Nanoparticle-based hollow microstructures formed by two-stage nematic nucleation and phase separation.

Rapid bulk assembly of nanoparticles into microstructures is challenging, but highly desirable for applications in controlled release, catalysis, and sensing. We report a method to form hollow microstructures via a two-stage nematic nucleation process, generating size-tunable closed-cell foams, spherical shells, and tubular networks composed of closely packed nanoparticles. Mesogen-modified nanoparticles are dispersed in liquid crystal above the nematic-isotropic transition temperature (TNI). On cooling through TNI, nanoparticles first segregate into shrinking isotropic domains where they locally depress the transition temperature. On further cooling, nematic domains nucleate inside the nanoparticle-rich isotropic domains, driving formation of hollow nanoparticle assemblies. Structural differentiation is controlled by nanoparticle density and cooling rate. Cahn-Hilliard simulations of phase separation in liquid crystal demonstrate qualitatively that partitioning of nanoparticles into isolated domains is strongly affected by cooling rate, supporting experimental observations that cooling rate controls aggregate size. Microscopy suggests the number and size of internal voids is controlled by second-stage nucleation.

Phase Transition-Driven Nanoparticle Assembly in Liquid Crystal Droplets.

When nanoparticle self-assembly takes place in an anisotropic liquid crystal environment, fascinating new effects can arise. The presence of elastic anisotropy and topological defects can direct spatial organization. An important goal in nanoscience is to direct the assembly of nanoparticles over large length scales to produce macroscopic composite materials; however, limitations on spatial ordering exist due to the inherent disorder of fluid-based methods. In this paper we demonstrate the formation of quantum dot clusters and spherical capsules suspended within spherical liquid crystal droplets as a method to position nanoparticle clusters at defined locations. Our experiments demonstrate that particle sorting at the isotropic-nematic phase front can dominate over topological defect-based assembly. Notably, we find that assembly at the nematic phase front can force nanoparticle clustering at energetically unfavorable locations in the droplets to form stable hollow capsules and fractal clusters at the droplet centers.

Plasmon-actuated nano-assembled microshells.

We present three-dimensional microshells formed by self-assembly of densely-packed 5 nm gold nanoparticles (AuNPs). Surface functionalization of the AuNPs with custom-designed mesogenic molecules drives the formation of a stable and rigid shell wall, and these unique structures allow encapsulation of cargo that can be contained, virtually leakage-free, over several months. Further, by leveraging the plasmonic response of AuNPs, we can rupture the microshells using optical excitation with ultralow power (<2 mW), controllably and rapidly releasing the encapsulated contents in less than 5 s. The optimal AuNP packing in the wall, moderated by the custom ligands and verified using small angle x-ray spectroscopy, allows us to calculate the heat released in this process, and to simulate the temperature increase originating from the photothermal heating, with great accuracy. Atypically, we find the local heating does not cause a rise of more than 50 °C, which addresses a major shortcoming in plasmon actuated cargo delivery systems. This combination of spectral selectivity, low power requirements, low heat production, and fast release times, along with the versatility in terms of identity of the enclosed cargo, makes these hierarchical microshells suitable for wide-ranging applications, including biological ones.

Brønsted Acid-Catalyzed Intramolecular Hydroarylation of ß-Benzylstyrenes.

Using triphenylmethylium tetrakis(pentafluorophenyl)borate as a convenient Brønsted acid precatalyst, ß-(α,α-dimethylbenzyl)styrenes are shown to cyclize efficiently to afford a variety of new indanes that possess a benzylic quaternary center. The geminal dimethyl-containing quaternary center is proposed to be necessary to arm the substrate for cyclization through steric biasing.

Comparison of Clinical Outcomes between Different Femoral Tunnel Positions after Anterior Cruciate Ligament Reconstruction Surgery.

BACKGROUND: It has been shown that the proper placement of ACL graft during the ACL reconstruction surgery significantly improves the clinical outcomes. This study investigated whether a change in the femoral tunnel position in both axial and coronal planes can significantly alter the postoperative functional and clinical outcomes of the patients. METHODS: This comparative, retrospective, single-center study was performed on 44 patients undergone single-bundle anterior cruciate ligament reconstruction (ACLR). Radiographic assessments were done to evaluate the tunnel position in coronal and axial planes. Patients were classified into 4 groups based on radiographic data. The time interval between surgery and last visit averaged 23.6 ± 2.2 months (18-30 mos.). Lysholm knee score and Cincinnati score were completed for all of the patients. Furthermore, the Lachman, anterior drawer and pivot-shift tests were performed. RESULTS: Of the 44 patients included in the study, 9 patients (20.4%) were classified as the low-anterior group, 17(38.6%) were classified as the low-posterior group and 18(40.9%) were classified as the high-posterior group. None of the patients were included in high-anterior group. A greater mean Lysholm score (96±3) in low-posterior group was the only significant difference between the three groups (P<0.001). CONCLUSION: Findings of the current study demonstrated that low-posterior placement of the ACL graft through the intercondylar notch, based on both antero-posterior (AP) and tunnel-view x-rays, is associated with better clinical outcomes in short-term compared to the routine tunnel placements.

Activity-based targeting of secretory phospholipase A2 enzymes: A fatty-acid-binding-protein assisted approach.

Syntheses and enzymological characterization of fluorogenic substrate probes targeting secretory phospholipase A2 (sPLA2) for detection and quantitative assays are presented. Three fluorogenic phosphatidylcholine analogs PC-1, PC-2, and PC-3 each containing the duo of 7-mercapto-4-methyl-coumarin fluorophore and 2,4-dinitroanaline quencher on either tail were synthesized from (R)-3-amino-1,2-propanediol and R-(-)-2,2-dimethyl-1,3-dioxolane-4-methanol. These small reporter groups are advantageous in preserving natural membrane integrity. Phosphocholine was incorporated into the sn-3 position of the glycerol backbone. Acyl amino group at the sn-1 position in PC-1 and PC-2 is meant to block sPLA1. The sn-1 and sn-2 positions of the glycerol backbone in PC-1 have a quencher terminated 12-carbon chain and fluorophore terminated 11-carbon chain respectively. PC-2 has a quencher terminated 3-carbon chain at the sn-2 and chain terminating fluorescent reporter at the sn-1 positions. PC-3 resembles PC-1 except for an ester instead of amide at the sn-1 position, because of which it is more similar to natural phospholipids than PC-1. It was designed to elucidate the effect of replacing the ester group with amide by comparing its hydrolysis rate with that of PC-1. Design principles apply to synthesis of other labeled phospholipids. Enzymological characterization using bee-venom sPLA2 was performed by a fatty-acid-binding-protein fluorescence assay and by pH-Stat method in which the amount of fatty acid released by hydrolysis is given by the amount of base required to maintain a constant pH of 8.0. Hydrolytic activity toward PC-1 and PC-3 were each about 238±25µmol/mg/min and 537µmol/mg/min on unmodified phospholipid. Ester to amide change did not affect hydrolysis rates. Activity toward PC-2 was about 45-µmol/mg/min. PC-1 and PC-3 show potential for targeted real-time spectrophotometric assay of sPLA2.