Cleaved Iron Oxide Nanoparticles as T2 Contrast Agents for Magnetic Resonance Imaging

Iron oxide nanoparticles as contrast agents are reported to effectively improve magnetic resonance imaging of tissues and cells. In this work, cleaved iron oxide nanoparticles (CIONPs) were generated from hydrophobic FeO nanoparticles (HIONPs) by coating their surfaces with PEG‐phospholipids, oxidizing them under water, and slowly removing the residual FeO phase in phthalate buffer. The synthesized CIONPs showed good r₂ values of up to 258 s^?1 mM ^?1. Thus, the CIONPs can be employed as vectors for drug delivery due to their unique structure with an empty inner space, which enables their use in a wide range of applications.     

Synthesis and computational oxidation mechanism study of novel organosoluble aramids with high modulus by low‐temperature solution polycondensation

A series of highly organosoluble polyamides with high modulus having propeller‐shaped triarylamine were synthesized using aromatic diacid chlorides by low‐temperature solution polycondensation. The polyamide films had strong, tough, flexible, and amorphous properties. These polymers revealed electrochromic characteristics both in the visible range and near‐infrared (NIR) region, with a color change from pale yellowish at its neutral state to green and blue at its oxidized state at applied potentials ranging from 0.00 to 1.35 V. Cyclic voltammetry (CV) of the polymer films cast onto an indium tin oxide (ITO)‐coated glass substrate exhibited two reversible redox couples at potentials of 0.80–0.87 V and 1.19–1.25 V, respectively, vs. Ag/Ag⁺ in acetonitrile solution. From the combination of the experimental and computational study, we proposed an oxidation mechanism based on molecular orbital (MO) theory, which well explains the CV experimental result. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Dielectric relaxation studies of dipolar aromatics in polyethylene I. Spherulitic low-density polyethylene

Dielectric relaxation studies have been used as a means of investigating the behavior of aromatic molecules dissolved in a semicrystalline polymer. All molecules show a relaxation in the vicinity of the γ loss peak of polyethylene, while several show an additional peak at lower temperatures. The latter is interpreted as an indicator of molecular motions below the glass transition and the former is to be associated with the onset of molecular motions on a local scale as the glass transition is approached. The α loss process of polyethylene is seemingly unaffected by the presence of the molecules. Integration of loss curves shows that, at most, 50% of the molecules are able to relax but that the fraction relaxing increases with increasing temperature, suggesting the presence of a wide distribution of sites within the polymer.     

Rhodium-catalyzed allyl transfer from homoallyl alcohols to acrylate esters via retro-allylation

Retro-allylation of homoallyl alcohols by rhodium catalysts occurs to generate allylrhodium species. Insertion of acrylate esters to the allylrhodiums proceeds to give the corresponding 2,5-hexadienoate esters in situ. Subsequent isomerization or iterative 1,4-addition takes place in the same pots to furnish the corresponding 2,4-hexadienoate esters or triesters in good yields.     

Thermomagnetic effect in ferrofluids with weakly coupled particles

Thermomagnetic curves for water based ferrofluid with large magnetic latex particles are analyzed. The particles are found to have extremely low barrier height of thermal relaxation (≤1200 K at temperatures below 100 K) whose field dependence is deduced. Work sponsored by the National Science Council of the R.O.C. under Grant No. NSC85-2112-M-001-020.     

An Alternative Mechanism of Non-contact Anterior Cruciate Ligament Injury During Jump-landing: In-vitro Simulation

In the United States, an estimated 100,000 anterior cruciate ligament (ACL) injuries occur every year. Despite decades of research, to this date, the mechanism or mechanisms of non-contact ACL injuries are not well understood. This is primarily because trials cannot be conducted on live subjects to understand the injury mechanism, and it is difficult to instrument a live human knee to measure the response of tissues during dynamic activities. In this paper, we present a dynamic knee injury simulator capable of in-vitro modeling of the ACL injury during jump-landing activity. This system was used to simulate jump-landing on cadaveric knees and to successfully test which conditions would result in isolated ACL injury. A restricted flexion of the hip (a hip that flexes minimally or not at all during landing), combined with low quadriceps and hamstring force levels during landing were found to be conducive to ACL injury. Elevated levels of quadriceps force prevented the injury from occurring even under restricted hip flexion conditions. The measured strain rates in the ACL tissue during injury causing activities were over 250%/s.     

Cage motion of a probe atom in a vacancy complex in Pt

The perturbation function of a Cd probe atom bound in a hydrogen-decorated vacancy complex in Pt is found to exhibit dynamical relaxation at 294 K, as measured by the technique of perturbed γ-γ angular correlations. Based on other characteristics of the complex, a model is proposed for the structure of the complex. In the undecorated state, it consists of a probe atom at the center of a tetrahedron of vacancies in the fcc structure. In the decorated state at low temperature, the probe atom returns to one of the four vacant lattice sites. The relaxation at room temperature is attributed to motion of the probe atom in a cage formed by the four vacant sites.     

Mesoscopic linear alignment and thermal-relaxation dynamics of aggregated gold nanorods

Aqueous gold nanorod colloids aggregated by Cl^- are further assembled into linearly aligned structures of linear bundles during evaporation on TEM grids. Gold nanorods in bundles are also oriented in nearly head-to-tail shapes in the microscopic scale. Induced dipolar long-range interactions in the mesoscopic scale are suggested to drive gold nanorods to aggregate. Although surface-plasmon absorption at transverse resonances decreases, that at longitudinal resonances increases with aggregation. The photon-thermalized heat of the dispersed and the aggregated gold nanorods dissipates to immediately surrounding media on the time scales of 100 and 800 ps, respectively.     

Synthesis and optical and electrochemical properties of copolymers consisting of 9,9‐dihexylfluorene and aromatic triazole chromophores

Aromatic triazole chromophores were incorporated into polyfluorene in an attempt to increase electron affinity, to promote emission efficiency, and to diminish excimer formation. Poly(9,9‐dihexylfluorene) ( P1 ) and new copolymers with aromatic triazoles ( P2 – P4 ) were prepared by Suzuki coupling polymerization. In P2 , the aromatic triazole (3.8 mol %) was attached exclusively as terminal groups, whereas P3 and P4 were main‐chain copolymers containing 3.9 and 10.3 mol % aromatic triazole chromophores, respectively. The copolymers were soluble in common organic solvents and showed high decomposition temperatures (437–458 °C). The twisted structure between the triazole and fluorene increased the emission efficiency and effectively prevented excimer formation in P2 – P4 . After the introduction of the triazole units, the absorption spectra showed a blueshift (from 388 to 381 nm in chloroform) due to confined conjugation, but the photoluminescence spectra remained almost the same (417–418 nm); this was attributed to oligofluorene segments. No emission of triazole fluorophores was observed because of efficient energy transfer from the triazole to oligofluorene segments. However, incomplete energy transfer was observed in CH₃COOH. The optical stability upon thermal annealing was also improved by the incorporation of aromatic triazole segments. From cyclic voltammetry results, P2 – P4 , containing triazole groups, showed greater electron affinity (lowest unoccupied molecular orbital level = ?2.67 to ?2.71 eV) than P1 (?2.52 eV). Electroluminescence devices of P1 – P4 all exhibited excimer emissions (483–521 nm), which could also be diminished by the introduction of aromatic triazole chromophores. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 136–146, 2007