Water-soluble cellulose derivatives prepared by the action of solutions of nitrogen dioxide in dimethylformamide

Cellulose derivatives soluble in water and in dilute alkali were prepared by dissolving a bleached sulfite pulp in solutions of nitrogen dioxide in dimethylformamide (DMF) and heating at 70–90°C for 1–3 hr. No cellulose oxidation was detected. Nitrite esters and apparently also, nitrate esters, were formed with degrees of substitution (DS) ranging from 0.18 to 0.55 and with nitrogen contents ranging from 1.47 to 4.32%. Solution viscosities in water increased with increasing nitrogen content. The degree of polymerization (DP) decreased rapidly in the initial stages of the reaction followed by a slow, gradual decrease with increasing reaction times.     

The Isolation,Structure, and Synthesis of Davana Ether,an Odoriferous Compound of the Oil of Artemisia pallens Wall.

Several stereoisomers of 2,6,10-trimethyl-2:5, 7:10-diepoxy-dodeca-3,5,11-triene ( 3 ) have been isolated from the oil of Artemisia pallens. The synthesis of the isomeric mixture is described.     

Elemental concentration in the cortex and hippocampus of Wistar rats by X-ray total reflection fluorescence with synchrotron radiation

Summary The study of trace element levels is of great importance due to their relevance in agingand several neurodegenerative diseases. This work compares the elemental concentrations in different postnatal ages and between the temporal cortex, entorhinal cortex and hippocampus from Wistar rats, using X-ray total reflection fluorescence with synchrotron radiation. Ten elements were determined in brain samples: Ti, Cr, Mn, Fe, Cu, Zn, (at trace level) and P, S, Cl and K (at major levels). The elements that increased with aging in cortical areas were: S, K, Fe, Cu and Zn. Ca and Zn levels decreased with advancing age in the hippocampus. In addition to this, Ti, Mn and Fe levels were more conspicuous in the entorhinal cortex.     

Atomistic molecular dynamics simulations of chemical force microscopy

Chemical force microscopy and related force measurement techniques have emerged as powerful tools for studying fundamental interactions central to understanding adhesion and tribology at the molecular scale. However, detailed interpretation of these interactions requires knowledge of chemical and physical processes occurring in the region of the tip-sample junction that experiments cannot provide, such as atomic-scale motions and distribution of forces. In an effort to address some of these open issues, atomistic molecular dynamics simulations were performed modeling a chemical force microscope stylus covered with a planar C12 alkylthiolate self-assembled monolayer (SAM) interacting with a solid wall. A complete loading-unloading sequence was simulated under conditions of near-constant equilibrium, approximating the case of infinitely slow tip motion. In the absence of the solid wall, the stylus film existed in a fluid state with structural and dynamic properties similar to those of the analogous planar SAM at an elevated temperature. When the wall was brought into contact with the stylus and pressed against it, a series of reversible changes occurred culminating with solidification of the SAM film at the largest compressive force. During loading, the chemical composition of the contact changed, as much of the film's interior was exposed to the wall. At all tip heights, the distribution of forces within the contact zone was uneven and subject to large local fluctuations. Analysis using the Johnson-Kendall-Roberts, Derjaguin-Muller-Toporov, and Hertz contacts mechanics models revealed significant deviations from the simulation results, with the JKR model providing best overall agreement. Some of the discrepancies found would be overlooked in an actual experiment, where, unlike the simulations, contact area is not separately known, possibly producing a misleading or incorrect interpretation of experimental results. These shortcomings may be improved upon by using a model that correctly accounts for the finite thickness of the compliant components and nonlinear elastic effects.     

CHRONIC METABOLIC MEASUREMENTS OF NORMAL BRAIN TISSUE RESPONSE TO PHOTODYNAMIC THERAPY

The metabolic response of normal rat brain to photodynamic therapy (PDT) was studied over a 1 week interval using in vivo 31P-NMR spectroscopy. Rats injected with 12.5 mg/kg Photofrin II were submitted to brain photoactivation 48 h after drug administration with either 140 or 70 J/cm2 light (630 +/- 1 nm) from an Argon dye laser. Control studies, animals not given drug or light, animals submitted only to brain illumination without drug, and animals given drug but no light, were also performed. The data revealed a transient metabolic degradation; a decrease in the ratio of beta-nucleotriphosphate to inorganic phosphate (P less than 0.001) at 24 h after PDT treatment was followed by a return to pretreatment spectral values. Brain tissue alkalosis was also noted, with significant (P less than 0.05) differences in brain tissue pH detected at 72 h post treatment between 70 J/cm2 PDT vs control studies and at 1 week post treatment between 140 J/cm2 vs 70 J/cm2, 140 J/cm2 vs no light-no drug and 140 J/cm2 vs drug only. The data suggest that there is no difinitive metabolic marker from 31P-NMR spectroscopy that can identify necrotic brain tissue caused by PDT. Phosphorus-31 NMR data are also presented which suggest that PDT damage to brain is not solely the result of microvascular occlusion causing ischemic necrosis.     

