Tm Values Research Articles

Engineering the plastic degradation enzyme Ple629 from marine consortium to improve its thermal stability

Petrochemical-derived polyester plastics such as polyethylene terephthalate (PET) and polybutylene adipate terephthalate (PBAT) have been widely used. However, the difficulty to be degraded in nature (PET) or the long biodegradation cycle (PBAT) resulted in serious environmental pollution. In this connection, treating these plastic wastes properly becomes one of the challenges of environment protection. From the perspective of circular economy, biologically depolymerizing the waste of polyester plastics and reusing the depolymerized products is one of the most promising directions. Recent years have seen many reports on polyester plastics degrading organisms and enzymes. Highly efficient degrading enzymes, especially those with better thermal stability, will be conducive to their application. The mesophilic plastic-degrading enzyme Ple629 from the marine microbial metagenome is capable of degrading PET and PBAT at room temperature, but it cannot tolerate high temperature, which hampers its potential application. On the basis of the three-dimensional structure of Ple629 obtained from our previous study, we identified some sites which might be important for its thermal stability by structural comparison and mutation energy analysis. We carried out transformation design, and performed expression, purification and thermal stability determination of the mutants. The melting temperature (Tm) values of mutants V80C and D226C/S281C were increased by 5.2 ℃ and 6.9 ℃, respectively, and the activity of mutant D226C/S281C was also increased by 1.5 times compared with that of the wild-type enzyme. These results provide useful information for future engineering and application of Ple629 in polyester plastic degradation.

A polyethylene glycol enhanced ligation-triggered self-priming isothermal amplification for the detection of SARS-CoV-2 D614G mutation

We presented a polyethylene glycol (PEG) enhanced ligation-triggered self-priming isothermal amplification (PEG-LSPA) for the detection D614G mutation in S-glycoprotein of SARS-CoV-2. PEG was employed to improve the ligation efficiency of this assay by constructing a molecular crowding environment. Two hairpin probes (H1 and H2) were designed to contain 18 nt and 20 nt target binding site at their 3′ end and 5′ end, respectively. In presence of target sequence, it complemented with H1 and H2 to trigger ligation by ligase under molecular crowding condition to form ligated H1–H2 duplex. Then 3′ terminus of the H2 would be extended by DNA polymerase under isothermal conditions to form a longer extended hairpin (EHP1). 5′ terminus of EHP1 with phosphorothioate (PS) modification could form hairpin structure due to the lower Tm value. The resulting 3’ end overhang would also fold back as a new primer to initiate the next round of polymerization, resulting in the formation of a longer extended hairpin (EHP2) containing two target sequence domains. In the circle of LSPA, long extended hairpin (EHPx) containing numerous target sequence domains was produced. The resulting DNA products can be monitored in real-time fluorescence signaling. Our proposed assay owns an excellent linear range from 10 fM to 10 nM with a detection limit down to 4 fM. Thus, this work provides a potential isothermal amplification method for monitoring mutations in SARS-CoV-2 variants.

Ambient Melting Behavior of Stoichiometric Uranium-Plutonium Mixed Oxide Fuel

Mixed oxides of uranium and plutonium (MOX) are currently considered as a reference fuel for the new generation of fast breeder reactors such as ASTRID. The key factor determining the performance and safety of a fuel such as MOX is its operational limits in the application environment which are closely related to the material’s structure and thermodynamic stability. They are in turn closely related to the ambient (zero pressure) melting point (Tm); thus, Tm is an important engineering parameter. Furthermore, PuO2 and UO2 are two endpoints of the phase diagram of MOX; therefore, their ambient Tms are fundamental reference points. However, the current knowledge of the Tm of MOX is limited and controversial as several studies available in the literature do not converge on the unique behavior of Tm as a function of x. Specifically, some studies produced Tm as a monotonically decreasing function of x such that, with Tm of UO2(x=0) of 3150 K, Tm of PuO2(x=1) is ∼2650 K, while other studies resulted in Tm having a local minimum at 0.5<x<1 such that Tm of PuO2 is ∼3000 K, so that the difference between the two values of Tm is as high as 350 K. In this study, using the ab initio Z method implemented with the Vienna Ab Initio Simulation Package (VASP), we carry out a suite of quantum molecular dynamics simulations to obtain the ambient Tm of MOX at several values of x, 0<x<1, including the two end points (x=0, x=1). Our results agree with the behavior of Tm of MOX as a function of x having a local minimum at x=0.7 and Tm of PuO2 of 3050 K. Our study suggests potential ambient density–melting point systematics of MOX which may be useful in subsequent research on MOX such as its thermoelasticity modeling.

