Potentiometric determination of silver with dithiooxamide

Potentiometric titration with dithiooxamide solution can be used to determine silver in the 0.0100–50.0 p.p.m range with an average accuracy of ca. 0.5% and a relative standard deviation ranging from 1.26% to 0.03% The metals commonly associated with silver can be masked with fluoride and EDTA The advantages of the method over other potentiometric and common spectrophotometric methods are outlined.     

Use of the Bell–Evans–Polanyi Principle to predict regioselectivity of nucleophilic aromatic photosubstitution reactions

Regioselectivity of nucleophilic aromatic photosubstitution has been shown experimentally to depend upon activation energies of the competing transition states. Computational means of determining relative activation energies were sought, therefore, in order to predict regioselectivity. Optimization of the three triplet transition states of 2-chloro-4-nitroanisole with hydroxide ion gave energies of insufficient accuracy to predict regioselectivity. Computed enthalpy changes from the first triplet transition state to the triplet σ-complexes correlated precisely with the experimental activation energies. This exemplifies the Bell–Evans–Polanyi Principle, and it provides an accurate means of assessing regioselectivity.     

Matrix Isolation Spectroscopic and Relativistic Quantum Chemical Study of Molecular Platinum Fluorides PtFn (n=1–6) Reveals Magnetic Bistability of PtF4

Molecular platinum fluorides PtF_n, n=1–6, are prepared by two different routes, photo-initiated fluorine elimination from PtF₆ embedded in solid noble-gas matrices, and the reaction of elemental fluorine with laser-ablated platinum atoms. IR spectra of the reaction products isolated in rare-gas matrices under cryogenic conditions provide, for the first time, experimental vibrational frequencies of molecular PtF₃, PtF₄ and PtF₅. Photolysis of PtF₆ enabled a highly efficient and almost quantitative formation of molecular PtF₄, whereas both PtF₅ and PtF₃ were formed simultaneously by subsequent UV irradiation of PtF₄. The vibrational spectra of these molecular platinum fluorides were assigned with the help of one- and two-component quasirelativistic DFT computation to account for scalar relativistic and spin–orbit coupling effects. Competing Jahn-Teller and spin–orbit coupling effects result in a magnetic bistability of PtF₄, for which a spin-triplet (³B_2g, D_2h) coexists with an electronic singlet state (¹A_1g, D_4h) in solid neon matrices.     

A study of the interactions between carboplatin and blood plasma proteins using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry

To study the carboplatin–protein interaction, a sensitive method using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC–ICP–MS) was developed. The complexes formed between plasma proteins and carboplatin were monitored and identified with this method. Composite blood plasma samples from patients who were undergoing chemotherapy were analyzed, and carboplatin was found to bind plasma proteins. In addition, blank plasma samples were spiked with carboplatin and were analyzed as a time course study, and the results confirmed that carboplatin formed complexes with plasma proteins, primarily albumin and γ-globulin. To further substantiate the study, these two proteins were incubated with carboplatin. The binding between carboplatin and these proteins was then characterized qualitatively and quantitatively. In addition to a one-to-one binding of Pt to protein, protein aggregation was observed. The kinetics of the binding process of carboplatin to albumin and γ-globulin was also studied. The initial reaction rate constant of carboplatin binding to albumin was determined to be 0.74 M⁻¹ min⁻¹, while that for γ-globulin was 1.01 M⁻¹ min⁻¹, which are both lower than the rate constant of the cisplatin–albumin reaction previously reported.     

Approximating dominant singular triplets of large sparse matrices via modified moments

A procedure for determining a few of the largest singular values and corresponding singular vectors of large sparse matrices is presented. Equivalent eigensystems are solved using a technique originally proposed by Golub and Kent based on the computation of modified moments. The asynchronicity in the computations of moments and eigenvalues makes this method attractive for parallel implementations on a network of workstations. Although no obvious relationship between modified moments and the corresponding eigenvectors is known to exist, a scheme to approximate both eigenvalues and eigenvectors (and subsequently singular values and singular vectors) has been produced. This scheme exploits both modified moments in conjunction with the Chebyshev semi-iterative method and deflation techniques to produce approximate eigenpairs of the equivalent sparse eigensystems. The performance of an ANSI-C implementation of this scheme on a network of UNIX workstations and a 256-processor Cray T3D is presented.This research was supported in part by the National Science Foundation under grant numbers NSF-ASC-92-03004 and NSF-ASC-94-11394.     

Bounds for the round-off errors in the richardson second order method

The application of the Richardson second order iterative method to positive definite, symmetric linear equations is investigated. Absolute and statistical bounds for the round-off error are derived. The statistical theory agrees well with numerical experiments, until the accumulated round-off error becomes of the order of magnitude of the error in the computed solution. After this point the statistical dependence between the local round-off errors makes the observed variances larger than the theoretical variances.This paper (and the Appendix) describe research carried out while both authors were employed by Space Technology Laboratories, Inc., Los Angeles, California.Presented at the IFIP Congress, 1962, under a National Science Foundation travel grant.     

New chiral anion mediated asymmetric chemistry

Chemical reactions and processes often involve chiral, yet racemic, cationic reagents, intermediates or products. To afford instead non racemic or enantiopure compounds, an asymmetric ion pairing of the cations with enantiopure anions can be considered--the counter ions behaving as asymmetric auxiliaries, ligands or reagents. Detailed herein is a short review of our approach towards gaining reliable and predictable control over stereoselective ion pairing phenomena through the synthesis and the use of novel configurationally stable hexacoordinated phosphate anions.