Rearrangements and stereomutations of metallacycles derived from allenes and imidozirconium complexes

The mechanisms of the rearrangements and stereoinversion of azametallacyclobutenes generated via [2+2] cycloaddition of allenes and imidozirconium complexes have been studied. Metallacycles derived from allenes bearing beta-hydrogen atoms racemize at room temperature by reversible beta-hydride elimination, a process which is also responsible for their eventual conversion to monoazadiene complexes. Metallacycles derived from diarylallenes racemize by reversible thermal bond homolysis at 95 degrees C; racemization of these metallacycles is also catalyzed by mild oxidants.     

Green chemical functionalization of single-walled carbon nanotubes in ionic liquids

Single walled carbon nanotubes (SWNTs) are exfoliated and functionalized predominantly as individuals by grinding them for minutes at room temperature with aryldiazonium salts in the presence of ionic liquids (ILs) and K(2)CO(3). This constitutes an extremely rapid and mild green chemical functionalization process for obtaining the individualized nanotube structures. A number of ILs and various reaction conditions were surveyed. Raman, XPS, UV/vis/NIR spectroscopies, thermogravimetric analysis, and atomic force and transmission electron microscopies were used to characterize the products.     

Explicit Construction and Uniqueness for Universal Operator Algebras of Directed Graphs

Given a directed graph, there exist a universal operator algebraand universal C*-algebra associated to the directed graph. Inthis paper we give intrinsic constructions for these objects.We also provide an explicit construction for the maximal C*-algebraof an operator algebra. We discuss uniqueness of the universalalgebras for finite graphs, showing that for finite graphs thegraph is an isomorphism invariant for the universal operatoralgebra of a directed graph. We show that the underlying undirectedgraph is a Banach algebra isomorphism invariant for the universalC*-algebra of a directed graph.     

Possibilities for refining an object program compiled with an ALGOL translator

The paper discusses possible improvements in connection with compilation of computer programs. Four different areas are mentioned where contributions should be possible: The language, the computer, the compiler, and the programmer. Although many of the points are quite general, ALGOL 60 is specifically taken into account.This paper was presented at the NordSAM conference in Stockholm, Aug. 1964.     

Solvation of ethylmaltol and of its iron(III) complex

Summary Solubilities of tris(ethylmaltolato)iron(III) (ethylmaltol = 3-hydroxy-2-ethyl-4-pyrone) were measured in MeOH-H₂O, t-BuOH-H₂O and diol-H₂O mixtures, and in several primary alcohols. Solvation of the ethylmaltol ligand and of two 4-pyridinone analogues has been investigated through solubility measurements in MeOH- H₂O and in t-BuOH-H₂O mixtures, and in a series of primary alcohols. The solvation characteristics of these compounds are compared with those of the parent maltol, its iron(III) complex and a number of other nonelectrolytes.     

Resolvable and near-resolvable decompositions ofDK v into oriented 4-cycles

Summary A resolvableX-decomposition ofDK _v (the complete symmetric digraph onv vertices) is a partition of the arcs ofDK _v into isomorphic factors where each factor is a vertex-disjoint union of copies ofX and spans all vertices ofDK _v . There are four orientations ofC ₄ (the 4-cycle), only one of which has been considered: Bennett and Zhang, Aequationes Math.40 (1990), 248–260. We give necessary and sufficient conditions onv for resolvableX-decomposition ofDK _v , whereX is any one of the other three orientations ofC ₄. A near-resolvableX-decomposition ofDK _v is as above except that each factor spans all but one vertex ofDK _v . Again, one orientation ofC ₄ has been dealt with by Bennett and Zhang, and we provide necessary and sufficient conditions onv for the remaining three cases. The construction techniques used are both direct (for small values ofv) and recursive.The author thanks Simon Fraser University for its support during her graduate studies when the research for this paper was undertaken.The author acknowledges the Natural Sciences and Engineering Research Council of Canada for financial support under grant A-7829.     

Acoustic response from adherent targeted contrast agents

In ultrasonic molecular imaging, encapsulated micron-sized gas bubbles are tethered to a blood vessel wall by targeting ligands. A challenging problem is to detect the echoes from adherent microbubbles and distinguish them from echoes from nonadherent agents and tissue. Echoes from adherent contrast agents are observed to include a high amplitude at the fundamental frequency, and significantly different spectral shape compared with free agents (p <0.0003). Mechanisms for the observed acoustical difference and potential techniques to utilize these differences for molecular imaging are proposed.     

New antitumour active platinum compounds containing carboxylate ligands in trans geometry: synthesis, crystal structure and biological activity

New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5'-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes.     

Intermolecular vibrational coherence in bacteriochlorophyll a with clustered polar solvent molecules

We show that resonant impulsive excitation of the Qy absorption band of bacteriochlorophyll a (BChl) launches a rapidly damped (gamma < 200 fs) ground-state coherent wave-packet motion that arises from intermolecular modes with clustered solvent molecules. Femtosecond pump-probe, dynamic-absorption signals were obtained at room temperature with BChl solutions in pyridine, acetone, and 1-propanol. The vibrational coherence observed in the 0-800-fs regime is modeled in the time domain by two (or three, in the case of 1-propanol) modulation components with asymmetric, inhomogeneously broadened line shapes and frequencies in the 100-200-cm(-1) range. The mean frequency of the vibrational coherence exhibits at least a quadratic dependence on the dipole moment of the solvent molecules and a y-intercept in the 100-cm(-1) regime. This trend is modeled by an expression for the natural frequency of a "6-12" potential composed of attractive terms from van der Waals forces and a repulsive term from the exchange (Pauli exclusion) force. The model suggests that comparable contributions to the potential are provided by the dipole-dipole and London dispersion interactions. These results support the hypothesis that the low-frequency vibrational modes in the 100-cm(-1) regime that are coupled to the light-driven charge-separation reactions in the reaction center from purple bacteria are derived from intermolecular vibrational modes between the chromophores and the surrounding protein medium.