Studies in polyphenol chemistry and bioactivity. 4.(1) Synthesis of trimeric,tetrameric, pentameric,and higher oligomeric epicatechin-derived procyanidins having all-4beta,8-interflavan connectivity and their inhibition of cancer cell growth through cell cycle arrest

We report an improved synthesis of bis(5,7,3',4'-tetra-O-benzyl)epicatechin 4beta,8-dimer (3) from 5,7,3',4'-tetra-O-benzylepicatechin (1) and 5,7,3',4'-tetra-O-benzyl-4-(2-hydroxyethoxy)epicatechin (2) by replacing the previously employed Lewis acid, titanium tetrachloride, with the clay mineral Bentonite K-10. Under the same conditions, the benzyl-protected all-4beta,8-trimer, -tetramer, and -pentamer were obtained regioselectively from their lower homologues, albeit in rapidly decreasing yields. Reaction of 2 with an organoaluminum thiolate generated from 2-mercaptobenzothiazole and trimethylaluminum followed by acetylation produced 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3',4'-tetra-O-benzylepicatechin (12). Medium-sized protected oligomers with 4beta,8-interflavan linkages are obtained in improved yields by using this compound as the electrophile and silver tetrafluoroborate as activator and are isolated by reversed-phase HPLC. Their deprotection by ester saponification followed by hydrogenolysis yielded the free procyanidins, which were characterized as their peracetates. The synthetic procyanidins are identical by normal-phase HPLC with fractions isolated from cocoa. The principle of chain extension by two members was demonstrated using a dimeric electrophile obtained by self-condensation of compound 12. Both the synthetic and natural pentamer 32 inhibit the growth of several breast cancer cell lines. Using the MDA MB 231 line, it was established that this outcome is based on the induction of cell cycle arrest in the G0/G1 phase. Subsequent cell death is more likely necrotic rather than apoptotic. Control experiments demonstrate that the polyphenol itself, rather than hydrogen peroxide potentially formed by its autoxidation, is the causative agent.     

On the behaviour of styrene-acrylonitrile copolymers in solution—VI. Presentation of light-scattering results according to excluded-volume theory

A new procedure for the evaluation of the excluded-volume parameter and the unperturbed dimensions from light-scattering data is described. The treatment is based upon a test recommended by Yamakawa. The principal feature is the fitting of an appropriate theoretical master-curve to the experimental points by shifting along the logarithmic x axis. The advantages are the graphical representation, the possibility of checking the chosen co-ordination of experimental and theoretical data by means of the known relation between expansion factor and molar mass, and the relatively small amount of protracted computation needed. The method is applied to azeotropic styrene/acrylonitrile copolymers and to azeotropic α-methylstyrene/acrylonitrile copolymers.     

Comparability of retention indices of polar substances at elevated temperatures

Summary The non-linear dependency of the retention indices of drugs on temperature is demonstrated hence an indication of the actual working temperature is essential. Fixed temperatures for the determination of retention indices of drugs are proposed. Interlaboratory comparisons of the retention indices of 14 drugs frequently encountered in analytical practice are made for the first time on two stationary phases in three laboratories and on four GC apparatus. The data show that, in comparison with literature values, the interlaboratory deviation is reduced by 1/3 to 1/2 if same temperatures are used. Standardization of the temperature of determination of the retention indices of drugs and unknown substances in biological specimens on OV-1 and OV-17 is proposed.     

Temperature-induced structural transitions and vibrational properties of microclusters: ab-initio molecular dynamics studies

We present the results of ab-initio molecular dynamics studies of selected microclusters of sodium, silicon and magnesium at finite temperatures, and especially discuss those obtained around room temperature. In particular, from the analysis of the atomic trajectories we can identify in some cases the existence of different isomers and the isomerization pathways. We have also calculated vibrational spectra at low temperatures and find that they can be used as a very sensitive structural probe also in sodium clusters, where the electronic properties are quite insensitive to the geometry.     

Non-linear density dependence of rotational line-broadening of HCl in dense argon

The rotational far-infrared spectra of HCl in argon at densities between 100 and 480 amagat and T = 162.5 K are presented. The observed density dependence of the width of the different rotational lines is non-linear and differs for high- and low-frequency lines. An Enskog correction to the collision frequency in the dense gas fails to account for the density dependence of the high rotational lines. It is argued that the many-body character of the relaxation mechanism should be taken into account. Comparison with the results of MD calculations on argon indicates that such an approach may explain the observed density dependence.     

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     

Thermal decomposition of lanthanum selenate pentahydrate in air and nitrogen

Thermogravimetric studies, supported by IR and X-ray diffraction measurements, were carried out for La₂(SeO₄)₃ · 5H₂O in order to establish its decomposition scheme under various experimental conditions. Several analytical methods were tested for the simultaneous determination of (Se(IV) and Se(VI) in the quenched samples. TG weight losses and analyses of the solid intermediates indicated that after dehydration La₂(SeO₄)₃ decomposes in nitrogen mainly to oxyselenite(IV) compoundsvia the normal selenite(IV) but in air the oxyselenate La₂O₂SeO₄ was detected as one of the intermediates. The final product of the thermal degradation is La₂O₃. TG curves of La₂(SeO₄)₃ · 5H₂O were also compared with those obtained for the isostructural neodymium compound.     

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.     

Bestimmung des Aluminiums in niedrig- und hochlegierten Stählen,in Erzen und Schlacken durch Atomabsorption

The measurement is carried out of aqueous solutions. The burner is supplied with a mixture of acetylene and nitrous oxide. Interfering influences by acid and iron concentrations of the sample solution as well as by organic solvents are shown. The standard deviation is ± 0.001%. The agreement with conventional analysis methods is very good. By this procedure a rapid and safe determination of aluminium will be possible.