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PubMed2004

Effect of high bicarbonate hemodialysis on ionized calcium and risk of metastatic calcification.

BACKGROUND: Disturbances in calcium and phosphate metabolism among chronic hemodialysis patients result in renal osteodystrophy and vascular calcification. Even though it is the ionized fraction of calcium that is metabolically active, this measurement is generally not available and decisions are made on the basis of total calcium. Formulae to predict ionized calcium concentrations are available. METHODS: The OPTI Critical Care Analyzer with E-Ca cuvettes was used on-site to measure acid-base parameters, electrolytes, and ionized calcium. Additional assays included total calcium, phosphate, and albumin. RESULTS: Using a dialysate with 1.25 or 1.5 mmol/l calcium and 40 mmol/l bicarbonate, we observed a statistically significant increase in pH and total CO2 concentrations in post-dialysis blood. Total and ionized calcium increased significantly only in the patients with central venous catheters but not in those with fistulas or grafts. All patients experienced a decrease in phosphate concentrations. CONCLUSIONS: The metabolic alkalosis induced by high bicarbonate dialysate was not associated with a decrease in ionized calcium or a change in the calculated concentration product ratio for hydroxyapatite formation in the immediate post-dialysis period. However, if a 40% phosphate rebound were to occur 2 h after termination of dialysis, the calculated risk of metastatic calcification would increase 2.8-fold compared to pre-dialysis conditions. Formulae to calculate ionized calcium are not useful in this population.

Adult↗
PubMed2005

Effect of ionization and the nature of the mobile phase in quantitative structure-retention relationship studies.

The octanol-water distribution constant, commonly called partition coefficient, Po/w, is a parameter often retained as a measure of the hydrophobicity of a molecule. log Po/w, for a given molecule, can be conveniently evaluated constructing correlation lines between standard retention factor logarithms (log k) in reversed-phase liquid chromatography (RPLC) and standard log Po/w values. Many compounds of pharmaceutical interest can be quite hydrophobic and have, simultaneously, basic nitrogen atoms or acidic sulfur containing groups in their structure. This renders them ionizable. The hydrophobicity of the molecular drug form (Po/w value) is completely different from its ionic form (log Po/w(+ or -) value). The actual hydrophobicity of such ionizable molecule depends on the pH. It can be represented by an apparent Papp value that takes into account the amount of compound in its molecular and ionic state combining the Po/w and Po/w(+ or -) values. In this work, log k in RPLC for ionizable as well as non-ionizable pharmaceutical compounds with different therapeutic properties (10 beta-blockers, seven tricyclic antidepressants (TA), eight steroids and 12 sulfonamides) were correlated with log Po/w. Similar correlations were done between log k and the corrected log Papp values at pH 3. Aqueous-organic mobile phases containing acetonitrile (conventional RPLC) and micellar-organic mobile phases (micellar liquid chromatography, MLC), prepared with the anionic surfactant sodium dodecyl sulfate and the organic solvents acetonitrile, propanol or pentanol, were also used to elute the compounds. All mobile phases were buffered at pH 3. Using conventional retention RPLC data, the correlation of log k with log Po/w, was satisfactory for steroids because they cannot ionize. For ionizable beta-blockers and TAs, the use of log Papp values improved the quality of the correlations, but yielded similar results for sulfonamides. In MLC, since an electrostatic interaction is added to hydrophobic forces, poorer correlations were obtained in all cases. The retention data obtained in RPLC also seems to correlate better with the biological activity of the drugs.

Chromatography, Liquid↗
PubMed2005

Serum ionized magnesium during magnesium sulfate administration for preterm labor and preeclampsia.

OBJECTIVE: The purpose of this study is to estimate the relations between ionized and total Mg levels during MgSO4 administration in patients with preterm labor and preeclampsia. METHODS: Forty-three pregnant patients who were candidates for MgSO4 were studied (preterm labor, 27; preeclampsia, 16). The administration method was intravenous injection of MgSO4 4 g over 30 min followed by 1-2 g/h. Ionized Mg was measured by the selective ion electrode method at bedside, and compared it with total Mg levels. RESULTS: Significant correlation was existed between levels of ionized and total Mg throughout therapy for both preterm labor (ionized Mg=0.19 x total Mg+0.19; r=0.61, p<0.001) and preeclampsia (ionized Mg=0.20 x total Mg+0.14; r=0.60, p<0.001). CONCLUSION: There are correlations between ionized and total Mg levels during administration of MgSO4 for both preterm labor and preeclampsia.

