Improved Thermal and Reusability Properties of Xylanase by Genipin Cross-Linking to Magnetic Chitosan Particles

Enzymes are gradually increasingly preferred over chemical processes, but commercial enzyme applications remain limited due to their low stability and low product recovery, so the application of an immobilization technique is required for repeated use. The aims of this work were to produce stable enzyme complexes of cross-linked xylanase on magnetic chitosan, to describe some characteristics of these complexes, and to evaluate the thermal stability of the immobilized enzyme and its reusability. A xylanase was cross-linked to magnetite particles prepared by in situ co-precipitation of iron salts in a chitosan template. The effect of temperature, pH, kinetic parameters, and reusability on free and immobilized xylanase was evaluated. Magnetization, morphology, size, structural change, and thermal behavior of immobilized enzyme were described. 1.0?±?0.1 μg of xylanase was immobilized per milligram of superparamagnetic chitosan nanoparticles via covalent bonds formed with genipin. Immobilized xylanase showed thermal, pH, and catalytic velocity improvement compared to the free enzyme and can be reused three times. Heterogeneous aggregates of 254 nm were obtained after enzyme immobilization. The immobilization protocol used in this work was successful in retaining enzyme thermal stability and could be important in using natural compounds such as Fe₃O₄@Chitosan@Xylanase in the harsh temperature condition of relevant industries.

     

Synthesis of novel thermosetting imide compounds having phenylethynyl carbonyl groups at both terminal ends and production of new network polymers based on the imide compounds

A novel thermosetting imide compound having a respective phenylethynyl carbonyl group at both terminal ends was newly synthesized from an acid anhydride having a phenylethynyl carbonyl group and various diamine compounds. The thermosetting behavior of the obtained novel thermosetting imide compound having phenylethynyl carbonyl groups was analyzed through differential scanning calorimetry measurements and infrared spectroscopic analysis. As a result, it became clear that a curing reaction of phenylethynyl carbonyl groups proceeds at approximately 200°C and that the curing reaction thereof proceeds at a temperature that is lower by 150°C or more compared with that of phenylethynyl groups. Examination of the polymerization reaction of the imide compounds having phenylethynyl carbonyl groups using model compounds revealed that a reaction that imparted an alkene C=C and polycyclic aromatic structure progressed. Moreover, a network polymer obtained from a thermosetting imide compound having respective phenylethynyl carbonyl groups at both terminal ends exhibited extremely superior heat resistance and thermal decomposition resistance. These superior thermal properties are thought to be due to the strong molecular interaction (molecular packing) that results from the polycyclic aromatic structures and alkenes produced through polymerization of the phenylethynyl carbonyl groups and to the suppression of the movement of the molecular chains.     

Relative hydrophobicity and hydrophilicity of some "ionic liquid" anions determined by the 1-propanol probing methodology: a differential thermodynamic approach

The excess partial molar enthalpy of 1-propanol (1P), H(E) (1P), was experimentally measured in ternary 1P-[NaPF(6), NaCF(3)SO(3) (OTF) or NaN(SO(2)CF(3))(2) (TFSI)]-H(2)O system. From the H(E) (1P), the enthalpic 1P-1P interaction function, H(E) (1P-1P), which is the compositional derivative of H(E) (1P), was evaluated graphically. On addition of the Na salt, the x(1P)-dependence pattern of H(E) (1P-1P) showed a characteristic change. This induced change is used as a probe to elucidate the effect of the sample Na-salt on H(2)O. Because we know the effect of Na(+) from our previous work, we show that each anion works as an amphiphile with hydrophobic and hydrophilic effects. Furthermore, the present method can quantify its relative hydrophobicity and hydrophilicity separately. The results indicate that the relative hydrophobicity ranking was in the order of TFSI(-) > PF(6-) approximately OTF(-), and the hydrophilicity TFSI(-) > PF6(- )> OTF-. Namely, TFSI- is the strongest amphiphile with the strongest hydrophobicity and the strongest hydrophilicity among the ionic liquid (IL) anions studied here. Using our earlier similar studies for normal ions, we map their relative hydrophobicity/hydrophilicity scales on a two-dimensional map together with those of the IL ions. The resulting map shows that the typical constituent ions for "ionic liquids" are strong amphiphiles; with more strongly hydrophobic and more strongly hydrophilic propensities than normal ions. Although the number of data points is limited, the melting points of ionic liquids consisting of TFSI(-) with the strongest hydrophobicity and the strongest hydrophilicity within the anions studied here are the lowest.     

Stereoselective synthesis of benzyl-protected β-galactosides by propionitrile-mediated glycosylation

β-Selective galactosylation was studied using a series of 2-O-benzylated phenyl 1-thio-galactosides and glycosyl acceptors in propionitrile with BSP-TTBP-Tf₂O. The glycosylation enabled us to synthesize useful precursors of N-acetyllactosamine and core 1 O-glycoserine derivatives in a highly convergent manner.     

Efficient free energy calculation of water across lipid membranes

An efficient free energy (FE) calculation of a water molecule to go across lipid membranes is presented. Both overlapping distribution and cavity insertion Widom methods are complementarily used. The former is useful for a dense region where water molecules are found, i.e., from the interfacial to bulk water region, while the latter works well in the low density region, i.e., the hydrocarbon region. Since both methods evaluate the excess chemical potential of water, the obtained FE profile is free from the fitting problem usually arisen when a FE difference method is used. A diphytanyl phosphatidylcholine bilayer is used for our test calculations. An excellent and fast convergence of the chemical potential is obtained when each method is applied for the appropriate region. The estimated FE barrier using the Ewald method for the electrostatic interaction is approximately 7.2 kcal/mol, which is higher than that using the interaction cutoff of 20 A by about 0.9 kcal/mol.     

