Phenol Coefficients and the Ferguson Principle*

Allawala, Naseem A.; Riegelman, Sidney

doi:10.1002/jps.3030430207

Cited by 21 publications

(3 citation statements)

References 14 publications

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“…However, such a high level of solubilization implies that the biocide is highly partitioned to the micellar pseudophase [1]. This strong partitioning effect, and its impact on phenolic biocide efficacy, has been reported in the literature for many years [2] and was explained from a physicochemical perspective by Allawala and Reigelman [3, 4]. Allawala and Reigelman showed that a governing factor of efficacy of a phenolic agent in surfactant solution was the % saturation of the phenolic (which is an index of its thermodynamic activity) in the solution, and not simply its total concentration; the two can be very different depending on the mode of solubilization.…”

Section: Introductionmentioning

confidence: 99%

Physicochemical factors affecting the rapid bactericidal efficacy of the phenolic antibacterial triclosan

Taylor

Seitz

Fox

et al. 2004

Intern J of Cosmetic Sci

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The antimicrobial activity of triclosan (TCS; 2,4,4'-trichloro-2'-hydroxydiphenyl ether) in aqueous solutions is shown to directly depend upon two key physicochemical parameters: % saturation and saturation solubility. Saturated solutions of TCS in water, water-propylene glycol (PG) mixtures, and aqueous surfactant systems are shown to effect rapid, potent bacterial reductions (e.g. >4 log(10) reduction of Staphylococcus aureus in 15 s contact time in a time kill suspension test). In surfactant solutions, increasing the surfactant: TCS ratio causes a decrease in antibacterial efficacy, consistent with a model for micellar solubilization where the micelle binding constant, K (=X/c(w)) increases with decreasing TCS concentration in the micelles (X), resulting in decreased concentration of bioavailable TCS in the water (continuous) phase (c(w)). The rapid and potent reductions of bacteria reported here were surprising and support the existence of a non-specific mode of action for TCS, such as gross membrane disruption, in addition to the specific modes of action reported by others.

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Section: Introductionmentioning

confidence: 99%

Physicochemical factors affecting the rapid bactericidal efficacy of the phenolic antibacterial triclosan

Taylor

Seitz

Fox

et al. 2004

Intern J of Cosmetic Sci

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“…Allawala & Riegelman have shown that equitoxic solutions of phenols of widely different solubilities are those in which the thermodynamic activities or the degrees of saturation, are the same, rather than solutions in which the actual or stoichiometric concentrations are the same. From a study of 23 different phenols Allawala & Riegelman (1954) showed that, while the concentrations (molesilitre) of equitoxic solutions varied by a factor of approximately 1 04, the degrees of saturation of equitoxic solutions of the phenols were all between 18 and 20%.…”

Section: Biological Activity and Degree Of Saturationmentioning

confidence: 98%

“…This principle has been further substantiated by an examination of the relative effectiveness of a large series of narcotics by Brink & Posternack (1948), and of factors governing the permeability of the insect cuticle by Webb (1949). The thermodynamic activity of a solute will, of course, depend upon the choice of standard state; one convenient method (Allawala & Riegelman, 1954) is to express it in terms of the per cent saturation, or degree of saturation, of the aqueous phase by setting the saturated solution as the standard state of reference. Allawala & Riegelman have shown that equitoxic solutions of phenols of widely different solubilities are those in which the thermodynamic activities or the degrees of saturation, are the same, rather than solutions in which the actual or stoichiometric concentrations are the same.…”

Section: Biological Activity and Degree Of Saturationmentioning

confidence: 99%

Applicability of the Ferguson principle to systems of mixed preservatives

1965

Journal of Pharmacy and Pharmacology

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Using solubility and distribution data for methyl and propyl p-hydroxybenzoates, the degree of saturation of the aqueous phase of a n oil-in-water emulsion has been calculated for various oil: water ratios. In emulsions of low oil content the propyl ester gives the higher degree of saturation of the aqueous phase, while in emulsions of high oil content the methyl ester gives the higher degree of saturation. Irrespective of the oil :water ratio, a mixture of the esters cannot give a higher degree of saturation or a higher thermodynamic activity of the aqueous phase, than either ester alone.The finding of many investigators that mixtures of the esters have higher biological activities than a single ester must therefore depend, not only on the degree of saturation, or thermodynamic activity of the aqueous phase, but also on some other unknown factors.ETERIORATION from mould formation or bacterial action of D cosmetic creams during storage occurs mainly in oil-in-water emulsions, and is rare in water-in-oil emulsions. Generally the organisms responsible for deterioration need an aqueous medium for growth, consequently cosmetic products contain preservatives which are effective in preventing growth in the aqueous phase. The most widely used preservatives are esters of p-hydroxybenzoic acid, the methyl and propyl esters being generally favoured.The literature contains conflicting views (Manowitz, 1962) about whether to use these preservatives singly (Atkins, 1950) or in combination (Boehm, 1959); those who advocate using the mixture claim a broader spectrum of microbiological activity than that given by their separate constituents, and also that the mixture exhibits a greater preservative action than would be expected from the individual activity (Boehm, 1959).It is well known from bacterial studies that the activity of the esters of p-hydroxybenzoic acid is related to the length of the alkyl chain; the propyl is more active. than the methyl ester but increasing the chain length reduces water' solubility and increases oil solubility, i.e. the oil : water distribution coefficients are markedly increased. As deterioration in cosmetic preparations occurs in the water phase, only that proportion of the added preservative which is dissolved in the aqueous phase can inhibit the growth of micro-organisms. But, is the greater bacterial activity of the propyl compared to the methyl ester more than offset by its lower water solubility and its higher oil solubility? Atkins (1950) claims that this is often so and that the methyl ester is then the more reliable preservative ; Atkins' data, therefore, do not support the widely held belief that a combination of the two esters is better than either alone.Since there is no apparent agreement in the published literature about whether a mixture of esters is better than a single ester in emulsion systems, calculations based on solubility and distribution data might throw

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Solubilized Systems in Pharmacy

Swarbrick

1965

Journal of Pharmaceutical Sciences

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Phenol Coefficients and the Ferguson Principle*

Cited by 21 publications

References 14 publications

Physicochemical factors affecting the rapid bactericidal efficacy of the phenolic antibacterial triclosan

Physicochemical factors affecting the rapid bactericidal efficacy of the phenolic antibacterial triclosan

Applicability of the Ferguson principle to systems of mixed preservatives

Solubilized Systems in Pharmacy

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