Binuclear 2,2′-bipyrimidine complexes derived from chromium,molybdenum and tungsten carbonyls

Reaction of 2,2′-bipyrimidine (bpym) with [Mo(CO)₄(diene)] gives [Mo(CO)₄(bpym)], which will react with [M(CO)₄(diene)] to form [MoM(CO)₈(bpym)] (M = Cr, Mo, W). The bipyrimidine complexes are characterised by microanalysis and spectroscopy (IR, ¹H and ¹³C NMR, UV/vis). Reduction of [Mo₂(CO)₈(bpym)] produces an anion in which the unpaired electron is localised on the bridging bpym ligand.     

Do The Twist: Efficient Heavy-Atom-Free Visible Light Polymerization Facilitated by Spin-Orbit Charge Transfer Inter-system Crossing

The use of visible light to drive polymerizations with spatiotemporal control offers a mild alternative to contemporary UV-light-based production of soft materials. In this spectral region, photoredox catalysis represents the most efficient polymerization method, yet it relies on the use of heavy-atoms, such as precious metals or toxic halogens. Herein, spin-orbit charge transfer intersystem crossing from boron dipyrromethene (BODIPY) dyads bearing twisted aromatic groups is shown to enable efficient visible light polymerizations in the absence of heavy-atoms. A ≈5–15× increase in polymerization rate and improved photostability was achieved for twisted BODIPYs relative to controls. Furthermore, monomer polarity had a distinct effect on polymerization rate, which was attributed to charge transfer stabilization based on ultrafast transient absorption and phosphorescence spectroscopies. Finally, rapid and high-resolution 3D printing with a green LED was demonstrated using the present photosystem.     

Quantitating the relative abundance of isoaspartyl residues in deamidated proteins by electron capture dissociation

Relative quantitation of aspartyl and isoaspartyl residue mixtures from asparagine deamidation is demonstrated using electron capture dissociation without prior HPLC separation. The method utilizes the linear relationship found between the relative abundance of the isoaspartyl diagnostic ion, z(n)-57, and % isoaspartyl content based on the ECD spectra of known isoaspartyl/aspartyl mixtures of synthetic peptides. The observed linearity appears to be sequence independent because the relationship exists despite sequence variations and changes in backbone fragment abundances when isoaspartyl and aspartyl residues are interchanged. Furthermore, a new method to calculate the relative abundances of isomer from protein deamidation without synthetic peptides is proposed and tested using a linear peptide released by protein digestion that contains the deamidation site. The proteolytic peptide can be rapidly aged to the expected 3:1 (isoaspartyl:aspartyl) mixture to generate a two-point calibration standard for ECD analysis. The procedure can then be used to determine the relative abundance of deamidation products from in vivo or in vitro protein aging experiments.     

What can electrochemistry tell us about individual enzymes?

We provide here a critical analysis of electrochemistry's potential and limitations in investigating single-enzyme catalysis, highlighting papers of interest from the past 2–3 years with an emphasis on nano-impact electrochemistry (NIE) and electrochemical scanning tunneling microscopy. NIE can report single-enzyme activity; however, its future broad applicability for studying freely diffusing individual enzymes is questionable. Electrochemical scanning tunneling microscopy, an alternative to NIE, measures single enzyme's electronic conductivity when suspended between two electrodes. Recent discoveries indicate that enzyme conductance depends directly on biophysical parameters such as substrate binding, oxidation state of the catalytic center, and structural fluctuations. We conclude with a short perspective on additional electrochemical routes and combinations of existing techniques that may be useful for studying single-enzyme characteristics.     

Synthesis of 1,2,3,4-tetrahydro-5H-[1]benzopyrano[3,4-c]pyridin-5-ones. I. 3-unsubstituted compounds

Synthesis of 1,2,3,4-tetrahydro-5H-[1]benzopyrano[3,4-c]pyridin-5-ones via a Pechmann condensation of 3-carbethoxy-1-methyl-4-piperidone with various phenols is described. The limitations of this method are discussed. Synthesis of the parent ring system 3a via reduction of 1,2,3,4-tetrahydro-3-(phenylmethyl)-8-[(1-phenyl-1H-tetrazol-5-yl)oxy]-5H-[1]benzopyrano[3,4-c]pyridin-5-one ( 5 ) is also described.     

