ANOTHER ROLE OF CHLOROPHYLL a/b BINDING PROTEINS OF HIGHER PLANTS: THEY MODULATE PROTOLYTIC REACTIONS ASSOCIATED WITH PHOTOSYSTEM II

Chlorophyll alb binding proteins serve as light-harvesting antennae. Additionally they seem to modulate proton pumping by photosystem II, because their covalent modification by N, N-dicyclohexylcarbodiimide is paralleled by a short-circuit of this activity. This side action was further characterized in comparative study with control thylakoids and thylakoids lacking chlorophyll alb binding proteins. The latter were derived from peas grown under intermittent light. They differed from controls in the following: (i) after incubation with A^A^-dicyclohexylcarbodiimide there was no protonic short circuit, (ii) under flashing light the rate of proton consumption at the acceptor side of photosystem II was accelerated and (iii) the periodical pattern of proton release from water oxidation was flattened out. It was obvious that chlorophyll alb binding proteins modulated the kinetics and the stoichiometry of proton release from water oxidation and proton uptake at the quinone binding pocket.     

Uncoupler-induced stimulation of photophosphorylation: Effects of carboxylic ionophores and amines at low concentrations on phosphorylation rate,phosphorylation potential and proton motive force in chloroplasts

The rate of steady-state photophosphorylation by spinach chloroplasts is stimulated upon the addition of methylamine and nigericin at concentrations of about 0.5 m M and 10 n M, respectively. Electron transport (H₂O → PS I acceptor) is increased simultaneously, and the ATP/2 e⁻ ratio is not altered by low, stimulating uncoupler concentrations. Stimulation of phosphorylation is observed with thylakoids freshly released from intact chloroplasts by hypotonic treatment, but is abolished by washing the thylakoids in 5 m M MgCl₂. The proton motive force (p.m.f.) in the steady state is lowered upon the addition of low concentrations of methylamine and nigericin; likewise, these uncouplers decrease the maximum attainable phosphorylation potential, [ATP]/{[ADP][Pi]}, from about 4.5 × 10⁴M⁻¹ to (3.0–3.5)× 10⁴M⁻¹. These data suggest that the rate of phosphorylation is under kinetic control, and that an uncoupler-induced removal of a kinetic barrier is responsible for the observed stimulation. The site of control could be the chloroplast coupling factor, and a working model of coupling factor 1 mediated uncoupler-induced stimulation of phosphorylation is proposed.     

The Lack of Lutein Accelerates the Extent of Light‐induced Bleaching of Photosynthetic Pigments in Thylakoid Membranes of Arabidopsis thaliana

The high light‐induced bleaching of photosynthetic pigments and the degradation of proteins of light‐harvesting complexes of PSI and PSII were investigated in isolated thylakoid membranes of Arabidopsis thaliana, wt and lutein‐deficient mutant lut2, with the aim of unraveling the role of lutein for the degree of bleaching and degradation. By the means of absorption spectroscopy and western blot analysis, we show that the lack of lutein leads to a higher extent of pigment photobleaching and protein degradation in mutant thylakoid membranes in comparison with wt. The highest extent of bleaching is suffered by chlorophyll a and carotenoids, while chlorophyll b is bleached in lut2 thylakoids during long periods at high illumination. The high light‐induced degradation of Lhca1, Lhcb2 proteins and PsbS was followed and it is shown that Lhca1 is more damaged than Lhcb2. The degradation of analyzed proteins is more pronounced in lut2 mutant thylakoid membranes. The lack of lutein influences the high light‐induced alterations in organization of pigment–protein complexes as revealed by 77 K fluorescence.     

439 — Photoelectrochemical and spectral properties of chlorophyll and its analogues in artificial membranes and liposomes

The results of spectral and photoelectrochemical investigations of artificial pigment—lipid membranes and liposomes are given, as well as data on the liposomal membrane structure obtained by electron microscopy.Chlorophyll (Chl) of artificial membranes is shown to be in monomeric (λ_abs = 670 nm) and crystalline (λ_abs = 740 nm) forms. The line with (δH_pp) of the e.p.r. signal of monomeric Chl cation-radical is within 8–9 G and that of crystalline is 1.7 G with g-factor = 2.0024. It was shown that about 22–28 Chl molecules were incorporated in the aggregates.The value of photoresporises generated by the membrane depends on the availability of electron donors and acceptors on the opposite sides of the membrane, the pH gradient via the membrane, as well as the external applied voltage. The membranes with incorporated Chl and pheophytin generate photopotentials of opposite signs.     

