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We present density functional theory (DFT) results on the structural, electronic, and optical properties of Cu−flavonoid complexes for molar ratios 1:1, 1:2, and 1:3. We find that the preferred chelating site is close to the 4-oxo group and in particular the 3−4 site followed by the 3′−4′ dihydroxy group in ring B. For the Cu−quercetin complexes, the large bathochromic shift of the first absorbance band upon complexation, which is in good agreement with experimental UV−vis spectra, results from the reduction of the electronic energy gap. The HOMO states for these complexes are characterized by π-bonding between the Cu d orbitals and the C, O p orbitals except for the case of 1:1 complex (spin minority), which corresponds to σ-type bonds. The LUMO states are attributed to the contribution of Cu pzorbitals. Consequently, the main features of the first optical absorption maxima are essentially due to π → π* transitions, while the 1:1 complex exhibits also σ → π* transitions. Our optical absorption calculations based on time-dependent DFT demonstrate that the 1:1 complex is responsible for the spectroscopic features at pH 5.5, whereas the 1:2 complex is mainly the one responsible for the characteristic spectra at pH 7.4. These theoretical predictions explain in detail the behavior of the optical absorption for the Cu−flavonoid complexes observed in experiments and are thus useful in elucidating the complexation mechanism and antioxidant activity of flavonoids. [ABSTRACT FROM AUTHOR]

We investigate the electronic coupling between a TiO 2nanowire and a natural dye sensitizer, using state-of-the-art time-dependent first-principles calculations. The model dye molecule, cyanidin, is deprotonated into the quinonoidal form upon adsorption on the wire surface. This results in its highest occupied molecular orbital (HOMO) being located in the middle of the TiO 2bandgap and its lowest unoccupied molecular orbital (LUMO) being close to the TiO 2conduction band minimum (CBM), leading to greatly enhanced visible light absorption with two prominent peaks at 480 and 650 nm. We find that excited electrons are injected into the TiO 2conduction band within a time scale of 50 fs with negligible electron−hole recombination and energy dissipation, even though the dye LUMO is located 0.1−0.3 eV lower than the CBM of the TiO 2nanowire. [ABSTRACT FROM AUTHOR]

Flavonoids exhibit antioxidant behavior believed to be related to their metal ion chelation ability. We investigate the complexation mechanism of several flavonoids, quercetin, luteolin, galangin, kaempferol, and chrysin, with iron, the most abundant type of metal ions in the body, through first-principles electronic structure calculations based on density functional theory (DFT). We find that the most likely chelation site for Fe is the 3-hydroxyl-4-carbonyl group, followed by 4-carbonyl-5-hydroxyl group and the 3‘-4‘ hydroxyl (if present) for all of the flavonoid molecules studied. Three quercetin molecules are required to saturate the bonds of a single Fe ion by forming six orthogonal Fe−O bonds, though the binding energy per molecule is highest for complexes consisting of two quercetin molecules and one Fe atom, in agreement with experiment. Optical absorption spectra calculated with time-dependent DFT serve as signatures to identify various complexes. For the iron-quercetin complexes, we find a redshift of the first absorbance peak upon complexation in good agreement with experiment; this behavior is explained by the narrowing of the optical gap of quercetin because of Fe(d)−O(p) orbital hybridization. [ABSTRACT FROM AUTHOR]

