Temperature-induced Spectral Changes Research Articles

2D Correlation Spectroscopy (2DCoS) Analysis of Temperature-Dependent FTIR-ATR Spectra in Branched Polyethyleneimine/TEMPO-Oxidized Cellulose Nano-Fiber Xerogels.

Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR), combined with a 2D correlation analysis, was here employed to investigate temperature-induced spectral changes occurring in a particular type of novel cellulosic-based nano-material prepared using 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) oxidized and ultra-sonicated cellulose nano-fibers (TOUS-CNFs) as three-dimensional scaffolds, and branched polyethyleneimine (bPEI) as cross-linking agent. The aim was to highlight the complex sequential events involving the different functional groups of the polymeric network, as well as to gain insight into the interplay between the amount of bPEI and the resulting sponge-like material, upon increasing temperature. In this framework, synchronous and asynchronous 2D spectra were computed and analyzed in three wavenumber regions (900–1200 cm−1, 1500–1700 cm−1 and 2680–3780 cm−1), where specific vibrational modes of the cellulosic structure fall, and over a T-range between 250 K and 340 K. A step-by-step evolution of the different arrangements of the polymer functional groups was proposed, with particular regard to how the cooperativity degree of inter- and intramolecular hydrogen bonds (HBs) changes upon heating. Information acquired can be useful, in principle, in order to develop a next-generation, T-sensitive novel material to be used for water remediation applications or for drug-delivery nano-vectors.

Reversible temperature-responsible emission in solutions within 293–333 K produced by dissociative behavior of multinuclear Cu(I) complexes with aminomethylphosphines

A series of multinuclear Cu(I) complexes (CuI)xLy, namely the previously reported (CuI)6L2 and (CuI)2L′ and novel (CuI)2L2, where L and L′ are 1,5-di(R)-3,7-bis(2-pyridine-2′-yl)ethyl-1,5-diaza-3,7-diphosphacyclooctanes are introduced. Both dissociative and oxidative behavior of the complexes in DMSO and DMF solutions are correlated with the time-dependent changes in their phosphorescence originated from 3(X + M)LCT transitions. The instability of butterfly-like (CuI)2L′ resulting in its oxidative degradation in DMSO and transformation into (CuI)L′2 in DMF solutions differentiates it from more stable linear complexes (CuI)6L2 and (CuI)2L2. The complexes (CuI)2L2 and (CuI)L2 produced by the dissociation of (CuI)6L2.in DMSO and DMF solutions are regarded as structural motifs responsible for both reversible blue-shifting by 10 nm of the emission band and the decrease in the excited states lifetime values upon the heating of the solutions within 293–333 K. This temperature-induced behavior along with the phosphorescence character of the emission of both complexes points to thermally activated delayed fluorescence as the reason for the reversible temperature-induced spectral changes of hexanuclear (CuI)6L2. Smaller nuclearity of (CuI)2L2 is the reason for partial reversibility of the spectral changes.

2D correlation analysis of the magnetic excitations in Raman spectra of HoMnO3

2D correlation analysis is performed on the temperature-dependent Raman spectra of HoMnO3 thin films. As the temperature of the HoMnO3 thin films decrease, the depletion of the spectral weight at 336, 656, and 1304cm−1 occurs at higher temperatures than the increase of the intensity at 508, 766, and 945cm−1 below ∼70K, the Néel temperature. The power spectrum asserts that all the changes in the spectral weight are strongly correlated. Most of the temperature-induced spectral changes of HoMnO3 occur at lower temperature than 70K, while there is slight depletion of the spectral weight at 336, 656, and 1304cm−1 even at higher temperature than 70K. PCA scores and loading vectors plots also support these 2D correlation results. Our 2D correlation analysis supports the existence of the short range spin correlations between Mn sites in HoMnO3 even above the Néel temperature.

Matrix isolation spectroscopy and molecular dynamics simulations for 2,7,12,17-tetra-tert-butylporphycene in argon and xenon

Electronic absorption spectra of 2,7,12,17-tetra-tert-butylporphycene (TTPC) have been recorded in low-temperature argon and xenon matrices for various deposition conditions. In the region of the S(0)-S(1) electronic transition, the spectra of TTPC in argon reveal a rich site structure, characterized by a series of more than 30 absorption peaks. Studies of the temperature dependence of the electronic spectra in solid argon demonstrated remarkable spectral changes, resulting in the broadening of all bands with increasing temperature. These temperature-induced spectral changes are, to a large degree, reversible, so lowering of temperature is accompanied by the recovery of the original fine-line spectrum. The absorption spectra in xenon reveal broad bands, on which a rich pattern of lines becomes superimposed at low temperatures. Trapping site distribution and the structure of the microenvironment around the TTPC chromophore, embedded in argon and xenon hosts, have been analyzed using molecular dynamics (MD) simulations. The MD results show that the trapping of TTPC in rare-gas solids is influenced by favorable embedding of the bulky tert-butyl groups inside the matrix cage. The crucial role of the tert-butyl groups for the thermodynamics and kinetics of matrix deposition is demonstrated by comparing the results with those obtained for the parent, unsubstituted porphycene.

