NMR studies of the dynamics of a bifunctional rhodamine probe attached to troponin C

Fluorescence polarization measurements of bifunctional rhodamine (BR) probes provide a powerful approach to determine the in situ orientation of proteins within ordered complexes such as muscle fibers. For accurate interpretation of fluorescence measurements, it is important to understand the probe dynamics relative to the protein to which it is attached. We previously determined the structure of the N-domain of chicken skeletal troponin C, BR-labeled on the C helix, in complex with the switch region of troponin I, and demonstrated that the probe does not perturb the structure or dynamics of the protein. In this study, the motion of the fluorescence label relative to the protein has been characterized using NMR relaxation measurements of 13C-labeled methyl groups on the BR probe and 15N-labeled backbone amides of the protein. Probe dynamics were monitored using off-resonance 13C-R(1rho), 13C-R(1) and {1H}-13C NOE at magnetic field strengths of 500, 600, and 800 MHz. Relaxation data were interpreted in terms of the overall rotational correlation time of the protein and a two-time scale model for internal motion of the BR methyl groups, using a numerical optimization with Monte Carlo parameter error estimation. The analysis yields a 1.5 +/- 0.4 ps correlation time for rotation around the three-fold methyl symmetry axis, and a 0.8 +/- 0.4 ns rotational correlation time for reorientation of the 13C-14N bond with an associated S2s of 0.79 +/- 0.03. Order parameters of the backbone NH vectors in the helix to which the probe is attached average S2 approximately 0.85, implying that the amplitude of independent reorientation of the BR probe is small in magnitude, consistent with results from fluorescence polarization measurements in reconstituted muscle fibers.     

XeOF2, F2OXeN identical with CCH3, and XeOF2.nHF: rare examples of Xe(IV) oxide fluorides

The syntheses of XeOF2, F2OXeNCCH3, and XeOF2.nHF and their structural characterizations are described in this study. All three compounds are explosive at temperatures approaching 0 degrees C. Although XeOF2 had been previously reported, it had not been isolated as a pure compound. Xenon oxide difluoride has now been characterized in CH3CN solution by 19F, 17O, and 129Xe NMR spectroscopy. The solid-state Raman spectra of XeOF2, F2OXeNCCH3, and XeOF2.nHF have been assigned with the aid of 16O/18O and 1H/2H enrichment studies and electronic structure calculations. In the solid state, the structure of XeOF2 is a weakly associated, planar monomer, ruling out previous speculation that it may possess a polymeric chain structure. The geometry of XeOF2 is consistent with a trigonal bipyramidal, AX2YE2, VSEPR arrangement that gives rise to a T-shaped geometry in which the two free valence electron lone pairs and Xe-O bond domain occupy the trigonal plane and the Xe-F bond domains are trans to one another and perpendicular to the trigonal plane. Quantum mechanical calculations and the Raman spectra of XeOF2.nHF indicate that the structure likely contains a single HF molecule that is H-bonded to oxygen and also weakly F-coordinated to xenon. The low-temperature (-173 degrees C) X-ray crystal structure of F2OXeNCCH3 reveals a long Xe-N bond trans to the Xe-O bond and a geometrical arrangement about xenon in which the atoms directly bonded to xenon are coplanar and CH3CN acts as a fourth ligand in the equatorial plane. The two fluorine atoms are displaced away from the oxygen atom toward the Xe-N bond. The structure contains two sets of crystallographically distinct F2OXeNCCH3 molecules in which the bent Xe-N-C moiety lies either in or out of the XeOF2 plane. The geometry about xenon is consistent with an AX2YZE2 VSEPR arrangement of bond pairs and electron lone pairs and represents a rare example of a Xe(IV)-N bond.     

Resolving the aluminum ordering in aluminosilicates by a combined experimental/theoretical study of 27Al electric field gradients

The discrimination between atomic species in light-element materials is a challenging question. An archetypal example is the resolution of the Al/Si ordering in aluminosilicates. Only an average long-range order can be deduced from powder X-ray or neutron diffraction, while magic-angle-spinning NMR provides an accurate picture of the short-range order. The long- and short-range orders thus obtained usually differ, hence raising the question of whether the difference between local and extended orders is intrinsic or caused by the difficulty of obtaining an accurate picture of the long-range order from diffraction techniques. In this communication we resolve this question for the monoclinic phases of BaAl2Si2O8 and SrAl2Si2O8 on the basis of 27Al NMR measurements and ab initio simulation of electric field gradient. Although the long- and short-range orders deduced from our XRD and NMR experiments differ, they become similar when the XRD atomic positions are optimized by ab initio electronic structure calculations.     

Discrete random bounds for general random variables and applications to reliability

We here propose some new algorithms to compute bounds for (1) cumulative density functions of sums of i.i.d. nonnegative random variables, (2) renewal functions and (3) cumulative density functions of geometric sums of i.i.d. nonnegative random variables. The idea is very basic and consists in bounding any general nonnegative random variable X   by two discrete random variables with range in hN$h\mathbb{N}$, which both converge to X as h goes to 0. Numerical experiments are lead on and the results given by the different algorithms are compared to theoretical results in case of i.i.d. exponentially distributed random variables and to other numerical methods in other cases.     