“Green synthesis” of benzothiazepine library of indeno analogues and their in vitro antimicrobial activity

A novel series of indeno-benzothiazepine derivatives was synthesised via a “green” route. Synthesis of these compounds involves the treatment of dinucleophiles such as 2-aminobenzenethiols with α,β-unsaturated ketones in poly(oxyethylene) (poly(ethylene glycol), PEG-400) catalysed by acetic acid. The synthone α,β-unsaturated ketones were obtained by Claisen-Schmidt condensation of indan-1-one with substituted pyrazole-2-carbaldehydes prompted by bleaching earth (pH 12.5) as catalyst and PEG-400 as “green” reaction solvent. Screening of all the synthesised compounds for antimicrobial activity revealed that most of these compounds exhibited moderate to significant antimicrobial activity.     

Synthesis,antibacterial and antioxidant activity of novel 2,3-dihydroquinazolin-4(1H)-one derivatives of dehydroabietylamine diterpene

A series of novel 2,3-dihydroquinazolin-4(1H)-ones was synthesized by a three-component reaction between dehydroabietylamine (DHA) diterpene, isatoic anhydride and different aromatic aldehydes in the presence of a catalytic amount of p-toluenesulfonic acid (13 mol%). Diastereomeric products were separated by preparative thin-layer chromatography and their structures were characterized by ¹H and ¹³C NMR, HMQC, IR and HR-ESI-MS. Antioxidant activities of the synthesized compounds were assessed by two different methods including DPPH and β-carotene-linoleic acid bleaching assays. Antibacterial activities of the compounds were also evaluated against two Gram-positive and one Gram-negative bacterial strains and in the case of Bacillus cereus a considerable inhibitory effect (MIC 4–16 μg/ml) was observed.     

The novel 4-hydroxyphenylpyruvate dioxygenase inhibitors in vivo and in silico approach: 3D-QSAR analysis,molecular docking,bioassay and molecular dynamics

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is not only an important target enzyme for the treatment of type I tyrosinemia, but also a new target for design bleaching herbicides, and it plays key role in the biosynthesis of tocopherol and plastoquinone. Thirty-six known active pyridine derivatives were collected, and comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) models based on common skeleton were constructed to obtain novel HPPD herbicides with higher activity. Two new HPPD inhibitors were rationally designed and synthesized according to the CoMFA and CoMSIA models and verified by enzyme activity, biological assays, and molecular docking. The promising compound W1 ((E)-5-(3-(4-bromophenyl)acryloyl)-6-hydroxy-2,3-dihydropyridin-4(1H)-one) showed better AtHPPD inhibitory activity, and the bioassay results revealed that some weeds showed bleaching symptoms. The good binding stability of W1 and protein was confirmed by molecular dynamics simulation in 100 ns. These results would be highly useful in the progress of new HPPD inhibitors discovery.     

Electronic structure and photochemical rearrangements of matrix-isolated C8H10 radical cations

The C₈H₁₀ isomers 1,3,5,7-octatetraene (OTE), 1,3,5-cyclooctatriene (COT) and bicyclo[4.2.0]octa-1,4-diene (BCO) were subjected to ionization by X-irradiation in argon matrices at 20 K. The electronic structure of the parent radical cations is discussed on the basis of their spectral properties and qualitative theoretical considerations. Photolysis of the cyclic cations leads to the formation of OTE¹ in at least six different conformation which can be distinguished by selective bleaching experiments. The complex band structure of the all-trans-OTE¹absorptions is demonstrated to arise from the presence of this species in at least five different matrix sites. By very narrow-bandwidth irradiation, single sites can be bleached or populated and the resulting difference spectra allow a detailed vibronic analysis of all-trans-OTE¹     

Photoelectrochemical reaction of chlorophyll immobilized with liquid crystal on metal surface

Chlorophyll was immobilized with liquid crystal on a platinum surface to prepare a photoexcitable electrode. Liquid crystals such as N-(p-methoxybenzylidene)-p-butylanil-ine were found to be effective on the photoexcitation of the immobilized chlorophyll. Such a chlorophyll-liquid crystal electrode produced photocurrent when it was coupled with a solution of nicotinamide adenine dinucleotide and exposed to light. The electron transfer accompanied by the photoelectrochemical reaction is discussed.     

Developments in the chemistry of tris(hydroxymethyl)phosphine

Tris(hydroxymethyl)phosphine, P(CH₂OH)₃, a water-soluble compound, has been known for about 50 years but development of its coordination chemistry has been slow and relatively recent. During some collaborative studies with a pulp and paper research institute on testing water-soluble catalysts for hydrogenation of lignin in pulp and the unsaturated functionalities in lignin model compounds, with the aim of bleaching pulps, we discovered new, in situ, Ru-P(CH₂OH)₃ hydrogenation catalysts. Interest in the coordination chemistry of this phosphine thus ensued, and this review covers this topic as well as the coordination chemistry of a diphosphine analogue, bis[bis(hydroxymethyl)phosphino]ethane, (HOCH₂)₂P(CH₂)₂P(CH₂OH)₂. The applications of the water-soluble metal complexes of these two phosphines in the areas of catalysis and medicinal drugs are also described. These phosphines, in the absence of metals, were found serendipitously to be effective bleaching agents for pulps (and also brightness stabilizing agents), and some relevant organo-phosphorus chemistry from our group is also briefly presented, particularly because of its possible significance in hydroformylation and hydrogenation processes catalyzed by metal–phosphine complexes.     