Physical,chemical and immunological characteristics of continuous-density lipoproteins isolated by single-spin gradient ultracentrifugation

The isolation of various lipoproteins of very low, intermediate, low and high density from 5 ml of serum was obtained by single-step ultracentrifugation in a potassium bromide density gradient obtained by smoothing a discontinuous gradient during the run (120 000g, 48 h, 4°C; Beckman SW27 rotor). The density profiles were reproducible. The lipoproteins were characterized by electron microscopy, fluorescence polarization, polyacrylamide gel electrophoresis and complete chemical assays. The composition of the entire lipoprotein spectrum was in accordance with previous results. The lipoprotein molecular mass, particle size distribution, Apo AI/AII ratio and microviscosity varied according to the density range.     

Comparative studies of reactions of commercial polymers with molecular oxygen,singlet oxygen,atomic oxygen and ozone—I. Reactions with cis-1,4-polybutadiene

The oxidation of cis-1,4-polybutadiene by molecular oxygen, singlet oxygen, atomic oxygen and ozone has been studied using u.v. and i.r. spectroscopic methods. Some possible implications of the results of oxidation in the presence of singlet oxygen (parallel free radical oxidation) and atomic oxygen (formation of NO₂ and its reaction with polymer) are discussed. Chain scission was observed during all types of oxidation. A new mechanism involving opening of double bonds and formation of biradicals has been considered in detail.     

Polarographische Simultanbestimmung von Niob und Zinn in der bin?ren Legierung

Zusammenfassung Die Möglichkeit der gleichzeitigen Bestimmung von Niob und Zinn mit Hilfe der Polarographie wird untersucht. Es wird gefunden, daß die Bestimmung zwar nicht gleichspannungspolarographisch, wohl aber square-wave-polarographisch durchführbar ist. Zur Analyse der binären Nb-Sn-Legierungen (etwa Nb₃Sn) ist 8,0±0,1 m HCl+10 Vol-% Äthylenglykol als Grundelektrolyt geeignet. In diesem Elektrolyten erscheinen die erste Reduktionswelle des Niobs, Nb^VIV, und die zweite Reduktionswelle des Zinns, Sn^IISn, gut getrennt und vermeßbar. Die Differenz der Spitzenpotentiale (E _pNb^V/IV= -0.26V, E _pSn^II/O= -0.46V gegen Quecksilber-Bodenelektrode) beträgt 200 mV.Die beschriebene Methode hat im Vergleich zu den bekannten nichtpolarographischen Analysenvorschriften den Vorzug, eine bis zu 100 mal kleinere Einwaage (bei vergleichbarer Reproduzierbarkeit) und einen verringerten Zeitaufwand zu erfordern.Bei Einwaagen von 2–14 mg beträgt die Genauigkeit der Niobbestimmung 1% rel., die der Zinnbestimmung 2% rel. Eine einzelne Niob-Zinn-Simultanbestimmung dauert 4 Std.

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Summary The possibility of a simultaneous polarographic determination of niob and tin is investigated.It has been found that the determination cannot be carried out by direct current polarography, but square-wave polarography yields good results.8.0±0.1 M HCl+10 vol-% ethylene glycol is suitable as supporting electrolyte for the analysis of the binary Nb-Sn-alloys (Nb₃Sn).In this supporting electrolyte the first reduction-wave of niobium Nb^VNb^IV, and the second reduction wave of tin, Sn^IISn⁰, are well developed and separated. The difference of the peak potential (E _pNb^V/IV= -0.26V, E _pSn^II/O= -0.46V vs. mercury-pool electrode) is 200 mV. Compared with conventional methods the method described has the advantage of requiring smaller amounts of sample (up to 100 times smaller by weight at comparable reproducibility) with a saving of time.With sample amounts of 2 to 14 mg the accuracy of the niobium determination is 1% rel., that of the tin determination is 2% rel. One single simultaneous determination of niobium and tin takes about four hours.

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Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet.     

Long-Range interaction coefficients between H,He+, He,and Li+

Using the new expression for the dynamic multipole polarizabilities in terms of effective oscillator strengths and effective transition energies derived from the variational procedure based on the total energy expansion in terms of induced multipole moments, we have calculated the long-range dispersion force coefficients and the leading relativistic correction to the long-range potential between H, He⁺, He, and Li⁺. We have in addition calculated the oscillator strength sum rules for the above systems. Our results are comparable with those obtained using both a hydrodynamic model to quantum mechanics and double perturbation theory.     

Comparison of analytical techniques to quantify malondialdehyde in milk powders

Several analytical methods were compared to quantify malondialdehyde (MDA) in milk powders. Modified thiobarbituric acid (TBA) methods, using either visible spectrophotometry (direct absorbance reading or after third derivative transformation of the spectrum) or HPLC, required derivatisation at elevated temperature, which appeared to catalyse artefactual MDA formation and thus overestimate the MDA content. In contrast to the TBA derivatisation method, the measurement of MDA as the dinitrophenylhydrazone derivative by HPLC or as the phenylhydrazone product by GC-MS with a deuterated internal standard resulted in lower estimates in the ranges of 2-17- and 3-30-fold, respectively; apparently due to the milder derivatisation conditions. The estimates of MDA determined by both HPLC-UV and GC-MS techniques result in lower values which are similar in magnitude even though the GC-MS technique is more sensitive.