Effects of monolauroyl-galactosylglycerol on membrane fatty acids and properties of Bacillus cereus.

The purpose of this study was to provide new ideas for the antibacterial mechanism of monolauroyl-galactosylglycerol (MLGG) from the perspective of cell membranes. The changes in cell membrane properties of Bacillus cereus (B. cereus) CMCC 66,301 exposed to different concentrations (1 × MIC (minimum inhibitory concentration), 2 × MIC, 1 × MBC (minimum bacterial concentration)) of MLGG were evaluated. It was found that the lag phase of B. cereus cells was prolonged at low concentration MLGG (1 × MIC and 2 × MIC), while about 2 log CFU/mL reduction in B. cereus populations were observed when exposed to high concentration MLGG (1 × MBC). MLGG treated B. cereus displayed obvious membrane depolarization, while membrane permeability had no change using PI (propidium iodide) staining. Significant increase in the membrane fluidity in response to MLGG exposure occurred, which was consistent with the modification of membrane fatty acids compositions, where the relative content of straight-chain fatty acids (SCFAs) and unsaturated fatty acids (UFAs) increased, while branched-chain fatty acids (BCFAs) decreased significantly. The decreased transition Tm value and cell surface hydrophobicity was also observed. Additionally, effect of MLGG on bacterial membrane compositions were explored at the submolecular level by infrared spectroscopy. Resistance tests of B. cereus to MLGG had demonstrated the advantages of MLGG as a bacteriostatic agent. Collectively, these studies indicate that modifying the fatty acid composition and properties of cellular membranes through MLGG exposure is crucial for inhibiting bacteria growth, providing new insights into the antimicrobial mechanisms of MLGG. KEY POINTS: • Monolauroyl-galactosylglycerol inserted into B. cereus lipid bilayer membrane • Monolauroyl-galactosylglycerol treatment caused B. cereus membrane depolarization • Monolauroyl-galactosylglycerol resulted in B. cereus membrane fatty acids alteration.

Structural and thermal characteristics of Ge30−xSbxTe10Se60 (0 ≤ x ≤ 20) glasses for electronic devices

Thermal characterization of different compositions of Ge30−xSbxTe10Se60 (x = 0, 5, 10, 15, 20 at.%) glassy materials has been investigated through differential scanning calorimetry (DSC). The tested glasses have been synthesized by melt-quench technique. Glassy materials display compositional phase separation at x = 0, 5, 10, 15 at.%. For additional increase in Sb content at x = 20 at.%, the separation of phases combines in the glass matrix. The glass transition temperature (Tg), initial temperature of crystallization (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) were found to be affected by both heating rate and composition. It is noticed that the increasing of antimony mass percentage in the glassy matrix is leading to decrease in Tg, Tc, Tp and Tm values. The melting temperature (Tm) of these glasses was found in the range 733–746 K for the first phase and in the range 740–792 K for the second phase. The activation energy of glass transition (Eg), activation energy for crystallization (Ec), Avrami index (n) and fragility index (Fi) were calculated using these specific temperatures. Eg decreases with increasing Sb content in all studied samples, but Eg is increasing in the sample with Sb content of 20%, and hence, it varies between 102.7 and 110.6 kJ approximately, whereas (Ec) decreases with the increase in the Sb content in all the tested samples and varies between 283 and 339 kJ. The fragility index varies between 10 and 26 indicating that the melts of these glasses are strong, and the fragility is minimum. The results were discussed in terms of the average coordination number NC and chemical bond approach.

Analysis of aptamer-target binding and molecular mechanisms by thermofluorimetric analysis and molecular dynamics simulation.

