Publisher Summary The vibrational spectrum of a molecule is determined by its three-dimensional structure and its vibrational force field. An analysis of this (usually infrared (IR) and Raman) spectrum can therefore provide information on the structure and on intramolecular and intermolecular interactions. The more probing the analysis, the more detailed is the information that can be obtained. Detailed analyses of the vibrational spectra of macromolecules, however, have provided a deeper understanding of structure and interactions in these systems. An important advance in this direction for proteins came with the determination of the normal modes of vibration of the peptide group in N-methylacetamide, and the characterization of several specific amide vibrations in polypeptide systems. Extensive use has been made of spectra-structure correlations based on some of these amide modes, including attempts to determine secondary structure composition in proteins. Polypeptide molecules exhibit many more vibrational frequencies than the amide modes. Over the years, some normal-mode calculations have provided greater insight into the spectra of particular molecules. However, these have often been based on approximate structures or have employed limited force fields. These force fields can now serve as a basis for detailed analyses of spectral and structural questions in other polypeptide molecules. The aim of this chapter is to present these recent developments in the vibrational spectroscopy of peptides, polypeptides, and proteins.

Vibrational spectroscopy and conformation of peptides, polypeptides, and proteins.

▪ Abstract The past 10 years have witnessed a tremendous acceleration in research devoted to non-fluorinated polymer membranes, both as competitive alternatives to commercial perfluorosulfonic acid membranes operating in the same temperature range and with the objective of extending the range of operation of polymer fuel cells toward those more generally occupied by phosphoric acid fuel cells. Important requirements are adequate membrane mechanical strength at levels of functionalization (generally sulfonation) and hydration allowing high proton conductivity, and stability in the aggressive environment of a working fuel cell, in particular thermohydrolytic and chemical stability. This review provides an overview of progress made in the development of proton-conducting hydrocarbon and heterocyclic-based polymers for proton exchange and direct methanol fuel cells and describes the various approaches made to polymer modification/synthesis and salient properties of the materials formed, including those relati...

Non-Fluorinated Polymer Materials for Proton Exchange Membrane Fuel Cells

Covalently bonded carbon nitride materials (e.g., g-C(3)N(4)) have numerous potential applications ranging from semiconductors to fuel cells. But their solubility is poor, which makes characterization and processing difficult. Moreover, the chemistry of the as-synthesized carbon nitrides has been widely neglected. Here we report that some of these handicaps might be overcome by a controllable and reversible protonation. It was found that protonation not only provides better dispersion and exposes a high surface area for g-C(3)N(4) but also enables an adjustment of electronic band gaps and higher ionic conductivity. Recovery or deprotonation toward the original g-C(3)N(4) could be obtained by simple heating, which enables improved sintering but also a potential preservation of the higher surface area of the protonated material. This proton-enhanced sintering process allowed for the first time direct measurement of the photoconductivity of the material. By aid of protonation, other promising g-C(3)N(4) based hybrid composites could also be facilely obtained by simple counteranion exchange.

Activation of Carbon Nitride Solids by Protonation: Morphology Changes, Enhanced Ionic Conductivity, and Photoconduction Experiments

Designing pi-conjugated polymers for organic electronics

The development of high-temperature PEM fuel cells (working at 150–200 °C) is pursued worldwide in order to solve some of the problems of current cells based on Nafion® (CO tolerance, improved kinetics, water management, etc.). Polybenzimidazole membranes nanoimpregnated with phosphoric acid have been studied as electrolytes in PEMFCs for more than a decade. Commercially available polybenzimidazole (PBI) has been the most extensively studied and used for this application in membranes doped with all sorts of strong inorganic acids. In addition to this well-known polymer we also review here studies on ABPBI and other polybenzimidazole type membranes. More recently, several copolymers and related derivatives have attracted many researchers' attention, adding variety to the field. Furthermore, besides phosphoric acid, many other strong inorganic acids, as well as alkaline electrolytes have been used to impregnate benzimidazole membranes and are analyzed here. Finally, we also review different hybrid materials based on polybenzimidazoles and several inorganic proton conductors such as heteropoly acids, as well as sulfonated derivatives of the polymers, all of which contribute to a quickly-developing field with many blooming results and useful potential which are the subject of this critical review (317 references).

