Electropolymerizable 2,2'-Carboranyldithiophenes. Structure-Property Investigations of the Corresponding Conducting Polymer Films by Electrochemistry, UV-Visible Spectroscopy and Conducting Probe Atomic Force Microscopy

Carborane-functionalized conducting polymer films have been electrogenerated in dichloromethane from the anodic oxidation of ortho- (1), meta- (3) and para-carborane (4) isomers linked to two 2-thienyl units. The corresponding electrochemical response was characterized by a broad reversible redox system corresponding to the p-doping/undoping of the polythiophene backbone, the formal potential of which increased in the order poly(1) < poly(3) < poly(4), from ca. 0.50 to 1.15 V vs Ag/Ag(+) 10(-2) M. From further UV-visible spectroscopy analysis, the optical band gap was estimated at 1.8, 2.0 and 2.2 eV for poly(1), poly(3) and poly(4), respectively. The more conjugated and electroconductive character of poly(1) is ascribed to a more planar conformation of the conjugated backbone resulting from an intramolecular β-β' cyclization reaction in the monomer, consequently yielding a fused conjugated polymer. Molecular modeling calculations using the DFT method support this hypothesis. The surface topography and maps of the conductive domains of the electropolymerized films were evaluated by conducting probe AFM. The three polymers exhibit fairly similar morphological characteristics and a surface roughness of ~2 nm. Current-voltage (I-V) characteristics of conducting AFM tip-carborane polymer-ITO junctions showed that poly(1) had the highest conductivity.     

Retinal Conformation and Dynamics in Activation of Rhodopsin Illuminated by Solid‐state 2H NMR Spectroscopy†

Solid‐state NMR spectroscopy gives a powerful avenue for investigating G protein‐coupled receptors and other integral membrane proteins in a native‐like environment. This article reviews the use of solid‐state ²H NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site‐specific ²H NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability ²H NMR spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three‐fold (C₃) axes with an order parameter for the off‐axial motion of For the dark state, the ²H NMR structure of 11‐cis‐retinal manifests torsional twisting of both the polyene chain and the β‐ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11=C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11‐cis to trans isomerization. In addition, ²H NMR has been applied to study the retinylidene dynamics in the dark and light‐activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the β‐ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the β‐ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid‐state ²H NMR thus provides information about the flow of energy that triggers changes in hydrogen‐bonding networks and helix movements in the activation mechanism of the photoreceptor.     

Thermodynamics of fuels with a bio-synthetic component (IV): (Vapor + liquid) equilibrium data for the ternary mixture (ethyl 1,1-dimethylethyl ether + 1-hexene + toluene) at T = 313.15 K

The paper reports experimental p–x data for the ternary system (ethyl 1,1-dimethylethyl ether + 1-hexene + toluene) at T = 313.15 K. The ether, synthesized from ethanol of biological origin, increases the interest of this compound as an additive for gasolines. An isothermal total pressure cell was used for the measurements. Data reduction by Barker’s method provides correlations for G^E, using Wilson, NRTL, UNIQUAC models and the Wohl expansion for the ternary system and the calculation of the vapor phase composition. Good results are obtained for the correlation by all the models.     

Two-colour screening in combinatorial chemistry: prospecting for enantioselectivity in a library of steroid-based receptors

The screening of resin-bound combinatorial libraries with pairs of dye-tagged substrates is a powerful strategy for discovering selective receptors. However, implementation has been hampered by a lack of complementary but chemically similar dyes. We now show that the well-established Disperse Red 1 and the recently-introduced Bristol Blue 1 can be used in parallel to synthesise ‘pseudoenantiomeric’ analogues of N-acetyl-α-amino acids and of the anti-inflammatory drug Naproxen. A steroid-based receptor library has been prepared and screened with these substrates. Preliminary results suggest that some members may be highly enantioselective receptors for N-acetyl-α-amino acids.     

The fractal dimension as estimator of the fractional content of metal matrix composite materials

Electrochemical techniques are applied to estimate the fractal dimension value of electroactive surface structures. However, the fractal dimension value is an abstract concept, which sometimes is hard to understand. Herein, this abstract concept is used to calculate the fractional content of the nickel/graphite–polypropylene hybrid composite material, putting into practice this concept in the study of composite materials.     

