Surface electrostatic immobilization of thin layers of water on silver halide. Experimental and calculated infrared spectrum of cyclic trimer of water and a ponderal isotope effect

Theory of new states, FEXs, Fast-formed EXcited states by the combination of an IR photon and water

In the IR spectra of water on polyethylene, polypropylene and polytetrafluoroethylene frequent and substantial negative peaks occurred and are explained by a theoretical analysis. New states, FEXs, Fast-formed EXcited states are formed by the combination of an IR photon and water and are now made manifest by inefficient energy transfer to the polymer combined with limited energy transfer to the small (0.5-1.0 μL) water sample.

Neutral dipole-dipole dimers: A new field in science

Dimer formation with dipole neutralization produces species such as low polarity water (LPW) compatible with hydrophobic surfaces (Phys. Chem. Chem. Phys. 2015, 17, 24895-24900) Dimerization and dipole neutralization occurs for N-methylacetamide on polyethylene, a behavior drastically different from its contortions in acetonitrile on AgBr:AgCl planar crystals (AgX) (ChemPhysChem 2014, 15, 3598-3607). The weak infrared absorption of the amide dimer on polyethylene is shown experimentally. Dimerization of palmitic acid is shown along with some of the many ramifications for intracellular systems. Polyoligomers of water are present on polyethylene surfaces. Some high resolution spectra of three of the polyoligomers of water are shown along with a mechanistic scheme for polyoligomer formation and dissolution. The structures of some of the oligomers are known from spectroscopic studies of water on AgX.

Low polarity water, a novel transition species at the polyethylene–water interface

Polyethylene sandwich or a single window cell: dark bars represent polyethylene (PE) windows (double or single) of a cell. Wavy lines are water (W) and low polarity water (LPW). Subtraction of the single window spectrum from the double window spectrum leaves the LPW spectrum as illustrated in the figure.

N-alkylacylamides in thin films display infrared spectra of 3₁₀-, α-, and π-helices with visible static and dynamic growth phases

A peptide model is a physical system containing a CONH group, the simplest being HCONHCH3 , N-methylformamide (NMF). We have discovered that NMF and N-methylacetamide (NMA), which form hydrogen-bonded oligomers in thin films on a planar AgX fiber, display infrared (IR) spectra with peaks like those of polypeptide helices. Structures can be assigned by their amide I maxima near 1672 (3(10)), 1655 (3(10)), 1653 (α), 1655 (π), and 1635 cm(-1) (π), which are the first IR data for the π-helix. Sharp peaks are an outcome of immobilization of polar species on the polar surface of silver halides. We report the first use of expanded thin-film IR spectroscopy, in which plots of every spectrum over the amide I-II range show pauses or slow stages in the increase or decrease of absorption. These are identified as static phases followed by dynamic phases, with the incremental gain or loss of a helix turn. A general theory can be stated for such processes. Density functional calculations show that the NMA α-helix pentamer (crystal structure geometry) is transformed into a π-helix-like form. For the first time, an entire sequence (3(10)-helix, α-helix, π-helix, quasiplanar species) of spectra has been recorded for NMA.

N-methyl-trimethylacetamide in thin films displays infrared spectra of π-helices, with visible static and dynamic growth phases, and then a β-sheet

The simplest (minimal) peptide model is HCONHCH3. An increase in the π-helix content with increased substitution in the acyl portion suggested the examination of N-methyl-trimethylacetamide) (NMT). NMT displays spectra, in which there is evolution of a set of helices defined by their amide I maxima near 1686 (3(10)), 1655 (first π), and, most importantly, at 1637 cm(-1) (π). Expanded thin-film infrared spectroscopy (XTFIS) shows pauses or slow stages, which are identified as static phases followed by dynamic phases with the incremental gain or loss of a helix turn. In addition, absorbance at 1637 cm(-1) suddenly increases at 82.1 s (30% over 0.3 s), indicating a phase change and crystallization of the π-helix, along with a coincidental decrease in the absorbance for the first π-helix. A sharp peak occurs at the maximum of the phase change at 82.5 s, representing a pure NMT π-helix. The spectra then undergo a decreasing general absorption loss over 150 s, with the π-helix evolving further to an antiparallel β-sheet fragment. The spectral quality arises from the immobilization of polar molecules on polar surfaces. The crystal structure is that of an antiparallel β-sheet.