Conformational Isomerism in Monomeric,Low‐Coordinate Group 12 Complexes Stabilized by a Naphthyl‐Substituted m‐Terphenyl Ligand

The synthesis and characterization of the first series of low‐coordinate bis(terphenyl) complexes of the Group 12 metals, [Zn(2,6‐Naph₂C₆H₃)₂] ( 1 ), [Cd(OEt₂)(2,6‐Naph₂C₆H₃)₂] ( 2 ) and [Hg(OEt₂)(2,6‐Naph₂C₆H₃)₂] ( 3 ) (Naph=1‐C₁₀H₇) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two‐coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three‐coordinate distorted T‐shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid‐state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution.     

Cumulant functions in optical coherence theory

Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders greater than some numberN ₀ vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would need to introduce cumulant tensors.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

Near-infrared Photoinactivation of Bacteria and Fungi at Physiologic Temperatures

We examined a laser system (870 and 930 nm), employing wavelengths that have exhibited cellular photodamage properties in optical traps. In vitro , with 1.5 cm diameter flat-top projections (power density of 5.66 W cm⁻²), at physiologic temperatures, we achieved photoinactivation of Staphylococcus aureus , Escherichia coli , Candida albicans and Trichophyton rubrum . Using nonlethal dosimetry, we measured a decrease in trans-membrane potentials (ΔΨmt and ΔΨp) and an increase in reactive oxygen species (ROS) generation in methicillin-resistant S. aureus (MRSA), C .  albicans and human embryonic kidney cells. We postulate that these multiplexed wavelengths cause an optically mediated mechano-transduction of cellular redox pathways, decreasing ΔΨ and increasing ROS. The cellular energetics of prokaryotic and fungal pathogens, along with mammalian cells, are affected in a similar manner when treated with these multiplexed wavelengths at the power densities employed. Following live porcine thermal tolerance skin experiments, we then performed human pilot studies, examining photodamage to MRSA in the nose and fungi in onychomycosis. No observable damage to the nares or the nail matrix was observed, yet photodamage to the pathogens was achieved at physiologic temperatures. The selective aspect of this near-infrared photodamage presents the possibility for its future utilization in human cutaneous antimicrobial therapy.     

Unfavorable electrostatic and steric interactions in DNA polymerase β E295K mutant interfere with the enzyme's pathway

Mutations in DNA polymerase β (pol β) have been associated with approximately 30% of human tumors. The E295K mutation of pol β has been linked to gastric carcinoma via interference with base excision repair. To interpret the different behavior of E295K as compared to wild-type pol β in atomic and energetic detail, we resolve a binary crystal complex of E295K at 2.5 ? and apply transition path sampling (TPS) to delineate the closing pathway of the E295K pol β mutant. Conformational changes are important components in the enzymatic pathway that lead to and ready the enzyme for the chemical reaction. Our analyses show that the closing pathway of E295K mutant differs from the wild-type pol β in terms of the individual transition states along the pathway, associated energies, and the active site conformation in the final closed form of the mutant. In particular, the closed state of E295K has a more distorted active site than the active site in the wild-type pol β. In addition, the total energy barrier in the conformational closing pathway is 65 ± 11 kJ/mol, much higher than that estimated for both correct (e.g., G:C) and incorrect (e.g., G:A) wild-type pol β systems (42 ± 8 and 45 ± 7 kJ/mol, respectively). In particular, the rotation of Arg258 is the rate-limiting step in the conformational pathway of E295K due to unfavorable electrostatic and steric interactions. The distorted active site in the closed relative to open state and the high energy barrier in the conformational pathway may explain in part why the E295K mutant is observed to be inactive. Interestingly, however, following the closing of the thumb but prior to the rotation of Arg258, the E295K mutant complex has a similar energy level as compared to the wild-type pol β. This suggests that the E295K mutant may associate with DNA with similar affinity, but it may be hampered in continuing the process of chemistry. Supporting experimental data come from the observation that the catalytic activity of wild-type pol β is hampered when E295K is present: this may arise from the competition between E295K and wild-type enzyme for the DNA. These combined results suggest that the low insertion efficiency of E295K mutant as compared to wild-type pol β may be related to a closed form distorted by unfavorable electrostatic and steric interactions between Arg258 and other key residues. The active site is thus less competent for proceeding to the chemical reaction, which may also involve a higher reaction barrier than the wild-type or may not be possible in this mutant. Our analysis also suggests further experiments for other mutants to test the above hypothesis and dissect the roles of steric and electrostatic factors on enzyme behavior.     

