scholarly journals Size-Exclusion Borane-Catalyzed Domino 1,3-Allylic/Reductive Ireland-Claisen Rearrangements: Impact of the Electronic and Structural Parameters on the 1,3-Allylic Shift Aptitude

2019 ◽  
Vol 25 (9) ◽  
pp. 2100-2100
Author(s):  
Dániel Fegyverneki ◽  
Natália Kolozsvári ◽  
Dániel Molnár ◽  
Orsolya Egyed ◽  
Tamás Holczbauer ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Size Exclusion ◽  
Claisen Rearrangements

Size-Exclusion Borane-Catalyzed Domino 1,3-Allylic/Reductive Ireland-Claisen Rearrangements: Impact of the Electronic and Structural Parameters on the 1,3-Allylic Shift Aptitude

2018 ◽  
Vol 25 (9) ◽  
pp. 2179-2183 ◽  
Author(s):  
Dániel Fegyverneki ◽  
Natália Kolozsvári ◽  
Dániel Molnár ◽  
Orsolya Egyed ◽  
Tamás Holczbauer ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Size Exclusion ◽  
Claisen Rearrangements

scholarly journals Molecular structure-property relations controlling mashing performance of amylases as a function of barley grain size

Amylase ◽  
2019 ◽  
Vol 3 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Wei Ping Quek ◽  
Wenwen Yu ◽  
Glen P. Fox ◽  
Robert G. Gilbert
Keyword(s):  
Molecular Structure ◽  
Grain Size ◽  
Structural Parameters ◽  
Barley Grain ◽  
Size Exclusion ◽  
Structure Property ◽  
Grain Sizes ◽  
Starch Fermentation ◽  
Underlying Mechanisms ◽  
The Impact

Abstract In brewing, amylases are key enzymes in hydrolyzing barley starch to sugars, which are utilized in fermentation to produce ethanol. Starch fermentation depends on sugars produced by amylases and starch molecular structure, both of which vary with barley grain size. Grain size is a major industrial specification for selecting barley for brewing. An in-depth study is given of how enzyme activity and starch structure vary with grain size, the impact of these factors on fermentable sugar production, and the underlying mechanisms. Micro-malting and mashing experiments were based on commercial methodologies. Starch molecular structural parameters were obtained using size-exclusion chromatography, and fitted using biosynthesis-based models. Correlation analysis using the resulting parameters showed larger grain sizes contained fewer long amylopectin chains, higher amylase activities and soluble protein level. Medium grain sizes released most sugars during mashing, because of higher starch utilization from the action of amylases, and shorter amylose chains. As starch is the substrate for amylase-driven fermentable sugars production, measuring its structure should be a prime indication for mashing performance, and should be used as an industry specification when selecting barley grains for brewing.

Preparation, characterisation and enantioselective separation properties of a chiral stationary phase based on silica beads coated with a 2-hydroxypropyl-β-cyclodextrin polymer

e-Polymers ◽  
2003 ◽  
Vol 3 (1) ◽  
Author(s):  
Benjamin Carbonnier ◽  
Ludovic Janus ◽  
André Deratani ◽  
Michel Morcellet
Keyword(s):  
Stationary Phase ◽  
Chiral Stationary Phase ◽  
Structural Parameters ◽  
Porous Silica ◽  
Nitrogen Adsorption ◽  
Water Soluble ◽  
Size Exclusion ◽  
Adsorption Method ◽  
Cyclodextrin Polymer ◽  
Silica Beads

Abstract This paper describes the preparation of a chiral stationary phase based on a 2-hydroxypropyl-β-cyclodextrin polymer coated on porous silica. This method requires first the synthesis of a water-soluble cyclodextrin polymer carried out by the polycondensation of 2-hydroxypropyl-β-cyclodextrin with epichlorohydrin under controlled conditions. In the second step, the obtained copolymer was immobilised onto the porous silica surface by physisorption. The macromolecular features of the copolymer were investigated by size exclusion chromatography coupled with a multiple angle laser-light scattering detector. The evolution of the structural parameters of the modified silica beads (specific surface area and pore size distribution) was determined using a nitrogen adsorption method. The enantio-separation capability of the coated silica phase was evaluated for different polycyclic molecules. It was found that the enantioselectivity was strongly influenced by the geometry and shape of the solutes under study and the presence of an acidic modifier in the mobile phase.

scholarly journals Statistical Copolymers of n-Butyl Vinyl Ether and 2-Chloroethyl Vinyl Ether via Metallocene-Mediated Cationic Polymerization. A Scaffold for the Synthesis of Graft Copolymers

Polymers ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1510 ◽  
Author(s):  
Zouganelis ◽  
Choinopoulos ◽  
Goulas ◽  
Pitsikalis
Keyword(s):  
Vinyl Ether ◽  
Graft Copolymers ◽  
Structural Parameters ◽  
Theoretical Models ◽  
Size Exclusion ◽  
Sequence Length ◽  
Reactivity Ratios ◽  
Scanning Calorimetry ◽  
Initiation System ◽  
Grafting From

