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At least 505 records · Page 28Linked to original sources
PubMed2002

Synthesis and characterization of hydroxyapatite crystals: a review study on the analytical methods.

For the synthesis of hydroxyapatite crystals from aqueous solutions three preparation methods were employed. From the experimental processes and the characterization of the crystals it was concluded that aging and precipitation kinetics are critical for the purity of the product and its crystallographic characteristics. The authentication details are presented along with the results from infrared spectroscopy, X-ray powder diffraction, Raman spectroscopy, transmission and scanning electron photographs, and chemical analysis. Analytical data for several calcium phosphates were collected from the literature, extensively reviewed, and the results were grouped and presented in tables to provide comparison with the data obtained here.

Crystallization↗
PubMed1990

Long-term organ culture of embryonic chick femora: a system for investigating bone and cartilage formation at an intermediate level of organization.

Bone organ culture is an experimental system in which skeletal cells remain within their extracellular matrix but are removed from systemic influences. Femurs from 14-day-old chick embryos, which contain bone and cartilage matrix in approximately equal proportions, were cultured for up to 9 days in a serum-free medium. Cell proliferation, differentiation into chondrocytes and osteoblasts, formation of bone and cartilage matrix, and in vitro mineralization as well as bone and cartilage resorption were assessed using histologic and analytic methods. Particular attention was paid to the differences between cartilage and bone growth and to interpreting analytic data in the light of histologic observations. The first 2 days of culture represented an "adaptation" period, characterized by the release of intracellular enzymes into the culture medium, probably as a consequence of cell breakdown. Days 3-9 in culture represented a period of "steady growth" during which skeletal cells continued to multiply in the absence of fetal serum and to secrete large amounts of bone and cartilage matrix. De novo mineralization could be induced by Ca-beta-glycerophosphate, but calcium deposits in tissues other than bone and cartilage were also induced. Resorption of bone or cartilage matrix was virtually absent. Bone organ culture facilitates the study of bone and cartilage formation at an intermediate level of organization and thereby provides the necessary link between in vivo studies and investigations at the cellular level.

Acid Phosphatase↗
PubMed2026

Pilot Evaluation of a Digital Pretest Education Platform for Genomic Counseling: Perspectives of Health Care Providers and Patients.

Traditional in-person consultations for genetic services create access barriers. We hypothesized that the Genetics Adviser platform-a web-based digital platform delivering clinical genomic services-could reduce these barriers. Focusing on pretest education and counseling, we tested a pilot version of the platform in medical genetics and pediatric endocrinology group practices. The multimethod design consisted of quantitative patient and caregiver surveys, Google Analytics data, and qualitative healthcare provider interviews. Surveys included validated measures of acceptability and empowerment. Transcribed interviews were thematically coded and analyzed using NVivo. Of the 102 patients and caregivers targeted for this study, 85/102 (83%) accessed the platform, 71/102 (70%) proceeded beyond the landing page, and 60/102 (59%) completed the post-module survey. Users expressed high confidence in genetic understanding and empowerment (Genomics Outcome Scale [GOS]: 77/100), and providers noted potential benefits and highlighted technological and content-related limitations. Further research is needed to validate effectiveness across diverse populations and to evaluate long-term impacts on patient outcomes and healthcare efficiency.

Humans↗
PubMedDate not supplied

Measurement of skeletal muscle motion in vivo with phase-contrast MR imaging.

The ability to measure skeletal muscle motion with phase-contrast magnetic resonance (MR) imaging was tested with a motion phantom that simulated muscle activity. Quantitative analytic data on unidimensional, bidirectional skeletal muscle motion measured in vivo was obtained in four healthy volunteers. MR images of the subjects' forearms were obtained during flexion and extension of the fingers and of the anterior and posterior muscle compartments of the lower leg with various resistances to ankle dorsiflexion and plantar flexion. It was necessary to correct the data for the effects of eddy currents. In vitro evaluation of the technique was done by studying through-plane sinusoidal motion of solid objects. The largest error was underestimation of the peak excursion of 11.5 mm by 0.09 mm (the root mean square error for the cycle was 0.04 mm) In vivo experiments demonstrated the contraction of muscles in relation to each other. Data acquisition and analysis techniques must be refined, but measuring skeletal muscle motion with phase-contrast MR imaging should enhance the understanding of bioengineering fundamentals and muscular changes in disease and adaptation.

