The study of cell wall structure and cellulose–cellulase interactions through fluorescence microscopy

The efficient decomposition of biomass into carbohydrates for the sustainable generation of biofuels has become the focus of much research. Yet, limited understanding exists on how the enzymes that catalyze the biochemical conversion of biomass, such as cellulases, interact with cellulose microfibrils and how cellulose structure is changed by cellulolytic enzymes. This has spurred the application of high-resolution imaging techniques, such as atomic force microscopy or fluorescence microscopy, to visualize the biomolecular interactions and structural changes that occur at the micro/nanoscale. In particular, fluorescence microscopy offers advantages such as high sensitivity and the ability to monitor species under biologically relevant conditions. Furthermore, the introduction of techniques, such as single molecule or super-resolution fluorescence microscopy, has allowed imaging biomolecules and macromolecular structures with near molecular resolution. These advantages make fluorescence microscopy ideally suited for the study of cell wall structure and cellulose–cellulase interactions. The application of fluorescence microscopy has already yielded key insights into the arrangement of structural polysaccharides in the plant cell wall, the reversibility and binding kinetics of cellulases, their molecular motion on crystalline cellulose, and the structural changes that occur as cellulose is depolymerized by cellulases. Yet, the application of fluorescence to study cellulose–cellulase interactions remains limited. This review aims at (1) providing an overview of fluorescence microscopy techniques suitable for the study of cellulose–cellulase interactions; (2) the applications of these techniques to date and the key insights obtained; and (3) the opportunities for future studies of the interaction of cell wall degrading enzymes with cellulosic materials.     

Structures of silylenoids and effects of metallic and haloid atoms on their stability

The structural characteristics of silylenoids, H2SiMX, where M = Li or Na and X = F or Cl, have been studied by ab initio calculations. H2SiMX can be represented as adducts of silylene H2Si with alkali metal halogenides, MX. The associative energies at different calculational levels of various structures of H2SiMX are given. Effects of metallic and haloid atoms on the stability of various structures of H2SiMX are also discussed in this paper.     

Qualitatively graph-theoretical study on stability and formation of fullerenes and nanotubes

Kekule structures of different carbon species have been determined. On the basis of Kekule structure and C-C bond counts as well as the surface curvature, stability of diverse carbon species, driving force for curling of graphite fragments and formation of fullerenes and nanotubes, have been discussed. Curling of graphite flat fragments, end-capping of nanotubes, and closure of curved structures are driven by a tremendous increase in Kekule structures as terminal carbon atoms couple their dangling bonds into C-C o bonds. The increasing tendency becomes particularly striking for large cages and nanotubes. Resonance among numerous Kekule structures will stabilize the curved structure and dominate formation of closed carbon species. For similar carbon cages with comparable Kekule structure counts in magnitude, the surface curvature of carbon cages, as a measure for the strain energy, also plays an important role in determining their most stable forms.     

Indole-based distinctive chemosensors for ‘naked-eye’ detection of CN and HSO4−, associated with hydrogen-bonded complex and their DFT study

Colorimetric detection of anions (HSO₄^? and CN^?) was achieved via analyte triggered colour changing of the dipodal and tripodal sensors in CH₃CN–H₂O (1:1). The sensors exhibited very sharp visual colour changes and fluorescence quenching–enhancing effect upon addition of the HSO₄^? and CN^?. The large downfield shift of the NH proton signals in ¹H-NMR complexation studies and quantum chemical DFT calculations proved the formation of hydrogen-bonded complexes where no proton transfer mechanism was found.     

Construction and visible-light photocatalytic performance of carboxyethyltin/transition metal–functionalized wheel-like tungstophosphates

