Publications

A comparison of the structure, spectroscopy, and oxygen atom-transfer reactivity of cofacial bisporphyrins anchored by xanthene (DPX) and dibenzofuran (DPD) pillars is presented. The synthesis and characterization of dicopper(II) and dinickel(II) complexes of DPD completes a homologous series of homobimetallic zinc(II), copper(II), and nickel(II) complexes for both cofacial platforms. X-ray crystallographic analysis of the parent free-base porphyrins H(4)DPX (1) and H(4)DPD (5) confirms the face-to-face arrangement of the two porphyrin macrocycles with a large available range of vertical pocket sizes: 1 (C(80)H(92)Cl(2)N(8)O), triclinic, space group P1 macro, a = 13.5167(12) A, b = 21.7008(18) A, c = 23.808(2) A, alpha = 80.116(2) degrees, beta = 76.832(2) degrees, gamma = 80.4070(10) degrees, Z = 4; 5 (C(80)H(83)N(8)O(2)), monoclinic, space group C2/c, a = 22.666(2) A, b = 13.6749(14) A, c = 42.084(4) A, beta = 94.554(2) degrees, Z = 8. EPR spectroscopy of dicopper(II) derivatives Cu(2)DPX (3) and Cu(2)DPD (7) complements the crystallographic studies by probing intramolecular metal-metal arrangements in frozen solution. Exciton interactions between the porphyrin subunits in fluid solution are revealed by steady-state and time-resolved electronic absorption and emission spectroscopy. The resulting compilation of structural and spectroscopic data provides a benchmark for the use of these and related platforms for the activation of small-molecule substrates. A structure-function relation is developed for the photoinduced oxygen atom-transfer reactions of bisiron(III) mu-oxo derivatives of DPX and DPD. The efficiency of the photochemical process is markedly dependent (approximately 10(4)-fold) on the vertical flexibility of cofacial architecture provided by the spacer.

Instruments developed in our laboratory permit the atomic and molecular level study of NPs under reaction conditions (SFG, ambient pressure XPS and high pressure STM). These studies indicate continuous restructuring of the metal substrate and the adsorbate molecules, changes of oxidation states with NP size and surface composition variations of bimetallic NPs with changes of reactant molecules.

Porphyrin architectures bearing a hydrogen-bonding scaffold have been synthesized. The H-bond pendant allows proton-coupled electron transfer (PCET) to be utilized as a vehicle for effecting catalytic O-O bond activation chemistry. Suzuki cross-coupling reactions provide a modular synthetic strategy for the attachment of porphyrins to a rigid xanthene or dibenzofuran pillar bearing the H-bond pendant. The resulting HPX (hanging porphyrin xanthene) and HPD (hanging porphyrin dibenzofuran) systems permit both the orientation and acid-base properties of the hanging H-bonding group to be controlled. Comparative reactivity studies for the catalase-like disproportionation of hydrogen peroxide and the epoxidation of olefins by the HPX and HPD platforms with acid and ester hanging groups reveal that the introduction of a proton-transfer network, properly oriented to a redox-active platform, can orchestrate catalytic O-O bond activation. For the catalase and epoxidation reaction types, a marked reactivity enhancement is observed for the xanthene-bridged platform appended with a pendant carboxylic acid group, establishing that this approach can yield superior catalysts to analogues that do not control both proton and electron inventories.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The mechanism of wear-particle formation during unlubricated sliding wear of several carbon and alloy steels has been investigated by scanning (SEM) and transmission electron microscopy (TEM). Individual debris particles are plate-like and typically 200 to 400 nm in thickness. The thinner particles are generally iron oxides except at low temperatures or in inert atmospheres when predominantly metallic particles result. The mean debris-particle width was 1 to 2 ..mu..m. TEM revealed a fine dislocation cell structure typical of large strain deformation to a depth of 10 to 50 ..mu..m. The subsurface cell dimensions and bending of pearlite colonies indicate that the shear strain near to the surface is at least 5. In many instances, a 200 to 300 nm wide zone of lower dislocation density, indicative of recovery, we noted immediately below the surface. Some cracks formed along dislocation cell walls at the boundary of the recovered zone; others were associated with decohesion of particle interfaces of subgrain triple points. Some oxidation then occurs during separation of the platelet from the parent material as a consequence of the highly pyrophoric nature of thin metal flakes. The sequence of the dry sliding wear process is discussed. 16 figures.

