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PubMed1988

Relevance of the reaction of a manganese(III) chelate with hydroxide ion to photosynthesis: Reaction of hydroxide ion with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) in ligating and nonligating solvents.

The reaction of HO(-) with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) chloride [(TMP)Mn(III)(Cl)] in ligating solvents (CH(3)CN, dimethyl sulfoxide, pyridine) results in formation of (TMP)Mn(II) ( approximately 10(6) M(-1).s(-r)), which in a slower reaction is converted to a product whose structure is suggested to be that of a porphyrin manganese(III) peroxo dimer. Admittance of O(2) at any time during these reactions leads to formation of the manganese(III) peroxide (TMP)Mn(III)(O(2))(-). In nonligating solvents [CH(2)Cl(2), (CH(3))(2)CO], the reaction of HO(-) with (TMP)Mn(III)(Cl) yields (TMP)Mn(IV)(OH)(2).

Journal Article↗
PubMed2001

Effect of calcium hydroxide form and placement on root dentine pH.

AIM: The aim of this study was to measure variations in dentinal pH following the placement of various forms of calcium hydroxide in either the root canal or the pulp chamber. METHODOLOGY: Extracted single-rooted human teeth were prepared, and the root canals instrumented using a conventional technique. Three cavities were drilled through the root dentine to within 1 mm of the canal wall at the cervical, middle and apical thirds. A total of 125 teeth were randomly divided into five groups; group 1: pure aqueous calcium hydroxide paste (calcium hydroxide/distilled water solution) was placed in the root canal; group 2: the same aqueous calcium hydroxide paste was placed in the pulp chamber; group 3: Hycal, a new form of calcium hydroxide paste, was placed in the pulp chamber; group 4: calcium hydroxide gutta-percha points were placed in the root canal; group 5: control group, wet canal (distilled water) without medication. The access cavities and apical ends were sealed, and the teeth were placed in individual vials containing phosphate-buffered saline, and stored at 37 degrees C. The pH was measured in the dentinal cavities at 8 h and at 1, 2, 3, 7, 14, and 21 days using a calibrated microelectrode. RESULTS: At 8 h and 1, 2, and 3 days, the highest pH values were obtained when the aqueous calcium hydroxide paste was placed in the pulp chamber. At 7 days, the pH had increased in the Hycal group without being significantly different from the aqueous calcium hydroxide paste placed either in the root canal or in the pulp chamber. At 14 days, Hycal( had the highest pH values (pH 10.65); however, at 21 days no significant difference was noted amongst these first three groups. Control group values ranged from 7.88 to 8.60; the pH created by the calcium hydroxide gutta-percha points was lower than for the control group. Whatever the product or placement location, cervical pH was similar to middle pH, and greater than apical. However, there was no significant difference between the three when all groups were combined. Overall, aqueous calcium hydroxide paste placed in the pulp chamber provided the highest pH values during the experiment, except at day 14. The aqueous calcium hydroxide paste placed in the root canal or Hycal had similar values at days 7 and 21. CONCLUSIONS: Under the conditions of this study, an aqueous calcium hydroxide paste placed in the pulp chamber increased dentinal pH more than the other techniques. The pH of dentine is affected by the form of calcium hydroxide used.

Calcium Hydroxide↗
PubMed2000

Influence of mixing vehicle on dissociation of calcium hydroxide in solution.

The antimicrobial effects of aqueous preparations of calcium hydroxide have been demonstrated in the past. Calcium hydroxide, when dissolved in water, dissociates into hydroxide and calcium ions. The presence of hydroxide ions in a solution makes it antimicrobial. Recently it was shown that the use of glycerin as a mixing vehicle facilitates placement of calcium hydroxide in the root canals. The influence of nonaqueous mixing vehicles on the dissociation of calcium hydroxide is not clearly understood. In this study the conductivity of aqueous and nonaqueous solutions of calcium hydroxide was measured. The conductivity values for saturated solutions of calcium hydroxide in water was 7.3+/-3 mS/cm. The conductivity of calcium hydroxide in pure glycerin or propylene glycol was essentially zero. It was concluded that use of nonaqueous mixing vehicles may impede the effectiveness of calcium hydroxide as a root canal dressing.

Anti-Infective Agents, Local↗
PubMed2000

"Bridging hydroxide effect" on mu-carboxylato coordination and electrochemical potentials of bimetallic centers: Mn2(II,II) and Mn2(III,III) complexes as functional models of dimanganese catalases.

