Amphiphilic Janus gold nanoparticles via combining "solid-state grafting-to" and "grafting-from" methods

Despite the great efforts that have been made toward obtaining Janus architectures, synthesizing sub-10 nanometer Janus nanoparticles (NPs) modified with different types of polymers remains a challenging task. In this Communication, "solid-state grafting-to" and "grafting-from" methods were combined to obtain Janus gold NPs (AuNPs) modified with two types of polymer chains on the opposite sides of the NP. We used functionalized polymer single crystals as the solid substrates to immobilize AuNPs. We then used atom transfer radical polymerization to grow polymer chains on the "free" side of the AuNPs. Amphiphilic polyethylene oxide (PEO)-Au-poly(methyl methacrylate), PEO-Au-poly(tert-butyl acrylate) and hydrophilic PEO-Au-poly(acrylic acid) were synthesized. The Janus nature was demonstrated using a platinum-nanoparticle-decoration method. Using polymer single crystals as the reaction substrates is advantageous because they afford higher throughput compared with self-assembled monolayers. Dissolution of the single crystal also leads to NPs with defined polymer patches. We anticipate that our approach could serve as a generic method for synthesizing polymer-functionalized, sub-10 nm Janus NPs. This unique system holds promises for achieving controlled assembly and tunable optic and electronic properties of NPs.     

Making "wheels" and "cubes" from triangles

[Mn(IV)Mn(II)3] triangular units directed by the presence of tripodal alcohols self-assemble in the presence of azide and acetate ligands to form either a [Mn24] "wheel" or a [Mn32] "cube".     

Synthesis of "solid solution" and "core-shell" type cobalt--platinum magnetic nanoparticles via transmetalation reactions

In this article, we report the synthesis of "solid solution" and "core-shell" types of well-defined Co--Pt nanoalloys smaller than 10 nm. The formation of these alloys is driven by redox transmetalation reactions between the reagents without the need for any additional reductants. Also the reaction proceeds selectively as long as the redox potential between the two metals is favorable. The reaction between Co(2)(CO)(8) and Pt(hfac)(2) (hfac = hexafluoroacetylacetonate) results in the formation of "solid solution" type alloys such as CoPt(3) nanoparticles. On the other hand, the reaction of Co nanoparticles with Pt(hfac)(2) in solution results in "Co(core)Pt(shell)" type nanoalloys. Nanoparticles synthesized by both reactions are moderately monodispersed (sigma < 10%) without any further size selection processes. The composition of the alloys can also be tuned by adjusting the ratio of reactants. The magnetic and structural properties of the obtained nanoparticles and reaction byproducts are characterized by TEM, SQUID, UV/vis, IR, EDAX, and XRD.     

"Demonstration" vs. "designation" of measurement competence: the need to link accreditation to metrology

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. "traceable" to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be "external" to the measurement laboratories which are being evaluated. This is realized in IRMM's International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using "metrology", the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be "demonstrated" rather than just "designated" and this can be shown to both customers and regulators. It inspires more confidence.     

"Polysiloxane-Pd" nanocomposites as recyclable chemoselective hydrogenation catalysts

Polysiloxane-encapsulated "Pd"-nanoclusters were generated by reduction of Pd(OAc)(2) with polymethylhydrosiloxane, which functions as a reducing agent as well as a capping material for production and stabilization of catalytically active "Pd"-nanoparticles. Chemoselective hydrogenation of functional conjugated alkenes was achieved by in-situ- or ex-situ-generated polysiloxane-stabilized "Pd"-nanoclusters under mild reaction conditions in high yields. Electron microscopy, UV-vis, and NMR studies of the reaction mixture during the catalytic transformation were performed and, in conjunction with catalyst poisoning experiments, demonstrated unequivocally the role of polysiloxane-encapsulated "Pd"-nanoclusters as the real catalytic species. The recyclability of the "Pd"-nanoclusters was established by reusing the solid left after the reaction.     

