环取代基对金属化聚苯胺衍生物膜修饰电极性能的影响

通过比较聚2，5－二甲氧基苯胺（PDMAn）、聚邻甲基苯胺（POT）和聚间氯苯胺（PmClAn）膜修饰电极的氧化还原电位、沉积在这3种聚合物上的铂微粒的表面形态与晶面取向以及异丙醇在分散Pt微粒的聚苯胺膜修饰电极上的氧化行为，从电子效应和立体效应探讨了聚合物电化学性质与环取代基的关系以及不同聚合基质对Pt沉积机理和有催化性能的影响,结果表明，在硫酸溶液中PDMAn膜修饰电极的氧化还原电位最负、POT次之、PmClAn最正，Pt在PDMAn和POT膜上的电沉积机理与在PmClAn膜上的不同，聚合物膜上沉积的Pt微粒呈现（200)晶面择优取向，其中POT膜上择优取向度最大，PDMAn次之，Pm-ClAn最小，异丙醇在金属化聚合物膜电极上的氧化电位取决于聚苯胺的本质，在POT膜修饰电极上异丙醇的电氧化主要发生在POT的活性电位区，而在PDMAn与PmClAn膜上的电氧化则主要发生在Pt上的氧化电位区，说明聚合物膜不仅作为Pt微粒的分散介质，而且本身有产生催化作用。     

Hydride-containing 2-Electron Pd/Cu Superatoms as Catalysts for Efficient Electrochemical Hydrogen Evolution

The first hydride-containing 2-electron palladium/copper alloys, [PdHCu₁₁{S₂P(OⁱPr)₂}₆(C≡CPh)₄] ( PdHCu₁₁ ) and [PdHCu₁₂{S₂P(OⁱPr)₂}₅{S₂PO(OⁱPr)} (C≡CPh)₄] ( PdHCu₁₂ ), are synthesized from the reaction of [PdH₂Cu₁₄{S₂P(OⁱPr)₂}₆(C≡CPh)₆] ( PdH₂Cu₁₄ ) with trifluoroacetic acid (TFA). X-ray diffraction reveals that the PdHCu₁₁ and PdHCu₁₂ kernels consist of a central PdH unit encapsulated within a vertex-missing Cu₁₁ cuboctahedron and complete Cu₁₂ cuboctahedron, respectively. DFT calculations indicate that both PdHCu₁₁ and PdHCu₁₂ can be considered as axially-distorted 2-electron superatoms. PdHCu₁₁ shows excellent HER activity, unprecedented within metal nanoclusters, with an onset potential of −0.05 V (at 10 mA cm⁻²), a Tafel slope of 40 mV dec⁻¹, and consistent HER activity during 1000 cycles in 0.5 M H₂SO₄. Our study suggests that the accessible central Pd site is the key to HER activity and may provide guidelines for correlating catalyst structures and HER activity.     

Layer-by-layer assembled composite films of side-functionalized poly(3-hexylthiophene) and CdSe nanocrystals: electrochemical, spectroelectrochemical and photovoltaic properties

Regioregular poly(3-hexylthiophene) containing one diaminopyrimidine side group per ten repeat units (P3HT-co-P3(ODAP)HT) can form molecular composites with 1-(6-mercaptohexyl)thymine capped CdSe nanocrystals (CdSe(MHT)) via hydrogen bonds directed molecular recognition. Here we report complementary spectroscopic, electrochemical and spectroelectrochemical investigations of both the functionalized poly(thiophene) and its composite with the nanocrystals, the latter being fabricated using the layer-by-layer (LbL) deposition technique. UV-Vis-NIR and Raman spectroelectrochemical investigations unequivocally show that the onset of the first anodic peak in the cyclic voltammogram of the copolymer can be attributed to the oxidation of the pi-conjugated backbone in the polymer chains. For this reason, it is possible to determine the width and the position of its band gap (corresponding to the pi-pi* transition) by UV-Vis spectroscopy combined with cyclic voltammetry. These studies show that the polymer exhibits a slightly larger band gap with the HOMO level insignificantly lower in energy (by 0.03 eV) as compared to the case of regioregular poly(3-hexylthiophene) of comparable degree of polymerization. Hydrogen bond interactions of the polymer with CdSe(MHT) in the molecular composite result in a hypsochromic shift of the band corresponding to the pi-pi* transition from 504 nm to 488 nm. This can be taken as a spectroscopic manifestation of the conformational changes induced by shortening of the conjugation length. The observed spectral modifications are consistent with electrochemically determined lowering of the polymer HOMO level (from -4.91 eV in the pure polymer to -4.99 eV in the composite). Cyclic voltammetry studies supported by spectroelectrochemistry also show that the redox stability of CdSe(MHT) in the molecular composite with P3HT-co-P3(ODAP)HT is lower than that determined for stearate-capped nanocrystals. Their irreversible oxidation starts at E = +0.7 V vs. Ag/0.1 M Ag(+)i.e. at potentials by ca. 0.3 V lower than the oxidation of stearate stabilized CdSe nanocrystals of the same size. We show that-despite these modifications-the alignment of the HOMO and LUMO levels of the composite components remains appropriate for its use in hybrid solar cells, which is demonstrated by the photovoltaic effect observed for the LbL-processed composite sandwiched between two electrodes.     