Introduction: Aptamers are valuable for bioassays, but aptamer-target binding is susceptible to reaction conditions. In this study, we combined thermofluorimetric analysis (TFA) and molecular dynamics (MD) simulations to optimize aptamer-target binding, explore underlying mechanisms and select preferred aptamer. Methods: Alpha-fetoprotein (AFP) aptamer AP273 (as the model) was incubated with AFP under various experimental conditions, and melting curves were measured in a real-time PCR system to select the optimal binding conditions. The intermolecular interactions of AP273-AFP were analysed by MD simulations with these conditions to reveal the underlying mechanisms. A comparative study between AP273 and control aptamer AP-L3-4 was performed to validate the value of combined TFA and MD simulation in selecting preferred aptamers. Results: The optimal aptamer concentration and buffer system were easily determined from the dF/dT peak characteristics and the melting temperature (Tm) values on the melting curves of related TFA experiments, respectively. A high Tm value was found in TFA experiments performed in buffer systems with low metal ion strength. The molecular docking and MD simulation analyses revealed the underlying mechanisms of the TFA results, i.e., the binding force and stability of AP273 to AFP were affected by the number of binding sites, frequency and distance of hydrogen bonds, and binding free energies; these factors varied in different buffer and metal ion conditions. The comparative study showed that AP273 was superior to the homologous aptamer AP-L3-4. Conclusion: Combining TFA and MD simulation is efficient for optimizing the reaction conditions, exploring underlying mechanisms, and selecting aptamers in aptamer-target bioassays.

Raman Spectroscopic Analysis of Highly-Concentrated Antibodies under the Acid-Treated Conditions

PurposeAntibody drugs are usually formulated as highly-concentrated solutions, which would easily generate aggregates, resulting in loss of efficacy. Although low pH increases the colloidal dispersion of antibodies, acid denaturation can be an issue. Therefore, knowing the physical properties at low pH under high concentration conditions is important.MethodsRaman spectroscopy was used to investigate pH-induced conformational changes of antibodies at 50 mg/ml. Experiments in pH 3 to 7 were performed for human serum IgG and recombinant rituximab.ResultsWe detected the evident changes at pH 3 in Tyr and Trp bands, which are the sensitive markers of intermolecular interactions. Thermal transition analysis over the pH range demonstrated that the thermal transition temperature (Tm) was highest at pH 3. Acid-treated and neutralized one showed higher Tm than that of pH 7, indicating that their extent of intermolecular interactions correlated with the Tm values. Onset temperature was clearly different between concentrated and diluted samples. Colloidal analyses confirmed the findings of the Raman analysis.ConclusionOur studies demonstrated the positive correlation between Raman analysis and colloidal information, validating as a method for evaluating antibody conformation associated with aggregation propensities.

A calorimetric and structural analysis of cooperativity in the thermal unfolding of the PDZ tandem of human Syntenin-1

Syntenin-1 is a multidomain protein containing a central tandem of two PDZ domains flanked by two unnamed domains. Previous structural and biophysical studies show that the two PDZ domains are functional both isolated and in tandem, occurring a gain in their respective binding affinities when joined through its natural short linker. To get insight into the molecular and energetic reasons of such a gain, here, the first thermodynamic characterization of the conformational equilibrium of Syntenin-1 is presented, with special focus on its PDZ domains. These studies include the thermal unfolding of the whole protein, the PDZ-tandem construct and the two isolated PDZ domains using circular dichroism, differential scanning fluorimetry and differential scanning calorimetry. The isolated PDZ domains show low stability (ΔG < 10 kJ·mol−1) and poor cooperativity compared to the PDZ-tandem, which shows higher stability (20–30 kJ·mol−1) and a fully cooperative behaviour, with energetics similar to that previously described for archetypical PDZ domains. The high-resolution structures suggest that this remarkable increase in cooperativity is associated to strong, water-mediated, interactions at the interface between the PDZ domains, associated to nine conserved hydration regions. The low Tm value (45 °C), the anomalously high unfolding enthalpy (>400 kJ·mol−1), and native heat capacity values (above 40 kJ·K−1·mol−1), indicate that these interfacial buried waters play a relevant role in Syntenin-1 folding energetics.

Isothermal Compressibility Perturbation as a Protein Design Principle for T1 Lipase Stability-Activity Trade-Off Counteracting.

