Clarifying and illustrating the electronic energy transfer pathways in trimeric and hexameric aggregation state of cyanobacteria allophycocyanin within the framework of Förster theory

Within the framework of the Förster theory, the electronic excitation energy transfer pathways in the cyanobacteria allophycocyanin (APC) trimer and hexamer were studied. The associated physical quantities (i.e., excitation energy, oscillator strength, and transition dipole moments) of the phycocyanobilins (PCBs) located in APC were calculated at time‐dependent density functional theory (TDDFT) level of theory. To estimate the influence of protein environment on the preceding calculated physical quantities, the long‐range interactions were approximately considered with the polarizable continuum model at the TDDFT level of theory, and the short‐range interaction caused by surrounding aspartate residue of PCBs were taken into account as well. The shortest energy transfer time calculated in the framework of the Förster model at TDDFT/B3LYP/6–31+G* level of theory are about 0.10 ps in the APC trimer and about 170 ps in the APC monomer, which are in qualitative agreement with the experimental finding that a very fast lifetime of 0.43–0.44 ps in APC trimers, whereas its monomers lacked any corresponding lifetime. These results suggest that the lifetime of 0.43–0.44 ps in the APC trimers determined by Sharkov et al. was most likely attributed to the energy transfer of α¹‐84 ? β³‐84 (0.23 ps), β¹‐84 ? α²‐84 (0.11 ps) or β²‐84 ? α³‐84 (0.10 ps). So far, no experimental or theoretical energy transfer rates between two APC trimmers were reported, our calculations predict that the predominate energy transfer pathway between APC trimers is likely to occur from α³‐84 in one trimer to α⁵‐84 in an adjacent trimer with a rate of 32.51 ps. © 2014 Wiley Periodicals, Inc.     

Antibacterial behaviour of quaternized poly(vinyl chloride)-g-poly(4-vinyl pyridine) graft copolymers

Amphiphilic graft copolymers consisting of poly(vinyl chloride)(PVC) main chains and poly(4-vinyl pyridine)(P4VP) side chains were synthesized via atom transfer radical polymerization(ATRP) using direct initiation of chlorine atoms. The successful synthesis of PVC-g-P4 VP graft copolymers was confirmed by Fourier transform infrared spectroscopy(FTIR) and proton nuclear magnetic resonance(1H-NMR). Transmission electron microscope(TEM) and small angle X-ray scattering(SAXS) analysis showed that PVC-g-P4 VP exhibited microphase-separated, ordered structure with 37.6 nm of domain spacing, which was not observed in neat PVC. For antibacterial applications, the tertiary nitrogen atoms of PVC-gP4 VP was quaternized using 1-bromohexane, as confirmed by FTIR measurements. Bacteria including Escherichia coli(E. coli), Staphylococcus aureus(S. aureus), Bacillus cereus(B. cereus), and Pseudomonas aeruginosa(P. aeruginosa) were completely killed in 24 h on the quaternized PVC-g-P4VP(46% grafting) surface, indicating its excellent antibacterial behavior while it showed to be cytotoxic to mammalian cell.     

Monodisperse AgSbS2 Nanocrystals: Size‐Control Strategy,Large‐Scale Synthesis,and Photoelectrochemistry

We report an efficient approach to the synthesis of AgSbS₂ nanocrystals (NCs) by colloidal chemistry. The size of the AgSbS₂ NCs can be tuned from 5.3 to 58.3 nm with narrow size distributions by selection of appropriate precursors and fine control of the experimental conditions. Over 15 g of high‐quality AgSbS₂ NCs can be obtained from one single reaction, indicative of the up‐scalability of the present synthesis. The resulting NCs display strong absorptions in the visible‐to‐NIR range and exceptional air stability. The photoelectrochemical measurements indicate that, although the pristine AgSbS₂ NC electrodes generate a cathodic photocurrent with a relatively small photocurrent density and poor stability, both of them can be significantly improved subject to CdS surface modification, showing promise in solar energy conversion applications.     

Dual Esterase‐ and Steroid‐Responsive Energy Transfer Modulation of Ruthenium(II) and Rhenium(I) Complex Functionalized Gold Nanoparticles

A number of adamantane‐containing ruthenium(II) and rhenium(I) complexes have been synthesized, characterized, and noncovalently functionalized with β‐cyclodextrin‐capped gold nanoparticles (β‐CD–GNPs) through the host–guest interaction between cyclodextrin and adamantane. The resultant nanoconjugates have been characterized by transmission electron microscopy (TEM), energy‐dispersive X‐ray analysis (EDX), and 2D ROESY ¹H NMR experiments. The Förster resonance energy transfer (FRET) properties of the nanoconjugates can be modulated by both esterase‐accelerated hydrolysis and competitive displacement of steroid, by monitoring the emission intensity and luminescence lifetime. The FRET efficiencies are found to vary with the nature of the chromophores and the length of the spacer between the transition metal complexes and the GNPs. This work constitutes a “proof‐of‐principle” assay method for the dual‐functional detection of important classes of biomolecules, such as enzymes and steroids.     

