Significant Downshifts Research Articles

Influence of Charge Distribution on Structural Changes of Aromatic Imide Derivatives upon One-Electron Reduction Revealed by Time-Resolved Resonance Raman Spectroscopy during Pulse Radiolysis.

Structural changes of aromatic imides upon one-electron reduction are investigated by time-resolved resonance Raman spectroscopy during pulse radiolysis. Significant downshifts are observed for both the aromatic ring stretching and carbonyl stretching modes, which are related to a reduction of the bond order and increase of the charge density on these moieties. For three aromatic imides, i.e., 1,8-naphthalene imide (1,8-NI), 2,3-naphthalene imide (2,3-NI), and naphthalene diimide (NDI), the extent of structural changes is found to follow the order: 2,3-NI > 1,8-NI > NDI, reflecting the influence of charge distribution on molecular structure. To further investigate this phenomenon, a series of homologous NDI derivatives with a substituted phenyl group at the imide position are studied. The Raman peaks between 1550 and 1600 cm-1, which are assigned to aromatic stretching vibrations of the NDI moieties,are found to be sensitive to the charge distribution: stronger electron-withdrawing substituents result in these peaks shifting to slightly higher wavenumbers. As supported by a spin density analysis, despite the fact that the added charge is mostly localized on the NDI moiety, in the presence of an electron-withdrawing group, the subtle charge is likely to delocalize on the phenyl fragment, alleviating the effect of one-electron reduction on the molecular structure.

Detection of Structural Changes upon One-Electron Oxidation and Reduction of Stilbene Derivatives by Time-Resolved Resonance Raman Spectroscopy during Pulse Radiolysis and Theoretical Calculations.

Stilbene (St) derivatives have been investigated for many years because of their interesting photochemical reactions such as cis-trans isomerization in the excited states and charged states and their relation to poly(p-phenylenevinylene)s. To clarify their charged state properties, structural information is indispensable. In the present study, radical cations and radical anions of St derivatives were investigated by radiation chemical methods. Absorption spectra of radical ion states were obtained by transient absorption measurements during pulse radiolysis; theoretical calculations that included the solvent effect afforded reasonable assignments. The variation in the peak position was explained by using HOMO and LUMO energy levels. Structural changes upon one-electron oxidation and reduction were detected by time-resolved resonance Raman measurements during pulse radiolysis. Significant downshifts were observed with the CC stretching mode of the ethylenic groups, indicative of the decrease in the bonding order. It was confirmed that the downshifts observed with reduction were larger than those with oxidation. On the other hand, the downshift caused by oxidation depends significantly on the electron-donating or electron-withdrawing nature of the substituents.

Visible and infrared spectroelectrochemistry of zinc and manganese porphinones: Metal vs. porphyrin reduction

The visible and infrared spectroelectrochemistry of zinc and manganese porphinones and porphinediones was carried out in THF solutions. The aim of this work was to use FTIR spectroelectrochemistry and DFT calculation to determine whether the reduction was centered predominantly on the metal or the macrocycle. For zinc(II), the first one-electron reduction must occur on the macrocyclic ring because the metal’s d-orbitals are filled (d10). The carbonyl bands on the macrocyclic ring were used to probe the electronic structure because they can be readily observed in the infrared spectra. The results of this study are complementary to previous spectroelectrochemical studies that have been reported for the iron and cobalt complexes of the same macrocycles. As expected for the formation of a π-radical anion species, significant downshifts in the carbonyl bands were observed. DFT calculations showed that the behavior of the porphinedione complexes were most sensitive to the electronic structure of the M(OEPdione)− species. If a MI species is formed, the two carbonyl groups will be downshifted by similar energies. For MII-radical anions, one carbonyl will be downshifted significantly, and the second one will be downshifted by a small amount. On the basis of this criterion, it was determined that cobalt(I) and iron(I) complexes were formed, while zinc and manganese formed π-radical anion species. The visible spectroelectrochemistry was also consistent with these electronic structures.

Strongly interacting two-dimensional Bose gases.

We prepare and study strongly interacting two-dimensional Bose gases in the superfluid, the classical Berezinskii-Kosterlitz-Thouless (BKT) transition, and the vacuum-to-superfluid quantum critical regimes. A wide range of the two-body interaction strength 0.05 < g < 3 is covered by tuning the scattering length and by loading the sample into an optical lattice. Based on the equations of state measurements, we extract the coupling constants as well as critical thermodynamic quantities in different regimes. In the superfluid and the BKT transition regimes, the extracted coupling constants show significant down-shifts from the mean-field and perturbation calculations when g approaches or exceeds one. In the BKT and the quantum critical regimes, all measured thermodynamic quantities show logarithmic dependence on the interaction strength, a tendency confirmed by the extended classical-field and renormalization calculations.

