Isolation, Characterization, and Stability of Discretely-Sized Nanolipoprotein Particles Assembled with Apolipophorin-III

Background: Nanolipoprotein particles (NLPs) are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins. NLPs assembled with human apolipoproteins have been used for myriad biotechnology applications, including membrane protein solubilization, drug delivery, and diagnostic imaging. To expand the repertoire of lipoproteins for these applications, insect apolipophorin-III (apoLp-III) was evaluated for the ability to form discretely-sized, homogeneous, and stable NLPs. Methodology: Four NLP populations distinct with regards to particle diameters (ranging in size from 10 nm to.25 nm) and lipid-to-apoLp-III ratios were readily isolated to high purity by size exclusion chromatography. Remodeling of the purified NLP species over time at 4uC was monitored by native gel electrophoresis, size exclusion chromatography, and atomic force microscopy. Purified 20 nm NLPs displayed no remodeling and remained stable for over 1 year. Purified NLPs with 10 nm and 15 nm diameters ultimately remodeled into 20 nm NLPs over a period of months. Intra-particle chemical cross-linking of apoLp-III stabilized NLPs of all sizes. Conclusions: ApoLp-III-based NLPs can be readily prepared, purified, characterized, and stabilized, suggesting their utilit

Regioselectivity of the 1,3-Oxathiolane Formation in the Lewis Acid-Catalyzed Reaction of Thioketones with Asymmetrically Substituted Oxiranes

The reactions of the aromatic thioketone 4,4'-dimethoxythiobenzophenone (1) with three monosubstituted oxiranes 3a - c in the presence of BF3 . Et2O or SnCl4 in dry CH2Cl2 led to the corresponding 1 : 1 adducts, i.e., 1,3- oxathiolanes 4a-b with R at C(5) and 8c with Ph at C(4). In addition, 1,3-dioxolanes 7a and 7c, and the unexpected 1 : 2 adducts 6a - b were obtained (Scheme 2 and Table 1) . In the case of the aliphatic, nonenolizable thioketone 1,1,3,3-tetramethylindane-2-thione (2) and 3a - c with BF3 . Et2O as catalyst, only 1 : 1 adducts, i.e. 1,3-oxathiolanes 10a - b with R at C(5) and 11a - c with R or Ph at C(4), were formed (Scheme 6 and Table 2). In control experiments, the 1:1 adducts 4a and 4b were treated with 2-methyloxirane (3a) in the presence of BF3 . Et2O to yield the 1:2 adduct 6a and 1:1:1 adduct 9, respectively (Scheme 5). The structures of 6a, 8c, 10a, 11a, and 11c were confirmed by X-ray crystallography (Figs. 1 - 5). The results described in the present paper show that alkyl and aryl substituents have significant influence upon the regioselectivity in the process of the ring opening of the complexed oxirane by the nucleophilic attack of the thiocarbonyl S-atom: the preferred nucleophilic attack occurs at C(3) of alkyl-substituted oxiranes (O-C(3) cleavage) but at C(2) of phenyloxirane (O-C(2) cleavage)