New insight into the mechanism of cellulose and callose biosynthesis: proteases may regulate callose biosynthesis upon wounding

Using a silver-enhanced, gold-secondary antibody immuno-location approach, we investigated the mechanisms for the switch from -1,4- to -1,3-glucan biosynthesis upon wounding. Antibodies against -1,4- and -1,3-glucan synthases were used to locate these synthases before and after wounding of Mung bean (Vigna radiata var Berken) hypocotyls. Within 5 min of wounding, -1,4-glucan synthases which were densely localized on plasma membranes adjacent to the secondary walls at the wound site completely disappeared, and -1,3-glucan synthases became labeled. The immuno-location of the -1,3-glucan synthases in the secondary walls was in good accordance with the region where the -1,4-glucan synthases were localized before wounding. Aniline blue was also utilized to visualize the deposition of callose upon wounding. Within 5 min of wounding, callose had accumulated in the corresponding region where the immuno-labeling of -1,3-glucan synthase was detected after wounding. The -1,3-glucan synthases were always detected from the sieve plate and plasmodesmata which are known to have constitutive synthesis of callose regardless of wounding. Secondary walls located distantly into the tissue away from the wound site were consistently labeled by the -1,4-glucan synthase antibody even after wounding. Immuno-blot analysis clearly shows that the levels of -1,4-glucan synthase subunit Ces A decreased dramatically within 30 min, whereas the -1,3-glucan synthase subunit CFL1 levels increased significantly after wounding. The intensity of labeling reached a maximum at the wound site, and gradually decreased in correspondence with the distance from the wound site. When a protease inhibitor cocktail was applied upon wounding, neither the -1,3-glucan synthase appeared nor callose was deposited during the first 5 min of wounding. On the other hand, -1,4-glucan synthase was detected at the wound site, implying that activation of -1,3-glucan synthase may rely on the degradation of the -1,4-glucan synthase. Our study may provide new insight into -glucan synthesis in higher plants.     

Preparation of polysiloxanes from silicic acid. V. Condensation of silicic acid butyl esters and formation of silica fiber from the ester solutions

The condensation of silicic acid butyl esters was investigated by gel permeation chromatographic (GPC) analysis. The results revealed that the condensation was greatly dependent on a degree of esterification of the esters. The ester with the lowest degree of esterification underwent condensation to form a highly polymerized ester. It was found that fibers could be drawn from the ester solution before gelation.     

New theoretical insight into the interactions and properties of formic acid: development of a quantum-based pair potential for formic acid

We performed ab initio quantum-chemical studies for the development of intra- and intermolecular interaction potentials for formic acid for use in molecular-dynamics simulations of formic acid molecular crystal. The formic acid structures considered in the ab initio studies include both the cis and trans monomers which are the conformers that have been postulated as part of chains constituting liquid and crystal phases under extreme conditions. Although the cis to trans transformation is not energetically favored, the trans isomer was found as a component of stable gas-phase species. Our decomposition scheme for the interaction energy indicates that the hydrogen-bonded complexes are dominated by the Hartree-Fock forces while parallel clusters are stabilized by the electron correlation energy. The calculated three-body and higher interactions are found to be negligible, thus rationalizing the development of an atom-atom pair potential for formic acid based on high-level ab initio calculations of small formic acid clusters. Here we present an atom-atom pair potential that includes both intra- and inter molecular degrees of freedom for formic acid. The newly developed pair potential is used to examine formic acid in the condensed phase via molecular-dynamics simulations. The isothermal compression under hydrostatic pressure obtained from molecular-dynamics simulations is in good agreement with experiment. Further, the calculated equilibrium melting temperature is found to be in good agreement with experiment.     

A stable intermediate: a new insight into the mechanism of Lewis acids-promoted formation of acylals from aldehydes

Treatment of m-nitrobenzaldehyde with acetic anhydride in the presence of Lewis acids, such as InBr₃, ZnBr₂, Cu(OTf)₂, gives a stable intermediate at the initial stage of reaction. Based on this new organic compound characterized by X-ray single crystal diffraction, a new mechanism for Lewis acids-promoted formation of acylals from aldehydes is proposed. Exchange reaction with different ratio of acetic anhydride to propionic anhydride, in the presence of Lewis acids, is studied.     

