Showed Intensity Changes Research Articles

Stability mechanism of Monascus pigment-soy protein isolate-maltodextrin complex.

Monascus pigment (MP) is a natural food coloring with vital physiological functions but prone to degradation and color fading under light conditions. This study investigated the effect of complex formation of soybean protein isolate (SPI), maltodextrin (MD), and MP on the photostability of MP. Light stability was assessed through retention rate and color difference. Fluorescence spectroscopy (FS), circular dichroism (CD), Fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) explored MP, SPI, and MD interactions, clarifying the MP-SPI-MD complex mechanism on the light stability of MP. Microstructure and differential scanning calorimetry (DSC) analyzed the morphology and thermal properties. The retention rate of MP increased to approximately 80%, and minimal color difference was observed when adding SPI and MD simultaneously. FS revealed hydrophobic interaction between MP and SPI. FTIR analysis showed intensity changes and peak shifts in amide I band and amide II band, which proved the hydrophobic interaction. CD showed a decrease in α-helix content and an increase in β-sheet content after complex formation, indicating strengthened hydrogen bonding interactions. Scanning electron microscopy (SEM) analysis demonstrated that MP was attached to the surface and interior of complexes. XRD showed MP as crystalline, while SPI and MD were amorphous, complexes exhibited weakened or absent peaks, suggesting MP encapsulation. The results of DSC were consistent with XRD. SPI and MD enveloped MP through hydrogen bonding and hydrophobic interaction, ultimately enhancing its light stability and providing insights for pigment-protein-polysaccharide interactions and improving pigment stability in the food industry. © 2024 Society of Chemical Industry.

Tryptophan Fluorescence Yields and Lifetimes as a Probe of Conformational Changes in Human Glucokinase.

Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.1) including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the entire protein. While the fluorescence quantum yield changes upon glucose binding, the enzyme's absorption spectra, emission spectra and fluorescence lifetimes change very little. These results are consistent with the existence of a dark complex for excited state Trp. Addition of glycerol, L-glucose, sucrose, or trehalose increases the binding affinity of glucose to the enzyme and increases fluorescence intensity. The effect of these osmolytes is thought to shift the protein conformation to a condensed, high affinity form. Based upon these results, we consider the nature of quenching of the Trp excited state. Amide groups are known to quench indole fluorescence and amides of the polypeptide chain make interact with excited state Trp in the relatively unstructured, glucose-free enzyme. Also, removal of water around the aromatic ring by addition of glucose substrate or osmolyte may reduce the quenching.

Adsorption of methylene blue from aqueous solution on modified ACFs by chemical vapor deposition

The adsorption behavior of activated carbon fibers (ACFs) modified by chemical vapor deposition (CVD) method on methylene blue (MB) was investigated in details. The Brunauer–Emmet–Teller (BET) surface area analysis, scanning electron microscope (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) analysis were employed to characterize the samples. The results showed that the pore size of the ACFs had a significant change after CVD modification. In addition, it was found that carbon nanotubes (CNTs) were well distributed on the surface of ACFs. FTIR analysis for modified ACFs after adsorption showed intensity changes of absorption peaks, in comparison to that before adsorption. The adsorption capacity at equilibrium increased with the increase of pH. Moreover, attempts were made to fit the isothermal data using Langmuir and Freundlich equations. The results manifested that the experimental data were well fitted by Freundlich equation. Furthermore, the adsorption kinetics was analyzed by pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The results demonstrated that the kinetic data were well described by pseudo-second-order kinetic model. The adsorption rate was controlled by intra-particle diffusion and film diffusion and thermodynamic parameters including ΔG, ΔH and ΔS were also determined. This showed that the adsorption process was a spontaneous, endothermic and increasing randomness process. The calculated Ea was 28.33kJ/mol, indicating that the adsorption could be a physisorption process.

Proteomic and activity profiles of ascorbate–glutathione cycle enzymes in germinating barley embryo

Enzymes involved in redox control are important during seed germination and seedling growth. Ascorbate–glutathione cycle enzymes in barley embryo extracts were monitored both by 2D-gel electrophoresis and activity measurements from 4 to 144 h post imbibition (PI). Strikingly different activity profiles were observed. No ascorbate peroxidase (APX) activity was present in mature seeds but activity was detected after 24 h PI and increased 14-fold up to 144 h PI. In contrast, dehydroascorbate reductase (DHAR) activity was present at 4 h PI and first decreased by 9-fold until 72 h PI followed by a 5-fold increase at 144 h PI. Glutathione reductase and monodehydroascorbate reductase activities were also detected at 4 h PI, and showed modest increases of 1.8- and 2.7-fold, respectively, by 144 h PI. The combination of functional analysis with the proteomics approach enabled correlation of the activity profiles and protein abundance. While gel spots containing APX showed intensity changes consistent with the activity profile from 0 to 72 h PI, DHAR spot intensities indicated that post-translational regulation may be responsible for the observed changes in activity. Transcript profiling, 2D-western blotting and mass spectrometric characterization of multiple APX spots demonstrated the presence of APX1 and minor amounts of APX2.