A stereoselective synthesis of anti-gamma,delta-alkynyl- and -alkenyl-beta-hydroxy-alpha-amino esters from tin(II) enolates of glycinate

Condensations between the tin(II) enolate 11 of ethyl N-tosylglycinate and conjugated ynals 12 and ynones 14 are highly diastereoselective, in favour of the anti-isomers 13 and 15; similar reactions of enals and enones 17 show lower but still useful levels of anti-stereoselectivity.     

Low-coordinate cobalt(ii) terphenyl complexes: precursors to sterically encumbered ketones

Cobalt(ii) diaryl complexes react with CO to afford Co(2)(CO)(8) and sterically encumbered ketones whose structure varies depending on the nature of the aryl ligands.     

Immobilization of acetylcholinesterase in lipid membranes deposited on self-assembled monolayers

Human red blood cell acetylcholinesterase was incorporated into planar lipid membranes deposited on alkanethiol self-assembled monolayers (SAMs) on gold substrates. Activity of the protein in the membrane was detected with a standard photometric assay and was determined to be similar to the protein in detergent solution or incorporated in lipid vesicles. Monolayer and bilayer lipid membranes were generated by fusing liposomes to hydrophobic and hydrophilic SAMs, respectively. Liposomes were formed by the injection method using the lipid dimyristoylphosphatidylcholine (DMPC). The formation of alkanethiol SAMs and lipid monolayers on SAMs was confirmed by sessile drop goniometry, ellipsometry, and electrochemical impedance spectroscopy. In this work, we report acetylcholinesterase immobilization in lipid membranes deposited on SAMs formed on the gold surface and compare its activity to enzyme in solution.     

Photodamage to Multidrug-resistant Gram-positive and Gram-negative Bacteria by 870 nm/930 nm Light Potentiates Erythromycin,Tetracycline and Ciprofloxacin

We have previously shown that 870 nm/930 nm wavelengths cause photodamage at physiologic temperatures in methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli via generation of endogenous radical oxygen species (ROS) and decreased plasma membrane potentials (ΔΨp). We tested MRSA (Strain HSJ216) in vitro with sublethal 870 nm/930 nm laser energy and subinhibitory concentrations of erythromycin, tetracycline, penicillin, rifampin and trimethoprim to surmise whether photodamage could potentiate these antimicrobials. We also tested patient isolates of fluoroquinolone-resistant MRSA and E. coli with subinhibitory concentrations of ciprofloxacin. In MRSA (Strain HSJ216) we observed 97% potentiation (a 1.5 log₁₀ CFU decrease) with erythromycin and tetracycline. In patient isolates of E. coli, we observed 100% potentiation (>3 log₁₀ CFU decrease) in all irradiated samples with ciprofloxacin. To assess whether staphyloxanthin pigment conferred protection against the generated ROS, we created an isogenic carotenoid-deficient mutant of S. aureus that was significantly less tolerant of 870 nm/930 nm exposure than the wild type strain (P < 0.0001). We suggest that antibiotic potentiation results from a photobiological attenuation of ATP-dependent macromolecular synthetic pathways, similar to that observed with daptomycin, via disruption of ΔΨp and endogenous generation of ROS. With erythromycin, tetracycline and ciprofloxacin, attenuation of energy-dependent efflux systems is also a possibility.     

铌酸锶钡薄膜的微结构与电光性能的研究

本文叙述了使用溶胶凝胶法在MgO(0 0 1)的衬底上制备铌酸锶钡薄膜的过程 ,膜层厚度可达 5 μm。通过X射线衍射、摇摆曲线、扫描、拉曼散射光谱等方法研究了薄膜的微结构性能 ,实验发现 ,铌酸锶钡薄膜具有了较好的 (0 0 1)方向的优先取向性能 ,并且随着薄膜厚度的增加 ,其晶体取向性也会随之不断改进。熔石英的透明衬底上生长的SBN薄膜具有较大的电致双折射效应 ,其有效电光系数能够高达 6 6 2× 10 -11m/V。