Evaluations of the Mechanism of Disintegrant Action

The disintegrant properties of eight tablet disintegrants (a cation exchange resin, cross-linked carboxymethyl cellulose, sodium starch glycolate, U.S.P., Crospovidone, U.S.P., corn starch, an insoluble anionic cellulose polymer, a modified food starch, and a soybean cellulose derivative) have been evaluated. Three techniques were applied to some or all of the materials. Water uptake rates and capacities were determined for all disintegrants in bulk powders. Disintegration times of tablets formulated with varying concentrations of the different disintegrants in a matrix comprising 75% unmilled dibasic calcium phosphate dihydrate and 25% anhydrous lactose were measured. For four disintegrants, a novel computer assisted cinsphotomicrographic technique was applied to investigate the interaction of water with individual disintegrant particles, both in terms of swelling rate and maximum water capacity

Comparative evaluation of tablet disintegrants and studies of the mechanism of disintegrant action have quite properly attracted the attention of a number of pharmaceutical scientists. (1-16) However, it is clear that at present there is no concensus concerning a general theory rationalizing disintegrant action and at least five separate mechanism have been proposed (1, 2, 4)

In the present paper, the disintegrant action of eight disintegrants has been studied using three separate approaches. Firstly, the rate and capacity of the bulk powders to take up water and to swell as a result has been evaluated using an apparatus similar to that used by Nogami and coworkers (5). Secondly, the disintegration times of tablets containing varying concentrations of disintegrant and compressed using a matrix of 75% unmilled dibasic calcium phosphate dihydrate and 25% anhydrous lactose were determined in a manner similar to that described by Rudnic and his associates (6). Thirdly, the authors are able to report - apparently for the first time - the use of a new method for evaluating the rate and extent of swelling of individual units in an assembly of disintegrant particles. This method exploits a cinephotomicrographic technique in which groups of disintegrant particles are photographed under a microscope by a high speed movie camera with the resultant film being analyzed by a special computer technique which allows the size of both individual and all particles, in any given visual field, to be followed over the very short period of time which elapses during the interaction of the disintegrant particles with water. The results presented in this paper demonstrate that a combination of the three methods described above and, in particular, the computer assisted cinemicrophotographic technique allow considerable insight to be gained of the disintegration process     

An optical cell for photographic studies of gas evolution during molten salt electrolysis

The simple optical cell described is useful for providing supplementary information on the evolution of gases during the electrolysis of fused salts or other electrolytes. Its use with PbS-PbCl₂ and PbS-PbCl₂-NaCl melts demonstrated that, for anodic sulphur gas production, residual gas evolution occurs, indicating the formation of a chemisorbed species as a reaction intermediate. Dissolution of the sulphur in the melt also takes place; its rate increases with increase in temperature and sulphide concentration.     

Electrolysis of molten salt solutions containing PbSO4

Low faradaic yields of Pb were found when electrolysing melts containing PbSO₄ in solvents of either LiCl-KCl eutectic or Li₂SO₄-K₂SO₄-Na₄SO₄ eutectic and employing low current densities. For all current densities employed, the decrease in current efficiency became greater as the lead sulphate concentration was increased but the influence of other sulphates was less pronounced. From studies of the reaction of lead with the melt and a chronopotentiometric study of cathodic processes, we have found the following two reactions occur:

1. Cathodic deposition of lead by the reversible reaction Pb²⁺ +2e?Pb
2. Secondary non-electrochemical reaction of the electrodeposit 4Pb+5PbSO₄→PbS+4PbO.PbSO₄

The rate of the latter reaction is sufficient to account for the lowering in current efficiencies. No evidence could be found to support direct reduction of the sulphate anion.     

Characteristics of women with a family history of ovarian cancer. I. Galactose consumption and metabolism