An insight into the process of tablet formation of microcrystalline cellulose

The present paper aims to show whether the shrinking of the microcrystalline cellulose (MCC) tablets can be derived from underlying processes and whether these processes can be visualized on a nanoscale level. Tableting of MCC was performed on an instrumented eccentric tableting machine to a maximum relative density (ρ_rel,max) of 0.90 of the tablets. The apparent density of the tablets was analyzed by helium pycnometry after tableting. The breaking surface of a MCC tablet was analyzed directly after tableting continuously by video in an environmental scanning electron microscope (ESEM) at constant humidity. Further the breaking surface was analyzed by transmission electron microscopy (TEM) after freeze fracturing. The results show that firstly apparent density by helium pycnometry increases after tableting and that secondly inside the tablet the fiber strength decreased while also the gaps between the fibers increased as was visualized by ESEM. Further the results by TEM indicate that the decrease in fiber strength is caused by a parallel orientation of the MCC microcrystals which is induced by a mechanical activation due to tableting. In conclusion the measured shrinking MCC tablets after tableting is caused by processes on a nanoscale level.     

Deeper insight into the mechanism of the reaction of photogenerated metallaketenes and imines

The reaction mechanism between Fischer carbene complexes and imines to produce beta-lactams has been studied by a combination of computational (DFT) and experimental methodologies. After the photogeneration of metalla-cyclopropanone species, the reaction initiates by 1,3-migration of the metal fragment from the former carbene carbon atom to the oxygen in the S o hypersurface. In spite of the endothermic nature of this rearrangement, it is biased by the more favorable HOMO(imine)-LUMO+1 interaction in the oxygen-coordinated ketene. This species reacts with the imine to yield metalla-zwitterions, which form the final products through a four electron conrotatory ring closure. The presence of the metal moiety during the whole reaction coordinate is demonstrated by the use of a chiral chromium(0) alkoxycarbene complex, which produces low but significant ee in the reaction with imines. The cis-trans stereoselection derives from the nucleophilic addition of the nitrogen atom of the imine to the oxygen-coordinated ketene, since there are no significant differences between the classical and the metallated processes in the electrocyclation step leading to the final 2-azetidinones.     

Preparation of polysiloxanes from silicic acid. VII. Effects of the degree of esterification and alkyl groups on condensations of silicic acid esters and formation of fibrous silica

Silicic acid esters were prepared by the reaction of the silicic acid in tetrahydrofuran with various alcohols such as such as methanol, ethanol, 2-propanol, 1-butanol, 2-methyl-2-propanol and 1-octanol, using an esterification apparatus designed especially to allow the preparation of silicic acid esters from alcohols with low boiling points or appreciable steric hindrance. With the intent of obtaining a spinnable ester solution by condensation of silicic acid esters, the effects of the degree of esterification (DE) and alkyl group on gel time and spinnability are investigated. An increase in the DE and the size of the alkyl group led to an increase in the gel time of the esters. Esters solutions with a good spinnability were prepared from n-butyl and isopropyl esters with DEs of 40–50%. In addition, the gel permeation chromatography of condensing esters with low DEs showed a rapid increase in molecular weight. The results showed that spinnability depended on DE and the ester's alkyl group. Fibers could be formed with length of about 10–100 cm from ethyl, isopropyl, and n-butyl esters with DEs 40–50% and with length of 10 cm from octyl ester with DE 26%.     

Polymerization and polymers of silicic acid

Linear relationships among molecular weight, polymerization time, and gelation for the condensation of any monomer, including those of unknown size and functionality, are developed and applied to data on soluble silicic acids generated from tetraethyl silicate and from sodium silicate. The results suggest the formation of monomers containing ca. 12–15 ? OSi units with functionality of ca. 2.05 that condense with a rate constant of ca. 10^?4 liter/mole sec and an activation energy of 40–70 kJ/mole. One model compatible with these characteristics and the stoichiometry involved is a ladder polymer ca. 3 ? SiO units wide. Polymer isolation was achieved by replacing residual ? OH with (CH₃)₃Sio? , as well as by freezing of of aqueous solutions, which yielded fibers under special conditions. Solutions of the uncapped and capped polymers and melts of the latter had low viscosity even for fractions with M?_n ～100,000. This implies a coiled or globular nature for the polymers, which is supported by their limited propensity for film and fiber formation. Attemps to improve this situation by copolymerization, the use of other capping agents, and by the polymerization of precapped monomers were unsuccessful.     

