Results on the relative perturbation of the singular values of a matrix

A highly accurate computation of the singular values of a matrix is a topic of current interest in the literature. In this paper we develop general bounds on relative perturbation of singular values. These bounds permit slight improvements in a unified derivation of some previous inequalities. The main result is a better criterion to neglect off-diagonal elements in the bidiagonal singular values decomposition.The present paper has been developed under the M. U. R. S. T. 40% National Program and the Interuniversity Center of Numerical Analysis and Computational Mathematics.     

Flow injection determination of isosorbide dinitrate with polarographic detection

Polarographic determination of isosorbide dinitrate (ISDN) was performed in a flow injection system assembled from commercially available units. The detector could be operated either as a dropping mercury electrode or as a hanging mercury drop electrode. In addition to the influence of injection volume, coil length and pumping rate on sensitivity and peak widths, peak heights also depended on the presence of surfactants in samples and carrier stream. When a pump of high quality was used, the system was equal to a normal polarograph with regard to quality of results and ease of operation. The working range was 0.05–1 mM ISDN and the limit of detection 0.01 mM. The maximum sampling frequency was about 100 samples per hour. No deaeration of samples and carrier stream was required, because the carrier stream contained sodium sulfite in a slightly alkaline medium.     

X-ray photoelectron spectra of ruthenium(II) phthalocyanines

Summary The Ru 3d_5/2 and 3p_3/2 x-ray photoelectron spectra of mono-and non-chlorinated ruthenium phthalocyanines were measured and the collected data on the core-level binding energies of ruthenium have been used to assess the oxidation state of the metal and the composition of the macrocyclic ligands.     

An expeditious total synthesis of kalkitoxins: determination of the absolute stereostructure of natural kalkitoxin

Kalkitoxin, a potent neurotoxin isolated from the marine cyanobacteria Lyngbya majuscula, and its congeners (1-7) were efficiently synthesized utilizing Hruby's diastereoselective 1,4-addition and the Wipf's oxazoline-thiazoline conversion as key steps. These synthetic efforts in combination with spectral studies of natural kalkitoxin clearly determined the absolute stereostructure of kalkitoxin to be 7.     

Supramolecular helices via self-assembly of 8-oxoguanosines

The cooperative effect of solvophobic interactions and hydrogen bonding has been exploited to self-assemble supramolecular helical architectures of 8-oxoguanosines in different environments. This self-assembly into helical structures is completely different from that of the parent guanosines which, in the same experimental conditions, form flat, ribbonlike structures. While optical microscopy and X-ray diffraction suggest a chiral columnar aggregate in the LC phase, NMR and Circular Dichroism reveal the presence of a helical structures in solution. Scanning Tunneling Microscopy made it possible to visualize hexagonally arranged G-quartets on graphite, which are sections of the helices packed with their long axis perpendicular to the basal plane of the substrate. Due to their rectifying electrical properties, such helices are interesting for fabricating (opto)electronic biodevices.     

Monomeric copper(II) and nickel(II) complexes of N,N,N′,N′-tetrakis [(2-benzimidazolyl)methyl]-1,2-cyclohexanediamine], a chelating ligand containing imidazole groups

Summary Cu^II and Ni^II coordination compounds with N,N,N,N-tetrakis[(2-benzimidazolyl)methyl]-1,2-cyclohexanediamine (CDTB) have been prepared and characterized. The crystal structure of [Cu(CDTB)](ClO₄)₂ has been determined. The geometry around the Cu atom is highly irregular and can best be described as a cis-distorted octahedron, with four short CuN bond distances of 1.988(3) Å and 2.028(3) Å, and two very long CuN bond lengths of 2.543(4) A. The cis NCuN chelate angles in the complex range from 68.8(2) for N(1)CuN(1) to 141.03° for N(4)CuN(1). The cyclic voltammogram of the complex shows a fully reversible one-electron redox wave at E _1/2 = 0.162V versus standard calomel electrode, corresponding to the Cu^I/II redox couple. The structure of [Ni(CDTB)](NO₃)₂ ·EtOH has also been determined. The geometry around the Ni atom in this compound can be described as distorted octahedral, with N(4), N(4), N(1), N(1) as the ligating atoms in the basal plane, with cis chelate angles ranging from 79.37(10) to 120.9(2)° with the trans N(2)NiN(2) angle at 175.1(2)°. The structural differences in these two compounds are undoubtedly electronic rather than steric.     

Theoretical and experimental investigation of novel iron(II)-based spin crossover compounds

Two novel spin crossover (SCO) compounds, namely [Fe(INMe)(pyN₄)]Br₂, and [Fe(IMMe)(pyN₄)](OTf)₂, where pyN₄ = 2,6-Bis(1′,3′-diamino-2′methyl-prop-2′yl)pyridine, INMe = isonicotinic acid methyl ester, IMMe = N-methyl-imidazole, and OTf = triflate, are characterized here both from experimental and theoretical viewpoints. In particular, we apply various density functionals and basis sets to obtain optimized geometries for low- (LS) and high-spin (HS) states, vibrational spectra, LS–HS splittings, and temperature-dependent UV/vis spectra. While geometries and spectra are in good agreement with experimental data, the well-known spin pairing problem makes it difficult to compute accurate LS–HS splitting energies and enthalpies. Based on TD–DFT calculations, the capacity of the compounds for use as reversibly photo-switchable molecules is discussed.     

Preparative weak cation-exchange chromatography of monoclonal antibody variants I. Single-component adsorption

The retention behavior of a monoclonal antibody has been characterized on a weak cation exchanger, Fractogel EMD COO(-)(s). This new generation of resin materials comprise of a higher mechanical strength compared to softer gel-type matrices while maintaining elevated capacities, resulting in higher productivity and longer lifetimes. These parameters are extremely important when working with large bio-molecules such as proteins, and in particular monoclonal antibodies. In the first part of this work a parameter estimation strategy is presented to fully characterize the retention behavior of a single monoclonal antibody and determine suitable model parameters. Literature correlations were used for the estimation of mass transfer rates. The transport limiting parameter, pore diffusion, was regressed experimentally. Various methods for the adsorption isotherm determination have been applied, their combinations resulting in little experimental effort and accurate predictions of elution profiles. The process has been modelled with a complete pore diffusion model and the agreement between experimental and predicted profiles is good in general. However, a very marked sensitivity to changes in the effective pore diffusion coefficient has been observed. A correlation describing the effect of the separation conditions on the diffusion rate is therefore needed in order to have a fully predictive mathematical model.     

Photoinduced Palladium‐Catalyzed Negishi Cross‐Couplings Enabled by the Visible‐Light Absorption of Palladium–Zinc Complexes

A visible‐light‐induced Negishi cross‐coupling is enabled by the activation of a Pd⁰–Zn complex. With this photocatalytic method, the scope of deactivated aryl halides that can be employed in the Negishi coupling was significantly expanded. NMR experiments conducted in the presence and absence of light confirmed that the formation of the palladium–zinc complex is key for accelerating the oxidative addition step.