Crystallization of a salt of a weak organic acid and base: solubility relations, supersaturation control and polymorphic behavior.

Control of crystallization processes for organic salts is of importance to the pharmaceutical industry as many active pharmaceutical materials are marketed as salts. In this study, a method for estimating the solubility product of a salt of a weak acid and weak base from measured pH-solubility data is described for the first time. This allows calculation of the supersaturation of solutions at known pH. Ethylenediammonium 3,5-dinitrobenzoate is a polymorphic organic salt. A detailed study of the effects of pH, supersaturation, and temperature of crystallization on the physical properties of this salt shows that the desired polymorph may be produced by appropriate selection of the pH and supersaturation of crystallization. Crystal morphology is also controlled by these crystallization conditions.

Systematic biases in measured PM10 values with U.S. Environmental Protection Agency-approved samplers at Owens Lake, California.

From 1993 through 1998, Wedding or Graseby high-volume PM10 samplers were collocated with tapered element oscillating microbalance (TEOM) samplers at three sites at Owens Lake, CA. The study area is heavily impacted by windblown dust from the dry Owens Lake bed, which was exposed as a result of water diversions to the city of Los Angeles. A dichotomous (dichot) sampler and three collocated Partisol samplers were added in 1995 and 1999, respectively. U.S. Environmental Protection Agency (EPA) operating procedures were followed for all samplers, except for a Wedding sampler that was not cleaned for the purpose of this study. On average, the TEOM and Partisol samplers agreed to within 6%, and the dichot, Graseby, and Wedding samplers measured lower PM10 concentrations by about 10, 25, and 35%, respectively. Surprisingly, the "clean" Wedding sampler consistently measured the same concentration as the "dirty" Wedding sampler through 85 runs without cleaning. The finding that the Graseby and Wedding high-volume PM10 samplers read consistently lower than the TEOM, Partisol, and dichot samplers at Owens Lake is consistent with PM10 sampler comparisons done in other fugitive dust areas, and with wind tunnel tests showing that sampler cut points can be significantly lower than 10 microns under certain conditions. However, these results are opposite of the bias found for TEOM samplers in areas that have significant amounts of volatile particles, where the TEOM reads low due to the vaporization of particles on the TEOM's heated filter. Coarse particles like fugitive dust are relatively unaffected by the filter temperature. This study shows that in the absence of volatile particles and in the presence of fugitive dust, a different systematic bias of up to 35% exists between samplers using dichot inlets and high-volume samplers, which may cause the Graseby and Wedding PM10 samplers to undermeasure PM10 by up to 35% when the PM10 is predominantly from coarse particulate sources.

A stereo model using LoG and Gabor filtering.

This paper presents a computational model for stereopsis. Laplacian of Gaussian filters are used to extract spatial features and a set of one-octave Gabor filters is used to extract orientation information from a scene. A mapping from a 3D space onto two 2D image planes is derived using a Gaussian sphere model. The determinant of the Jacobian of the mapping is derived and matching is performed using zero-crossings associated with their orientation information. Relaxation labelling is used as a co-operative process for solving the correspondence problem.

Scientific writing courses for pediatrics fellows.

A six-week course in scientific writing and publishing was developed for pediatrics fellows at the University of Florida College of Medicine in 1984. It covered three areas: (1) grammar, syntax, and prose style; (2) construction of scientific papers; and (3) the submissions and review process. Increasing enrollment and the requests of course graduates led to the development of a second course, Advanced Scientific Writing; both courses are now offered annually. Class materials consist of texts in scientific writing, comprehensive syllabi, and handouts; the focus is on workshop activities, exercises, collaboration with peers, and individual consultations with the instructor. At the end of each course, participants complete detailed evaluation instruments, and the data obtained are used to modify the course's structure and content the following year.

Radon-222 levels in New York State homes.

