Kinetics and mechanism of the reaction of CF3 radicals with NO2

The reaction of CF₃ with NO₂ was studied at 296 ± 2K using two different absolute techniques. Absolute rate constants of (1.6 ± 0.3) × 10⁻¹¹ and (2.1 _−0.3⁺⁰⁷) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were derived by IR fluorescence and UV absorption spectroscopy, respectively. The reaction proceeds via two reaction channels: CF₃ + NO₂ → CF₂O + FNO, (70 ± 12)% and CF₃ + NO₂ → CF₃O + NO, (30 ± 12)%. An upper limit of 11% for formation of other reaction products was determined. The overall rate constant was within the uncertainty independent of total pressure between 0.4 to 760 torr. © 1996 John Wiley & Sons, Inc.     

Parameter estimation in systems of differential equations,based on three-way data arrays and random time changes

Consider a system of n₁ × n₂ differential equations depending on a vector θ of unknown parameters. We suggest an iterative estimation procedure for θ, based on a three-way array of observations. The method involves random time changes driven by multidimensional integrated Ornstein-Uhlenbeck processes.     

Degenerate Second Order Differential Operators Generating Analytic Semigroups in Lp and W1,p

We deal with the problem of analyticity for the semigroup generated by the second order differential operator Au ≔ αu″ + βu′ (or by some restrictions of it) in the spaces L^p(0, 1), with or without weight, and in W^1,p(0, 1), 1 < p < ∞. Here α and β are assumed real‐valued and continuous in [0, 1], with α(x) > 0 in (0, 1), and the domain of A is determined by the generalized Neumann boundary conditions and by Wentzell boundary conditions.     

Solid State Structures of AsCl5 and SbCl5

Arsenic pentachloride has a trigonal bipyramidal structure in the solid state with As‐Cl_eq = 210.6, 211.9 pm, As‐Cl_ax= 220.7 pm, space group Pmmn, a = 706.2 (1); b = 760.3 (2), c = 623.3 (1) pm. Antimony pentachloride exists in two modifications: above −54.1 °C it is also trigonal bipyramidal with Sb‐Cl_eq = 227.0 and Sb‐Cl_ax = 233.3 pm, space group P6₃/mmc, a = 741.4 (1), c = 799.0(2)pm. Below −54.1 °C it changes reversibly into a double chlorine bridged dimer resulting in an edge shared double octahedral structure, space group P2₁/c, a = 952.4 (1), b = 1189.9 (1), c = 1219.7 (1) pm, β = 108, 27 (1): In presence of water the formation of AsCl₅ is hindered, two salts containing the octahedral anion AsCl₆⁻ have been isolated, [(H₅O₂⁺)₅AsCl₆⁻(Cl⁻)₄], space group C2/c, a= 1416.9 (2), b = 1316.6 (3), c = 1215.3 (2) pm, β; = 94.96 (1)°, and [(H₅O₂⁺)(AsCl₆⁻)·AsOCl₃], space group P2₁/n, a = 771.6 (3), b = 904.5 (3), c = 2140.7(2)pm, β = 100.21(1). The AsOCl₃ moiety in this compound appears as a monomer, in contrast to pure AsOCl₃, which is a doubly oxygen bridged dimer in the solid state.     

Physical and Chemical Characterization of Cellulose Based Textiles Modified by Periodate Oxidation

Conversion of dihydroxyl groups to dialdehyde by periodate oxidation is a useful method widely used in derivatization of cellulose to activate the polymer to further reactions as grafting polymerization. To investigate the cellulose behavior at different level of oxidation and to better understand the influence of the crystallinity on the effects induced by oxidative reactions on different cellulose materials, linen and cotton textiles have been oxidized with periodate solutions in different conditions. Oxidized cellulose samples have been characterized by several techniques: solid-state ¹³C NMR, Wide Angle X-Ray diffraction, and SEM. Moreover the mechanical properties of the untreated and oxidized yarns have been evaluated by means of tensile tests, the oxidation degree has been measured by means of the hydroxylamine hydrochloride method.     

