Polysorbates structures

Figure 1 A generalized diagram of the structure of the cetostearyl alcohol gel found in topical and vaginal creams. The bilayers are formed principally of cetostearyl alcohol. The hydrophilic poly(oxyethylene) chains attached to the 5-carbon sorbitan rings in Polysorbate 60 retard water drainage from the interlamellar space and keep the lamellae from collapsing into a dense crystalline structure.

Emulsifiers. The chemical structures of emulsifiers, or surfactants, enable these materials to reduce the surface tension at the interface of two immiscible surfaces, thus allowing the surfaces to mix and form an emulsion. An emulsifier consists of a polar group, which is attracted to aqueous substances, and a hydrocarbon chain, which is attracted to lipids. Emulsifiers include mono- and diglycerides, lecithin, propylene glycol esters, luctylated esters, sorbttan and sorbitol esters, polysorbate.x, and sucrose esters. 

Morris, K. R., G. T. Knipp, and A. T. M. Serajuddin. 1992. Structural properties of polyethylene glycolj-polysorbate 80 mixture, a solid dispersion vehidie.harm ScB1 1185-1188. 

In certain cases, cholesterol is required for vesicle formation. It is commonly accepted that the hydrophilic lipophilic balance (HLB) is a parameter that could indicate the vesicleforming potential of surfactants. For amphiphils such as sorbitan esters and alkyl ethers, low HLB values could predict vesicle formation [52,55]. However, niosomes were obtained from polysorbate 20 (HLB 16.7), a highly hydrophilic molecule, when cholesterol at an appropriate concentration was added to the amphiphil [44], In this case it could be assumed that a kind of amphiphilic complex with a lower HLB was responsible for the vesicle formation. An excellent review on the structure, characteristics, chemical composition, and mechanism of action of niosomes was published by Uchegbu and Vyas [41]. 

Fig. 12 Structure for the nonclassical surfactants cholic acid and generic structural features for polysorbates and...

Release of methotrexate, metoclopramide and sodium chloride from type A, B and C w/isopropyl myristate/w emulsions have been compared (Fig. 5 a,b,c). In all cases, release from the type C emulsion is not prolonged, which may be a reflection of stability or structure or a combination of these two parameters. In the case of methotrexate, variation of the concentration of secondary surfactant (polysorbate 80) from 0.5 to 20% had no significant effect on the rate of drug release from the system. 

Structural identifications have been made431,432 of polycyclic methylpolysiloxanes of the general formula [(CH iOj 5)]x - [(CH3)2SiO]j, x and y being between 2 and 5 based on retention index additivity. Retention data for a series of siloxanes were determined on squalane, Apiezon L, QF-1 or Polysorbate 60. The value of the retention index is related to the structural characteristics of the molecule, which are regarded as additive and to a stationary phase factor. 

Polysorbate-20, 60, and SO. These have the same acceptable daily intake as sorbitan esters but are characterized by the property of enhancing the absorption of fat-soluble substances (38). This property can be an advantage or an adverse effect depending on the drug. Furthermore, poly-sorbates can also provoke hypersensitivity following topical application. They may disrupt normal membrane structures (39). 

These very hydrophilic emulsifiers, also called polysorbates, are produced by reacting sorbitan mono fatty acid esters with 5-20 mol of ethylene oxide, and the resulting products are very complex in composition and not very well defined in structure. A possible formula is shown in Table 5.6. 

Surfactants are also used to promote penetration of ingredients with systemic activity through the nasal mucosa. Their mechanism of action is based on a change of the permeability by disturbing (reversibly or irreversibly) the structural integrity of the mucosa. Polysorbate 80, for instance, has a strong negative effect on the cilia, which is however reversible. 

---