Excellent chemical and material cellulose from tunicates: diversity in cellulose production yield and chemical and morphological structures from different tunicate species

The high crystallinity and the high microfibrils aspect ratio of tunicate cellulose (TC) indicate TC’s excellent chemical and material applications. However, its quantity and quality from different species have never been systematically reported and compared. In this study, the tunics of Ciona intestinalis (CI), Ascidia sp. (AS), Halocynthia roretzi (HR) and Styela plicata (SP) were processed to TC after an identical prehydrolysis-kraft cooking-bleaching sequence, while the tunicate fibrils were chemically and structurally characterized in situ and during the sequence. All tunics studied were composed of crystalline cellulose embedded with protein, lipids, sulfated glycans and mucopolysaccharides. The native composite structures are all very compact. However, the tunics from Phlebobranchia order (CI and AS) are soft, while those from Stolidobranchia, HR and SP, are hard. Fibrous cellulose could be prepared after removing the lipids, sulfated glycans and mucopolysaccharides through prehydrolysis, protein removal through kraft cooking and a final purification by bleaching. The final product is ~100 % pure cellulose which is in large molecular masses, composed of highly crystalline I_β crystals, in elementary microfibrils form, with high specific surface area and thermal stability. There were lower TC yields from the soft tunics than from the hard ones. The cellulose fibrils had a section shape of lozenges with higher crystallinity. This study demonstrates that TC could be obtained in different yields and exhibited different chemical and morphological structures depending on the species. There is a great potential of tunicate resources for preparing excellent chemical and material cellulose.     

Bleaching earth clay (pH 12.5): a green catalyst for rapid synthesis of pyranopyrazole derivatives via a tandem three-component reaction

Efficient three-component synthesis of pyranopyrazole derivatives by reacting substituted aromatic aldehydes (1), (4-chlorophenyl)acetonitrile (2) and 3-methyl-1H-pyrazol-5(4H)-one (3) using bleaching earth clay (pH 12.5) as heterogeneous catalyst and PEG-400 as green solvent is reported in the present communication. The reaction time and product yields are excellent. Catalyst and solvent recovery and reusability are very good. This is a simple, green and rapid method for synthesis of pyranopyrazole derivatives.     

Temperature dependence of the vibrational population lifetime of OH(ν = 1) in fused silica

An infrared picosecond transient bleaching technique was used to measure vibrational lifetimes (T₁) of hydroxyl groups in fused silica over the temperature range 100–1450 K. T₁ decreases from 109 to 15 ps in this range. The T₁ temperature dependence is compared to non-radiative relaxation theory for the decay of the OH(ν = 1) quantum by a multiphonon mechanism.     

Studies under Continuous Irradiation of Photochromic Spiro[fluorenopyran‐thioxanthenes]

New indeno‐fused spiro[benzopyran‐thioxanthenes] were synthesized (see 3a – d in Scheme 3) and their photochromic properties evaluated under continuous irradiation (Table 1). When submitted to irradiation for several minutes with a Xe lamp, the system behaved as one constituted by two open colored forms with different thermal bleaching rates and different susceptibilities to degradation. An increase in irradiation time led to significant degradation and to the apparent predominance of the open colored form with the faster bleaching rate.     

A mathematical model of electron and proton transport in oxygenic photosynthetic systems

Results of simulation of electron and proton transport in higher plant chloroplasts, taking into account the lateral heterogeneity of their lamellar system, were summarized. The existence of heterogeneous lateral profiles of pH inside thylakoids and in gaps between the thylakoids of grana was predicted. The basic kinetic relationships were simulated for photoinduced redox transformations of P₇₀₀, the primary electron donor for PS1. It was shown that, along with changes in pH inside thylakoids, an essential role in controlling the electron transport in chloroplasts can belong to alkalinization of the gap between thylakoids of grana, caused by deceleration of diffusion of hydrogen ions from the stroma to the PS2 complexes in thylakoids of grana.     

