A modification of the heteropoly blue method for the microgram determination of arsenic in biological materials

Summary A sensitive method has been developed for analysis of trace amounts of arsenic in biological materials using the heteropoly blue method. The method employs a closed apparatus and a nitrogen atmosphere, and allows the detection of arsenic in ppm concentration using samples of 100 mg.

---

Zusammenfassung Eine empfindliche Methode zur Bestimmung von Arsenspuren in biologischem Material im Wege der Molybdänblaumethode wurde ausgearbeitet. Man arbeitet dabei in einer geschlossenen Apparatur in Stickstoffatmosphäre und kann so in 100-mg-Proben Arsenkonzentrationen in der Größenordnung von ppm bestimmen.

---

---

Presented at the 6th Annual Northeast Regional Meeting of the American Chemical Society, Burlington, Vermont, August 19, 1974.     

Die kathodische Sauerstoffreduktion an pyrolytisch abgeschiedenem Kohlenstoff in peroxidhältigen alkalischen Elektrolyten

The kinetics of the system O₂/HO₂ ^?, OH^? were studied at pyrolytic carbon in alkaline electrolytes. The rest potentials are close to the reversible values. They decrease by 30 mV when the HO₂ ^?-concentration is increased by a factor 10. CathodicTafel lines displayb-values between 70 and 95 mV. The exchange current densities are evaluated by extrapolation ofTafel lines to zero overvoltage and from the charge transfer resistance. Two different succeeding charge transfer reactions occur in course of the overall process, the first of which is the rate-determining step. A cathodic reaction order of zero is obtained with respect to HO₂ ^?. Theb values of anodicTafel lines are between 60 and 80 mV, the corresponding reaction order concerning the HO₂ ^? concentration is found to be +0.5. The kinetic studies prove the reversibility of the system O₂/HO₂ ^?, OH^? at carbon electrodes. The reaction mechanism is: $$\begin{array}{*{20}c} {O_2 + e^ - \rightleftarrows O_2 } \\ {O_{2^ - } + H_2 O \rightleftarrows HO_2 + OH - } \\ {HO_2 + e^ - \rightleftarrows HO_{2^ - } } \\ \end{array} $$ .     

Beitrag zum Stabilisierungsmechanismus des Wollkeratins durch einige Metalle

Zusammenfassung Das Verhalten des Wollkeratins ist im kochenden Wasser nach Behandlung mit Kupfer-, Kadmium-, Silber- und Quecksilbersalzen unnormal, nicht nur verglichen mit dem Verhalten des metallfreien Proteins, sondern auch gegenüber des unter gleichen Bedingungen mit anderen Metallen behandelten Keratins. Die beobachteten Phänomene werden in einigen Fällen entweder mit der Annahme der Bildung von Vernetzungen zwischen benachbarten Polypeptidketten durch Komplexbildung des Metalls mit einigen Gruppen des Keratins oder durch Blockieren des Cysteins und der Verhinderung des Disulfidaustausches erklärt. In anderen Fällen jedoch, besonders bei Silber, ist die Erklärung der eintretenden Veränderung mit Hilfe dieser zwei Mechanismen nicht möglich, und es wird die direkte Reaktion des Metalls mit dem Schwefel des Cystins vorgeschlagen. Hierbei wird das Cystin und damit die Disulfidbindung gespalten. Die Spaltung dieser Bindung und die Verhinderung ihrer Rückbildung, entweder in derselben oder in anderer Lage, senkt die Zahl der Quervernetzungen im Keratin herab und damit die Fixierung der Polypeptidketten in ihrer ursprünglichen Lage. Hieraus resultiert eine Schrumpfung der Ketten und die Kontraktion der Faser.

---

Summary Wool fibres containing cadmium, copper, mercury or silver set in a different way than the untreated ones or the fibres which contain other metals. This behaviour is explained in some cases by assuming the formation of complexes between the metal and the protein or by the disulphide exchange mechanism. In other cases, however, and particularly with silver this is not possible, and therefore the direct reaction between the metal and the sulphur of cystine is proposed. According to this mechanism the contraction of the fibre is due to the breakdown of the disulphide bond and the inability of its reformation.

---

---

Mit 10 Abbildungen und 2 Tabellen     

Tast polarography of europium(III)-l-histidine complex

Study of europium(III)-l-histidine complex has been made in sodium perchlorate at μ=0.1 by tast polarography. The reduction process appears to be quasi irreversible. The apparent rate constants have been determined byGellings method¹. With the knowledge ofE ₁ ^2/r and use ofLingane's method, one complex Eu(Histd)²⁺ with the instability constant 6.77×10^?5 is reported.     

