Facile aqueous synthesis and stabilization of nearly monodispersed gold nanospheres by poly(L‐proline)

A facile strategy is developed to synthesize Au nanoparticles (Au‐NPs) using water‐soluble poly(L ‐proline) (PLP). The synthesized NPs were characterized by TEM, FTIR and NMR spectroscopy, thermogravimetric analysis, and circular dichroism. It was found that PLP has a “dual” role as an efficient reductant of Au(III) and simultaneously as a stabilizing agent of Au‐NPs. The influence of PLP molecular weight, temperature, initial Au(III) concentration, and Au(III)/PLP molar ratio on the size and dispersity of Au‐NPs is examined. It was found that the unique extended secondary structure of PLP II resulted in the facile formation of highly crystalline Au‐NPs in water at a very low Au(III)/PLP molar ratio. These Au‐NPs have the smallest dimensions and size distributions among NPs synthesized so far by polymeric materials in aqueous media, and exhibit enduring colloidal stability. Therefore, by utilizing biocompatible and benign materials in water, we managed to obtain Au‐NPs, so as the final product is ready‐to‐use for biomedical applications. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Determination of Mn, Fe, and Cu in chemically-treated wood pulps by the XRF addition method

A rapid X-ray fluorescence addition method has been developed for quantification of the technically most important metals in wood pulp matrix (Mn, Fe, and Cu). Pretreatment consisted of just two steps: first, acid was added to the sample to achieve homogeneous distribution of the metals; the pulp was then pressed lightly on to Mylar film. Total analysis time was less than 10 min. The concentration range investigated was up to 15 mg kg^–1 for Mn and up to 5 mg kg^–1 for Fe and Cu. Metal concentrations in Scandinavian pulps are not expected to exceed these amounts. The quantification limit was 2 mg kg^–1 for all three metals. The reproducibilities and repeatabilities were concentration-dependent and varied between 3 and 19% and between 1 and 17%, respectively. The squares of the linear correlation coefficients between measured intensity and added metal concentration were 0.994, 0.950, and 0.932 for Mn, Fe, and Cu, respectively.     

Pairwise effects of chlorine substituents on the 13C NMR chemical shifts of dichlorobicyclo[2.2.1]heptanes (norbornanes)

The ¹³C NMR spectra of nine dichlorinated bicyclo[2.2.1]heptanes (norbornanes) have been measured and assigned. The pairwise effects of chlorine substituents which cause deviations from the additivity of single-substituent effects were investigated and are discussed. The largest effect found is the high-field shift of carbons bearing vicinal cis substituents. In the case of geminal substitution deviations from additivity were found to be to low field and large in the γ, smaller in the β and negligible in the α chemical shifts. The observed deviations for 1,3-disubstituted cases vary from ?3.2 to +1.1 ppm at different carbons, allowing no simple explanation. Replacement of α-hydrogen in a diaxial 1,3-arrangement by CH₃, OH or CI causes the single substituent effect, namely the γ_a effect, to change considerably.     

Re-evaluation of the First and Second Stoichiometric Dissociation Constants of Oxalic Acid at Temperatures from 0 to 60 °C in Aqueous Oxalate Buffer Solutions with or without Sodium or Potassium Chloride

