2,4,6‐Tri‐tert‐butylphenyl and 2,4‐di‐tert‐butyl‐6‐methylphenyl groups: Look similar,react differently

The crystal structures of molecules with two phosphaalkene groups have been determined. Differences in the stabilization of the PC π‐bond by the 2,4,6‐tri‐tert‐butylphenyl and 2,4‐di‐tert‐butyl‐6‐methylphenyl groups were observed. It has been found that lithium supermesityl(trimethylsilyl)phosphide could be a very efficient base to remove a proton from acetonitrile.© 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:662–666, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10083     

Syntheses and Crystal Structures of Potassium–Lanthanoid(III) Complexes with the 1,2‐Benzenedisulfonate Ligand

The complexes [K(H₂O)₂LnL₂] (Ln = La or Nd; L = 1,2‐benzenedisulfonate) and [K(H₂O)Yb(H₂O)₄L₂] were initially isolated fortuitously from attempts to prepare the corresponding Ln₂L₃ complexes from Ln₂O₃ and H₂L in water. Indeed the bulk products from these reactions have the composition Ln₂L₃. Subsequently, deliberate syntheses by reacting equimolar amounts of Ln₂L₃ with K₂L in water gave the complexes in good yield. X‐ray crystal structures of [K(H₂O)₂LnL₂] (Ln = La or Nd) showed the complexes to be isostructural with a two dimensional polymeric network structure in which LnL₂ units are linked into chains crosslinked by potassium ions. Each Ln is nine coordinate with solely sulfonate oxygen donor atoms. Between adjacent lanthanoid ions there are three different types of sulfonate bridges and two examples of each. Most noteworthy is highly unsymmetrical bridging through μ‐η²‐sulfonate oxygen atoms. Consequently, one Ln–O bond is ca. 0.5 Å longer than the other eight. Potassium is nine‐coordinate with seven sulfonate oxygen atoms and two aqua ligands, and surprisingly <K–O(sulfonate)> is much longer than <K–O(H₂O)>. Pairs of potassium ions are linked by two μ‐η²‐sulfonate oxygen atoms, which are unsymmetrically bridging. The structure of [K(H₂O)Yb(H₂O)₄L₂] comprises discrete tetranuclear units containing two independent ytterbium ions, each coordinated by four water molecules and two chelating (via seven membered rings) disulfonate ligands, and two potassium ions, each coordinated by six sulfonate oxygen atoms and a water molecule. For each potassium, four of the coordinated sulfonate oxygen atoms are from sulfonate ligands bonded to one ytterbium atom and two from sulfonate ligands attached to the other ytterbium atom. In contrast to the Nd and La complexes, <K–O(sulfonate)> is shorter than <K–O(H₂O)>.     

Influence of Perfluoroarene–Arene Interactions on the Phase Behavior of Liquid Crystalline and Polymeric Materials

A stabilization of the liquid-crystalline mesophase and thus an enlarged temperature range of the mesogenic phase is achieved by adding perfluorotriphenylene to a chiral liquid-crystalline triphenylene. This mesophase is based on 1:1 perfluoroarene–arene interactions (see picture). In a polymer with triphenylenes as mesogens in the side chains, the addition of perfluorotriphenylene led to crystallization.     

Stepwise Solid-Phase Synthesis of Peptide-Oligonucleotide Conjugates on New Solid Supports

Several peptide-oligonucleotide and peptide-(oligonucleotide phosphorothioate) conjugates were synthesized on new solid supports. These supports are designed to link the 3′-terminus of an oligonucleotide to the C-end of a peptide via a phosphodiester or phosphorothioate bond in the process of stepwise solid-phase assembly.     

Polyelectrolytes bearing azobenzenes for the functionalization of multilayers

Thin polymeric films are assembled by the alternating adsorption of oppositely charged polyelectrolytes. The polyions are functionalized by azobenzenes, typically carrying donor-acceptor substituents. The azobenzene chromophores are exploited as versatile analytical tools, to study the assembling process, and to control the film quality. A high concentration of ionic groups does not seem to be advantageous per se for good film growth, but rather the matching of the charge densities of the polyelectrolyte pair used seems to be important. Also, the influence of the strongly interacting, form-anisotropic character of the azobenzenes on the internal film structure was investigated. Although even high concentrations of azobenzenes and of other mesogens do not induce particular ordering, a few polymer pairs allowed the construction of real multilayer films, exhibiting e.g. Bragg peaks.     

Nonlinear least squares fitting applied to copolymerization modeling

The choice of the statistical method to determine the reactivity ratios in copolymerization modeling is shown to be very important. Problems in literature, as well as possible pitfalls when using available statistical programs that are in itself correct are pointed out. These problems mainly involve (knowledge of) the error structure, as the error structure determines the weighting scheme of the data points in fitting procedures. A simple, robust, statistically correct non-linear least squares (NLLS) method is reintroduced which is based on the visualization of the sum of squares of residuals in the so-called sum of squares space (SSS). The advantages of this method include the fact that the method is easy to understand and can be implemented in simple computer programs, as well as the fact that the method allows important aspects of the error structure to be incorporated. Furthermore, in the SSS the joint confidence interval (JCI) with exact shape can be constructed. The exact shape of the JCI is not always ellipsoidal and following a normal distribution, depending on the linearity of the fitted equations. This can sometimes lead to wrong conclusions.     

Charge transfer interactions in polymers and the fabrication of high frequency electro-optic modulators

The synthesis and processing of second order nonlinear optical polymeric materials for application in electro-optic devices is described with particular emphasis on (1) the synthesis and incorporation into hardened polymer lattices of chromophores characterized by large μβ (where μ is the dipole moment and β is the molecular first hyperpolarizability) values; (2) the synthesis and incorporation into hardened polymer lattices of chromophores which are capable of undergoing photo-induced conformational changes and which can be processed by new multi-color photolithography techniques into buried channel active waveguides; and (3) the processing of polymeric nonlinear optical materials appropriate for the realization of full integration with very large scale integration (VLSI) drive electronics and with silica fiber optic transmission lines. Prototype modulators have been fabricated and shown to be suitable for broadband operation from 0 to 113 GHz. Optical losses associated with waveguide wall roughness and with mode mismatch in transitioning between silica and polymeric waveguides are reduced by control of the conditions of reactive ion etching and by use of the new technique of multi-color photochemical lithography.