Studies on the colloidal properties of papain with titanium dioxide sol

Summary The coagulation concentration for a titania sol decreases if the concentration of a mixture of electrolytes and papain decreases. If the concentration of papain is increased then lesser amount of electrolytes is needed to coagulate the sol. If glycine is added as an additional substance then the value decreases more rapidly. There is no significant change in the p_H and the electrical conductance of the sol by the addition of papain or electrolytes. There is a little change, when glycine is added as an additional substance. These observations are explained due to the formation of negative papain ions in a low p_H region. The possibility of the adsorption or the release of the counter ions is ruled out.The authors wish to thank Dr.R. C. Mehrotra, Professor and the Head of the Chemistry Department for providing all the facilities for this work. We are also thankful to the Ministry of Education, Government of India, for the award of a research scholarship to one of us (V.K.S.).     

Theoretical and experimental studies of the electrochemistry of <Emphasis Type="Italic">p</Emphasis>-aminophenol on a golden electrode

The geometric parameters, vibrational frequencies, and thermochemical values of p-quinonimine (p-AQ) and p-aminophenol (p-AP) were computed ab initio (IIF) and by the density functional theory (DFT) method with the 6-31G(d, p) basis set. Cyclic voltammetry with a golden electrode of p-AP solutions in phosphate buffers at pH 7.30 showed that the standard electrode potential of half reaction for p-QI and p-AP was 0.728 V. The standard electrode potentials of half reactions for p-QI and p-AP were calculated using the free energies and solvation energies of p-QI, p-AP, p-benzoquinone (p-BQ), and hydroquinone (p-HQ). The results showed that the standard electrode potential of half reaction for p-QI and p-AP was 0.743 V at the B3LYP/6-31G(d, p) level and 0.755 V at the HF/6-31G(d, p) level. The standard electrode potentials computed at the B3LYP/6-31G(d, p) and HF/6-31G(d, p) levels were close to their experimental values. The article is published in the original.     

Kinetik der Diazotierung der Chloraniline in methanolischer Chlorwasserstofflösung

The kinetics of the diazotization of o-, m-, p-chloroaniline in 0.005n- to 0.4n-methanolic HCl-solution at 25, 15, 0, ?10 ?20, and ?30°C was invertigated. It was found that the nitrosation reaction (the same as in¹) $$C_6 H_4 ClNH_2 + NOCl \mathop \rightleftharpoons \limits^k C_6 H_4 ClNH_2 NO^ + + Cl^ - $$ is a proceeding advance-back-reaction. The decomposition of C₆H₄ClNH₂NO⁺ by splitting off a proton is the rate determining step. The free activation enthalpies ΔG ^* for the nitrosation reaction, the activation entropies ΔS ^*, the activation enthalpies ΔH ^* and the activation energiesE _a at the given temperatures are calculated. The experimentally found and the calculated velocities are given in Tables 1–6. The equilibrium constants of the o-, m-, p-chloroanilinium ions, and nitrosyl-chloride in methanol are indicated in Table 7, diagram 1. TheK _M values (the ionic products of methanol, extrapolated at infinite dilution) together with theK _A values of Table 7 give theK _B values (p. 2) using the table¹⁰. The ΔG _B values can be calculated using equation ΔG _B = ?RTlnK _B Fig 2 shows the linear dependance of the logarithmus of the ΔG ^* values from the logarithmus of theK _B values.     

Polarisabilites moléculaires et effet diélectrique de milieu à l'état liquide. Étude théorique de la molécule d'eau et de ses diméres

The model of Onsager in which a polar molecule undergoes a reaction field due to the polarization of the molecular surroundings is used to evaluate by a S.C.F. calculation (CNDO/2 approximation) the modifications of a molecular structure in the liquid state.Application to water molecule and to three polar dimers for values of the dielectric constant varying between 3 and 78, shows that most of geometric parameters and dipoles moments vary of few per cent when the molecule is inserted in a liquid. In the liquid state dipole moments do not depend very much on the dielectric constant but energies and relative stabilities of isomers are strongly dependent on the medium.[/p]

     

Bestimmung von Aminosäuresequenzen in α-Keratose

Zusammenfassung Aus einem durch Trypsinabbau von -Keratose erhaltenen Gemisch von Peptiden wurden 15 neutrale, 5 saure und 2 basische Peptide durch Kombination papierchromatographischer und papierelektrophoretischer Methoden getrennt und in sehr geringen Mengen isoliert. Es wurden neben der Aminosäurezusammensetzung 14N-terminale Aminosäuren sowie einige Teilsequenzen in den untersuchten Peptiden ermittelt.Die mittlere Kettenlänge der Peptide beträgt 5,8 Aminosäuren.Mit 1 Tabelle3. Mitt. über Untersuchungen an -Keratose. 2. Mitt.:M. Fell undE. Schnabel, Hoppe-Seyler's Z. physiol. Chem.333, 218 (1963).