New Polymers from Natural Phenols Using Horseradish or Soybean Peroxidase

The flavonol quercetin, its glycoside rutin, the flavanol catechin, the isoflavone daidzein and 5,6,4′‐trihydroxyisoflavone can be oxidatively polymerized via a radical polyrecombination mechanism catalyzed by horseradish or soybean peroxidase in a mixture of phosphate buffer (pH 7) and 1,4‐dioxane. The average molecular weights of the polymers were found to be in the range 4 000–12 000 g/mol. Daidzein derivatives with a methoxy (formononetin) or nitro group or a hydrogen atom at C‐4′ could not be polymerized under these conditions. These results and molecular modeling studies suggest that polymerization preferentially occurs via the electron‐rich ring B of the isoflavonoids. The polymers were characterized by means of FT‐IR and UV spectroscopy, and their redox behavior was analyzed using cyclic voltammetry.     

Hyaluronic Acid-Conjugated Carbon Nanomaterials for Enhanced Tumour Targeting Ability

Hyaluronic acid (HA) has been implemented for chemo and photothermal therapy to target tumour cells overexpressing the CD44⁺ receptor. HA-targeting hybrid systems allows carbon nanomaterial (CNM) carriers to efficiently deliver anticancer drugs, such as doxorubicin and gemcitabine, to the tumour sites. Carbon nanotubes (CNTs), graphene, graphene oxide (GO), and graphene quantum dots (GQDs) are grouped for a detailed review of the novel nanocomposites for cancer therapy. Some CNMs proved to be more successful than others in terms of stability and effectiveness at removing relative tumour volume. While the literature has been focused primarily on the CNTs and GO, other CNMs such as carbon nano-onions (CNOs) proved quite promising for targeted drug delivery using HA. Near-infrared laser photoablation is also reviewed as a primary method of cancer therapy—it can be used alone or in conjunction with chemotherapy to achieve promising chemo-photothermal therapy protocols. This review aims to give a background into HA and why it is a successful cancer-targeting component of current CNM-based drug delivery systems.     

Application of Sputter-Assisted EPMA to Depth Profile Analysis

 A common problem in depth profile measurement is the calibration of the depth scale. The new technique of sputter assisted electron probe microanalysis offers the possibility of calculating the composition as well as the depth scale solely from the acquired X-ray intensity data without further information, e.g. sputter rates. To achieve a depth resolution that is smaller than the depth of information of the electron probe, i.e. 0.1–1 μm, special deconvolution algorithms must be applied to the acquired data. To assess the capabilities of this new technique it was applied to a Ti/Al/Ti multilayer on Si under different measurement conditions. Quantitative depth profiles were obtained by application of a deconvolution algorithm based on maximum entropy analysis. By comparison of these profiles with AES depth profiles and AFM roughness measurements, it was shown that the limiting factor to the achievable depth resolution is the occurrence of surface roughening induced by the sputtering process rather than the relatively large depth of information of the electron probe. We conclude that for certain applications sputter-assisted EPMA can be regarded as a valid depth profiling technique with a depth resolution in the nm range.     

Spectrofluorimetric Determination of Methyl Paraben in Pharmaceutical Preparations by Means of its Dansyl Chloride Derivative

 A spectrofluorimetric method for the determination of methyl paraben based on derivatization with the labelling reagent dansyl chloride (DNS-Cl), is presented. The effect of the reaction variables (pH, DNS-Cl concentration, temperature, reaction time) and instrumental parameters, has been examined. A linear calibration graph in the ng/ml range has been established. The limit of detection is 18 ng/ml with relative standard deviation less than 3%. The proposed method has been satisfactorily applied to determination of the paraben in two pharmaceutical preparations. Received May 25, 1999. Revision October 20, 1999.