Semiclassical glory analyses in the time domain for the H + D2(v(i) = 0, j(i) = 0) → HD(v(f) = 3, j(f) = 0) + D reaction

We make the first application of semiclassical (SC) techniques to the plane-wavepacket formulation of time-domain (T-domain) scattering. The angular scattering of the state-to-state reaction, H + D(2)(v(i) = 0, j(i) = 0) → HD(v(f) = 3, j(f) = 0) + D, is analysed, where v and j are vibrational and rotational quantum numbers, respectively. It is proved that the forward-angle scattering in the T-domain, which arises from a delayed mechanism, is an example of a glory. The SC techniques used in the T-domain are: An integral transitional approximation, a semiclassical transitional approximation, a uniform semiclassical approximation (USA), a primitive semiclassical approximation and a classical semiclassical approximation. Nearside-farside (NF) scattering theory is also employed, both partial wave and SC, since a NF analysis provides valuable insights into oscillatory structures present in the full scattering pattern. In addition, we incorporate techniques into the SC theory called "one linear fit" and "two linear fits", which allow the derivative of the quantum deflection function, Θ?(')(J), to be estimated when Θ?J exhibits undulations as a function of J, the total angular momentum variable. The input to our SC analyses is numerical scattering (S) matrix data, calculated from accurate quantum collisional calculations for the Boothroyd-Keogh-Martin-Peterson potential energy surface No. 2, in the energy domain (E-domain), from which accurate S matrix elements in the T-domain are generated. In the E-domain, we introduce a new technique, called "T-to-E domain SC analysis." It half-Fourier transforms the E-domain accurate quantum scattering amplitude to the T-domain, where we carry out a SC analysis; this is followed by an inverse half-Fourier transform of the T-domain SC scattering amplitude back to the E-domain. We demonstrate that T-to-E USA differential cross sections (DCSs) agree well with exact quantum DCSs at forward angles, for energies where a direct USA analysis in the E-domain fails.     

Engineered cells as biosensing systems in biomedical analysis

Over the past two decades there have been great advances in biotechnology, including use of nucleic acids, proteins, and whole cells to develop a variety of molecular analytical tools for diagnostic, screening, and pharmaceutical applications. Through manipulation of bacterial plasmids and genomes, bacterial whole-cell sensing systems have been engineered that can serve as novel methods for analyte detection and characterization, and as more efficient and cost-effective alternatives to traditional analytical techniques. Bacterial cell-based sensing systems are typically sensitive, specific and selective, rapid, easy to use, low-cost, and amenable to multiplexing, high-throughput, and miniaturization for incorporation into portable devices. This critical review is intended to provide an overview of available bacterial whole-cell sensing systems for assessment of a variety of clinically relevant analytes. Specifically, we examine whole-cell sensing systems for detection of bacterial quorum sensing molecules, organic and inorganic toxic compounds, and drugs, and for screening of antibacterial compounds for identification of their mechanisms of action. Methods used in the design and development of whole-cell sensing systems are also reviewed.     

Solid-state reactions from isothermal heat conduction microcalorimetry theoretical approach and evaluation via simulated data

Several recent publications from this laboratory have reported developments in the capacity to calculate thermodynamic and kinetic parameters, such as rate constant, enthalpy, order of reaction, from isothermal micro-calorimetric data. To date these developments have all been associated with the calculation of the desired parameters from solution phase reactions. This paper furthers these developments to a theoretical consideration of solid-state reactions and the calculation of the values for the rate coefficient, k, the fitting parameters m and n, the total number of joules released over the lifetime of reaction, Q, and hence either the specific enthalpy or the molar enthalpy of reaction, H. This revised version was published online in July 2006 with corrections to the Cover Date.