Chemistry – An Asian Journal

Reversible polymerization has a great potential for the generation of reusable nanomaterials and complete repair of cracks or breaks in self-healing materials. In their Communication on page 908 ff., Young Hwan Jung et al. report on a surface-initiated, reversible polymerization of DNA that is processed by enzymatic reactions. Elongation of DNA, catalyzed by Taq DNA polymerase, is performed from a self-priming oligodeoxynucleotide anchored onto gold, and reversible de-polymerization and re-polymerization are achieved in a sequence-specific manner by using a restriction enzyme and Taq DNA polymerase. The cover picture was designed by Juno Lee.

Surface-passivated SBA-15-supported gold nanoparticles that were nearly superhydrophobic, with a contact angle of 144°, were prepared by surface passivation based on a modified impregnation method, as reported by Jinsuo Gao et al. in their Full paper on page 934 ff. In their study, which is featured on the Inside Cover, the authors found that the catalytic activity of these nanoparticles regarding the reduction of nitrobenzene was significantly increased (>14 times) when compared with non-passivated SBA-15. Interestingly, the catalyst exhibited almost no catalytic activity for the more hydrophilic substrate 4-nitrophenol. Accordingly, such surface-passivated catalysts may find use in the selective catalysis of hydrophobic substrates.

A noble bunch: Highly luminescent noble metal nanoclusters have recently emerged as promising probes for constructing high-performance optical sensors. This review summarizes the common syntheses and the luminescence properties of water-soluble luminescent thiolate- and protein-protected gold and silver nanoclusters and discusses the recent progress in their use as optical sensors with an emphasis on the underlying signal-generation mechanisms.

Out of the pybox: We have developed a novel chiral calcium iodide catalyst from CaI₂ and a pybox that is stable under moisture and oxygen. This catalyst was applied to catalytic asymmetric Mannich-type reactions of malonates with both N-Boc-protected aromatic and aliphatic imines, and resulted in moderate to high yields with high enantioselectivities. To the best of our knowledge, this is the first example of highly enantioselective metal-catalyzed asymmetric Mannich-type reactions of malonates with N-Boc-protected aliphatic imines. The Mannich adduct was successfully converted into the α-hydroxy β-amino acid derivative. We have also shown the unique structure of the chiral Ca complexes with malonates.

3, 2, 1 go! An unprecedented one-pot, catalyst-free, three-component aminomethylation of α-substituted nitroacetates, formalin, and amines has been reported, thereby enabling the highly efficient synthesis of α,β-diamino acid precursors with great structural diversity.

A novel cascade reaction involving oxidative dearomatization/semipinacol rearrangement of indol-2-yl cyclobutanols is explored with N-sulfonyloxaziridine (Davis oxaziridines) as oxidant, generating various 2-spiroquaternary 3-oxindoles in modest to good yields. This method might be useful in the synthesis of indole-based alkaloids bearing 2-spiroquaternary carbon centers. PTS=p-toluenesulfonic acid monohydrate.

Al in: A new strategy was introduced to modify the electronics and steric hindrance of the Pd^II ion in order to change its reactivity towards benzene hydroxylation. In trifluoroacetic acid, free Pd^II ions provide dominantly biphenyl, with phenol as minor product. Ligation of bpym to the Pd^II ion results in its deactivation with regard to benzene functionalization. The addition of the redox inactive Al^III ion to the Pd^II(bpym) complex recovers its catalytic activity, and alters the reactivity of Pd^II ion from benzene coupling to hydroxylation.

On the move: A novel PtCl₂-catalyzed tandem 1,6-enyne cyclization/1,2-acyloxy migration reaction was developed, which was shown to be controlled by substitution effects. Using this method, a series of substituted enol esters containing the cyclopentenyl motif were prepared in moderate to high yields.

Fits like a glove: Separationless and selective electrochemical oxidation of the α-naphthol (α-NAP) isomer yields naphthoquinone species on the surface of multiwalled carbon nanotubes, which can further catalyze the electro-oxidation of NADH and hydrazine at different potentials. The β-NAP isomer failed to show any such electro-oxidation.

Team work: Mesoporous Pt–Ru alloy particles with uniform sizes are synthesized by controlled chemical reduction with ascorbic acid using mesoporous silica as a hard template. Elemental mapping shows uniform distribution of Pt and Ru particles. The electrochemical activity and stability of the alloys towards methanol oxidation much higher than that of mesoporous Pt and commercial Pt catalyst.

Back and forth: Enzymatic, reversible polymerization on gold surfaces was efficiently carried out from surface-tethered self-priming oligodeoxynucleotides in a sequence-specific fashion by using two kinds of enzymes. Taq DNA polymerase, acting as a catalyst, facilitated DNA polymerization, and DNA restriction enzymes cut DNA polymers from the surface.

When shape matters: A facile phosphine-free method for synthesizing PbSe nanocrystals (NCs) with well-controlled size and morphology is reported. These high quality NCs were obtained by the reaction of elemental Se and PbCl₂ using oleylamine as both the ligand and reaction medium. The as-produced PbSe NCs display strong optical limiting effects.

