Reactive patches

Spherical reaction site with reactive patches 813... 

Pairwise Brownian dynamics has been primarily used for the analysis of diffusion controlled reactions involving the reaction between isotropic molecules with complex reactive sites. Since its introduction by Northrup et al. [58], the pairwise Brownian dynamics method has been considerably refined and modified. Some of the developments include the use of variable time steps to reduce computational times [61], efficient calculation methods for charge effects [63], and incorporation of finite rates of reaction [58,61,62]. We review in the following sections, application of the method to two example problems involving isotropic translational diffusion reaction of isotropic molecules with a spherical reaction surface containing reactive patches and the reaction between rodlike molecules in dilute solution. 

Spherical reaction site with reactive patches We apply both the methods for finite rates of reaction discussed above to the case of a reactive molecule with reactive patches as shown in Figure 12, for comparison. The diffusing molecules are isotropic, and the site molecule is large enough to be stationary. In this case, the probabilities depend only on theangle 6 because of symmetry. Thus, for the survival probability method we have... 

The particle surface may have reactive patches, often called hot spots. Emulsion droplets, for instance, may have an adsorbed layer with patches of protein (surface area fraction 6), while the remainder is covered... 

Numerous positive delayed skin tests in patients with contrast medium-induced non-immediate skin reactions have been reported when the patients were tested with the culprit contrast medium [summarized in 1]. In a large European multicenter study, 37% of patients with non-immediate reactions were positive in delayed IDEs and/or patch tests [13]. The majority of the patients also reacted to the culprit contrast medium and also to other, structurally similar RCM. Notably, in more than 30% of those skin test-positive patients a RCM had been administered for the first time. Thus, there is a lack of a sensitization phase. Again it may be hypothesized that these previously non-exposed patients may have already been sensitized. Different patterns of RCM cross-reactivity indicate that several chemical entities could be involved. No positive skin tests have been obtained with other contrast medium excipients, such as ethylenediaminetetraacetic acid (EDTA), and only rarely patients have been found to react to inorganic iodide. 

Although most patch testing is done with nickel sulfate because it is less irritating than nickel chloride, exposure of the skin to nickel alloys results in the release of nickel chloride from the influence of human sweat. Therefore, nickel chloride is the more relevant form of nickel for examining threshold concentrations (Menne 1994). Menne and Calvin (1993) examined skin reactions to various concentrations of nickel chloride in 51 sensitive and 16 nonsensitive individuals. Although inflammatory reactions in the sweat ducts and hair follicles were observed at 0.01% and lower, positive reactions to nickel were not observed. To be scored as a positive reaction, the test area had to have both redness and infiltration, while the appearance of vesicles and/or a bullous reaction were scored as a more severe reaction. At 0.1%, 4/51 and 1/51 tested positive with and without 4% sodium lauryl sulfate. Menne et al. (1987) examined the reactivity to different nickel alloys in 173 nickel-sensitive individuals. With one exception (Inconel 600), alloys that released nickel into synthetic sweat at a rate of <0.5 pg/cmVweek showed weak reactivity, while alloys that released nickel at a rate of >1 pg/cm /week produced strong reactions. 

Menne T, Brandrup F, Thestrup-Pedersen K, et al. 1987. Patch test reactivity to nickel alloys. Contact Dermatitis 16 255-259. 

Contact allergy to glucocorticoids is not rare in patients with atopic dermatitis. In patients with known contact allergy to budesonide, allergic skin reactions can also occur when inhaled forms of the drug are used, as shown by a randomized, double-bhnd, placebo-controlled study in 15 non-asthmatic patients with budesonide hypersensitivity on patch testing (101). In four of seven patients who used inhaled budesonide, there was reactivation of the 6-week-old patch test sites and they had new distant skin lesions. No flare-up reactions were observed in the other 11 patients (three had used inhaled budesonide and eight placebo for 1 week). None of the patients developed respiratory symptoms spirometry and peak expiratory flow rates remained normal. 

The methods for assessing reactivity previously outlined are simple, convenient, inexpensive, and noninvasive or minimally invasive 6 However, cutaneous reactivity depends on many factors. None of the previous methods give a full picture of the characteristics of sensitive skin, only susceptibility of skin to irritants. Subtle manifestations of endogenous cutaneous conditions must still be clinically excluded. Exclusion of allergic contact dermatitis must still be performed by patch testing, exclusion of contact urticaria by open tests or PUT/ROAT, and exclusion of photoallergy by photopatch testing. 

Could one make use of the specificity of enzymes in reacting with specific molecules in solution, which would exist only in a body carrying a certain disease For example, if a blood sample were made to flow past a test electrode containing, say, 100 pinhead-sized patches, each one of a different enzyme reactive to a molecule characteristic of a specific disease and each connected by individual wiring to an outside circuit, current would flow only from the patch containing the enzyme reacting with its disease molecule in the blood. Such a device is a research goal for the twenty-first century. 

Linear, one-dimensional interfaces. Perhaps the most interesting theory of promoter action is that the linear boundary on the surface between two surfaces of different composition is the seat of the catalysis, i.e. the active patch. There is abundant evidence that such linear interfaces often possess unusual reactive powers. They are undoubtedly... 

Responses are evaluated 30 min to 1 h after patch removal (to allow hydration and pressure effects to subside), and again 24 h after the patch is removed. Persistent reactions may be evaluated for 3 to 4 days. The Draize scales can be used to evaluate erythema and edema however, the integrated scales ranging from 4 to 16 points are preferred. Such integrated scales are able to score popular, vesicular or bullous responses in addition to erythema/edema evaluation. Up to 10 materials can be tested simultaneously on each subject. The position that the materials are placed on the skin (i.e., upper right back, lower left back, etc.) should be systematically varied within each study since skin reactivity varies by body region. 

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