Female↗
PubMed2004

Temperature-programmed pyrolysis hyphenated with metastable atom bombardment ionization mass spectrometry (TPPy/MAB-MS) for the identification of additives in polymers.

Thermoanalytical techniques are currently used for the analysis of additives contained in polymers that cannot be easily dissolved, extracted, or hydrolyzed. With these techniques, the polymers are heated to liberate the additives trapped in the polymer matrix. If the polymer is heated slowly, up to its thermal degradation, the technique is called temperature-programmed pyrolysis (TPPy). For TPPy experiments, mass spectrometry is generally used as the detection method. The ionization sources commonly used in mass spectrometry, such as CI and EI, can cause fragmentation during the ionization process. Fragmentation decreases the sensitivity of the molecular ions and increases the risks of interferences with the compounds coming from the matrix. An energy-tunable ionization technique, called metastable atom bombardment (MAB), is proposed for TPPy/MS experiments. With this ionization source, the energy of ionization depends on the metastable gas used. With low-energy metastable gases such as Xe or N(2), fragmentation is reduced compared to CI, whereas with medium-energy metastable gases such as Ar or Kr, the fragmentation is similar to that observed with CI. TPPy/MAB-MS was performed on an unknown polyurethane-based car paint. The detection of molecular ions and characteristic fragments with MAB(N(2)) led to the identification of two light stabilizers: Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate (BPPS) and 2-(2H-benzotriazol-2-yl)-4,6- di-tert-pentylphenol (PTPP). Using MAB(Ar) to simulate CI, the molecular ion and one of the two characteristic fragments of BPPS were not detected, thus confirming the advantage of using MAB(N(2)) ionization for TPPy/MS experiments.

Journal Article↗
PubMed1990

Fluoride release from glass-ionomer cements in de-ionized water and artificial saliva.

Most of the data reported on the release of fluorides from glass-ionomer cements are based upon measurements made in de-ionized water. De-ionized water does not represent the complex chemistry of the oral environment. In this study, an artificial saliva solution was used, and the data on the fluoride ions released into it from four glass-ionomer cements were compared with those obtained in de-ionized water. The glass-ionomer cements used were: Ketac-Fil (ESPE), Ketac-Silver (ESPE), Fuji-II (GC), and Miracle Mix (GC). Ten disc samples (2 cm x 0.1 cm) of each cement were prepared. Each was individually suspended in either de-ionized water or artificial saliva (five samples in each medium) and stored for 24 h at 37 degrees C, then transferred to fresh media for a total of 60 days. Collected media were buffered with TISAB, and fluoride was measured by a specific electrode. Artificial saliva was prepared according to Fusayama et al. (1963). The data obtained showed that: (1) glass-ionomer cements released more fluoride in de-ionized water than in artificial saliva; (2) Ketac-Fil released 20% more fluoride in saliva than did Fuji-II, the latter releasing 49% more fluoride than Ketac-Fil in de-ionized water; and (3) conventional glass ionomers released more fluoride than did meta-reinforced ones in both media.

Cermet Cements↗
PubMed2001

Protective role of superoxide dismutases against ionizing radiation in yeast.

The protective role of superoxide dismutases (SODs) against ionizing radiation, which generates reactive oxygen species (ROS) harmful to cellular function, was investigated in the wild-type and in mutant yeast strains lacking cytosolic CuZnSOD (sod1Delta), mitochondrial MnSOD (sod2Delta), or both SODs (sod1Deltasod2Delta). Upon exposure to ionizing radiation, there was a distinct difference between these strains in regard to viability and the level of protein carbonyl content, which is the indicative marker of oxidative damage to protein, intracellular H2O2 level, as well as lipid peroxidation. When the oxidation of 2',7'-dichlorofluorescin was used to examine the hydroperoxide production in yeast cells, the SOD mutants showed a higher degree of increase in fluorescence upon exposure to ionizing radiation as compared to wild-type cells. These results indicated that mutants deleted for SOD genes were more sensitive to ionizing radiation than isogenic wild-type cells. Induction and inactivation of other antioxidant enzymes, such as catalase, glucose 6-phosphate dehydrogenase, and glutathione reductase, were observed after their exposure to ionizing radiation both in wild-type and in mutant cells. However, wild-type cells maintained significantly higher activities of antioxidant enzymes than did mutant cells. These results suggest that both CuZnSOD and MnSOD may play a central role in protecting cells against ionizing radiation through the removal of ROS, as well as in the protection of antioxidant enzymes.

