Tweens and Spans

Latterly, some oil-in-water adjuvants have been developed. Many are squalene-in-water emulsions. Emulsifiers most commonly used include polyalcohols, such as Tween and Span. In some cases, immunostimulatory molecules (including MDP and TDM see Section 13.5.4) have also been incorporated in order to enhance adjuvanticity. These continue to be carefully assessed and may well form a future family of useful adjuvant preparations. 

An auspicious new strategy, in order to perform biocatalysis with hydrophobic substrates in w/o-microemulsion, is the usage of whole cells instead of purified enzymes [3,124,141]. There exist only a few surfactant-oil systems, in which whole cells are stable and suitable for a segmentation. Mainly the biodegradable surfactant based on sorbitan (Tween and Span) seems to be well suited for the solubilisation of whole cells in organic reaction media [142,143]. 

Glycerides, glucosides, saccharides, sorbitan derivatives, Tweens and Spans, etc. also belong to the class of nonionic surfactants. Mono- and diesters of fatty acids and multiatomic alcohols are oil soluble surfactants with low solubility in water. Sulfoesterification of these compounds followed by subsequent neutralization allows one to obtain water soluble surfactants. Many representatives of this group, such as sucrose esters, are non-toxic, tasteless and odorless, which makes them attractive for use in the pharmaceutical, food and perfume industries. 

For example, nonionic partially hydrolyzed polyvinyl alcohol (PVA), methylcellulose, tween, and span. 

Primarily for toxicity reasons, work has focused on the use of nonionic surfactants, particularly Tweens and Spans. Pouton (20) and Wakericy el al. (21) have screened a range of surfactants, finding that in general molecules with unsat-uraced acyl chains were most efficiem emulsifiers, particularly the oleates with an HLB value of approximately II. The authors also reported that the sorbitan esters and ethoxylated triglycerides such as Tagat TO were more efficient than the fatty acid ethoxylates, possibly due to the polydispersity of the latter. 

One area of rapidly expanding interest is the use of reverse micellar systems of sugar-based surfactants in the extraction of proteins and other sensitive materials. The use of hydrophilic, nonionic, sugar-based surfactants for membrane protein extraction is well known to be effective due to the mild, nondenaturing properties of these surfactants when compared with ionic surfactants or polyoxyethylene derivatives. For the same reasons, protein extraction into reverse micellar systems is now becoming a popular medium for such applications. Alkyl sorbitan esters and ethoxylated sorbitan esters, such as Tween 85 [107] and Span 60 [108], have been used successfully to form reverse micellar systems for protein extraction. Blends of Tween and Span have also been found to be effective for this purpose [109]. More recently, commercially available sucrose fatty acid esters have been shown to form biocompatible reverse micellar systems into which cytochrome c is effectively extracted [110]. 

The O/W stabilizing ability of Tweens and Spans, widely used in the food and pharmaceutical industries, have been studied by a Japanese group [116, 117]. O/W emulsions prepared with Tween 20-Span 80 mixtures were unstable over the whole HLB range possible with these surfactants (4.3 to 16.9) the authors... 

Cytarabine loaded W/OAV multiple emulsions were prepared using nonionic surfactants (Tween and Span ) by the emulsification-sonication technique and characterized by studying the osmotic behavior. The system exhibited prolonged release pattern (Kim et al., 1995). 

Figure 13.22 shows the resolution of the surfactants Tween 80 and SPAN. The high resolution obtained will even allow the individual unreacted ethylene oxide oligomers to be monitored. Figure 13.23 details the resolution of many species in both new and aged cooking oil. Perhaps the most unique high resolution low molecular weight SEC separation we have been able to obtain is shown in Fig. 13.24. Using 1,2,4-trichlorobenzene as the mobile phase at 145°C with a six column 500-A set in series, we were able to resolve Cg, C, Cy, Cg, C9, Cio, and so on hydrocarbons, a separation by size of only a methylene group. Individual ethylene groups were at least partially resolved out to Cjg. This type of separation should be ideal for complex wax analysis.

Concerning the SLN produced by hot homogenization as described by Olbrich et al. [19], as lipidic matrix Compritol ATO 888 or paraffin were used, as tenside a mixture of Tween 80 and Span 85 was used, and as charge carrier either EQ1 [N,N-di-(()-s(eaoryI e(liyI)-.V,A -di methylammonium chloride] or cetylpyridinium chloride were used. The resulting particles were characterized by size between 101 and 105 nm and showed zeta potentials around 40 mV at pH 7.4. 