Polymer microcapsules with "foamed" membranes

This article describes the preparation of capsules displaying craters at their surfaces and independent holes inside their membranes. These poly(methylmethacrylate) capsules of 20 to 200 microm diameter are prepared by a solvent evaporation process and typically contain a dispersant, polyvinyl alcohol, and an excipient, namely, a fatty acid triglyceride (miglyol 812). Spectroscopic methods showed that, depending on the miglyol content, the craters at the surface exhibited sizes of about 1 to 2 microm, whereas the core structure of the membrane changed significantly, typically from "soft-part-of-bread" up to "foamed"-like aspects. Among several spectroscopy techniques, confocal fluorescence microscopy confirmed that the capsules retained the miglyol in their core and not in the craters or holes, even after centrifugation and handling. This technique also showed that holes in the membrane are filled with water. A possible analysis of the "foaming" phenomenon based on the surface tensions of different oils, as well as their optimal hydrophile-lipophile balance (HLBO), is added to generalize the concept.     

Polymersomes in "gelly" polymersomes: toward structural cell mimicry

We demonstrate here the formation of compartmentalized polymersomes with an internal "gelly" cavity using an original and versatile process. Nanosize polymersomes of poly(trimethylene carbonate)-b-poly(L-glutamic acid) (PTMC-b-PGA), formed by a solvent displacement method are encapsulated with a rough "cytoplasm mimic" in giant polymersomes of poly(butadiene)-b-poly(ethylene oxide) PB-b-PEO by emulsion-centrifugation. Such a system constitutes a first step toward the challenge of structural cell mimicry with both "organelles" and "cytoplasm mimics". The structure is demonstrated with fluorescence labeling and confocal microscopy imaging with movies featuring the motion of the inner nanosize polymersomes in larger vesicles. Without "cytoplasm mimic", the motion was confirmed to be Brownian by particle tracking analysis. The inner nanosize polymersomes motion was blocked in the presence of alginate, but only hindered in the presence of dextran. With the use of such high molecular weight and concentrated polysaccharides, the crowded internal volume of cells, responsible for the so-called "macromolecular crowding" effect influencing every intracellular macromolecular association, seems to be efficiently mimicked. This study constitutes major progress in the field of structural biomimicry and will certainly enable the rise of new, highly interesting properties in the field of high-added value soft matter.     

Chromene "lock", thiol "key", and mercury(II) ion "hand": a single molecular machine recognition system

A regenerative, molecular machine-like "ON-OFF-ON" chemosensor based on a chromene molecule with the pyran ring "OFF-ON-OFF" cycle is reported for the first time. It behaves as a molecular lock that requires a thiol "key" to open the lock and a mercury(II) ion "hand" that unlatches the key for unsheathing the key to close the lock.     

X-ray and neutron diffraction studies on "Li4.4Sn"

A chemical analysis and detailed structural characterization, using X-ray single crystal and neutron powder diffraction, of the binary lithium-tin compound "Li(4.4)Sn" is presented. Phase analyses and subsequent structural refinements result in the reformulation of "Li(4.4)Sn" as Li(17)Sn(4). The lithium-rich binary phase crystallizes with a complex cubic structure in the space group Ffourmacr;3m, with a = 19.6907(11) A, Z = 20. The improved crystal structure determination indicates well-defined lithium atom positions, some of which differ from those previously reported. The nearly Zintl phase Li(17)Sn(4) exhibits poor metallic behavior similar to that of heavily doped semiconductors. Comparisons of the refined crystal structure with previously reported X-ray crystal structures associated with "Li(4.4)Sn" are discussed.     

High performance "ionic liquid" chromatography

We firstly developed high performance liquid chromatography methods with "ionic liquids" as eluents (HPILC) and successfully demonstrated the analysis of various biopolymers including scarcely soluble highly polymerized cellulose by means of HPILC with highly polar ionic liquid.     

Probing the donor-acceptor proximity on the physicochemical properties of porphyrin-fullerene dyads: "tail-on" and "tail-off" binding approach.

