Solvent Influence on Cellulose 1,4‐β‐Glycosidic Bond Cleavage: A Molecular Dynamics and Metadynamics Study

We explore the influence of two solvents, namely water and the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EmimAc), on the conformations of two cellulose models (cellobiose and a chain of 40 glucose units) and the solvent impact on glycosidic bond cleavage by acid hydrolysis by using molecular dynamics and metadynamics simulations. We investigate the rotation around the glycosidic bond and ring puckering, as well as the anomeric effect and hydrogen bonds, in order to gauge the effect on the hydrolysis mechanism. We find that EmimAc eases hydrolysis through stronger solvent–cellulose interactions, which break structural and electronic barriers to hydrolysis. Our results indicate that hydrolysis in cellulose chains should start from the ends and not in the centre of the chain, which is less accessible to solvent.     

Mass spectrometric study of glucose and cellobiose produced during enzymatic hydrolysis of α‐cellulose extracted from oak late‐wood annual rings

We present the first results concerning interannual variations in concentrations of glucose and cellobiose, obtained through enzymatic hydrolysis of α‐cellulose. The α‐cellulose was extracted from late‐wood of oak. The tree‐ring chronologies, wood components and their physical and chemical properties provide information about the ecosystem in which the tree grew, and thus information regarding climate variability and the impact of human activity in the past. The large molecular size and insolubility make it difficult to determine precisely the chemical and physical properties of the intact cellulose polymer. Enzymatic hydrolysis is the principal method of degradation of cellulose. In this study the feasibility has been examined of characterizing α‐cellulose through analysis by mass spectrometry (MS) of the degradation products from hydrolysis. Degradation of α‐cellulose was possible without using alkaline or acid buffers. Analysis by MS provided the opportunity to obtain information on the biodegradation of saccharides. The presence of cellobiose and glucose in the degradation product was evidenced by the mass spectra. We have compared the abundances of these glucose and cellobiose ions with carbon isotope ratios, the efficiency of extraction of α‐cellulose from the wood and tree‐ring width indices. The challenge is to establish, with respect to climate changes and environmental conditions, the significance of the variations from one year to another in the observed abundances of glucose and cellobiose ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of 2‐Hydroxy‐1,4‐oxazin‐3‐ones through Ring Transformation of 3‐Hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams and a Study of Their Reactivity

The reactivity of 3‐hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams with regard to the oxidant sodium periodate was evaluated, unexpectedly resulting in the exclusive formation of new 2‐hydroxy‐1,4‐oxazin‐3‐ones through a C3? C4 bond cleavage of the intermediate 4‐formyl‐3‐hydroxy‐β‐lactams followed by a ring expansion. This peculiar transformation stands in sharp contrast with the known NaIO₄‐mediated oxidation of 3‐alkoxy‐ and 3‐phenoxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams, which exclusively leads to the corresponding 4‐formyl‐β‐lactams without a subsequent ring enlargement. In addition, this new class of functionalized oxazin‐3‐ones was further evaluated for its potential use as building blocks in the synthesis of a variety of differently substituted oxazin‐3‐ones, morpholin‐3‐ones and pyrazinones. Furthermore, additional insights into the mechanism and the factors governing this new ring‐expansion reaction were provided by means of density functional theory calculations.     

Glycosidic linkage,N‐acetyl side‐chain,and other structural properties of methyl 2‐acetamido‐2‐deoxy‐β‐d‐glucopyranosyl‐(1→4)‐β‐d‐mannopyranoside monohydrate and related compounds