Catalase↗
PubMed2003

Analysis of acetaminophen glucuronide conjugate accompanied by adduct ion production by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry.

Liquid chromatography-mass spectrometry (LC-MS) is an effective method for the analysis of polar compounds. A coupling of LC-MS, which is used under conventional conditions, and atmospheric-pressure chemical ionization (APCI), which applies mild ionization for the analysis of water-soluble drug conjugates, would offer a very convenient method. The APCI method is effective for ionizing low- and medium-polarized compounds, but not for highly polarized compounds. In this study, we have tried derivatization of carboxyl group of glucuronic acid, to which direct ionization is difficult to apply under the APCI method, was conducted using glucuronides. Methyl ester derivatives were found to be effectively ionized. Furthermore, acetaminophen glucuronide conjugate was investigated in detail. Methyl ester derivatives of acetaminophen glucuronide conjugate (ACEG) were detected at m/z 373 as O(2) adduct ion [M+O(2)](-) in the negative mode, and p-nitrophenyl beta-D-glucuronide (PNPG) demonstrated ionization behaviors very similar to ACEG. Quantitation of ACEG was examined using PNPG as an internal standard, and satisfactory results were obtained for the recovery test and quantification.

Acetaminophen↗
PubMed1998

Serum ionized magnesium in premature and term infants.

Magnesium is the element with the second highest concentration in the body and is found almost entirely in the intracellular compartment. The small serum component gives a poor representation of the active, physiologic state of the metal. This state is assessed much better by measuring ionized magnesium in the serum, which can now be performed with a sensitive ion-selective electrode. This study was undertaken to establish the normal serum ionized magnesium levels in newborn infants and to define normal serum ionized calcium/ionized magnesium ratios. Ninety-seven infants were investigated. Six were born before 32 weeks gestation, 28 between 33 and 37 weeks gestation, and 63 were term. Ionized magnesium levels were 0.69 +/- 0.14 mmol/L, 0.63 +/- 0.10 mmol/L, and 0.57 +/- 0.07 mmol/L in each group, respectively. These findings demonstrate a significant decline in serum ionized magnesium with increasing maturity. This decrease may relate to a greater need for magnesium uptake during earlier gestation, more magnesium-induced vasodilation to maintain adequate blood flow to developing tissues and organs, or immature parathormone function earlier in pregnancy. The progressive rise in serum ionized calcium/ionized magnesium ratios found herein supports the latter hypothesis.

Blood Chemical Analysis↗
PubMed1999

Ionizing radiation-induced mutagenesis: radiation studies in Neurospora predictive for results in mammalian cells.

Ionizing radiation was the first mutagen discovered and was used to develop the first mutagenicity assay. In the ensuing 70+ years, ionizing radiation became a fundamental tool in understanding mutagenesis and is still a subject of intensive research. Frederick de Serres et al. developed and used the Neurospora crassa ad-3 system initially to explore the mutagenic effects of ionizing radiation. Using this system, de Serres et al. demonstrated the dependence of the frequency and spectra of mutations induced by ionizing radiation on the dose, dose rate, radiation quality, repair capabilities of the cells, and the target gene employed. This work in Neurospora predicted the subsequent observations of the mutagenic effects of ionizing radiation in mammalian cells. Modeled originally on the mouse specific-locus system developed by William L. Russell, the N. crassa ad-3 system developed by de Serres has itself served as a model for interpreting the results in subsequent systems in mammalian cells. This review describes the primary findings on the nature of ionizing radiation-induced mutagenesis in the N. crassa ad-3 system and the parallel observations made years later in mammalian cells.

Animals↗
PubMed1994

Influence of pH on retention and selectivity in micellar liquid chromatography: consequences of micellar-induced shifts of ionization constants.

