Xylanase properties.

<p>Note: T_opt: optimal reaction temperature for activity, t_1/2: thermal in-activation half-life, after incubation at 50°C for different intervals, residual activity was determined and expressed as a ratio to the un-incubated enzyme, and data were fitted with Arrhenius function. The t_1/2 was calculated according to the decay function to indicate enzyme thermostability. Using the Student’s t-Test (<i>p</i><0.05), the XynΔC is more thermostable than the Xyn, and it is more thermostable than the XynΔN and the XynΔNC. The latter two enzymes are statistically similar thermostable. Kinetics was determined for birch-wood xylan at each enzyme pH_opt and T_opt conditions, and the data were fitted with Hill function to calculate V_max and K_m.</p

Xylanase thermostability and kinetics.

<p>After incubation at 50°C at 10-min interval from 10 to 30 min, the residual activity was assayed and expressed as a ratio relative to the un-incubated xylanase activity. The data were fitted with the equation <i>y = A^*e^-kt</i> (Origin, version 8.0), and thermostability (t_1/2) was calculated according to the decay function. The kinetics were assayed at T_opt and pH_opt conditions using birch-wood xylan at concentrations from 0 to 13 mg/ml. The data were fitted with the Hill function to calculate maximal activity (V_max) and K_m (Origin, version 8.0).</p

Construction of the deletion mutants.

<p>The <i>Aspergillus niger</i> Xyn secondary structural units (upper) were shown as irregular segment in thinner line (yellow), strand in middle line (blue), and helix in wider line (red). The genes, <i>Xyn</i>Δ<i>N</i>, <i>Xyn</i>Δ<i>C</i>, and <i>Xyn</i>Δ<i>NC</i> and <i>Xyn,</i> were amplified with primers p2/p3, p1/p4, p2/p4, and p1/p3, respectively. The recombinant pET20b(+) plasmids containing accurate genes appeared on the 1.4% gel as discrete bands at more than 2.3 kb (left), and the proteins appeared on the 12.5% SDS-PAGE as ∼29 kDa (right).</p

Xylanase optimal pH and optimal temperature.

<p>The pH_opt was determined from pH 3.2 to 4.2 at 0.2 unit interval in 50 mM imidazole-biphthalate buffer (left). The T_opt was determined from 42 to 54°C at 2°C interval (right).</p

Novel 3D Alkali–Lanthanide Heterometal–Organic Frameworks with Pyrazine-2,3,5,6-tetracarboxylic Acid: Synthesis, Structure, and Magnetism

Three novel alkali–lanthanide heterometal–organic frameworks, namely, [K₅Ln₅­(pztc)₅­(H₂O)₁₉]·​7H₂O [Ln = Dy (<b>1</b>), Ho (<b>2</b>), and Yb (<b>3</b>); H₄pztc = pyrazine-2,3,5,6-tetracarboxylic acid], have been facilely synthesized. X-ray crystallographic analysis reveals that complexes <b>1</b>–<b>3</b> are isostructural, featuring unique 3D open frameworks, which possess a rare (4,8)-connected net with the Schläfli symbol of (4¹⁵·6¹²·8)­(4⁵·6)₂. The 3D coordination framework involves a ladder-like square column structure by pztc^4– ligands bridging metal ions, exhibiting 1D channels along the <i>b</i> axis. The magnetic analysis suggests that complexes <b>1</b> and <b>3</b> exhibit frequency-dependent out-of-phase signals in alternating current magnetic susceptibility measurements, indicating their slow magnetic relaxation characteristics. It is the first report of slow magnetic relaxation behavior existing in Yb³⁺-based HMOFs

Synthesis, Crystal Structure, and Luminescent Properties of 2-(2,2,2-Trifluoroethyl)-1-indone Lanthanide Complexes

A new β-diketone, 2-(2,2,2-trifluoroethyl)-1-indone (TFI), which contains a trifluorinated alkyl group and a rigid indone group, has been designed and employed for the synthesis of two series of new TFI lanthanide complexes with a general formula [Ln­(TFI)₃L] [Ln = Eu, L = (H₂O)₂ (<b>1</b>), bpy (<b>2</b>), and phen (<b>3</b>); Ln = Sm, L = (H₂O)₂ (<b>4</b>), bpy (<b>5</b>), and phen (<b>6</b>); bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline]. X-ray crystallographic analysis reveals that complexes <b>1</b>–<b>6</b> are mononuclear, with the central Ln³⁺ ion eight-coordinated by six oxygen atoms furnished by three TFI ligands and two O/N atoms from ancillary ligand(s). The room-temperature photoluminescence (PL) spectra of complexes <b>1</b>–<b>6</b> show strong characteristic emissions of the corresponding Eu³⁺ and Sm³⁺ ions, and the substitution of the solvent molecules by bidentate nitrogen ligands essentially enhances the luminescence quantum yields and lifetimes of the complexes