The wheel-like tungstophosphate ([P₈W₄₈O₁₈₄]⁴⁰⁻, abbreviated as P₈W₄₈) reacted with estertin trichloride (Cl₃SnRCH₃, R = CH₂CH₂COO) in aqueous solution, resulting in a new wheel-like polyoxometalate (POM) containing six SnR fragments, formulated as K₆Na₂₄[{(SnR(H₂O))₂(μ-OH)(μ-SnR(H₂O))}₂(P₈W₄₈O₁₈₄)]·59H₂O (abbreviated as Sn ₆ - P ₈ W ₄₈ ). Based on this, the transition metal (TM) was further introduced into the Sn ₆ - P ₈ W ₄₈ system, self-assembling three other wheel-like POMs with the general formula K_xNa_yH_{26 − x − y}[{TM(H₂O)₃(SnR(H₂O))₂(μ-OH)(μ-SnR(H₂O))}₂(P₈W₄₈O₁₈₄)]·nH₂O (abbreviated as TM ₂ - Sn ₆ - P ₈ W ₄₈ , TM = Mn, Co, Ni; x = 0, 1, 2; y = 19, 22, 15; n = 72, 85, 75, respectively). The structures of these new organometal and TM co-modified compounds were characterized using infrared, UV–Vis. spectroscopy, ¹¹⁹Sn NMR, and powder- and single-crystal X-ray diffraction analysis. The estertin precursor hydrolyzed into carboxyethyltin (SnR) fragment in these crystalline POM materials, which can improve their adhesion to titanium dioxide (TiO₂). The photocatalytic performance of Sn ₆ - P ₈ W ₄₈ , TM ₂ - Sn ₆ - P ₈ W ₄₈ , and their TiO₂ composites was examined by studying the degradation of a model dye pollutant Rhodamine B (RhB) under visible-light irradiation without adding hydrogen peroxide (H₂O₂), and the photocatalytic mechanism was also discussed. The experimental results show that the title compounds exhibit a quicker and better photocatalytic degradation effect on RhB compared with their parent compound, indicating that the introduced organotin groups play a significant role. Moreover, it was found that H₂O₂ was produced after illumination pretreatment for POM solution, promoting the photocatalytic reaction.     

Physicochemical characterization and molecular modeling study of host–guest systems of aripiprazole and functionalized cyclodextrins

Journal of Thermal Analysis and Calorimetry - Aripiprazole (ARP), an innovative atypical antipsychotic drug, exhibits very low aqueous solubility, affecting its dissolution and absorption and high...     

Preparation of conjugates of α-amylase with a protease inhibitor and their stability

A method for obtaining conjugates of -amylase with a trypsin inhibitor and separating them into fractions has been developed. Two fractions have been obtained—thermostable and thermolabile. The thermostable fraction retained about 80% of its amylase activity after incubation at 50°C for 2 h, with activation of the enzyme during the first 30 min. In the presence of trypsin the conjugated enzyme, retained 91% of its initial activity after incubation for 1 h, although the activity of the native enzyme fell to 35% under the same conditions.Mirzo Ulugbek [Ulugh-Beg] Tashkent State University. Translated from Khimiya Prirodnykh Soedimenii, No. 2, pp. 201–204, Marhc–April, 1998.     

Synthesis of Z-β-siloxyacrylonitriles and study of their dienophilic properties

A general method for the synthesis of Z-β-siloxyacrylonitriles from isoxazoles is reported. Their dienophilic activity is also described.     

Interactions between anionic mixed micelles and α-cyclodextrin and their inclusion complexes: conductivity, NMR and fluorescence study

Mixed micelle formation of anionic surfactants sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied in water and in 5, 10, and 15 mM concentrations of α-cyclodextrin (α-CD) over mole fraction range of α _SDS from 0 to 1. From the conductivity curves, the critical micellar concentration (CMC) for the pure and binary mixtures were evaluated. The degree of counterion association (χ) or counterion dissociation (δ), the equivalent ionic conductivities of the monomeric species (Λ _m), the associated species (Λ _assc), and the micelle (Λ _mic) were evaluated from the slope of the conductivity vs concentration plots. The CMC values have been used to calculate the thermodynamic parameters such as the standard free energy of micelle formation and a transfer of standard free energy of micelle from the aqueous medium to additive medium computed. The apparent CMC of the surfactants varies linearly with α-CD concentrations. From the dependence of CMC of the surfactants on α-CD concentration, we are able to determine the association constant (K) of surfactant-α-CD inclusion complexes assuming 1:1 stoichiometry. Mixed micelle behaves ideally in the pure water as well as at the different concentrations of α-CD, which was evaluated by using the Clint equation, the regular solution approximation, and Motomura’s formulation. Self-diffusion coefficients of the micelle increased upon the induction of SDS into the micelle. 2D-rotating frame Overhauser effect spectroscopy spectra of SDS and SLAS were recorded in the presence of α-CD to investigate the interaction between H-atoms of the alkyl chain of the surfactants and H-atoms of the hydrophobic cavity of α-CD indicating multiple complexation. The fluorescence anisotropy of rhodamine B has been measured to observe the structural behavior of mixed micelle.     