Manipulation of shape anisotropy of building blocks is creating diverse and complex assemblies, in particular in the field of colloid science. Self-assembly of block copolymers has created a great number of nano-objects and/or nanostructures. Herein we report the design and synthesis of a series of block copolymers with varying shape anisotropy using polyhedral oligomeric silsesquioxane (POSS) cluster and linear poly(ethylene oxide)s (PEO) with different molecular weights. The POSS-b-PEO block copolymers were prepared by means of first gathering one to four POSS clusters using short linear or dendritic linkers and then covalently linking them with linear PEO blocks. In this way, the shape anisotropy of the POSS-b-PEO block copolymers is varied widely. We found that the PEO block crystallization in a selected solvent drives the block copolymers to self-assemble into large nanothick sheets. We characterized the sheets using TEM and XRD and found a structure of one PEO crystalline layer sandwiched by two POSS layers. Then, we measured the melting, recrystallization, and remelting processes of the sheets using DSC and observed an effect of varying shape anisotropy on the melting and recrystallization temperatures of the PEO and POSS layer and the crystallinity of the crystalline PEO layer. We proposed ideal molecular structures to depict PEO crystalline structure and POSS packing in the sheets and then semiquantitatively discussed the effect of the varying shape anisotropy on the sheet formation from solution and on PEO melting and crystallization in the nanoconfined space. [ABSTRACT FROM AUTHOR]

A novel Lewis acid catalyzed formalintramolecular [3 + 3] cross-cycloaddition(IMCC) of cyclopropane 1,1-diesters has been successfully developed.This supplies an efficient and conceptually new strategy for constructionof bridged bicyclo[2.2.2]octane skeletons. This [3 + 3]IMCC couldbe run up to gram scale and from easily prepared starting materials.This [3 + 3]IMCC, together with our previously reported [3 + 2]IMCCstrategy, can afford either the bicyclo[2.2.2]octane or bicyclo[3.2.1]octaneskeletons from the similar starting materials by regulating the substituentson vinyl group. [ABSTRACT FROM AUTHOR]

A tandem isomerization/intramolecular[3 + 2] cross-cycloaddition(IMCC) of cyclopropane 1,1-diesters with α,β-unsaturatedketones/aldehydes under a cooperative catalysis of photo and Lewisacids has been successfully developed. This supplied a general andefficient strategy for construction of medium-sized carbocyclic (8-,9-, and 10-membered) skeletons as well as such carbocycle-based bridgedoxa-bicyclo[n.2.1] (n= 4–6)skeletons. [ABSTRACT FROM AUTHOR]

A cheap gas–liquid–solid method to prepare a nanodeposition of iron on the surface of a micrometer-size flaky graphite powder is described. This method is suited not only for spherical, but also nonspherical small substrates. The method is only a one-step process, in which decomposition of iron pentacarbonyl is induced by nitrogen gas in a 90 °C reactor. This synthetic route simplifies the operation procedure and manufacturing equipment, and decreases the reaction temperature, compared with conventional liquid–solid-phase methods and gas–solid-phase methods. [ABSTRACT FROM AUTHOR]

(-)-Englerin A was synthesized in 20 steps from the commercially available material (R)-(+)-limonene. In addition, (-)-englerin B, (+)-orientalol E/F and (-)-oxyphyllol were obtained from the intermediate in the route. The key steps include a hydroxyl-directing stereoselective and regioselective intramolecular cyclopropanation and a multi-gram-scale stereoselective formal intramolecular [3 + 2] cross cycloaddition ([3 + 2]-IMCC) of a cyclopropane 1,1-diester with a carbonyl. A precursor of 7,10-diastereoisomer of englerins was also obtained. [ABSTRACT FROM AUTHOR]

Nitroxyl (HNO) is a derivative of nitric oxide (NO) that plays an essential role in various biological and pharmacological events. Until now, the in situ trapping and specific detection of HNO in living samples is still challenging. In this project, we fabricated a novel BODIPY-based micellar nanoprobe for monitoring nitroxyl in vitro and in vivo in ratiometric mode in aqueous solution. The probe (P-BODIPY-N) contains an asymmetrical BODIPY dye for fluorescent signaling and a diphenylphosphinobenzoyl as the trigger moiety; then we encapsulated P-BODIPY-N into the hydrophobic interior of an amphiphilic copolymer (mPEG-DSPE) and prepared a novel BODIPYbased micellar nanoprobe: NP-BODIPY-N. As far as we know, this probe is the first reported ratiometric fluorescent nanoprobe for HNO, which exhibits ultrasensitivity, high selectivity, and good biocompatibility. Above all, this nanoprobe shows favorable cellular uptaken and was successfully used to detect intracellular HNO released by Angeli's salt in living cells and zebrafish larvae. These results indicate that our newly designed nanoprobe will provide a promising tool for the studies of HNO in living system. [ABSTRACT FROM AUTHOR]