The crystal structure of methyl 2‐acetamido‐2‐deoxy‐β‐d ‐glycopyranosyl‐(1→4)‐β‐d ‐mannopyranoside monohydrate, C₁₅H₂₇NO₁₁·H₂O, was determined and its structural properties compared to those in a set of mono‐ and disaccharides bearing N‐acetyl side‐chains in βGlcNAc aldohexopyranosyl rings. Valence bond angles and torsion angles in these side chains are relatively uniform, but C—N (amide) and C—O (carbonyl) bond lengths depend on the state of hydrogen bonding to the carbonyl O atom and N—H hydrogen. Relative to N‐acetyl side chains devoid of hydrogen bonding, those in which the carbonyl O atom serves as a hydrogen‐bond acceptor display elongated C—O and shortened C—N bonds. This behavior is reproduced by density functional theory (DFT) calculations, indicating that the relative contributions of amide resonance forms to experimental C—N and C—O bond lengths depend on the solvation state, leading to expectations that activation barriers to amide cis–trans isomerization will depend on the polarity of the environment. DFT calculations also revealed useful predictive information on the dependencies of inter‐residue hydrogen bonding and some bond angles in or proximal to β‐(1→4) O‐glycosidic linkages on linkage torsion angles ? and ψ. Hypersurfaces correlating ? and ψ with the linkage C—O—C bond angle and total energy are sufficiently similar to render the former a proxy of the latter.     

Hydrogen bonding and π–π interactions in 1‐benzofuran‐2,3‐dicarboxylic acid and its 1:1 cocrystals with pyridine,phenazine and 1,4‐phenylenediamine

The structure of 1‐benzofuran‐2,3‐dicarboxylic acid (BFDC), C₁₀H₆O₅, (I), exhibits an intramolecular hydrogen bond between one –COOH group and the other, while the second carboxyl function is involved in intermolecular hydrogen bonding to neighbouring species. The latter results in the formation of flat one‐dimensional hydrogen‐bonded chains in the crystal structure, which are π–π stacked along the normal to the plane of the molecular framework, forming a layered structure. 1:1 Cocrystallization of BFDC with pyridine, phenazine and 1,4‐phenylenediamine is associated with H‐atom transfer from BFDC to the base and charge‐assisted hydrogen bonding between the BFDC⁻ monoanion and the corresponding ammonium species, while preserving, in all cases, the intramolecular hydrogen bond between the carboxyl and carboxylate functions. The pyridinium 2‐carboxylato‐1‐benzofuran‐3‐carboxylic acid, C₅H₆N⁺·C₁₀H₅O₅⁻, (II), and phenazinium 3‐carboxylato‐1‐benzofuran‐2‐carboxylic acid, C₁₂H₉N₂⁺·C₁₀H₅O₅⁻, (III), adducts form discrete hydrogen‐bonded ion‐pair entities. In the corresponding crystal structures, the two components are arranged in either segregated or mixed π–π stacks, respectively. On the other hand, the structure of 4‐aminoanilinium 2‐carboxylato‐1‐benzofuran‐3‐carboxylic acid, C₆H₉N₂⁺·C₁₀H₅O₅⁻, (IV), exhibits an intermolecular hydrogen‐bonding network with three‐dimensional connectivity. Moreover, this fourth structure exhibits induction of supramolecular chirality by the extended hydrogen bonding, leading to a helical arrangement of the interacting moieties around 2₁ screw axes. The significance of this study is that it presents the first crystallographic characterization of pure BFDC, and manifestation of its cocrystallization with a variety of weakly basic amine molecules. It confirms the tendency of BFDC to preserve its intramolecular hydrogen bond and to prefer a monoanionic form in supramolecular association with other components. The aromaticity of the flat benzofuran residue plays an important role in directing either homo‐ or heteromolecular π–π stacking in the first three structures, while the occurrence of a chiral architecture directed by multiple hydrogen bonding is the dominant feature in the fourth.     

Dimethyl 6‐[1,2‐bis(methoxycarbonyl)‐2‐(triphenyl‐λ5‐phosphanylidene)ethylideneamino]‐2‐methylsulfanyl‐3,4‐pyridinedicarboxylate forms a chain of hydrogen‐bonded rings

In the title compound, C₃₄H₃₁N₂O₈PS, the intramolecular distances provide evidence for polarization of the molecular–electronic structure. The molecules are linked into complex chains of rings by three independent C—H...O hydrogen bonds. The significance of this study lies in its finding that two of the four carbonyl O atoms play no role in the hydrogen bonding, despite the large excess of potential hydrogen‐bond donors present.     

