ROLE OF SUCROSE-LDH HYDROGEN BOND FOR THERMAL STABILIZING EFFECT OF SUCROSE ON FREEZE-DRIED LDH

Relationship between thermal stabilizing effect of sugar on freeze-dried protein and sugar-protein hydrogen bond is studied. Sucrose and lactate dehydrogenase (LDH) are used as models for sugar and protein. Samples of freeze-dried LDH involved in sucrose of different crystallinity were prepared, and measurement of X-ray diffractometry (XRD)/ and Fourier-Transform Infrared (/FT-IR)/ spectroscopy was done. It is found that when sucrose is amorphous, the degree of hydrogen bond formation is high and LDH is stabilized; when sucrose is crystalline, hydrogen bond is less formed and LDH is inactivated. These results indicate that the stabilizing effect of sugar is closely related to sugar-protein hydrogen bond. It is also found that there is an optimum sucrose content for the thermal stabilizing effect. This is because amorphous structure of sucrose is stabilized and protected from crystallization by LDH. Thus we car deduce that sugars and proteins work together to keep the activities of proteins.     

Polyethylene glycol‐sugar composites as shape stabilized phase change materials for thermal energy storage

Polyethylene glycol (PEG)‐sugar composites have been investigated as cost effective shape‐stabilized phase change materials for thermal energy storage. PEGs form internal hydrogen bonds stabilizing their chains at solid state. However low molecular weight PEGs are liquid due to short chains as high molecular weight PEGs have too little concentration of hydroxyl groups. Therefore, glucose, fructose, and lactose are used as hydrogen bond source in this study. Consequently it is found that sugars stabilized PEGs up to 90% PEG constitution in solid state except for 90%PEG10,000/10% fructose blend. Fourier transform‐infrared (FT‐IR) analysis revealed considerable interactions between PEGs. The maximum changes in the spectra were observed in the OH stretching region as band broadening due to increasing hydrogen bonding interactions. Differential scanning calorimetry (DSC) analysis are used to determine phase change temperatures and enthalpy of the shape‐stabilized composites that are slightly lower than those of PEG precursors due to the interference effect of sugar in crystallization process. The enthalpies of the blends are 89%, 95%, and 94% of expected from 90%PEG/10% glucose blends, 93%, 94%, and 93% of expected from 90% PEG/10% fructose blends, and 99%, 96%, and 96% of expected from 90% PEG/10% lactose blends respectively when PEGs with 1,000; 6,000; and 10,000 g/mol average molecular weights are used respectively. The diameter of the spherulitic crystals of PEGs decreases with the addition of any of sugar derivatives and spherulites of the composites turns to semi‐amorphous solid structures at temperatures above melting point of PEG precursor. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Redistribution of Protein Biological Activity in a Freeze-Dried Cake

Lactate dehydrogenase (LDH) solutions were freeze dried in order to investigate the redistribution of the remaining LDH activity in the dried cake. D-Mannitol and a polysaccharide (κ-carrageenan, ι-carrageenan, or dextran) were mixed and used as stabilizers in freeze drying. It was found that the remaining LDH activity was significantly redistributed in the freeze-dried cake, and the enzyme concentration was not uniform along the axis of the dried cake due to variations in the freeze-drying conditions and stabilizer concentration. In some cases, active enzymes were highly localized in a specific portion of the dried cake. This was mainly due to the redistribution of the protein content. Further freeze-drying tests employing bovine serum albumin (BSA) and the above-mentioned polysaccharides showed that proteins (BSA) tended to accumulate in the lower portions of the dried cake, forming concentration gradients. Therefore, the concentration gradient in the freeze-dried cake was mainly due to the freezing process. This redistribution of protein content contributed considerably to the apparent redistribution of enzyme activity. The results suggest that a process that can control the redistribution of protein content in a freeze-dried cake would further improve the biological activity of freeze-dried proteins.     