Synthesis and DNA‐binding properties of 1,10‐phenanthroline analogues as intercalating‐crosslinkers

We synthesized a series of bis(bromomethyl)‐1,10‐phenanthrolines as novel anticancer lead compounds and examined their DNA‐binding properties. 5,6‐Bis(bromomethyl)‐1,10‐phenanthroline showed DNA intercalating activity and DNA crosslinking activity, furthermore it is stable in aqueous solution.     

Synthesis, structure, and transannular pi-pi interaction of three- and four-layered [3.3]paracyclophanes

The synthesis of three- and four-layered [3.3]paracyclophanes ([3.3]PCPs) 3-5 has been accomplished by utilizing the (p-ethylbenzenesulfonyl)methyl isocyanide (EbsMIC) method. The structures of the three- to four-layered [3.3]PCPs 3- 5 and their diones 8, 10, and 11 have been elucidated based on the (1)H NMR spectra and finally by X-ray structural analysis. In the three-layered [3.3]PCP-dione 8, the trimethylene bridges of the [3.3]PCP unit assume a chair conformation similar to that of 2, while the [3.3]PCP-2,11-dione unit assumes a boat conformation different from that of [3.3]PCP-dione 1 with a chair conformation. On the other hand, the two [3.3]PCP units in three-layered [3.3]PCP 3 both assume a boat conformation. In the four-layered [3.3]PCP-dione 10, the two outer [3.3]PCP units assume a boat conformation while the inner dione unit has a chair conformation. The trimethylene bridges in the four-layered [3.3]PCP 4 are highly disordered even at -150 degrees C. All the outer benzene rings are distorted into a boat form while the inner ones are distorted into a twist form. In the electronic spectra, bathochromic shift and hyperchromic effect are observed, but the magnitude decreases with an increase in the number of layers and the spectra become structureless. In the charge-transfer (CT) bands of the three- to four-layered [3.3]PCPs 3- 5 with tetracyanoethylene (TCNE), two absorption maxima (lambda(max)) are observed. The effect of an increase in the layers becomes significant, and the changes in the longest wavelength lambda(max) values from two to three and three to four are ca. 60 and 50 nm, respectively. By comparison of the stereoisomeric four-layered [3.3]PCPs 4 (meso) and 5 (racemic), the helical arrangement of the trimethylene bridges of 5 shows a more efficient transannular pi-electronic interaction. In the three- to four-layered [3.3]PCP-diones, a magnitude of the CT interaction almost comparable to that of [3.3]PCP 2 was observed, and this indicates that the -CH(2)COCH(2)- bridges inhibit the CT interaction and that this tendency is supported by the calculated HOMO energy levels and observed oxidation potentials. Three- and four-layered [3.3]PCPs 3- 5 show reversible redox processes, and 4 and 5 show an electron-donating ability almost comparable to that of [3 6]CP. Very good correlation between the lambda(max) of the CT bands with TCNE and the oxidation potentials is observed.     

A caffeine-sensitive membrane electrode: previous misleading report and present approach

Although a previous study [S.S.M. Hassan, M.A. Ahmed, M.M. Saoudi, Anal. Chem. 57 (1985) 1126] had shown that a caffeine-sensitive electrode made with picrylsulfonate and 1-octanol as a cation-exchanger and a solvent mediator, respectively, had a wide working pH range (5.5–9.5) and exhibited a Nernstian response, we could not find such response in this electrode. The present result was reasonable, because the pK_a value of caffeinium ion was reported to be around 0.7 and the neutral form of caffeine was predominant in the pH range examined. Thus, we reinvestigated the response characteristics of a caffeine electrode, taking into consideration the pK_a value, and constructed a new electrode with a combination of the lipophilic cation-exchanger, tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate (HFPB), and the solvent mediator with high degree of dielectric constant, 2-fluoro-2′-nitrodiphenyl ether (FNDPE). This electrode showed a pH-dependent response to caffeinium ion and gave a detection limit of 50 μM with a slope of 55 mV per concentration decade at pH 2. The use of other solvent mediators was less effective than that of FNDPE. The electrode was applied for the determination of caffeine in some central stimulants.     

Biodegradable poly(l-lactic acid) nanofiber prepared by a carbon dioxide laser supersonic drawing

Biodegradable poly(l-lactic acid) (PLLA) nanofiber was prepared by a carbon dioxide (CO₂) laser supersonic drawing which was carried out by irradiating the laser on an as-spun fiber in a supersonic jet. The supersonic jet was generated by blowing off air into a vacuum chamber from a fiber supplying orifice. The flow velocity from the orifice can be estimated by applying Graham’s theorem from the pressure difference between the atmospheric pressure and the pressure of the vacuum chamber. The fastest flow velocity estimated was 396 m s⁻¹ when the chamber pressure was 6 kPa. The PLLA nanofiber having an average diameter of 0.132 μm was obtained when the supersonic drawing was carried out by irradiating the laser at 177 W cm⁻² on the as-spun fiber supplied at 0.1 m min⁻¹ in the vacuum chamber at 6 kPa. The obtained nanofiber had a draw ratio of about 323,000 and a degree of crystallinity of 45%, and its diameter uniformity was high. The CO₂ laser supersonic drawing was a new route for preparation of various nanofibers without using any solvent.