The Cardiac Purkinje Fiber (CPF) is the last branch of the heart conduction system, which is meshed with the normal ventricular myocyte. Purkinje fiber plays a key role in the occurrence of ventricular arrhythmia and maintenance. Does the heart Purkinje fiber cells have the same memory function as the cerebral nerve? In this paper, the cardiac Hodgkin–Huxley equation is taken as the object of study. In particular, we find that the potassium ion-channel [Formula: see text] and the sodium ion-channel [Formula: see text] are memristors. We also derive the small-signal equivalent circuits about the equilibrium points of the CPF Hodgkin–Huxley model. According to the principle of local activity, the regions of Locally-Active domain, Edge of Chaos domain and Locally-Passive domain are partitioned under parameters [Formula: see text], and the domain exhibiting the normal human heartbeat frequency range (Goldilocks Zone) is identified. Meanwhile, the Super-Critical Hopf bifurcation of the CPF Hodgkin–Huxley model is identified. Finally, the migration changes between different state domains under external current [Formula: see text] excitation are analyzed in detail. All of the above complex nonlinear dynamics are distilled and mapped geometrically into a surreal union of intersecting two-dimensional manifolds, dubbed the Hodgkin–Huxley’s magic roof.

Plasmid replication during the Escherichia coli division cycle has been investigated using the membrane-elution technique to produce cells labelled at different times during the division cycle and subsequent quantitation of the label incorporated into the plasmids. The results indicate that the naturally-occurring, low-copy F plasmid and P1 prophage replicate in a cell-cycle-specific manner, with replication occurring approximately one-half generation between subsequent rounds of chromosome replication initiation. In contrast, the naturally-occurring, high-copy R6K, pSC101, and ColE1-type plasmids replicate in a cell-cycle-independent manner. The cell-cycle replication patterns of two mini-F plasmids were investigated in an attempt to determine the genetic locus regulating cell-cycle-specific F plasmid replication. A mini-F plasmid containing the oriV and oriS F plasmid origins replicates in a cell-cycle-specific manner, whereas a mini-F plasmid containing only the oriS F plasmid origin replicates in a cell-cycle-independent manner and is maintained at a higher copy number than the two-origin mini-F plasmid. These results imply that the oriV origin contributes in some way to the cell-cycle-specific replication behavior of the F plasmid. A conceptual model of cell-cycle-specific plasmid replication has been developed in order to understand the mechanism responsible for the replication pattern. The experimental data support the model prediction that the mechanisms timing low-copy plasmid replication and initiation of chromosome replication are similar: initiation of replication occurs when a constant mass per origin is achieved, but at a different mass per origin for the low-copy plasmids than for the chromosome. Mathematical modelling of high-copy plasmid replication is simplified by the finding that its replication is cell-cycle independent. A detailed kinetic model of the known molecular biology of the ColE1 plasmid has been developed and the relevant parameters have been extracted from the biology literature. Time constant analysis was used to reduce this complex model to a simple, realistic description of the overall replication kinetics. The analysis leads to the identification of key parameters governing plasmid replication and to the estimation of parameters that are difficult to determine experimentally. The overall kinetics of ColE1-type plasmid replication are zeroth-order in production and first order in dilution. Experimental data confirm these predictions.

Abstract: This study investigated the rate of psychological impairment and stressful life events in survivors of motor vehicle accidents. Fifty‐six patients who had been hospitalised because of motor‐vehicle‐accident‐related injuries were reviewed twelve months after the accident. In this sample, 41 per cent of patients reported significant levels of psychological impairment. Patients reporting psychological disturbance were characterised by having more pain, unemployment, substance abuse, avoidance of road transport and compensation claims. Only 44 per cent of patients reporting significant psychological impairment had sought professional help for their conditions. Psychological dysfunction following motor vehicle accidents appears to be a common occurrence, and education of medical personnel and survivors is required to enhance identification and management of this problem.

We present a new approach for modeling and rendering existing architectural scenes from a sparse set of still photographs. Our modeling approach, which combines both geometry-based and imagebased techniques, has two components. The first component is a photogrammetric modeling method which facilitates the recovery of the basic geometry of the photographed scene. Our photogrammetric modeling approach is effective, convenient, and robust because it exploits the constraints that are characteristic of architectural scenes. The second component is a model-based stereo algorithm, which recovers how the real scene deviates from the basic model. By making use of the model, our stereo technique robustly recovers accurate depth from widely-spaced image pairs. Consequently, our approach canmodel large architectural environmentswith far fewer photographs than current image-based modeling approaches. For producing renderings, we present view-dependent texture mapping, a method of compositing multiple views of a scene that better simulates geometric detail on basic models. Our approach can be used to recover models for use in either geometry-based or image-based rendering systems. We present results that demonstrate our approach's ability to create realistic renderings of architectural scenes from viewpoints far from the original photographs.