Conformational analysis of the disaccharide methyl α‐d‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d‐mannopyranoside monohydrate

The crystal structure of methyl α‐d ‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d ‐mannopyranoside monohydrate, C₁₅H₂₆O₁₂·H₂O, ( II ), has been determined and the structural parameters for its constituent α‐d ‐mannopyranosyl residue compared with those for methyl α‐d ‐mannopyranoside. Mono‐O‐acetylation appears to promote the crystallization of ( II ), inferred from the difficulty in crystallizing methyl α‐d ‐mannopyranosyl‐(1→3)‐β‐d ‐mannopyranoside despite repeated attempts. The conformational properties of the O‐acetyl side chain in ( II ) are similar to those observed in recent studies of peracetylated mannose‐containing oligosaccharides, having a preferred geometry in which the C2—H2 bond eclipses the C=O bond of the acetyl group. The C2—O2 bond in ( II ) elongates by ～0.02 Å upon O‐acetylation. The phi (?) and psi (ψ) torsion angles that dictate the conformation of the internal O‐glycosidic linkage in ( II ) are similar to those determined recently in aqueous solution by NMR spectroscopy for unacetylated ( II ) using the statistical program MA′AT, with a greater disparity found for ψ (Δ = ～16°) than for ? (Δ = ～6°).     

Hydroarylation of 2‐Aryloxybut‐1‐en‐3‐ynes via Pd/Acid‐Catalyzed C−H Bond Activation: A Concise Synthesis of 2,3‐Bismethylene‐2,3‐dihydrobenzofurans

An intramolecular exo ‐hydroarylation of 2‐aryloxy‐1,4‐disilylbut‐1‐en‐3‐ynes via ortho ‐C−H bond activation under palladium(0) and acid catalysis was found to give 2,3‐bis(silylmethylidene)‐2,3‐dihydrobenzofurans. The two silyl groups present probably promoted the reaction and played a key role in stabilizing the diene moiety in the product. The products readily led to functionalized condensed cycles by a Diels–Alder reaction.     

Synthesis of β‐Arylacyl/β‐Heteroarylacyl‐β‐alkylidene Malonates and Their Application in Substituted Pyridone Synthesis

A novel approach has been developed for the synthesis of β‐arylacyl/β‐heteroarylacyl‐β‐alkylidine malonates in moderate to good yields by the reaction of Stork aryl and heteroaryl enamine with β‐chloroalkylidene malonates. The reaction involves conjugate (Michael) addition of Stork enamine on β‐chloroalkylidene malonates and elimination of chloride ion. These Michael adducts were utilized as intermediates for the synthesis of highly substituted 1,4‐dialkyl‐2‐oxo‐6‐aryl/hetreoaryl‐1,2‐dihydro‐pyridine‐3‐carboxylic acid ethyl esters via 5 + 1 ring annulation protocol.     

Selective 17‐β‐estradiol molecular imprinting

An efficient novel method for the synthesis of a covalent molecularly imprinted polymer (MIP) highly specific to β‐estradiol have been developed. MIP prepared by both covalent and non covalent techniques, demonstrated high selectivity toward β‐estradiol. MIPs were synthesized by radical polymerization of 17‐β‐estradiol 4‐vinyl‐benzene carboxyl or sulfonyl esters used as covalent functional monomers, methacrylic acid as noncovalent functional monomer, ethylene glycol dimethacrylate as crosslinking agent, and acetonitrile as swelling and porogenic component. Almost 35% (w/w) of 17‐β‐estradiol was successfully removed from the polymer network by basic hydrolysis. The binding ability of MIP was 10.73 μg/mg MIP following removal of 17‐β‐estradiol in the 2 mg/mL β‐estradiol solution. Selective rebinding of β‐estradiol toward MIP was tested in the presence of competitive binders including estrone, 19‐nortestosterone, epiandrosterone, and cholesterol. Estrone having closest similar chemical structure to β‐estradiol exhibited only 0.6 μg/mg MIP competitive binding, being exposed to equivalent concentrations. Moreover, other competitive steroids demonstrated negligible affinity toward MIP indicating high selectivity of novel MIP system toward β‐estradiol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5534–5542, 2009     

