Guo H, Liu Z, Li J, Nie S, Pan W. Effects of isopropyl palmitate on the skin permeation of drugs. Biol Pharm Bull. 2006 Nov;29(11):2324-6. doi: 10.1248/bpb.29.2324. PMID: 17077540.

Abstract. The model penetrants oxaprozin, nimesulide, gliclazide, and ribavirin, because of their different lipophilicities, were selected to assess the enhancing activity of pre-treatment solutions consisting of isopropyl palmitate (IP) in ethanol (5%, 10%, 15%and 20%, w/w, respectively) across excised rat skin using Franz diffusion cells and HPLC detection. All pre-treatment solutions produced a significant increase in the flux and permeation of all four penetrants (p<0.001) and a relationship between penetrant lipophilicity and enhancement effect was observed. The general order of IP effectiveness at concentration was 20%>15%>10%>5% (w/w). The lag-time of drugs did not significantly change except for ribavirin.

Ruan J, Wan X, Quan P, Liu C, Fang L. Investigation of Effect of Isopropyl Palmitate on Drug Release from Transdermal Patch and Molecular Dynamics Study. AAPS PharmSciTech. 2019 Apr 25;20(5):174. doi: 10.1208/s12249-019-1370-7. 

Abstract. Chemical penetration enhancers are widely used in transdermal drug delivery system. However, few studies have focused on changes of concentration in chemical penetration enhancers. In this study, the effect of concentrations of enhancers on drug release and its mechanism were investigated. Zolmitriptan (ZOL) was used as a model drug and isopropyl palmitate (IPP) was used as a model enhancer to investigate drug release behaviors in pressure-sensitive adhesives (PSAs). The IPP concentrations were 2, 5, 10, 12, and 15%. Drug release percents increased by 4.8, 11.5, 16, 15.1, and 14.8%, respectively. Interestingly, the linear relationship between concentrations of IPP and release percents was improved in the 0-10% and remained unchanged in the 10-15%. Moreover, thermal and rheology studies were performed to investigate changes of the fluidity of PSAs. FT-IR and molecular dynamics simulation were conducted to confirm the interaction strength among ZOL, IPP, and PSAs. The results elucidated that IPP increased fluidity of PSAs and vied for drug from PSAs. As a result, the interaction among three components played a major role in changing release behaviors of ZOL, but the increased fluidity only worked in the concentration of less than 10%.

Boonme P, Krauel K, Graf A, Rades T, Junyaprasert VB. Characterisation of microstructures formed in isopropyl palmitate/water/Aerosol OT:1-butanol (2:1) system. Pharmazie. 2006 Nov;61(11):927-32. 

Abstract. The aim of this work was to determine the type and microstructure of microemulsion samples formed in IPP/water/AerosolOT:1-butanol (2:1) systems as a case study for the investigation of microemulsions. The concentration of the surfactant/cosurfactant mixture was kept constant while the ratio of water to oil was varied. Several techniques were used to investigate the types and phase transitions of the microemulsion formulations. The experimental methods used included visual observation cross-polarized light microscopy (PLM) appearance, conductivity, viscosity, cryo-field emission scanning electron microscopy (cryo-FESEM), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and fluorescence resonance energy transfer (FRET). Taken together, the results of the various techniques imply that the systems investigated are undergoing two transitions as a function of water concentration. Between 10-15%w/w of water, the systems change from headgroup hydrated surfactant solutions in oil (or possibly very small reversed micellar systems) to w/o microemulsions. These systems then change to o/w microemulsions between 25-30%w/w of water. The transitions however, appear to be gradual, as for example the DSC data indicates a transition between 15-20%w/w of water. Furthermore, for some methods the changes observed were very weak, and only with supportive data of other techniques can the phase behaviour of the microemulsion systems be interpreted with confidence. Interestingly, no indication of the presence of a bicontinuous intermediate microstructure was found. Liquid crystal formation was detected in samples containing 55%w/w of water.

Boonme P, Krauel K, Graf A, Rades T, Junyaprasert VB. Characterization of microemulsion structures in the pseudoternary phase diagram of isopropyl palmitate/water/Brij 97:1-butanol. AAPS PharmSciTech. 2006 May 12;7(2):E45. doi: 10.1208/pt070245. 