Tween 85 is used extensively for RME [84]. Russell and coworkers [234] used Tween 85/isopropanol microemulsions in hexane to solubilize proteins and not only showed >80% solubilization of cytochrome C at optimum conditions, but also proved that Tween 85 does not have a detrimental effect on the structure, function, and stability of subtilisin and cytochrome C. There are other reports available on the extraction and purification of proteins using Tween 85-RMs and also on the stability of protein activity in these systems [234]. It has also been shown that Tween 85-RMs can solubilize larger amounts of protein and water than AOT. Tween 85 has an HLB of 11, which indicates that it is soluble in organic solvents. In addition, it is biodegradable and can be successfully used as an additive in fertihzers [235,236]. Pfammatter et al. [35] have demonstrated that RMs made of Tween 85 and Span 80 can be successfully used for the solubilization and growth of whole cells. Recently, Hossain et al. [84] showed an enhanced enzymatic activity of Chromobacterium viscosum Hpase in AOT/Tween 85 mixed reverse micellar systems when compared to that in classical AOT-RMs. This is due to the modification of the interface in AOT-RMs caused by the co-adsorption of Tween 85, and increased availability of the oHve oil molecules (substrate) to the enzyme. 

Table II. Effect of Adding Triton X-100 and Span 20 plus Tween 20 on Spread of...

Fig. H. Weight per cent of bulk phases separated from o/w concentrated emulsions by heating at 50 °C for 24 h plotted against HLB values of surfactant blends. The concentrated emulsions were prepared at 25 °C and had a volume fraction of the dispersed phase of 0.9. The total surfactant blends concentration in each emulsion was held constant at 6.5 x 10 2 moll 1. O and denote o/w concentrated emulsions of styrene and water prepared using surfactant blends of Tween 20-Span 85 and Tween 40-Span 85, respectively. denotes o/w concentrated emulsions of butyl acrylate and water prepared using surfactant blends of Tween 20-Span 85. A and A denote o/w concentrated emulsions of methyl methacrylate and water prepared using surfactant blends of Tween 20-Span 20 and Tween 20-Span 85, respectively...

Since 1958 when paper electrophoresis of serum proteins was reviewed in this series (P3), there have been no major technical developments in the art. The incorporation of nonionic detergents (Tween 80, Span 20, etc.) in the conventional barbiturate buffer (D14, G18, L14) and the use of tris -borate as buffer (A14, S27) have led to the separation of 7 to 11 globulin fractions. After zone electrophoresis in borate-containing buffer, an increased number of bands can be visualized by staining, but these are not revealed by the schlieren scanning technique after free electrophoresis in similar buffers (S27) the effects of this buffer may be due to interaction between borate and proteins having a high carbohydrate content. 

Any pair of emulsifying agents that fall at opposite ends of the HLB scale - for example. Tween 80 (sorbitan monooleate with 20 mol EO, HLB = 15) and Span 80 (sorbitan monooleate, HLB = 5) - can be taken and used in various proportions to cover a wide range of HLB numbers. The emulsions should be prepared in the same fashion, with a few percent of the emulsifying blend. The stability of the emulsions can then be assessed at each HLB number, either from the rate of coalescence or qualitatively by measuring the rate of oil separation. In this way it should be possible to determine the optimum HLB number for a given oil. Subsequently, having found the most effective HLB value, various other surfactant pairs can be compared at this HLB value to identify the most effective pair. 

Lv et al. have demonstrated the ability of the microemulsions to improve the hydrolytic stability of a known anti-microbial agent chloramphenicol [5]. The components of mi-croemulsion included IPM, Tween 20 and Span 20, which have good ocular acceptability. The accelerated stability studies on chloramphenicol microemulsions and commercial solution were carried out for 3 months demonstrated significantly lower hydrolysis of chloramphenicol (14.38%) as compared to that of solutions (27.11%). H NMR studies on microemulsions confirmed that the chloramphenicol was embedded in the surfactant chains that may provide higher stability. 

The use of pharmaceuticals in form of emulsions is of special interest. Thus, for example, o/w emulsions stabilised by surfactants, such as mono- and diglycerides, are successfully used as pseuo-doxime-proxetil protection from intestinal lumen hydrolysis through oral administration [128]. Multiple w/o/w emulsions stabilised by Tween 20/Span 20 or Tween 80/Span 80 mixtures contributed to a prolonged retention of cytarabine in one of the phases, and its gradual release ensured a prolonged action of the drug [129]. 

FIGURE 6.19 Transfection efficiency (quantified as relative light units [RLU]/mg protein) of three different SLN formulations (all made from 4% cetyl pahnitate, 2% Tween 80/Span 85 [7 3], and 0.5% [S0.5], and 1.0% [SI] or 2.0% [S2] of the cationic hpid DOTAP) without medium (Medium) and with medium and 100 piM chloroquine phosphate (Med. + 100 J,M QC). The chloroquine addition enhanced transfection activity for all tested SLN in different extends. 

Sagiri, S.S. et al. Effect of composition on the properties of tween-80-span-80-based organogels. Designed Monomers and Polymers, 2012.15(3) 253-273. 

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