Synthesis, solution structures, and electrochemistry of several dinuclear Mn2(II,II) complexes (1-4) and Mn2(III,III) complexes (6 and 8), derived from a functional catalase mimic [(L1,2)Mn2(II,II)(mu 13-O2CCH3)]2+ (1) are described that enable testing of the role of intramolecular hydroxide ligands on the redox properties. Addition of 1 equiv of hydroxide to 1 or 3 forms [(L1,2)Mn2(II,II)(mu 13-O2CCH3)(mu- OH)]+ (7A or 7B, respectively), possessing two six-coordinate Mn(II) ions bridged by hydroxide and acetato ligands. Two-electron oxidation of 7 with O2 occurs by forming [(L1,2)Mn2(III,III)(mu 1,3-O2CCH3)(mu-OH)]3+ (8) and H2O2 with no ligand rearrangements in methanol. Reaction of 8 with 2-3 equiv hydroxide forms [(L1,2)Mn2(III,III)(mu-O)(OH)(O2CCH3)]+ in which deprotonation of mu-OH- to yield mu-O2- favors subsequent addition of a terminal hydroxide ligand, accommodated by a bridging-to-terminal "carboxylate-shift". Preservation of six-coordinate Mn(II) ions throughout all hydroxide-induced transformations is observed, including oxidation by O2. Cyclic voltammetry reveals that addition of mu-OH- converts the two-electron redox couple II,II/III,III for complexes 1-4 to sequential one-electron couples at lower reduction potentials, yielding substantial stabilization of the II,III and III,III oxidation states by delta E = 440 and 730 mV, respectively. Binding of a second OH- to 7A or 7B forms (L1,2)Mn2(II,II)(mu 13-O2CCH3)(OH)2, containing two six-coordinate Mn(II) ions with two terminal hydroxides and a mu 1,3-bridging acetato. Electrochemistry reveals that displacement of the bridging hydroxide to a terminal site upon addition of the second OH- restores a two-electron redox couple II,II/III,III but now at a higher reduction potential with considerable loss of the electrochemical stabilization energy provided by the mu-OH- (delta E = 250 and 350 mV loss for Mn2(II,II) and Mn2(III,III), (respectively). These results indicate a considerably stronger influence of bridging vs terminal hydroxide ligands in stabilizing the higher oxidation states and separating the one-electron redox potentials of bimetallic centers. By contrast, in the absence of mu-OH- bridges the longer separation with the mu 1,3-carboxylato bridge in dimanganese(II,II) complexes leads to nearly complete uncoupling of the Mn(II) oxidation potentials, thus yielding a two-electron redox transition to (III,III). We hypothesize that this "bridging hydroxide effect" may be due to both greater screening of the repulsive intermetallic electric potential energy and increased resonance stabilization of the mixed-valence (II,III) oxidation state by charge delocalization . These data provide a physicochemical basis for interpretation of the catalase activity of these complexes and of dimanganese catalase enzymes (see the following manuscript).

Catalase↗
PubMedDate not supplied

[Investigation of chemical reaction and isolation of calcium hydroxide and Zn-phosphate cement in vitro conditions].

An important question in conservative dentistry is whether in direct contact of calcium hydroxide paste and phosphate cement the neutralization of pH calcium hydroxide occurs and how it can be prevented. Chemical investigations performed in vitro conditions (in the test tube) concerned 3 groups, each of which had 12 samples. In the A group (control group) calcium hydroxide paste was put at the bottom of the test tube and ZOOK paste and phosphate cement layer were put over it; in the B group, Tubulitec base in 2 layers was applied over calcium hydroxide cement and then the phosphate cement; and in the C group, the calcium hydroxide paste and phosphate cement were put in the test tube in direct contact. Within 12 weeks, after 7 days, the 3 samples were investigated (1 in each group). Contrary to expectations the results showed that in direct contact of calcium hydroxide paste and phosphate cement no change occurred in pH calcium hydroxide, and that its average value was 12.70. Further were there was no statistically significant difference in values of pH calcium hydroxide paste among the A, B and C groups. On the basis of these studies and in the opinion of other authors, it may be concluded that, although there was no decrease in pH calcium hydroxide in direct contact of calcium hydroxide paste and phosphate cement, it should be necessary to make the mutual isolation of these materials; in practice this is most efficiently done on two-layer Tubulitec base.

Calcium Hydroxide↗
PubMed2000

Chemical preservation of whole broiler carcasses utilizing alkaline hydroxides.

The chemical preservation of whole broiler carcasses utilizing aqueous alkaline hydroxide solutions was examined as an alternative method of mortality management. Conversion of the preserved carcasses and solutions into an acceptable poultry by-product meal was examined. This research identified the basic parameters for effective preservative solutions that simultaneously hydrolyzed feathers and preserved the carcass. Euthanized, fully feathered, mature broilers were placed in potassium hydroxide (0.5 to 2.0 M) and sodium hydroxide (0.12 to 2.0 M) solutions for 5 and 10 d. Effectiveness was evaluated by visible feather degradation and carcass solubilization, odor production, inhibition of microbial growth, and solids content of the alkaline solutions. Sodium hydroxide at 1.9 and 2.0 M diffused throughout the carcass and produced adequate preservation without apparent putrefaction through 10 d. Aerobic bacteria were not recovered from sodium hydroxide solutions, carcass skin, or intestine samples at the 1.9 M concentration. Treatments of 2.0 M potassium hydroxide and a mixture of 1.5 M potassium hydroxide with 0.5 M sodium hydroxide produced the highest degree of carcass liquification at 10 d without visible putrefaction. Sodium hydroxide solution (2.0 M):carcass weight ratios ranging from 1:1 through 4:1 (wt:wt) were effective in preserving individual carcasses for more than 60 d without putrefaction.

