Persistent bidirectional optical switching in the 2D high-spin polymer {[Fe(bbtr)3](BF4)2}∞

In the covalently linked 2D coordination network {[Fe(bbtr)(3)](BF(4))(2)}(∞), bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, the iron(II) centers stay in the high-spin (HS) state down to 10 K. They can, however, be quantitatively converted to the low-spin (LS) state by irradiating into the near-IR spin allowed (5)dd band and back again by irradiating into the visible (1)dd band. The compound shows true light-induced bistability below 100 K, thus, having the potential for persistent bidirectional optical switching at elevated temperatures.     

Synthesis of Substituted Coumarins via Brønsted Acid Mediated Condensation of Allenes with Substituted Phenols or Anisoles

Coumarins were obtained from the condensation of electron-rich arenes with allenes in the presence of TfOH in good yield. Depending on the substituent pattern of allenes employed, the general synthetic method of 4-substituted and 3,4-disubstituted 3-arylcoumarins has been developed. Readily available allenes were employed as the three-carbon atom sources constituting the coumarin skeleton.     

Michael addition kinetics of ethyl acetoacetate and 2-ethylhexyl acrylate in ionic liquids

The Michael addition is one of the most common and versatile methods for making carbon–carbon bonds, however little is known about the potential of utilizing ionic liquids as solvents in these reactions. Initial work from our laboratory is presented, showing that model imidazolium- and phosphonium-based ionic liquid solvents can be used as effective reaction media in the Michael addition. Kinetic data are also reported and the results indicate that the use of ionic liquids as reaction media resulted in an observed rate enhancement when compared with more common organic solvents such as toluene, THF, and DMF. Observed rates were comparable to those observed in DMSO.     

Effect of a perfluorocyclopentene core unit on the structures and photoluminescence of fluorene- and anthracene-based compounds

A novel series of blue luminescent compounds, in which three identical functional groups, such as fluorene, anthracene, and spiro-bifluorene, are linked distortedly around a perfluorocyclopentene core, have been synthesized and characterized. The introduction of a perfluorocyclopentene linkage into the molecular framework leads to an enhancement of the photoluminescence (PL) efficiency and thermal stability. All compounds exhibit intense blue photoluminescence, which has been attributed to fluorene- or anthracene-based π→π* transitions. The maximum emission wavelengths of all compounds at room temperature are in the region of 420-480 nm, with higher PL quantum efficiencies than in 9,10-diphenylanthracene. The electroluminescent (EL) properties of compound 4, 1,2-bis(9,9′-spirobifluoren-2-yl)-3,3,4,4,5,5-hexafluorocyclopentene, were investigated. A multilayer EL device with the configuration of ITO/2TNATA(60 nm)/NPB(20 nm)/ADN:2%-compound-4(35 nm)/Alq₃(20 nm)/LiF(2 nm)/Al has been successfully fabricated.     

Monitoring metal ion binding in single-layer Pseudomonas aeruginosa biofilms using ATR-IR spectroscopy

The binding of metal ions to Pseudomonas aeruginosa PAO1 cells attached to a ZnSe surface has been observed in this research through cation exchange experiments using ATR-IR spectroscopy. A biofilm consisting of a single layer of Pseudomonas aeruginosa PAO1 cells was formed on a ZnSe prism by flowing a bacterial suspension in a 0.03 mol L(-)(1) NaNO(3) solution at pH 5.0 across its surface. Exposure of the biofilm to chromium(III) nitrate solution resulted in increases in all band absorbances. This absorbance increase has been attributed to the binding of chromium(III) to the bacterial exopolymers associated with the prism surface. The chromium(III) binding causes the exopolymers to contract and move the bacterial cell closer to the ZnSe surface. Further study of chromium(III) ion exchange using a mutant P. aeruginosa with a truncated lipopolysaccharide (LPS) chain resulted in much smaller absorbance changes. This observation supports the view that the extension of bacterial exopolymers and hence the distance of the bacterial cell from the surface is strongly influenced by environmental factors such as the presence of metal cations. Following chromium(III) cation exchange, the bacterial band absorbances remained constant even when the bacteria were washed with a 0.03 mol L(-)(1) NaNO(3) solution, indicating that the chromium(III) was irreversibly bound. Ion exchange with nickel(II) and cobalt(II) nitrate solutions within identical biofilms showed that these cations caused relatively small increases in absorbances that were reversible, indicating that nickel(II) and cobalt(II) are less strongly bound than chromium(III) within P. aeruginosa biofilms. The absence of discernible IR spectral changes with metal binding appears to indicate a predominantly electrostatic mechanism for binding of Cr(III), Ni(II), and Co(II) ions by bacteria in the early stages of biofilm formation.     

Quantum-state resolved reaction dynamics at the gas-liquid interface: direct absorption detection of HF(v,J) product from F(2P)+squalane

Exothermic reactive scattering of F atoms at the gas-liquid interface of a liquid hydrocarbon (squalane) surface has been studied under single collision conditions by shot noise limited high-resolution infrared absorption on the nascent HF(v,J) product. The nascent HF(v,J) vibrational distributions are inverted, indicating insufficient time for complete vibrational energy transfer into the surface liquid. The HF(v=2,J) rotational distributions are well fit with a two temperature Boltzmann analysis, with a near room temperature component (T(TD) approximately equal to 290 K) and a second much hotter scattering component (T(HDS) approximately equal to 1040 K). These data provide quantum state level support for microscopic branching in the atom abstraction dynamics corresponding to escape of nascent HF from the liquid surface on time scales both slow and fast with respect to rotational relaxation.     

Statistical mechanical theory for steady state systems. IV. Transition probability and simulation algorithm demonstrated for heat flow

Two microscopic transition theorems are given for the probability of nonequilibrium work performed on a subsystem of a thermal reservoir along the trajectory in phase space of the subsystem. The resultant transition probability is applied to the case of heat flow down an applied temperature gradient. A combined molecular dynamics and Monte Carlo algorithm is given for such a nonequilibrium steady state. Results obtained for the thermal conductivity are in good agreement with previous Green-Kubo and nonequilibrium molecular dynamics results.     

Labeling the planar face of crystalline cellulose using quantum dots directed by type-I carbohydrate-binding modules

We report a new method for the direct labeling and visualization of crystalline cellulose using quantum dots (QDs) directed by carbohydrate-binding modules (CBMs). Two type-I (surface binding) CBMs belonging to families 2 and 3a were cloned and expressed with dual histidine tags at the N- and C-termini. Semiconductor (CdSe)ZnS QDs were used to label these CBMs following their binding to Valonia cellulose crystals. Using this approach, we demonstrated that QDs are linearly arrayed on cellulose, which implies that these CBMs specifically bind to a planar face of cellulose. Direct imaging has further shown that different sizes (colors) of QDs can be used to label CBMs bound to cellulose. Furthermore, the binding density of QDs arrayed on cellulose was modified predictably by selecting from various combinations of CBMs and QDs of known dimensions. This approach should be useful for labeling and imaging cellulose-containing materials precisely at the molecular scale, thereby supporting studies of the molecular mechanisms of lignocellulose conversion for biofuels production.     

Metal‐Free,Regioselective Triazole Ligations that Deliver Locked cis Peptide Mimetics

Metal‐free triazole turns : 1,5‐Disubstituted peptidyl triazoles are obtained regioselectively from the 1,3‐dipolar cycloaddition of peptidyl phosphoranes and azides. Peptide turns are thus formed that contain a conformationally locked cis peptide bond. Being regioselective and free of heavy metals, this reaction may find broad application in chemical biology and medicinal chemistry.