Dynamic light scattering,a probe of brownian particle dynamics

The principles and techniques of dynamic light scattering (DLS) are outlined and its application to the study of suspensions of interacting colloidal particles is discussed. We show how, under appropriate conditions, DLS can measure long-time collective and self-diffusion coefficients as well as study short-time motions (characterized by the cumulants). These theoretical considerations are illustrated by experimental data. Finally, we discuss the relevance of certain characteristic timescales to theories of the diffusion of interacting particles.     

Modification chimique des polyalcadiènes par les composés du type CX3Z—I Addition catalysée des composés CCl3Z sur les polybutadiènes-1,2

The influence of catalysis on chemical modification of 1,2-polybutadienes (M_n < 10,000) by CX₃Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl₃POCl₂) and ethyl trichloroacetate (CCl₃CO₂Et) in the presence of solvents such as C₆H₆, CH₂Cl₂. Among the compounds tested as catalysts for the addition of CX₃Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl₂, FeCl₃, RuCl₃ 3H₂O, Fe₂(CO)₉ and Cl₂Ru(PPh₃)₃ were found to show high catalytic activity. The most active is Cl₂Ru(PPh₃)₃: used without or with cocatalysts (Et₃NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX₃Z. The activity of the other catalysts is generally dependent on CX₃Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found.     

Study of the microstructure of tetrahydrofuran-3,3 dimethyloxetane copolymers by 13C-NMR spectroscopy.

The microstructure of tetrahydrofuran (A)-3,3 dimethyloxetane (B) copolymers was studied by ¹³C-{¹H}-NMR spectroscopy. Only the methyl carbons corresponding to the 3,3 dimethyloxetane unit appear as a singlet, whereas the other carbons present a more complicated spectral pattern than it would be expected if ? effects were negligible. The assignment of the resonance signals allowed the determination of the values of the probabilities of the different triads, which were in good agreement with those obtained from the reactivity ratios.     

Construction and analytical applications of an extractive electrode sensitive to mercury(I)

The construction and characteristics of a new type of extractive electrode sensitive to Hg(2+)(2) are described. The performance of the electrode is compared with that of an ion-selective electrode with mercurous dithizonate as the active substance. The Hg(2+)(2) -extractive electrode contains Pd(HDz)(2) in its membrane. Its stability and sensitivity are remarkable. It has been used as indicator electrode for the titration of halides alone and in mixtures, and for determination of mercury(I), mercury(II), silver, and of substances containing or reacting with mercury. The basis of the electrode response is discussed.     

Hétérocyclisations intramoléculaires par réaction d'oxymercuration. I — synthèse et configurations des hétérocycles

We have accomplished the intramolecular oxymercuration of γ-δ ethylenic alcohols, with different mercuric salts under different conditions. By “in situ” reduction, or by direct reduction of isolated mercuric compounds, we obtain, in some cases, diastereoisomers with different relative yields.     

Spectrophotometric determination of the protolytic dissociation constants of the new chromogenic reagent "palladiazo"-I Investigations with sodium hydroxide, perchloric acid and different aqueous buffer solutions

The "palladiazo" reagent has been subjected to a detailed spectrophotometric investigation in concentrated perchloric acid, different aqueous buffers and concentrated sodium hydroxide solutions. K(1)-K(10) and (1)-(10) values corresponding to the instability constants of the protolytic equilibria involved and to the molar absorptivities at 540 and 630 run of the different proton complex species of the system have been calculated by a number of analytical and graphical spectrophotometric methods. Special attention has been paid to the study of the complicated phenomena implied by the interaction of the reagent with perchloric acid, which has been shown to give rise to alteration of the initial isomeric composition of the reagent and to the formation of addition and/or oxidation products derived from side-reactions undergone by the reagent with the medium. All the instability constants and molar absorptivities, which have been determined by several methods, are tabulated for comparison.     

Critical evaluation of spiking of low-grade ore samples in activation analysis for gold and uranium

In applying non-destructive neutron-activation analysis for gold and uranium in spiked low-grade ore samples, the following extrapolated unspiked concentrations were measured: 0.27₈ ± 0.01₅ ppm gold (chemical assay: 0.20₂ ± 0.02₀ ppm gold); 25.1 ± 1.1 ppm uranium (chemical assay value: 19.5 ±2.0 ppm uranium). Different approaches to the fitting of results, and the influence of spiking non-uniformity, are discussed.     