Animals↗
PubMed1990

Insights into the function of the zinc hydroxide-Thr199-Glu106 hydrogen bonding network in carbonic anhydrases.

The exact functional role of the zinc hydroxide (water)-Thr199-Glu106 hydrogen bond network in the carbonic anhydrases is unknown. However, from the results of molecular dynamics simulations (MD) we are able to better define its function. From computer graphics analysis and MD simulations on the zinc hydroxide form of human carbonic anhydrase II we find that this interaction forces the hydroxide hydrogen atom to be in a "down" position relative to the deep water-binding pocket. From previous work we have found that this pocket is a high-affinity binding site for CO2. We also note that during the timescale of our simulation (126 ps) the hydrogen bonds between the hydroxide hydrogen atom and Thr199 and the one between Thr199 and Glu106 are not fluxional. We propose that the role of the zinc hydroxide (water)-Thr199-Glu106 hydrogen bond network is to lock the hydrogen atom in the down position in order to expose the CO2 molecule bound in the deep water pocket to a lone pair of the hydroxide oxygen atom. This would allow for the rapid reaction of the CO2 molecule around the zinc ion. Furthermore, if the hydroxide hydrogen atom were not locked in the down position the binding of CO2 to the deep water pocket could be interfered with by the unrestrained hydroxide hydrogen atom (e.g. the N-Zn-O-H torsion could undergo rotational transitions that would partially block the deep water pocket). In summary, the roles we ascribe to this hydrogen bonding network are (1) to allow for facile access of CO2 to the deep water pocket and (2) to allow for maximal exposure of a hydroxide oxygen lone pair to the CO2 carbon atom.

Binding Sites↗
PubMed2005

Surface complexation of condensed phosphate to aluminum hydroxide: an ATR-FTIR spectroscopic investigation.

Two model compounds, sodium pyrophosphate (pyro-P) and sodium tripolyphosphate (tripoly-P), were employed to elucidate the binding mechanisms of condensed phosphate on aluminum hydroxide by utilizing attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Peak assignments for the condensed phosphates in the solution phase and those adsorbed on the surface of aluminum hydroxide were made. Electron delocalization and polarization were employed to explain the peak shifts and the complexation of condensed phosphate with aluminum hydroxide. The tripoly-P and pyro-P were adsorbed on aluminum hydroxide by forming inner-sphere complexes. The adsorbed condensed phosphates were deprotonated in the pH range from 4 to 10. Monodentate, bidentate, and binuclear complexes were formed when pyro-P was adsorbed on aluminum hydroxide, while monodentate and binuclear complexes were formed when tripoly-P was adsorbed. Based on the FTIR data, we proposed that when either bidentate or binuclear complexes were formed, the two oxygen atoms participating in the complexation with aluminum hydroxide could not be originated from the same terminal phosphate moiety. The AlO bond formed in the complexation of pyro-P or tripoly-P with aluminum hydroxide (AlPO(-3)) was not as strong as the HO bond in terminal HPO(-3). The bridging PO(-2) of tripoly-P did not coordinate with aluminum hydroxide. The real-time ATR-FTIR study on condensed phosphate adsorption revealed that a long contact time between condensed phosphates and aluminum hydroxide particles can result in a transformation of an initially formed species into a thermodynamically more stable phase.

Adsorption↗
PubMed2003

Removal of phosphate by aluminum oxide hydroxide.

The development and manufacture of an adsorbent to remove phosphate ion for the prevention of eutrophication in lakes are very important. The characteristics of phosphate adsorption onto aluminum oxide hydroxide were investigated to estimate the adsorption isotherms, the rate of adsorption, and the selectivity of adsorption. Phosphate was easily adsorbed onto aluminum oxide hydroxide, because of the hydroxyl groups. The adsorption of phosphate onto aluminum oxide hydroxide was influenced by pH in solution: the amount adsorbed was greatest at pH 4, ranging with pH from 2 to 9. The optimum pH for phosphate removal by aluminum oxide hydroxide is 4. The selectivity of phosphate adsorption onto aluminum oxide hydroxide was evaluated based on the amount of phosphate ion adsorbed onto aluminum oxide hydroxide from several anion complex solutions. It is phosphate that aluminum oxide hydroxide can selectively adsorb. The selectivity of phosphate onto aluminum oxide hydroxide was about 7000 times that of chloride. This result indicated that the hydroxyl groups on aluminum oxide hydroxide have selective adsorptivity for phosphate and could be used for the removal of phosphate from seawater.

