Uticaj dužine hidrofobnog segmenta homolognih polisorbata na termodinamičke parametre binarnih mešovitih micela polisorbata i Tritona X-100

Abstract

Binarne mešovite micele su značajne u farmaceutsko-farmakološkim primenama, u kojima lek kao površinska aktivna supstanca može da bude gradivna jedinica binarne micelle (promena bioraspoloživosti, mehanizam resorpcije itd.). Takođe su važne i mešovite micele kod kojih su gradivne jedinice biosurfaktanti (biokompatibilni solubilizatori lekova). U kozmetičkoj, prehrambenoj i industriji detergenata mešovite micele su uveliko zastupljene. Važno je nalaženje binarnih sistema surfaktanata koji u mešovitim micelama poseduju sinergističko međudelovanje (negativna vrednost interakcionog parametra). Takva binarna smeša surfaktanata ima nižu vrednost kritične micelarne koncentracije od hidrofobnije komponente smeše. U prvom delu rada je ispitivan uticaj dužine hidrofobnog segmenta homolognih Tween-ova iz mešovitih micela sa Triton-om X100 na interakcioni parametra ( i, j β ) i dodatnu Gibbs-ovu energiju (GE ), takođe ispitivao se i uticaj temperature na stabilnost proučavanih mešovitih micela (273,15-328,115 K). Kritične micelarne koncentracije čistih surfaktanata i njihovih binarnih smeša su određeni spektrofluorometrijski uz primenu pirena kao probnog molekula. Nađeno je da na svakoj ispitivanoj temperaturi povećanje dužine zasićenog alifatičnog niza polisorbata povećava stabilnost mešovite micele ( , 0 i j β < i GE < 0 ) u odnosu na idealnu mešovitu micelu. Prisustvo C9 dvostruke veze u ostatku oleinske kiseline Tween-a 80 umanjuje sinergistički efekat ovog polisorbata u odnosu na Tween 60, koji ima hidrofobni segment sa istim brojem C atoma, ali bez olefinske veze. Dodatna slobodna entalpija ispod temperature 298.15 K određena je entropijskim doprinosem, a iznad 298.15 K entalpijskim doprinosom. U drugom delu rada ispitivane su binarne smeše surfaktanata Tween 85/Triton X100 i Tween 85/Triton X165 u vodenom rastvoru u intervalu temperature od 273.15 K do 323.15 K. Pri temperaturama od 273.15 K i 283.15 K između različitih gradivnih jedinica binarnih mešovitih micela postoje sinergističke interakcije na čiju veličinu ne utiče razlika u dužini polioksietlienskih nizova Triton-a X100 i Triton-a X165. Na većim vrednostima temperature duži polioksietilenski niz Triton-a X165 pokazuje stabilizirajuči efekat u mešovitoj miceli sa Tween-om 85 u odnosu na mešovite micele Tween 85/Triton X100. Kod ispitivanih binarnim mešovitim micela ne može se prihvatiti aproksimacija regularnih smeša o nula vrednosti dodatne entropije formiranja binarne mešovite micele.

Binary micelles are important in pharmaceutical-pharmacological applications, in which drug as surface active substance can be building unit of binary micelle (influencing bioavailability change, change of resorption mechanism etc.). Mixed micelles in which building units are biosurfactants (biocompatible drug solubilizers) are also important. In cosmetics, food and detergent industry mixed micelles are widely present. It is important to find binary surfactant systems having synergistic interactions (negative value of interaction parameter). That binary surfactant mixture has lower critical micelle concentration value than more hydrophobic component of the mixture. In the first parth of this work, influence of hydrophobic segment length of homologues Tweens in mixed micelles with Triton X-100 on the interaction parameter value ( i, j β ) and an excess Gibbs energy (GE ) was investigated. Also, influence of temperature on the stability of investigated mixed micelles has been investigated (273.15-328.15 K). Critical micelle concentration values of pure surfactants and their binary mixtures were determined spectrofluorimetrically using pyrene as a probe molecule. It was found for every investigated temperature that increase in length of saturated aliphatic side chain of a polisorbate increases the stability of investigated mixed micelles (β < and GE < 0 ) compared to ideal mixed micelles. Presence of the C9 double bond in oleic acid residue of Tween 80 reduces synergistic effect of this polysorbate compared to Tween 60 which contains hydrophobic segment with the same number of C atoms but without olefin bond. Excess free enthalpy below the 298.15 K is determined with entropic contribution, but above 298.15 K with enthalpic contribution. In the second parth of this work, binary surfactant mixtures of Tween 85/Triton X100 and Tween 85/Triton X165 have been investigated in water solution in the temperature range from 273.15 K to 323.15 K. At the temperatures of 273.15 K and 283.15 K between different building units of binary mixed micelles synergistic interactions exist, which size is not affected by difference in length of the polyoxyethylene chains. At higher temperatures, longer polyoxyethylene chain of Triton X165 shows more stabilizing effect in mixed micelle with Tween 85 than in mixed micelles of Tween 85/Triton X100. For investigated binary mixed micelles, regular solution theory approximation about zero value of excess entropy of binary mixed micelle formation cannot be accepted.