Studies on the interaction of the carbohydrate binding module 3 from the Clostridium thermocellum CipA scaffolding protein with cellulose and paper fibres

The adsorption of a carbohydrate binding module (CBM3) from the Clostridium thermocellum scaffolding protein (CipA) to cellulose was analysed in this work. The effect of CBM-PEG on the drainability of E. globulus and P. sylvestris pulps and on the physical properties of the respective papersheets was also studied. The CBM binding to cellulose is often described as “irreversible”, but this classification does not fully characterize this interaction. Indeed, the results obtained demonstrate that, although the adsorption on cellulose is rather stable, CBM inter-fibre mobility may be observed. The results also showed that the CBM-PEG conjugate improves the drainability of E. globulus and P. sylvestris pulps without affecting the physical properties of the papersheets.     

Nonproteolytic cleavage of aspartyl proline bonds in the cellulosomal scaffoldin subunit from Clostridium thermocellum

Previous work from our group [Morag (Morgenstern), E., Bayer, E. A., and Lamed, R. (1991), Appl. Biochem. Biotechnol. 30, 129–136] has demonstrated an anomalous electrophoretic mobility pattern for scaffoldin, the 210-kDa cellulosome-integrating subunit of Clostridium thermocellum. Subsequent evidence [Morag, E., Bayer, E. A., and Lamed, R. (1992), Appl. Biochem. Biotechnol. 33, 205–217] indicated that the effect could be attributed to a nonproteolytic fragmentation of the subunit into a defined series of lowermolecular-weight bands. In the present work, a recombinant segment of the scaffoldin subunit was employed to determine the site(s) of bond breakage. An Asp-Pro sequence within the cohesin domain was identified to be the sensitive peptide bond. This sequence appears quite frequently in the large cellulosomal proteins, and the labile bond may be related to an as yet undescribed physiological role in the hydrolysis of cellulose by cellulosomes.     

Stereoisomeric flavor compounds LXXVII: 3-Butylhexahydrophthalides: Simultaneous enantioselective analysis,structure elucidation,and sensorial properties of the stereoisomers

Using heptakis-(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cy-clodextrin as the chirul stationary phase in enantioselective gas chromatography, the simultaneous enantioselective analysis of all eight 3-butylhexahydrophthalide Stereoisomers was achieved. Fur-thermore, the odor characteristics and odor thresholds were investigated by enantioselective gas chromatography/olfactometry. Racemic standards were synthesized via hydrogenation and subsequent base catalyzed epimerization. Starting from racemic 3-butylphthalide. After separation by high performance liquid chromatography. Relative configurations of the pure diastereoisom-ers were determined by means of NOE-difference spectroscopy. The absolute configuration at C-3 was determined starting from (3S)-butylphthalide as an educt for hydrogenation and epimerization. Absolute configurations of all eight 3-butylhexahydrophtbalide stereoisomers are unambiguously concluded from the NOE-experi-ments in connection with the determination of the absolute configuration at C-3.     

Structural and mechanistic analysis of protein interactions in module 3 of the 6-deoxyerythronolide B synthase

We report the 2.6 A X-ray crystal structure of a 190 kDa homodimeric fragment from module 3 of the 6-deoxyerthronolide B synthase covalently bound to the inhibitor cerulenin. The structure shows two well-organized interdomain linker regions in addition to the full-length ketosynthase (KS) and acyltransferase (AT) domains. Analysis of the substrate-binding site of the KS domain suggests that a loop region at the homodimer interface influences KS substrate specificity. We also describe a model for the interaction of the catalytic domains with the acyl carrier protein (ACP) domain. The ACP is proposed to dock within a deep cleft between the KS and AT domains, with interactions that span both the KS homodimer and AT domain. In conjunction with other recent data, our results provide atomic resolution pictures of several catalytically relevant protein interactions in this remarkable family of modular megasynthases.     

Structure elucidation from 2D NMR spectra using the StrucEluc expert system: detection and removal of contradictions in the data

The elucidation of chemical structures from 2D NMR data commonly utilizes a combination of COSY, HMQC/HSQC, and HMBC data. Generally COSY connectivities are assumed to mostly describe the separation of protons that are separated by 1 skeletal bond (3JHH), while HMBC connectivities represent protons separated from carbon atoms by 1 to 2 skeletal bonds (2JCH and 3JCH). Obviously COSY and HMBC connectivities of lengths greater than those described have been detected. Though experimental techniques have recently been described to aid in the identification of the nature of the couplings the detection of whether a coupling is 2-bond or greater still remains a challenge in most laboratories. In the StrucEluc software system the common lengths of the connectivities, 1-bond for COSY and 1- or 2-bond for HMBC, derived from 2D NMR data are set as the default. Therefore, in the presence of any extended connectivities contradictions can appear in the 2D NMR data. In this article, algorithmic methods for the detection and removal of contradictions in 2D NMR data that have been developed in support of StrucEluc are described. The methods are based on the analysis of molecular connectivity diagrams, MCDs. These methods have been implemented in the StrucEluc system and tested by solving 50 structural problems with 2D NMR spectral data containing contradictions. The presence of contradictions was detected by the algorithm in 90% of the cases, and the contradictions were automatically removed in approximately 50% of the problems. A method of "fuzzy" structure generation in the presence of contradictions has been suggested and successfully tested in this work. This work will demonstrate examples of the application of developed methods to a number of structural problems.     

