In situ observations of water production and distribution in an operating H2/O2 PEM fuel cell assembly using 1H NMR microscopy

Proton NMR imaging was used to investigate in situ the distribution of water in a polymer electrolyte membrane fuel cell operating on H2 and O2. In a single experiment, water was monitored in the gas flow channels, the membrane electrode assembly, and in the membrane surrounding the catalysts. Radial gradient diffusion removes water from the catalysts into the surrounding membrane. This research demonstrates the strength of 1H NMR microscopy as an aid for designing fuel cells to optimize water management.     

Mechanisch-chemische Reaktionen in künstlichen organischen Fasern

Zusammenfassung Die beim Verstrecken sowie Mahlen von künstlichen organischen Fasermaterialien (Polyester-, Polyamid- und Viskosefasern) als Folge homolytischer Kettenspaltungen auftretende Freiradikalbildung wurde untersucht.

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Mechanochemical reactions in synthetic organic fibres

The formation of free radicals due to homolytic chain fission occurring in the course of stretching and grinding of synthetic organic fibres (polyester, polyamide, and viscose fibres) has been investigated by means of ESR spectroscopy.

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Die Elektronspinresonanz-Messungen wurden im Chemischen Institut der Sir George Williams University, Montreal, Canada, durchgeführt.     

Supramolecular Metal Complex with Ferrocene-conjugated Macrocyclic Triaza Crown Ether as Ligand and Its Electrochemical Property

LigandscontainingelectrochemicallyresponsivecentrearegoodsubjectsforthestUdyofintfamolecularandhost-guestillteraction.Forthisreason,tYemendousamoulltsofsuchligandsandtheircomplexeshavebeensynthesized.'-'AnobservationfromthestudiesofthesecomPlexesisthattheguestionhasapermrbationonthehostcelltre.2'7-9Forexample,itwasdocumelltedthatintroductionofCo(II)ionontoN-ferrocenylmethyl-l,4,7-triazacyclononane(fcmtacn)causesapositiveshiftintheredoxpotentialofferrocenylgroupfromthatofferrocenegroupinfree…     

The use of 1H NMR microscopy to study proton-exchange membrane fuel cells.

To understand proton-exchange membrane fuel cells (PEMFCs) better, researchers have used several techniques to visualize their internal operation. This Concept outlines the advantages of using 1H NMR microscopy, that is, magnetic resonance imaging, to monitor the distribution of water in a working PEMFC. We describe what a PEMFC is, how it operates, and why monitoring water distribution in a fuel cell is important. We will focus on our experience in constructing PEMFCs, and demonstrate how 1H NMR microscopy is used to observe the water distribution throughout an operating hydrogen PEMFC. Research in this area is briefly reviewed, followed by some comments regarding challenges and anticipated future developments.     

A STUDY OF THE SAFRANINE-ASCORBIC ACID PHOTOCHEMICAL REDOX REACTION

Abstract— Flash-photolysis of safranine in deoxygenated 5 per cent aqueous pyridine produces a transient bleaching, which disappears by a second order process. Very probably this transient species consists of a pair of radicals or radical ions and not of the safranine in the triplet state. These radicals are also produced in chlorophyll sensitized reactions. Present results combined with previous work by us[I] indicate that the chlorophyll sensitization of safranine bleaching involves the formation of these radicals.
The direct photochemical reduction of safranine to its leuco form occurs through the intermediate formation of the radicals. The appearance and disappearance of these radicals is fast compared to the role of photochemical formation and thermal disappearance of leuco safranine. Ascorbic acid influences but is not essential to the photo-bleaching of safranine in 5 per cent aqueous pyridine. An increase in ascorbic acid concentration increases the steady-state yield of the radicals but decreases the steady-state yield of the leuco safranine. In the absence of ascorbic acid or other added substance, safranine photobleaches irreversibly in deoxygenated 5 per cent aqueous pyridine. A plausible mechanism is proposed in explanation of the direct photochemical reduction of safranine.     

Design and characterization of libraries of molecular fragments for use in NMR screening against protein targets

We have designed four generations of a low molecular weight fragment library for use in NMR-based screening against protein targets. The library initially contained 723 fragments which were selected manually from the Available Chemicals Directory. A series of in silico filters and property calculations were developed to automate the selection process, allowing a larger database of 1.79 M available compounds to be searched for a further 357 compounds that were added to the library. A kinase binding pharmacophore was then derived to select 174 kinase-focused fragments. Finally, an additional 61 fragments were selected to increase the number of different pharmacophores represented within the library. All of the fragments added to the library passed quality checks to ensure they were suitable for the screening protocol, with appropriate solubility, purity, chemical stability, and unambiguous NMR spectrum. The successive generations of libraries have been characterized through analysis of structural properties (molecular weight, lipophilicity, polar surface area, number of rotatable bonds, and hydrogen-bonding potential) and by analyzing their pharmacophoric complexity. These calculations have been used to compare the fragment libraries with a drug-like reference set of compounds and a set of molecules that bind to protein active sites. In addition, an analysis of the overall results of screening the library against the ATP binding site of two protein targets (HSP90 and CDK2) reveals different patterns of fragment binding, demonstrating that the approach can find selective compounds that discriminate between related binding sites.     