Given the widely existing stability-activity trade-off in enzyme evolution, it is still a goal to obtain enzymes embracing both high activity and stability. Herein, we employed an isothermal compressibility (βT) perturbation engineering (ICPE) strategy to comprehensively understand the stability-activity seesaw-like mechanism. The stability and activity of mutants derived from ICPE uncovered a high Pearson correlation (r = 0.93) in a prototypical enzyme T1 lipase. The best variant A186L/L188M/A190Y exhibited a high Tm value up to 78.70 °C, catalytic activity of 474.04 U/mg, and a 73.33% increase in dimethyl sulfoxide resistance compared to the wild type, one of the highest comprehensive performances reported to date. The elastic activation mechanism mediated by conformational change with a ΔβT range of -6.81 × 10-6 to -1.90 × 10-6 bar-1 may account for the balancing of stability and activity to achieve better performing enzymes. The ICPE strategy deepens our understanding of stability-activity trade-off and boosts its applications in enzyme engineering.

Simultaneous enhancement of thermostability and catalytic activity of κ-carrageenase from Pseudoalteromonas tetraodonis by rational design

κ-Carrageenase provides an attractive enzymatic approach to preparation of κ-carrageenan oligosaccharides. Pseudoalteromonas tetraodonis κ-carrageenase is active at the alkaline conditions but displays low thermostability. To further improve its enzymatic performance, two mutants of Q42V and I51H exhibiting both improved thermostability and enzyme activity were screened by the PoPMuSiC algorithm. Compared with the wild-type κ-carrageenase (WT), Q42V and I51H increased the enzyme activity by 20.9% and 25.4%, respectively. After treatment at 50 ℃ for 40 min, Q42V and I51H enhanced the residual activity by 31.1% and 25.9%, respectively. The Tm values of Q42V, I51H, and WT determined by differential scanning calorimetry were 58.2 ℃, 54.8 ℃, and 51.2 ℃, respectively. Compared with untreated and HCl-treated κ-carrageenans, Q42V-treated κ-carrageenan exhibited higher pancreatic lipase inhibitory activity. Molecular docking analysis indicated that the additional pi-sigma force and hydrophobic interaction in the enzyme-substrate complex could account for the increased catalytic activity of Q42V and I51H, respectively. Molecular dynamics analysis indicated that the improved thermostability of mutants Q42V and I51H could be attributed to the less structural deviation and the flexible changes of enzyme conformation at high temperature. This study provides new insight into κ-carrageenase performance improvement and identifies good candidates for their industrial applications.

Effects of interfacial interactions on structural, optical, thermal degradation properties and photocatalytic activity of low-density polyethylene/BaTiO3 nanocomposite

Barium titanate (BaTiO3) filled low density polyethylene (LDPE), (LDPE)100−x/(BaTiO3)x (where x = 0, 2, 4, 6 and 10) nanocomposites are prepared via a solvent-free melt-mixing method. The effects of nano-sized BaTiO3 (nBT) on the structural, optical and thermal degradation properties of LDPE are investigated to address the qualitative interfacial interaction effects due to the spatial distribution of nBT particles in the LDPE matrix. X-ray diffraction (XRD) results confirm the uniform dispersion of nBT nano-fillers in the LDPE polymer matrix. The crystallite size of LDPE increases with increasing the nBT content. Fourier transform infrared spectroscopy (FTIR) results indicate the enhancement in interfacial physical interactions between the polymer and nano-fillers with increasing nano-filler content. The band gap energy of the nanocomposites decreases with increasing nano-filler content, which suggests chemical imperfections close to the interfaces. DSC results depict higher Tm values for the composites which is attributed to the heterogeneous nucleating effects of the nBT particles. Thermo-gravimetric analysis (TGA) results indicate an increase in the decomposition temperature (TD), thermal stability and good dispersibility probability of nBT with increasing nBT. The photocatalytic decomposition of MB is highest (73.52%) for the 10% nBT incorporated LDPE nanocomposite sample. These results correlate with the effect of the interfacial interactions between the nBT fillers and the LDPE polymer matrix.

