The Mn cluster in the S(0) state of the oxygen-evolving complex of photosystem II studied by EXAFS spectroscopy: are there three Di-mu-oxo-bridged Mn(2) moieties in the tetranuclear Mn complex?

A key component required for an understanding of the mechanism of the evolution of molecular oxygen by the photosynthetic oxygen-evolving complex (OEC) in photosystem II (PS II) is the knowledge of the structures of the Mn cluster in the OEC in each of its intermediate redox states, or S-states. In this paper, we report the first detailed structural characterization using Mn extended X-ray absorption fine structure (EXAFS) spectroscopy of the Mn cluster of the OEC in the S(0) state, which exists immediately after the release of molecular oxygen. On the basis of the EXAFS spectroscopic results, the most likely interpretation is that one of the di-mu-oxo-bridged Mn-Mn moieties in the OEC has increased in distance from 2.7 A in the dark-stable S(1) state to 2.85 A in the S(0) state. Furthermore, curve fitting of the distance heterogeneity present in the EXAFS data from the S(0) state leads to the intriguing possibility that three di-mu-oxo-bridged Mn-Mn moieties may exist in the OEC instead of the two di-mu-oxo-bridged Mn-Mn moieties that are widely used in proposed structural models for the OEC. This possibility is developed using novel structural models for the Mn cluster in the OEC which are consistent with the structural information available from EXAFS and the recent X-ray crystallographic structure of PS II at 3.8 A resolution.     

A novel liquid chromatography/tandem mass spectrometry based depletion method for measuring red blood cell partitioning of pharmaceutical compounds in drug discovery

A novel liquid chromatography/tandem mass spectrometry (LC/MS/MS)-based depletion method for measuring compound partitioning between human plasma and red blood cells (RBC) in a drug discovery environment is presented. Conventionally, RBC partitioning is determined by separate measurements of drug concentrations in equilibrating plasma and whole blood or RBC using separate standards prepared in their respective matrices, i.e., in plasma and whole blood or RBC lysates. The process is very tedious, labor-intensive, and difficult to automate. In addition, interferences from the heme and other highly abundant cellular composites make the measurement of the drug concentration in whole blood or RBC inevitably variable even with a highly specific LC/MS/MS method. Therefore, there is an imminent need to develop a straightforward and fast method to assess the partitioning of drug-like compounds in RBC.This work describes an LC/MS/MS-based depletion assay that measures the compound concentration in plasma that has been equilibrating with RBC. Compounds were spiked into fresh human whole blood and plasma respectively to a final concentration of 500 nM. Both the spiked whole blood and plasma control were incubated at 37 degrees C for up to 60 min. During the time course, aliquots of plasma and whole blood from both incubation mixtures were sampled at 10 and 60 min. The whole blood samples were centrifuged to yield the plasma. The plasma samples from both incubations were extracted using a protein precipitation method, and analyzed using LC/MS/MS under the multiple-reaction monitoring (MRM) mode. The RBC partitioning ratio was calculated using the analyte peak area responses of the plasma samples through an equation deduced in this work.The method was first tested using two commercial compounds, phenoprobamate and acetazolamide, to determine the optimal incubation conditions and the concentration dependency of the assay. The assay reproducibility was also assessed by three inter-day assays for phenoprobamate. This method was further evaluated using 20 commercial compounds of different classes with a wide range of RBC partitioning coefficients and the results were compared with those reported in the literature. Excellent correlation (R2=0.9396) was found between the measured and literature values. In addition, several proprietary compounds were assayed using both the new and traditional methods and the measured partitioning ratios from the two methods are equivalent. The experiments in this work demonstrate that the LC/MS/MS-based depletion method can provide direct and accurate measurement of RBC partitioning for compounds in drug discovery.     

The discrete fundamental group of the order complex of <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A few years ago Kramer and Laubenbacher introduced a discrete notion of homotopy for simplicial complexes. In this paper, we compute the discrete fundamental group of the order complex of the Boolean lattice. As it turns out, it is equivalent to computing the discrete homotopy group of the 1-skeleton of the permutahedron. To compute this group we introduce combinatorial techniques that we believe will be helpful in computing discrete fundamental groups of other polytopes. More precisely, we use the language of words, over the alphabet of simple transpositions, to obtain conditions that are necessary and sufficient to characterize the equivalence classes of cycles. The proof requires only simple combinatorial arguments. As a corollary, we also obtain a combinatorial proof of the fact that the first Betti number of the complement of the 3-equal arrangement is equal to 2 ^n?3(n ²?5n+8)?1. This formula was originally obtained by Björner and Welker in 1995.     

Ultrasonic effects on titanium tanning of leather

The effects of ultrasound on titanium tanning of leather were investigated. Either 20 or 40 kHz ultrasound was applied to the titanium tanning of pigskins. Five different treatment conditions were carried out and the effects were examined, such as leather shrinkage temperature (T(s)), titanium content and titanium distribution in the leather. Overall heat loading was carefully controlled. Results showed that 20 kHz ultrasound effectively improves titanium agent penetration into the hide and increases the leather's shrinkage temperature. Doubling the frequency to 40 kHz produced negligible enhancements. An impressive 105.6 degrees C T(s) was achieved using 20 kHz ultrasound pretreatment of the tanning liquor followed by 20 kHz ultrasound in the tanning mixture (liquor plus pigskins) in a special salt-free medium. Finally, using a unique ultrasonic tanning drum with 26.5 kHz ultrasound, the T(s) reached a record level of 106.5 degrees C, a value not achieved in conventional (no ultrasound) titanium tanning. The ultrasonic effects on titanium tanning of leather are judged to make a superior mineral tanned leather.     