Improvement of UV stability and mechanical properties of biopolyesters through the addition of β-carotene

β-carotene, the most abundant carotenoid in nature and a natural antioxidant, has been added at a concentration of 2 × 10⁻⁴ g per mL of polymer film forming solution to three biopolyester matrices, poly(lactic acid) (PLA), polycaprolactone (PCL) and polyhydroxybutyrate-co-valerate (PHBV). The dispersion and stability of the antioxidant within the films was studied using confocal Raman imaging spectroscopy, colorimetry and UV/visible spectrophotometry. The films were characterized in terms of thermal and mechanical properties in comparison with control films without β-carotene. Addition of β-carotene to the three biopolyesters studied resulted in significant increases in the deformation at break and lower Young modulus. This antioxidant is thought to act as a plasticizer in the biopolyesters, thus increasing their free volume and causing a change in their thermal properties. Moreover, when exposed to UV light the mechanical properties of the films with β-carotene were less affected displaying, in general, higher modulus and similar ultimate tensile strength while keeping the films more ductile than the pure films. Therefore, β-carotene can be potentially used as a natural additive to increase the UV stability of the biopolyesters.     

Synthesis and characterization of allyl functionalized poly(α-hydroxy)acids and their further dihydroxylation and epoxidation

In this study, the synthesis of an allyl functionalized aliphatic polyester and the subsequent oxidation of the double bonds was investigated. Allylglycolide (3-allyl-1,4-dioxane-2,5-dione) was synthesized and its homopolymer and copolymers with l-lactide were prepared by ring opening polymerization in the melt using benzyl alcohol and SnOct₂ as initiator and catalyst, respectively. The polymerizations proceeded with high yields and conversions and good control over molecular weights and copolymer composition. The obtained polymers were amorphous materials and their T_g increased with increasing lactide content. Dihydroxylation of the double bonds in poly(allylglycolide) and copolymers with lactide was attempted with osmiumtetroxide/4-methylmorpholine-4-oxide (OsO₄/NMO). However, particularly the polymers rich in allylglycolide could not be isolated after dihydroxylation because they likely underwent degradation during workup. Optimizing the reaction conditions gave partially dihydroxylated copolymers only for copolymers with high lactide content (50 and 75 mol%) with a conversion of the double bonds of only ∼60%. GPC analysis showed that chain scission had occurred during the dihydroxylation reaction and/or workup.The allyl groups of poly(allylglycolide) homopolymers and copolymers with lactide were oxidized using m-chloroperoxy benzoic acid (mCPBA) to yield the corresponding epoxidated polymers in high yield. NMR analysis showed that conversion of the double bonds to epoxides was quantitative, whereas GPC analysis showed that the epoxidation was not associated with chain scission. All epoxidated polymers were amorphous materials with a T_g depending on the composition.     

Understanding the extraction mechanism,radiolytic stability and stripping behavior of thorium by ionic liquid based solvent systems: evidence of ‘ion-exchange’ and ‘solvation’ mechanism

The extraction efficiency for thorium followed the trend: Cyanex-923 > Cyanex-272 > DHOA > TBP. In case of TBP and DHOA the extraction proceeded via ‘solvation mechanism’ through Th(NO₃)₄·2L, while for Cyanex-923 and Cyanex-272 it proceeded via ‘ion exchange’ mechanism through (Th(NO₃)₂·2L)²⁺. The extraction process followed slower kinetics while change in Gibb’s energy revealed the spontaneity of the process. These ionic liquid based systems were found to be radiolytically stable, highly efficient and selective for Th. Oxalic acid was found to be suitable for almost quantitative stripping of Th from extracted ionic liquid phase.     

