Dirhodium paddlewheel with functionalized carboxylate bridges: new building block for self-assembly and immobilization on solid support

A new dirhodium(II,II) paddlewheel complex, [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)] (1), has been synthesized using a predesigned functionalized carboxylate, namely, 4-(ethoxycarbonyl)benzoate. The target product has been crystallized from the acetone solution and structurally characterized as a bis-acetone adduct, [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)(OCMe(2))(2)]·C(6)H(14) (2). By utilizing the ability of dangling ester groups to coordinate to open axial ends of neighboring dirhodium units, 1 can self-assemble to form 2D networks upon crystallization from solutions of noncoordinating solvents such as chlorobenzene and chloroform. The resulting [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)]·2C(6)H(5)Cl (3) and [Rh(2)(O(2)CC(6)H(4)COOC(2)H(5))(4)]·2CHCl(3) (4) products have microporous solid state structures with the pores filled with the corresponding disordered solvent molecules. Notably, 3 and 4 represent unique examples of 2D extended frameworks based on dirhodium tetracarboxylate paddlewheel units devoid of any exogenous ligands. In solution, the dangling ends of carboxylate bridges of 1 have been successfully utilized for condensation reaction with the selected solid support, benzylamine-functionalized polystyrene, allowing successful heterogenization of dirhodium units through the equatorial covalent attachment to the substrate. The resulting solid product was tested as a catalyst in the cyclopropanation reaction of styrene with methyl phenyldiazoacetate to show good yields and diastereoselectivity.     

Oxyanion-encapsulated caged supramolecular frameworks of a tris(urea) receptor: evidence of hydroxide- and fluoride-ion-induced fixation of atmospheric CO2 as a trapped CO3(2-) anion

A tris(2-aminoethyl)amine-based tris(urea) receptor, L, with electron-withdrawing m-nitrophenyl terminals has been established as a potential system that can efficiently capture and fix atmospheric CO(2) as air-stable crystals of a CO(3)(2-)-encapsulated molecular capsule (complex 1), triggered by the presence of n-tetrabutylammonium hydroxide/fluoride in a dimethyl sulfoxide solution of L. Additionally, L in the presence of excess HSO(4)(-) has been found to encapsulate a divalent sulfate anion (SO(4)(2-)) within a dimeric capsular assembly of the receptor (complex 2) via hydrogen-bonding-activated proton transfer between the free and bound HSO(4)(-) anions. Crystallographic results show proof of oxyanion encapsulation within the centrosymmetric cage of L via multiple N-H···O hydrogen bonds to the six urea functions of two inversion-symmetric molecules. The solution-state binding and encapsulation of oxyanions by N-H···O hydrogen bonding has also been confirmed by quantitative (1)H NMR titration experiments, 2D NOESY NMR experiments, and Fourier transform IR analyses of the isolated crystals of the complexes that show huge spectral changes relative to the free receptor.     

Wound infection kinetics probed by MALDI-MS: rapid profiling of Staphylococcus aureus in mice

Using direct matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS), we were able to investigate the role of the clinically important bacteria, Staphylococcus aureus, in wound infections using mice. The infection kinetics of S. aureus at the wound site and the host immune response has been investigated using MALDI-MS. In this study, for the first time, we report the growth pattern of S. aureus infection at a wound site. Using mice wound infection models; the following study fingerprints the bacterial-host (mice) response at the wound site as a function of increasing wound infection in order to establish the infection pattern of Staphylococcus aureus in wounds. The current approach is extremely simple, rapid, highly selective, sensitive and established MALDI-MS as a versatile tool for detecting bacteria in clinical samples, such as those collected from wound sites.     

Tracing the pathogen Staphylococcus aureus on laboratory ants using physical preconcentration coupled ZnO nanoparticle assisted MALDI-TOF MS

