Syntheses of 2,6-O-alkyl celluloses: influence of methyl and ethyl groups regioselectively introduced at O-2 and O-6 positions on their solubility

2,6-Di-O-ethyl (2E6E) (1), 2-O-ethyl-6-O-methyl (2E6M) (2), and 6-O-ethyl-2-O-methyl (6E2M) (3) celluloses were synthesized via ring-opening polymerization of glucose orthopivalate derivatives. 2,6-Di-O-methyl cellulose (2M6M) was insoluble in any common solvents, though it was not expected. On the other hand, cellulose derivative 1 (2E6E) was soluble in chloroform. Introduced positions of alkyl groups on cellulose affected solubilities of cellulose derivatives. Their solubility in chloroform decreased in the order: polymer 1 (2E6E) > polymer 2 (2E6M) > polymer 3 (6E2M) ≫ 2M6M.     

Synthesis and thermal properties of poly(methyl methacrylate)-graft-(cellobiosylamine-C15)

Model experiments for synthesis of a comb-shaped copolymer with cellulose side-chains were performed with cellobiose derivatives. A novel cellobiose monomer, N-(15-methacryloyloxypentadecanoyl)-2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-β-d-glucopyranosylamine (2) was prepared from heptaacetylcellobiosyl- amine. Homopolymerization of cellobiose monomer 2 and copolymerization of monomer 2 with methyl methacrylate (MMA) were performed using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator to obtain homopolymers 3-i (i = 1–4) and copolymers 3-i (i = 5–7), poly(methyl methacrylate)-graft-(heptaacetylcellobiosylamine-C15). The size exclusion chromatography—multi-angle laser light scattering (SEC-MALS) measurements revealed that comb-shaped homopolymers 3-i (i = 1–4) had more compact structures compared to copolymers 3-i (i = 5–7) at the same elution volume. Selective deacetylation of polymers 3-i (i = 1–7) gave novel cellobiose polymers 4-i (i = 1–7), poly(methyl methacrylate)-graft-(cellobiosylamine-C15). The amide linkages between cellobiose moiety and long-chain alkyl group, and the ester linkages between PMMA main-chain and long-chain alkyl group remained after deprotection. The differential scanning calorimetry (DSC) measurements revealed that the T _gs of the polymers 4-i (i = 1, 5, 6, 7) increased with increasing cellobiose composition in the polymers. It was indicated that cellobiose moieties of polymers 4-i (i = 1, 5, 6, 7) reduced the mobility of PMMA main-chain.     

Schrödinger’s Cat Meets Einstein’s Twins: A Superposition of Different Clock Times

The phenomenon of quantum superposition, which allows a physical system to exist in different states ‘simultaneously’, is one of the most bizarre notions in physics. Here we illustrate an even more bizarre example of it: a superposed state of a physical system consisting of both an ‘older’ version and a ‘younger’ version of that system. This can be accomplished by exploiting the special relativistic effect of time dilation featuring in Einstein’s famous twin paradox.     

Generalized phase space method in spin systems-spin coherent state representation

A generalized phase space method for spin operators is developed. With the use of a spin coherent state representation, mapping rules from spin operators onto ac-number space are established; simple formulas to calculate the mappedc-number functions are also derived. A product theorem, which gives a way of mapping a product of operators, is obtained in an intuitive form. This can be advantageously used to transform a Liouville equation into ac-number equation. As an illustrative example, the method is applied to the Heisenberg model of a magnet.     

Electrochemical determination of superoxide anions generated from a single neutrophil

The oxidation current of superoxide anions generated from a single neutrophil stimulated with Immunoglobulin G or phorbol myristate acetate has been determined with a carbon fibre microelectrode. Superoxide generation by a stimulated porcine or human neutrophil is initiated 1 min after the stimulation, reaches a maximum around 5 min later, and ends within 20 min. The current—time profiles thus determined agreed well to the time-course curves of superoxide generation obtained from conventional techniques using macroscopic numbers of cells. A sampled dc voltammogram of superoxide anions having a redox potential at around −0.3 V vs. Ag/AgCl was obtained using carbon fibre microelectrode.     

Block co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides as model compounds for methylcellulose and its dissolution/gelation behavior

