Oxone as an inexpensive, safe, and environmentally benign oxidant for C-H bond oxygenation

[reaction: see text] This paper describes the application of peroxide-based oxidants in the Pd(OAc)(2)-catalyzed acetoxylation and etherification of arene and alkane C-H bonds. Oxone in acetic acid and/or methanol proved particularly effective, and these transformations were applied to a wide variety of substrates.     

Dynamics of a viral infectiology under treatment

This paper deals with a nonlinear model of the viral dynamics which describes the interactions between the human immune system and the virus. The novelty of this work is the introduction of combined treatments in the dynamics to modify the model. We investigate the qualitative behavior of the model and find a threshold parameter that guarantees the asymptotic stability of the equilibrium points, this parameter is known as the basic reproduction number. We estimated the parameters of the model by least-squares minimization between the numerical solution of the system and clinical data of cell cultures. It is also demonstrated that critical drug efficacy in terms of the model parameter is greatly useful to curtail the spreading of the disease.     

Spectroscopic study of solid benzene and benzene isolated in rare-gas matrices

Absorption and luminescence excitation spectra of solid benzene and benzene isolated in rare-gas matrices have been studied. The absolute absorption cross sections of various electronic band systems including the Rydberg region of C₆H₆ are obtained using transmission spectra of C₆H₆-doped rare-gas films of different thickness. An interpretation of the structure in the Rydberg region is given in terms of two Rydberg series using the quantum defect method. A comparative study has been made of luminescence excitation spectra of matrix-isolated and of pure C₆H₆. The luminescence excitation spectra of matrix-isolated benzene gives information on the internal conversion and medium-induced vibrational relaxation.     

Structure of poly(methyl methacrylate) chains adsorbed on sapphire probed using infrared-visible sum frequency generation spectroscopy

We have studied the orientation of the train segments of a poly(methyl methacrylate) (PMMA) adsorbed layer at the CCl4-sapphire interface using surface-sensitive IR-visible sum frequency generation (SFG) spectroscopy. The SFG spectra of PMMA chains adsorbed on sapphire indicate ordered ester methyl groups. In comparison, we did not observe any significant contributions from the backbone methylene and alpha methyl groups, suggesting that these groups are disordered. No change in the structure of the adsorbed layer is observed upon cooling the solvent below the theta temperature; this is consistent with the picture of flat adsorbed chains on the surface. Interestingly, the orientation of the ester methyl groups of a spin-coated PMMA film at the PMMA-sapphire interface is similar to that of the same groups in the chains adsorbed from solution.     

Adsorption properties of thermally stable and biologically active polyurea: its synthesis and spectral aspects

Novel polymer metal complexes were prepared by the condensation polymerization of a polymeric ligand with transition metal ions of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). The polymeric ligand was prepared by the addition polymerization of urea with toluene 2,4‐diisocyanate in 1:1 molar ratio. The polymeric ligand and its polymer metal complexes were characterized by elemental analysis, Fourier transform infrared spectroscopy, ¹³C‐NMR, and¹H‐NMR (nuclear magnetic resonance). The geometry was determined by electronic spectra and magnetic moment measurement. Thermogravimetric analysis (TGA) was utilized to find out the degradation process of the polyurea ligand and the polymer metal complexes. The TGA data revealed that all the metal‐containing polyureas are much more thermally stable than the corresponding polyurea ligand. The surface morphology of the polyurea ligand and cobalt(II)‐containing polyureas was determined by scanning electron micrographs. The antibacterial and antifungal activities of all the synthesized polymers were investigated against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis (bacteria) and Aspergillus niger, Candida albicans, and Aspergillus flavus (fungi). These compounds show remarkably good biocidal activities, which were enhanced after complexation with the metal. Batch adsorption studies of the ligand were carried out for malachite green dye, and the polyurea ligand was found to be a good adsorbent for this dye. Copyright © 2011 John Wiley & Sons, Ltd.     

A distal pocket Leu residue inhibits the binding of O2 and NO at the distal heme site of cytochrome c'

Cytochromes c' are pentacoordinate heme proteins with sterically hindered distal sites that bind NO and CO but do not form stable complexes with O(2). Removal of distal pocket steric hindrance via a Leu→Ala mutation yields favorable O(2) binding (K(d) ~49 nM) without apparent H-bond stabilization of the Fe-O(2) moiety, as well as an extremely high distal heme-NO affinity (K(d) ~70 fM). The native Leu residue inhibits distal coordination of diatomic ligands by decreasing k(on) as well as increasing k(off). The connection between distal steric constraints, k(off) values, and distal to proximal heme-NO conversion is discussed.     

Challenges of sulfur SAD phasing as a routine method in macromolecular crystallography

The sulfur SAD phasing method allows the determination of protein structures de novo without reference to derivatives such as Se‐methionine. The feasibility for routine automated sulfur SAD phasing using a number of current protein crystallography beamlines at several synchrotrons was examined using crystals of trimeric Achromobacter cycloclastes nitrite reductase (AcNiR), which contains a near average proportion of sulfur‐containing residues and two Cu atoms per subunit. Experiments using X‐ray wavelengths in the range 1.9–2.4 Å show that we are not yet at the level where sulfur SAD is routinely successful for automated structure solution and model building using existing beamlines and current software tools. On the other hand, experiments using the shortest X‐ray wavelengths available on existing beamlines could be routinely exploited to solve and produce unbiased structural models using the similarly weak anomalous scattering signals from the intrinsic metal atoms in proteins. The comparison of long‐wavelength phasing (the Bijvoet ratio for nine S atoms and two Cu atoms is ～1.25% at ～2 Å) and copper phasing (the Bijvoet ratio for two Cu atoms is 0.81% at ～0.75 Å) for AcNiR suggests that lower data multiplicity than is currently required for success should in general be possible for sulfur phasing if appropriate improvements to beamlines and data collection strategies can be implemented.     

On‐line optical and X‐ray spectroscopies with crystallography: an integrated approach for determining metalloprotein structures in functionally well defined states

X‐ray‐induced redox changes can lead to incorrect assignments of the functional states of metals in metalloprotein crystals. The need for on‐line monitoring of the status of metal ions (and other chromophores) during protein crystallography experiments is of growing importance with the use of intense synchrotron X‐ray beams. Significant efforts are therefore being made worldwide to combine different spectroscopies in parallel with X‐ray crystallographic data collection. Here the implementation and utilization of optical and X‐ray absorption spectroscopies on the modern macromolecular crystallography (MX) beamline 10, at the SRS, Daresbury Laboratory, is described. This beamline is equipped with a dedicated monolithic energy‐dispersive X‐ray fluorescence detector, allowing X‐ray absorption spectroscopy (XAS) measurements to be made in situ on the same crystal used to record the diffraction data. In addition, an optical microspectrophotometer has been incorporated on the beamline, thus facilitating combined MX, XAS and optical spectroscopic measurements. By uniting these techniques it is also possible to monitor the status of optically active and optically silent metal centres present in a crystal at the same time. This unique capability has been applied to observe the results of crystallographic data collection on crystals of nitrite reductase from Alcaligenes xylosoxidans, which contains both type‐1 and type‐2 Cu centres. It is found that the type‐1 Cu centre photoreduces quickly, resulting in the loss of the 595 nm peak in the optical spectrum, while the type‐2 Cu centre remains in the oxidized state over a much longer time period, for which independent confirmation is provided by XAS data as this centre has an optical spectrum which is barely detectable using microspectrophotometry. This example clearly demonstrates the importance of using two on‐line methods, spectroscopy and XAS, for identifying well defined redox states of metalloproteins during crystallographic data collection.