A new approach of probing proximity effects in porphyrin-fullerene dyads by using an axial ligand coordination controlled "tail-on" and "tail-off" binding mechanism is reported. In the newly synthesized porphyrin-fullerene dyads for this purpose, the donor-acceptor proximity is controlled either by temperature variation or by an axial ligand replacement method. In o-dichlorobenzene, 0.1 M (TBA)ClO(4), the synthesized zincporphyrin-fullerene dyads exhibit seven one-electron reversible redox reactions within the accessible potential window of the solvent and the measured electrochemical redox potentials and UV-visible absorption spectra reveal little or no ground-state interactions between the C(60) spheroid and porphyrin pi-system. The proximity effects on the photoinduced charge separation and charge recombination are probed by both steady-state and time-resolved fluorescence techniques. It is observed that in the "tail-off" form the charge-separation efficiency changes to some extent in comparison with the results obtained for the "tail-on" form, suggesting the presence of some through-space interactions between the singlet excited zinc porphyrin and the C(60) moiety in the "tail-off" form. The charge separation rates and efficiencies are evaluated from the fluorescence lifetime studies. The charge separation via the singlet excited states of zinc porphyrin in the studied dyads is also confirmed by the quick rise-decay of the anion radical of the C(60) moiety within 20 ns. Furthermore, a long-lived ion pair with lifetime of about 1000 ns is also observed in the investigated zinc porphyrin-C(60) dyads.     

"Separated" versus "contact" ion-pair structures in solution from their crystalline states: dynamic effects on dinitrobenzenide as a mixed-valence anion

Qualitative structural concepts about dynamic ion pairs, historically deduced in solution as labile solvent-separated and contact species, are now quantified by the low-temperature isolation of crystalline (reactive) salts suitable for direct X-ray analysis. Thus, dinitrobenzenide anion (DNB(-)) can be prepared in the two basic ion-paired forms by potassium-mirror reduction of p-dinitrobenzene in the presence of macrocyclic polyether ligands: L(C) (cryptand) and L(E) (crown-ethers). The crystalline "separated" ion-pair salt isolated as K(L(C))(+)//DNB(-) is crystallographically differentiated from the "contact" ion-pair salt isolated as K(L(E))(+)DNB(-) by their distinctive interionic separations. Spectral analysis reveals pronounced near-IR absorptions arising from intervalence transitions that characterize dinitrobenzenide to be a prototypical mixed-valence anion. Most importantly, the unique patterns of vibronic (fine-structure) progressions that also distinguish the "separated" from the "contact" ion pair in the crystalline solid state are the same as those dissolved into THF solvent and ensure that the same X-ray structures persist in solution. Moreover, these distinctive NIR patterns are assigned with the aid of Marcus-Hush (two-state) theory to the "separated"ion pair in which the unpaired electron is equally delocalized between both NO(2)-centers in the symmetric ground state of dinitrobenzenide, and by contrast, the asymmetric electron distribution inherent to "contact"ion pairs favors only that single NO(2)-center intimately paired to the counterion. The labilities of these dynamic ion pairs in solution are thoroughly elucidated by temperature-dependent ESR spectral changes that provide intimate details of facile isomerizations, ionic separations, and counterion-mediated exchanges.     

The spectroscopic signature of the "all-surface" to "internally solvated" structural transition in water clusters in the n = 17-21 size regime

The existence of a transitional size regime where preferential stabilization alternates between "all-surface" (all atoms on the surface of a cluster) and "internally solvated" (one water molecule at the center of the cluster, fully solvated) configurations with the addition or the removal of a single water molecule, predicted earlier with the flexible, polarizable (many-body) Thole-type model interaction potential (TTM2-F), has been confirmed from electronic structure calculations for (H2O)n, n = 17-21. The onset of the appearance of the first "interior" configuration in water clusters occurs for n = 17. The observed structural alternation between interior (n = 17, 19, 21) and all-surface (n = 18, 20) global minima in the n = 17-21 cluster regime is accompanied by a corresponding spectroscopic signature, namely, the undulation in the position of the most redshifted OH stretching vibrations according to the trend: interior configurations exhibit more redshifted OH stretching vibrations than all-surface ones. These most redshifted OH stretching vibrations form distinct groups in the intramolecular region of the spectra and correspond to localized vibrations of donor OH stretches that are connected to neighbors via "strong" (water dimer-like) hydrogen bonds and belong to a water molecule with a "free" OH stretch.     

