Synthesis,Structure, Photophysical Properties,and Photostability of Benzodipyrenes

This work explores the syntheses, structures, photophysical properties, and photostability of benzodipyrenes (BDPs). BDPs were synthesized through an InCl₃-AgNTf₂-catalyzed, four-fold alkyne benzannulation reaction. The structures of BDP 4 a and its corresponding endoperoxide product were unambiguously confirmed by X-ray crystallography. The BDPs reported here can also be recognized as peri- and cata-benzannulated pentacenes with a non-functionalized central ring. Unlike the previous reported pentacene-based polycyclic aromatic hydrocarbons, the absorbances of the BDPs were blueshifted by ca. 40 nm relative to pentacene, even after extension of π-conjugation. The newly synthesized BDP products exhibit relatively good stability with half-lives as high as 4612 min in THF.     

Bistability in a hyperchaotic system with a line equilibrium

A hyperchaotic system with an infinite line of equilibrium points is described. A criterion is proposed for quantifying the hyperchaos, and the position in the three-dimensional parameter space where the hyperchaos is largest is determined. In the vicinity of this point, different dynamics are observed including periodicity, quasi-periodicity, chaos, and hyperchaos. Under some conditions, the system has a unique bistable behavior, characterized by a symmetric pair of coexisting limit cycles that undergo period doubling, forming a symmetric pair of strange attractors that merge into a single symmetric chaotic attractor that then becomes hyperchaotic. The system was implemented as an electronic circuit whose behavior confirms the numerical predictions.     

Conformational Properties of the Phosphate Rings of Neutral Phosphoramidate Derivatives of Ribo- and 2′-Deoxyribonucleoside Cyclic 3′,5′-Monophosphates

Abstract

An investigation of the effects of changing the nature of X, nitrogen base (B), and amino substituent (R₂N) on the equilibrium 1?2 was carried out.

The influence of the above structural changes on the time-averaged coupling constants J_AP and J_BP, determined at 300 MHz, were used to follow changes in K_eq. With constant R₂N, small effects from variation of X and B were found. A large range in K_eq arose from changes in the steric size of R₂N. These results will be related to the question of the ease of chair to twist interconversion of the phosphate ring essential to the biological activities of the naturally occurring diesters, cAMP and cGMP.     

Mean-field versus microconvection effects in nanofluid thermal conduction

Transient hot-wire data on thermal conductivity of suspensions of silica and perfluorinated particles show agreement with the mean-field theory of Maxwell but not with the recently postulated microconvection mechanism. The influence of interfacial thermal resistance, convective effects at microscales, and the possibility of thermal conductivity enhancements beyond the Maxwell limit are discussed.     

Systematic Study of Selected Diagonalization Methods for Configuration Interaction Matrices

Several modifications to the Davidson algorithm are systematically explored to establish their performance for an assortment of configuration interaction (CI) computations. The combination of a generalized Davidson method, a periodic two‐vector subspace collapse, and a blocked Davidson approach for multiple roots is determined to retain the convergence characteristics of the full subspace method. This approach permits the efficient computation of wave functions for large‐scale CI matrices by eliminating the need to ever store more than three expansion vectors ( b _i) and associated matrix‐vector products ( σ _i), thereby dramatically reducing the I/O requirements relative to the full subspace scheme. The minimal‐storage, single‐vector method of Olsen is found to be a reasonable alternative for obtaining energies of well‐behaved systems to within μE_h accuracy, although it typically requires around 50% more iterations and at times is too inefficient to yield high accuracy (ca. 10^?10 E_h) for very large CI problems. Several approximations to the diagonal elements of the CI Hamiltonian matrix are found to allow simple on‐the‐fly computation of the preconditioning matrix, to maintain the spin symmetry of the determinant‐based wave function, and to preserve the convergence characteristics of the diagonalization procedure. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1574–1589, 2001     

Tracking regression and progression of atherosclerosis in human carotid arteries using high-resolution magnetic resonance imaging

