The Use of Fractal Geometry in Pharmaceutical Systems

The nature of surface irregularity affects many phenomena including adsorption/desorption, catalysis, crystal growth, drug dissolution and chromatography. Many excellent models have been developed with the oversimplified assumption that all particles are smooth spheres; fractal geometry allows these models to be expanded to irregular surfaces by providing a quantitative means of assessing surface roughness.

An overview of fractal analysis is presented in the following, and the state of the art, as far as pharmaceutical systems are concerned are outlined. Erroneous approaches, as well as the directions pharmaceutical research and technology might take in the area of fractal analysis are suggested.

From a historical perspective, micromeritics (the science of particle size, shape and surface area) were first developed with the assumptions that all particles were smooth spheres.

Much excellent work has been developed with such an oversimplified model. For example, numerous workers have shown that particle flow through an orifice is a function of “particle diameter”, and experiments have most often been carried out on particles as close to spherical as possible, and as monodisperse as possible.

The science of micromeritics, the science of small particles, is the making of Dalla Valle (1943) who coined the term in a book of the same name which describes methods of particle size measurement, mostly used by soil scientists.¹     

Personal therapy for psychotherapists before and after entering professional practice.

A national survey of 749 practicing psychotherapists was conducted to examine their use of personal psychotherapy before and after entering professional practice. A usable return rate of 44% (N?=?318) was obtained. Variables related to the use of personal therapy are identified, and a discussion of the results is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned changes in the rate of respiratory pumping in Aplysia fasciata in response to increases and decreases in seawater concentration.

In Aplysia fasciata, the sea hare, shock paired with moderate increases or decreases in the seawater concentration leads to pairing-specific increases in the respiratory pump rate in response to the same solutions an hour later. A common neural circuit underlies learned changes to increased and decreased seawater concentration, as shown by complete generalization of learning between these stimuli. Different neural circuitry controls learning after pairing a shock with pH 7 seawater, as shown by a lack of generalization of learning to this stimulus. Preexposure to strong changes in the seawater leads to sensitization of respiratory pumping. The hypothesis was tested that associative learning and sensitization arise from activation of common pathways. However, patterns of generalization of sensitization elicited by preexposure to altered seawaters differ from those produced by associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Esterification of 8,11,14-eicosatrienoate and arachidonate into alkylacyl- and diacylglycerophosphocholine by vascular endothelial cells

Agonist-stimulated phospholipases release arachidonate, but not 8,11,14-eicosatrienoate, from human endothelial cells. One source of the arachidonic acid is deacylation of 1-alkyl-2-arachidonoyl-glycerophosphocholine, with subsequent conversion of some of the resultant lysophospholipid to platelet-activating factor. This study has compared the distribution of incorporated 8,11,14-[¹⁴C]-eicosatrienoate in alkylacyl-GPC and diacyl-GPC with that of [¹⁴C]arachidonate synthesized endogenously by desaturation of the 8,11,14-[¹⁴C]eicosatrienoate. Cells were incubated for 24 or 48 hr with 8,11,14-[¹⁴C]eicosatrienoate, and the resultant mixture of¹⁴C-fatty acids in the cellular lipids was characterized by gas chromatography. The choline phospholipids were then separated, hydrolyzed with phospholipase C and derivatized to diradylbenzoates. Gas chromatographic analysis indicated extensive incorporation of [¹⁴C]eicosatrienoate, as well as [¹⁴C]arachidonate, into alkylacyl-GPC. Although the ratio of esterified [¹⁴C]arachidonate to [¹⁴C]eicosatrienoate was greater in alkylacyl-GPC than in diacyl-GPC, the enrichment with [¹⁴C]arachidonate was far less than the ratio of arachidonate/eicosatrienoate released from these cells. These results thus support the hypothesis that the acyl specificity of polyunsaturated fatty acid release is provided by the agonist-stimulated phospholipase A₂ rather than the composition of the alkylacyl-GPC.     