Proximity effect in the 13C NMR spectra of alkylpyridines: An aid in structure elucidation

The structures of seven polysubstituted alkylpyridines, recently isolated from coal tar, were elucidated using their ¹³C NMR spectra. For tri- and tetra-substituted derivatives the correct isomeric structure was found from their conformity with the proximity effect, i.e. the deviations from additivity when calculating chemical shifts from substituent increments (SCS) for sterically crowded molecules. This effect manifests itself both on the ring and on the alkyl carbon signals, and in most cases shifts their position upfield.     

Production of microfibrillated cellulose from unbleached kraft pulp of Kenaf and Scotch Pine and its effect on the properties of hardwood kraft: microfibrillated cellulose paper

This work investigated the effect of using Kenaf bast fibre kraft pulps compared to Scotch Pine kraft pulps for producing microfibrillated cellulose (MFC) and its employment for improving mechanical and physical properties of handsheets made from unbleached kraft hardwood pulp. It was shown that MFC based on Kenaf fibres can be produced at higher consistencies [>5 % (w/w)] compared to when Scotch Pine is employed [≈2 % (w/w)] as raw material. The possibility of using a higher consistency when processing Kenaf is beneficial for the processing in microfluidizers. The rheological properties of the products were shown to be consistent with what is known for MFC-based systems. The studies indicate that the mechanical properties of handsheets from unbleached kraft hardwood pulp can be improved by replacing part of the unbleached kraft hardwood pulp fibres with either unbleached kraft Kenaf pulp or unbleached Scotch Pine kraft pulp. However, the same levels of improvements were obtained when using only a small amount [≈6 % (w/w)] of MFC based on Kenaf or Scotch Pine, when introduced into the system either as a dry strength additive or by coating pre-made handsheets. Finally, it was shown that the incorporation of MFC in handsheets decreases the air-permeability; this effect became amplified when the MFC was applied as a coating onto the handsheets.     

Removal of natural uranium from water produced in the oil industry using Algerian bentonite

Batch sorption experiments have been carried out to remove natural uranium (NORM) from water obtained together with crude oil and natural gas, using Algerian bentonites. The effect of some important factors such as S/L ratio, pH, initial concentration, particle size was evaluated and a kinetic study performed. The value of the distribution coefficient (K _d) at equilibrium for natural uranium varied from 30 to 600 cm³·g⁻¹ and 50 to 1100 cm³·g⁻¹ (∼10% margin error) using natural bentonite and drilling bentonite, respectively. The isotherms showed that the data are consistent with both Freundlich and Langmuir models.     

Formyl migration product of chanoclavine-I aldehyde in the presence of the old yellow enzyme FgaOx3 from Aspergillus fumigatus: a NMR structure elucidation

A previous study showed that together with the festuclavine synthase FgaFS, the old yellow enzyme FgaOx3 from Aspergillus fumigatus catalyzed the conversion of chanoclavine-I aldehyde to festuclavine in the biosynthesis of ergot alkaloids. In the absence of FgaFS, a mixture containing two compounds with a ratio of 7:3 was detected in the enzyme assay of FgaOx3. NMR experiments including (DQF)-COSY, HSQC, HMBC and NOESY identified their structures as E/Z isomers of N-methyl-N-[(5R,10R)-10-(2-oxo-propyl)-2,4,5,10-tetrahydrobenzo[cd]indol-5-yl]formamide and proved the migration of the formyl group at C-8 in chanoclavine I-aldehyde to N-6 in the identified products.     

Liphagal, a Selective inhibitor of PI3 kinase alpha isolated from the sponge akacoralliphaga: structure elucidation and biomimetic synthesis

[structure: see text] Liphagal (1), a selective inhibitor of PI3K alpha, has been isolated from the marine sponge Aka coralliphaga collected in Dominica. The "liphagane" meroterpenoid carbon skeleton of liphagal (1) is new. A biomimetic total synthesis has been used to confirm the constitution of liphagal (1) and support a proposed biogenesis.     

