15 research outputs found
The Development of the Virtual Notebook, a Wiki-Based Ready Reference Technology
Traditionally, library professionals have
used a variety of ready reference technologies
to assist in providing reference and
user services. Technologies such as card
files, vertical files, and reference notebooks
are frequent components of library service
desks. Ready reference technologies serve
many purposes, most notably, helping staff
to answer frequently asked questions and
facilitating the sharing of information between
library staff. This paper traces the
development of the Virtual Notebook, a
wiki-based ready reference technology, at
Purdue University. The tool is placed within
the historical context of ready reference
technologies within the library profession
and at Purdue. The authors present preliminary
results from the implementation of
the Virtual Notebook and discuss the tool’s
future. The manuscript is an outgrowth of
a presentation at the 2008 Brick and Click
Symposium at Northwest Missouri State
University
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DNA as supramolecular scaffold for porphyrin arrays on the nanometer scale
Tetraphenyl porphyrin substituted deoxyuridine was used as a building block to create discrete multiporphyrin arrays via site specific incorporation into DNA. The successful covalent attachment of up to 11 tetraphenyl porphyrins in a row onto DNA shows that there is virtually no limitation in the amount of substituents, and the porphyrin arrays thus obtained reach the nanometer scale (~10 nm). The porphyrin substituents are located in the major groove of the dsDNA and destabilize the duplex by Tm 5-7 °C per porphyrin modification. Force-field structure minimization shows that the porphyrins are either in-line with the groove in isolated modifications or aligned parallel to the nucleobases in adjacent modifications. The CD signals of the porphyrins are dominated by a negative peak arising from the intrinsic properties of the building block. In the single strands, the porphyrins induce stabilization of a secondary helical structure which is confined to the porphyrin modified part. This arrangement can be reproduced by force-field minimization and reveals an elongated helical arrangement compared to the double helix of the porphyrin-DNA. This secondary structure is disrupted above ~55 °C (Tp) which is shown by various melting experiments. Both absorption and emission spectroscopy disclose electronic interactions between the porphyrin units upon stacking along the outer rim of the DNA leading to a broadening of the absorbance and a quenching of the emission. The single-stranded and double-stranded form show different spectroscopic properties due to the different arrangement of the porphyrins. Above Tp the electronic properties (absorption and emission) of the porphyrins change compared to room temperature measurements due to the disruption of the porphyrin stacking at high temperature. The covalent attachment of porphyrins to DNA is therefore a suitable way of creating helical stacks of porphyrins on the nanometer scale