Many hexapod groups originated earlier and withstood extinction events better than previously realized: inferences from supertrees.

Comprising over half of all described species, the hexapods are central to understanding the evolution of global biodiversity. Direct fossil evidence suggests that new hexapod orders continued to originate from the Jurassic onwards, and diversity is presently higher than ever. Previous studies also suggest that several shifts in net diversification rate have occurred at higher taxonomic levels. However, their inferred timing is phylogeny dependent. We re-examine these issues using the supertree approach to provide, to our knowledge, the first composite estimates of hexapod order-level phylogeny. The Purvis matrix representation with parsimony method provides the most optimal supertree, but alternative methods are considered. Inferring ghost ranges shows richness of terminal lineages in the order-level phylogeny to peak just before the end-Permian extinction, rather than the present day, indicating that at least 11 more lineages survived this extinction than implied by fossils alone. The major upshift in diversification is associated with the origin of wings/wing folding and for the first time, to our knowledge, significant downshifts are shown associated with the origin of species-poor taxa (e.g. Neuropterida, Zoraptera). Polyneopteran phylogeny, especially the position of Zoraptera, remains important resolve because this influences findings regarding shifts in diversification. Our study shows how combining fossil with phylogenetic information can improve macroevolutionary inferences.

Self-Built Tensile Strain in Large Single-Walled Carbon Nanotubes

Abnormal Raman scattering from a large-diameter ultralong single-walled carbon nanotube (SWCNT) is studied in detail. Along the SWCNT, the Raman spectra show the frequencies of 1553, 1563, and 2597 cm(-1) for G(+), G(-), and G' peaks, respectively, much lower than the corresponding frequencies well-reported both experimentally and theoretically. The significant downshifts in the peaks frequencies can be attributed to self-built tensile strain, which is likely caused by carbon nanodots decorated on the tube. After infrared laser heating is performed to one point of it, all of the Raman modes are found to shift to higher frequencies and approach their conventional values. We suggest that the SWCNTs with larger diameters easily possess such self-built strain compared to small-diameter SWCNTs because of the weaker curvature effect for the larger ones.

Resonance Raman Investigation of the R481 Mutants of Cytochrome c Oxidase from R. sphaeroides

The enzymes of the heme-copper oxidase superfamily have a highly conserved arginine residue (R438, R481, and R473 of the bovine, R. sphaeroides, and P. denitrificans cytochrome c oxidases, respectively), which is located close to the heme-propionate substituents of the heme a and heme a3 moieties. To explore the structural and functional implications of this conserved arginine, we used resonance Raman spectroscopy to study the heme vibrational spectra of the R481 mutant proteins (R481H, R481Q, and R481L) of cytochrome c oxidase from R. sphaeroides. All the mutants showed significant down-shifts in the C=O stretching vibrational frequencies of the heme a and a3 formyl substituent groups in the fully oxidized state, while they showed up- and down-shifts of the a and a3 formyl C=O stretching modes, respectively, in the fully reduced state. On the basis of these observations, the role of the conserved arginine will be discussed.

Purification and partial characterization of xyloglucan‐hydrolyzing enzymes from watermelon placental tissue

AbstractBACKGROUND: Watermelon (Citrullus lanatus (Thunb.) Matsum &amp; Nakai) fruit matrix glycans are comprised largely of xyloglucans (XGs). As in other fruits, these polymers show significant molecular mass downshifts during ripening. In the present study, we describe the purification and characteristics of a number of xyloglucanases (XGases) from the placental tissue of ripe watermelon. XGases were extracted from watermelon fruit placental tissue and purified by sequential ion‐exchange, gel‐permeation and concanavalin A chromatography.RESULTS: Five XGases (P1S2, P2S2, P3S1, P3S2, P3S3) were recovered with molecular masses ranging from 30.5 to 77.5 kDa on SDS‐PAGE. All XGases showed maximum activity at pH 5–5.5 and 35–40 °C against tamarind seed XG and were also active against XG‐rich matrix glycans from watermelon fruit. The enzymes were strongly inhibited by mercury and hydrolyzed XG without generation of oligomers or monomers. P3S3 had the highest activity against XG. The purified enzymes were active toward carboxymethylcellulose, indicating that they were not XG specific.CONCLUSION: The pattern of molecular mass downshifts during XG hydrolysis by the purified XGases and the absence of monomeric and oligomeric products are consistent with endo‐type catalysis for the XGases and with a role for these enzymes in the degradation of cell wall XG during ethylene‐induced watersoaking of watermelon fruit placental tissues. Copyright © 2009 Society of Chemical Industry

Redox Potential Difference between Desulfovibrio vulgaris and Clostridium beijerinckii Flavodoxins