Ankle↗
PubMed1977

[Anabolic and catabolic enzymes of urea metabolism in a carbohydrate-utilizing strain of Candida guilliermondii].

The yeast "H" of the genus Candida guilliermondii can grow on hydrocarbons as the only source for carbon. Urea can serve as a nitrogen source for this yeast which lacks detectable urease activity. During urea metabolism ammonia has never been accumulated in the culture medium. However, transferring the yeast from complete urea-medium into an urea containing phophate-buffer, the degradation of urea continues and ammonia is accumulated as well as CO2 evolved. In cell-free extracts of the yeast urea amidolyase activity was detected in the presence of ATP, biotin and specific cations. Obviously, the synthesis of urea amidolyase is induced by urea and arginine and repressed by the catabolite ammonia. Similarly the synthesis of arginase is regulated by arginine and ammonia. The analytical data of the arginase action differ significantly in relation to the carbon source of the culture medium. Both the level of arginase and ornithine carbamyl-transferase change in a characteristic way during the batch-culture. From the lower level of arginase in relation to ornithine carbamyltransferase it can be concluded that especially in alkane-metabolizing yeast the arginine catabolism is not very intensive.

Arginase↗
PubMed1975

Determination of mercury-containing pharmaceuticals by vapor phase atomic absorption spectroscopy.

A procedure was developed for the determination of mercurials of pharmaceutical interest. Protic acid cleavage of the compound was followed by reduction of the resulting mercuric ion and vapor phase atomic absorption spectroscopy. This procedure was applied to 11 different mercurial compounds in various pharmaceutical preparations and offers excellent sensitivity with respect to presently used compendial assays. Comparative analytical data between this procedure and compendial methodology are presented.

Chemistry, Pharmaceutical↗
PubMed1977

Synthesis and anticancer screening of 2-indolyl 5-(1,2,3,6-tetrahydropyridyl) ketones.

Several derivatives of 2-indolyl 5-(1,2,3,6-tetrahydropyridyl) ketone with various substituents on the pyridine nitrogen and with or without a benzenesulfonyl group on the indole nitrogen were synthesized and characterized by spectroscopic and analytical data. Only one showed erratic but confirmed activity in the P-388 screen. The other derivatives were inactive in the L-1210 leukemia screen.

Alkylation↗
PubMed1980

High-performance liquid chromatographic determination of epimers, impurities, and content of the glucocorticoid budesonide and preparation of primary standard.

The new glucocorticoid budesonide, a 1:1 mixture of two epimers, was evaluated analytically with respect to drug content, impurities, and epimer distribution in the drug substance. Reversed-phase high-performance liquid chromatographic (HPLC) systems using octadecylsilane columns with different ethanol-water mixtures as eluents were used. Budesonide and its epimers were determined with recoveries of 100.3% (+/- 0.16 SD) and 99.7% (+/- 0.27 SD), respectively. Individual foreign steroids in the ranges of 0.05--0.2 and 0.2--2% were determined with mean recoveries of 93% (+/- 7.6 SD) and 97% (+/- 2.5 SD), respectively. Analysis of eight small-scale production batches of budesonide gave a recovery of 99.9% (+/- 0.39 SD) for the sum of budesonide and impurities. Analytical data and the procedure for preparation of a budesonide primary standard are given. The proposed HPLC procedure is faster, more accurate, more precise, and more selective than the usual pharmacopeial methods for corticosteroids.

Budesonide↗
PubMed2006

Headspace solvent microextraction as a simple and highly sensitive sample pretreatment technique for ultra trace determination of geosmin in aquatic media.

A headspace solvent microextraction method was developed for the trace determination of geosmin, an odorant compound, in water samples. After performing the extraction by a microdrop of an organic solvent, the microdrop was introduced directly into a GC-MS injection port. One-at-the-time optimization strategy was applied to investigate and optimize some important extraction parameters such as type of solvent, drop volume, temperature, stirring rate, ionic strength, sample volume, and extraction time. The analytical data exhibited an RSD of less than 5% (n = 5), a linear calibration range of 5-900 ng/L (r2 > 0.998), and a detection limit of 0.8 and 3.3 ng/L using two different sets of selected ions. The proposed method was successfully applied to the extraction and determination of geosmin in the spiked real water sample and reasonable recovery was achieved.

