Multiple hydrogen bonding for reversible polymer surface adhesion

Specific and reversible adhesion of a terminal thymine-functionalized polystyrene (PS-thymine) was demonstrated for a silicon surface with complementary adenine recognition sites. A novel adenine-containing triethoxysilane (ADPTES), which was suitable for covalent attachment to silanol containing surfaces, was synthesized in one step from adenine and 3-isocyanatopropyl triethoxysilane (IPTES). 1H and 13C NMR spectroscopy and fast atom bombardment mass spectroscopy confirmed the chemical structure, and 29Si NMR spectroscopy indicated the absence of any premature hydrolysis of the alkoxysilane derivative. X-ray photoelectron spectroscopy (XPS) and water contact angle measurements indicated the attachment of PS-thymine to silicon surfaces that were modified with a mixture of ADPTES and 3-mercaptopropyl triethoxysilane (MPTES). PS-thymine attachment to surfaces that were modified with only MPTES was not observed. The exclusive attachment of PS-thymine to an ADPTES/MPTES-modified surface confirmed hydrogen bonding-mediated adenine-thymine association to silicon surfaces containing a sufficiently low concentration of adenine recognition sites. Although PS-thymine attachment to the ADPTES/MPTES-modified surfaces was insensitive to THF rinsing, the PS-thymine was completely removed from the surface upon DMSO rinsing because of the disruption of adenine-thymine hydrogen bonding with a more polar aprotic solvent. PS-thymine was successfully reattached to the ADPTES/MPTES-modified surface following the DMSO rinse, demonstrating the solvato-reversible nature of the adenine-thymine association.     

Effect of ligand structure on synergism in Tb3+-aromatic acid complexes: fluorescence lifetime studies

The fluorescence of Tb3+ sensitized by aromatic carboxylic acid ligands (benzoic, monomethylphthalic, monomethylterephthalic, trimesic, terephthalic, isophthalic, phthalic and mellitic acids) and the synergism displayed by these complexes when treated with TOPO/Triton X-100 have been studied by measuring lifetimes of Tb3+ emission. The lifetime of Tb3+ fluorescence was not significantly altered following complex formation with aromatic carboxylic acids, even though a significant enhancement in the Tb3+ fluorescence intensity was observed in every single case. However, when these Tb3+-aromatic acid complexes were treated with TOPO/Triton X-100, the lifetimes of the Tb3+ fluorescence increased markedly, but only with certain acids. Interestingly, even amongst the acids that showed an increase in lifetime with TOPO/Triton X-100, the lifetimes as a function of the pH of the solution was strongly dependent on the structure of the ligand. These differences and the reasons for such behavior are discussed, which shed light on the role of the structure of the ligand on the synergism process.     

Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange

A series of new 1,4,7,10-tetraazacyclododecane-derivatives having a combination of amide and ketone donor groups as side-arms were prepared, and their complexes with europium(III) studied in detail by high resolution NMR spectroscopy. The chemical shift of the Eu(3+)-bound water resonance, the chemical exchange saturation transfer (CEST) characteristics of the complexes, and the bound water residence lifetimes (τ(m)) were found to vary dramatically with the chemical structure of the side-arms. Substitution of ketone oxygen donor atoms for amide oxygen donor atoms resulted in an increase in residence water lifetimes (τ(m)) and a decrease in chemical shift of the Eu(3+)-bound water molecule (Δω). These experimental results along with density functional theory (DFT) calculations demonstrate that introduction of weakly donating oxygen atoms in these complexes results in a much weaker ligand field, more positive charge on the Eu(3+) ion, and an increased water residence lifetime as expected for a dissociative mechanism. These results provide new insights into the design of paramagnetic CEST agents with even slower water exchange kinetics that will make them more efficient for in vivo imaging applications.     

Facile one-pot solvothermal-assisted synthesis of uniform sphere-like Nb2O5 nanostructures for photocatalytic applications

Research on Chemical Intermediates - Preparation of semiconductor nanomaterials with controlled morphology and uniform porous surface is of great interest for enhanced photocatalytic applications....     