Further insight into the mechanism of poly(styrene‐co‐methyl methacrylate) microsphere formation

Polymeric microspheres have been used in a broad range of applications from chromatographic separation techniques to analysis of air flow over aerodynamic surfaces. The preparation of microspheres from many polymer families has consequently been extensively studied using a variety of synthetic approaches. Although there are a myriad of polymeric microsphere synthesis methods, free‐radical initiated emulsion polymerization is one of the most common techniques. In this work, poly(styrene‐co‐methyl methacrylate) microspheres were synthesized via surfactant‐free emulsion polymerization. The effects of co‐monomer composition and addition time on particle size distribution, particle formation, and particle morphology were investigated. Particles were characterized using dynamic light scattering and scanning electron microscopy to gain further insight into particle size and size distributions. Reaction kinetics were analyzed through consideration of characterization results. A particle formation mechanism for poly(styrene‐co‐methyl methacrylate) microspheres was proposed based on characterization results and known reaction kinetics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2249–2259     

Analogues of Zinpyr-1 provide insight into the mechanism of zinc sensing

Three compounds structurally related to the fluorescent zinc sensor Zinpyr-1 (ZP1) have been synthesized and characterized. In each of these ZinAlkylPyr (ZAP) analogues, an alkyl group (methyl, benzyl) replaces one of the metal-binding picolyl moieties in ZP1. The methyl-for-picolyl substitutions in ZAP1 and ZAP2 have a negligible effect on the optical spectrum of the fluorophore but elevate the quantum yields (Phi = 0.82 (ZAP1), 0.74 (ZAP2)) to values near that of Zn2+-saturated ZP1 (Phi = 0.92). The benzyl-for-picolyl substitution in ZAP3 similarly enhances the quantum yield (Phi = 0.52) relative to that of metal-free ZP1 (Phi = 0.38). As previously observed for methylated ZP1 sensors, methylation of the 6-position of the pyridyl ring diminishes the emission by lowering both the molar extinction coefficient and the quantum yield. Although these new ZAP compounds cannot detect Zn2+ fluorimetrically at neutral pH, complexation of Zn2+ does occur, as evidenced by sizable changes in the optical spectra. The ZAP1-3 probes can detect Zn2+ fluorimetrically at pH 9, indicating that proton-induced background emission obscures any Zn2+-induced fluorescence at pH 7. The tertiary amine groups in ZAP1-3 are less basic than those in ZP1, which implies that the additional pyridine rings are responsible for the emissive response to Zn2+ at pH 7.0.     

Preparation of polysiloxanes from silicic acid. IX. Partially silylated silicic acid and its spinnability

The reaction in different molar ratios of trimethylchlorosilane to silicic acid offered partially silylated silicic acids PSSX (X = OH) with various degrees of silylation. Esterification and acetylation of PSSX (X = OH) with 1-butanol or acetylchloride gave polysiloxanes PSSX (X = OBuⁿ and OCOCH₃). Some of them showed an excellent spinnability and provided a fine fiber with a length of about 250 cm. A fiber drawing test from concentrated PSSX solutions of various solvents revealed that spinnability markedly depended on the DS, functional group X of PSSX, and solvent. Spinnability may also be correlated to solubility parameter of PSSX and solvent.     

Rapid formation of metal-organic nano-capsules gives new insight into the self-assembly process

Metal-organic pyrogallol[4]arene nano-capsules, mixed pyrogallol[4]arene nano-capsules, and mixed metal analogues have been rapidly synthesised by addition of excess copper nitrate to a methanol solution of the corresponding macrocycle(s) (or gallium nano-capsules for the mixed metal system); improved solubility allows for thorough study and elucidation of the assembly process for these discrete metal-organic assemblies.     

New insight into the mechanism of methyl transfer during the biosynthesis of fosfomycin

Hydroxyethylphosphonate is a required intermediate in fosfomycin biosynthesis.     

Metal switch for amyloid formation: insight into the structure of the nucleus

The role of Zn2+ in pre-organizing Abeta(10-21) amyloid formation is shown to preferentially alter the relative rate of fibril nucleation and to have little influence on fibril propagation. Fibril morphology, as determined by small angle neutron scattering (SANS) and transmission electron microscopy (TEM), was unchanged in the presence and absence of Zn2+ in Abeta(10-21), as well as in a series of site-specifically altered variants. The metal-independence of the Abeta(10-21)H13Q peptide suggested that the increase in nucleation rate in Abeta(10-21) is due to Zn2+-mediated inter-sheet interactions, involving both histidine 13 and histidine 14.