Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λ_max = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL⁻¹ with sample throughput of 15 h⁻¹. The limit of detection was 0.5 ng mL⁻¹ and a relative standard deviation for 10 ng mL⁻¹ molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.     

Enzymatic degradation of oxidized cellulose hydrogels

The cellulose-based hydrogel with abundant aldehyde groups was prepared by periodate oxidation of cellulose hydrogel prepared by dissolution-regeneration of cellulose by aqueous LiOH/urea solvent. Aldehyde groups could be introduced retaining the nanoporosity of the cellulose gel. The enzymatic degradation of three grades of oxidized cellulose hydrogel, with aldehyde contents of 3.3, 8.1 and 18.6 per 100 glucose unit, was carried out using solutions containing cellulase and β-glucosidase at 37 °C up to 48 h. The degradation of oxidized gels was remarkably slower than that of original cellulose gel, depending strongly on the degree of oxidation. The portion except for the amount of glucose released was greater than the degree of oxidation, but became closer to the latter with increase in the degree of oxidation. This behavior can be interpreted in terms of the enzymatic recognition of the chemically modified cellulose chains.     

In vitro self-assembly of bacteriochlorophyll c derivatives monoesterified with α,ω-diols isolated from the green sulfur photosynthetic bacterium Chlorobaculum tepidum

Esterifying chains of chlorophyllous pigments play important roles in the formation of photosynthetic supramolecules, but their effects have not thoroughly been unraveled yet. Substitution of the esterifying chains in these pigments will be one possible strategy to elucidate this enigma. Recently, unnatural bacteriochlorophylls (BChls) c possessing a hydroxy group at the terminus of the esterifying chains were successfully biosynthesised in the green sulfur bacterium Chlorobaculum (Cba.) tepidum grown by supplementation of α,ω-diols. In this paper, in vitro assembling behaviours of unnatural BChls c isolated from Cba. tepidum grown with 1,8-octanediol, 1,12-dodecanediol and 1,16-hexadecanediol were characterised in aqueous Triton X-100 micelles to investigate the effects of the terminal hydroxy group in the esterifying chains of BChls c on self-aggregates such as chlorosomes, major antenna complexes in green photosynthetic bacteria. The bacteriochlorophyll (BChl) c derivatives monoesterified with α,ω-diols formed chlorosomal self-aggregates, but their formations were much slower than those of natural BChl c. The Q_y absorption bands of the residual monomers of these BChl c derivatives were larger than those of natural BChl c. These suggest that the esterifying α,ω-diols in these unnatural BChls c somewhat interfered with formation of chlorosome-like aggregates compared with the natural esterifying farnesol.     

First-principles study on electronic structure of Sr2Bi2O5 crystal

The electronic structure of Sr₂Bi₂O₅ is calculated by the GGA approach. Both of the valence band maximum and the conduction band minimum are located at Γ-point. This means that Sr₂Bi₂O₅ is a direct band-gap material. The wide energy-band dispersions near the valence band maximum and the conduction band minimum predict that holes and electrons generated by band gap excitation have a high mobility. The conduction band is composed of Bi 6p, Sr 4d and O 2p energy states. On the other hand, the valence band can be divided into two energy regions ranging from −9.5 to −7.9 eV (lower valence band) and from −4.13 to 0 eV (upper valence band). The former mainly consists of Bi 6s states hybridizing with O 2s and O 2p states, and the latter is mainly constructed from O 2p states strongly interacting with Bi 6s and Bi 6p states.     

Crystal structure of stable protein CutA1 from psychrotrophic bacterium Shewanella sp. SIB1

CutA1 is widely found in bacteria, plants and animals, including humans. The functions of CutA1, however, have not been well clarified. It is known that CutA1s from Pyrococcus horikoshii, Thermus thermophilus and Oryza sativa unfold at temperatures remarkably higher than the growth temperatures of the host organisms. In this work the crystal structure of CutA1 from the psychrotrophic bacterium Shewanella sp. SIB1 (SIB1-CutA1) in a trimeric form was determined at 2.7?? resolution. This is the first crystal structure of a psychrotrophic CutA1. The overall structure of SIB1-CutA1 is similar to those of CutA1 from Homo sapiens, Escherichia coli, Pyrococcus horikoshii, Thermus thermophilus, Termotoga maritima, Oryza sativa and Rattus norvergicus. A peculiarity is observed in the β2 strand. The β2 strand is divided into two short β strands, β2a and β2b, in SIB1-CutA1. A thermal denaturation experiment revealed that SIB1-CutA1 does not unfold completely at 363?K at pH 7.0, although Shewanella sp. SIB1 cannot grow at temperatures exceeding 303?K. These results indicate that the trimeric structural motif of CutA1 is the critical factor in its unusually high stability and suggest that CutA1 needs to maintain its high stability in order to function, even in psychrotrophs.     

