Remotely triggered liposome release by near-infrared light absorption via hollow gold nanoshells

An elusive goal for systemic drug delivery is to provide both spatial and temporal control of drug release. Liposomes have been evaluated as drug delivery vehicles for decades, but their clinical significance has been limited by slow release or poor availability of the encapsulated drug. Here we show that near-complete liposome release can be initiated within seconds by irradiating hollow gold nanoshells (HGNs) with a near-infrared (NIR) pulsed laser. Our findings reveal that different coupling methods such as having the HGNs tethered to, encapsulated within, or suspended freely outside the liposomes, all triggered liposome release but with different levels of efficiency. For the underlying content release mechanism, our experiments suggest that the microbubble formation and collapse due to the rapid temperature increase of the HGN is responsible for liposome disruption, as evidenced by the formation of solid gold particles after the NIR irradiation and the coincidence of a laser power threshold for both triggered release and pressure fluctuations in the solution associated with cavitation. These effects are similar to those induced by ultrasound and our approach is conceptually analogous to the use of optically triggered nano-"sonicators" deep inside the body for drug delivery. We expect HGNs can be coupled with any nanocarriers to promote spatially and temporally controlled drug release. In addition, the capability of external HGNs to permeabilize lipid membranes can facilitate the cellular uptake of macromolecules including proteins and DNA and allow for promising applications in gene therapy.     

Formate as a CO surrogate for cascade processes: Rh-catalyzed cooperative decarbonylation and asymmetric Pauson-Khand-type cyclization reactions

A rhodium-(S)-xyl-BINAP complex-catalyzed tandem formate decarbonylation and [2 + 2 + 1] carbonylative cyclization is described; this cooperative process utilizes formate as a condensed CO source, and the newly developed cascade protocol can be extended to its enantioselective version, providing up to 94% ee of the cyclopentenone adducts.     

Structures and vibrational spectra of the sulfur-rich oxides SnO (n = 4-9): the importance of pi*-pi* interactions

The structures of a large number of isomers of the sulfur oxides S(n)O with n = 4-9 have been calculated at the G3X(MP2) level of theory. In most cases, homocyclic molecules with exocyclic oxygen atoms in an axial position are the global minimum structures. Perfect agreement is obtained with experimentally determined structures of S(7)O and S(8)O. The most stable S(4)O isomer as well as some less stable isomers of S(5)O and S(6)O are characterized by a strong pi*-pi* interaction between S==O and S==S groups, which results in relatively long S--S bonds with internuclear distances of 244-262 pm. Heterocyclic isomers are less stable than the global minimum structures, and this energy difference approximately increases with the ring size: 17 (S(4)O), 40 (S(5)O), 32 (S(6)O), 28 (S(7)O), 45 (S(8)O), and 54 kJ mol(-1) (S(9)O). Owing to a favorable pi*-pi* interaction, preference for an axial (or endo) conformation is calculated for the global energy minima of S(7)O, S(8)O, and S(9)O. Vapor-phase decomposition of S(n)O molecules to SO(2) and S(8) is strongly exothermic, whereas the formation of S(2)O and S(8) is exothermic if n<7, but slightly endothermic for S(7)O, S(8)O, and S(9)O. The calculated vibrational spectra of the most stable isomers of S(6)O, S(7)O, and S(8)O are in excellent agreement with the observed data.     

Mechanism of metal chloride-promoted Mukaiyama aldol reactions

Ab initio calculations (MP2/6-311+G**//B3LYP/6-31G*) were employed to investigate the mechanism of metal chloride-promoted Mukaiyama aldol reaction between trihydrosilyl enol ether and formaldehyde. The metal chlorides considered include TiCl4, BCl3, AlCl3, and GaCl3. In contrast to the concerted pathway of the uncatalyzed aldol reaction, the Lewis acid-promoted reactions favor a stepwise mechanism. Three possible stepwise pathways were located. The lowest energy pathway corresponds to a simultaneous C-C bond formation and a chlorine atom shift in the first (rate-determining) step. This process is calculated to have a low activation barrier of 12 kJ mol-1 for the TiCl4-promoted reaction. The alternative [2+2] cycloaddition and direct carbon-carbon bond formation pathways are energetically competitive. BCl3, AlCl3, and GaCl3 are predicted to be efficient catalysts for the silicon-directed aldol reaction as they strongly activate the formaldehyde electrophile. Formation of a stable pretransition state intermolecular pi-pi complex between enol silane and the activated formaldehyde (CH2=O...MCln) is a key driving force for the facile metal chloride-promoted reactions.     

The effect of protein structural conformation on nanoparticle molecular imprinting of ribonuclease A using miniemulsion polymerization

One of the major difficulties faced in the molecular imprinting of proteins is the inherently fragile and flexible nature of the protein template which makes it incompatible with most polymerization systems. Miniemulsion polymerization is a possible approach for preparing molecularly imprinted nanoparticles, and in this study, the method of initiation, the high-shear homogenization, and the surfactant used for the polymerization reaction had been considered as possible factors that can denature the template protein, ribonuclease A (RNase A). The conformation of the protein in a miniemulsion was studied using circular dichroism (CD). It was found that redox initiation was more suitable for protein imprinting and that the addition of poly(vinyl alcohol) (PVA) as a co-surfactant had proved to be effective in preserving the template protein structural integrity. On the basis of the results of the study, polymeric nanoparticles imprinted with RNase A were prepared via miniemulsion polymerization using methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) as the functional and cross-linker monomers, respectively, with the conditions of the polymerization system optimized to best preserve the integrity of the protein template. In the subsequent investigation for the recognition properties of the prepared nanoparticles through batch and competitive rebinding tests, the imprinted nanoparticles prepared through the conventional (nonoptimized) miniemulsion polymerization lacked the target specificity as displayed by those prepared under the optimized conditions. This illustrated the importance of protein structural integrity in protein imprinting.     

Synthesis of Unsymmetric Bipyridine–PtII–Alkynyl Complexes through Post‐Click Reaction with Emission Enhancement Characteristics and Their Applications as Phosphorescent Organic Light‐Emitting Diodes

Two unsymmetric bipyridine–platinum(II)–alkynyl complexes have been synthesised by a post‐click reaction. These metal complexes are found to exhibit emission enhancement properties. The photoluminescence quantum yield can be significantly increased from 0.03 in solution to 0.72 in solid‐state thin films. Efficient solution‐processable organic light‐emitting diodes have been fabricated by utilizing these complexes as phosphorescent dopants. A high external quantum efficiency of up to 5.8 % has been achieved.     

Ethenedithione (S=C=C=S): Does It Obey Hund's Rule?

Significantly higher in energy (24 kJ mol⁻¹) than the triplet ground state (³Σ_g⁻) is the ¹Δ_g state of ethenedithione (S=C=C=S), in agreement with Hund's rule. This result was obtained from high-level ab initio calculations. Thus, ethenedithione cannot, as had been proposed, be considered as the first example for the violation of Hund's rule in an equilibrium structure.