The retention and selectivity of ionizable solutes in the two-surfactant-mediated reversed-phase LC techniques (micellar and ion pair) are compared through the use of a general retention equation for mono- and zwitterionic solutes. In RPLC with different mobile-phase modifiers (organic solvents, surfactants), the influence of pH can be quantitatively described by one general equation. The existing theory for the secondary chemical equilibria has been applied to compare selectivity effects in micellar and ion-pair chromatography. In order to predict the influence of different mobile-phase compositions on the selectivity of ionizable compounds, one should determine how a mobile-phase parameter influences the ionization equilibria (i.e., selective shifts of pKa) and self-selectivity (defined as the ratio of retention factors of the acid/conjugate base). For example, the first ionization constants of amino acids and peptides in aqueous mobile phase are between pH 2.3 and 3.4. Consequently, the pH required to maximize the retention of these solutes by ion suppression is less than the operational pH range of silica-based columns. In addition, since the pKa1 values of these solutes are similar, adjustment of pH has little effect on separation selectivity. In contrast, ion-pairing and micellar mobile phases with SDS surfactant increase the magnitude and range of the ionization constants. These trends are more pronounced with micellar mobile phase. The displacement of solute ionization constants to higher PH with micellar mobile phase allows the maximal, limiting, retention of zwitterionic solutes to be observed within the pH limits of silica-based columns.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, High Pressure Liquid↗
PubMed2003

Resonance and nonresonant laser ionization of sputtered uranium atoms from thin films and single microparticles: evaluation of a combined system for particle trace analysis.

The resonance and nonresonant laser ionization of uranium atoms sputtered from thin metal films and individual micrometer-size uranium oxide particles, respectively, was studied to evaluate a new setup for the analysis of actinide-containing micrometer-size particles. Experiments using nonresonant (193-nm) ionization of atoms and molecules sputtered from micrometer-size uranium oxide particles have shown that the uranium detection efficiencies for sputtered neutral atoms are approximately 2 orders of magnitude higher than for secondary ions. In uranium particles of 0.5-microm diameter, 6 x 10(6) atoms of 235U were easily detected and the isotopic ratio of 235U/238U = 0.0048 +/- 4.6% is in excellent agreement with the certified value. The use of two-color, two-step resonance ionization of the sputtered neutral uranium atoms from thin films was investigated. Several excitation schemes were tested, and a significant population of several low-lying metastable states after ion sputtering was observed. Autoionizing states for double-resonant ionization were determined, and the high selectivity of ionization schemes involving these autoionizing states was illustrated by comparing the flight-time distributions of different sputtered species obtained both by resonance and nonresonant multiphoton (355-nm) laser postionization. Ideally, the options for resonance as well as nonresonant ionization would be combined in a single setup, to obtain a large gain in sensitivity and selectivity. Thus, information about the main components as well as specific isotopic information of a trace element could be obtained from the same single particle.

Journal Article↗
PubMed1981

Perturbations in the free energy and enthalpy of ionization of histidine-159 at the active site of papain as determined by fluorescence spectroscopy.

Fluorometric titrations of papain, succinyl-papain, and the corresponding methylthio derivatives of Cys-25 (papain-S-SCH3 and succinyl-papain-S-SCH3) were determined. Removal of the methylthio group from Cys-25 resulted in an increase of approximately 4 pK units in the fluorometrically determined pK value. The correspondence between the ionization behavior as determined by proton NMR and fluorometric titrations indicated that fluorescence titrations reflect the ionization behavior of His-159 in both the active enzyme and the methylthio derivative. The ionic strength dependence of the pK was analyzed in terms of simple electrostatic theory and was shown to be consistent with the charge on the protein. The temperature dependence of the pK values of His-159 indicated an increase in the heat of ionization from about 0 to 8 kcal/mol upon removal of the methylthio blocking group from Cys-25. Measurements of the effect of solvent on the pK's and heats of ionization of simple model compounds indicated that the observed shift in enthalpy of ionization of His-159 upon removal of th methylthio group from Cys-25 is not unreasonable in light of the accompanying perturbation is more than 4 pK units in the pK of His-159. The perturbations in enthalpies and free energies are attributed to formation of an ion pair. The ionization behavior of His-159 in thiol-blocked derivatives of papain is consistent with the involvement of His-159 in the deacylation step in papain catalysis.