Mesoporous‐Silica‐Functionalized Nanoparticles for Drug Delivery

The ever‐growing interest for finding efficient and reliable methods for treatment of diseases has set a precedent for the design and synthesis of new functional hybrid materials, namely porous nanoparticles, for controlled drug delivery. Mesoporous silica nanoparticles (MSNPs) represent one of the most promising nanocarriers for drug delivery as they possess interesting chemical and physical properties, thermal and mechanical stabilities, and are biocompatibile. In particular, their easily functionalizable surface allows a large number of property modifications further improving their efficiency in this field. This Concept article deals with the advances on the novel methods of functionalizing MSNPs, inside or outside the pores, as well as within the walls, to produce efficient and smart drug carriers for therapy.     

Nucleophilic β‐Carbon Activation of Propionic Acid as a 3‐Carbon Synthon by Carbene Organocatalysis

Direct β‐carbon activation of propionic acid (C₂H₅CO₂H) by carbene organocatalysis has been developed. This activation affords the smallest azolium homoenolate intermediate (without any substituent) as a 3‐carbon nucleophile for enantioselective reactions. Propionic acid is an excellent raw material because it is cheap, stable, and safe. This approach provides a much better solution to azolium homoenolate synthesis than the previously established use of acrolein (enal without any substituent), which is expensive, unstable, and toxic.     

β-Octafluorinated tetrakis(ethoxycarbonyl)porphyrin

Tetrakis(alloxycarbonyl)porphyrin and its β-octafluoro-substituted derivatives were synthesized via Lindsey method and transformed to their zinc complexes.Single crystal X-ray structures of corresponding Zn(Ⅱ) porphyrins revealed that β-octafluorination will give more compactness of porphyrin moieties in the crystal structure owing to the hydrogen bonding interactions involving β-fluorine atoms.An unusual six-coordinated Zn(Ⅱ) was found via intramolecular coordination of oxygen atom of meso-substituents with central Zn(Ⅱ).     

Temperature‐Induced Transformation from Large Compound Vesicles to Worm‐like Aggregates by ABC Triblock Copolymer

Two triblock polymers, tetraaniline‐block‐poly(N‐isopropyl acrylamide)‐block‐poly(hydroxyethyl acrylate) (TA‐b‐PNIPAM‐b‐PHEA) and TA‐b‐PHEA‐b‐PNIPAM, were synthesized with unambiguous structure by a two step method. The difference of these two diblock polymers is the connection order of carboxyl group to block, e.g., carboxyl group to PNIPAM block for PNIPAM‐b‐PHEA and to PHEA block for PHEA‐b‐PNIPAM. Secondly, block tetraaniline was linked to the diblock polymer through amidation to yield the corresponding triblock copolymer. Both of them have almost the identical chemical compositions. The only difference is the connection order of each block in the triblock polymers. When they were self‐assembled at 45°C in a suitable solution, both of their aggregates have spherical shape with slight defects on their surface with the average diameter of about 400 nm. However, when their aggregate dispersion was cooled down to 20°C, only TA‐b‐PHEA‐b‐PNIPAM's morphology changed, forming worm‐like aggregates with the diameter of about 100–200 nm transformed from spherical aggregates. Both amphiphilic property and position of each block in this triblock copolymer are very essential for this morphology transformation. Since the worm‐like aggregates presented here by our group have hollow structure inside, its controlled release properties for doxorubicin were evaluated. Drug release experiment indicated that along with the temperature changes, the rearrangement of the intermediate layer structure caused morphology change in aggregate, thus accelerating the speed of drug release.     

硫酸肼比浊法测定微量硒

依据硒(Ⅳ)在以甘油为稳定剂,盐酸为反应介质的条件下,被过量硫酸肼还原,使体系形成稳定悬浊液的原理,建立了比浊法测定硒的方法。探讨了盐酸用量、甘油用量、反应温度和反应时间以及硫酸肼用量等5个关键因素的影响,确定了最佳测定条件。实验结果表明:大量的共存物质不干扰测定。在选定的实验条件下,线性方程为:ΔA750nm=12.725ρ+0.0076,在2.0×10-4~3.2×10-2mg·m L-1范围内线性关系良好,相关系数(R2)=0.9911,方法的检出限为1.2×10-4mg·m L-1。方法用于测定强化营养盐中总硒,回收率在97.0~103.5%之间,RSD为1.8%。     

Excellent Stability of a Lithium‐Ion‐Conducting Solid Electrolyte upon Reversible Li+/H+ Exchange in Aqueous Solutions

Batteries with an aqueous catholyte and a Li metal anode have attracted interest owing to their exceptional energy density and high charge/discharge rate. The long‐term operation of such batteries requires that the solid electrolyte separator between the anode and aqueous solutions must be compatible with Li and stable over a wide pH range. Unfortunately, no such compound has yet been reported. In this study, an excellent stability in neutral and strongly basic solutions was observed when using the cubic Li₇La₃Zr₂O₁₂ garnet as a Li‐stable solid electrolyte. The material underwent a Li⁺/H⁺ exchange in aqueous solutions. Nevertheless, its structure remained unchanged even under a high exchange rate of 63.6 %. When treated with a 2 M LiOH solution, the Li⁺/H⁺ exchange was reversed without any structural change. These observations suggest that cubic Li₇La₃Zr₂O₁₂ is a promising candidate for the separator in aqueous lithium batteries.