Abstract. This research was aimed to characterize microemulsion systems of isopropyl palmitate (IPP), water, and 2:1 Brij 97 and 1-butanol by different experimental techniques. A pseudoternary phase diagram was constructed using water titration method. At 45% wt/wt surfactant system, microemulsions containing various ratios of water and IPP were prepared and identified by electrical conductivity, viscosity, differential scanning calorimetry (DSC), cryo-field emission scanning electron microscopy (cryo-FESEM) and nuclear magnetic resonance (NMR). The results from conductivity and viscosity suggested a percolation transition from water-in-oil (water/oil) to oil-in-water (oil/water) microemulsions at 30% wt/wt water. From DSC results, the exothermic peak of water and the endothermic peak of IPP indicated that the transition of water/oil to oil/water microemulsions occurred at 30% wt/wt water. Cryo-FESEM photomicrographs revealed globular structures of microemulsions at higher than 15% wt/wt water. In addition, self-diffusion coefficients determined by NMR reflected that the diffusability of water increased at higher than 35% wt/wt water, while that of IPP was in reverse. Therefore, the results from all techniques are in good agreement and indicate that the water/oil and oil/water transition point occurred in the range of 30% to 35% wt/wt water.

Sommer E, Neubert RHH, Mentel M, Tuchscherer B, Mrestani Y, Wohlrab J. Dermal peptide delivery using enhancer molecules and colloidal carrier systems. Part III: Tetrapeptide GEKG. Eur J Pharm Sci. 2018 Nov 1;124:137-144. doi: 10.1016/j.ejps.2018.08.034. 

Koike K, Takeuchi K, Mino H, Takaiwa M, Tohoh T, Tadokoro T, Tsutoh K, Ito S. A repeat-batch membrane bioreactor with a phase inversion for the desaturation of isopropyl palmitate by a mutant Rhodococcus strain. J Biotechnol. 2000 Jun 23;80(2):101-7. doi: 10.1016/s0168-1656(00)00255-8. 

Abstract. A repeat-batch membrane bioreactor was constructed for the novel bioconversion of isopropyl hexadecanoate to isopropyl cis-6-hexadecenoate by a Rhodococcus mutant. The addition of glutamate, thiamine, and MgSO(4) was very effective in improving not only the rate and yield of the bioconversion but also the maintenance of desaturation activity during cell recycling. An oil-in-water (O/W) type emulsion of the reaction medium was inverted to a water-in-oil (W/O) type by discharging the water phase from the reaction mixture. The continuous oil phase containing the product could effectively be recovered through a hydrophobic hollow-fiber module. By decreasing the oil-to-water ratio upon addition of fresh medium, the medium was spontaneously inverted again to an O/W type emulsion to proceed with the next conversion. The batch reaction coupled with the phase inversion could be repeated more than 13 times for over about 300 h operation. Finally, a highly purified product was obtained with high yield by the urea adduct procedure.

Koike K, Takaiwa M, Ara K, Inoue S, Kimura Y, Ito S. Production of isopropyl cis-6-hexadecenoate by regiospecific desaturation of isopropyl palmitate by a double mutant of a Rhodococcus strain. Biosci Biotechnol Biochem. 2000 Feb;64(2):399-404. doi: 10.1271/bbb.64.399. 

Abstract. Resting cells of a double mutant noted as KSM-MT66, derived from Rhodococcus sp. strain KSM-B-3 by UV irradiation, were found to cis-desaturate isopropyl hexadecanoate, yielding isopropyl cis-6-hexadecenoate. Addition of sodium glutamate (1.0%), Mg SO4 (2 mM), and thiamine (2 mM) increased the productivity of the unsaturated product in phosphate buffer. Optimal temperature and pH for the reaction were around 26 degrees C and 7, respectively. Under the optimized conditions, more than 50 g/l of isopropyl cis-6-hexadecenoate was produced after a 3-day incubation by resting cells of the mutant. Thus, cis-6-hexadecenoic acid, the main component of human sebaceous lipids, can be manufactured economically by the rhodococcal bioconversion.

Boddu SH, Alsaab H, Umar S, Bonam SP, Gupta H, Ahmed S. Anti-inflammatory effects of a novel ricinoleic acid poloxamer gel system for transdermal delivery. Int J Pharm. 2015 Feb 1;479(1):207-11. doi: 10.1016/j.ijpharm.2014.12.051. Epub 2014 Dec 24. PMID: 25542985.