Temperature-dependent Fourier Transform Infrared Spectroscopy Research Articles

Thermal performance and phase transformation of S-alkylated poly(vinyl chloride) comb-like polymers

A series of S-alkylated poly(vinyl chloride) (PVCS(n)) comb-like polymers, where the S atom acted as the chemical junction between PVC backbone and alkyl side chain, were prepared through the nucleophilic substitution reaction between PVC and n-alkyl mercaptan. Structure and properties of PVCS(n) are analyzed by 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis and X-ray scattering. An ordered crystal structure for PVCS(n) comb-like polymers appears with the increased side-chain length, which is originated from the regular packed side-chain crystallites. The increased carbon atoms per side chain from n = 12 to 18 also brings an improved thermal property. Obviously regular packed orthorhombic (βO) phase easily appears at room temperature, indicating the flexible PE backbone can allow much more CH2 groups entering an ordered phase structure. Phase transformation from βO to hexagonal phase is demonstrated by the temperature-dependent FTIR and WAXS. The chain packing manner for the pended side alkyl chains onto PVC backbone shows a dependence upon side-chain length, and the chemical junction also presents a certain influence on the phase transformation of side-chain crystallites. The variations for the phase behavior, chain packing and thermal property of PVCS(n) are detailed analyzed and characterized from the aspect of side-chain crystallization.

Phase transition analysis of V-shaped liquid crystal: Combined temperature-dependent FTIR and density functional theory approach

Temperature-dependent Fourier transform infrared spectroscopy (FTIR) combined with density functional theory (DFT) is employed to study the mechanism of phase transitions of V-shaped bent-core liquid crystal. Since it has a large number of flexible bonds, one-dimensional potential energy scan (PES) was performed on the flexible bonds and predicted the most stable conformer I. A detailed analysis of vibrational normal modes of conformer I have been done on the basis of potential energy distribution. The good agreement between the calculated spectrum of conformer I and observed FTIR spectrum at room temperature validates our theoretical structure model. Furthermore, the prominent changes observed in the stretching vibrational bands of CH3/CH2, CO, ring CC, ring CO, ring CH in-plane bending, and ring CH out-of-plane bending at Iso→nematic phase transition (at 155°C) have been illustrated. However, the minor changes in the spectral features observed for the other phase transitions might be due to the shape or bulkiness of molecules. Combined FTIR and PES study beautifully explained the dynamics of the molecules, molecular realignment, H-bonding, and conformational changes at the phase transitions.

Mid-Infrared Intersubband Absorption from p-Ge Quantum Wells Grown on Si Substrates