Three Redox States of Nitrosyl: NO+, NO., and NO−/HNO Interconvert Reversibly on the Same Pentacyanoferrate(II) Platform

Not so elusive : [Fe^II(CN)₅(HNO)]^3? has been characterized spectroscopically after the two‐electron reduction of nitroprusside (see scheme). The complex is stable at pH 6, slowly decomposing to [Fe(CN)₆]^4? and N₂O. It is deprotonated at increasing pH value with oxidation of bound NO^? to [Fe^II(CN)₅(NO)]^3?. [Fe^II(CN)₅(HNO)]^3? is the first non‐heme iron–nitroxyl complex prepared in aqueous solution that is reversibly redox‐active under biologically relevant conditions.

     

Stir bar sorptive extraction for the analysis of short‐chain chlorinated paraffins in water

An optimised method using stir bar sorptive extraction (SBSE) and a thermal desorption‐GC‐electron capture detector (GC‐ECD) for the determination of short‐chain chlorinated paraffins from water samples was developed. Recoveries near to 100% were obtained by using 20 mm×0.5 mm (length×film thickness) PDMS commercial stir bars from 200 mL spiked water samples and 20% methanol addition with an extraction period of 24 h. Method sensitivity, linearity and precision were evaluated for surface water and wastewater spiked samples. A LOD of 0.03 and 0.04 μg/L was calculated for surface and wastewater, respectively. The precision of the method given as an RSD was below 20% for both matrices. The developed method was applied for the analysis of two real samples from a contaminated river and a wastewater treatment plant. Results were in accordance with those obtained using a previously developed method based on solid phase microextraction (SPME).     

Crystal Structures of the 1,2-Dihydroquinazolinium-4-yl Pd(II) Complexes [PdI{C=N(Xy)CH(R)NHC6H4-2}(CNXy)2]OTf (R?=?Me, CH?=?CH2, C6H4Me-4) and of the 2-Iminoaryl Pd(II) Complex [PdI(C6H4{N=C(H)C6H4Me-4}-2)(2,2′-bipyridine)]

Abstract  

The crystal structures of trans-[PdI{C=N(Xy)CH(R)NHC₆H₄-2}(CNXy)₂]OTf (R = Me (1·CHCl₃) space group P-1, a = 8.7665(4) ?, b = 15.5346(8) ?, c = 16.2415(8) ?, α = 72.698(2)o, β = 78.310(3)o, γ = 88.310(2)o, CH = CH₂ (2·0.5Et₂O) space group P2₁/c, a = 15.7868(6) ?, b = 14.5066(6) ?, c = 18.5814(7) ?, β = 106.707(2)o, C₆H₄Me-4 (Tol) (3) space group P-1, a = 11.96075(5) ?, b = 12.9452(51) ?, c = 13.1263(5) ?, α = 93.306o, β = 95.822(2)o, γ = 94.572(2)o) have been measured. The structural data suggest the existence of some electron delocalization over the heterocyclic ring, the extension of which seems to depend on the R substituent. The complex [PdI{C₆H₄(N=CHTol)-2}(bpy)] (Tol = C₆H₄Me-4, bpy = 2,2′-bipyridine, 4) is the fourth imino-substituted aryl palladium complex. Complex 4 crystallizes in triclinic P-1 with a = 8.7873(5) ?, b = 8.8936(5) ?, c = 13.8375(8) ?, α = 90.116(2)o, β = 92.760(2)o, γ = 106.243(2)o.     

Histamine Molecule and Dianion Oxalate are Efficient Blocks for Building 2D Supramolecular Networks

Abstract  

One salt and two Cu(II) complexes (H₂hsm)(ox), 1, [Cu(hsm)(ox)], 2, and [Cu(hsm)(ox)H₂O], 3, have been synthesized and X-ray characterized (hsm is histamine and ox²⁻ is the oxalate dianion). Starting from the prochiral tetracoordinated complex 2, pentacoordinated complex 3 crystallizes as a racemic mixture of the enantiomeric Δ and Λ isomers, in space group P2₁/c. In all cases, the side chain of the hsm group is gauche, allowing the formation of strong hydrogen bonds in the salt 1, and to chelate the metal center in complexes 2 and 3. The combination hsm/ox seems to favor the formation of 2D supramolecular structures (planes or wavy planes), through efficient networks of N–H···O hydrogen bonds. Cell parameters: 1, P2₁/c, a = 6.260 (2) ?, b = 11.500 (4) ?, c = 12.525 (4) ?, β = 104.047 (17)o; 2, C2/c, a = 10.7966 (13) ?, b = 15.5622 (16) ?, c = 11.3996 (15) ?, β = 106.261 (11)o; 3, P2₁/c, a = 7.0627 (6) ?, b = 7.1323 (6) ?, c = 20.0296 (19) ?, β = 91.529 (7)o.