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This contribution reports on the synthesis of hyperbranched polylysines via thermal polymerization of L‐lysine hydrochloride. Polymerization of L‐lysine hydrochloride in the presence of one equivalent KOH at 150 °C resulted in polymers with a number‐average molecular weight of 4600 g/mol and a polydispersity of 2.6 after 48 h. The rate of polymerization could be significantly enhanced and the polymer molecular weight improved by carrying out the polymerization with 3 mol % of an amidation catalyst. Among the different catalysts that were investigated Zr(OnBu)4 was found to be the most effective. Unequivocal support for the branched architecture of the polymers was obtained from 1H NMR spectroscopy, which allowed the identification and quantification of the four different structural units that constitute the polymer, viz. Nα and Nε linked linear units, dendritic units and terminal units. The structure of the polymers was found to be relatively independent of the reaction conditions. The degree of branching and the average number of branches varied between 0.35–0.45 and 0.15–0.25, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5494–5508, 2007

The synthesis of a novel family of optically active 4-(N,N-dimethylamino)pyridine carbamate derivatives has been achieved with excellent isolated yields using different linear diamines as starting materials to produce dimeric compounds of variable length. Optically active homodimeric 4-(N,N-dimethylamino)pyridine carbamate derivatives obtained through this chemoenzymatic route present interesting structural properties as possible ligands or nucleophilic catalysts in asymmetric catalysis.

Dedicated to Professor Dr. Rolf Huisgen on the occasion of his 85th birthdayWe report the synthesis and physical properties of novel fullerene ± oligoporphyrin dyads. In these systems, the C-spheres are singly linked to the terminal tetrapyrrolic macrocycles of rod-like meso,meso-linked or triplylinked oligoporphyrin arrays. Monofullerene ± mono(Zn II porphyrin) conjugate 3 was synthesized to establish a general protocol for the preparation of the target molecules (Scheme 1). The synthesis of the meso,meso-linked oligopophyrin ± bisfullerene conjugates 4 ± 6, extending in size up to 4.1 nm (6), was accomplished by functionalization (iodination followed by Suzuki cross-coupling) of the two free meso-positions in oligomers 21 ± 23 (Schemes 2 and 3). The attractive interactions between a fullerene and a Zn II porphyrin chromophore in these dyads was quantified as DG À 3.3 kcal mol À1 by variable-temperature (VT) 1 H-NMR spectroscopy ( Table 1). As a result of this interaction, the C-spheres adopt a close tangential orientation relative to the plane of the adjacent porphyrin nucleus, as was unambiguously established by 1 H-and 13 C-NMR (Figs. 9 and 10), and UV/VIS spectroscopy (Figs. 13 ± 15). The synthesis of triply-linked diporphyrin ± bis[60]fullerene conjugate 8 was accomplished by Bingel cyclopropanation of bis-malonate 45 with two C 60 molecules (Scheme 5). Contrary to the meso,meso-linked systems 4 ± 6, only a weak chromophoric interaction was observed for 8 by UV/VIS spectroscopy ( Fig. 16 and Table 2), and the 1 H-NMR spectra did not provide any evidence for distinct orientational preferences of the C-spheres. Comprehensive steady-state and time-resolved UV/VIS absorption and emission studies demonstrated that the photophysical properties of 8 differ completely from those of 4 ± 6 and the many other known porphyrin ± fullerene dyads: photoexcitation of the methano[60]fullerene moieties results in quantitative sensitization of the lowest singlet level of the porphyrin tape, which is low-lying and very short lived. The meso,meso-linked oligoporphyrins exhibit 1 O 2 sensitization capability, whereas the triply-fused systems are unable to sensitize the formation of 1 O 2 because of the low energy content of their lowest excited states (Fig. 18). Electrochemical investigations ( Table 3, and Figs. 19 and 20) revealed that all oligoporphyrin arrays, with or without appended methano[60]fullerene moieties, have an exceptional multicharge storage capacity due to the large number of electrons that can be reversibly exchanged. Some of the Zn II porphyrins prepared in this study form infinite, one-dimensional supramolecular networks in the solid state, in which the macrocycles interact with each other either through H-bonding or metal ion coordination (Figs. 6 and 7).

Because of the unequal reactivity of the two amine groups of l-lysine hydrochloride, thermal polymerization of this asymmetrical AB2 monomer results in hyperbranched polymers, which contain ∼2.5 times more Nε-linked linear compared to Nα-linked linear structural units. This report discusses the feasibility of three approaches to control polymer architecture during the thermal hyperbranched polymerization of l-lysine hydrochloride. The reactivity of the more reactive ε-NH2 group was modulated by introducing temporary protective groups that preferentially block the ε-NH2 position. This was achieved by (i) addition of o-vanillin to the polymerization, (ii) copolymerization of N ε-benzylidene-l-lysine, and (iii) copolymerization of α-amino-ε-caprolactam. Analysis of the degree of branching (DB) and the average number of branches (ANB) of the obtained polymers did not provide evidence for any significant structural changes. Analysis of the distribution of structural units, in contrast, revealed major structural changes and indicated a rearrangement from Nε-linked linear structural units to Nα-linked linear structural units upon addition of o-vanillin and N ε-benzylidene-l-lysine. Unlike o-vanillin and N ε-benzylidene-l-lysine, α-amino-ε-caprolactam was found to be rather ineffective in modulating polymer architecture.