Predictive Nature of High-Throughput Assays in ADC Formulation Screening

Utilization of high-throughput biophysical screening techniques during early screening studies is warranted due to the limited amount of material and large number of samples. But the predictability of the data to longer-term storage stability is critical as the high-throughput methods assist in defining the design space for the longer-term studies. In this study, the biophysical properties of two ADCs in 16 formulation conditions were evaluated using high-throughput techniques. Conformational stability and colloidal stability were evaluated by determining Tm values, kD, B22, and Tagg. In addition, the samples were placed on stability and the extent of aggregate formation over the 8-week interval was determined. The rank order of the 16 different formulations in the high-throughput assays was compared to the rank order observed during the stability studies to assess the predictive capabilities of the screening methods. It was demonstrated that similar rank orders can be expected between high-throughput physical stability indicating assays such as Tagg and B22 and traditional aggregation by SEC data, whereas conformational stability read-outs (Tm) are less predictive. In addition, the high-throughput assays appropriately identified the poor performing formulation conditions, which is ultimately what is desired of screening assays.

Real-time PCR application in confirmation test of Salmonella Typhimurium on instant noodle

Real-Time PCR is a molecular biology testing instrument used for various types of food product testing applications to monitor the quality of a product. In addition, the real-time PCR technique can also be used to test the detection of pathogenic bacteria in some foods and processed products. The purpose of this study was to detect Salmonella typhimurium using real-time PCR. This research can be a source of information and a reference for similar research. The test method used is the real-time PCR method with the green SYBR kit. Data analysis was carried out by looking at the results of interpreting Ct values and Tm values. Positive results are indicated by the formation of the Ct curve and the Tm curve. From the research conducted, it was found that the Ct value was in the range of 11.90 - 12.10 with an average of 12.02, while the Tm value was in the range of 85.10 - 85.20 with an average of 85.15. From the study results, it can be concluded that the use of real-time PCR for testing the detection of Salmonella typhimurium in instant noodle products can be applied.

Thermal Properties and Morphological Studies of Poly(ethylene oxide) with the Addition of Salt or Nanofiller

AbstractThe increasing demand of the functional polymers in the global industry has led to extensive development of new polymeric materials with enhanced properties. This work focuses on the effect of addition of lithium perchlorate (LiClO4) or titanium dioxide (TiO2) on the thermal properties (i.e., glass transition temperature [Tg], change in heat capacity [ΔCP], crystallinity [X*], melting temperature [Tm]) and morphology of poly(ethylene oxide) (PEO) investigated by using differential scanning calorimetry (DSC) and polarized optical microscope (POM). The Tg and ΔCP of PEO at a mass fraction of salt, WS ≤ 0.0196, increase with the addition of salt. Whereas the values of crystallinity and Tm of PEO at the same salt fraction decrease slightly with increasing salt fraction, suggesting the presence of an interaction between the salt molecules and PEO matrix. However, at WS ≥ 0.107, the Tg, crystallinity, and Tm of PEO decrease significantly with the addition of salt, suggesting the phase separation of the binary mixtures of PEO and salt into salt‐rich and salt‐poor phases are developed. This observation is supported by optical inspections where the salt precipitations can be seen. Meanwhile, the values of Tg, ΔCP, crystallinity, and Tm of PEO show insignificant changes with increasing nanofiller fraction indicating no interaction between PEO and the nanofiller. The two‐phase of PEO and nanofiller in the PEO‐TiO2 can be observed clearly from the optical inspection for all PEO‐nanofiller compositions. Hence, the addition of LiClO4 at low content exhibits relatively prominence on the PEO matrix than the TiO2. LiClO4 possesses better molecular interaction with PEO than TiO2 with PEO.

Engineering D-allulose 3-epimerase from Clostridium cellulolyticum for improved thermostability using directed evolution facilitated by a nonenzymatic colorimetric screening assay

D-Allulose 3-epimerase (DAEase) is a biocatalyst of concern for D-allulose enzymatic synthesis; however, it exhibits comparatively low thermal stability. To facilitate the directed evolution of DAEase, a nonenzymatic colorimetric assay was developed for high-throughput screening of enhanced DAEase mutants. One desirable mutant, MT4 (S38F/F42N/A70P/T119P), was screened based on purifying selection of the randomly mutagenesis library and positive screening of the randomly shuffled library. Compared to the wild-type, the combinational mutant MT4 had higher catalytic activity (1.23-fold) and showed 5, 6.2, and 6.92 °C increases in Topt, T50, and Tm values, respectively. Furthermore, at 60 °C, the t1/2 value of mutant MT4 was 7.30nullh, exhibiting an 11.4-fold increase in comparison to the wild-type. When the mutant MT4 was used in D-allulose production, the yield reached 28.3%, higher than the 25.1% achieved by the wild-type. Dynamic property and structural change analysis demonstrated that the enhanced properties of mutant MT4 were largely attributed to the β4-α4 loop rigidification and active-site tunnel entrance constriction. This work expands the industrial application value of DAEase and provides a robust method as the basis for further protein engineering to achieve better performance of this enzyme.

