Electron transfer/transport at metal-molecule interfaces probed by femtosecond time-resolved two-photon photoemission: Heptane and fullerene on Au(111)

Electron transfer and transport at metal-molecule interfaces has been a central problem in a number of disciplines. There is renewed interest in this problem from the rapidly growing field of molecule-based electronics, where the so-called “contact problem” is usually probed in transport measurements. Here, we probe interfacial electron transfer/transport using time-resolved two-photon photo-emission spectroscopy. Such an approach allows us to quantitatively measure the energetic alignment of occupied and unoccupied molecular orbitals to the metal Fermi level, the electronic coupling strength (or spectral density) between the molecular orbital and the metal substrate, and electronic-nuclear coupling leading to dynamic localization. These three types of information are in fact key ingredients in quantitative theories for electron transfer and transport at molecule-metal surfaces. Recent examples from our laboratory are used to illustrate the point. They include femtosecond dynamics of image potential resonances on heptane-covered Au(111) and exciton relaxation dynamics in C₆₀ epitaxial films on Au(111). On heptane/Au(111), the lifetime of the n = 1 image potential resonance increases from 52 fs at one monolayer (ML) coverage to 700 fs at 2 ML and 2.8 ps at 3 ML. On C₆₀/Au(111), the Frenkel exciton (involving the LUMO+1 level) couples over long distance to the metal substrate, with lifetime of 350 fs at 30 ML to 80 fs at 2 ML coverage. The film-thickness-dependent decay dynamics in both cases can be attributed to interfacial electron transfer. Fitting the distance-dependent electron transfer rates to a simple exponential function gives the characteristic distance parameter of ß = 0.6 ± 0.1 and 0.023 ± 0.005 Å⁻¹ for heptane- and C₆₀-covered Au(111), respectively. The difference in the ß parameters illustrates the essential role of the electronic structure of molecules in mediating interfacial electron transfer/transport.     

跟踪式热平衡温度测量

介绍了跟踪式热平衡温度测量的原理：当检测头与被测体靠近时，通过对流换热形成梯度为零的温度场，因而二者温度相等。这种梯度为零的温度场是通过对检测头的一端制冷（或加热）跟踪被测体的温度形成的．最后给出了静态和动态实验的测试结果。     

Isomeric Carborane Neuromuscular Blocking Agents

We synthesized a family of neuromuscular blocking agents (NMB) based on decamethonium, but containing a carborane cluster in the methylene chain between the two quaternary ammonium groups. The carborane cluster isomers o-NMB, m-NMB, and p-NMB were tested in animals for neuromuscular block and compared with agents used clinically: rocuronium and decamethonium. All three isomers caused reversible muscle weakness in mice as determined by grip strength and inverted screen tests, with a potency rank of p-NMB > rocuronium > decamethonium > m-NMB > o-NMB. The mechanism of action of the compounds was determined by using the in vitro rat phrenic nerve hemi-diaphragm preparation and electrophysiologic measurements in cells. Neostigmine reversed hemi-diaphragm weakness caused by the three isomers and rocuronium, but not succinylcholine. In electrophysiologic recordings of currents through acetylcholine receptor channels, the carborane compounds did not activate channel activity but did inhibit channel activation by acetylcholine. These results demonstrate that the carborane neuromuscular blocking agents are non-depolarizers in contrast to the depolarizing action of the parent compound.     

Native Mass Spectrometry for the Study of PROTAC GNE-987-Containing Ternary Complexes

PRO teolysis TA rgeting C himeras (PROTACs) promote the degradation, rather than inhibition, of a drug target as a mechanism for therapeutic treatment. Bifunctional PROTAC molecules allow simultaneous binding of both the target protein and an E3-Ubiquitin ligase, bringing the two proteins into close spatial proximity to allow ubiquitinylation and degradation of the target protein via the cell's endogenous protein degradation pathway. We utilized native mass spectrometry (MS) to study the ternary complexes promoted by the previously reported PROTAC GNE-987 between Brd4 bromodomains 1 and 2, and Von Hippel Lindeau E3-Ubiquitin Ligase. Native MS at high resolution allowed us to measure ternary complex formation as a function of PROTAC concentration to provide a measure of complex affinity and stability, whilst simultaneously measuring other intermediate protein species. Native MS provides a high-throughput, low sample consumption, direct screening method to measure ternary complexes for PROTAC development.     

ACE-Asia intercomparison of a thermal-optical method for the determination of particle-phase organic and elemental carbon

A laboratory intercomparison of organic carbon (OC) and elemental carbon (EC) measurements of atmospheric particulate matter samples collected on quartz filters was conducted among eight participants of the ACE-Asia field experiment The intercomparison took place in two stages: the first round of the intercomparison was conducted when filter samples collected during the ACE-Asia experiment were being analyzed for OC and EC, and the second round was conducted after the ACE-Asia experiment and included selected samples from the ACE-Asia experiment Each participant operated ECOC analyzers from the same manufacturer and utilized the same analysis protocol for their measurements. The precision of OC measurements of quartz fiber filters was a function of the filter's carbon loading but was found to be in the range of 4-13% for OC loadings of 1.0-25 microg of C cm(-2). For measurements of EC, the precision was found to be in the range of 6-21% for EC loadings in the range of 0.7-8.4 microg of C cm(-2). It was demonstrated for three ambient samples, four source samples, and three complex mixtures of organic compounds that the relative amount of total evolved carbon allocated as OC and EC (i.e., the ECOC split) is sensitive to the temperature program used for analysis, and the magnitude of the sensitivity is dependent on the types of aerosol particles collected. The fraction of elemental carbon measured in wood smoke and an extract of organic compounds from a wood smoke sample were sensitive to the temperature program used for the ECOC analysis. The ECOC split for the three ambient samples and a coal fly ash sample showed moderate sensitivity to temperature program, while a carbon black sample and a sample of secondary organic aerosol were measured to have the same split of OC and EC with all temperature programs that were examined.     

Temporal changes in macroinvertebrate assemblages following experimental flooding in permanent and temporary wetlands in an Australian floodplain forest

The River Murray, Australia, is a highly regulated river from which almost 80% of mean annual flow is removed for human use, primarily irrigated agriculture. Consequent changes to the pattern and volume of river flow are reflected in floodplain hydrology and, therefore, the wetting/drying patterns of floodplain wetlands. To explore the significance of these changes, macroinvertebrate samples were compared between permanent and temporary wetlands following experimental flooding in a forested floodplain of the River Murray. Weekly samples from two permanent wetlands and four associated temporary sites were used to track changes in macroinvertebrate assemblage composition. Non‐metric multidimensional scaling was used to ordinate the macroinvertebrate data, indicating consistent differences between the biota of permanent and temporary wetlands and between the initial and later assemblages in the temporary sites. There were marked changes over time, but little sign that the permanent and temporary assemblages were becoming more alike over the 25‐week observation period. The apparent heterogeneity of these systems is of particular importance in developing river management plans which are likely to change flooding patterns. Such plans need to maintain a mosaic of wetland habitats if floodplain biodiversity is to be supported. Copyright © 2002 John Wiley & Sons, Ltd.