Leucine aminopeptidase (LAP) is an important cancer-related biomarker, which shows significant over- expression in malignant tumor cells like liver cancer. Developing an effective method to monitor LAP in tumor cells holds great potential for cancer diagnosis, treatment, and management. In this work, we report a novel BODIPY-based fluorescent probe (BODIPY-C-Leu) capable of monitoring LAP in vitro and in vivo in both ratiometric and turn-on model. BODIPY-C-Leu contains an asymmetrical BODIPY dye for fluorescent signaling and a dipeptide (Cys-Leu) as the triggered moiety. Activation occurs by cleavage of the amide bond in dipeptides and subsequently an intramolecular S → N conversion to convert sulfur-substituted BODIPY to amino-substituted BODIPY, resulting in a dramatic fluorescence variation to realize the detection of LAP. Furthermore, we have successfully employed BODIPY-C-Leu to monitor LAP activity in different cancer cells, indicating that HeLa cells have a higher level of LAP activity than A549 cells. Importantly, we demonstrated the capability of the probe for real-time monitoring the drug-induced LAP level changes in zebrafish. [ABSTRACT FROM AUTHOR]

Clusters are an important class of nanoscale molecules or superatoms that exhibit an amazing diversity in structure, chemical composition, shape, and functionality. Assembling two types of clusters is creating emerging cluster-assembled materials (CAMs). In this paper, we report an effective approach to produce quasi two-dimensional (2D) CAMs of two types of spherelike clusters, polyhedral oligomeric silsesquioxanes (POSS), and polyoxometalates (POM). To avoid macrophase separation between the two clusters, they are covalently linked to form a POM-POSS cocluster with Janus characteristics and a dumbbell shape. This Janus characteristics enables the cocluster to self-assemble into diverse nanoaggregates, as conventional amphiphilic molecules and macromolecules do, in selective solvents. In our study, we obtained micelles, vesicles, nanosheets, and nanoribbons by tuning the n-hexane content in mixed solvents of acetone and n-hexane. Ordered packing of clusters in the nanosheets and nanoribbons were directly visualized using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) technique. We infer that the increase of packing order results in the vesicle-to-sheet transition and the change in packing mode causes the sheet-to-ribbon transitions. Our findings have verified the effectivity of creating quasi 2D cluster-assembled materials though the cocluster self-assembly as a new approach to produce novel CAMs. [ABSTRACT FROM AUTHOR]

Selective conversion of glucosamine (GlcNH2) to deoxyfructosazine (DOF) and fructosazine (FZ) with additives was investigated. Significantly enhanced yield of DOF can be improved to 40.2% with B(OH)3 as the additive. Chemical shift titration (via one-dimensional nuclear magnetic resonance (1D ¹H and 13C NMR)) and two-dimensional nuclear magnetic resonance (2D NMR) including ¹H-13C HSQC and ¹H-¹H COSY are used to investigate intermolecular interactions between B(OH)3 and GlcNH2. Diffusion-ordered NMR spectroscopy (DOSY) was further employed to identify intermediate species. Mechanistic investigation by NMR combined with electron spray ionization-mass spectroscopy (ESI-MS) discloses that a mixed 1:1 boron complex was identified as the major species, shedding light on the promotional effects of B(OH)3, which is substantiated by density functional theory (DFT). Boron coordination effects make ring-opening and subsequent dehydration reaction thermodynamically and kinetically more favorable. Dehydration of dihydrofructosazine is a key step in controlling overall process (49.7 kcal/mol). Interestingly, chelating effect results in substantial reduction of this free-energy barrier (31.5 kcal/mol). Notably, FZ was gradually becoming the main product (yield up to 25.3%), with H2O2 as the oxidant. [ABSTRACT FROM AUTHOR]