BACKGROUND AND PURPOSE: Magnetic resonance imaging (MRI) can accurately and reproducibly measure the volume of atherosclerotic plaque in human carotid arteries. Atherosclerotic plaques may either progress or regress over time, depending on individual risk factors and treatment regimens. This study was designed to determine if regression or progression of human carotid atherosclerosis in patients receiving statin therapy over 24 months can be detected by high-resolution MRI. METHODS: In 11 subjects who had undergone unilateral carotid endarterectomy and were on statin therapy, volumes for total carotid artery, concentric wall (normal wall), eccentric wall (plaque), and lumen were quantified at 0, 16 and 24 months using a 1.5-T human imager equipped with 6-cm phased array coils. RESULTS: The interobserver mean coefficient of variation (CV) was lowest for the lumen volume (3.1%) and highest for the plaque volume (9.8%). The interscan mean CV was lowest for the total artery volume (3.2%) and highest for the plaque volume (9.9%). As much as 26% regression and 35% progression were observed in individual subject's carotid artery eccentric wall (plaque) volumes over time. Mean eccentric wall volume increased 5% by 16 months and 8% by 24 months. Mean total wall volume increased slightly at both 16 and 24 months (+1.2% and +1.8%). CONCLUSIONS: High-resolution MRI provides a noninvasive reproducible method of tracking changes in carotid atherosclerosis. This pilot study detected changes in individual subjects at both 16 and 24 months. MRI tracking of changes in atherosclerotic plaques should prove useful in assessing vascular disease risk and monitoring the efficacy of interventions designed to induce regression or retard progression.     

Discrimination of components in atherosclerotic plaques from human carotid endarterectomy specimens by magnetic resonance imaging ex vivo

Specific MRI techniques have been used to determine the dimensional and compositional properties of atherosclerotic lesions in carotid endarterectomy tissues. A quantitative comparison of areas of specific features in typical tissue segments was performed using MR images and histologic images. The mean difference for the measurements by the two methods was 4.5% for the total vessel, 5.3% for the internal carotid artery lumen, and 5.0% for the external carotid lumen. For other less abundant components, the mean difference was 14.2%. For direct characterization, individual tissue components were isolated by microdissection and their T1 and T2 relaxation times measured. Highly calcified areas typically had rather short T1 (452-837 ms) and short T2 (10.4-18.4 ms). In contrast, regions enriched in lipid had much longer T1 (1,380-1,480 ms) and longer T2 (35.3-49.0 ms). Other components such as thrombus had intermediate T1 (1,180 ms) and short T2 (15.4 ms). T2 parametric imaging was used as a complementary approach for segmentation and quantitation of tissue components. In fresh tissue, several different components exhibited different T2 ranges: calcified/solid lipid (13-18 ms). cellular/ECM (9-30 ms), fluid lipid (35-40 ms): fibrous (50-60 ms). These results demonstrate the utility of MRI for identifying and quantifying specific components of atherosclerotic plaque ex vivo, and suggest its value for these measurements in vivo as well.     

Crystals from concentrated glyme mixtures. The single-crystal structure of LiClO4

A procedure for the preparation of high-quality single crystals from concentrated glyme mixtures is presented. Anhydrous single crystals of LiNO(3) and LiClO(4) were prepared in this manner, and the single-crystal structure of LiClO(4) (orthorhombic, Pnma, a = 8.6447(12) A, b = 6.8512(10) A, c = 4.8254(7) A, Z = 4) was determined as an example. This procedure is expected to be widely applicable for not only salts but also a wide range of other materials solvated by glymes.     

Synthesis and Characterization of Dinuclear Ruthenium(II) Complexes Based on 4,4′‐Bipyridyl Type Bridging Ligands

The synthesis, spectroscopic, electrochemical and photophysical characterization of a series of dinuclear ruthenium(II) complexes of the type [(bpy)₂Ru(NnN)₂RuCl(bpy)₂](PF₆)₃, where NnN = 4,4′‐bipyridyl (N0N), 1,2‐bis(4‐pyridyl)ethylene (NEN), 1,2‐bis(4‐pyridyl)ethane (N2N), and 4,4′‐trimethylenedipyridine (N3N) are reported. The photophysical and electrochemical properties are discussed with particular emphasis on the ability of the bridging ligands to support intercomponent interaction.     

Method for the direct determination of available carbohydrates in low-carbohydrate products using high-performance anion exchange chromatography

An improved method for direct determination of available carbohydrates in low-level products has been developed and validated for a low-carbohydrate soy infant formula. The method involves modification of an existing direct determination method to improve specificity, accuracy, detection levels, and run times through a more extensive enzymatic digestion to capture all available (or potentially available) carbohydrates. The digestion hydrolyzes all common sugars, starch, and starch derivatives down to their monosaccharide components, glucose, fructose, and galactose, which are then quantitated by high-performance anion-exchange chromatography with photodiode array detection. Method validation consisted of specificity testing and 10 days of analyzing various spike levels of mixed sugars, maltodextrin, and corn starch. The overall RSD was 4.0% across all sample types, which contained within-day and day-to-day components of 3.6 and 3.4%, respectively. Overall average recovery was 99.4% (n = 10). Average recovery for individual spiked samples ranged from 94.1 to 106% (n = 10). It is expected that the method could be applied to a variety of low-carbohydrate foods and beverages.