Cremophor EL Nano-Emulsion Monomerizes Chlorophyll a in Water Medium

Abstract

In this paper, the application of a non-ionic detergent Cremophor EL for monomerization of chlorophyll a in an aqueous medium is studied. The spectrophotometric properties of chlorophyll a encapsulated into the Cremophor EL nano-emulsion system were characterized by electronic absorption, steady-state and time-resolved fluorescence as well as circular dichroism spectroscopy. The results have shown that chlorophyll a dissolves more efficiently in the aqueous medium containing low-level Cremophor (5 wt%) than at an ethanolic solution even in the concentration of 10−4 M. The molecular organization of the chlorophyll a in the Cremophor EL nano-micelles was also investigated by means of Raman spectroscopy. The spectral changes in the frequency of the C=O stretching group were used to distinguish the aggregation state of chlorophyll. It was revealed that chlorophyll a exists dominantly in the monomeric form in the Cremophor EL aqueous solution. The promising aspect of the use of Cremophor EL nano-emulsion as a delivery system is to maintain stable chlorophyll monomer in an aqueous medium. It would open the potential for a new, practical application of chlorophyll a in medicine, as a dietary supplement or studies on molecular organization of chlorophyll a in the well-defined artificial system.

Stability of Chlorophyll a Monomer Incorporated into Cremophor EL Nano-Micelles under Dark and Moderate Light Conditions

“…In Figure 2 , the electronic absorption ( Figure 2 A) and fluorescence emission ( Figure 2 B) spectra of chl a dissolved in the CrEL nano-emulsion are presented. To compare, chl a was also dissolved in 96% EtOH ( Figure 2 C,D) because chl a at the 10 −5 M molar concentration in 96% EtOH should also be monomeric [ 10 ]. Moreover, EtOH is an important organic solvent extensively used in the food, pharmaceutical, and cosmetic industries.…”

“…The fluorescence emission spectrum has a maximum at 677 nm for chl a dissolved in the CrEL emulsion ( Figure 2 B) and at 675 nm for chl a dissolved in EtOH ( Figure 2 D). The position of the bands in the absorption and fluorescence emission spectra points out to the chl a monomerization in the solutions [ 10 ]. Thus, the question of whether “If the monomeric form of chl a is still present in the CrEL nano-emulsion over time” is addressed in this paper.…”

“…As chls degrade and discolor readily beyond nature (mainly in the presence of oxygen), their stability and degradation in the artificial systems have been a subject of interest for many scientific studies. In such an environment as water [ 10 , 22 ], the mixture of water and EtOH [ 10 , 22 , 23 ], PVA films [ 24 , 25 ], polymeric nanomaterials [ 5 , 26 ], mesoporous materials [ 27 ], silica gel [ 27 , 28 ], chl a is aggregated. It was proved that chl a aggregates remain stable in such systems for few months.…”

“…In this context, recently it has been reported that chl a dissolves more efficiently in the aqueous medium containing the low-level (5 wt%) non-ionic detergent—Cremophor EL (CrEL) than in an ethanolic solution [ 10 ]. Cremophor EL (polyoxyl 35 castor oil) is a polyoxyethylated derivative of hydrogenated castor oil that contains about 87% of ricinoleic acid.…”

“…This nano-emulsion attracted much attention in the pharmaceutical applications for encapsulation and solubilization of various hydrophobic bioactive compounds [ 11 , 12 , 13 , 14 , 15 ]. The results have shown that the molecular organization of chl a in the CrEL nano-emulsion is monomeric [ 10 ]. This is relevant due to the high photoactivity of chl monomer [ 16 ] and the expected efficient uptake of such a small molecule but not a larger aggregated form.…”