Biophysical characterization of folded state type II luciferase‐like monooxygenase

We noticed that the Priestia megaterium genome contains five Luciferase‐like monooxygenase (LLM) encoding genes, however, their functions are unknown. The objective of this work was to characterize the biophysical properties of the recombinant LLM2 from Priestia megaterium PSA10 through in vitro and in silico approaches. We successfully cloned into the pET vector system and expressed the recombinant LLM2 in Escherichia coli BL21(DE3). The recombinant LLM2 was overproduced and purified in the form of an inclusion body with a molecular weight of ±39.5 kDa when it was analyzed in 15% SDS‐PAGE. The inclusion body of recombinant LLM2 was then refolded and characterized for its biophysical properties by measuring the UV spectrum of 200 to 250 nm wavelength and determining the change of enthalpy (ΔH) and entropy (ΔS) at the melting temperature. The refolded recombinant LLM2 exhibited a strong spectrum at 205 nm, while the unfolded recombinant LLM2 did not. The Tm, ΔHTm, and ΔSTm values of the refolded recombinant LLM2 were determined to be 318.31±4.4 K, 11.76±1.3 kJ.mol‐1, and (3.74±0.48)x10‐2 kJ.mol‐1.K‐1, respectively. The predicted 3D structure of LLM2 showed that the protein contains the TIM‐barrel, resembling the common global fold of bacterial luciferases. Determination of the cofactor preference suggested that the LLM2 preferred FAD for its cofactor.

A new approach for the direct acylation of bio-oil enriched with levoglucosan: Kinetic study and lipase thermostability

Lignocellulosic biomass can be valorized by fast pyrolysis, generating a bio-oil with levoglucosan (BoE), anhydrous sugar applied as building block for several compounds of great industrial interest. In this work we demonstrated for the first time the direct transesterification of BoE with different acyl donors by free and immobilized lipases. Influence of acetonitrile (ACN) and cyrene (CYE) in the stability of lipases from Candida rugosa and Candida antarctica B by differential scanning Nano fluorimetry (NanoDSF), at substrate concentrations of 20–300 mM as well as the alkyl chain effect for synthesis of the carbohydrate fatty acid esters (CFAEs) were carried out at 55 °C. Best results were obtained with Novozym® 435 in ACN and ethyl octanoate (C8) with 74% of conversion against 58% in CYE and ethyl palmitate (C16). In general it was observed that increasing on hydrophobicity of acyl donor contributed to greater regioselectivity for the hydroxyl bound to carbon 4 with up to 87% for C16 in ACN. Thermostability profile of CalB and CR suggested higher stabilty in CYE with values of Tm = 61 °C for CalB and Tm = 53 °C for CR. Finally, the kinetic parameters were obtained through the Michaelis-Menten constants generated by the double-reciprocal plot and indicated an inhibition by the LG substrate. Moreover, catalytic efficiency data suggest higher enzyme-substrate affinity in CYE.

Fabrication of hollow [formula omitted] spheres (x = 0.0, 0.5, 1.0) as high-performance electromagnetic absorber material

Hollow Ni1-xZnxFe2O4 spheres (x = 0.0, 0.5, 1.0) were synthesized using the solvothermal process. All samples were subjected to X-ray diffraction analysis to determine their crystal structure. Raman spectroscopy was used to investigate the vibrational properties of the material. While field emission scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy were employed to confirm the morphologies and distribution of elements. The prepared hollow spheres exhibited improved magnetic properties for NiFe2O4 and ZnFe2O4 samples, while Ni0.5Zn0.5Fe2O4 showed a relatively smaller value. This variation in magnetic properties is discussed in terms of mixed cation distribution and the relatively large specific surface area of the hollow spheres. The complex permittivity and permeability were measured at microwave frequencies (2 – 11 GHz) using cavity resonator approaches. The Ni0.5Zn0.5Fe2O4 sample exhibited a high attenuation constant, better impedance matching, and a high reflection loss value of −20.6 dB at 5.4 GHz for a modeled thickness of 3 mm when dispersed in paraffin wax. Furthermore, an investigation of the quarter wavelength model for best matching thickness reveals a high degree of agreement between experimental and simulated absorber thickness (tm) values. Overall, the findings demonstrate that hollow structures are more efficient than their bulk counterparts. This work shows that hollowNi0.5Zn0.5Fe2O4 spheresare a potential candidate for an enhanced and dominant microwave absorption field.