Journal Article↗
PubMed2005

Synthesis and NMR spectral study of some t(3)-aryl-r(2),c(4)-bisethoxycarbonyl-t(5)-hydroxy-c(5)-methylcyclohexanones.

Six t(3)-aryl-r(2),c(4)-bisethoxycarbonyl-t(5)-hydroxy-c(5)-methylcyclohexanones (6-11) were synthesized by condensing ArCHO (Ar = Ph, p-O(2)NC(6)H(4), p-CH(3)OC(6)H(4), p-ClC(6)H(4), m-O(2)NC(6)H(4) and m-C(6)H(5)O(6)H(4)) with ethyl acetoacetate in the presence of methylamine and their (1)H and (13)C NMR spectra were recorded. (1)H-(1)H COSY and NOESY spectra were recorded for 6 and 7 and also HSQC and HMBC spectra for 6 and 8. Elemental analysis was carried out for all compounds. The mass spectrum was recorded for 8. All analytical data are consistent with the proposed molecular formulae. Analysis of NMR spectral data suggests that these compounds largely adopt chair conformations with the hydroxyl group occupying an axial orientation and all the other substituents occupying equatorial orientations. Long-range coupling (2-3 Hz) between the OH proton and the axial methylene proton at C-6 is observed in 6, 7, 8 and 11.

Journal Article↗
PubMed1995

Worldwide regulations for mycotoxins in 1994.

Since the discovery of the aflatoxins in the 1960s, regulations have been established in many countries to protect the consumer from harmful effects of mycotoxins that may contaminate foodstuffs. Various factors play a role in the decision-making process of setting limits for mycotoxins. These include scientific factors such as availability of survey data, toxicological data, analytical methodology, and knowledge about the distribution of mycotoxins in contaminated commodities. Economical and political factors such as commercial interests and sufficiency of food supply have their impact as well. International enquiries on existing mycotoxin regulation in foodstuffs and animal feedstuffs have been carried out several times in the 1980s and details about tolerances, legal bases, responsible authorities, official protocols of analysis and sampling have been published. The most recent enquiry is currently taking place as part of a contract with the Food and Agriculture Organization. At least 77 countries now have regulations for mycotoxins. An overview is presented of the tentative results of this enquiry, including frequency distributions of existing tolerances for aflatoxins and current trends.

Food Analysis↗
PubMed2005

Identification of degradation products formed during performic oxidation of peptides and proteins by high-performance liquid chromatography with matrix-assisted laser desorption/ionization and tandem mass spectrometry.

Oxidation of proteins with performic acid is extensively used to cleave disulfide bonds. Due to its efficiency and many other advantages it deserves more attention especially in proteomics as a method for sample treatment. However, some unwanted degradations can occur during performic oxidation. In this work the degradation products during performic oxidation of two peptides and bovine serum albumin as model substrates were explored by coupling high-performance liquid chromatography (HPLC) to matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-TOF/TOFMS). In addition to well-known modifications such as oxidation of tryptophan and oxidation and chlorination of tyrosine, novel degradation products including nonspecific cleavage after asparagine or tryptophan, formylation of lysine, and beta-elimination of cysteine, were observed. Although almost all of these modification/degradation products except oxidation products of tryptophan were formed at sub-stoichiometric levels, they can cause confusion as a result of the sensitivity of mass spectrometry in analysis of the oxidized samples, especially in proteomics research. The results presented here will facilitate the interpretation of analytical data for performate-oxidized samples, and help to select appropriate methods for each unique sample.

Amino Acid Sequence↗
PubMed2002

Self-esterification of fulvic acid model compounds in methanolic solvents as observed by electrospray ionization mass spectrometry.

The self-esterification of two fulvic acid model compounds in methanolic solvents was studied by electrospray ionization mass spectrometry (ESI-MS). The strongly acidic tetrahydrofurantetracarboxylic acid rapidly self-esterified to form mono- and dimethyl esters when stored in methanol, even at reduced temperatures. The weakly acidic analogue, cyclopentanetetracarboxylic acid, reacted minimally under the same conditions. The use of 50:50 methanol/water as a solvent reduced self-esterification of the strong acid. However, the presence of water promoted the formation of multiply charged ions in the ESI mass spectra. The use of water and 50:50 acetonitrile/water as solvents eliminated self-esterification but the mass spectra still contained multiply charged ions. This study implies that the use of methanolic solvents with humic substances may compromise analytical data through the formation of methyl esters.