Impact of Nonthermal Atmospheric Plasma on the Structure of Cellulose: Access to Soluble Branched Glucans

We have investigated the effect of non‐thermal atmospheric plasma (NTAP) on the structure of microcrystalline cellulose. In particular, by means of different characterization methods, we demonstrate that NTAP promotes the partial cleavage of the β‐1,4 glycosidic bond of cellulose leading to the release of short‐chain cellodextrins that are reassembled in situ, preferentially at the C6 position, to form branched glucans with either a glucosyl or anhydroglucosyl terminal residue. The ramification of cellulosic chain induced by NTAP yields branched glucans that are soluble in DMSO or in water, thus opening a straightforward access to processable glucans from cellulose. Importantly, the absence of solvent and catalyst considerably facilitates downstream processing as compared to (bio)catalytic processes which typically occur in diluted conditions.     

Azocinoindole Synthesis by a Gold(I)‐Catalyzed Ring Expansion of 2‐Propargyl‐β‐Tetrahydrocarboline

A new methodology taking advantage of gold(I)‐catalyzed ring expansion has been developed to assemble tricyclic 1H‐azocino[5,4‐b]indoles from 2‐propargyl‐β‐tetrahydrocarbolines. The azocinoindoles were obtained in moderate to excellent yields; the structure of which was established by X‐ray crystallographic analysis. A mechanism involving regioselective intramolecular hydroarylation, [1,2]‐alkenyl migration and carbon–carbon bond‐fragmentation was proposed.     

Crystal Structure and Spectroscopic Properties of cis‐β‐Diazido(1,4,7,11‐tetraazaundecane)chromium(III) Bromide

The new complex, cis‐β‐[Cr(2,2,3‐tet)(N₃)₂]Br (2,2,3‐tet = 1,4,7,11‐tetraazaundecane), was prepared and its structure was determined by single‐crystal X‐ray diffraction. The chromium(III) atom is in a distorted octahedral environment coordinated by four nitrogen atoms of 2,2,3‐tet and two azido ligands in a cis‐β arrangement, with bent Cr–N₃ linkages at the coordinating azide nitrogen atoms. The mean Cr–N(2,2,3‐tet) and Cr–N(azide) bond lengths are 2.084(5) and 2.021(5) Å, respectively. The crystal structure is stabilized by ionic interactions, supported by N–H ··· N(azide) and N–H ··· Br hydrogen bonds. The IR and electronic spectroscopic properties are also discussed.     

Methyl 4‐O‐β‐l‐fucopyranosyl α‐­d‐­glucopyranoside hemihydrate

The crystal structure of methyl 4‐O‐β‐l ‐fuco­pyran­osyl α‐d ‐gluco­pyran­oside hemihydrate C₁₃H₂₄O₁₀·0.5H₂O is organized in sheets with antiparallel strands, where hydro­phobic interaction accounts for partial stabilization. Infinite hydrogen‐bonding networks are observed within each layer as well as between layers; some of these hydrogen bonds are mediated by water mol­ecules. The conformation of the disaccharide is described by the glycosidic torsion angles: ?_H = ?6.1° and ψ_H = 34.3°. The global energy minimum conformation as calculated by molecular mechanics in vacuo has ?_H = ?58° and ψ_H = ?20°. Thus, quite substantial changes are observed between the in vacuo structure and the crystal structure with its infinite hydrogen‐bonding networks.     