Equations were developed for the calculation of the first stoichiometric (molality scale) dissociation constant (K _m1) of oxalic acid in buffer solutions containing oxalic acid, potassium hydrogen oxalate, and potassium chloride from the determined thermodynamic values of this dissociation constant (K _a1) and the molalities of the components in the solutions. Similar equations were also developed for the second stoichiometric dissociation constant (K _m2) of this acid in buffer solutions containing sodium or potassium hydrogen oxalate, oxalate and chloride. These equations apply at temperatures from 0 to 60 °C up to ionic strengths of 1.0 mol⋅kg⁻¹ and they have been based on single-ion activity coefficient equations of the Hückel type. For the equations for K _m1, the activity parameters of oxalate species and the K _a1 values were determined at various temperatures from the Harned cell data of a recent tetroxalate buffer paper (Juusola et al., J. Chem. Eng. Data 52:973–976, 2007). By using the resulting equations for K _m1, the activity parameters of oxalate species for K _m2 and the K _a2 values were then determined from the new Harned cell data and from those of Pinching and Bates (J. Res. Natl. Bur. Stand. (U.S.) 40:405–416, 1948) for solutions of sodium or potassium oxalates with NaCl or KCl. The resulting simple equations for calculation of K _m1 and K _m2 for oxalic acid were tested with all important thermodynamic data available in the literature for this purpose. The equations for ln (K _a1) and ln (K _a2) are of the form ln (K _a)=a+b(t/°C)+c(t/°C)². The coefficients for ln (K _a1) are the following: a=−2.8737, b=0.000159, and c=−0.00009. The corresponding coefficients for ln (K _a2) are −9.6563, −0.003059, and −0.000125, respectively. The new activity coefficient equations were used to evaluate the pH values of the tetroxalate buffer solution (i.e., of the 0.05 mol⋅kg⁻¹ KH₃C₄O₈ solution) for comparison with the pH values recommended by IUPAC at temperatures from 0 to 60 °C and to develop a new two-component oxalate pH buffer of 0.01 mol⋅kg⁻¹ KHC₂O₄+0.05 mol⋅kg⁻¹ Na₂C₂O₄ for which pH values are given from 0 to 60  °C. Values of p(m _H) calculated from these equations are tabulated for these buffers as well as for buffer solutions with KCl and KH₃C₄O₈ as the major component and minor component, respectively. Tables of p(m _H) are also presented for 0.001 mol⋅kg⁻¹ KHC₂O₄+0.005 mol⋅kg⁻¹ Na₂C₂O₄ solutions in which KCl is the supporting electrolyte.     

AC losses in high-temperature superconductors: revisiting the fundamentals of the loss modelling

The fundamentals of the electromagnetic modelling of high-temperature superconductors are discussed. Special attention is paid to intrinsic features of high-temperature superconductors different to those of low-temperature superconductors. Examples of those features are strong thermal fluctuations, which results in enhanced flux creep and slanted E(J)-characteristics, anisotropy of critical current density and material resistivity, and the granularity of the material. Having established the fundamental principles for the loss modelling, the influence of thermal fluctuations, anisotropy and granularity on the AC losses are considered.     

13C NMR spectroscopy of four tertiary methyl norbornenols and norbornanols

Carbon chemical shifts and direct ¹³C? ¹H coupling constants of 2-endo-methyl-5-norbornen-2-exo-ol, 2-exo-methyl-5-norbornen-2-endo-ol, 2-endo-methylnorbornan-2-exo-ol and 2-exo-methylnorbornan-2-endo-ol have been measured from single samples using a dual probe pulse Fourier transform method.     

Re-evaluation of the Activity Coefficients of Aqueous Hydrochloric Acid Solutions up to a Molality of 16.0 mol·kg<Superscript>−1</Superscript> Using the Hückel and Pitzer Equations at Temperatures from 0 to 50 °C

