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Membranes based on graphite oxide (GO) are promising materials for the separation of polar liquids and gases. Understanding the properties of solvents immersed in GO is important for the development of various technological applications. Here, the molecular motions of the TEMPO nitroxide spin probe in acetonitrile intercalated into the GO inter-plane space were studied using electron paramagnetic resonance (EPR), including its pulsed version, and electron spin echo (ESE). For a sample containing 75% acetonitrile relative to equilibrium sorption at room temperature, ESE-detected stochastic librations were observed for TEMPO molecules above 135 K. Since these librations are an inherent property of molecular glasses, this fact indicates that intercalated acetonitrile forms a two-dimensional glass state. Above 225 K, an acceleration of stochastic librations was observed, indicating the manifestation of a glass-like dynamical cross-over. Continuous wave (CW) EPR spectra of TEMPO showed the absence of overall tumbling motions in the entire investigated temperature range of up to 340 K, indicating that the intercalated acetonitrile does not behave as a bulk liquid (the melting point of acetonitrile is 229 K). Dynamical librations of TEMPO molecules detected by CW EPR were found to accelerate above 240 K. [ABSTRACT FROM AUTHOR]

Trichogin GA IV is a membrane-active lipopeptide, theantibioticactivity of which was proposed to be based on its capability to induceleakage due to formation of pores into the bacterial cell membrane.However, less attention has been paid to its biological selectivity,i.e., discrimination between bacterial versus cholesterol containing(mammalian) membranes. This is the reason which motivated us to studythe role of cholesterol on penetration of the peptide into the membraneand formation of water channels. The ESEEM technique was used to measurethe modulation amplitudes for TOAC spin-labeled trichogin GA IV peptideanalogues in hydrated membranes of phosphatidylcholine (PC) lipidin the presence of 50 mol % cholesterol-d7. From the interaction between the nitroxide spin-label and the nearbylocated deeply membrane inserted deuterons, the N-terminus was foundto be positioned at the core of the membrane. Separately, ESEEM measurementsfor the FTOAC-8 labeled peptide, but in D2O hydrated cholesterol/PCmembranes, provide strong evidence for the polar C-terminus situatednear the membrane surface. The apparently too high modulation amplitudemeasured for the buried FTOAC-1 label is likely attributed to thepresence of peptide associated water. In cholesterol depleted membrane,however, the long axes of the helical molecules are found orientedparallel to the membrane surface even at high peptide concentration.Continuous wave EPR spectroscopy indicates that, for cholesterol containingmembrane, peptide insertion is accompanied by self-aggregation ofparallelly aligned transmembrane peptide molecules, while for cholesterollacking membranes they are monomolecularly distributed. Thus, cholesteroltends to stabilize the transmembrane peptide aggregate. [ABSTRACT FROM AUTHOR]

In this work, an extensive set of spectroscopic and biophysical techniques (including FT-IR absorption, CD, 2D-NMR, fluorescence, and CW/PELDOR EPR) was used to study the conformational preferences, membrane interaction, and bioactivity properties of the naturally occurring synthetic 14-mer peptaibiotic chalciporin A, characterized by a relatively low (≈20%), uncommon proportion of the strongly helicogenic Aib residue. In addition to the unlabeled peptide, we gained in-depth information from the study of two labeled analogs, characterized by one or two residues of the helicogenic, nitroxyl radical-containing TOAC. All three compounds were prepared using the SPPS methodology, which was carefully modified in the course of the syntheses of TOAC-labeled analogs in view of the poorly reactive α-amino function of this very bulky residue and the specific requirements of its free-radical side chain. Despite its potentially high flexibility, our results point to a predominant, partly amphiphilic, α-helical conformation for this peptaibiotic. Therefore, not surprisingly, we found an effective membrane affinity and a remarkable penetration propensity. However, chalciporin A exhibits a selectivity in its antibacterial activity not in agreement with that typical of the other members of this peptide class., (© 2017 Wiley Periodicals, Inc.)