Cholesterol degradation in archaeological pottery mediated by fired clay and fatty acid pro-oxidants

Cholesterol is generally absent in animal fat residues preserved in archaeological ceramic vessels. It is known from edible oil refining that during bleaching with activated clay sterols are degraded, largely via oxidation. Laboratory heating experiments using fired clay from replica pottery vessels promoted rapid degradation of cholesterol via oxidation. Furthermore, heating cholesterol with fatty acids (saturated and unsaturated) revealed additional degradation to occur independently of the ceramic matrix. As both conditions are met in archaeological pottery during animal (and plant) product processing involving heating, the very rare detection of sterols in organic residues can be explained.     

A new class of fluorescent dyes based on 1,3-benzodioxole and [1,3]-dioxolo[4.5-f]benzodioxole

We report on synthesis and photophysical properties of a new class of fluorescent dyes. They are characterized by large Stokes-shifts, long fluorescence lifetimes in organic solvents and a pronounced dependency of the fluorescence lifetime on the solvent polarity. Also worthy of note is the high bleaching stability. To provide access to biochemical and medical applications a series of derivatives were prepared, which exhibit specific reactivity towards different biologically relevant functional groups (carboxylic acids, amines, maleimides, N-hydroxysuccinimide esters). Furthermore, two alkynes were prepared, which could be used in ‘Click’ chemistry.     

Comparative Analysis of VOCs from Winter Melon Pomace Fibers before and after Bleaching Treatment with H2O2

In this study, the trend of Volatile Organic Compounds (VOCs) in dietary fiber samples from the winter melon (Cucumis Melo var. Inodorus, Yellow Canary type) were investigated. This foodstuff, obtained as a by-product of agri-food production, has gained increasing attention and is characterized by many bioactive components and a high dietary-fiber content. As regards fiber, it is poorly colored, but it may be whitened by applying a bleaching treatment with H₂O₂. The result is a fibrous material for specific applications in food manufacturing, for example, as a corrector for some functional and technological properties. This treatment is healthy and safe for consumers and widely applied in industrial food processes. In this study, a method based on headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC-MS) was applied for the characterization of the aromatic profile of the dried raw materials. Furthermore, VOC variation was investigated as function of the bleaching treatment with H₂O₂. The bleached samples were also analyzed after a long storage period (24 months), to assess their stability over time. As a result, the VOC fraction of the fresh raw fiber showed nine classes of analytes; these were restricted to seven for the bleached fiber at t₀ time, and further reduced to four classes at the age of 24 months. Alcohols were the main group detected in the fresh raw sample (33.8 % of the total chromatogram area), with 2,3-butanediol isomers as the main compounds. These analytes decreased with time. An opposite trend was observed for the acids (9.7% at t₀), which increased with time and became the most important class in the 24-month aged and bleached sample (57.3%).     

Analysis of impurities occurring in a totally chlorine free-bleached Kraft pulp

A set of impurities (specks) occurring in a TCF (totally chlorine free)-bleached Kraft pulp of Eucalyptus globulus wood was studied. The impurities were Soxhlet extracted with acetone, and the extracts subsequently analyzed by gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) using high-temperature capillary columns. The lipophilic fraction isolated from E. globulus wood extractives was also analyzed for comparison. The composition of the acetone extracts was very similar to that of E. globulus wood. Fatty acids, steroid hydrocarbons, sterols, steroid ketones and sterol esters, arising from E. globulus wood extractives survived the cooking and bleaching processes and accumulated in the pulp. On the other hand, the residue left after acetone extraction was studied by pyrolysis–GC–MS. The results indicated that it was composed of small particles of polyisoprene rubber. In conclusion, the speck impurities studied here seems to be composed of two different moieties, a lipophilic part arising from wood extractives and a core of small particles of synthetic polymers (polyisoprene rubber).     

Thermostable and Alkalistable Endoxylanase of the Extremely Thermophilic Bacterium Geobacillus thermodenitrificans TSAA1: Cloning, Expression, Characteristics and Its Applicability in Generating Xylooligosaccharides and Fermentable Sugars

Xylanase encoding gene (1,224 bp) from Geobacillus thermodenitrificans was cloned in pET28a (+) vector and successfully expressed in Escherichia coli BL21 (DE3). The deduced amino acid sequence analysis revealed homology with that of glycosyl hydrolase (GH) 10 family with a high molecular mass (50 kDa). The purified recombinant xylanase is optimally active at pH 9.0 and 70 °C with T _1/2 of 10 min at 80 °C, and retains greater than 85 % activity after exposure to 70 °C for 180 min. The enzyme liberates xylose as well as xylooligosaccharides from birchwood xylan and agro-residues, and therefore, this is an endoxylanase. The xylan hydrolytic products (xylooligosaccharides, xylose, and xylobiose) find application as prebiotics and in the production of bioethanol. The xylanase being thermostable and alkalistable, it has released chromophores and phenolics from the residual lignin of pulps, suggesting its utility in mitigating chlorine requirement in pulp bleaching.