For conjugates Ac-Hel 1 -Ala n -OH, n ) 1-6, of the previously characterized reporting, conformational template Ac-Hel 1 , increases in helicity induced by trifluoroethanol (TFE) in water have been related to a simple function of the peptide length n, yielding the helix propagation constant s Ala , which increases from 1.0 to 1.5 for χ TFE ) 0-20 mol %. The per-residue helicity increase is similar to the increase in te state stability induced by TFE in monoamide conjugates Ac-Hel 1 -NHR. Addition of TFE to water significantly increases the rate of interconversion of s-cis/s-trans amide conformers for Ac-Pro-NHMe, consistent with a significant and selective destabilization of the planar resonance-stabilized amide. In dilute aqueous solution TFE increases helicity by selectively destabilizing amide functions that are solvent exposed, with the consequence that compact conformations such as helices that maximize intramolecular amide-amide hydrogen bonding and minimize amide solvent exposure are selectively favored.Medium-sized peptides with an intrinsic tendency to assume helical conformations in water often show a dramatic increase in helicity upon addition of relatively low concentrations of certain alcohols, of which the most efficient appears to be trifluoroethanol (TFE). Since its discovery by Goodman and co-workers, 1 this helix-enhancing effect of TFE has found many applications, most recently for NMR-based characterization of short helices derived from natural proteins. 2 Because TFE extends the range of detectable helicity to include polypeptides that are predominantly unstructured in water, titrations with TFE permit comparisons of relative R-helical propensities between members of peptide series or within regions of the same peptide. 3 Helicity changes resulting from TFE titrations of synthetic peptides have been correlated with amino acid composition, sequence, and helicity-inducing local features. 4,5 Unfortunately, TFE titrations are often difficult to interpret, since the mechanism by which TFE acts to enhance helicity is widely viewed as uncertain or unknown. 2d,3a,c,d A definitive helix enhancement mechanism presumes complete characterization of the effects of TFE on the solvation states of both starting materials and products. Characterization at this level is difficult, since key features of the structure of water itself remain undefined. We address the following practical questions in this report: (1) Which of the two global states is energetically perturbed by TFE? Does TFE selectively raise the energy of the nonhelical random coil state, or lower the energy of the helical state, or both? (2) If the helical state is stabilized, does TFE interact directly with the helix and, if so, with which of its functionalities? (3) If TFE acts by decreasing the stability of the coil state, can the overall stability change be approximated as a sum of effects at each amino acid residue? If it can, does the per-residue effect arise primarily from energy changes involving the amino acid side chains or the a...

A revised indirect mechanism is proposed for the effect of 2,2,2-trifluoroethanol on peptide conformation (TFE effect) that suggests tighter solvent shells in pure water for helical states than random coil states. The alcoholic cosolvent stabilizes the helical state preferentially by disrupting the solvent shell, which causes unfavorable enthalpic and favorable entropic contributions to the free energy of helix formation. This revised mechanism was adopted because it best explained the solvent-dependent thermodynamic behavior of the coil/helix transition. To define the TFE effect, solvent-dependent physicochemical behaviors of two molecular probes for solvent character were monitored and compared with the solvent dependence of peptide helix formation. The rate of decarboxylation of 6-nitro-3-carboxybenzisoxazole was determined in aqueous mixtures as a function of concentration for DMSO, EtOH, MeOH, i PrOH, HFIP, and TFE. To relate these rate studies to the cosolvent-dependent thermodynamics of helix formation, ΔH ⧧ and ΔS ⧧ as a function of concentration for EtOH and TFE were determined and interpreted. The mixed solvent dependence of the UV spectrum of a solvatochromic ketone was also monitored to correlate the behavior of the mixed solvent systems with a microscopic polarity index.

This paper presents a wireless, passive, remote query CO2 sensor comprising a ribbon-like magnetoelastic thick-film coated with a mass-changing CO2 responsive polymer synthesized from acrylamide and isooctylacrylate. In response to a magnetic field impulse, the magnetostrictive magnetoelastic sensor vibrates at a characteristic resonant frequency that is inversely dependent upon the mass of the attached CO2 responsive polymer. The mechanical vibrations of the magnetostrictive sensor launch magnetic flux, which can be detected remotely using a pickup coil. By monitoring the resonant frequency of the passive sensor, the atmospheric CO2 concentration can be determined without the need for physical connections to the sensor or specific alignment requirements. The effect of humidity and the CO2 responsive copolymer composition on the measurement sensitivity are reported. Greatest sensitivity is achieved with a polymer comprising a 1:1 mole ratio of acrylamide to isooctyl acrylate. A 0.7% change in atmospheric CO2 concentration can be detected for a 20 microns thick polymer coated sensor.

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This study aimed to elucidate the structural nature of the polydisperse, nanoscopic components in the solution and the solid states of partially reduced polyoxomolybdate derived from the [Mo132] keplerate, [(Mo)Mo5]12-[Mo2 acetate]30. Designer tripodal hexamine-tris-crown ethers and nanoscopic molybdate coprecipitated from aqueous solution. These microcrystalline solids distributed particle radii between 2-30 nm as assayed by transmission electron microscopy (TEM). The solid materials and their particle size distributions were snap shots of the solution phase. The mother liquor of the preparation of the [Mo132] keplerate after three days revealed large species (r=20-30 nm) in the coprecipitate, whereas [Mo132] keplerate redissolved in water revealed small species (3-7 nm) in the coprecipitate. Nanoparticles of coprecipitate were more stable than solids derived solely from partially reduced molybdate. The TEM features of all material analyzed lacked facets on the nanometer length scale; however, the structures diffracted electrons and appeared to be defect-free as evidenced by Moiré patterns in the TEM images. Moiré patterns and size-invariant optical densities of the features in the micrographs suggested that the molybdate nanoparticles were vesicular.