Thermal Behavior of Biodegradable Compositions of Polylactide and Poly(3-hydroxybutyrate) with Chitosan and the Effect of UV Radiation on Their Structure

The negative influence of water pollution by heavy metals ions on human health represents a serious ecological problem which requires effective methods in the search for its solution. The creation of eco-friendly biodegradable polymer materials capable of performing the sorption of the water media of heavy metals followed by decomposition into harmless substances after the end of their service life presents an actual task. To this aim, binary compositions synthesized from natural raw polyesters polylactide (PLA) and poly(3-hydroxybutyrate) (PHB) with polysaccharide chitosan, corresponding to these requirements, were obtained in the liquid phase. The polyesters have mechanical characteristics close to the characteristics of synthetic polymers, while the chitosan containing the amino groups is capable of performing the sorption of heavy metals. The use of compositions on their base allows one to create the new inexpensive biodegradable sorbents stable in aqueous media as well as apply them as packing materials. The sorption capacity of PLA–chitosan and PHB–chitosan compositions in relation to iron ions from aqueous solutions was explored by a method of X-ray fluorescence analysis and it was established that the sorption of Fe3+ ions by PHB–chitosan composition is more than twice as high as that by the PLA–chitosan composition (2.30 and 0.66 wt. %, correspondingly, after sorption from 0.008 mol/L FeCl3 solution during 24 h). A comparative study of thermophysical parameters and the degree of crystallinity of PLA and PHB, as well as in their initial compositions and compositions, containing sorbed iron ions, was carried out by DSC method. The DSC analysis of the PLA–chitosan and PHB–chitosan compositions, containing sorbed iron ions, showed a slight decrease in the values of Tg, Tcc, and Tm as well as an increase in the enthalpy of cold crystallization and a reduction in the degree of crystallinity of these polyesters. At the same time, an increasing of the thermal stability of polyester compositions in the presence of iron ions was established. The influence of UV irradiation on the structure of PLA and PHB for 2, 5, 24, and 144 h was analyzed by FTIR spectroscopy and significant changes in the spectrum were observed. Based on the analysis of the IR spectra of PHB and PLA, it was concluded that, under the action of UV radiation, the destruction of ester bonds takes place, which is expressed in the appearance of intense bands characterizing the formation of new structural units, resulting in the decrease in the molecular weight of polyesters.

Characterization of a thermostable PL-31 family alginate lyase from Paenibacillus ehimensis and its application for alginate oligosaccharides bioproduction

Currently, people pay more attention to marine sugars, because of their unique physiological effects. Alginate oligosaccharides (AOS) are the degradation products of alginate and have been used in food, cosmetic, and medicine fields. AOS display good physical characteristics (low relative molecular weight, good solubility, high safety, and high stability) and excellent physiological functions (immunomodulatory, antioxidant, antidiabetic, and prebiotic activities). Alginate lyase plays a key role in the AOS bioproduction. In this study, a novel PL-31 family alginate lyase from Paenibacillus ehimensis (paeh-aly) was identified and characterized. It was extracellularly secreted in E. coli and exhibited a preference for the substrate poly β-D-mannuronate. Using sodium alginate as the substrate, it showed the maximum catalytic activity (125.7 U/mg) at pH 7.5 and 55 °C with 50 mM NaCl. Compared with other alginate lyases, paeh-aly exhibited good stability. About 86.6% and 61.0% residual activity could be maintained after 5 h incubation at 50 and 55 °C respectively, and its Tm value was 61.5 °C. The degradation products were AOS with DP 2–4. Paeh-aly demonstrated strong promise for AOS industrial production because of its excellent thermostability and efficiency.