A novel synthetic method for co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides was designed. These oligomers are of importance as model compounds for investigations on the dissolution behavior of commercial methylcelluloses. In this connection, insights into the chemical structure of ‘cross linking loci’ in the thermo reversible gelation of aqueous solution of methylcellulose are of particular significance. The synthetic procedure consists of glycosylation using glycosyl fluoride and oligomerization of sugar orthoester. Thus, phenyl 2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-1-thio-β-d-glucopyranoside (1) as a glycosyl acceptor was glycosylated with 4-O-acetyl-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranosyl fluoride (2) as a glycosyl donor converted to give a cellotetraose derivative (3). Both reactants have been prepared from commercially available cellobiose. After deacetylation of 3, 3-O-benzyl-6-O-pivaloyl-α-d-glucopyranose 1,2,4-orthopivalate (5) was reacted with 4-hydroxyl group at non-reducing-end of cellotetraose derivative (4) to give the block co-oligomer (6). After the deprotection of compound 6, tri-O-methylated-block-unmodified cello-oligosaccharides (18 and 18′) (DP = 4 − 8, DS = 2.79 − 1.38) were obtained, monitored by MALDI-TOF MS spectra. Chloroform-soluble methylated cellotetraose derivatives (18 and 18′ (DP=4, n=0), DS=2.57, and 2.79, respectively) were also soluble in the water solution of tri-O-methylated-block-unmodified cello-oligosaccharides (DP=4−8, DS=2.79−1.50). This fact indicated that hydrophobic methylated cello-tetraose derivatives were encapsulated within a micelle of amphiphlic tri-O-methylated-block-unmodified cello-oligosaccharides. It was found that solubilities of 18 and 18′ (DP=4−8, DS=2.79−1.38) in water and chloroform were obviously different in the mixtures, depending on their DP and DS values. The substituent distribution of the tri-O-methylated-block-unmodified cello-oligosaccharides along one molecule and between molecules plays an important role in its solubility in water and chloroform.     

Steady-state photocatalytic epoxidation of propene by O2 over V2O5SiO2 photocatalysts

A silica-supported, lowly loaded vanadium oxide (V2O5/SiO2) photocatalyst promotes the photocatalytic epoxidation of propene with O2 at steady state in a flow reactor system. Very little deep oxidation of propene into CO2 takes place over V2O5/SiO2, in contrast to the results obtained over a TiO2 photocatalyst in which total oxidation is the main path. With each loading, the sums of the selectivities into propene oxide (PO) and propanal (PA) at steady state were almost the same. The monomeric VO4 tetrahedral species dispersed on SiO2 yield PO under UV irradiation. The less dispersed vanadium oxide species on SiO2 promote the isomerization of PO into PA. We utilized a flow reactor system in which the short contact time reduced the isomerization and resultant decomposition of PO over the catalyst surface.     

Catalytic cyclopropanation of alkenes via (2-furyl)carbene complexes from 1-benzoyl-cis-1-buten-3-yne with transition metal compounds

The reaction of alkenes with conjugated ene-yne-ketones, such as 1-benzoyl-2-ethynylcycloalkenes, with a catalytic amount of Cr(CO)(5)(THF) gave 5-phenyl-2-furylcyclopropane derivatives in good yields. The key intermediate of this cyclopropanation is a (2-furyl)carbene complex generated by a nucleophilic attack of carbonyl oxygen to an internal alkyne carbon in pi-alkyne complex or sigma-vinyl cationic complex. A wide range of late transition metal compounds, such as [RuCl(2)(CO)(3)](2), [RhCl(cod)](2), [Rh(OAc)(2)](2), PdCl(2), and PtCl(2), also catalyzes the cyclopropanation of alkenes with ene-yne-ketones effectively. When the reactions were carried out with dienes as a carbene acceptor, the more substituted or more electron-rich alkene moiety was selectively cyclopropanated with the (2-furyl)carbenoid intermediate.     

Preparation and Characterization of 6-<Emphasis Type="Italic">O</Emphasis>-(4-stearyloxytrityl)Cellulose acetate Langmuir–Blodgett Films

Multilayer films of 2,3-di-O-acetyl-6-O-(4-stearyloxytrityl)cellulose (ASTC) were prepared and investigated. The fairly high surface pressure (π)–area (A) isotherms (36– 47 mN/m) suggest that the balky and hydrophobic trityl group contribute to form a condensed monolayer. The cellulose derivative formed a homogeneous monolayer at 10 mN/m. The monolayer on the water surface was transferred successfully at 10 mN/m onto various substrates by modifying the preparation methods, to form Z-type multilayer films. The ultraviolet–visible (UV–Vis) absorbance was independent of the number of layers, indicating that each layer is made of definite number of anhydroglucose unit (AGU). The monolayer thickness determined from atomic force microscope (AFM) and ellipsometry was calculated to be about 1.9 nm, suggesting that the long alkyl chain in the film has a so-called hairy-rod type structure. This is the first paper about the Z-type LB film prepared from cellulose derivatives having long mono-alkyl chain only at 6-O-position.     

An expeditious total synthesis of kalkitoxins: determination of the absolute stereostructure of natural kalkitoxin

Kalkitoxin, a potent neurotoxin isolated from the marine cyanobacteria Lyngbya majuscula, and its congeners (1-7) were efficiently synthesized utilizing Hruby's diastereoselective 1,4-addition and the Wipf's oxazoline-thiazoline conversion as key steps. These synthetic efforts in combination with spectral studies of natural kalkitoxin clearly determined the absolute stereostructure of kalkitoxin to be 7.