Titrimetric study of the reaction of chloramine-T with ammonia

A titrimetric study of the reaction between chloramine-T (CAT) and ammonia is described. The effects of the presence of bromide, the ratio of CAT to ammonia concentrations, the time for reaction and the pH of the reaction media are all significant in the quantitativeness of the reaction that occurs.     

THz spectroscopic investigation of 2,4-dinitrotoluene

We have investigated the terahertz (THz) spectrum of 2,4-DNT by using Fourier transform infrared spectroscopy in the 0.2–19.5 THz region. We also examined low-frequency intermolecular or phonon modes between 0.2 and 1.8 THz via THz time-domain spectroscopy. The extracted absorption coefficient and refractive index of an intermolecular band at 1.08 THz are 110 cm⁻¹ and 1.67, respectively. Density functional theory (DFT) was applied to obtain structure and vibrational frequencies of 2,4-DNT. The calculated results are in agreement with the experimental data. Observed vibrational frequencies have been interpreted using DFT. Two intermolecular or phonon modes were identified at 1.08 and 2.52 THz.     

Semi-automated determination of aluminium with Xylenol Orange

The photometric determination of aluminium by automated colour development with Xylenol Orange is described. The reagent has been found to act faster if used in alcohol solution.     

Structural changes in the monomeric despentapeptide (B30-B26) insulin crystal

Insulin modified by the removal of its 5 B chain C terminal residues is monomeric but remains substantially potent. The crystal structures of the beef and insulin (dpi) with two molecules in the asymmetric unit has been determined by x-ray analysis. The 3-dimensional structure ofdpi proves to be generally similar to that of native molecule in 2Zn insulin. More detailed comparison reveals that the slight differences in the two independent molecules of beefdpi are distributed uniformly throughout the structure in contrast to insulin in 2Zn insulin, where the structural changes are concentrated in specific regions. The loss of symmetry in thedpi crystal appears to be the inability of the A9 serine to pack effectively in the C2 cell. The efficient packing of the sheepdpi molecule whose crystal structure has also been determined and where A9 is glycine supports this conclusion.     

Degradation of polymer mixtures. VI. Blends of poly(vinyl chloride) with polystyrene

The degradation of films containing both PS and PVC has been examined by TVA and TG. Stabilization of both polymers, more notably PS, is observed, but the degradation products are the same as when the polymers are degraded alone. Molecular weight measurements indicate a more rapid decrease in the molecular weight of PS when PVC is present. The possibility of grafting or other processes leading to chlorine incorporation in PS has been excluded by the results of experiments using ³⁶Cl-labeled PVC. The mechanisms of possible interactions between the degrading polymers are discussed. Processes involving reaction of chlorine radicals with PS at lower temperatures and reaction of PS radicals with the residue of PVC dehydrochlorination or its decomposition products at higher temperatures appear probable.     

A Sustainable Freeze‐Drying Route to Porous Polysaccharides with Tailored Hierarchical Meso‐ and Macroporosity

Bio‐derived polysaccharide aerogels are of interest for a broad range of applications. To date, these aerogels have been obtained through the time‐ and solvent‐intensive procedure of hydrogel fomation, solvent exchange, and scCO2 drying, which offers little control over meso/macropore distribution. A simpler and more versatile route is developed, using freeze drying to produce highly mesoporous polysaccharide aerogels with various degrees of macroporosity. The hierarchical pore distribution is controlled by addition of different quantities of t‐butanol (TBA) to hydrogels before drying. Through a systematic study an interesting relationship between the mesoporosity and t‐butanol/water phase diagram is found, linking mesoporosity maxima with eutectic points for all polysaccharides studied (pectin, starch, and alginic acid). Moreover, direct gelation of polysaccharides in aqueous TBA offers additional time savings and the potential for solvent reuse. This finding is a doorway to more accessible polysaccharide aerogels for research and industrial scale production, due to the widespread accessibility of the freeze drying technology and the simplicity of the method.

     

Thallium(II) in the chemically induced thallium(I)-Thallium(III) exchange

The rate of the electron exchange between thallium(I) and thallium(III) induced by iron(II) has been measured at various concentrations of Tl(I), Tl(III), and Fe(II).²⁰⁴Tl tracer, initially in the Tl(I) state, was used. Exchange induced by the separation method was less than 0.01%. The mechanism earlier discussed is $$\begin{gathered} Tl^{III} + Fe^{II} \rightleftharpoons Tl^{II} + Fe^{III} \left( {k_1 ,k_{ - 1} } \right) \hfill \\ Tl^{II} + Fe^{II} \rightharpoonup Tl^I + Fe^{III} \left( {k_2 } \right) \hfill \\ *Tl^I + Tl^{II} \rightleftharpoons *Tl^{II} + Tl^I \left( {k_I } \right) \hfill \\ *Tl^{II} + Tl^{III} \rightleftharpoons *Tl^{III} + Tl^{II} \left( {k_{III} } \right), \hfill \\ \end{gathered} $$ which provides an exchange path in addition to the two-electron reaction^*Tl^I+Tl^III?^*Tl^III+Tl^I (k_ex). The rate law deduced from this mechanism agrees with experiment over a limited range of conditions but fails to account for the observed effect at low concentrations of Tl(I). The additional rate can be represented by inclusion of a term in which the rate of the induced exchange is independent of the concentration of Tl(I). When treated according to the resulting complete rate law the data are consistent with earlier photochemical studies. The present results in combination with other data give k₂=3·10⁶ M^?1·sec^?1 in 1M perchloric acid at 25°C. This is in satisfactory agreement with a recent pulse radiolysis measurement as well as with independent flash photolysis studies.     

Parity-violating electron deuteron scattering and the proton's neutral weak axial vector form factor

We report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles at Q2=0.038 (GeV/c)2. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry A=-3.51+/-0.57 (stat)+/-0.58 (syst) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also consistent with theoretical predictions.