Benzopyrans↗
PubMed2007

Bias reduction in effectiveness analyses of longitudinal ordinal doses with a mixed-effects propensity adjustment.

A mixed-effects propensity adjustment is described that can reduce bias in longitudinal studies involving non-equivalent comparison groups. There are two stages in this data analytic strategy. First, a model of propensity for treatment intensity examines variables that distinguish among subjects who receive various ordered doses of treatment across time using mixed-effects ordinal logistic regression. Second, the effectiveness model examines multiple times until recurrence to compare the ordered doses using a mixed-effects grouped-time survival model. Effectiveness analyses are initially stratified by propensity quintile. Then the quintile-specific results are pooled, assuming that there is not a propensity x treatment interaction. A Monte Carlo simulation study compares bias reduction in fully specified propensity model relative to misspecified models. In addition, type I error rate and statistical power are examined. The approach is illustrated by applying it to a longitudinal, observational study of maintenance treatment of major depression.

Adult↗
PubMed1989

A comparison of estimated proportional hazards models and regression trees.

We present examples of the usage of regression trees for censored response via two real world datasets, one a rheumatoid arthritis survival study and the other a hip replacement study, and draw comparisons with the results of Cox proportional hazards modelling. The two methods pursue different goals. Motivation of the tree techniques is the desire to extract meaningful prognostic groups while the proportional hazards model enables assessment of the impact of risk factors. The methods are thus complementary. For the arthritis study the two techniques corroborate one another, although the flavour of the conclusions derived differ. For the hip replacement study, however, the regression tree approach reveals structure that would not emerge from a routine proportional hazards analysis. We also discuss the treatment of data analytic issues such as the handling of missing values and influence in the presence of non-uniform censoring.

Aged↗
PubMed2004

Assessment of toxic interactions of heavy metals in a multicomponent mixture using Lepidium sativum and Spirodela polyrrhiza.

The toxicities of copper, chromium, cadmium, nickel, manganese, zinc, and lead ions and various concentrations of mixtures of them were studied using the aquatic plant Spirodela polyrrhiza and the terrestrial plant Lepidium sativum. The composition of the model mixture was based on average analytical data of the annual amounts of representative heavy metals (HM) in wastewater discharged from the Ignalina Nuclear Power Plant (Lithuania) during 1996. The observed and predicted effects of the HM mixture on tested plants were evaluated and compared with the prediction models used in describing the toxic interactions of heavy metals in the mixture. The type of toxic interaction at each tested concentration of the mixture was assessed by a statistical approach that tested the null hypothesis of additive toxicity (Ince et al., 1999) and the mixture toxicity index (MTI; Könemann, 1981). For both plant organisms the effect of the HM mixture calculated using the MTI was synergistic. However, assessment of the HM interaction type at 50% effect concentrations using the hypothesis of additive toxicity showed a synergistic effect for Spirodela polyrrhiza and an additive effect for Lepidium sativum. Though the results obtained using both prediction models for assessing the HM mixture's toxicity were similar, in our opinion, the additive toxicity model is more suitable than the MTI model because the former allows evaluation of the impact of various mixture concentrations, not only those with a 50% effect.

Araceae↗
PubMed1996

Determination of intermediates of hemoglobin-haptoglobin complex of haptoglobin polymers by "Crossed hemoglobin electrophoresis".

We designed a "crossed hemoglobin electrophoresis" to be able to detect the intermediates of a hemoglobin-haptoglobin complex without the need for the purification step of haptoglobin molecules. Native polyacrylamide gel electrophoresis was performed as the first dimensional electrophoresis followed by a cross to hemoglobin as the second dimensional electrophoresis. Using this method, we found that a number of intermediates of normal Hp 2-2, Hp 2-1 polymers, particularly those from the trimer to the pentamer, were detected on a polyacrylamide gel. Each of their polymers combined to the hexamer with at least an equimolar content of hemoglobin. In the process of detecting the haptoglobin serotype of more than 10,000 patients for the clinical utilization of quantitative analytical data, we observed two haptoglobin variants, the Hp Johnson and a haptoglobin serotype similar to the Carlberg type. Using our crossed hemoglobin electrophoresis, we also detected the capacity for combining with hemoglobin of each polymer of these variants.

Electrophoresis, Gel, Two-Dimensional↗