Photoinitiators with functional groups. VII. Covalently bonded camphorquinone—amines

Camphorquinone (CQ), a widely used photoinitiator (PI) in dental applications, was covalently bonded to aromatic amines to enhance the rate of electron and proton transfer effect due to the close vicinity of the diketone and the amine group. 10‐bromocamphorquinone and 10‐bromomethylcamphorquinone were selected as suitable precursors for esterification with the carboxyl group containing aromatic amines based on 4‐dimethylaminobenzoic acid. Properties of the new photoinitiating systems were investigated by UV spectroscopy and differential scanning photocalorimetry in lauryl acrylate. Compared to physical mixtures, in all cases similar or even better performance was obtained. Surprisingly, 10‐acetyl derivatives 7 – 9 and 18 especially, were found to be highly reactive. Compared to CQ/ethyl 4‐dimethylaminobenzoate, the rate of photopolymerization was increased by a factor of up to 2. Intramolecular reaction was confirmed by photo‐differential scanning calorimetry experiments with varying PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4948–4963, 2004     

Ab initio predictions of zeolite structures and Si NMR chemical shifts

A recent shell-model potential parameterized on ab initio data is used for predicting the all-silica structures of zeolites MFI, MEI, MTW, TON, FAU and of α-quartz. Cluster models are defined around each site and the ²⁹Si NMR shielding constants are calculated by ab initio techniques (GIAO-HF). Good agreement with observed ²⁹Si NMR chemical shifts is found. Comparison is made with shifts calculated for observed structures. The structures predicted by the ab initio shell-model potential prove as accurate as the observed ones when judged on the quality of the calculated ²⁹Si NMR spectra.     

A high-current electron beam ion trap as an on-line charge breeder for the high precision mass measurement TITAN experiment

The precision of atomic mass measurements in a Penning trap is directly proportional to the charge state q of the ion and, hence, can be increased by using highly charged ions (HCI). For this reason, charge breeding with an electron beam ion trap (EBIT) is employed at TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) on-line facility in Vancouver, Canada. By bombarding the injected and trapped singly charged ions with an intense beam of electrons, the charge state of the ions is rapidly increased inside the EBIT. To be compatible with the on-line requirements of short-lived isotopes, very high electron beam current densities are needed. The TITAN EBIT includes a 6 Tesla superconducting magnet and is designed to have electron beam currents and energies of up to 5 A and 60 keV, respectively. Once operational at full capacity, most species can be bred into a He-like configuration within tens of ms. Subsequently, the HCI are extracted, pass a Wien filter to reduce isobaric contamination, are cooled, and injected into a precision Penning trap for mass measurement. We will present the first results and current status of the TITAN EBIT, which has recently been moved to TRIUMF after assembly and commissioning at the Max-Planck-Institute (MPI) for Nuclear Physics in Heidelberg, Germany.     

1.2-Bis(pentamethylcyclopentadienyl)tetrachlorodisilane and its reduction to decamethylsilicocene

Reaction of pentamethylcyclopentadienyl(pentachloro)disilane (2), prepared from hexachlorodisilane and potassium pentamethylcyclopentadienide (Cp^*K), with a further equivalent of Cp^*K leads selectively to the title compound Cp^* ₂ Si ₂ Cl ₄ (3) which was characterized by NMR and X-ray structural data. Dehalogenation of 3 with four equivalents of sodium naphthalenide offers an alternative route for the synthesis of decamethylsilicocene (1). Dedicated to Professor Mitsuo Kira on the occasion of being honoured with the Wacker Silicon Award 2005.     

Concerning the Thermal Diastereomerization of the Green Fluorescent Protein Chromophore

Summary. Two model compounds for the green fluorescent protein chromophore were prepared. One of them incorporates the natural 4-hydroxybenzylidene group of the natural tyrosin derived chromophore, the other one bears a methyl group instead of the hydroxy group. Whereas the photochemically prepared (E)-diastereomer of the first compound very effectively reverted thermally (room temperature) to the thermodynamically stable (Z)-diastereomer, the (E)-diastereomer of the second derivative proved to be stable even at elevated temperatures for more than a day. This finding can be rationalized by constructing the appropriate resonance structures showing that only in the first case an effective delocalization enables partial single bond character of the benzylidene double bond. From the standpoint of chemical etiology, only Nature’s choice of the tyrosin derived chromophore of the green fluorescent protein provides an efficient radiationless thermal relaxation channel for the unwanted photo-diastereomerization product formed after excitation besides the dominating fluorescence channel of its chromophore.     

Lanthanoid-nickel-phosphides with ThCr2Si2-type structure

The new compounds YNi₂P₂ and LnNi₂P₂ (Ln = La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm) were prépared by sintering the elemental components in silica tubes. Well-developed crystals were obtained using tin as a flux. They crystallize with the ThCr₂Si₂ (CeGa₂Al₂)-type structure which was refined from single-crystal X-ray data for EuNi₂P₂ to a conventional R value of 0.049 for 118 unique structure factors. While the P atoms in formally isotypic EuCo₂P₂ are isolated from each other, they form pairs in EuNi₂P₂. This results in a different $\text{c}\text{a}$ ratio and an entirely different bonding situation. A comparison of cell volumes shows that Eu in EuNi₂P₂ has an intermediate valence.     

Solid-Phase Synthesis of a Sialyl-Tn-Glycoundecapeptide of the MUC1 Repeating Unit

The synthesis of glycopeptides carrying tumour-associated antigens is of interest for cancer diagnosis and treatment. Here, a very efficient route lo disaccharide threonine building block 8 is presented which allows the introduction of the sialyl-Tn antigen into a peptide. The syntheses of the undecapeptide and the sialyl-Tn-containing glycoundecapeptide, which are a part of the repeating unit of MUC1, were performed by solid-phase synthesis with an allylic anchor cleavable under neutral conditions. After detachment from the resin, the peptide and the glycopeptide arc completely deprotected giving the target compounds 13 and 15 , respectively.