Electrochemical biosensors for food analysis

Abstract  Food analysis has become a very important and interesting area of research because of the rapid expansion of food trade and highly increased mobility of today’s populations. Food quality control is essential both for consumer protection and also for the food industry. Application of the electrochemical biosensors in the field of food analysis is promising. This review covers the recent developments and issues in electrochemical biosensors for food analysis, such as ease of preparation, robustness, sensitivity, and realization of mass production of the detection strategies. This review also emphasizes the current development of electrochemical biosensors combined with nanotechnology. Graphical abstract        

Cofluorescence of Eu in complexes of aromatic carboxylic acids

The fluorescence of Eu³⁺ in certain Eu³⁺–aromatic acid complexes were enhanced by over two orders of magnitude, by the addition of La³⁺; a process referred to as cofluorescence. Cofluorescence was observed only with certain aromatic acid ligands; trismesic acid, pyromellitic acid and mellitic acid; thereby clearly establishing a correlation between the structure of the ligand and the process of cofluorescence. While cofluorescence has been extensively studied using β-diketones as ligands, our studies demonstrate cofluorescence for the first time in ligands other than β-diketones. Furthermore, the mechanism of cofluorescence in the aromatic acid complexes studied by us appears to be different from that operating in the β-diketones. While intermolecular energy transfer is believed to occur in the β-diketones, formation of polynuclear complexes appears to be responsible for cofluorescence in the aromatic acid ligands.     

Synthesis-enabled exploration of chiral and polar multivalent quaternary sulfides

An innovative method of synthesis is reported for the large and diverse (RE)₆(TM)_x(Tt)₂S₁₄ (RE = rare-earth, TM = transition metals, Tt = Si, Ge, and Sn) family of compounds (∼1000 members, ∼325 contain Si), crystallizing in the noncentrosymmetric, chiral, and polar P6₃ space group. Traditional synthesis of such phases involves the annealing of elements or binary sulfides at elevated temperatures. The atomic mixing of refractory components technique, presented here, allows the synthesis of known members and vastly expands the family to nearly the entire transition metal block, including 3d, 4d, and 5d TMs with oxidation states ranging from 1+ to 4+. Arc-melting of the RE, TM, and tetrel elements of choice forms an atomically-mixed precursor, which readily reacts with sulfur providing bulk powders and large single crystals of the target quaternary sulfides. Detailed in situ and ex situ experiments show the mechanism of formation, which involves multiphase binary sulfide intermediates. Crystal structures and metal oxidation states were corroborated by a combination of single crystal X-ray diffraction, elemental analysis, EPR, NMR, and SQUID magnetometry. The potential of La₆(TM)_x(Tt)₂S₁₄ compounds for non-linear optical applications was also demonstrated.

Synthesis from atomically-mixed precursors opens up a phase space to hundreds of chiral and polar sulfide semiconductors with almost any transition metal in variable oxidation states.     

Lithium-substituted cobalt oxide spinels LixM1−xCo2O4 (M = Co2+, Zn2+; 0 ≤ x ≤ 0.4)

Substitution of Li⁺ into Co₃O₄ and ZnCo₂O₄ gives rise to the solid solution series Li_xM_1?xCo₂O₄ (M = Co²⁺ or Zn²⁺) having the spinel structure upto x = 0.4. X-Ray diffraction intensities show that the spinel solid solutions are likely to have the following cation distributions: (Co²⁺)_t[Li⁺_xCo³⁺_2?3xCo⁴⁺_2x]₀O₄ and (Zn²⁺_1?xCo²⁺_x)_t[Li⁺_xCo³⁺_2?3xCo⁴⁺_2x]₀O₄. Electrical resistivity and Seebeck coefficient data indicate that the electron transport in these systems occurs by a small-polaron hopping mechanism.     

Add a Pinch of Tetrel: The Transformation of a Centrosymmetric Metal into a Nonsymmorphic and Chiral Semiconductor

Centrosymmetric skutterudite RhP₃ was converted to a nonsymmorphic and chiral compound RhSi_0.3P_2.7 (space group P2₁2₁2₁) by means of partial replacement of Si for P. The structure, determined by a combination of X-ray crystallography and solid state ³¹P NMR, exhibits branched polyanionic P/Si chains that are unique among metal phosphides. A driving force to stabilize the locally noncentrosymmetric cis-RhSi₂P₄ and fac-RhSi₃P₃ fragments is π-electron back-donation between the Rh t_2g-type orbitals and the unoccupied antibonding Si/P orbitals, which is more effective for Si than for P. In situ studies and total energy calculations revealed the metastable nature of RhSi_0.3P_2.7. Electronic structure calculations predicted centrosymmetric cubic RhP₃ to be metallic which was confirmed by transport properties measurements. In contrast, the electronic structure for chiral orthorhombic RhSi_0.3P_2.7 contained a bandgap, and this compound was shown to be a narrow gap semiconductor.