Results are presented from a statewide survey that measured annual 222Rn concentrations in over 2000 single-family, owner-occupied homes in New York state. The participants were selected by a random-digit-dialing telephone interview approach developed by Mitofsky-Waksberg which allows inferences to be made from the sample to the statewide population. After completing a telephone questionnaire and agreeing to have their homes monitored, eligible households were mailed alpha-track detectors with instructions to place one detector in the main living area for 2 mo (during the winter heating season), a second in the main living area for 1 y, and a third in the basement (if applicable) for 1 y. The statewide median concentration for the heating-season, living-area readings was 31.6 Bq m-3, with a median of 24.0 Bq m-3 for the annual living-area readings and 51.8 for the annual basement readings. For the state, approximately 95% of the living-area concentrations and 86% of the basement concentrations were below 148 Bq m-3 (4 pCi L-1). In addition, only 1.4% of the readings in the basement were above 740 Bq m-3 (20 pCi L-1).

The monensin-mediated transport of Na+ and K+ through phospholipid bilayers studied by 23Na- and 39K-NMR.

Addition of monesin to preparations of large unilamellar vesicles made from egg yolk phosphatidylcholine (EPC) in sodium or potassium chloride solution and from dioleoylphosphatidylcholine (DOPC) in sodium chloride solutions gives rise to dynamic 23Na- and 39K-NMR spectra. The dynamic spectra arise from the monensin-mediated transport of the metal ions through the membrane. The kinetics of the transport are followed as a function of monensin and metal ion concentrations and are compatible with a model in which one monensin molecule transports one metal ion. Rate constants for the association and dissociation of the monensin-metal complex in the membrane/water interface are extracted and the stability constants for complex formation are evaluated. The rate constants in DOPC are similar to those in EPC, confirming that diffusion is not rate-limiting in the transport process and that dissociation of the complex is the rate-limiting step. Although potassium on its own is transported more rapidly, sodium forms the more stable complex and is therefore transported preferentially in competition with potassium.

Extraction of potassium p-nitrophenoxide with macrocyclic crown ethers and cryptands from aqueous medium into diverse organic solvents: a systematic evaluation.

A systematic study has been made of the extraction of potassium p-nitrophenoxide from aqueous medium into a number of organic solvents that are immiscible or partly miscible with water, in the presence of several macrocyclic crown ether and cryptand complexing agents. The efficiency of extraction varies extremely widely with the nature of the ligand and the solvent. For some solvent systems, DC-18-C-6 is more efficient than [2.2.2] cryptand as an extradant. The extraction values, however, provide only limited insight into the fundamental reasons behind the observed results. Hence equilibria involved have been considered and the results analysed in terms of the equilibrium constants. The microscopic and macroscopic properties of these systems are discussed.

Elementary steps in the reaction mechanism of chicken liver fatty acid synthase: reduced nicotinamide adenine dinucleotide phosphate binding and formation and reduction of acetoacetyl-enzyme.

The kinetics of reduced nicotinamide adenine dinucleotide phosphate (NADPH) binding to fatty acid synthase from chicken liver and of the reduction of enzyme-bound acetoacetyl by NADPH (beta-ketoacyl reductase) and the steps leading to formation of the acetoacetyl-enzyme have been studied in 0.1 M potassium phosphate-1 mM ethylenediaminetetraacetic acid (EDTA), pH 7.0, at 25 degrees C by monitoring changes in NADPH fluorescence with a stopped-flow apparatus. Improved fluorescence detection has permitted the use of NADPH concentrations as low as 20 nM. The kinetics of the binding of NADPH to the enzyme is consistent with a simple bimolecular binding mechanism and four equivalent sites on the enzyme (presumably two beta-ketoacyl reductase sites and two enoyl reductase sites). The bimolecular rate constant is 12.7 X 10(6) M-1 s-1, and the dissociation rate constant is 76.7 s-1, which gives an equilibrium dissociation constant of 6.0 microM. The formation of the acetoacetyl-enzyme and its subsequent reduction by NADPH could be analyzed as two consecutive pseudo-first-order reactions by mixing enzyme-NADPH with acetyl-CoA and malonyl-CoA under conditions where [acetyl-CoA], [malonyl-CoA] much greater than [enzyme] much greater than [NADPH]. From the dependence of the rate of reduction of aceto-acetyl-enzyme by NADPH on enzyme concentration, an independent estimate of the equilibrium dissociation constant for NADPH binding to the enzyme of 5.9 microM is obtained, and the rate constant for the reduction is 17.5 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Steady-state kinetic study of fatty acid synthase from chicken liver.