Stabilization of apoflavodoxin by replacing hydrogen-bonded charged Asp or Glu residues by the neutral isosteric Asn or Gln

Knowledge of protein stability principles provides a means toincrease protein stability in a rational way. Here we explorethe feasibility of stabilizing proteins by replacing solvent-exposedhydrogen-bonded charged Asp or Glu residues by the neutral isostericAsn or Gln. The rationale behind this is a previous observationthat, in some cases, neutral hydrogen bonds may be more stablethat charged ones. We identified, in the apoflavodoxin fromAnabaena PCC 7119, three surface-exposed aspartate or glutamateresidues involved in hydrogen bonding with a single partnerand we mutated them to asparagine or glutamine, respectively.The effect of the mutations on apoflavodoxin stability was measuredby both urea and temperature denaturation. We observed thatthe three mutant proteins are more stable than wild-type (onaverage 0.43 kcal/mol from urea denaturation and 2.8°C froma two-state analysis of fluorescence thermal unfolding data).At high ionic strength, where potential electrostatic repulsionsin the acidic apoflavodoxin should be masked, the three mutantsare similarly more stable (on average 0.46 kcal/mol). To ruleout further that the stabilization observed is due to removalof electrostatic repulsions in apoflavodoxin upon mutation,we analysed three control mutants and showed that, when thecharged residue mutated to a neutral one is not hydrogen bonded,there is no general stabilizing effect. Replacing hydrogen-bondedcharged Asp or Glu residues by Asn or Gln, respectively, couldbe a straightforward strategy to increase protein stability.     

重组HIV-1腺病毒载体活疫苗的冻干保护剂研究

目的研制重组HIV-1腺病毒载体活疫苗的冻干保护剂。方法在重组HIV-1腺病毒载体活疫苗中加入不同配比的保护剂,在适宜条件下制备成冻干剂型。根据冻干后外观、病毒滴度和热稳定性试验等结果,筛选出冻干保护剂的最适配方。结果以人血白蛋白、海藻糖、甘露醇、右旋糖苷和蔗糖等成分按比例配伍制备的保护剂,对重组HIV-1腺病毒载体活疫苗显示了较好的保护作用。冻干前后疫苗病毒感染性滴度下降在0.17LogCC ID50/ml以内;37℃放置1周,滴度下降0.3LogCC ID50/ml左右;37℃放置3周后,滴度下降约为0.6LogCC ID50/ml。而无保护剂的液体疫苗对照于37℃放置1周,滴度下降近2.5个LogCC ID50/ml。结论以人血白蛋白、海藻糖、甘露醇、右旋糖苷和蔗糖等配伍而制备的保护剂效果较好。     

Sugar fatty acid ester surfactants: Biodegradation pathways

In previous work, we found that the presence of a sulfonyl or alkyl group adjacent to the ester bond of sugar ester surfactants is associated with a dramatic reduction in the rate of biodegradation relative to that of unsubstituted esters. In this study, we investigated the pathways followed during the biodegradation of sucrose laurate, sucrose α-sulfonyl laurate, and sucrose α-ethyl laurate to determine the reasons for their different biodegradation rates. Through the use of high-performance liquid chromatography and proton nuclear magnetic resonance spectroscopy, the nature of the intermediates formed during the biodegradation of these three key sugar esters was determined. It was found that sucrose laurate biodegradation occurs via initial ester hydrolysis. In contrast, sucrose α-sulfonyl laurate degrades by initial alkyl chain oxidation. This indicates that the ester hydrolysis pathway is blocked by the sulfonyl group adjacent to the ester bond so that biodegradation is forced to proceed via the slower alkyl chain oxidation pathway. Sucrose α-ethyl laurate was degraded at least in part by alkyl chain oxidation, indicating that ester hydrolysis was also inhibited by the presence of an ethyl group. It is therefore concluded that previously observed relationships between structure and biodegradability arise because of the influence that different structural elements have on the pathways followed during biodegradation.     