There are many applications in the mid-infrared part of the electromagnetic spectrum which include thermal imaging [1] and the unique identification of molecules through absorption spectroscopy [2]. For all these applications, sources of mid-infrared light and photodetectors are key to enable any application. III-V and II-VI semiconductor materials have dominated over the last decades with both interband and intersubband emission and/or absorption devices [1-3] but there is now significant interest in developing technology on silicon substrates to enable far cheaper systems for mass market applications in environmental sensing, personalised healthcare and security. SiGe quantum well (QW) intersubband photodetectors (QWIPs) have previously been demonstrated [4] but the number of QWs was limited by the SiGe critical thickness thereby limiting performance. Now Ge QWs have the potential to improve this performance significantly in the mid-infrared and the number of QWs can be increased using strain symmetrisation of the QWs and barriers to allow improved absorption in the longer wavelength mid-infrared. Here we demonstrate strain symmetrized growth of 500 periods of Ge QWs with Si0.5Ge0.5 barriers on Si0.2Ge0.8 virtual substrates grown on top of (001) Si. The samples were grown by low energy plasma enhanced chemical vapour deposition. Transmission electron microscopy, Raman spectroscopy and x-ray diffraction were used to characterize the heterolayer thicknesses, Ge contents, strain and defects. The layers demonstrate excellent quality with low defect densities. Three samples with QW thicknesses (barrier thicknesses) of 5.4 ± 0.4 nm (3.5 ± 0.4 nm), 8.1 ± 0.5 nm (5.2 ± 0.6 nm) and 9.2 ± 0.6 nm (6.1 ± 0.6 nm) have been fully characterized by Fourier transform infrared spectroscopy (FTIR) to understand the potential for mid-infrared QWIPs. An 8-band k.p modelling tool has been used to understand the results. For the lowest QW width, only z-polarised absorption is observed at ~ 7 µm wavelength from the light hole 1 (LH1) to LH2 transition. Despite surface-normal illumination, the z-polarized transition is observed since the heterolayers and substrate will scatter some of the light into the z-polarized mode. For the thicker QWs, only xy-polarized (surface normal) absorption is measured with absorption peaks centred at 7.5 µm and 7.8 µm corresponding to the heavy hole 1 (HH1) to LH2 transition. Temperature dependent FTIR measurements demonstrate virtually no shift in the wavelength of absorption with temperature as is typical for intersubband transitions. Photoluminescence (PL) demonstrates a completely different behavior to the absorption due to the population of states being different through the heating of the samples by the 532 nm PL laser. We will demonstrate how to design QWIPs using a HH1 to LH bound-to-continuum transitions that will enable surface-normal QWIPs to be designed with large pixel numbers and produced cheaply on a silicon substrate using any silicon foundry with SiGe growth capability. The research leading to these results has received funding from the European Unions Seventh Framework Programme under grant agreement no. 613055 and U.K. EPSRC (Project no. EP/N003225/1). [1] A. Rogalski, J. Appl. Phys. 93, 4355 (2003) [2] L. Baldassarre, E. Sakat, J. Frigerio, A. Samarelli, K. Gallacher, E. Calandrini, G. Isella, D. J. Paul, M. Ortolani, and P. Biagioni, Nano Lett. 15, 7225 (2015) [3] A. Rogalski, Infrared Phys. Technol. 38, 295 (1997). [4] R. P. G. Karunasiri, J. S. Park, Y. J. Mii, and K. L. Wang, Appl. Phys. Lett. 57, 2585 (1990) Figure 1

Spectroscopic examinations of hydrogen bonding in hydroxy-functionalized ADMET chemistry.

Wide-angle X-ray scattering (WAXS) and temperature-dependent Fourier transform infrared spectroscopy (FTIR) spectroscopy are used to study hydrogen bonding interactions of a hydroxyl-functionalized polyethylene (PE) prepared by acyclic diene metathesis (ADMET) chemistry. The hydroxyl polymer exhibits an orthorhombic unit cell structure with characteristic reflection planes at (110) and (200), comparable to pure crystalline PE. These data unequivocally demonstrate that the OH branch is excluded from the PE lamellae. Furthermore, the polymer melts 100 °C higher than all previous analogous polymers possessing precision placed long aliphatic branches that also are excluded from PE lamellae. Temperature-dependent FTIR spectroscopy from ambient to 150 °C, followed by cooling to 125 °C supports exclusion of the hydroxyl group from the crystalline lattice. It is concluded that these hydroxyl groups form stable physical networks in the amorphous region via hydrogen bonding and are important for the overall morphology of such polymers.

Synthesis, crystal structure and temperature-dependent behavior of gallogermanate tetrahydroborate sodalite |Na8(BH4)2|[GaGeO4

Tetrahydroborate enclathrated gallogermanate sodalite was successfully synthesized under mild hydrothermal conditions and characterized by X-ray powder diffraction and Fourier transform infrared (FTIR) spectroscopy. The crystal structure was refined in space group P4¯3n using the Rietveld method: a=912.581(1)pm, V=760.0(1)·10−6pm3, RB=0.019. Within the sodalite cage formed by corner-sharing oxygen coordinated gallium and germanium tetrahedra, the hydrogen atoms of the enclathrated BH4− anions were refined on 8e (x, x, x) crystallographic position. The boron–hydrogen distances were restrained to 124.7pm as calculated from the respective bond valence sums. High temperature behavior was investigated using temperature-dependent X-ray diffraction, FTIR and Raman spectroscopy and TG-DTA methods. A two-step sodalite decomposition reaction to the beryllonite analogous phase NaGaGeO4 was observed. The temperature-dependent development of the sodalite structural parameters evaluated by Rietveld analysis of the XRD data indicate a beginning transformation of the enclathrated NaBH4 at about 528K followed by a decomposition of the sodalite framework starting at about 648K. These findings are confirmed by the results obtained from temperature-dependent Raman and FTIR data evaluation.