Transport-limited current and microsonoreactor characterization at 3 low frequencies in the presence of water, acetonitrile and imidazolium-based ionic liquids

A microsonoreactor, specially designed to carry out electrochemical tests in a room-temperature ionic liquid medium (RTIL), was studied. The cell, based on a particular design consisting of off-setting the ultrasonic probe out of the reaction volume, was characterized by several methods such as calorimetry, dosimetry and mass transfer measurements. The main result concerns the specific behaviour of the ionic liquid under ultrasonic irradiation. For example, the mass-transfer enhancement is particularly high, characterized by an average Sherwood number of 6500 while the value obtained with an electrode rotating at 4500 rpm is only 1200.     

The preparation of new phosphorus-centered functional groups for modified oligonucleotides and other natural phosphates

Efforts to develop synthetic methodologies allowing the preparation of alpha,alpha- difluorophosphonothioates, alpha,alpha-difluorophosphonodithioates, alpha,alpha-difluorophosphono- trithioates, and alpha,alpha-difluorophosphinates are reviewed in the light of applications in the field of modified oligonucleotides and cyclitol phosphates. Two successful approaches have been developed, based either on the addition of phosphorus-centered radicals onto gem-difluoroalkenes or on a process involving the addition of lithiodifluorophosphono- thioates 91 onto a ketone and the subsequent deoxygenation reaction of the adduct. The radical route successfully developed a practical route to alpha,alpha-difluoro-H-phosphinates which proved to be useful intermediates to a variety of phosphate isosters. The ionic route led to the first preparation of phosphonodifluoromethyl analogues of nucleoside- 3'-phosphates.     

Donor/acceptor-substituted anthradithiophene materials: synthesis, optical and electrochemical properties

The synthesis and characterization of two new anthradithiophene (ADT) derivatives bearing electron donating (triphenylamine) or accepting (5-formylthiophen-2-yl unit) moieties have been performed to assess their potential as materials for organic photovoltaics. Optical spectroscopy was used to evaluate the effect of electron rich/poor substituents on the visible absorption spectrum and on the stability towards photo-oxidation. The results are interpreted with the assistance of quantum-chemical calculations and cyclic voltammetry experiments.     

Synthese et N-Acylation Regiospecifique de 1,2,5-Thiadiazolidines 1,1-Dioxydes Chirales

The regiospecific synthesis of chiral N-acyl cyclosulfamides (sulfa-analogues of cyclic ureas) was carried out starting from chlorosulfonyl isocyanate (CSI), 1-substituted N-benzyl-2-chloroethylamine hydrochloride and acyl chloride. Chiral N-acyl-thiadiazolidines 1,1-dioxides have been prepared in high yield starting from the corresponding cyclosulfamides acyl chloride, triethylamine and a catalytic amount of 4-(N,N-dimethylamino)pyridine. L'accès régiospécifique aux cyclosulfamides chiraux N-acylés (analogues sulfonés d'urèes cycliques) a été développé à partir de l'isocyanate de chlorosulfonyle, de N-benzyl-2-chloroéthylamine chirale substituée en position 1 et de chlorure d'acide. Les N-acyl thiadiazolidines 1,1-dioxydes chirales ont été préparées avec des rendements élevés à partir du cyclosulfamide correspondant par traitement avec un chlorure d'acide en présence de triéthylamine et une quantité catalytique de 4-(N,N-dimethylamino)pyridine.     

New Application of the Mitsunobu Reaction for the Preparation of (Δ-2) Derivatives in Terpenic Series

Application of the Mitsunobu reaction to various 3β-(equatorial)-hydroxy-4,4-dimethyl terpenic compounds provides the 2-ene-derivatives in good yields. A discussion about the mechanisms involved, and full details on the modified experimental protocol are given.