27 research outputs found
An Origin of Complicated Infrared Spectra of Perfluoroalkyl Compounds Involving a Normal Alkyl Group
Perfluoroalkyl (Rf) compounds containing a normal alkyl group often yield highly complicated infrared (IR) spectra especially in the CāF stretching vibration (Ī½CāF) region. To reveal the reason behind this, the IR p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) is employed to measure a monolayer of CF3(CF2)9(CH2)3COOH deposited on a silicon substrate. The compound is known to spontaneously aggregate to form a molecular assembly with the closest packing, in which the molecules are oriented perpendicular to the substrate. The IR pMAIRS spectra apparently prove that the complexity of the Ī½CāF region is due to the normal alkyl part directly connected to the Rf group because the carbons in the Rf group are vibrated as a coupled oscillator, and the oscillation of the alkyl part propagates to the Rf part along the molecular axis
Five Amino Acid Residues Responsible for the High Stability of Hydrogenobacter thermophilus Cytochrome c552
Five amino acid residues responsible for extreme stability have been identified in cytochrome c552 (HT c552) from a thermophilic bacterium, Hydrogenobacter thermophilus. The five residues, which are spatially distributed in three regions of HT c552, were replaced with the corresponding residues in the homologous but less stable cytochrome c551 (PA c551) from Pseudomonas aeruginosa. The quintuple HT c552 variant (A7F/M13V/Y34F/Y43E/I78V) showed the same stability against guanidine hydrochloride denaturation as that of PA c551, suggesting that the five residues in HT c552 necessarily and sufficiently contribute to the overall stability. In the three HT c552 variants carrying mutations in each of the three regions, the Y34F/Y43E mutations resulted in the greatest destabilization, by ā13.3 kJ molā1, followed by A7F/M13V (ā3.3 kJ molā1) and then I78V (ā1.5 kJ molā1). The order of destabilization in HT c552 was the same as that of stabilization in PA c551 with reverse mutations such as F34Y/E43Y, F7A/V13M, and V78I (13.4, 10.3, and 0.3 kJ molā1, respectively). The results of guanidine hydrochloride denaturation were consistent with those of thermal denaturation for the same variants. The present study established a method for reciprocal mutation analysis. The effects of side-chain contacts were experimentally evaluated by swapping the residues between the two homologous proteins that differ in stability. A comparative study of the two proteins was a useful tool for assessing the amino acid contribution to the overall stability.This work was supported in part by grants from Hiroshima University, the Noda Institute for Scientific Research, and the Japanese Ministry of Education, Science and Culture (grants-in-aid for Scientific Research on Priority Areas)
Fluorous Property of a Short Perfluoroalkyl-Containing Compound Realized by Self-Assembled Monolayer Technique on a Silicon Substrate
Fluorous properties represented by water-and-oil repellency are perfluoroalkyl (Rf) compound-specific characteristics, which are widely used for surface coating of glass, electronic devices and textiles for preventing water and grease fouling. According to the stratified dipole-arrays (SDA) theory, the minimum Rf length of (CFā)ā is theoretically necessary for realizing fluorous properties. Unfortunately, however, production of compounds involving this chemical unit is strictly banned because of concerns of environmental pollution, which is a big dilemma. Here, we show that the fluorous properties can be realized by self-assembled monolayer (SAM) even with a short Rf-containing compound, since the SAM technique makes the best use of the self-aggregation property of the Rf groups, and it readily makes the molecules immobile
Surface properties of a single perfluoroalkyl group on water surfaces studied by surface potential measurements
A discriminative study of a single perfluoroalkyl (Rf) group from a bulk material is recently recognized to be necessary toward the total understanding of Rf compounds based on a primary chemical structure. The single molecule and the bulk matter have an interrelationship via an intrinsic two-dimensional (2D) aggregation property of an Rf group, which is theorized by the stratified dipole-arrays (SDA) theory. Since an Rf group has dipole moments along many CāF bonds, a single Rf group would possess a hydrophilic-like character on the surface. To reveal the hydration character of a single Rf group, in the present study, surface potential (ĪV) measurements are performed for Langmuir monolayers of Rf-containing compounds. From a comparative study with a monolayer of a normal hydrocarbon compound, the hydration/dehydration dynamics of a lying Rf group on water has first been monitored by ĪV measurements, through which a single Rf group has been revealed to have a unique ādipole-interactiveā character, which enables the Rf group interacted with the water āsurface.ā In addition, the SDA theory proves to be useful to predict the 2D aggregation property across the phase transition temperature of 19 Ā°C by use of the ĪV measurements
Study of Perfluoroalkyl Chain-Specific Band Shift in Infrared Spectra on the Chain Length
The CF<sub>2</sub> symmetric stretching vibration (Ī½<sub>s</sub>(CF<sub>2</sub>)) band of a perfluoroalkyl (Rf) group in an
infrared (IR) spectrum exhibits a unique character, that is, an apparent
high wavenumber shift with increasing the chain length, which is an
opposite character to that of the CH stretching vibration band of
a normal alkyl chain. To reveal the mechanism of the unusual IR band
shift, two vibrational characters of an Rf chain are focused: (1)
a helical conformation of an Rf chain, (2) the carbon (C) atoms having
a smaller mass than the fluorine (F) atom dominantly vibrate as a
coupled oscillator leaving F atoms stay relatively unmoved. These
indicate that a ācoupled oscillation of the skeletal C atomsā
of an Rf chain should be investigated considering the helical structure.
In the present study, therefore, the coupled oscillation of the Rf
chain dependent on the chain length is investigated by Raman spectroscopy,
which is suitable for investigating a skeletal vibration. The Raman-active
Ī½<sub>s</sub>(CF<sub>2</sub>) band is found to be split into
two bands, the splitting is readily explained by considering the helical
structure and length with respect to group theory, and the unusual
peak shift is concluded to be explained by the helical length