A new way to understand quaternary structure changes of hemoglobin upon ligand binding on the basis of UV-resonance Raman evaluation of intersubunit interactions

The single residue vibrational spectra of tryptophan (Trp) and tyrosine (Tyr) residues in human adult hemoglobin (HbA), which play important roles in cooperative oxygen binding, were determined for the deoxy and CO-bound forms by applying UV resonance Raman spectroscopy to various variant Hbs. It was found that Trpβ37, Tyrα42, Tyrα140, and Tyrβ145 at the α(1)-β(2) subunit interface underwent transitions between two contact states (named as T and R) upon ligand binding, while Trpα14, Trpβ15, and Tyrβ35 displayed little changes. The corresponding spectral changes were identified only for the α(2)β(2) tetramer, but not the isolated α and β chains in the oligomeric forms, and therefore were exclusively attributed to a quaternary structure change. Ligand binding as well as allosteric effectors and pH altered only the number of the T-contacted Tyr and Trp residues without varying the two contact states themselves. A new method to semiquantitatively evaluate the amount of T-contacted Tyr and Trp residues in a given liganded form is here proposed, and with it a quaternary structure was determined for various symmetrically half-liganded forms obtained with ligand-hybrid, metal-hybrid, and valency-hybrid Hbs. It was found that ligand binding to the α or β subunits yielded different subunit contacts and that the contact changes of the Trp and Tyr residues were not always concerted. The contact changes at the α(1)-β(2) (α(2)-β(1)) interface are correlated with the proximal strain exerted on the Fe-His(F8) bond, which is noted to be much larger in the α than β subunits in the α(2)β(2) tetramer.     

Self-assembly of zinc chlorophyll derivatives possessing a pyrenyl group at the 17-propionate residue and effects of additional γ-cyclodextrins on their optical properties

Two kinds of zinc 3¹-hydroxy-13¹-oxo-chlorins 1 and 2 possessing a pyrenyl group at the 17-propionate residue, of which the linker length between the chlorin and the pyrene moieties was varied, were synthesised from naturally occurring chlorophyll a, and were self-assembled in an aqueous solution. Both zinc chlorins 1 and 2 exhibited Q_y absorption bands around 720 nm accompanying circular dichroism signals in the Q_y region, indicating that these zinc chlorins could form self-aggregates like chlorosomes of green photosynthetic bacteria. Addition of γ-cyclodextrin into an aqueous solution containing the self-aggregates of zinc chlorin 1 esterified with 1-pyrenylmethanol induced the appearance of excimer emission of the pyrene moieties around 480 nm as well as increased the fluorescence intensities of the pyrene monomers at 378 and 396 nm, while only an increase in fluorescence from the monomeric pyrene moiety was observed in the case of 2 esterified with 4-(1-pyrenyl)butanol. Exogenous γ-cyclodextrin unchanged the spectral features derived from the chlorin moieties of 1 and 2 in the aqueous phase. These suggest that the encapsulation of the pyrenyl groups in the zinc chlorins unchanged their assembling states under the present conditions.     

Controlling molecular conformation of regenerated wild silk fibroin by aqueous ethanol treatment

Regenerated Antheraea pernyi silk fibroin film was prepared by dissolution of native silk fiber in aqueous lithium thiocyanate. The influence of aqueous ethanol treatment of the dried regenerated film on molecular conformation was studied by X‐ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. While the initial regenerated film consisted of α‐helix and random coil components, aqueous ethanol treatment of the film resulted in significant increase in β‐sheet component and improvement of water resistance of the film. This effect was strongly dependent on ethanol concentration, and 40–60% (w/w) ethanol was most effective due to balance of hydrophilic/hydrophobic action of the solvent. Copyright © 2003 John Wiley & Sons, Ltd.     

Aqueous pretreatment for reactive ball milling of cellulose

Aqueous swelling pretreatment of cellulose was found highly effective for reactive ball milling to prepare surface-esterified cellulose nanofibers. Compared with starting from dry cellulose, water- or 2 % NaOH-pre-swollen materials were esterified and dispersed in significantly shorter milling time. Especially commercial kraft pulp was difficult to disperse even with water pretreatment, but 2 % NaOH treatment gave full surface esterification with a bulk degree of substitution of 0.69 by 12-h ball milling, presumably because of removal of non-cellulosic components.     

Role of urea in alkaline dissolution of cellulose

To elucidate the role of urea in dissolution of cellulose in aqueous alkali-urea solvent, the dissolution process was monitored by differential scanning calorimetry and X-ray diffractometry. Urea had no direct interaction with cellulose in dissolution process, but promoted the decrease of crystallinity. Moreover, the addition of urea increased the dissolved fraction of cellulose in the solvent by 1.5–2.5 times and improved the thermal stability of the solution. Urea might help alkali hydrate to penetrate into crystalline region of cellulose by stabilizing the alkali-swollen cellulose molecules, leading to an increase in dissolved fraction of cellulose. This stabilization may be due to the local accumulation of urea on the hydrophobic surface, preventing the hydrophobic association of dissolved cellulose molecules.