Synthesis and analgesic‐antiinflammatory activities of ethyl 2‐[3‐(1‐phenoxy(methoxy)carbonyl‐4‐aryl‐(alkyl)‐1,4‐dihydropyridyl)]acetates

Reaction of ethyl 2‐(3‐pyridyl)acetate 4a or ethyl 2‐methyl‐2‐(3‐pyridyl)acetate 4b , with phenyl chloroformate or methyl chloroform ate, afforded the intermediate pyridinium salt 5 which undergoes regioselective nucleophilic attack at C‐4 upon reaction with a Grignard reagent in the presence of a cuprous iodide catalyst at ?23° to yield the corresponding ethyl 2‐[3‐(1‐phenoxy(methoxy)carbonyl‐4‐aryl(alkyl)‐1,4‐dihydropyridyl)]acetates 6a‐f in 64–96% chemical yield. No product arising from reaction of the ester substituent of the pyridinium salt 5 with the Grignard reagent was observed. The ¹H nmr spectra of 6a‐f exhibited dual resonances for the 1,4‐dihydropyridyl H‐2, H‐5 and H‐6 protons at 25° in deuteriochloroform. These dual resonaces were attributed to two different rotameric configurations resulting from restricted rotation about the nitrogen‐to‐carbonyl carbamate bond due to its double bond character. Compound 6 generally exhibited superior analgesic and antiinflammatory activities, compared to the reference drugs aspirin and ibuprofen, respectively. These structure‐activity correlations indicate the 1,4‐dihydropyridyl ring system present in 6 is a suitable bioisostere for the aryl (heteroaryl) ring present in aryl(heteroaryl)acetic acid non‐steroidal antiinflammatory drugs.     

Improved Stability and Photodynamic Activity of Water‐Soluble 5,15‐Diazaporphyrins Incorporated in β‐(1,3‐1,6)‐d‐Glucan with On‐Off Switch

5,15‐Diazaporphyrins, which have a large absorption at wavelengths over 600 nm, were dissolved in water by complex formation with β‐(1,3‐1,6)‐d ‐glucans. Aqueous solutions of these complexes were relatively stable compared with their trimethyl‐β‐cyclodextrin‐complexed analogues. β‐Glucan‐complexed diazaporphyrins showed quenched fluorescence and had low singlet‐oxygen‐generation abilities owing to random self‐aggregation. However, external stimuli, such as the presence of liposomes or intracellular uptake, restored the fluorescence and singlet‐oxygen‐generation abilities of β‐glucan‐complexed diazaporphyrins. Consequently, β‐glucan‐complexed diazaporphyrins showed very high photodynamic activities toward HeLa cells.     

3‐Deoxy‐β‐d‐ribo‐hexopyranose (3‐deoxy‐β‐d‐glucopyranose)

The β‐pyranose form, (III), of 3‐deoxy‐d ‐ribo‐hexose (3‐deoxy‐d ‐glucose), C₆H₁₂O₅, crystallizes from water at 298 K in a slightly distorted ⁴C₁ chair conformation. Structural analyses of (III), β‐d ‐glucopyranose, (IV), and 2‐deoxy‐β‐d ‐arabino‐hexopyranose (2‐deoxy‐β‐d ‐glucopyranose), (V), show significantly different C—O bond torsions involving the anomeric carbon, with the H—C—O—H torsion angle approaching an eclipsed conformation in (III) (−10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo‐ and exocyclic C—C and C—O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C—O bond conformations and/or hydrogen‐bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg).     