Characterization of the mechanical properties of cross-linked serum albumin microcapsules: effect of size and protein concentration

A microfluidic technique is used to characterize the mechanical behavior of capsules that are produced in a two-step process: first, an emulsification step to form droplets, followed by a cross-linking step to encapsulate the droplets within a thin membrane composed of cross-linked proteins. The objective is to study the influence of the capsule size and protein concentration on the membrane mechanical properties. The microcapsules are fabricated by cross-linking of human serum albumin (HSA) with concentrations from 15 to 35 % (w/v). A wide range of capsule radii (～40–450 μm) is obtained by varying the stirring speed in the emulsification step. For each stirring speed, a low threshold value in protein concentration is found, below which no coherent capsules could be produced. The smaller the stirring speed, the lower the concentration can be. Increasing the concentration from the threshold value and considering capsules of a given size, we show that the surface shear modulus of the membrane increases with the concentration following a sigmoidal curve. The increase in mechanical resistance reveals a higher degree of cross-linking in the membrane. Varying the stirring speed, we find that the surface shear modulus strongly increases with the capsule radius: its increase is two orders of magnitude larger than the increase in size for the capsules under consideration. It demonstrates that the cross-linking reaction is a function of the emulsion size distribution and that capsules produced in batch through emulsification processes inherently have a distribution in mechanical resistance.     

Substituted γ-lactones: On the structural elucidation of the reaction products from 4-aroyl-3-hydroxy-2(5H)-furanones and 1,2-diamines

The reaction pathway of 4-aroyl-3-hydroxy-2(5H)-furanones 1 with diamines depends on the nature of the amine as well as on the applied reaction conditions. Thus, the reaction of 1a-d with 5,6-diamino-1,3-dimethyluracil 5 led to the formation of two isomeric Schiff bases 7a-d and 8a-d . Conversely type 1 compounds reacted with 4,5-diaminopyrimidine 9 or 2,3-diaminopyridine 10 to form the mono acid-base adducts 11a and 11b respectively. When type 1 compounds were reacted with aliphatic diamines 13a-d or p-phenylenediamine and p-xylenediamine, respectively also an immediate formation of acid-base adducts 15a-f was observed. The reaction of a number of O-methylated type 1 compounds with 1,2-ethylenediamine afforded the novel seven-membered ring compounds 18a-d in good yields. The analogous reaction of O-alkylated 1a with o-phenylenediamine 2 or 2,3-diaminonaphthalene gave the expected tricyclic ring systems 19 or 20 .     

Assessing the effect of PLA,cellulose microfibers and CaCO3 on the properties of starch-based foams using a factorial design

The effect of polylactic acid (PLA), cellulose microfibers (CEL), and calcium carbonate (CaCO₃) on the equilibrium moisture content (EMC), density and flexural mechanical properties of starch-based bio-foams was studied using a full factorial design 2³. Also, a moisture aging study was carried out. The results show the three factors studied changed the bio-foams morphology, contribute to density increment, enhance dimensional stability and improve both the moisture resistance and the mechanical flexural properties. The moisture aging studies show that, although the flexural mechanical properties decrease with increasing humidity, the bio-foams exceed the mechanical properties of commercial expanded polystyrene (EPS) trays. These findings suggest the bio-composites could be used in regions where the humidity conditions are moderate to very humid, guaranteeing their dimensional stability and functional properties. Thus, these new bio-foams are an attractive and sustainable option to replace the non-biodegradable EPS commercial trays.     

Ligand effect in epoxidatidns by hydroperoxides using molybdenum catalyst: epox idation of 3-carene

Epoxidation of (+)-3-carene with pinane hydroperoxide in presence of various transition metal catalysts, has been evaluated as a preparative method for (+)-3α,4α-epoxycarane. Catalysts based on Mo(VI) were found to be most suitable. A distinct ligand effect was noted for this oxidation and a plausible rationale is put forward.     

Electrosynthesis of poly(3-methylthiophene) films: salt effect on the electrochemical and impedance properties

We studied the electrosynthesis of poly(3-methylthiophene) films in different electrolytes, i.e. 0.1?M quaternary ammonium salt solutions in acetonitrile. The analysis of the different results enabled us to explain the role of the cations and the anions of the electrolyte (doping agents) in the electrochemical synthesis and film properties. The films obtained with tetramethylammonium hexafluorophosphate (TMAPF₆) are more electroactive than those prepared using tetramethylammonium tetrafluoroborate (TMABF₄). This unexpected difference of behavior is due to the difference of hygroscopic properties of the two salts. We then characterized the films by electrochemical impedance spectroscopy. This technique, used to investigate the electrochemical properties, allowed us to virtually design identical electrical-equivalent circuits for the two types of film (prepared either with TMAPF₆ or with TMABF₄). We noted dissimilarities in the values of the components of those equivalent circuits. The different components were separately studied and their differences were explained by the salt effects.