Dosimetry of Room-Air Germicidal (254 nm) Radiation Using Spherical Actinometry

A method is demonstrated for measuring germicidal (254 nm) ultraviolet radiation (GUVR) in an omnidirectional manner. This method has application for those situations in which GUVR from more than one direction or source impinges on a three-dimensional object, and when it is of interest to determine the radiant fluence experienced by the object. For this purpose spherical quartz vessels were constructed varying from 0.8 to 1.25 cm in outside diameter. The vessels were filled with an actinometric solution consisting of KI and KIO3. This solution is optically opaque at 254 nm and is insensitive to room light. Upon exposure to GUVR this solution, which counts all of the 254 nm photons, forms triiodide. Following radiation, the contents of the vessel are removed, the absorbance of triiodide measured and the fluence rate determined based on a relationship that takes the volume to cross-sectional area of the actinometer into account. It is demonstrated that, in accordance with theory, the area of the sphere that intercepts the radiant energy is equal to the cross-sectional area of the sphere. A demonstration of the utility of this method was carried out in a test facility 90 m3 equipped with five GUVR lamps, one in each corner and one in the center of the room, arranged so as to irradiate the air in the upper portion of the room. Twenty spherical actinometers were evenly distributed around the room and exposed for either 30 or 90 min. The fluence rate varied from one part of the room to another, peaking near the GUVR lamps at 65-85 microW per cm2. By averaging over all 20 points, a pseudoaverage fluence rate for the room was found to be 42 and 44 microW per cm2 for the 30 and 90 min exposures, respectively. The similarities in the values for this metric demonstrates that the actinometric response is linear over this exposure range.     

Poly Lactic Acid (PLA) Nanocomposites: Effect of Inorganic Nanoparticles Reinforcement on Its Performance and Food Packaging Applications

Poly lactic acid (PLA) is a compostable, as well as recyclable, sustainable, versatile and environmentally friendly alternative, because the monomer of PLA-lactide (LA) is extracted from natural sources. PLA’s techno-functional properties are fairly similar to fossil-based polymers; however, in pristine state, its brittleness and delicacy during processing pose challenges to its potential exploitation in diverse food packaging applications. PLA is, therefore, re-engineered to improve its thermal, rheological, barrier and mechanical properties through nanoparticle (NP) reinforcement. This review summarises the studies on PLA-based nanocomposites (PLA NCs) developed by reinforcing inorganic metal/metallic oxide, graphite and silica-based nanoparticles (NPs) that exhibit remarkable improvement in terms of storage modulus, tensile strength, crystallinity, glass transition temperature (Tg) value, antimicrobial property and a decrease in water vapour and oxygen permeability when compared with the pristine PLA films. This review has also discussed the regulations around the use of metal oxide-based NPs in food packaging, PLA NC biodegradability and their applications in food systems. The industrial acceptance of NCs shows highly promising perspectives for the replacement of traditional petrochemical-based polymers currently being used for food packaging.     

A radioactive tracer dilution method to determine the mass of molten salt

A new technique for molten salt mass determination, termed radioactive tracer dilution, that uses ²²Na as a tracer was validated at bench scale. It has been a challenging problem to determine the mass of molten salt in irregularly shaped containers, where a highly radioactive, high-temperature molten salt was used to process nuclear spent/used fuel during electrochemical recycling (pyro-processing) or for coolant/fuel salt from molten salt reactors. A radioactive source with known activity is dissolved into the salt. After a complete mixture, a small amount of the salt is sampled and measured in terms of its mass and radioactivity. By finding the ratio of the mass to radioactivity, the unknown salt mass in the original container can be precisely determined.

     

Gamma-ray spectra analyses of molten salts in spent nuclear fuels pyroprocessing facilities for mass measurement

Journal of Radioanalytical and Nuclear Chemistry - To evaluate radioactive tracer dilution and gamma spectroscopy as a safeguards technique for monitoring the mass of liquid salt in molten salt...     

Primary decomposition and the fractal nature of knot concordance

For each sequence P=(p₁(t),p₂(t),...){\mathcal{P}=(p_1(t),p_2(t),\dots)} of polynomials we define a characteristic series of groups, called the derived series localized at P{\mathcal{P}}. These group series yield filtrations of the knot concordance group that refine the (n)-solvable filtration. We show that the quotients of successive terms of these refined filtrations have infinite rank. The new filtrations allow us to distinguish between knots whose classical Alexander polynomials are coprime and even to distinguish between knots with coprime higher-order Alexander polynomials. This provides evidence of higher-order analogues of the classical p(t)-primary decomposition of the algebraic concordance group. We use these techniques to give evidence that the set of smooth concordance classes of knots is a fractal set.