The steady-state kinetics of chicken liver fatty acid synthase has been studied over the pH range 5.9-8.6 in 0.1 M potassium phosphate/1 mM EDTA at 25.0 degrees C. The steady-state initial velocity, v, which was determined by measuring the rate of consumption of NADPH spectrophotometrically over a wide range of substrate concentrations, followed the rate law v = (formula; see text), in which Ac-CoA is acetyl-CoA, Mal-CoA is malonyl-CoA, the Kj are Michaelis constants, the Kj,i are inhibition constants, kcat is the turnover number, and [E0] is the total enzyme concentration. The product CoA is an inhibitor at high concentrations but activates the enzyme at low concentrations when the concentration of Ac-CoA is high. The rate law can be derived from a simple multistep mechanism; in terms of this mechanism, the Michaelis constants are lower bounds to the substrate dissociation constants, and the turnover number contains the first-order rate constants characterizing the reactions required to produce palmitic acid. Plots of kcat, kcat/KN, kcat/KA, and kcat/KM versus pH are bell shaped. Analysis of the results in terms of two ionizable groups indicates that in all cases an ionizable group with an apparent pKa of approximately equal to 6 is of importance. For kcat and kcat/KN, the apparent pKa of the second ionizable group is approximately equal to 7.8, whereas for kcat/KA and kcat/KM, it is approximately equal to 7.

Presurgical counseling needs of laryngectomaes: a survey of 78 patients.

Studies of candidated for laryngectomy have revealed a wide range of misconceptions about this surgery and its siquellae. To evalute current preoperative counseling practices, counseling deficits, and needs as perceived by the patient and his family, we surveyed all persons who had undergone laryngectomy at this institution since January 1974. The data indicated that present presurgical counseling practices are inadequate for most patients. There was considerable discrepancy between the actual counseling the patients received and what they considered ideal. For example, most received preoperative information only from their surgeons. Yet many indicated that laryngectomy candidates should be counseled by nurses, speech pathologists, recovered laryngectomees, and others. Almost all reported that the spouse should be present during counseling. Many survey respondents indicated that printed materials and/or audiovisual programs would also be desirable.

Treatment of hypoparathyroid patients with chlorthalidone.

In an effort to maintain normal serum calcium levels without inducing hypercalciuria, we treated seven hypoparathyroid patients for up to 25 months with chlorthalidone, a thiazide-like sulfonamide diuretic, plus a salt-restricted diet, without added vitamin D. Mean 24-hour calcium excretion decreased from 179 to 88 mg (P less than 0.001), and mean serum calcium increased from 8.2 to 9.3 mg per deciliter (P less than 0.05). Diuretic therapy or moderate salt restriction alone was not as effective as combined therapy. Beneficial effects were sustained for as long as therapy was maintained. The rise in serum calcium, which involves the filterable and ionized fractions, cannot be due entirely to reduced excretion and may in part be explained by increased intestinal absorption. Oral chlorthalidone plus a low salt diet appears to be an effective alternative to vitamin D in the maintenance therapy of at least some patients with hypoparathyroidism.

A mandatory course in scientific writing for undergraduate medical students.

All students at Mayo Medical School take a course in scientific writing during their sophomore and junior years. Early in the sophomore year they receive a self-instructional text designed to help them avoid 15 common writing faults. Comparison of pretest and posttest results for two classes, with a total of 89 students, indicates significant improvement (p less than .001). Later in his sophomore year, each student writes a minithesis; and during his junior year he reports on work done in a clinical or laboratory research project, preparing it as a paper submissible to a scientific journal. Professional editors work as preceptors with the students, critiquing their manuscripts, which are revised until they receive satisfactory ratings.