Proton-conducting membranes based on benzimidazole polymers for high-temperature PEM fuel cells. A chemical quest

Polybenzoxazoles of high molecular weight were prepared easily by the solution polycondensation of 3,3′-dihydroxybenzidine dihydrochloride or 3,3′-diamino-4,4′-dihydroxybiphenyl dihydrochloride with both aromatic and aliphatic dicarboxylic acids in polyphosphoric acid. Polybenzothiazoles were prepared from 3,3′-dimercaptobenzidine dihydrochloride and dicarboxylic acids by the same procedure.



Aromatic polybenzoxazoles and polybenzothiazoles showed an excellent thermal stability up to 450°C. in air. They were insoluble in organic solvents.



Polybenzoxazole hohen Molekulargewichtes konnen leicht hergestellt werden durch Polykondensation von 3,3′-Dihydroxybenzidin-dihydrochlorid oder 3,3′-Diamino-4,4′-dihydroxybiphenyl-dihydrochlorid mit aromatischen und aliphatischen Dicarbonsauren in Polyphosphorsaure. Polybenzothiazole lassen sich nach der gleichen Methode aus 3,3′-Dimercaptobenzidin-dihydrochlorid und Dicarbonsauren herstellen.



Aromatische Polybenzoxazole und Polybenzothiazole zeigen eine ausgezeichnete thermische Stabilitat bis 450°C in Luft. Die Polymeren sind unloslich in organischen Losungsmitteln.

Polybenzoxazoles and polybenzothiazoles

Far-infrared spectra of poly-L-alanines having the α-helical conformation and the β-form structure were measured. The spectra of glycine–L-alanine copolymer, silk fibroin, and copoly-D,L-alanines with different D:L compositions were also measured. In addition to the bands so far reported, four bands at 190, 107, 120, and 90 cm−1were found for the α-helix conformation and the two bands at 442 and 247 cm−1 were found for the β form. The 442 cm−1 band consists of the parallel 432 cm−1 and perpendicular 445 cm−1 bands. The 247 cm−1 band is well defined and has strong dichroism parallel to the direction of stretching. These two bands appear also for silk fibroin and glycine–L-alanine copolymer. All the far-infrared bands of copoly-D,L-alanines can be interpreted as α-helix bands, the three peaks at 580, 478, and 420 cm−1 being ascribed to the D-residue incorporated into the right-handed α-helix or to the L-residue in the left-handed α-helix.

Far-infrared spectra of polyalanines with α-helical and β-form structures

The copolymerization of methyl methacrylate with glycidyl methacrylate and the kinetic of the reaction of copolymer with secondary amines were investigated. Three model compounds of the copolymer were prepared in order to compare their reactivity with that of copolymer. It was found that these compounds have an isokinetic relationship and the isokinetic temperature was 331°K.



Die Copolymerisation von Methacrylsauremethylester mit dem Glycidester derselben Saure und die Kinetik der Reaktion des Copolymeren mit sekundaren Aminen wurden untersucht. Die Reaktionsfahigkeit dreier Modellsubstanzen und des Copolymeren wurden verglichen. Die Modellverbindungen zeigten eine isokinetische Beziehung; die isokinetische Temperatur betrug 331°K.

Copolymerization of methyl methacrylate with glycidyl methacrylate and the reaction of the copolymer with amines

High molecular weight aromatic polyketones were prepared from p- and m-phenoxybenzoic acid in polyphosphoric acid by heating the reaction mixture at 100°C. High molecular weight aromatic polyamide was derived from the polyketone obtained through Schmidt reaction or Beckmann rearrangement. The polyamide obtained by Schmidt reaction was found to have some regularity in an arrangement of its repeating units. The thermal stability of the polyketone and the polyamide were good.

Syntheses of aromatic polyketones and aromatic polyamide

2-Sulfoterephthalic acid (STA) and disulfoisophthalic acid (DSIA) were synthesized through the sulfonation and the oxidation of m- and p-xylene. The polycondensation reactions of STA and DSIA with aromatic tetraamines gave polybenzimidazoles which contained one or two sulfonic acid groups for each repeating unit. The polymer obtained was soluble in sulfuric acid, some organic solvents, and aqueous strong alkaline solution. The polymers were stable up to 400°C, but they gave polybenzimidazoles above 400°C by eliminating sulfonic acid groups, instead of ring closure.

Yoshio Iwakura

Papers

Polybenzoxazoles and polybenzothiazoles

Far-infrared spectra of polyalanines with α-helical and β-form structures

Copolymerization of methyl methacrylate with glycidyl methacrylate and the reaction of the copolymer with amines

Syntheses of aromatic polyketones and aromatic polyamide

Synthesis of polybenzimidazoles with sulfonic acid groups