Application of the energy gap law to the decay of charge transfer excited states,solvent effects

Values of non-radiative decay rate constants (k_nr) and emission energies (E_cm) have been obtained for Os(Phen₃)²⁺ in a series of solvents and the results are consistent with the energy gap law. For hydroxylic solvents like water or methanol related studies suggest the existence of strong, specific contributions to the vibrational trapping energy of the solvent.     

SLIM: A Short‐Linked,Highly Redox‐Stable Trityl Label for High‐Sensitivity In‐Cell EPR Distance Measurements

The understanding of biomolecular function is coupled to knowledge about the structure and dynamics of these biomolecules, preferably acquired under native conditions. In this regard, pulsed dipolar EPR spectroscopy (PDS) in conjunction with site‐directed spin labeling (SDSL) is an important method in the toolbox of biophysical chemistry. However, the currently available spin labels have diverse deficiencies for in‐cell applications, for example, low radical stability or long bioconjugation linkers. In this work, a synthesis strategy is introduced for the derivatization of trityl radicals with a maleimide‐functionalized methylene group. The resulting trityl spin label, called SLIM, yields narrow distance distributions, enables highly sensitive distance measurements down to concentrations of 90 nm , and shows high stability against reduction. Using this label, the guanine‐nucleotide dissociation inhibitor (GDI) domain of Yersinia outer protein O (YopO) is shown to change its conformation within eukaryotic cells.     

Substituted 1,8-naphthyridin-2(1H)-ones are superior to thymine in the recognition of adenine in duplex as well as triplex structures

The synthesis and evaluation of a series of novel nucleobases based on substituted 1,8-naphthyridin-2(1H)-ones are reported. The nucleobases were designed to meet the requirements for incorporation into peptide nucleic acids (PNAs) and were evaluated as part of PNA duplex and triplex nucleic acid recognition systems. Of the various nucleobases tested, only the 7-chloro-1,8-naphthyridin-2(1H)-one (7-Cl-bT) nucleobase led to consistently increased affinity in all recognition systems, duplex (Watson-Crick) as well as triplex (Hoogsteen). For multiply modified systems, the increase in thermal stability per modification was dependent on the sequence context, ranging from 2.0 degrees C (in separate positions) to 3.5 degrees C (in adjacent positions) in PNA-DNA duplexes and from 1.2 degrees C (in separate positions) to 3.2 degrees C (in adjacent positions) in PNA-RNA duplexes. Singly mismatched oligonucleotide targets were employed to demonstrate uncompromised sequence discrimination. When part of multiply modified triplex (Hoogsteen) recognition systems, the 7-Cl-bT unit gave rise to increases in the thermal stability ranging from 2.7 to 3.5 degrees C when incorporated into separated and adjacent positions, respectively. Our results furthermore indicate that the duplex stabilization is predominantly enthalpic and therefore most likely not a consequence of single-strand preorganization. Finally, and most surprisingly, we find no direct correlation between the end-stacking efficiency of this type of nucleobase and its helix stabilization when involved in Watson-Crick base pairing within a helix.     

Etude par RMN 13C de Dérivés Aromatiques Phénylés: Observation de Substituants Phényles en Rotation Restreinte

The restricted rotation of phenyl groups has been directly observed in several phenyl-substituted aromatic compounds. Barriers range from 14–>18 kcal mol^?1. Useful rules have been established for the structural analysis of phenylated aromatic compounds.     

Adsorption of CO2 on mesocellular siliceous foam iteratively functionalized with dendrimers

Melamine-type dendrimers are grafted to mesocellular siliceous foam (MCF) with ultralarge mesopores by stepwise alternating treatments of the substrate with 2,4,6-trichlorotriazine and ethylenediamine. MCF grafted dendrimers up to 4th generation are prepared and characterized. Very high organic loadings (55 wt% at the 4th generation) are achieved, with half of the initial substrate mesopores volume remaining unoccupied—leaving room for the rapid ingress and egress of small gas molecules. The product materials possess relatively high thermal stability—their decomposition starts at around 300 °C. Adsorption measurements suggest that only the primary amine groups of these melamine type structures are active for CO₂ chemisorption. The CO₂ adsorption capacities of these adsorbents are improved relative to the unfunctionalized MCF, especially when considered on a wt% substrate basis.