Resonances of an elastic plate in a compressible confined fluid

We present a theoretical study of the resonances of a fluid–structureproblem, an elastic plate placed in a duct in the presence ofa compressible fluid. The case of a rigid plate has been largelystudied. Acoustic resonances are then associated to resonantmodes trapped by the plate. Due to the elasticity of the plate,we need to solve a quadratic eigenvalue problem in which theresonance frequencies k solve the equations (k) = k², where are the eigenvalues of a self-adjoint operator of the formA + kB. First, we show how to study the eigenvalues locatedbelow the essential spectrum by using the min–max principle.Then, we study the fixed-point equations. We establish sufficientconditions on the characteristics of the plate and of the fluidto ensure the existence of resonances. Such conditions are validatednumerically.     

Three-dimensional green water velocity on a model structure

Flow kinematics of green water due to plunging breaking waves impinging on a simplified, 3D model structure was investigated in the laboratory. Two breaking wave conditions were tested: one with waves impinging on the vertical wall of the model at still water level, and the other with waves impinging on the horizontal deck surface. The bubble image velocimetry (BIV) technique was used to measure flow velocities. Measurements were taken on both vertical and horizontal planes. Evolution of green water flow kinematics in time and space was revealed and was found to be quite different between the two wave conditions, even though the incoming waves are essentially identical. The time history of maximum velocity is demonstrated and compared. In both cases, the maximum velocity occurs near the green water front and beneath the free surface. The maximum horizontal velocity for the deck impinging case is 1.44C with C being the wave phase speed, which is greater than 1.24C for the wall impingement case. The overall turbulence level is about 0.3 of the corresponding maximum velocity in each wave condition. The results were also compared with 2D experimental results to examine the 3D effect. It was found that the magnitude of the maximum vertical velocity during the runup process is 1.7C in the 3D model study and 2.9C in the 2D model study, whereas the maximum horizontal velocity on the deck is similar, 1.2C in both 3D and 2D model studies.     

An anytime multistep anticipatory algorithm for online stochastic combinatorial optimization

The one-step anticipatory algorithms (1s-AA) is an online algorithm making decisions under uncertainty by ignoring the non-anticipativity constraints in the future. It was shown to make near-optimal decisions on a variety of online stochastic combinatorial problems in dynamic fleet management and reservation systems. Here we consider applications in which 1s-AA is not as close to the optimum and propose Amsaa, an anytime multi-step anticipatory algorithm. Amsaa combines techniques from three different fields to make decisions online. It uses the sampling average approximation method from stochastic programming, search algorithms for Markov decision processes from artificial intelligence, and discrete optimization algorithms. Amsaa was evaluated on a stochastic project scheduling application from the pharmaceutical industry featuring endogenous observations of the uncertainty. The experimental results show that Amsaa significantly outperforms state-of-the-art algorithms on this application under various time constraints.     

Fluoride-ion acceptor properties of WSF4: synthesis, characterization, and computational study of the WSF5(-) and W2S2F9(-) anions and 19F NMR spectroscopic characterization of the W2OSF9(-) anion

The new [N(CH(3))(4)][WSF(5)] salt was synthesized by two preparative methods: (a) by reaction of WSF(4) with [N(CH(3))(4)][F] in CH(3)CN and (b) directly from WF(6) using the new sulfide-transfer reagent [N(CH(3))(4)][SSi(CH(3))(3)]. The [N(CH(3))(4)][WSF(5)] salt was characterized by Raman, IR, and (19)F NMR spectroscopy and [N(CH(3))(4)][WSF(5)]·CH(3)CN by X-ray crystallography. The reaction of WSF(4) with half an aliquot of [N(CH(3))(4)][F] yielded [N(CH(3))(4)][W(2)S(2)F(9)], which was characterized by Raman and (19)F NMR spectroscopy and by X-ray crystallography. The WSF(5)(-) and W(2)S(2)F(9)(-) anions were studied by density functional theory calculations. The novel [W(2)OSF(9)](-) anion was observed by (19)F NMR spectroscopy in a CH(3)CN solution of WOF(4) and WSF(5)(-), as well as CH(3)CN solutions of WSF(4) and WOF(5)(-).     

ChemInform Abstract: A Raman Spectroscopic Study of the XeOF4/XeF2 System and the X‐Ray Crystal Structure of α‐XeOF4·XeF2.

The interaction of XeF₂ with excess XeOF₄ leads to the formation of a mixture of α‐XeOF₄·XeF₂ and β‐XeOF₄·XeF₂.     

Abibalsamins A and B, two new tetraterpenoids from Abies balsamea oleoresin

Abibalsamins A (1) and B (2), two unprecedented tetraterpenoids featuring a 3,4-seco-rearranged lanostane system fused with a β-myrcene lateral chain via a [4 + 2] Diels-Alder cycloaddition, were isolated from the oleoresin of Abies balsamea. Their structures were elucidated by means of extensive 2D NMR, IR, and MS spectroscopy analyses. The absolute configuration of 1 was determined by single-crystal X-ray diffraction. Both compounds exhibited significant cytotoxic activity against cancer cell lines.