Green solid-phase peptide synthesis 4. γ-Valerolactone and N-formylmorpholine as green solvents for solid phase peptide synthesis

Herein, we report the use of γ-valerolactone (GVL) and N-formylmorpholine (NFM) as DMF substitutes in polystyrene based SPPS. The solubility of selected amino acids and coupling reagents were studied in GVL and NFM, followed by their use in the successful synthesis of Aib-enkephalin pentapeptide (H-Tyr-Aib-Aib-Phe-Leu-NH₂) and Aib-ACP decapeptide (H-Val-Gln-Aib-Aib-Ile-Asp-Tyr-Ile-Asn-Gly-NH₂).     

Chloride‐Selective Electrodes Based on “Two‐Wall” Aryl‐Extended Calix[4]Pyrroles: Combining Hydrogen Bonds and Anion–π Interactions to Achieve Optimum Performance

The performance of chloride‐selective electrodes based on “two‐wall” aryl‐extended calix[4]pyrroles and multiwall carbon nanotubes is presented. The calix[4]pyrrole receptors bear two phenyl groups at opposite meso‐positions. When the meso‐phenyl groups are decorated with strong electron‐withdrawing substituents, attractive anion–π interactions may exist between the receptor’s aromatic walls and the sandwiched anion. These anion–π interactions are shown to significantly affect the selectivity of the electrodes. Calix[4]pyrrole, bearing a p‐nitro withdrawing group on each of the meso‐phenyl rings, afforded sensors that display anti‐Hofmeister behavior against the lipophilic salicylate and nitrate anions. Based on the experimental data, a series of principles that help in predicting the suitability of synthetic receptors for use as anion‐specific ionophores is discussed. Finally, the sensors deliver excellent results in the direct detection of chloride in bodily fluids.     

On similarity of hydrogen-bonded networks in liquid formamide and water as revealed in the static dielectric studies

The paper presents the experimental verification of the result obtained with the molecular dynamics simulation which revealed the differences in the topology of the hydrogen-bonded networks in liquid formamide and water, namely, the differences in their intermolecular cyclization process (I. Bakó, et al. J. Chem. Phys. 2010, 132, 014506). It is shown in our paper that the difference in the (simulated) size distribution of the hydrogen-bonded molecular rings in water (a relatively sharp maximum at about 6 molecules) and formamide (a broad maximum at about 11 molecules) strongly manifests itself in the experimental values of the Kirkwood correlation factor of the compounds. A much larger number of molecules included in the cyclic species (of more or less compensated dipole moment) leads to significant decrease of the Kirkwood correlation factor of formamide in comparison to that of water. Besides, as a consequence of an enhancement in formation of the cyclic multimers of formamide, one observes an essential reduction of the orientational entropy increment of that liquid, in comparison to the entropy effect related to liquid amides where the chain multimers are formed.     

Counterions and water in polyelectrolyte multilayers: a tale of two polycations

Attenuated total internal reflectance Fourier transform infrared, ATR-FTIR, spectroscopy was used to compare the water uptake and doping within polyelectrolyte multilayers made from poly(styrene sulfonate), PSS, and a polycation, either poly(allylamine hydrochloride), PAH, or poly(diallyldimethylammonium chloride), PDADMAC. Unlike PDADMA/PSS multilayers, whose water content depended on the solution ionic strength, PAH/PSS multilayers were resistant to doping by NaCl to a concentration of 1.2 M. Using (infrared active) perchlorate salt, the fraction of residual counterions in PDADMA/PSS and PAH/PSS was determined to be 3% and 6%, respectively. The free energy of association between the polymer segments, in the presence of NaClO4, was about 5 kJ mol-1 and -10 kJ mol-1, respectively, for PDADMA/PSS and PAH/PSS, indicating the relatively strong association between the polymer segments in the latter relative to the former. Varying the pH of the solution in contact with the PAH/PSS multilayer revealed a transition to a highly swollen state, interpreted to signal protonation of PAH under much more basic conditions than the pKa of the solution polymer. The increase in the multilayer pKa suggested an interaction energy for PAH/PSS in NaCl of ca. 16 kJ mol-1.     

Dielectric and orientational properties of nematogenic 4-<Emphasis Type="Italic">n</Emphasis>-octyl(4′-cyanophenyl)benzoate

Experimental studies of the dielectric properties in the nematic and isotropic phases of 4-cyanophenyl-4′-n-octylbenzoate (8CPB) have been performed in the frequency range from 50 kHz to 100 MHz. The relaxation process related to the rotation around the short molecular axis has been analysed. The results obtained have revealed that in the vicinity of the I-N phase transition, the molecular subdiffusional rotation process occurs. It is connected with the pretransitional effects which are observed both in the static and dynamic dielectric measurements. On the basis of the temperature dependence of the relaxation time in the nematic and isotropic phases, the orientational order parameter 〈P₂〉 has been determined. The values of 〈P₂〉 obtained in this way have been compared with those evaluated from the measurements of the polarized electronic absorption of the dichroic dye, dissolved as guest probe in the mesogenic host.     

Static and dynamic dielectric effects in the vicinity of the isotropic to nematic phase transition in 7CB

Static and dynamic dielectric measurements were performed with very high accuracy on a mesogenic compound n‐heptylcyanobiphenyl (7CB) in the isotropic (I) and nematic (N) phases. The critical‐like temperature behaviour of the static permittivity of isotropic 7CB in the vicinity of the I–N phase transition can be described with the critical exponent close to 0.5, indicating the tricritical nature of the transition. Anomalously slow rotational diffusion (subdiffusion), characterized by a fractal value of the diffusion exponent α, is observed in the vicinity of the I–N transition with a lambda‐like profile of the exponent temperature dependence.     

Investigating green ethers for the precipitation of peptides after global deprotection in solid-phase peptide synthesis

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Photoinduced Electron Transfer in Clicked Ferrocene-BODIPY-Fullerene Conjugates

Ferrocene-BODIPY (Fc-BDP) conjugates in which one or two ferrocene entities are linked to the β-positions of the BODIPY core by an ethynyl bridge have been developed. These derivatives were easily and efficiently grafted onto a dual-clickable fullerene platform using CuAAC reactions, leading to a clickable Fc-BDP-C₆₀ triad and a clickable [Fc]₂-BDP-C₆₀ tetrad which can be used for further derivatization with complex structures. Due to the extended π-conjugation and the presence of an intramolecular charge transfer band from Fc to BDP, all these conjugates display a broad absorption in the visible region, which is bathochromically shifted when two Fc are appended to the BDP core. Ultrafast multistep electron transfers leading to charge stabilization were demonstrated in the Fc-BDP-C₆₀ triad and [Fc]₂-BDP-C₆₀ tetrad by femtosecond transient absorption studies.