Organometallic photonucleases: synthesis and DNA-cleavage studies of cyclopentadienyl metal-substituted dendrimers designed to increase double-strand scission

[reaction: see text] A series of metal complex-substituted polyamine dendrimers have been synthesized and examined for their ability to cleave plasmid DNA in a double-stranded manner. While photolysis of the dimetallic spermine derivative and the tetrametallic DAB-Am-4 complex led to double-strand scission, in the larger DAB-Am-8 and DAB-Am-16 systems, DNA aggregation/precipitation was the predominant competing process observed.     

Four complementary theoretical approaches for the analysis of NMR paramagnetic relaxation

Four theoretical and computational approaches used at the University of Michigan to analyze NMR paramagnetic relaxation enhancement (NMR-PRE) are described. The primary objective of the theory is to describe the relationship of the NMR-PRE phenomenon to the electron spin hamiltonian and the spin energy level structure when zero field splitting interactions are significant. Four formulations of theory are discussed: (1) spin dynamics simulation; (2) the laboratory frame "constant H(S)" formulation; (3) the Molecular Frame "constant H(S)" formulation; and (4) the zfs-limit "constant H(S)" formulation. No single theoretical approach describes all important aspects of the relaxation mechanism in a fully satisfactory way. We use the four formulations in a complementary manner to provide as complete a picture of the relaxation mechanism as possible. We also discuss the integration of NMR-PRE theory and recently developed theory of electron spin relaxation which accounts for effects of the permanent zfs hamiltonian.     

Temporal onset-order discrimination through the tactual sense

Tactual temporal-onset order thresholds were measured for two sinusoidal vibrations of different frequencies delivered to two separate locations (thumb and index finger) of a multi-finger tactual stimulating device. The frequency delivered to the thumb was fixed at 50 Hz and that to the index finger at 250 Hz. The amplitude and duration of each of the two sinusoidal vibrations were roved independently from trial to trial in a 1-interval, 2AFC procedure. Performance, measured as a function of stimulus-onset asynchrony (SOA), indicated that the temporal-onset-order threshold averaged 34 ms across four subjects. The data were further classified into subsets according to both the amplitude and duration of the two stimuli in each trial of the roving-discrimination paradigm. The results indicated that the amplitude differences of the two stimuli in each trial had a substantial effect on onset-order discrimination, while duration differences generally had little effect. The effects of amplitude differences are explained qualitatively in terms of amplitude latency relationships and stimulus interactions such as temporal masking. Overall, the results not only contribute to an enhanced understanding of the temporal sensitivity of the tactual system but also provide guidelines for the design of tactual aids for hearing-impaired persons.     

The first direct evaluation of the two-active site mechanism for chitin synthase

Chitin synthase polymerizes UDP-GlcNAc to form chitin (poly-beta(1,4)-GlcNAc) and is essential for fungal cell wall biosynthesis. The alternating orientation of the GlcNAc residues within the chitin chain has led to the proposal that chitin synthase possesses two active sites. We report the results of the first direct test of this possibility. Two simple uridine-derived dimeric inhibitors are shown to exhibit 10-fold greater inhibition than a monomeric control, consistent with the presence of two active sites. This observation has important implications for the development of antifungal agents, as well as the understanding of polymerizing glycosyltransferases.     

Arrested chloride abstraction from trans-RuCl2(DMeOPrPE)2 with TlPF6; formation of a 1-D coordination polymer having unusual octahedral coordination around thallium(I)

An "arrested" chloride abstraction occurs in the reaction of trans-RuCl(2)(DMeOPrPE)(2) with TlPF(6); the product is a 1-D coordination polymer in which the Tl(I) centers have an unusual octahedral coordination geometry with a stereochemically active 6s(2) lone pair.     

Coherent shear phonon generation and detection with ultrashort optical pulses

Using an optical technique we generate and detect picosecond shear and quasishear coherent acoustic phonon pulses in the time domain. Thermoelastic and piezoelectric generation are directly achieved by breaking the sample lateral symmetry using crystalline anisotropy. We demonstrate efficient detection in isotropic and anisotropic media with various optical incidence geometries.     

