect underwent almost complete desensitization, while in the contralateral nostril, treated with the vehicle, the response to capsaicin was unaffected. 3. The pain response produced in the human nasal mucosa by topical application (50 microliters) or kallidin (50-500 nmol), NaCl (10-20%) or citric acid (pH 1.5-1) solutions was then studied before and after local capsaicin desensitization. 4. The pain response to pH 1.5 or 1 citric acid was markedly reduced (by 60% and 75%, respectively) in the capsaicin-treated nostril. However, the pain response to 10% or 20% NaCl or the mild pain response to 50 or 500 nmol kallidin were unaffected by capsaicin pre-treatment. 5. The present results suggest that prolonged topical capsaicin treatment to the human nasal mucosa may lead to selective desensitization to certain algesic stimuli such as capsaicin itself and hydrogen ions.

Administration, Intranasal↗
PubMed1976

Hypercalcemia in acute uremia and following citric acid administration: differential effect on parathyroid gland microtubule content.

Hypercalcemia, which occurs 4 hr after bilateral nephrectomy in normal rats, is not seen 4 hr after either bilateral ureterotomy or sham surgery. These results indicate that it is loss of renal mass per se, not the uremic syndrome, which is responsible for the hypercalcemia. Citric acid levels also increase 4 hr after nephrectomy, and a degree of hypercalcemia and hypercitricemia comparable to that which follows nephrectomy can be produced by administration of citric acid to normal rats. In an attempt to evaluate the role of the parathyroid gland in the development of hypercalcemia in these two situations, the microtubule content of parathyroid gland chief cells was determined by ultrastructural sterologic techniques 4 hr after either bilateral nephrectomy or citric acid administration. The results of these measurements indicate that parathyroid gland chief cell microtubule content increases after citric acid administration but not following bilateral nephrectomy. The significance of these results is not clear. However, since a previous study has suggested a correlation between increased microtubule content and increased secretory status in the chief cell, one may speculate that increased microtubule content resulting from citric acid administration may also be associated with increased parathyroid hormone secretion. By this formulation, citric acid-induced hypercalcemia would be secondary to increased parathyroid hormone secretion, but the transient hypercalcemia that occurs after nephrectomy would take place in the absence of an increase in parathyroid hormone secretion. In this latter instance, it is possible that loss of the kidney, a major site of parathyroid hormone removal from plasma, leads to an increase in circulating parathyroid hormone level, and hypercalcemia, in the absence of an increase in hormone secretion rate.

Animals↗
PubMed2000

Influence of admixed citric acid on the release profile of pelanserin hydrochloride from HPMC matrix tablets.

Pelanserin is a weakly basic experimental drug with a short half-life and a prolonged release formulation was developed using hydroxypropyl methylcellulose (HPMC) and citric acid to set up a system bringing about gradual release of this drug. For this purpose powder mixtures were wet granulated with water and compressed with a hydraulic press at 55 MPa. Dissolution studies were made using 900 ml HCl 0.1 N, the first 3 h, and phosphate buffer pH 7.4, h 3-8. Dissolution curves were described by M(t)/M(inf)=kt(n), applied separately for each dissolution medium. The dissolution mechanism involved a coupled diffusion/relaxation with a trend favoring the diffusion mechanism with increasing citric acid concentrations. Increasing concentrations of citric acid produced increasing values of the kinetic constants, in a cubic relationship. Higher HPMC proportions produced slower dissolution rates but with a citric acid compensating more clearly a decreased solubility of pelanserin at pH 7.4. Individually calculated dissolution curves showed experimental 8 h pelanserin dissolution in a range of 65-99% for matrices with 100 mg HPMC/tab., while those with 200 mg HPMC/tab. were in the range 57-73%.

Antihypertensive Agents↗
PubMed2000

Another unusual type of citric acid cycle enzyme in Helicobacter pylori: the malate:quinone oxidoreductase.

The only enzyme of the citric acid cycle for which no open reading frame (ORF) was found in the Helicobacter pylori genome is the NAD-dependent malate dehydrogenase. Here, it is shown that in this organism the oxidation of malate to oxaloacetate is catalyzed by a malate:quinone oxidoreductase (MQO). This flavin adenine dinucleotide-dependent membrane-associated enzyme donates electrons to quinones of the electron transfer chain. Similar to succinate dehydrogenase, it is part of both the electron transfer chain and the citric acid cycle. MQO activity was demonstrated in isolated membranes of H. pylori. The enzyme is encoded by the ORF HP0086, which is shown by the fact that expression of the HP0086 sequence from a plasmid induces high MQO activity in mqo deletion mutants of Escherichia coli or Corynebacterium glutamicum. Furthermore, this plasmid was able to complement the phenotype of the C. glutamicum mqo deletion mutant. Interestingly, the protein predicted to be encoded by this ORF is only distantly related to known or postulated MQO sequences from other bacteria. The presence of an MQO shown here and the previously demonstrated presence of a 2-ketoglutarate:ferredoxin oxidoreductase and a succinyl-coenzyme A (CoA):acetoacetyl-CoA transferase indicate that H. pylori possesses a complete citric acid cycle, but one which deviates from the standard textbook example in three steps.

Citric Acid Cycle↗
PubMed2006

Influence of sodium nitrilotriacetate (NTA) and citric acid on phenolic and organic acids in Brassica juncea grown in excess of cadmium.

Brassica juncea cv. 426308 was grown in soils containing 150 mg Cd(2+)kg(-1) soil. After 38 days, the soil was amended with two rates of citric acid or NTA (10 and 20 mmol kg(-1) soil). Control soil was not amended with chelates. Plants were harvested during growth, immediately before and seven days after chelate addition. Shoot composition of organic and phenolic acids and shoot Cd(2+) concentration were determined. Cadmium concentration remained constant during the growth and increased following NTA and citric acid amendments depending on chelate type and concentration. The highest increments in Cd(2+) were measured after the addition of NTA. Compared to the control, 10 and 20 NTA-treated plants showed two- and three-fold increases, respectively. At 150 mg Cd(2+)kg(-1) soil the amount of organic and phenolic acids in the leaves of B. juncea was always higher than that detected in the control. A direct correlation between organic acid concentration and cadmium content was detected both during growth and after chelate addition. On the contrary, the amount of phenols seemed to be correlated with the metal content only in non-amended and NTA-treated plants. The 10 and 20 citric acid additions caused 45% and 90% increases in shoot phenolic acids although cadmium content rose to a smaller extent. The inhibition of citrate synthase and the entrance of phosphoenolpyruvate in shikimate pathway leading to the formation of aromatic compounds might come into play. The increase in phenylalanine ammonialyase activity following citric acid amendments suggested this metabolic response.

Acids↗