BACKGROUND: Galactose metabolism may be a risk factor for ovarian cancer based upon evidence that galactose causes ovarian failure and that ovarian cancer arises from premature ovarian failure. This study examines galactose-1-phosphate uridyl transferase (GALT) activity in women with a family history of ovarian cancer (FOC) to determine if low GALT activity occurs in women who are at risk for but in whom ovarian cancer has not yet developed. METHODS: The authors studied 106 premenopausal women (FOC patients) with one primary or two second-degree relatives with ovarian cancer compared with 116 age matched control subjects without a family history of ovarian cancer (FOC controls). All women completed questionnaires and had blood drawn to measure GALT activity and genotype. RESULTS: Mean erythrocyte GALT activity, in micromoles of hexose conversion per hour per gram of hemoglobin was 21.5 in FOC patients, significantly lower than the mean of 23.1 observed in FOC control subjects, (P = 0.001). FOC patients more frequently displayed the Duarte variant of galactosemia as detected by electrophoresis. In a subset of 87 patients and 113 control subjects for whom DNA was available, the allelelic frequency of the Duarte variant based upon molecular genetic detection of the N314D mutation that is associated with the Duarte variant was 15.5% among FOC cases compared with 7.5% among control subjects (P < 0.02). Galactose consumption did not differ between FOC patients and control subjects. CONCLUSION: Galactose metabolism differs between women with and without a family history of ovarian cancer, suggesting that it may be a genetic risk factor for ovarian cancer, possibly mediated through oocyte toxicity from galactose.     

High power, diffraction-limited emission from monolithically integrated active grating master oscillator power amplifier (lasers)

A novel monolithically integrated master oscillator power amplifier with a distributed amplifier/grating output coupler is demonstrated which emits 370 mW in a single-frequency diffraction-limited beam without any form of active phase control. The distributed amplifier/grating output coupler results in a guided mode power that saturates along the direction of propagation, providing a uniform carrier density to preserve the flatness of the radiated phase front.<>     

Significance of Blood Flow in Calculations of Temperature in Laser Irradiated Tissue

A dimensionless solution of the heat conduction equation for laser irradiation of tissue has been extended to include transport of heat owing to blood flow. The importance of the heat loss term is discussed in relation to the perfusion rate and exposure duration.     

Identification and characterization of isomeric intermediates in a catalyst formation reaction by means of speciation analysis using HPLC-ICPMS and HPLC-ESI-MS

Information on chemical speciation is much needed in mechanistic and kinetic studies on catalyst formation processes in pharmaceutical research. Speciation analysis was applied to the identification and quantification of various rhodium species involved in a ligand exchange process leading to formation of catalyst dirhodium(II) tetrakis[methyl 2-oxopyrrolidin-5(S)-carboxylate]. Inductively coupled plasma mass spectrometry (ICPMS) was used as an element-specific detector following species separation by reversed-phase high-performance liquid chromatography (RP-HPLC), and electrospray ionization mass spectrometry (ESI-MS) was used for species identification and confirmation. A novel interface between the HPLC and ICPMS, which consisted of an eluent splitter, a desolvation unit, and the ICPMS built-in peristaltic pump, enabled the use of RP-HPLC with gradient elution and up to 100% organic components in the LC eluent without organic loading in the plasma. A variety of reaction intermediates were identified and quantified along the pathway to formation of the desired product, including isomeric di-, tri-, and tetrasubstituted species previously believed to be absent. This has provided new insights into the mechanism and kinetics of the reaction. The combination of HPLC-ICPMS and HPLC-ESI-MS has proven to be a valuable tool for the investigation of species evolution in catalyst formation process.     

The effects of electronic alert letters for internet surveys of academic scientists

Scientometrics - Survey alert letters improve response rates and assure potential respondents that the research is legitimate and of high quality. Pre-notification by mail increases response rates...     

Measuring Symmetry in Drawings of Graphs

Layout symmetry is an important and desired feature in graph drawing. While there is a substantial body of work in computer vision around the detection and measurement of symmetry in images, there has been little effort to define and validate meaningful measures of the symmetry of graph drawings. In this paper, we evaluate two algorithms that have been proposed for measuring graph drawing symmetry, comparing their judgments to those of human subjects, and investigating the use of stress as an alternative measure of symmetry. We discuss advantages and disadvantages of these measures, possible ways to improve them, and implications for the design of algorithms that optimize the symmetry in the layout.     

Formaldehyde-free durable-press finishes

Durable-press finishing agents that neither contain nor release formaldehyde when applied to cotton fabrics are reviewed and compared with conventional N-methylolamides in regard to fabric wrinkle resistance, smooth drying properties, strength retention and yellowing imparted. The need for agents that are not derived from formaldehyde results from international recognition that formaldehyde is a probable human carcinogen. When formaldehyde-free cellulose crosslinking agents are screened to eliminate those having toxicity, odour and environmental problems of their own, the most likely candidates are seen to be polycarboxylic acids and 1,3-dimethyl-4, 5-dihydroxy-ethyleneurea (also known as DHDMI). These differ in cost and effectiveness, and will require further research and development to become fully practical.