In situ determination of the adsorption characteristics of a zeolite membrane

A methodology based on adsorption-branch porosimetry is described for in situ measurement of the adsorption of condensable gases within the pore structure of inorganic membranes. The method is applied to the study of n-hexane and p-xylene adsorption in a high-silica, MFI zeolite membrane. The results, interpreted in terms of a simple model for competitive adsorption effects on the permeance of a non-adsorbing gas, yield Langmuir adsorption constants and Henry’s law constants for n-hexane and p-xylene that are in excellent agreement with measurements on bulk materials. The method is proposed for the fundamental study of fouling characteristics of inorganic membranes, especially in cases where a true bulk surrogate is not available.     

Quantitative Evaluation of Oxygenation and Metabolism in the Human Skeletal Muscle

The forearm muscles of five healthy males were monitored for changes in microvessel hemoglobin saturation (SO_2-TRS) by near infrared time-resolved spectroscopy (NIR_TRS) and changes in phosphorus metabolites by magnetic resonance spectroscopy (³¹P-MRS) during 12 min of resting arterial occlusion. Muscle oxygenation and phosphorus metabolites were also measured during grip exercises at varying intensities. Upon the initiation of occlusion, SO_2-TRS fell progressively until it reached a plateau in the latter half of the occlusion. Phosphocreatine (PCr) began to decrease around 6 min after the initiation of arterial occlusion. The resting O₂ store and O₂ consumption were 295 μM and 0.95 μM/sec, respectively-values which reasonably agree with the reported results. A significant correlation was observed between the changes in SO_2-TRS and PCr during exercise (r² = 0.80, p < 0.001). These results indicate that NIR_TRS is able to provide reliable information about resting metabolism and oxidative rate during exercise. NIR_TRS and MRS are useful to monitor oxygenation and energetics noninvasively in the human muscle.     

Theoretical Studies of Charged Defect States in Doped Polyacetylene and Polyparaphenylene

Defect statecalculations have been per formed for polyacetylene and polybparaphenylene in the fraamework of the Su, schriever, and Heeger Hamiltonian. In polyacetylene, the study of the energetics of the separation of the radical(natural defect)-ion(charged defect) pair induced upon doping indicates that the two defects tend to remain close to each other. This results in the formatn of polarons whose binding energy is estimated to be of the order of 0.05 eV Absorption spectra at low doping levels are consistent with polaron formation. Interaction between polarons leads to the formation of charged solitions. In poly(p-phenylene), defects are always correlated in pairs. Upn doping, polarons are formed (binding energy ～ 0.03 eV), wit the relaxation of the lattice extending over about four rings. Calculations suggest the possibility of bipolarons (doubly charged defects) that yield conductivity without Pauli susceptibility.     

Development of a microsecond X‐ray protein footprinting facility at the Advanced Light Source

X‐ray footprinting (XF) is an important structural biology tool used to determine macromolecular conformations and dynamics of both nucleic acids and proteins in solution on a wide range of timescales. With the impending shut‐down of the National Synchrotron Light Source, it is ever more important that this tool continues to be developed at other synchrotron facilities to accommodate XF users. Toward this end, a collaborative XF program has been initiated at the Advanced Light Source using the white‐light bending‐magnet beamlines 5.3.1 and 3.2.1. Accessibility of the microsecond time regime for protein footprinting is demonstrated at beamline 5.3.1 using the high flux density provided by a focusing mirror in combination with a micro‐capillary flow cell. It is further reported that, by saturating samples with nitrous oxide, the radiolytic labeling efficiency is increased and the imprints of bound versus bulk water can be distinguished. These results both demonstrate the suitability of the Advanced Light Source as a second home for the XF experiment, and pave the way for obtaining high‐quality structural data on complex protein samples and dynamics information on the microsecond timescale.     

Simultaneous fluorometry and phosphorometry of Langendorff perfused rat heart: ex vivo animal studies

Fluorescence imaging of intrinsic fluorophores of tissue is a powerful method to assess metabolic changes at the cellular and intracellular levels. At the same time, exogenous phosphorescent probes can be used to accurately measure intravascular tissue oxygenation. Heart failure is the leading cause of death in America. A rat heart can potentially model the human heart to study failures or other abnormalities optically. We report simultaneous fluorescence and phosphorescence measurements performed on a rat heart. We have used two different optical systems to acquire fluorescence signals of flavoprotein and nicotinamide adenine dinucleotide--the two intrinsic fluorophores of mitochondria--and the phosphorescence signal of an intravascular oxygen probe to extract intracellular and intravascular metabolism loads, respectively.     

Longitudinal flow of protons from (2-8)A GeV central Au+Au collisions

Rapidity distributions of protons from central 197Au+197Au collisions measured by the E895 Collaboration in the energy range from (2-8)A GeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, (L), as a function of the logarithm of beam energy.     

The nature and origin of structural defects in polymeric sulfur nitride

Defect structures in (SN)_x crystals obtained by solid-state polymerization are so numerous and varied that they are likely to conceal inherent property aspects of the defect-free polymer. In addition to frequent macroscopic twinning, three different kinds of defect sites are observed. These sites are related to the disruption of molecular orientational order about the chain axis direction and the sequencing of chain types in the periodic phase. The origin of these defects is explained by the nonuniqueness of solid-state polymerization and recrystallization processes, which transform the initial dimer phase to the final polymer phase. The orientational relationship between the dimer and polymer phase is predicted from the observed twinning mode and the structural relationship between these phases. The change from dimer phase (at zero and at intermediate conversions involving solid solution formation) to polymer phase can be described by a shear transformation on the (001) dimer plane. This observation suggests an analogy with known martensitic reactions and a method for improving the perfection of (SN)_x.     

Knoevenagel condensation catalyzed by K2NiP2O7. Synthesis of (E)-methyl-α-cyanocinnamates in high yields

The Knoevenagel reaction of benzaldehyde and several chloroderivatives with methyl cyanoacetate catalyzed by K₂NiP₂O₇ leads to methyl (E)--cyanocinnamate derivatives in 40 min with yields of 71.65–83.45%. Pure products are easily obtained in crystalline form, uncontaminated by side products or by stereoisomers. Methyl 2-chlorocyanocinnamate, methyl 2,4-dichlorocyanocinnamate, and a new polymorph of methyl cyanocinnamate have been characterized by single crystal X-ray diffraction.     

The Beamline X28C of the Center for Synchrotron Biosciences: a National Resource for Biomolecular Structure and Dynamics Experiments Using Synchrotron Footprinting

Structural mapping of proteins and nucleic acids with high resolution in solution is of critical importance for understanding their biological function. A wide range of footprinting technologies have been developed over the last ten years to address this need. Beamline X28C, a white‐beam X‐ray source at the National Synchrotron Light Source of Brookhaven National Laboratory, functions as a platform for synchrotron footprinting research and further technology development in this growing field. An expanding set of user groups utilize this national resource funded by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health. The facility is operated by the Center for Synchrotron Biosciences and the Center for Proteomics of Case Western Reserve University. The facility includes instrumentation suitable for conducting both steady‐state and millisecond time‐resolved footprinting experiments based on the production of hydroxyl radicals by X‐rays. Footprinting studies of nucleic acids are routinely conducted with X‐ray exposures of tens of milliseconds, which include studies of nucleic acid folding and their interactions with proteins. This technology can also be used to study protein structure and dynamics in solution as well as protein–protein interactions in large macromolecular complexes. This article provides an overview of the X28C beamline technology and defines protocols for its adoption at other synchrotron facilities. Lastly, several examples of published results provide illustrations of the kinds of experiments likely to be successful using these approaches.