Benzoates↗
PubMed2002

A prototype for catalyzed amide bond cleavage: production of the [NH(3), H(2)O](*)(+) dimer from ionized formamide and its carbene isomer.

The reaction of ionized formamide H(2)NCHO(*)(+) with water leads to an exclusive loss of CO from the complex. This contrasts with the unimolecular reaction of low-energy ionized formamide, which loses exclusively one hydrogen atom. The unimolecular loss of CO is not observed because it involves several H-transfers corresponding to high-energy barriers. Experimental and theoretical studies of the role of solvation by water on the fragmentation of ionized formamide leads to three different results: (i) In contrast with different systems previously studied, in which solvation plays only a role on one or two steps of a reaction, a molecule of water is efficient in the catalysis of the decarbonylation process because water catalyzes all the steps of the reaction of ionized formamide, including the final dissociation of the amide bond. (ii) The catalyzed isomerization of carbonylic radical cations into their carbene counterparts is shown to be an important step in the process. To study this step, a precise probe, characterizing the carbene structure by ion-molecule reaction, is for the first time described. (iii) Finally, decarbonylation of ionized formamide yields the [NH(3), H(2)O](*)(+) ion, which has not been generated and experimentally studied previously. By this method, the [NH(3), H(2)O](*)(+) ion is generated in abundance and with a low internal energy content, allowing one either to prepare, by ligand exchange, a series of other solvated radical cations or to generate covalent structures such as distonic ions. First results on related systems indicate that the conclusions obtained for ionized formamide are widespread.

Journal Article↗
PubMed2005

Electron propagator calculations show that alkyl substituents alter porphyrin ionization energies.

The effect of alkyl substituents on the four lowest vertical ionization energies of porphyrins is determined with ab initio electron propagator calculations on porphine and octamethylporphyrin. With the use of the partial third-order approximation, predicted ionization energies are in close agreement with recent photoelectron spectra. These data and the associated Dyson orbitals, which describe changes in electronic structure that accompany photoionization, enable assignment of photoelectron spectra and determination of alkyl-induced shifts. Hyperconjugation is most evident in the Dyson orbitals associated with the third and fourth ionization energies of octamethylporphyrin and is least prominent in the Dyson orbital of the second ionization energy. There is a positive correlation between the shift in an ionization energy produced by alkyl substitution and the degree of hyperconjugation in the associated Dyson orbital. Alkyl substitutions, therefore, may be employed to adjust the ionization energies of porphyrins and, consequently, their reactivity patterns that depend on charge-transfer capabilities and disposition to electrophilic attack.

Alkylation↗
PubMed2005

On the titanium oxide neutral cluster distribution in the gas phase: Detection through 118 nm single-photon and 193 nm multiphoton ionization.

Titanium oxide clusters are generated in a supersonic expansion by laser ablation of the metal and reaction with oxygen (0.1-6%) in He expansion gas. Mass spectra of the titanium oxide clusters are observed by photoionization with lasers of three different wavelengths: 118, 193, and 355 nm. Only the 118 nm (10.5 eV) light can ionize Ti(m)O(n) neutral clusters without fragmentation. Both the 193 nm (6.4 eV) and 355 nm (3.5 eV) multiphoton ionization cause fragmentation of the neutral clusters during the ionization process and, thus, can complicate the determination of the stable neutral Ti(m)O(n) gas-phase species. Employing 118 nm single-photon ionization and line-width data, the Ti(m)O(2m) and Ti(m)O(2m+1) series are found to be the most stable neutral cluster species for high oxygen content in the expansion gas. Fragmentation during the multiphoton ionization process for 193 nm light yields the cluster ions Ti(m)O(2m-1,-2)+. These ions are formed by the loss of one or two oxygen atoms from Ti(m)O(2m,2m+1) neutral species. The dominant cluster growth process is suggested to be through the addition of TiO2 species. For low oxygen content (<2%) in the expansion gas, oxygen-deficient clusters of the form Ti(m)O(2m-1,-2) are also observed. These latter series are not fragmented by the 193 nm ionization process.