Adsorption↗
PubMed1997

Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: a potential clinical problem.

When a ZnOE type sealer was placed in root canals treated previously with calcium hydroxide dressing, an accelerated sealer setting rate occasionally occurred. This clinical observation led to the present experimental design aiming to investigate the effect of calcium hydroxide on a ZnOE cement and ZnOE type sealers and to preliminarily assess the removal efficiency of a calcium hydroxide preparation from root canal systems. Micro-MIR FTIR spectroscopy was used to quantify the effect of calcium hydroxide on the setting reactions of a ZnOE cement and two ZnOE type sealers. The removal efficiency of calcium hydroxide from root canal systems was evaluated after treatment with NaOCl; NaOCl and filing; and NaOCl plus EDTA and filing. Calcium hydroxide preferentially interacted with eugenol inhibiting the ZnO-eugenol chelate formation. The Ca(OH)2-eugenol interaction was rapid, and kinetically dependent, leading to residual eugenol in the set product. The set ZnOE cement and the ZnOE type sealers in contact with calcium hydroxide were brittle in consistency and granular in structure. Although none of the treatments tested completely removed calcium hydroxide from root canals, treatment with EDTA significantly reduced the extent of residual calcium hydroxide.

Analysis of Variance↗
PubMed2002

Influence of calcium hydroxide intracanal medication on apical seal.

AIM: The aim of this study was to determine the influence of calcium hydroxide intracanal medication and various techniques for its removal on the sealing ability of gutta-percha root fillings with a zinc oxide-eugenol sealer. METHODOLOGY: Eighty extracted mature human mandibular molar roots were divided into three groups of similar root-canal configuration. Calcium hydroxide paste was made by mixing calcium hydroxide powder with distilled water at a powder to liquid ratio of 1:1.25. After root canals were prepared and enlarged to a minimum of size 30 with the Profile 0.06 system, calcium hydroxide paste was placed in the canals of two groups, but no medication was placed in the control group. The intracanal calcium hydroxide was removed with two different techniques, 1 week after medication: K-files one size larger than the master apical file (MAF) were used with 2.5% NaOCl and 15% EDTA solutions in one group, whilst K-files the same size as the MAF were used with 2.5% NaOCl solution in another group. Canals were obturated with gutta-percha and Tubli-Seal cement using the lateral condensation technique. The apical sealing-ability was assessed by dye leakage and cross-sections of the specimens were examined under a stereomicroscope. The dye-penetration level was measured and analyzed using Fisher's exact test and Duncan's multiple range test. RESULTS: The calcium hydroxide-medicated groups showed significantly more dye leakage than the non-medicated control group (P < 0.05). However, there was no significant difference between the two calcium hydroxide-medicated groups (P > 0.05). The stereomicroscopic views showed a relatively uneven and thicker layer of sealer in the calcium hydroxide-medicated groups. CONCLUSION: Calcium hydroxide intracanal medication may increase apical leakage of gutta-percha root fillings when a zinc oxide-eugenol sealer is used.

Calcium Hydroxide↗
PubMed1991

Advantage of early initiation of aluminum hydroxide administration for the prevention of experimental progressive renal disease.

Aluminium hydroxide, a phosphate binder, is regarded as a strong candidate to halt the progression of chronic renal disease. In order to determine the most effective time to start treatment, aluminium hydroxide was administered either immediately (ADR-0w), or at 8 weeks (ADR-8w) or 16 weeks (ADR-16w) after repeated injection of Adriamycin (ADR) inducing glomerular sclerosis. In the aluminium hydroxide-untreated group the survival rate at the end of the experiment was 50%, while the early initiation of aluminium hydroxide (ADR-0w) resulted in a greater survival rate of 90%. Serum phosphate concentration and serum calcium-phosphate product were significantly less in the aluminium hydroxide groups (ADR-0w, 8w, 16w) than in the untreated group after week 20. Urinary protein excretion was significantly less in the ADR-0w and ADR-8w groups at week 12 or 16 compared to the aluminium hydroxide-untreated group. Blood urea nitrogen in the aluminium hydroxide groups was significantly less than that in the untreated group at week 34. Histological examination revealed that glomerular sclerosis was less severe in the ADR-0w and ADR-8w groups than in the aluminium hydroxide-untreated group, and glomerular hypertrophy was significantly decreased in the ADR-0w group. We conclude that early treatment with aluminium hydroxide was effective in preventing renal deterioration in focal glomerular sclerosis induced by Adriamycin.

Aluminum Hydroxide↗