In this work, we report the preparation of complex nano-objects by means of a stepwise self-assembly of two polymer-polyoxometalate hybrids (PPHs) in solution. The PPHs are designed and synthesized by tethering two linear poly(e-caprolactone)s (PCL) of different molecular weights (MW) on a complex of a Wells-Dawson-type polyoxometalate (POM) cluster and its countraions. The higher MW PCL-POM self-assembled into nanosheets, while the lower MW PCL-POM assembled into nanotubes just by altering the ratio of water in the DMF-water mixed solvent system. The two nano-objects have a similar membrane structure in which a PCL layer is sandwiched by the two POM-based complex layers. The PCL layer in the nanosheets is semicrystalline, while the PCL layer in the nanotubes is amorphous. We further exploited this MW-dependence to self-assemble the nanotubes on the nanosheet edges to create complex tube-graft-sheet nano-objects. We found that the nanotubes nucleate on the four {110} faces of the PCL crystal and then further grow along the crystallographic b-axis of the PCL crystal. Our findings offer hope for the further development of nano-objects with increasing complexity. [ABSTRACT FROM AUTHOR]

The unique performance of natural materials stems from their hierarchical hybrid structures formed through self-assembly. The selfassembly principles of natural materials have been exploited to create artificial materials. Herein, we demonstrate a bottom-up approach that produces polymer nanocomposites as well as a self-assembled nanoenhancer for tailoring the polymer properties. The polymer is a poly(ethylene glycol) (PEG), and the nanoenhancer is aggregates formed by self-assembly of a hybrid. The hybrid is prepared through covalent bonding of a surfactant-encapsulated polyoxometalate (S-POM) complex with a PEG chain and can form aggregates composed of an S-POM complex bilayer sandwiched by two PEG layers. The lateral size of aggregates changes, depending on the conditions used in the sample preparation. Hence, we examined four nanostructures in the solid samples of nanocomposites: hybrid self-assembled nanosheets, PEG crystallized lamellae, PEG/hybrid cocrystallized lamellae, and hybrid crystallized lamellae. Because of a strong interaction among the S-POM complexes as well as good miscibility of the PEG layers with the PEG matrix, the stable aggregate homogeneously disperses in the melted PEG matrix, and hence it can enhance the performance of the melted PEG. For instance, the shear storage moduli of nanocomposites are adjustable over many orders of magnitude at temperatures above the PEG melting point. These findings provide a novel approach to generate synthetic nanocomposites with self-assembled enhancers that Experimental details and additional experimental results. [ABSTRACT FROM AUTHOR]

Surface functionalization and water solubility of magnetic nanoparticles are crucial for bioapplication. Here, we describe a synthetic approach for direct preparation of a wide range of functionalized and hydrophilic magnetic polymer particles (MPPs) that is both simple and general and involves using different polymers as the source of functional groups. This simple strategy of changing the polymer used in the reaction can give rise to a wide variety of hydrophilic MPPs with a high number of functional groups. For the purpose of bioapplication, we synthesized three types of MPPs with typical functional groups, such as hydroxyl groups (−OH), amino groups (−NH2), and carboxyl groups (−COOH), and further characterized these MPPs by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The magnetic saturation of the MPPs was also studied and was adequate for most bioapplications. MPPs were shown to have good biocompatibility using cell proliferation and apoptosis assays. Two types of MPPs with different functional groups were used successfully for intracellular imaging and antibody purification. Our results demonstrate that this simple and general synthesis strategy has potential for designing hydrophilic magnetic nanoparticles with multifunctionalities that cater for a range of bioapplications. [ABSTRACT FROM AUTHOR]