Ants and humans coexist closely and for the most part happily. We consider ants to be harmless, small beings--we have no problem picking them out of our tea cups or sugar jars, throwing them away and continuing to consume the food. This paper is an eye-opener that these ants are not as harmless as they may seem. In particular, our relationship with those present in bacteria-rich environments (e.g. a microbiological lab) need to be reconsidered. From an analytical point of view we have applied the physical preconcentration coupled ZnO NPs assisted MALDI-MS (PP-MALDI-MS) as a novel and sensitive technique for detecting bacteria on the surface of a species of ant present in our laboratory. The preconcentration methods consist of simple techniques comprising of vortex combined with centrifugation or ultrasonication resulting in increasing sample concentration up to the MALDI-MS detection limit. ZnO NPs were used to further enhance the bacterial signals for culture free rapid analysis using MALDI-MS. The importance of a vortex-combined centrifugation approach, using a large number of samples (large number of ants) and decreasing the suspension volume and addition of sample to ZnO NPs (3.5g L(-1)) were found to be crucial prerequisites for increasing MALDI-MS detection of bacteria on ants. We were able to identify the pathogenic clinically important Staphylococcus aureus on the surface of the ants. The bacterial identification was validated using ClinPro 2.1.     

A Convergent Synthesis of a Twelve‐Membered Macrolide Natural Product, (6R,12S)‐6‐Hydroxy‐12‐methyl‐1‐oxacyclododecane‐2,5‐dione

A new polyketide metabolite, the twelve‐membered macrolide 1 , isolated from the endophytic fungal strain Cladosporium tenuissimum LR 463 of Maytenus hookeri, whose structure had been determined as (6R,12S)‐6‐hydroxy‐12‐methyl‐1‐oxacyclododecane‐2,5‐dione, was synthesized for the first time by a convergent strategy via Yamaguchi esterification of 2 with 3 and ring‐closing metathesis (RCM) to afford the cyclic ester 1 that was eventually transformed to the target molecule. However, the total synthesis revealed that the assigned structure of the natural product is not correct.     

Photoinduced effects in nematic liquid crystals

Temperature, concentration of the solvent and pressure are the parameters that are well known to bring about phase transitions in liquid-crystalline systems. In recent years a new parameter has been added to this list: light. The principle behind these photoinduced transitions is the light-driven shape transformation of certain photoactive materials like, e.g., azobenzene. In this article, we present results of various aspects of our recent investigations on such photoinduced transitions in the nematic phase and highlight the feature that light is a new tool to study phase transitions and the associated critical phenomena.     

EPR,optical absorption and superposition model studies of Fe3+-doped cesium chloride single crystals: a case of substitutional as well as interstitial sites

An electron paramagnetic resonance study of Fe³⁺-doped cesium chloride single crystals was carried out at room temperature. Three sites are observed. The spin Hamiltonian parameters were determined from the angular variation of the observed resonance lines. The hyperfine structure is observed due to the presence of Fe⁵⁷ centers. At site I, Fe³⁺ enters the lattice substitutionally, replacing Cs⁺ in the cubic symmetry of the crystal, whereas at sites II and III, Fe³⁺ enters the lattice interstitially. The local site symmetry of Fe³⁺ in the host lattice is considered to be orthorhombic. An optical absorption study of the crystal was also performed at room temperature. The observed bands were assigned and the Racah inter-electronic repulsion parameters (B and C) and the cubic crystal field splitting parameter (Dq) were determined. On the basis of EPR and optical data, the nature of the metal–ligand bonding in the crystal was determined. The crystal field parameters were evaluated using the superposition model and then used in the microscopic spin Hamiltonian and perturbation equations to determine the zero-field splitting parameters (ZFSPs) theoretically for all sites observed. The theoretical ZFSPs are in good agreement with the experimental values.     

High Pressure Studies on Partially Bilayer and Monolayer Smectics

We have carried out pressure studies on the eighth and ninth members of the homologous series 4-alkoxybenzoyloxy-4′-cyanoazobenzene (nOBCAB). It is found that the pressure behavior of the monolayer smectic A (A₁) phase is entirely different from that of the partially bilayer smectic A (A₁) phase. The A₁ -nematic phase boundary is a straight line at all pressures and the range of the A_d phase increases with increasing pressure. On the other hand, the A_d -nematic phase boundary is elliptic in shape and the A_d phase gets bounded. These results emphasize the fact that the pressure behavior of the A phase is strongly related to the extent of overlap of the molecules in the layer.     

Late time acceleration in f(G) model

Late time transition is obtained with a function of Gauss Bonnet curvature $f(G)$ in the Einstein Hilbert action with a matter field in a FLRW spacetime assuming an ansatz without a specific $f(G)$ . Late time accelerating expansion is either a phantom era without Big Rip singularity or a quintessence era or a de-Sitter era of expansion. The equation of state parameter, jerk and snap parameters support observational data and the function $f(G)$ obtained from the solution supports earlier works.