Synovial chondromatosis originating from the synovium of the anterior cruciate ligament: a case report

A case of synovial chondromatosis originating from the synovium of the anterior cruciate ligament (ACL) resulting in a mechanical block to knee extension is reported. A 36-year-old man complained of a restricted range of left-knee motion and pain when walking. Plain roentgenograms showed normal appearance, however, magnetic resonance imaging showed intensity changes in the ACL. Arthroscopically, numerous small free bodies were observed. Proliferation of synovium and cartilaginous tissues were identified around the ACL. There were no significant findings in the synovium except around the ACL. The synovium around the ACL was resected and free bodies were washed out. This is the first report of synovial chondromatosis originating from the synovium of the ACL.

Consequence of a Defect on the Terahertz Spectra of l-Asparagine Monohydrate

Abstract We measured the terahertz vibrational spectra of a solid solution of l-asparagine and l-aspartic acid monohydrate at 0.5 to 6.0 THz using a GaP Raman THz spectrometer. The absorption peaks at below 2.5 THz clearly showed intensity changes reflecting the change in hydrogen bonding between molecules. The peaks in the higher frequency region were indirectly affected by intermolecular bonding, which resulted in broadening.

A density functional theory and resonance Raman study of a benzotriazole dye used in surface enhanced resonance Raman scattering

Quantitative surface enhanced resonance Raman scattering (SERRS) requires effective adsorption of the analyte onto the metal surface. A range of dyes incorporating the benzotriazole group has been specifically designed to achieve this and they have proved successful labels for obtaining very sensitive analysis. However, if the spectra were more fully understood, the differences between the Raman spectrum in solution and on the surface could provide unique structural information on the nature of the surface layer. Using density functional theory (DFT) calculations the Raman and Infra-red (IR) spectra of the dye 3,5-dimethoxy-4-(6′-azobenzotriazolyl)-phenylamine (ABT-DMOPA) were assigned. A good correlation was found between the computed and experimental frequencies. Two competing isomers were compared and gave a largest error in fit for any clearly assigned band in the Raman spectrum of 41 cm −1 and an overall fit error of ∼15 cm −1. For the IR spectrum the largest error was 24 cm −1 with an overall fit error of ∼8 cm −1. Comparison of resonance Raman, SERS and SERRS spectra of the dye showed intensity changes which suggest the formation of a complex with silver on the surface. In the 1600–1630 cm −1 region, one vibration is reduced in intensity whilst one is greatly enhanced as surface attachment occurs, giving a good marker for surface attachment.

Selective excitation of self-assembled quantum dots by using shaped pulse

We carried out optical selective excitation of individual self-assembled quantum dots by using phase-modulated pulses. Based on scattered photoluminescence excitation resonances in individual QDs, the excitation pulses modulated in the spectral region allows for addressing individual ground states emission. The photoluminescence spectra including several QDs showed intensity changes according to both the modulation energies and phases. The results also suggested the individual control of selective QDs even in collective excitation.

Gradient-echo imaging of hemorrhage at 1.5 Tesla.

We report in vitro and in vivo MR studies of hemorrhage using the gradient-echo pulse sequence, FISP (steady state free precession) and FLASH (spoiling of transverse magnetization) at 1.5 Tesla. Phantoms containing methemoglobin, ferromagnetic particles, human serum and blood clot were scanned using both spin-echo and gradient-echo techniques. FLASH signal intensities were more sensitive to methemoglobin concentration than high T1-weighted spin-echo images. FISP showed little change in signal intensity with varying concentrations of methemoglobin and a contrast relationship similar to T2-weighted spin-echo techniques. FISP and FLASH showed intensity changes at lower concentrations of ferromagnetic material than T2-weighted spin-echo sequences. In vitro blood clot was less intense when observed by FISP and FLASH sequences than on the T2-weighted spin-echo sequences. Maximum contrast between clot and other blood components occurred at a flip angle of 45 degrees for FLASH and 60 degrees for FISP. FISP and FLASH scans of patients with hemorrhage demonstrated a marked decrease in signal intensity in the region of blood clot. This decrease was more pronounced with the gradient-echo sequences than with T2-weighted spin-echo images. We conclude that FLASH is useful for detecting methemoglobin and that both FISP and FLASH are useful for evaluating hemorrhage because of their sensitivity to methemoglobin.

Applications of synchrotron radiation to protein crystallography. II. Anomalous scattering, absolute intensity and polarization

The synchrotron X-ray beam produced by the SPEAR storage ring at the Stanford Linear Accelerator Center has been used as a tuneable and intense source for single-crystal-protein diffraction experiments. A measurement of the absolute intensity of a focused, monochromatized X-ray beam gave a value of 3 × 109 photons s-1 at a wavelength of 1.74 Å for typical machine operating conditions. A series of hk0 precession photographs were obtained from a crystal of the Fe-containing protein rubredoxin to investigate anomalous scattering effects and study their use in phase determination. Seven discrete wavelengths of radiation were used, some above and some below the Fe K absorption edge (1.743 Å = 7.111 keV). The rubredoxin diffraction data showed intensity changes due to f' varying with wavelength as well as from Bijvoet differences. The Fe site could be correctly located from difference Patterson and Fourier maps based either on f' or f”. The signal to noise ratio at the iron site was enhanced by calculating combined f' and f” maps. The phases of the Bragg reflections were also obtained from three films collected at different wavelengths. When compared with the known phases for rubredoxin, the differences average to 60°, which indicates that some phasing information was available even from the relatively poor data and that this method will be potentially useful in future applications. A method for calculating the Lp factor which has to be applied to precession photographs taken with the polarized synchrotron X-ray beam is described in the Appendix.