Synthesis via pummerer intermediates. IV. Synthesis of 1-(4-hydroxy-2-oxo-2H-1-benzopyran-3-yl)pyridinium hydroxide inner salt derivatives and 3-(2H)benzofuranones by the action of phosgene in pyridine on 2-hydroxy-1-[(methylsulfinyl)acetyl]benzene derivatives

The treatment of ketosulfoxide 1 with phosgene in pyridine gave a mixture of 1-(4-hydroxy-8-methoxy-2-oxo-2H-1-benzopyran-3-yl)pyridinium hydroxide inner salt ( 4 ) and 7-methoxy-2-(methylthio)-3-(2H)benzofuranone ( 7 ). Ketosulfoxides 8 and 11 behaved similarly. The inner salt structure assigned to compounds 4, 10 , and 13 was confirmed by the unambiguous synthesis of 10 and 13 from hydroxycoumarins 15 and 18 .     

An Investigation of 1:1 Adducts of Gallium Trihalides with Triarylphosphines by Solid‐State 69/71Ga and 31P NMR Spectroscopy

Several 1:1 adducts of gallium trihalides with triarylphosphines, X₃Ga(PR₃) (X=Cl, Br, and I; PR₃=triarylphosphine ligand), were investigated by using solid‐state ^69/71Ga and ³¹P NMR spectroscopy at different magnetic‐field strengths. The ^69/71Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the ⁷¹Ga quadrupolar coupling constants (C_Q(⁷¹Ga)) range from approximately 0.9 to 11.0 MHz . The spans of the gallium magnetic shielding tensors for these complexes, δ₁₁?δ₃₃, range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In^III–phosphine complexes. This experimental trend, attributed to spin‐orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C_Q(^69/71Ga) for some of the adducts were determined from the analysis of the ³¹P NMR spectra acquired with magic angle spinning (MAS). The ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga, ³¹P) values, as well as their signs, were also determined; values of ¹J(⁷¹Ga,³¹P) range from approximately 380 to 1590 Hz. Values of ¹J(^69/71Ga,³¹P) and ΔJ(^69/71Ga,³¹P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi‐contact and spin‐dipolar Fermi‐contact mechanisms make important contributions to the ¹J(^69/71Ga,³¹P) tensors. The ³¹P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single‐crystal X‐ray diffraction data for Br₃Ga[P(p‐Anis)₃] and I₃Ga[P(p‐Anis)₃] were obtained.     

超拉伸聚乙烯的弹性模量和导热性能

为了揭示聚合物分子链伸展、取向的本征特性，发展了两个新的测量方法和实验装置，用于研究拉伸比高达２００的超拉伸聚乙烯凝胶的弹性性能、传热性能和聚合物结构的关系．应用激光脉冲热致超声法给出材料拉伸方向和横向杨氏模量，应用激光脉冲光热辐射法给出拉伸方向，横向和厚度方向的导热系数．随拉伸比λ的增加，轴向杨氏模量急剧的增加，而横向的仅有少许减小．导热系数具有相似的特性．本文发现当λ＝２００时，这种拉伸取向聚乙烯的轴向模量可达钢的８０％，而导热系数甚至可达２倍，直至成为热的良导体，这是由于在高拉伸比时形成了相当数量的伸展分子链构成的针状晶体———晶桥．本文提出晶桥作为短纤维分散相的取向聚合物的结构模型，对于超拉伸聚乙烯的上述特性可以进行统一描述和定量化分析，和实验结果很好符合．     

含9-丁基咔唑基二炔/聚炔汞及二炔金配合物的合成与性质

合成了9-丁基咔唑基聚炔汞聚合物[—HgC≡CRC≡C—]n及其二聚体[MeHgC≡CRC≡CHgMe]和金的二聚体[(PPh3)AuC≡CRC≡CAu(PPh3)](R=9-丁基咔唑基). 用 1H NMR, 13C NMR, 31P NMR, FTIR, FAB-MS, UV-Vis, Fluorescence及Phosphorescence 光谱对其进行了表征. 结果表明, 体系中金和汞产生的重原子效应可以促进单线激发态S1与三线激发态T1的系间跃迁, 使标题化合物产生有机三线态发光.