Catalysis³: The semihydrogenation of various alkynes by Pd nanocubes was investigated. The nanocubes exhibited high alkene selectivity and complete cis-selectivity, thus surpassing the Lindlar catalyst. The shape control of Pd nanocrystals provides a simple and efficient way for generating highly selective catalysts for the semihydrogenation of alkynes.

Finger on the pulse: The 2D self-assembly of 2-hydroxy-7-alkoxy-9-fluorenones has been investigated by STM. The structural transition was driven by a voltage pulse applied to the STM tip, owing to the existence of different types of hydrogen bonds.

Passive aggressive: Surface-passivated SBA-15-supported gold nanoparticles that were almost superhydrophobic, with a contact angle of 144°, were prepared by surface passivation. The catalytic activity of this catalyst was more than 14-times that of non-passivated SBA-15 for the reduction of nitrobenzene. This method is a general method for the preparation of surface-passivated catalysts.

Novel organic sensitizers containing the thiazolo[5,4-d]thiazole moiety have been designed and synthesized. A power conversion efficiency of 5.1 % was achieved for quasi-solid-state dye-sensitized solar cells based on (see figure).

Square peg into a round hole: A facile route, based on Steglich esterification, was developed to efficiently synthesize a large variety of C₆₀–porphyrin (Por)-based sphere–square shape amphiphiles (see picture). Photophysical studies suggest an edge-to-face alignment for the C₆₀ and Por moieties.

Anchorman: Porphyrin dyes that contained pyridine moieties as an anchoring group showed intense light adsorption and broadening of their absorption peak. These porphyrin complexes were successfully employed as sensitizers in dye-sensitized solar cells, which exhibited a power-conversion efficiency of 4 % under full-sunlight irradiation (AM 1.5G, 100 mW cm⁻²).

Show and tellurium: CrMn trigonal-bipyramidal clusters, [E₂CrMn₂(CO)₉]²⁻ (E=S, Se, Te), their carbonylated square-pyramidal (SP) clusters, [E₂CrMn₂(CO)₁₀]²⁻ (E=Se, Te), and an arachno-cluster, [Te₂CrMn₂(CO)₁₁]²⁻, are reported. The Te SP cluster was an electron-precise paramagnetic species, whilst the Se analogue diamagnetic. DFT calculations were performed to elucidate their formation, electrochemistry, and UV/Vis absorption.

Who's the boss? In a comprehensive study of catalytic S_N1 type direct substitution of alcohols, the catalysts do not show any general variance in efficiency or selectivity with respect to the alcohols but are highly variable with respect to the nucleophiles. The reactivity of the alcohols is independent of the electrophilicity of the generated carbocations but highly dependent on the ease of formation of the cation.

Don't lose trace: Three Zn^II metal–organic frameworks (Zn-MOFs) based on mixed ligands have been synthesized by a hydrothermal method. Compounds 1 and 2 are 3-dimensional frameworks, and 3 is a layered structure. Changes in the luminescence of the three Zn-MOFs dispersed in different solvents allow for the detection of trace amounts of nitro compounds through a fluorescence quenching mechanism.

Hot rods: Nanorod-assembled FHA microspheres with controllable F contents were synthesized through a facile one-step method without using any template directing agent. The self-assembly process was elucidated according to the change of the morphology of the FHA crystals under different conditions. In addition, FHA showed higher chemical stability than HA under acidic conditions.

A double take: A highly enantioselective catalytic double-Michael addition reaction of substituted benzofuran-2-ones with divinyl ketones promoted by readily accessible tertiary amine–thiourea Cinchona alkaloids has been developed. A number of optically enriched spirocyclic benzofuran-2-ones were prepared in very good yields (up to 99 %), diastereoselectivities (up to 19:1 d.r.), and very good enantioselectivities (up to 92 % ee).

Let′s get (co)rolling: Light absorption in an assembly consisting of a free-base corrole and a Zn porphyrin connected by 1,8 naphthaleneimide results in a sequence of electronic energy transfer processes, ultimately concentrating the energy at the corrole extremity with a yield higher than 90 %.

Do you cross the bridge or do you fade away: Doubly β-to-β bridged cyclic Zn^II porphyrin arrays with carbazole, fluorene, and fluorenone as bridges were constructed. The incorporation of bridge units with different electronic effects results in different photophysical properties of the cyclic Zn^II porphyrin arrays.

Salty but sweet: 1,1,3,3-Tetra(1H-tetrazol-5-yl)propane-based energetic salts were synthesized in a simple and straightforward manner. These salts showed high positive enthalpies of formation, high nitrogen content, good thermal stabilities, and showed moderate detonation properties.

Coming up for ArI: A manganese-catalyzed cross-coupling reaction of thiols with aryl iodides that furnishes aryl thioethers in good to excellent yields has been reported. Functional groups such as unprotected alcohols and chloro substituents are tolerated under these reaction conditions. Moreover, this catalytic system enables the sterically demanding aryl iodides to couple with thiols (see scheme; R=aryl or alkyl).

Outer beauty: The sizes and surface states of carbon quantum dots (CQDs) were tuned by chemical methods. The photoluminescent behavior is related to both the sizes and surface states of the CQDs, but the photocatalytic activities are determined by the surface states alone. The separation and recombination of electron–hole pairs are determined by the degree of upward band bending induced by oxygen-containing groups on the surface of CQDs.