Acetylcholine receptor at neuromuscular junctions by EM autoradiography using mask analysis and linear sources

Several methods of analyzing EM autoradiograms are now available. Two such procedures, the grain density distribution (or histogram) method and the mask method use the resolution of the EM autoradiographic technique to generate grain distributions expected from postulated sources, and compare these with the observed grains in the autoradiograms. These two methods are here compared in the analysis of label on linear sources: the distribution of labeled acetylcholine receptor (AChR) down the postjunctional folds of lizard and frog neuromuscular junctions. The receptors were labeled with I-25-α-bungarotoxin and the autoradiograms coated with the high resolution Kodak emulsion 129–01. We found that both methods gave similar results in confirming that the bulk of the AChR is concentrated on the thickened region of the membrane at the top ∼2000 A of the junctional folds, and that there may be a gradient of receptor concentration down the folds. The grain density distribution method is simpler, but does not lend itself easily to quantifying the extent of deviation from simple models. Although computer graphics is not necessary for either method, its use allows the expected grains from linear sources to be generated quickly, making the mask analysis a feasible routine method for assigning the extent of label in different membrane regions.     

Resolving scientific disputes by the joint design of crucial experiments by the antagonists: Application to the Erez–Latham dispute regarding participation in goal setting.

In this monograph we describe a unique method for resolving scientific disputes: the joint design of crucial experiments by the antagonists themselves with the help of a mediator. This method was applied to the issue of the effect of participation on goal commitment and performance. In research on this topic, Latham and his colleagues had obtained markedly different results from those obtained by Erez and her colleagues. With Locke serving as a third party mediator, Latham and Erez designed four experiments to resolve the discrepancies. The experiments were conducted at the University of Washington and the University of Maryland. The results revealed that the major reason for the difference was that Erez gave very brief tell instructions to her assigned goal subjects, whereas Latham used a tell and sell approach. Four additional factors also contributed to the earlier difference in findings: goal difficulty, setting personal goals before goal treatments were introduced, self-efficacy-inducing instructions, and instructions to reject disliked goals. It was concluded that (a) the differences between Latham and Erez can be explained on the basis of differences in specific procedures, and (b) the method used to resolve this dispute should be used by other investigators. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calcium lactate effect on the shelf life of osmotically dehydrated guavas

The effect of calcium lactate on osmodehydrated guavas in sucrose and maltose solutions was monitored during storage under passive modified atmosphere for 24 d at 5 °C. Sample texture and color characteristics, microbial spoilage, sensory acceptance, structural changes, and gas composition inside the packages were periodically evaluated. Calcium lactate inhibited microbial growth on guavas, with yeast and mold counts in the order of 10(2) CFU/g throughout storage. The calcium salt reduced respiration rate of guava products, showing O(2) and CO(2) concentrations around 18% and 3% inside the packages. A firming effect on fruit texture, with up to 5 and 2 times higher stress and strain at failure values and tissue structure preservation could also be attributed to calcium lactate use. However, fruits treated with calcium lactate, osmodehydrated in maltose and sucrose solutions, showed sensory acceptance scores below the acceptability limit (4.5) after 13 and 17 d of storage, respectively.     

Thermo‐mechanical properties of candelilla wax and dotriacontane organogels in safflower oil

The thermo‐mechanical properties of organogels developed by a complex mixture of n‐alkanes present in candelilla wax (CW) were investigated and compared with the ones of organogels developed by a pure n‐alkane, dotriacontane (C₃₂). In both cases, the liquid phase used was safflower oil high in triolein (SFO) and the variables studied were two levels of gelator concentration (1 and 3%), cooling rates of 1 and 10 °C/min, and two gel setting temperatures, 5 and 25 °C (T_set). Based on comparisons of the organogels made with C₃₂, the presence of minor molecular components in CW had a profound effect on the crystal habit of the n‐alkanes in CW‐based organogels, and therefore on their physical properties. Thus, independent of the cooling rate and T_set, C₃₂ showed a higher solubility and higher self‐assembly capability in the SFO than CW. Nevertheless, for the same gelator concentration and time‐temperature conditions, C₃₂ organogels had lower G' profiles than CW organogels. Additionally, independent of the type of gelator, more stable organogel structures were developed at T_set = 5 °C and using the lower cooling rate. The rheological behavior of the organogels was explained considering the formation of a rotator phase by the n‐alkanes, its solid‐solid transition, and their dependence as a function of the cooling rate and T_set. The results here obtained showed that it is possible to gelate SFO through organogelation with CW and without the use of trans fats.