Copolymerization of ε‐caprolactone and glycolide—A comparison of bismuth(III) hexanoate and tin(II) octanoate as initiators

ε‐Caprolactone and glycolide were copolymerized in bulk either with tin(II) 2‐ethylhexanoate (SnOct₂) or with bismuth(III) n‐hexanoate (BiHex₃) as initiators and with tetra(ethylene glycol) as a coinitiator. The temperature was varied from 100 to 160 °C. The sequences were characterized with ¹H and ¹³C NMR spectroscopy. Surprisingly, it was found that higher temperatures favored the formation of alternating sequences. Furthermore, the content of alternating dyads was significantly higher when BiHex₃ was used instead of SnOct₂. An increase in reaction time caused partial randomization of the sequences regardless of the initiator. Size exclusion chromatography measurements in chloroform yielded number‐average molecular weights in agreement with the feed ratios. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3268–3277, 2005     

The radical character of the acenes: a density matrix renormalization group study

We present a detailed investigation of the acene series using high-level wave function theory. Our ab initio density matrix renormalization group algorithm has enabled us to carry out complete active space calculations on the acenes from napthalene to dodecacene correlating the full pi-valence space. While we find that the ground state is a singlet for all chain lengths, examination of several measures of radical character, including the natural orbitals, effective number of unpaired electrons, and various correlation functions, suggests that the longer acene ground states are polyradical in nature.     

Retention of histidine-containing peptides on a nickel affinity column

The retention of histidine-containing peptides in immobilized metal-affinity chromatography is studied using several hundred modeled peptides. Retention is driven primarily by the number of histidine residues; however, the amino acid composition in the immediate vicinity plays a significant role. Specifically, the arginine and tryptophan content has to be taken into consideration. During the course of this study, an alternative tag that can be used similarly to a polyhistidine tag is discovered.     

Homologer Radioimmunoassay zur Bestimmung C-terminaler Fragmente des humanen Parathormons

Ohne Zusammenfassung

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Homologous radioimmunoassay for the determination of the C-terminal fragment of human parathyroid hormone

     

Diffusion-controlled growth of lamellar crystals in an isotactic polystyrene–polyphenylene oxide blend

The growth rates of lamellar crystals grown onto preseeded fibrillar crystals (“shishes”) in isotactic polystyrene and blends of isotactic polystyrene (iPS) with polyphenylene oxide are followed by using transmission electron microscopy. The preseeded fibrillar crystals avoid the problem of timedependent primary nucleation. The time dependence of lamellar growth is investigated. At a concentration of 50% PPO in iPS, the lateral lamellar growth rate of the precipitating isotactic polystyrene crystals conforms to a time law characteristic of diffusion-controlled growth (R ∝ t^1/2). Diffusion coefficients are estimated from the growth kinetics. The method could prove a simple means of measuring diffusion coefficients in polymer blends in which one component is crystallizable.     

über die Reaktion zwischen Arsenwasserstoff und SilberdiÄthyldithiocarbamidat

AsH₃ and silver diethyldithiocarbamidate [Ag(DDTC)] in pyridine were reacted with one another in different molar ratios. The absorption spectra of these solutions differed with the experimental conditions. When determining arsenic quantitatively by this method it is necessary to use a concentration of at least 20 mg Ag(DDTC)/10 ml pyridine. Red solutions generated under standard conditions were studied by thin-layer chromatography. By this means the “red substance” could be separated from the excess of Ag(DDTC). It was shown, that As(DDTC)₃ was formed in the reaction. The following equation is proposed: AsH₃+6 Ag(DDTC) → 6 Ag+3 HDDTC+As(DDTC)₃. The colloidal nature of the “red substance” was confirmed by its behaviour in an ultracentrifuge.