Temperature-Dependent Fourier Transform Infrared Spectroscopy and Raman Mapping Spectroscopy of Phase-Separation in a Poly(3-hydroxybutyrate)–Poly(l-Lactic Acid) Blend

Variable-temperature Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic mapping measurements were applied to study the phase separation of a poly(3-hydroxybutyrate) (PHB)-poly(L-lactic acid) (PLA) (50 : 50 wt.%) polymer-blend film as a function of temperature between 25 and 175 °C. Because of the better band separation compared with the fundamental absorptions, the first overtones of the ν(C=O) bands of PHB and PLA were used to evaluate the temperature-dependent FT-IR images as PLA-PHB and PHB-PLA band-ratio contour plots, respectively. From the visualization of the band-ratio FT-IR images, it could be derived that even beyond the melting point of PLA (145 °C), the lateral position and the geometry of the PHB-rich and PLA-rich phases were retained up to 165 °C. Furthermore, the FT-IR images derived during and after the melting of PHB (174 °C) provided an interesting insight into the homogenization process of the polymer melt. By exploiting its higher lateral resolution, valuable additional information became available from the Raman mapping measurements. Based on the Raman data, the scenario of phase-separated PHB-rich and PLA-rich domains of about 50 μm size, based on the FT-IR imaging measurements, had to be revised. Instead, the originally interpreted PHB-rich and PLA-rich domains are actually clusters of much smaller grains. Additionally, the Raman images measured in the same temperature interval revealed that the clusters of small PHB-rich grain structures aggregated as a function of temperature increase. These investigations prove that FT-IR and Raman imaging in combination with variable-temperature measurements can provide new (and so far unavailable) insights into structural phenomena of phase-separated polymer blends.

Solid State Self-Assembly Mechanism of RADA16-I Designer Peptide

We report that synthetic RADA16-I peptide transforms to β-strand secondary structure and develops intermolecular organization into β-sheets when stored in the solid state at room temperature. Secondary structural changes were probed using solid state nuclear magnetic resonance spectroscopy (ssNMR) and Fourier transform infrared spectroscopy (FTIR). Intermolecular organization was analyzed via wide-angle X-ray diffraction (WAXD). Observed changes in molecular structure and organization occurred on the time scale of weeks during sample storage at room temperature. We observed structural changes on faster time scales by heating samples above room temperature or by addition of water. Analysis of hydration effects indicates that water can enhance the ability of the peptide to convert to β-strand secondary structure and assemble into β-sheets. However, temperature dependent FTIR and time dependent WAXD data indicate that bound water may hinder the assembly of β-strands into β-sheets. We suggest that secondary structural transformation and intermolecular organization together produce a water-insoluble state. These results reveal insights into the role of water in self-assembly of polypeptides with hydrophilic side chains, and have implications on future optimization of RADA16-I nanofiber production.

Tuning methyl 4,6-O-benzylidene α-d-glucopyranosides’ gelation ability by minor group modifications

Ten methyl 4,6-O-benzylidene α-d-glucopyranosides were synthesized for the purpose of studying systematically the effect of small group changes at position 4 of the aromatic ring on the ability to gelate organic solvents. The gelation properties are discussed on the basis of small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) measurements, and scanning electron microscopy (SEM) observations. Sol–gel transition temperatures were determined simultaneously by DSC and temperature-dependent FTIR measurements. The current study emphasizes that carbohydrates furnish not only valuable information about structural requirements for organogelator design, but also for molecular assembly systems in general.