Local Coordination Geometry Perturbed β‑Diketone Dysprosium Single-Ion Magnets

A series of three β-diketone mononuclear dysprosium complexes, namely, Dy­(TFI)₃(H₂O)₂ (<b>1</b>), Dy­(TFI)₃(bpy) (<b>2</b>), and [Dy­(TFI)₃(Phen)]·0.02CHCl₃ (<b>3</b>) (TFI = 2-(2,2,2-trifluoroethyl)-1-indone, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been designed and synthesized. Crystal structure analysis reveals that complexes <b>1</b>–<b>3</b> have haveisomorphic structures in which the central Dy­(III) ion is eight-coordinated by six oxygen atoms from three TFI ligands and two O/N atoms from auxiliary ligands, forming a distorted bicapped trigonal prismatic geometry for <b>1</b>, a distorted dodecahedral geometry for <b>2</b>, and a distorted square antiprismatic geometry for <b>3</b>, respectively. Magnetic studies indicate that complex <b>2</b> with <i>D</i>_2<i>d</i> symmetry and <b>3</b> with <i>D</i>_4<i>d</i> symmetry exhibit slow magnetic relaxation with barrier heights (<i>U</i>_eff/<i>k</i>_B) of 48.8 K for <b>2</b> and 57.9 K for <b>3</b>. Strikingly, the relaxation time (τ) of 0.0258 s for <b>3</b> is about 20 times that for <b>2</b>, which is presumably associated with larger rotation of the SAP surroundings for <b>3</b>. Further, complexes <b>2</b> and <b>3</b> exhibit essential magnetic hysteresis loops at 1.8 K. These extend the recent reports of the single-ion magnets (SIMs) of β-diketone mononuclear dysprosium complexes

Single-Molecule Magnet of a Tetranuclear Dysprosium Complex Disturbed by a Salen-Type Ligand and Chloride Counterions

A series of three salen-type lanthanide complexes, e.g., [Dy₄(L)₂(HL)₂Cl₂(μ₃-OH)₂]₂Cl₂(OH)₂·3CH₃CH₂OH·H₂O (<b>1</b>) and [Ln₄(L)₂(HL)₂Cl₂(μ₃-OH)₂]­Cl₂·5CH₃OH·4CH₂Cl₂ (Ln = Tb^III, <b>2</b>; Ho^III, <b>3</b>) have been isolated by the reactions of H₂L (H₂L = <i>N</i>,<i>N</i>′-bis­(3-methoxysalicylidene)­cyclohexane-1,2-diamine) with LnCl₃·6H₂O. X-ray crystallographic analysis reveals that all complexes <b>1</b>–<b>3</b> are isostructural, in which four Ln ions and eight O atoms form the distorted defective dicubane {Dy₄O₈} cores. Magnetic studies indicate that complex <b>1</b> exhibits two slow magnetic relaxation processes with effective energy barrier <i>U</i>_eff = 55.71 K under a zero direct-current field, which is attributed to the two coordination geometries of the Dy^III ions with a salen-type ligand and coordination of a chloride counterion. It represents the highest energy barrier among the salen-type tetranuclear lanthanide single-molecule magnets

Synthesis, Crystal Structure, and Luminescent Properties of 2-(2,2,2-Trifluoroethyl)-1-indone Lanthanide Complexes

A new β-diketone, 2-(2,2,2-trifluoroethyl)-1-indone (TFI), which contains a trifluorinated alkyl group and a rigid indone group, has been designed and employed for the synthesis of two series of new TFI lanthanide complexes with a general formula [Ln­(TFI)₃L] [Ln = Eu, L = (H₂O)₂ (<b>1</b>), bpy (<b>2</b>), and phen (<b>3</b>); Ln = Sm, L = (H₂O)₂ (<b>4</b>), bpy (<b>5</b>), and phen (<b>6</b>); bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline]. X-ray crystallographic analysis reveals that complexes <b>1</b>–<b>6</b> are mononuclear, with the central Ln³⁺ ion eight-coordinated by six oxygen atoms furnished by three TFI ligands and two O/N atoms from ancillary ligand(s). The room-temperature photoluminescence (PL) spectra of complexes <b>1</b>–<b>6</b> show strong characteristic emissions of the corresponding Eu³⁺ and Sm³⁺ ions, and the substitution of the solvent molecules by bidentate nitrogen ligands essentially enhances the luminescence quantum yields and lifetimes of the complexes