Theoretical insights into the excited‐state process of 4‐tert‐butyl‐2‐(5‐(5‐tert‐butyl‐2‐methoxyphenyl)thiazolo[5,4‐d]thiazol‐2‐yl)‐phenol

In this paper, we theoretically explore the motivation and behaviors of the excited‐state intramolecular proton transfer (ESIPT) reaction for a novel white organic light‐emitting diode (WOLED) material 4‐tert‐butyl‐2‐(5‐(5‐tert‐butyl‐2‐methoxyphenyl)thiazolo[5,4‐d]thiazol‐2‐yl)‐phenol (t‐MTTH). The “atoms in molecules” (AIM) method is adopted to verify the formation and existence of the hydrogen bond O? H···N. By analyzing the excited‐state hydrogen bonding behaviors via changes in the chemical bonding and infrared (IR) vibrational spectra, we confirm that the intramolecular hydrogen bond O? H···N should be getting strengthened in the first excited state in four kinds of solvents, thus revealing the tendency of ESIPT reaction. Further, the role of charge‐transfer interaction is addressed under the frontier molecular orbitals (MOs), which depicts the nature of the electronic excited state and supports the ESIPT reaction. Also, the electron distribution confirms the ESIPT tendency once again. The scanned and optimized potential energy curves according to variational O? H coordinate in the solvents demonstrate that the proton transfer reaction should occur in the S₁ state, and the potential energy barriers along with ESIPT direction support this reaction. Based on the excited‐state behaviors reported in this work, the experimental spectral phenomenon has been reasonably explained.     

Capillary electrophoresis‐based enzyme assays for β‐lactamase enzymes

Generic in‐capillary as well as offline CE‐based enzyme assays were developed for serine‐β‐lactamases and metallo‐β‐lactamases. The hydrolysis of benzylpenicillin to benzylpenicilloic acid was analyzed using 100 mM sodium phosphate solution, pH 6.0, as a background electrolyte. In‐capillary assays employed an uncoated as well as a polyethylene oxide‐coated capillary, while the offline assays employing long end and short end injection were performed in an uncoated capillary. Using procaine hydrochloride or 4‐hydroxybenzoic acid as internal standard, the respective assays were validated with regard to linearity, LOD and LOQ, repeatability, precision, and accuracy. The assays were applied to the determination of the Michaelis‐Menten parameters K_m and V_max of Bacillus cereus penicillinase as well as New Delhi metallo‐β‐lactamase 1 and Verona integrin‐encoded metallo‐β‐lactamase 2. Furthermore, the inhibition of the enzymes by irreversible and competitive inhibitors was evaluated. Comparable data were obtained with all assays. The use of a simple substrate ensured broad applicability to the various types of β‐lactamases.     

Separation and Retention Behavior of Aromatic Carboxylic Acid Isomers by High‐Performance‐Liquid‐Chromatography Using β‐Cyclodextrin Bonded Phase with Diamine‐s‐Triazine Moiety

A β‐cyclodextrin (β‐CD) bonded phase with diamine‐s‐triazine moiety was prepared. The separation and retention behavior of the isomers of five aromatic carboxylic acids, including toluic acid, aminobenzoic acid, nitrobenzoic acid, hydroxybenzoic acid, and naphthoic acid were investigated by a high‐performance liquid chromatography (HPLC) using the β‐CD bonded phase prepared. The influence of mobile phase pH in the range of 2.7‐3.6 on the retention of these analytes was examined. The isomers of the aromatic carboxylic acids, with the exception of nitrobenzoic acid, were optimally and effectively separated at pH 2.7, while the three isomers of nitrobenzoic acid could be well separated at pH 3.3. Compared with the chromatographic results obtained previously on the amine‐s‐triazine‐β‐CD bonded phase, the retention factors of the isomers of aromatic carboxylic acid on the diamine‐s‐triazine‐β‐CD bonded phase increase to a relatively much greater extent. Thus, the functionality of the spacer arm of the bonded phase playing an important role in the retention of aromatic carboxylic acid isomers is demonstrated. The results also imply that the hydrogen‐bonding interaction and the mechanism of anion exchange sorption as well may contribute significantly to the retention mechanisms.