"Asymmetric" catalysis by lanthanide complexes

Catalysis with lanthanide (Ln) complexes has been underestimated for long time, although Ln(III) complexes have great advantages as Lewis acid catalysts for "asymmetric" carbon-carbon bond-forming reactions. Lanthanide complexes are highly active in ligand-substitution reactions, especially with hard ligands. The association with substrates and dissociation of products are achieved fast enough for high catalyst efficiency. The asymmetric catalysis of organic reactions can be greatly advanced by the use of Ln complexes with chiral ligands such as binaphthol (binol). Ln(II) complexes are good reducing agents, which can be used in a wide variety of synthetically important reactions; when chiral ligands are used, many of these reactions are highly stereoselective. In the context of "green chemistry", the development of asymmetric Ln catalysts, and their recyclable use, is of increasing importance. This review gives an overview of the most recent developments in catalysis with lanthanide(II) and lanthanide(III) complexes.     

Algorithm for coding DNA sequences into "spectrum-like" and "zigzag" representations

An algorithm for encoding long strings of building blocks, like 4 DNA bases (adenine-A, cytosine-C, thymine-T, and guanidine-G), 20 natural amino acids (from Alanine Ala to Valine-Val, plus the stop triplet), or all 64 possible base triplets (from AAA to TTT), into "zigzag" or "spectrum-like" representations is suggested. The new encoding scheme can be derived in the 3-, 2-, or 1-dimensional form depending on the user's wishes. The only information, besides the string for which the "spectrum-like" representation is sought, is the initial positioning of the complete set of units from which the string is composed, i.e., four positions for A, C, G, and T, or 20 positions for natural amino acids plus stop, etc. This initial positioning can be initialized in either the 3-, 2-, or 1-D form. As an illustration of the suggested encoding scheme of the visual and chemometric comparison of the first 10 exon strings of the beta globin gene of 10 different species, each string consisting of about 100 basic amino acids long is shown.     

Graphitic molecules with partial "zig/zag" periphery

A new synthetic protocol that affords novel hexa-peri-hexabenzocoronene (HBC) derivatives with partial "zig/zag" periphery and dramatically different electronic properties has been developed, which represents an important step toward understanding structure-property relationships of graphitic materials. The scope of this methodology was broadened by application to a much larger polycyclic aromatic hydrocarbon (PAH) with a more extended "zig/zag" character.     

Gallium cluster "magic melters"

Calorimetry measurements (using a method based on multicollision induced dissociation) have been performed for unsupported gallium clusters, Gan+ (n = 30-50 and 55). Melting transitions have been identified from spikes in the heat capacities recorded as a function of temperature. There are enormous fluctuations in the melting temperatures and the heats of fusion with cluster size. Clusters with n = 31, 33, 37, and 45-47 are "magic melters" with particularly well-defined melting transitions. There is a strong correlation between the heats of fusion, entropies of fusion, and the stabilities of the clusters. However, these quantities are not strongly correlated with the melting temperatures.     

"Orthogonal" separations for reversed-phase liquid chromatography

A general procedure is proposed for the rapid development of a reversed-phase liquid chromatographic (RP-LC) separation that is "orthogonal" to a pre-existing ("primary") method for the RP-LC separation of a given sample. The procedure involves a change of the mobile-phase organic solvent (B-solvent), the replacement of the primary column by one of very different selectivity, and (only if necessary) a change in mobile phase pH or the use of a third column. Following the selection of the "orthogonal" B-solvent, column and mobile phase pH, further optimization of peak spacing and resolution can be achieved by varying separation temperature and either isocratic %B or gradient time. The relative "orthogonality" of the primary and "orthogonal" RP-LC methods is then evaluated from plots of retention for one method versus the other. The present procedure was used to develop "orthogonal" methods for nine routine RP-LC methods from six pharmaceutical analysis laboratories. The relative success of this approach can be judged from the results reported here.