Site-Specific Unfolding Thermodynamics of a Helix-Turn-Helix Protein

The thermal unfolding of a 40-residue helix-turn-helix subdomain of the P22 viral coat protein was investigated using circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) with site-specific 13C isotopic labeling. Helix-turn-helix is the simplest alpha-helical structural motif that combines both secondary and tertiary structural elements. The CD of individual helical fragments reveals that the P22 subdomain is stabilized by tertiary interhelical interactions. Overall the temperature-dependent CD and FTIR data can be described by a three-state process with a partially folded intermediate. However, the analysis of the site-specific 13C IR signals reveals distinct unfolding thermodynamics for each of the labeled sites. The thermodynamic parameters of the thermal unfolding of each of the labeled segments were obtained using singular value decomposition in combination with target transformation and global fitting. The P22 subdomain unfolds from the N-terminus toward the helical segments near the turn. Our results show that as few as two 13C labeled residues can be detected in a 40 residue protein and provide local, site-specific structural information about protein unfolding, which is not resolved by standard, nonsite-specific spectroscopic probes.

Concentration-Dependent Conformation of Alkyl Tail in the Nanoconfined Space: Hexadecylamine in the Silicate Galleries

The conformation and melting of both hexadecylammonium ion, n-CH3(CH2)15NH3+, and neutral hexadecylamine, n-CH3(CH2)15NH2, within the clay silicate galleries have been studied by Fourier transform infrared spectroscopy (FTIR). The conformational ordering of the alkyl tail in the confined system shows strong dependence on amine concentration and orientation. While the amine chains with orientation parallel to the silicate layers are in various disordered states, those with orientation radiating from the clay surface take mostly ordered conformation. Ammonium ion shows a similar trend of ordering dependence on the concentration as neutral amine, although the former has lower ordering than the latter, under the same concentration level. Temperature-dependent FTIR study shows that the melting behavior of confined amine corresponds to the chain melting process.

The Role of the Native Lipids and Lattice Structure in Bacteriorhodopsin Protein Conformation and Stability as Studied by Temperature-dependent Fourier Transform-Infrared Spectroscopy

We report the effect of partial delipidation and monomerization on the protein conformational changes of bacteriorhodopsin (bR) as a function of temperature. Removal of up to 75% of the lipids is known to have the lattice structure of the purple membrane, albeit as a smaller unit cell, whereas treatment by Triton monomerizes bR into micelles. The effects of these modifications on the protein secondary structure is analyzed by monitoring the protein amide I and amide II bands in the Fourier transform-infrared (FT-IR) spectra. It is found that removal of the first 75% of the lipids has only a slight effect on the secondary structure at physiological temperature, whereas monomerizing bR into micelles alters the secondary structure considerably. Upon heating, the bR monomer is found to have a very low thermal stability compared with the native bR with its melting point reduced from 97 to 65 degrees C, and the pre-melting transition in which the protein changes conformation in native bR at 80 degrees C could not be observed. Also, the N[bond]H to N[bond]D exchange of the amide II band is effectively complete at room temperature, suggesting that there are no hydrophobic regions that are protected from the aqueous medium, possibly explaining the low thermal stability of the monomer. On the other hand, 75% delipidated bR has its melting temperature close to that of the native bR and does have a pre-melting transition, although the pre-melting transition occurs at significantly higher temperature than that of the native bR (91 degrees C compared with 80 degrees C) and is still reversible. Furthermore, we have also observed that the reversibility of this pre-melting transition of both native and partially delipidated bR is time-dependent and becomes irreversible upon holding at 91 degrees C between 10 and 30 min. These results are discussed in terms of the lipid and lattice contribution to the protein thermal stability of native bR.

Medical Headlines

Ten methyl 4,6-O-benzylidene α-d-glucopyranosides were synthesized for the purpose of studying systematically the effect of small group changes at position 4 of the aromatic ring on the ability to gelate organic solvents. The gelation properties are discussed on the basis of small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) measurements, and scanning electron microscopy (SEM) observations. Sol–gel transition temperatures were determined simultaneously by DSC and temperature-dependent FTIR measurements. The current study emphasizes that carbohydrates furnish not only valuable information about structural requirements for organogelator design, but also for molecular assembly systems in general.