EMISSION SPECTRA FROM SYNTHETIC POLYNUCLEOTIDES AND DEOXYRIBONUCLEIC ACID IN AQUEOUS SOLUTIONS†

A study has been made of the emission spectra at 77°K from poly A, poly U, poly C, their complexes, and from native and heat-denatured DNA in buffered aqueous solutions containing 0·25 per cent glucose: no emission was observed from these polynucleotides at room temperature. The spectra differed from those obtained in the polyalcoholic glasses used by other workers. The principal differences between the emission spectra of poly A and adenosine at pH 7 in a water-glucose mixture were: (a) a decrease in both P/F and the overall intensity in poly A; (b) absence of the structure normally found in adenosine phosphorescence; and (c) appearance of a new short-lived component in the phosphorescence decay. Further changes in the emission characteristics (e.g. the increase of P/F, the proportional increase of the short-lived component in the phosphorescence decay) from poly A were observed at pH 5. These can not be explained solely by protonization of adenosine residues, but rather appear to depend upon exciton interactions of the most intense π–π* transition in double-stranded poly A. and perturbation of the lowest-lying emitting band. When poly A or poly C is complexed with poly U or poly I the luminescence intensity decreases in two-strand complexes and is completely quenched in poly (A + 2U), poly (A+2I) and poly (C⁺+I); no emission was observed from either, single-strand poly I or poly U. Identical emission patterns were obtained from native and heat-denatured samples of DNA. The comparison of polynucleotide emission spectra in the water-glucose medium with those obtained from polyalcoholic glasses leads to the conclusion that the emission spectra depend most critically upon the relative proportions of base-solvent and base-base interactions in each environment: the possible importance of proton tunneling and/or triplet-triplet transfer mechanisms is briefly discussed.     

Crystal structure,Mössbauer,and magnetic behavior of mixed valence compounds in the BaFeS system: Ba3(Ba1−xAlx)Fe2S6[S1−y(S2)y]

The compounds $\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{[S}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{S}{}_2\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{]}$ and Ba_3.6Al_0.4Fe₂S₆[S_0.6(S₂)_0.4], designated I and II, were prepared by reacting BaS, Fe, and S powders and Al foils in graphite containers sealed in evacuated quartz ampoules at approximately 1100°C. The crystal structure of I was determined using 1682 independent, nonzero X-ray reflections, while 3589 were used for II. They are triclinic, $\text{A}\text{l}$:

$\text{a=9.002(2)}\text{A}\text{?}\text{,b=6.7086(8)}\text{A}\text{?}\text{,c=24.658(4)}\text{A}\text{?}\text{α91.49(2)°,}$

$\text{β=105.10(2)°y=90.74(2)°,ψ}{}_{\mathrm{calc}}\text{=4.15g/cm}{}^3\text{,for I:}$

$\text{a=8.993(6)}\text{A}\text{?}\text{,b=6.708(7)}\text{A}\text{?}\text{,c=24.70(1)}\text{A}\text{?}\text{α91.11(6)°,}$

$\text{β=105.04(6)°y=90.90(9)°,ψ}{}_{\mathrm{calc}}\text{=3.90g/cm}{}^3\text{,for II:}$

BaS₆ trigonal prisms share edges to form distorted hexagonal rings which form one-dimensional chains leaving two free lateral edges. The chains link in a stairstep manner with the rings offset along the [301] direction. These stairsteps join in a complicated manner to form a three-dimensional network. Fe ions are in two sites forming isolated FeS₄ tetrahedra and isolated Fe₂S₆ dimers by edge-sharing tetrahedra. The Al substitution occurs in the trigonal prisms which have free edges with Al replacing Ba. Room-temperature Mössbauer isomer shifts are 0.20 mm/sec. for I and 0.30 mm/sec for II. These data indicate that upon Al substitution charge compensation occurs by reducing Fe³⁺. Valence calculations indicate that Fe in edge-sharing tetrahedra are reduced while the Fe in the isolated tetrahedron remains unchanged. The effective charge distribution in the Al substituted compound is approximately Fe³⁺, Fe^2.5+ with electron delocalization across the shared edge. Room temperature electrical resistivity is 10⁵ ohm/cm. The compositions of the crystals are best represented by the formulas $\text{[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_7\text{]}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{·[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{(S}{}_2\text{)]}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ and [Ba₃AlFe₂S₇]_0.4·[Ba₄Fe₂S₇]_0.2·[Ba₄Fe₂S₆(S₂)]_0.4. The replacement of a sulfide by a disulfide ion is thought to be strongly dependent on the sulfur activity during the preparation.     

Properties of molten carboxylates part 5. A quantitative differential thermal analysis study of mesophase formation in the sytems lead(II)dodecanoate/lead(II) oxide and lead(II)dodecanoate/hendecane

Measurements have been made of the temperatures and enthalpy changes of phase transitions in the systems lead dodecanoate/lead oxide and lead dodecanoate/hendecane. The data have been discussed in terms of the R theory of amphiphylic mesophases. The concepts of the R theory are shown to be useful in the interpretation of phase transitions in molten carboxylate systems.