The cationic statistical copolymerization of n-butyl (be) and 2-chloroethyl vinyl ether (CEVE), is efficiently conducted using bis(η5-cyclopentadienyl)dimethyl zirconium (Cp2ZrMe2) in combination with tetrakis(pentafluorophenyl)borate dimethylanilinum salt [B(C6F5)4]–[Me2NHPh]+, as an initiation system. The reactivity ratios are calculated using both linear graphical and non-linear methods. Structural parameters of the copolymers are obtained by calculating the dyad sequence fractions and the mean sequence length, which are derived using the monomer reactivity ratios. The glass transition temperatures (Tg) of the copolymers are measured by Differential Scanning Calorimetry (DSC), and the results are compared with predictions based on several theoretical models. The statistical copolymers are further employed as scaffolds for the synthesis of graft copolymers having poly(vinyl ether)s as a backbone and either poly(ε-caprolactone) (PCL) or poly(l-lactide) (PLLA) as side chains. Both the grafting “onto” and the grafting “from” methodologies are employed. The reaction sequence is monitored by Size Exclusion Chromatography (SEC), NMR and IR spectroscopies. The advantages and limitations of each approach are thoroughly examined.

Crystal structures of plant inorganic pyrophosphatase, an enzyme with a moonlighting autoproteolytic activity

2019 ◽  
Vol 476 (16) ◽  
pp. 2297-2319 ◽  
Author(s):  
Marta Grzechowiak ◽  
Milosz Ruszkowski ◽  
Joanna Sliwiak ◽  
Kamil Szpotkowski ◽  
Michal Sikorski ◽  
...  
Keyword(s):  
Site Directed Mutagenesis ◽  
Size Exclusion ◽  
Inorganic Pyrophosphatase ◽  
Prolonged Storage ◽  
Mitochondrial Targeting ◽  
Cleavage Rate ◽  
Inorganic Pyrophosphate ◽  
Putative Signal Peptide ◽  
Targeting Peptide

Abstract Inorganic pyrophosphatases (PPases, EC 3.6.1.1), which hydrolyze inorganic pyrophosphate to phosphate in the presence of divalent metal cations, play a key role in maintaining phosphorus homeostasis in cells. DNA coding inorganic pyrophosphatases from Arabidopsis thaliana (AtPPA1) and Medicago truncatula (MtPPA1) were cloned into a bacterial expression vector and the proteins were produced in Escherichia coli cells and crystallized. In terms of their subunit fold, AtPPA1 and MtPPA1 are reminiscent of other members of Family I soluble pyrophosphatases from bacteria and yeast. Like their bacterial orthologs, both plant PPases form hexamers, as confirmed in solution by multi-angle light scattering and size-exclusion chromatography. This is in contrast with the fungal counterparts, which are dimeric. Unexpectedly, the crystallized AtPPA1 and MtPPA1 proteins lack ∼30 amino acid residues at their N-termini, as independently confirmed by chemical sequencing. In vitro, self-cleavage of the recombinant proteins is observed after prolonged storage or during crystallization. The cleaved fragment corresponds to a putative signal peptide of mitochondrial targeting, with a predicted cleavage site at Val31–Ala32. Site-directed mutagenesis shows that mutations of the key active site Asp residues dramatically reduce the cleavage rate, which suggests a moonlighting proteolytic activity. Moreover, the discovery of autoproteolytic cleavage of a mitochondrial targeting peptide would change our perception of this signaling process.

Optimal design of a high homogeneous and small-size shim coil for atomic spin gyroscope based on 0-1 linear programming

2020 ◽  
Vol 64 (1-4) ◽  
pp. 165-172
Author(s):  
Dongge Deng ◽  
Mingzhi Zhu ◽  
Qiang Shu ◽  
Baoxu Wang ◽  
Fei Yang
Keyword(s):  
Linear Programming ◽  
Power Consumption ◽  
Low Power ◽  
Optimization Design ◽  
Structural Parameters ◽  
Axial Position ◽  
Low Power Consumption ◽  
Optimal Method ◽  
Atomic Spin ◽  
Shim Coil

It is necessary to develop a high homogeneous, low power consumption, high frequency and small-size shim coil for high precision and low-cost atomic spin gyroscope (ASG). To provide the shim coil, a multi-objective optimization design method is proposed. All structural parameters including the wire diameter are optimized. In addition to the homogeneity, the size of optimized coil, especially the axial position and winding number, is restricted to develop the small-size shim coil with low power consumption. The 0-1 linear programming is adopted in the optimal model to conveniently describe winding distributions. The branch and bound algorithm is used to solve this model. Theoretical optimization results show that the homogeneity of the optimized shim coil is several orders of magnitudes better than the same-size solenoid. A simulation experiment is also conducted. Experimental results show that optimization results are verified, and power consumption of the optimized coil is about half of the solenoid when providing the same uniform magnetic field. This indicates that the proposed optimal method is feasible to develop shim coil for ASG.

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