Coppen et al examine the crystallography and properties of polyoxotitanate nanoclusters. They provide a summary of synthetic methods and explore topics such as the geometrical aspects of ...polyoxotitanate clusters, the geometry of doped polyoxotitanate nanoclusters and frameworks of polyoxotitanate nanoparticles.
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Time-resolved diffraction by laser pump−X-ray probe methods for the determination of the geometry of molecular excited states is discussed. A number of examples are presented and compared with ...theoretical results. The increasing brightness and time resolution of new light sources now becoming available will likely enable the tracking of dynamic processes in solids on femtosecond time scales.
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A short description of some of the paradigm-changing developments of the study of light-induced structural changes in molecular crystals is presented. The review is by no means comprehensive. The ...extensive literature on the subject should be consulted for further information.
A number of examples illustrate structural-dynamics studies of picosecond and slower photo-induced processes. They include molecular rearrangements and excitations. The information that can be ...obtained from such studies is discussed. The results are complementary to the information obtained from femtosecond studies. The point is made that all pertinent time scales should be covered to obtain comprehensive insight in dynamic processes of chemical and biological importance.
Careful control of the temperature and duration of the reaction between titanium tert-butoxide and acetic acid leads to the formation of new polyoxotitanate clusters with 14, 18, and 28 Ti atoms. ...They are considered intermediates in the growth of Ti/O nanoclusters of increasing size. The Ti28 cluster is the largest crystallized to date. UV/vis spectroscopy on this cluster reveals that the optical band gap is blue-shifted with respect to a cluster containing only 17 titanium atoms indicating that the optical properties are more heavily influenced by the internal structure of the particle than its size.
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The seminal discovery of light-induced changes in transition-metal nitrosyl complexes in the late 1970s and their identification as metastable linkage isomers almost 20 years after the initial ...discoveries have in recent years motivated a plethora of experimental and theoretical studies. Coppens et al summarize the current knowledge in the still-developing field and discuss photoinduced metastable isomers of related substances.
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The binding of carboxylate- and acetylacetonate-linked chromophores to homodisperse polyoxotitanate nanoclusters with 17 Ti atoms or more are surveyed and found to be limited to chelate-bidentate and ...the bridging modes, the former being dominant for the acetylacetonate-linked chromophores, the latter for the carboxylate linkers. Chromophores with acetylacetonate linking groups invariably bind in the chelate mode, whereas carboxylic acid terminated chromophores more frequently are observed to have the bridging mode, with the exception of three cases in which a strong electron-donating substituent is present on two different sensitizers. The calculations for isonicotinateand nitrophenylacetylacetonate functionalized Ti17 clusters show the observed binding modes to correspond to the lower energy functionalized clusters, but do not predict the difference between the cinnamic acid and dimethylaminocinnamic acid binding to Ti17, which are bridging and chelate respectively. Both binding modes were never observed to occur for a single chromophore, even when synthetic conditions were varied. Density of state calculations show broadening and splitting of the chromophore LUMO on complexation due to interaction with the cluster’s conduction band, as well as frequent penetration of sensitizer orbitals into the bandgap of the functionalized nanoparticle.
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The structures of three newly synthesized phosphonate‐substituted polyoxotitanates are reported. The Ti/O core of Ti4O(OEt)12(PhenylPO3) (1) is the building block for two larger ...phosphonate‐substituted nanoclusters, Ti25O26(OEt)36(PhenylPO3)6 (2) and Ti26O26(OEt)39(PhenylPO3)6Br (3). All compounds exhibit a not previously recognized triply bridging binding mode of the phosphonate anchor with short connecting TiO bonds, the average of which is 2.010(7) Å. Comparison with previously reported work suggests that the binding mode of the phosphonate anchor is strongly dependent on the structure of the underlying substrate.
Drop your anchor! How does the phosphonate linker bind to semiconductor surfaces? The binding mode of the phosphonate anchor to the surface of polyoxotitanate nanoclusters can answer this question. It is shown to be tridentate, with short TiO bonds connecting to the nanoparticle, indicating a strong linkage (see figure).
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A comprehensive version of the theoretical databank of transferable aspherical pseudoatoms is described, and its first application to protein−ligand interaction energies is discussed. The databank ...contains all atom types present in natural amino acid residues and other biologically relevant molecules. Each atom type results from averaging over a family of chemically unique pseudoatoms, taking into account both first and second neighbors. The spawning procedure is used to ensure that close transferability is obeyed. The databank is applied to the syntenin PDZ2 domain complexed with four-residue peptides and to the PDZ2 dimer. Analysis of the electrostatic interactions energies calculated by the exact-potential/multipole-moment-databank method stresses the importance of the P0 and P- 2 residues of the peptide in establishing the interaction, whereas the P- 1 residue is shown to play a much smaller role. Unexpectedly, the charged P- 3 residue contributes significantly to the interaction. The class I and II peptides are bound with the same strength by the syntenin PDZ2 domain, though the electrostatic interaction energy of the P- 2 residue is smaller for class I peptides. There is no difference between the interaction energies of the peptides with PDZ2 domains from single-domain protein fragments and those from PDZ1−PDZ2 tandems.
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•What is meant by “topological approach”?•“Topological approach” and chemical concepts.•Measurable quantities from “topological approaches”.•Predicting the outcome of a “topological ...approach”.•New domains of application.
The paper collects the answers of the authors to the following questions:
•What is the significance of topological approach?•Can new chemical concepts be found by a topological approach?•What is the status of a chemical concept within a topological approach?•Should topological approaches provide measurable quantities?•Is it possible to predict the outcome of a topological approach without performing a calculation on a computer?•What are new domains for which topological approaches would be useful?
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