Chiral alignment of OPV chromophores: exploitation of the ureidophthalimide-based foldamer

The ability of foldamers to adopt a secondary structure in solution has been exploited to organize peripheral functionality. Our previously reported poly(ureidophthalimide) foldamer proved to be an excellent scaffold for the chiral organization of peripherally positioned oligo(p-phenylenevinylene) (OPV) chromophores. Facile high-yielding synthesis gave access to the required OPV-decorated building blocks. A condensation polymerization provided polymers of sufficient length to allow construction of a helical architecture comprising several turns. Short and long chains were separated by chromatography. Circular dichroism studies in THF of the longer chains indicate the presence of helically arranged OPVs. However, such an effect is not observed in CHCl3. Remarkable are the measurements of the OPV foldamers in heptane. A bisignate Cotton effect is observed in heptane of a sample with a THF history. No Cotton effect is observed in heptane of a sample with a CHCl3 history. In this example of supramolecular synthesis, the solvent dictates the expression of supramolecular chirality in a secondary structure. The short-chain oligomeric fractions that are unable to create a full turn revealed on scanning tunneling microscopy analysis the presence of circular architectures at the graphite/1-phenyloctane interface. This is in full agreement with the proposed conformation of the decorated foldamers.     

Synthesis of 3,6-diaminophthalimides for ureidophthalimide-based foldamers

[reaction: see text]. Herein, we report an improved methodology for the synthesis of a variety of 3,6-diaminophthalimides in high yields. This enables decoration of the periphery of foldamers with a wide range of functionalities.     

Double cation adduction in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of electron deficient anthraquinone derivatives

Six anthraquinone derivatives were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS). Clear (pseudo) molecular ions were observed for all the compounds. Interestingly, for some derivatives, strong ions with double cation adduction were also recorded in the positive mode. It is remarkable that all these ions are singly charged. In this work, possible mechanisms for the double cation adduction were investigated and discussed. It appears that the double cation adduction was due to the electron deficient nature of the derivatives, and formed by taking up two singly charged cations and one electron. Substituents on the anthraquinone ring were found to have a significant effect on the double cation adduction. In contrast, no considerable influence of the acidity of MALDI matrix/solution was observed, even on the double proton adduction. Furthermore, it was demonstrated that double cation adduction might occur in the MALDI gas-phase plume. In addition to the anthraquinones, three more electron deficient compounds of different types, i.e. a perylene bisimide derivative (PB), 3,7-decanoylamino-4,8-dihydrobenzo[1,2-b:4,5-b']dithiophene-4,8-dione (TQ) and 6,6-phenyl C61-butyric acid methyl ester (PCBM), were also analyzed with MALDI TOF MS. The results indicate that the 'abnormal' double cation adduction might be a 'normal' phenomenon in the MALDI TOF MS analysis of many electron deficient compounds.     

To D or not to D? On estimating the microenvironment polarity of biomolecular cavities

Knowledge of the local polarity of specific cavities in biopolymers can facilitate the design of selective low MW ligands that impact the structure and function of macromolecules. The most common tools for interrogating local polarity are fluorescent probes that are sensitive to their microenvironment. Researchers often evaluate and express this local polarity using dielectric constants, a parameter that reflects an inherent bulk property. A more appropriate expression should take into account solvent-solute interactions at the molecular level. Reevaluation of commonly used fluorophores illustrates the improved correlation between observed Stokes shift changes and E(T)(30) values as compared to the corresponding dielectric constants.     

Reflection of plane waves from the boundary of a pre-stressed compressible elastic half-space

The effect of pre-stress on the propagation and reflection ofplane waves in an incompressible isotropic elastic half-spacehas been examined recently by the authors (Ogden & Sotiropoulos,1997). In the present paper the corresponding analysis for compressiblematerials is detailed. In the two-dimensional context consideredfor incompressible materials the (homogeneous) plane waves werenecessarily shear waves. By contrast, in the compressible contextpure shear waves can propagate only in specific directions inthe considered principal plane and, in a general direction,a quasi-shear wave may be accompanied by a quasi-longitudinalwave, as is the case in the anisotropic linear theory. The dependenceof the (in-plane) slowness section on the pre-stress (and finitedeformation) and on the choice of constitutive law is elucidated.This information is used to determine the reflection coefficientsfor reflection of either a (quasi-) shear wave or a (quasi-)longitudinal wave from the boundary of the half-space and tocharacterize the different cases which arise depending on thegeometry of the slowness section. The theoretical results are illustrated by numerical calculationsfor the range of possible types of behaviour with referenceforms of strain-energy function and different states of finitedeformation and to the question of stability of the half-space.