Noncentrosymmetric phase of submicron NaNbO3 crystallites

The temperature and pressure characteristics of a noncentrosymmetric crystal modification of NaNbO3 were studied by Raman spectroscopy. A transition towards the bulk-like structure of NaNbO3 occurs in the temperature range from 280 to 360 °C. High-pressure Raman spectroscopy revealed successive pressure-induced phase transitions at around 2, 6.5 and 10 GPa. Raman scattering profiles recorded above 7 GPa correspond to those reported for the bulk. The temperature-induced spectral changes were completely reversible between −150 and 450 °C. Those induced by pressure were almost reversible from ambient pressure up to 15.9 GPa. Piezoresponse force microscopy demonstrated the occurrence of piezoelectric activity for submicron NaNbO3 crystals with particle size ranging from 200 to 400 nm. The noncentrosymmetric crystallographic structure plays a critical role for the enhancement of piezoelectricity.

In situ observation of pressure-induced increased thermostability of two β-galactosidases with FT-IR spectroscopy in the diamond anvil cell

We have previously reported that high hydrostatic pressure protected two β-galactosidases against thermal inactivation. Here, the Fourier transform infrared spectroscopy (FT-IR) technique was used to examine the pressure- and temperature-induced changes occurring in the structure of these two proteins. A thermostated diamond anvil cell allowed to follow in situ conformational changes against the variation of both temperature and pressure. FT-IR measurements have been carried out on proteins in D 2O-based solutions. Using D 2O, the amide I′ band (N-deuterated) can be measured without solvent interference. Analysis of the reduction in amide II intensities, which is due to peptide H–D exchange upon heating of the Aspergillus oryzae β-galactosidases in D 2O, showed that the temperatures for which H–D exchange acceleration occurred were 55, 65 and 60 °C at atmospheric pressure (0.1 MPa), 285 and 430 MPa, respectively. With the Escherichia coli β-galactosidase, these temperatures were 49, 52 and 51 °C at 0.1, 230 and 410 MPa, respectively. Interestingly, for the two enzymes considered, these values correlate quite well with the temperatures for which an irreversible activity loss of 50% is observed following a 30 min incubation. The pressure- and temperature-induced spectral changes in the amide I/I′ vibrational band of these two proteins are also discussed.

Temperature and guanidine induced unfolding of dodecameric glutamine synthetase from E. coli

Abstract

Lincomycin-induced alteration in the contents of chlorophyll-protein complexes of dimorphic maize chloroplasts and its effect on the temperature-induced spectral changes

Lincomycin-induced alteration in the contents of chlorophyll-protein complexes of dimorphic maize chloroplasts and its effect on the temperature-induced spectral changes

Temperature jump relaxation kinetics of the P-450cam spin equilibrium.

The ferric spin-state equilibrium and relaxation rate of cytochrome P-450 has been examined with temperature jump spectroscopy using a number of camphor analogues known to induce different mixed spin states in the substrate-bound complexes [Gould, P., Gelb, M., & Sligar, S. G. (1981) J. Biol. Chem. 256, 6686]. All temperature-induced spectral changes were monophasic, and the spin-state relaxation rate reached a limiting value at high substrate concentrations. The ferric spin equilibrium constant, Kspin, is defined in terms of the rate constants k1 and k-1 via Kspin = k1/k-1 = [P-450(HS)]/[P-450(LS)] where HS and LS represent high-spin (S = 5/2) and low-spin (S = 1/2) ferric iron, respectively, and the spectrally observed spin-state relaxation rate by kobsd = k1 + k-1. A strong correlation between the fraction of high-spin species and the rate constant, k-1, is observed. For a 3 degrees C temperature jump (from 10 to 13 degrees C), the 23% high-spin tetramethylcyclohexanone complex (Kd = 45 +/- 20 microM) is characterized by a ferric spin relaxation rate of kobsd = 1990 s-1, while the rates for the d-fenchone (41% high spin, Kd = 42 +/- 10 microM) and kobsd = 1990 s-1, while the rates for the d-fenchone (41% high spin, Kd = 42 +/- 10 microM) and camphoroquinone (75% high spin, Kd = 15 +/- 5 microM) complexes are 1430 and 346 s-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature-induced ultraviolet absorption changes of heavy meromyosin: An application of a computerized spectrophotometer system

The UV absorption of HMM (heavy meromyosin) was measured at various temperatures with a computerized spectrophotometer system. HMM showed temperature-induced absorption changes in the presence and absence of nucleotides. The temperature-induced absorption change at 293 nm, which is due to conformational changes around the tryptophan residues of HMM, was enhanced in the presence of nucleotides. The temperature-induced difference spectra of HMM + AMPPNP relative to HMM obtained by using a conventional spectrophotometer [(1977) J. Biochem. (Tokyo) 81, 313–320] could be reproduced by subtracting the temperature-induced spectral changes of HMM from those of HMM + AMPPNP.