Evidence from Infra-Red Spectroscopy on the Structure of Proteins

Ultra-stable fully-aromatic microporous polyamide membrane for molecular sieving of nitrogen over volatile organic compound

Microporous polymer membranes are promising candidates for industrial membrane-based gas separation because of their high separation performance. However, their relatively low stability due to the local rearrangement of polymer chains during usage remains a problem. Hence, we propose the construction of a fully aromatic polymer structure in a microporous polymer membrane to enhance membrane stability. Four triptycene-based microporous polyamides were synthesized via the polymerization of 2,6,14-triaminotriptycene with aromatic acyl chloride and/or aliphatic acyl chlorides. Their properties were characterized and compared by using nuclear magnetic resonance (NMR) and Brunauer-Emmett-Teller analyses. The synthesized polyamides were fabricated into composite membranes by employing a solution process; their stability was evaluated for the molecular sieving of nitrogen over volatile organic compounds such as cyclohexane. Low-field NMR and X-ray photoelectron spectroscopy were used to investigate the differences in the properties of membranes with different structures at different times. The results showed that the fully aromatic polyamide membrane made from 2,6,14-triaminotriptycene and aromatic acyl chloride displayed constant rejection (99 %) and nitrogen permeability (approximately 50 Barrer) for the molecular sieving of nitrogen over cyclohexane during 100-d experiments, indicating good stability. This approach paves the way for the industrialization of microporous polymer membranes from a theoretical perspective.

Sum frequency generation spectroscopy of the attachment disc of a spider

The pyriform silk of the attachment disc of a spider was studied using infrared-visible vibrational sum frequency generation (SFG) spectroscopy. The spider can attach dragline and radial lines to many kinds of substrates in nature (concrete, alloy, metal, glass, plant branches, leaves, etc.) with the attachment disc. The adhesion can bear the spider's own weight, and resist the wind on its orb web. From our SFG spectroscopy study, the NH group of arginine side chain and/or NH₂ group of arginine and glutamine side chain in the amino acid sequence of the attachment silk proteins are suggested to be oriented in the disc. It was inferred from the observed doublet SFG peaks at around 3300 cm^-1 that the oriented peptide contains two kinds of structures.

Spectroscopic investigations and structural confirmation studies on thiourea

The Fourier transform infrared and Raman spectra of thiourea have been studied in the region 4000-400 and 4000-10 cm(-1), respectively. A complete vibrational analysis on the molecular structure of thiourea has been made on the basis of C(2upsilon) point group symmetry. The validity of the vibrational assignments on the structure of thiourea is supported by evaluating the molecular constants and the potential energy distribution.

In situ polymerization of molecular macroclusters on a silica surface: poly(N-isopropylacrylamide) nanofilms

We have found that alcohols, carboxylic acids, and amides self-assemble into a unique molecular architecture, a hydrogen-bonded molecular macrocluster, when they are selectively adsorbed onto silica (glass and oxidized silicon) surfaces in nonpolar solvents such as cyclohexane. In our previous study, this phenomenon could be successfully applied to fabricate molecularly flat and defect-free nanofilms of several tens of nanometers thickness. In this study, we prepared a poly(N-isopropylacrylamide) [poly(NIPAAm)] film on the basis of in situ polymerization of a monomer macrocluster layer formed on silica surfaces and investigated how the molecular arrangement of the adsorbed NIPAAm monomers affects the efficiency of the polymerization of them. Poly(NIPAAm) films were prepared by the following two methods: (1) the one-solution method, the in situ photopolymerization of an NIPAAm monomer adsorption layer on silica in one solution (chloroform, cyclohexane, and toluene), and (2) the solution exchange method, adsorption of NIPAAm monomers onto a silica surface from NIPAAm (0.1 mol %) in chloroform, exhange of the solution to 0.005 mol % NIPAAm in cyclohexane, and then polymerization by UV irradiation. By the solution exchange method, molecularly flat, defect-free, and thermoresponsive films were obtained and the thickness could be controlled by the irradiation time, while only several nanometers thickness could be attained by the one-solution method. The structure of NIPAAm adsorption layers formed in each solution condition was characterized by attenuated total reflection Fourier transform infrared spectroscopy. It was revealed that only the solution exchange procedure induced the beta-sheet-like adsorbed structure of NIPAAm in which the double bonds of neighboring NIPAAm monomers were closely located, which should have resulted in effective polymerization.

The structure of synthetic polypeptides. II. Investigation with polarized infra-red spectroscopy

Methods of producing oriented films of synthetic polypeptides when prepared from various solvents are described. The polarized infra-red spectra of a number of these films have been measured. It is shown, in agreement with earlier work, that the polypeptides can exist in a folded ( α ) and an extended ( β ) configuration. In the α form the N—H and C═O stretching modes of the polypeptide chain show parallel dichroism while the N—H deformation mode shows perpendicular dichroism. In the β form these conditions are reversed. The α form has characteristic frequencies of about 1660 and 1560 cm. -1 , while the β form has characteristic frequencies of about 1640 and 1530 cm. -1 . When highly dispersed in an inert polymer or liquid solvent it is shown that all the hydrogen bonds of the polypeptide chain can be internally satisfied. It is concluded that in the folded state the chain is maintained in the form of seven-membered rings by intra -molecular hydrogen bonds.

Polymorphism of cephaloridine

Infrared spectra of Nujol mulls and X-ray powder photographs have shown that cephaloridine can exist in at least six different crystalline forms. The preparation, interconversion and properties of these forms are discussed. Proton magnetic resonance spectroscopy has been used to check their chemical identity.