A biacylhydrazone-based chemosensor for fluorescence ‘turn-on’ detection of Al3+ with high selectivity and sensitivity

A simple Al³⁺ fluorescent chemosensor (1) based on diacylhydrazone has been designed and synthesized by the condensation reaction of 2-hydroxy naphthaldehyde and metaphthalic hydrazide. The chemosensor 1 displays a specific and sensitive response to Al³⁺ over other cations in DMSO solution. Upon the addition of DMSO solution of Al³⁺, the sensor 1 shows an immediate fluorescence ‘turn-on’ response and emitting strong blue emission with visible color change from colorless to green. The fluorescence quantum yield enhanced from 7.24% to 48.68%. Meanwhile, the fluorescence and UV absorption spectra detection limits of the chemosensor 1 for Al³⁺ were 2.0 × 10^?7 M and 5.6 × 10^?7 M respectively, indicating the high sensitivity of 1 to Al³⁺. Furthermore, test strips based on 1 were fabricated, which could be used as a convenient test kit for the detection of Al³⁺ and an efficient Al³⁺ controlled fluorescent security display materials.     

Synthesis of novel modified β-cyclodextrins and their fluorescence studies of inclusion complexation with Rhodamine B

Three novel β-cyclodextrin derivatives have been synthesized and their inclusion complexation behavior with Rhodamine B (RhB) was investigated by the fluorescence spectroscopy.     

Synthesis of conducting polyaniline—polyanion interpolymer complexes and study of their composition and properties

The polymerization of aniline in the presence of poly(4-styrenesulfonic acid) and poly(2-acryla-mido-2-methyl-1-propanesulfonic acid) results in interpolyelectrolyte complexes with a composition and a dispersion stability depending on the aniline-to-polyanion ratio in the initial reaction mixture. As opposed to polymerization mediated by poly(4-styrenesulfonic acid), the template polymerization of aniline conducted in the presence of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) leads to the structural template effect that manifests itself as the formation of polyaniline containing 1,2- and 1,4-substituted benzene rings. It is found that the electron conductivity of the polyaniline-polyanion interpolyelectrolyte complexes depends not only on the content but also on the nature of the used polyacid and proves to be higher in the case of stoichiometric interpolyelectrolyte complexes formed in the presence of poly(4-styrenesulfonic acid).     

Divergent Construction of Diverse Scaffolds through Catalyst-Controlled C−H Activation Cascades of Quinazolinones and Cyclopropenones

A transition-metal-catalyzed C−H activation cascade strategy to rapidly construct diverse quinazolinone derivatives in a one-pot manner is reported. The catalysts play an important role in the different transformations. Additionally, the procedure is scalable, proceeds with high efficiency and good chemo-/regio-selectivity, and tolerates a range of functional groups.     

A theoretical study of the stability and electronic properties of GenRu (n = 2–10) clusters and their sensitivity toward SO2 adsorption

Structural Chemistry - In this work, the stability and electronic properties of the Ru-doped germanium clusters were investigated with DFT calculations at the TPSS/SDD level. The adsorption of the...     

Synthesis of functionalized pyrroles and fused pyrroles through intermolecular [3 + 2] cycloaddition reaction

A facile and efficient synthesis of pyrrole and pyrrole-fused heterocyclic compounds has been demonstrated. The current protocol involves the in situ generation of azomethine ylides which undergoes intermolecular cycloaddition reaction and subsequent treatment with DDQ provides the pyrrole and fused heterocyclic compounds in good yields.     

‘Apples’ and ‘oranges’: comparing the structural aspects of biomineral- and ice-interaction proteins

The title of this review describes structural comparisons of protein classes whose task is to identify and interact with biological solids (minerals and ice). To date, the following trends have been noted: (1) biomineral-interaction proteins typically adopt unfolded, open conformations, and, where mineral binding motifs have been identified, these sequences exhibit structural trends towards extended, random coil, or other unstable secondary structures; (2) ice-interaction proteins typically adopt folded structures, featuring stable secondary structure preferences (α-helix, β-sheet, β-helix, etc.) and stable, planar ice binding motifs that exploit hydrophobicity and van der Waals’ interactions for ice binding.