Measurement of enzyme kinetics using microscale steady-state kinetic analysis

This paper describes a new technique--microscale steady-state kinetic analysis (microSKA)--that enables the rapid and parallel analysis of enzyme kinetics. Rather than physically defining a microscopic reactor through microfabrication, we show how the relative rates of reaction and transport in a macroscopic flow chamber, where the enzyme is immobilized on one wall of the chamber, results in the confinement of an enzyme-catalyzed reaction to a microscopic reactor volume adjacent to this wall. This volume has linear dimensions that are orders of magnitude smaller than the physical dimensions of the system (i.e., micrometer vs millimeter). Conversion within this volume is monitored at steady state as a function of position, rather than time. In this way, limitations due to reactor dead time and mixing are avoided. We use microSKA to determine kinetic parameters for the alkaline phosphatase-catalyzed de-phosphorylation of nonfluorescent methylumbelliferyl phosphate (MUP) to fluorescent 7-hydroxy-4-methylcoumarin (HMC) at two different values of pH. Kinetic parameters measured with microSKA are in good agreement with values obtained using conventional methods, if one takes into account effects of immobilization on enzyme activity. This technique provides a rapid and simple method for determining enzyme kinetics using small amounts of sample material and may be useful for applications in proteomics, drug discovery, biocatalyst development, and clinical diagnostics.     

Ordered mesoporous organic-inorganic hybrid materials containing microporous functional calix[8]arene amides

Ordered mesoporous organic-inorganic hybrid materials containing microporous functional calix[8]arene amides have been synthesized and characterized for the first time, and are shown to be effective in removal of trace humic acid contaminant from water.     

The dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase from Haemophilus influenzae is a dinuclear metallohydrolase

The Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra, of the dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE) from Haemophilus influenzae have been recorded in the presence of one or two equivalents of Zn(II) (i.e. [Zn_(DapE)] and [ZnZn(DapE)]). The Fourier transforms of the Zn EXAFS are dominated by a peak at ca. 2.0 A, which can be fit for both [Zn_(DapE)] and [ZnZn(DapE)], assuming ca. 5 (N,O) scatterers at 1.96 and 1.98 A, respectively. A second-shell feature at ca. 3.34 A appears in the [ZnZn(DapE)] EXAFS spectrum but is significantly diminished in [Zn_(DapE)]. These data show that DapE contains a dinuclear Zn(II) active site. Since no X-ray crystallographic data are available for any DapE enzyme, these data provide the first glimpse at the active site of DapE enzymes. In addition, the EXAFS data for DapE incubated with two competitive inhibitors, 2-carboxyethylphosphonic acid and 5-mercaptopentanoic acid, are also presented.     

Polystyrene/decahydronaphthalene/propane phase equilibria and polymer conformation properties from intrinsic viscosities

The influence of dissolved propane (up to 31.2 wt %) on the phase equilibria of 5 wt % polystyrene (PS) dissolved in 66/34 wt % trans/cis‐decahydronaphthalene (DHN) was measured over the temperature range of 323–423 K. A suitable temperature, pressure, and propane composition operating space was defined to measure intrinsic viscosities of a single fluid phase. Intrinsic viscosities of PS in cosolvent mixtures of propane and trans/cis‐DHN were measured between 323 and 423 K and between 70 and 208 bar. The addition of propane to the isomeric mixture of DHN resulted in a decreased solvent quality for PS, causing a contraction of the PS coil. The most dramatic decrease in solvent quality with the addition of propane occurred at 323 K and 70 bar with approximately a 36% reduction in the viscometric radius with the addition of 45 mol % propane to DHN. At 423 K, the solvent quality was less sensitive to the addition of propane and only a 13% reduction in the viscometric radius was observed at 70 bar and 45 mol % propane in DHN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011