Journal Article↗
PubMed2005

Enthalpy changes upon dilution and ionization of poly(L-glutamic acid) in aqueous solutions.

The enthalpy changes accompanying the dilution and ionization of poly(L-glutamic acid) in water have been measured at 25 degrees C for two degrees of polymerization (DP = 115 and DP = 480) at various degrees of ionization, alpha, for a concentration range from about 0.2 to 0.002 monomol/L. The heat of dilution displays an unusual dependence on the degree of ionization, which is in sharp contrast to the behavior of other weak carboxylic polyelectrolytes, such as poly(acrylic acid). The exothermic heat effects observed at low values of alpha become endothermic for the region where the helix-coil transition is most pronounced, and for high degrees of ionization, they are exothermic again. Evidently, an endothermic heat effect, produced by an additional conformational transition in the dilution process, is superimposed on the exothermic enthalpy of dilution, and it overweighs the latter in the region of alpha where the conformational transition is prevailing. The calorimetric titration curve, which gives the dependence of the heat of ionization, deltaH(i), on alpha, has a maximum and is typical for poly(carboxylic acids) which undergo pH-induced conformational transition, such as poly(methacrylic acid). The values of deltaH(i) obtained at two polymer concentrations indicate that the enthalpy of ionization depends on the polypeptide concentration.

Acrylic Resins↗
PubMed1999

Ionization constants and distribution coefficients of phenothiazines and calcium channel antagonists determined by a pH-metric method and correlation with calculated partition coefficients.

The pH-metric technique was used to determine the ionization constants and distribution coefficients of 10 phenothiazines and five ionizable calcium channel antagonists. Because the studied compounds were poorly water soluble and quite lipophilic with partition coefficients in the range of 3.5 to 5.5, organic cosolvents had to be added for the determination of the ionization constants to avoid precipitation of the free bases. The effect of the cosolvents dioxane and methanol on the extrapolation to pure water was compared. For both cosolvents a very good agreement with accessible published ionization constants was obtained, however the slope of the regression line was much smaller for dioxane, yielding more reliable estimates according to the standard deviation of the extrapolated values. Thus, dioxane might be preferable to methanol as a cosolvent for the determination of ionization constants of sparingly water soluble bases. Also the n-octanol/water partition coefficients were determined and compared with published data and values calculated with the ClogP, ACD, and HINT programs. Although the obtained values were approximate in conformity with the published data, the calculated partition coefficients differed from the experimental ones considerably for the majority of the investigated compounds. Furthermore, the ion pair partitioning and the distribution coefficients at physiological pH 7.4 were determined. The pH-dependent distribution profiles showed the strong influence of the ionization constants and of the distribution of the ion pairs on the overall distribution. This result strongly suggests that greater use should be made of measured distribution coefficients in quantitative structure-activity relationship studies. The potentiometric method is a convenient way to determine the distribution properties of drug molecules at pH values relevant for the biological system under investigation.

Algorithms↗
PubMed2002

The use of a genetically engineered herpes simplex virus (R7020) with ionizing radiation for experimental hepatoma.

The herpes simplex virus (HSV) recombinant virus R7020 is an attenuated virus designed as a candidate for immunization against both HSV-1 and HSV-2 infections. It was extensively tested in an experimental animal system and in a healthy human adult population without significant untoward effects. We report on the use of R7020 with ionizing radiation as an oncolytic agent for hepatomas. Two hepatoma cell lines were studied, Hep3B and Huh7. R7020 replicated to higher titers in Hep3B cells than in Huh7 cells. Tissue culture studies correlated with hepatoma xenograft responses to R7020. R7020 was more effective in mediating Hep3B tumor xenograft regression compared with Huh7. Ionizing radiation combined with R7020 also showed differential results in antitumor efficacy between the two cell lines in tumor xenografts. Ionizing radiation enhanced the replication of R7020 in Hep3B xenografts. Moreover, the combination of ionizing radiation and virus caused a greater regression of xenograft volume than either R7020 or radiation alone. Ionizing radiation had no effect on the replication of R7020 virus in Huh7 xenografts. These results indicate that a regimen involving infection with an appropriate herpesvirus such as R7020 in combination with ionizing radiation can be highly effective in eradicating certain tumor xenografts.

Animals↗