The redox potential of the flavin mononucleotide (FMN) hydroquinones for one-electron reduction in the Desulfovibrio vulgaris ( D. vulgaris) flavodoxin ( E sq/hq for FMNH (*)/FMNH (-)) was calculated using the crystal structure of the relevant hydroquinone form and compared to the results of the Clostridium beijerinckii ( C. beijerinckii) flavodoxin. In D. vulgaris and C. beijerinckii flavodoxins, the protein side chain causes significant downshifts of 170 and 240 mV in E sq/hq, respectively. In the C. beijerinckii flavodoxin, the E sq/hq downshift because of the protein side chain is essentially compensated by the counter influence of the protein backbone ( E sq/hq upshift of 260 mV). However, in the D. vulgaris flavodoxin, the corresponding protein backbone influence on E sq/hq is significantly small, i.e., less than half of that in the C. beijerinckii flavodoxin. In particular, there is a significant difference in the influence of the protein backbone of the so-called 60s loop region between the two flavodoxins. The E sq/hq difference can be best explained by the lower compensation of the side chain influence by the backbone influence in the D. vulgaris flavodoxin than in the C. beijerinckii flavodoxin.

Matrix glycan depolymerisation and xyloglucan endohydrolase activities in ethylene‐treated watermelon (Citrullus lanatus) fruit

AbstractBACKGROUND: Ethylene‐induced placental tissue water soaking in harvested watermelon fruit is accompanied by cell separation and collapse, depolymerisation of water‐ and chelator‐soluble pectins, a reducton in total uronic acids and increased polygalacturonase activity. The aim of this study was to investigate whether ethylene‐induced changes in placental tissue cell walls also affected matrix glycans (hemicelluloses).RESULTS: Polymers from 0 and 6 day air‐treated fruits were similar in molecular mass distribution, with the majority of polymers eluting within the void volume of Sepharose 6B. Polymers from ethylene‐treated fruit showed significant molecular mass downshifts involving xyloglucan. Xylose and glucose together comprised nearly 70% of 2 mol L−1 alkali‐soluble neutral sugars. Treatment of watermelon fruit with ethylene was not accompanied by changes in matrix glycan composition, indicating that in situ depolymerisation did not result in altered solubility and/or loss of xyloglucan. Cell‐free protein extracts from watermelon placental tissue from both air‐ and ethylene‐treated fruits degraded tamarind seed xyloglucan, resulting in significant molecular mass downshifts without production of oligomers and monomers. The capacity of cell‐free extracts to degrade tamarind xyloglucan and watermelon matrix glycans was similar for 6 day ethylene‐ and air‐treated fruits.CONCLUSION: Collectively the data suggest that enhanced depolymerisation of xyloglucan in ethylene‐treated watermelon fruit arises from factors other than altered enzyme levels. Accordingly, the depolymerisation of pectin and matrix glycans would not appear to be solely responsible for ethylene‐induced water soaking in watermelon. Copyright © 2007 Society of Chemical Industry

The ORF3 Protein of Porcine Circovirus Type 2 Is Involved in Viral Pathogenesis In Vivo

Porcine circovirus type 2 (PCV2) is the primary causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome. We previously showed that a novel identified protein, ORF3, was not essential for PCV2 replication in cultured PK15 cells and played a major role in virus-induced apoptosis. To evaluate the role of the ORF3 protein in viral pathogenesis in vivo, we inoculated 8-week-old BALB/c mice that have been developed for PCV2 replication with ORF3-deficient mutant PCV2 (mPCV2). By 42 days postinoculation, all of the mice inoculated with the mPCV2, as well as with wild-type PCV2 (wPCV2), had seroconverted to PCV2 capsid antibody, and the mutant induced levels of PCV2 antibodies that were higher than those of the wPCV2. The PCV2 genomic copy numbers in serum were significantly higher (P<0.05) in the wPCV2-inoculated mice than in mice inoculated with the mPCV2. Also, the wPCV2 caused microscopic lesions characterized by lymphocyte depletion with histiocytic infiltration of lymphoid organs, but the mutant virus failed to induce any obvious pathological lesions. In situ hybridization and immunohistochemical analyses also showed that larger amounts of viral DNA and antigens were detected in the lymph nodes of the wPCV2-inoculated than mPCV2-inoculated mice. Furthermore, animals of the wPCV2-inoculated group showed significant downshifts of CD8(+) T-cell subsets of peripheral blood lymphocytes compared to the control mice (P<0.05) at various time points postinoculation. Also, the proportions of the CD4(+) and CD4(+) CD8(+) cells were significantly reduced in wPCV2-inoculated mice at some time points postinoculation. In contrast, there are some reductions in the proportions of these subsets in the mutant virus-inoculated mice, but the proportions do not decrease significantly. Taken together, these results demonstrate that the ORF3 protein is also dispensable for viral replication in vivo and that it plays an important role in viral pathogenesis.

