Fourier transform-infrared spectroscopy, hydrogen bonds

Poly(vinyl acetate). The dielectric and mechanical spectra of hybrids produced by mixing a poly (vinyl acetate)—THF solution with TEOS, followed by the addition of HC1 have been investigated (45). Mixtures were made which were believed to be 0, 5, 10,15, and 20 wt °/o Si02, respectively. These composites were transparent and Fourier transform infrared spectroscopy (ftir) revealed hydrogen bonding between the silicate network and carbonyl units of the poly(vinyl acetate) (PVAc). No shift in the T of the composites from that of the pure PVAc was observed. Similady, the activation... 

Noguchi, T., Inoue, Y., and Tang, X-S. (1999) Hydrogen bonding interaction between primary quinone acceptor Qa and a histidine side chain in Photosystem II as revealed by Fourier transform infrared spectroscopy, Biochemistry 38, 399403. 

Using diffuse reflectance Fourier transform infrared spectroscopy, Adhikari et al. studied the binding of oleic acid (88), triacylglycerol (89), and phosphatidylcholine (90) on silica gel at room temperature. Their interpretation was that oleic acid and triacylglycerols bind to silica surface hydroxyls via hydrogen bonding interactions between the carboxylate and ester carbonyls of these molecules, respectively. In contrast, phospholipids hydrogen bond to silica surface hydroxyls via the phosphate... 

Oximes and oxime ethers exist as a mixture of E and Z isomers with a relatively low difference of AG° and a moderate energy barrier to isomerization (<10 kcal mol-1) [28]. They show some similarities with imines and may interconvert at room temperature, spontaneously, by an acid- or base-catalyzed isomerization involving a nitronium ion, and photochemically [29,30]. Oxime ethers have been employed as amide surrogates in peptides where they display a marked Z-E isomerism which is mainly controlled by the formation of H-bonds, which stabilize a given isomer. As an example, the structure of pseudopeptide 6 was investigated by Fourier transform infrared spectroscopy (FTIR) and NMR spectroscopy which both showed that Z-6 is folded in a /Mike conformation by a strong bifurcate hydrogen bond whereas the E isomer adopts an extended conformation (Fig. 13.5) [31]. 

Lin et al. [36] used Fourier transform infrared spectroscopy (FTIR) and dialysis in conjunction with conductivity measurements to study the influence of the LiCl stabilizer on the morphology of FBI in DMAc solutions ([FBI] = 2.0 mg mL- and [LiCl]/[Bl] = 3.63-14.51 M ratio or [LiCl]/[FBl] = 0.5-2.0 by weight ratio). It was demonstrated that interpolymer hydrogen bonding was developed via the -N-H- N=C- interaction for FBI in DMAc solutions (Fig. 12.10). On the basis of the dialysis measurements, it was shown that the -N-H N=C- hydrogen bonds were disrupted... 

Reference 25. The experimental value corresponds to the fraction of hydrogen bonds in the semicrystalline phase of PA-66 calculated by Fourier-transform infrared spectroscopy. 

Differential scanning calorimetry and Fourier transform infrared spectroscopy techniques were used to study the structure of water molecules in polyvinyl alcohol and polyethylene grafted acrylate hydrophilic polymers. Varying amounts of water were added to test samples and the samples conditioned to the sorption equilibrium state in sealed containers for 24 hours prior to evaluation. It was concluded that below a threshold water content, depending on the polymers physical and chemical stmcture, water molecules absorbed in hydrophilic polymer cannot form ice crystals in the polymer matrix. Above this threshold content, the water crystallises but below zero. It was also demonstrated that the absorbed water in hydrophilic polymers develops differing hydrogen bonds in the first and second hydration layers. It was concluded that the potential influence of these intermolecular interactions should therefore be taken into account whenever a polymer is used with a solvent. 25 refs. 

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