The simple three-parameter Pitzer and extended Hückel equations were used for calculation of activity coefficients of aqueous hydrochloric acid at various temperatures from 0 to 50 °C up to a molality of 5.0 mol·kg^?1. A more complex Hückel equation was also used at these temperatures up to a HCl molality of 16 mol·kg^?1. The literature data measured by Harned and Ehlers J. Am. Chem. Soc. 54, 1350–1357 (1932) and 55, 2179–2193 (1933) and by Åkerlöf and Teare [J. Am. Chem. Soc. 59, 1855–1868 (1937)] on galvanic cells without a liquid junction were used in the parameter estimations for these equations. The latter data consist of sets of measurements in the temperature range 0 to 50 °C at intervals of 10 °C, and data at these temperatures were used in all of these estimations. It was observed that the estimated parameters follow very simple equations with respect to temperature. They are either constant or depend linearly on the temperature. The values for the activity coefficient parameters calculated by using these simple equations are recommended here. The suggested new parameter values were tested with all reliable cell potential and vapor pressure data available in literature for concentrated HCl solutions. New Harned cell data at 5, 15, 25, 35, and 45 °C up to a molality of 6.5 mol·kg^?1 are reported and were also used in the tests. The activity coefficients obtained from the new equations were compared to those calculated by using the Pitzer equations of Holmes et al. [J. Chem. Thermodyn. 19, 863–890 (1987)] and of Saluja et al. [Can. J. Chem. 64, 1328–1335 (1986)] at various temperatures, and by using the extended Hückel equation of Hamer and Wu [J. Phys. Chem. Ref. Data 1, 1047–1099 (1972)] at 25 °C.     

Alkali treatment of birch kraft pulp to enhance its TEMPO catalyzed oxidation with hypochlorite

Alkali treatment was used to increase the reactivity of birch kraft pulp prior to its 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) catalyzed oxidation with hypochlorite, which is a process commonly applied to prepare nanofibrillated cellulose. On contrary to the traditional use of NaBr as a cocatalyst, TEMPO was activated with HOCl prior to the oxidation. Commonly, the lack of bromide increases the oxidation time and impairs the formation of carboxylic groups. However, the reaction time of the bromide-free TEMPO catalyzed oxidation could be shortened from 2.5 to 0.5 h when the pulp was treated with 1 M NaOH prior to the oxidation (2.4 mmol NaOCl/g pulp). The beneficial effect was obtained even if the alkali treatment was executed at room temperature and only for few minutes. Moreover, the alkali pretreatment enabled selective production of a pulp with carboxylate content as high as 1.6 mmol/g with NaOCl dosage of 4.4 mmol/g. The changes in the cellulosic raw material during the alkali treatment were assessed by water retention value and carbohydrate analysis.     

Characterization of proton-bound acetate dimers in ion mobility spectrometry

Ionized acetates were used as model compounds to describe gas-phase behavior of oxygen containing compounds with respect to their formation of dimers in ion mobility spectrometry (IMS). The ions were created using corona discharge at atmospheric pressure and separated in a drift tube before analysis of the ions by mass spectrometry. At the ambient operational temperature and pressure used in our instrument, all acetates studied formed dimers. Using a homolog series of n-alkyl-acetates, we found that the collision cross section of a dimer was smaller than that of a monomer with the same reduced mass. Our experiments also showed that the reduced mobility of acetate dimers with different functional groups increased in the order n-alkyl 相似文献   

The structure of MgO-SiO2 glasses at elevated pressure

The magnesium silicate system is an important geophysical analogue and neutron diffraction data from glasses formed in this system may also provide an initial framework for understanding the structure-dependent properties of related liquids that are important during planetary formation. Neutron diffraction data collected in situ for a single composition (38 mol% SiO(2)) magnesium silicate glass sample shows local changes in structure as pressure is increased from ambient conditions to 8.6 GPa at ambient temperature. A method for obtaining the fully corrected, total structure factor, S(Q), has been developed that allows accurate structural characterization as this weakly scattering glass sample is compressed. The measured S(Q) data indicate changes in chemical ordering with pressure and the real-space transforms show an increase in Mg-O coordination number and a distortion of the local environment around magnesium ions. We have used reverse Monte Carlo methods to compare the high pressure and ambient pressure structures and also compare the high pressure form with a more silica-poor glass (Mg(2)SiO(4)) that represents the approach to a more dense, void-free and topologically ordered structure. The Mg-O coordination number increases with pressure and we also find that the degree of continuous connectivity of Si-O bonds increases via a collapse of interstices.