Cell wall‐degrading enzymes and pectin solubility and depolymerization in immature and ripe watermelon (Citrullus lanatus) fruit in response to exogenous ethylene

Watermelon fruit have been shown to be extremely sensitive to exogenous ethylene, exhibiting acute symptoms of whole‐fruit softening and placental‐tissue water‐soaking following short periods of exposure to the gas. This study addressed the firmness, specific activities of cell wall hydrolases, and solubility and molecular mass properties of polyuronides in placental tissue in response to treatment of intact fruit with ethylene. Watermelon fruit were harvested at the immature and full‐ripe stages and exposed to 50 µl l−1 ethylene for 6 days at 20°C. The firmness of placental tissue from ethylene‐treated ripe and immature fruit decreased nearly 80% during 6 days of ethylene exposure, whereas the firmness of placental tissue from fruit maintained in air remained relatively constant up to day 3 and then decreased slightly (12%) during the following 3 days of storage. Although ethylene treatment in some cases influenced the levels of extractable placental‐tissue polygalacturonase (EC 3.2.1.15), pectinmethylesterase (EC 3.2.1.11), and α‐(EC 3.2.1.22) and β‐galactosidase (EC 3.2.1.23) specific activities, these effects were not observed for fruit of both developmental stages and appeared not to be directly involved in the water–soaking syndrome. Symptoms of water‐soaking were accompanied by increases in the levels of water‐ and CDTA (trans‐1,2‐cyclohexanediamine‐N,N,N',N′‐tetraacetic acid)‐soluble polyuronides and significant molecular mass downshifts in polyuronides in both immature and ripe watermelon fruit. Polyuronide depolymerization in ethylene‐treated ripe fruit was extensive. The parallel trends of enzyme changes in ethylene‐ compared with air‐treated fruit indicate that extractable enzyme levels are not associated with development of the water‐soaking disorder. The potential involvement of membrane dysfunction in the water‐soaking phenomenon is discussed.

Purification and catalytic properties of polygalacturonase isoforms from ripe avocado (Persea americana) fruit mesocarp.

Endo-polygalacturonase (PG; EC 3.2.1.15) was recovered from the cell walls of avocado mesocarp (Persea americana Mill cv. Lula) tissue and purified by sequential ion exchange and gel permeation chromatography. Two isoforms (S-I and S-II) were recovered, exhibiting molecular masses of about 41 kD on size exclusion media and about 48 (S-I) and 46 (S-II) kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Both isoforms exhibited maximum activity at pH 6.0 against polygalacturonic acid (PGA) and hydrolyzed PGA of about 180 kDa to polymers of about 4 kDa. The catalytic activity of the 48-kDa isoform against PGA was slightly higher than that of the 46-kDa isoform. The purified PGs catalyzed significant molecular mass downshifts in the polyuronides of pre-ripe avocados; however, the capacity of the enzymes to solubilize polyuronides from cell walls of pre-ripe fruit was limited.

Resonance Raman characterization of the triplet state of zinc tetraphenylchlorin

The T{sub 1} excited state of zinc(II) tetraphenylchlorin, ZnTPC, has been studied by nanosecond time-resolved transient absorption (TA) and transient resonance Raman (TR{sup 3}) spectroscopy. The TA difference spectrum shows an induced absorption at 450 nm that is assigned as arising from a {sup 3}({pi},{pi}*) state. The most striking feature of the {sup 3}(ZnTPC) TR{sup 3} spectrum is the significant frequency downshifts and strong intensity enhancements of the pyrrole half-ring stretch, {nu}{sub 4}, and of other pyrrole ring motions which together produce a broad band in the 1150-1300-cm{sup -1} region. In addition, the enhancement of C{sub 12}C{sub m} modes ({nu}{sub 2} and {nu}{sub 11}) changes with their phasing between the S{sub 0} and T{sub 1} states. Weaker intensity enhancements, with no frequency shifts, are seen for the phenyl substituent ring mode, {Phi}{sub 4} and {nu}{sub 1}, and C{sub m}-phenyl stretch. These findings suggest that there is less electronic participation from the phenyl rings in the resonant triplet state, T{sub n}, for ZnTPC than for its parent metalloporphyrin, ZnTPP. 31 refs., 4 figs., 1 tab.

Effects of pseudostuttering on normal speaker's self-ratings of beauty

Forty-three undergraduate and 12 graduate students provided numerical evaluations of their own outer beauty and inner beauty, both in class, and immediately following a pseudostuttering assignment. Both groups had significant downshifts in both parameters of beauty. The undergraduate students had greater downshifts in both areas than did the graduate students. It was concluded that, (1) pseudostuttering assignments represent a viable instrument for allowing student clinicians to experience negative feelings as a result of stuttering, and (2) graduate students manifested greater stability in their self-evaluations than did the undergraduate students.