Functionalized polyvinyl chloride/layered double hydroxide nanocomposites and its thermal and mechanical properties

In this work, to inquire the impact of layered double hydroxide (LDH) nanoclay on functionalized poly(vinyl chloride) (PVC) through solution intercalation method, four kinds of nanocomposites were prepared. Mg-AL LDH and the obtained functionalize PVC composites were characterized through FT-IR, UV–Vis spectroscopy, TEM, XRD, contact angle, DSC, and UTM. Obtained results revealed that the functionalized PVC uniformly dispersed in the layer of LDH nanoclay. It is revealed that partially intercalated and disordered structure formed in PVC/LDH, PVC-TS (thiosulfate)/LDH, and PVC-S (sulfate)/LDH nanocomposites, whereas fully exfoliated structures formed in the PVC-TU (thiourea)/LDH nanocomposites. Further, it has been observed that the ultimate tensile strength for all the polymer nanocomposites enhanced with increased in the LDH content. These nanocomposites further exhibited higher thermal stability by at least by 51°C higher than the pristine PVC. Along with these, further it has been found that the functionalized PVC/LDH nanocomposites are proved to be effective as thermal stabilizer for PVC processing. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48894.     

Temperature dependence of hydrogen bond in Fe‐OCAP/polyurethane blends

Fourier transform infrared (FTIR) thermal analysis was utilized to study the temperature dependence of hydrogen bond in Fe‐octacarboxyl acid phthalocyanine (Fe‐OCAP)/polyurethane (PU) blends. Two regions in the FTIR spectra were concerned to investigate the difference of the degree of hydrogen bond in the samples: the ? NH stretching region (3210–3460 cm^?1) and carbonyl stretching region (1680–1760 cm^?1). It was found that the average strength of hydrogen bond in the modified samples was stronger than that in pure PU. With increasing Fe‐OCAP content, the hydrogen bonded ? NH and carbonyl groups were increased, while with increasing temperature they decreased. The equilibrium between free and hydrogen bonded carbonyl groups was discussed. The dissociation enthalpy for hydrogen bonded carbonyl of the samples was increased with increasing Fe‐OCAP content. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2265–2271, 2013     

Effect of amino acids on the autoxidation of safflower oil in emulsions

Oxygen absorption rates were measured on liquid emulsions containing safflower oil and various amino acids. The antioxidant effects of the several amino acids were quite variable depending on the type of emulsifier used, the pH of the system and the presence of added sugar. Preliminary tests with Maillard reaction products obtained by heating dextrose with lysine showed little stabilizing effect. In freeze-dried emulsions, methionine, threonine, lysine and histidine all exhibited antioxidant activity. With sodium caseinate as the matrix, methionine was much better than any of the other amino acids. The inclusion of sugar enhanced the rate of oxidation. Porosity measurements on the freeze-dried powders revealed that oxygen diffusion was not rate-determining. When xanthan gum was used to replace caseinate in these dried emulsions, oxidation rates increased.     

无卤膨胀阻燃PP/PA6合金性能研究

研究了以聚磷酸铵（APP）、三聚氰胺（MA）和层状复合金属氢氧化物（LDH）复配得到的膨胀阻燃剂（IFR）对聚丙烯／尼龙6（PP／PA6）合金性能的影响，分析了不同阻燃体系对PP／PA6合金的阻燃性能、力学性能、热性能和微观形态的影响。结果表明，当APP／MA／LDH为21．0／7．5／1．5（质量比）时，PP／PA6合金具有较好的阻燃性能并能保持较高的力学性能。LDH可以提高阻燃材料的热稳定性和残炭量，而且SEM照片显示炭层微观形态为“面包”状的膨松状。     

Rheological and mechanical properties of dynamic covalent polymers based on imine bond

Dynamic covalent polymers based on imine bond (FPIs), which are capable of reorganizing their constitution on the molecular level, are prepared from bio-based dimer fatty acids. The irregular structure of carbon chains in dimer fatty acids leads to the amorphous nature of FPIs. The effect of imine bond on the glass transition temperature of FPIs is studied by differential scanning calorimetry. The linear viscoelasticity of FPIs is investigated by small amplitude oscillatory shear tests and analyzed by using the Likhtman-McLeish theory. It is found that the rheological behavior of FPIs is similar with that of static, linear entangled polymers predicted by Likhtman-McLeish theory, when the dynamic chain arrangements caused by imine-bond exchange is not active enough. For FPIs, the temperature variation of viscosity is still following the Arrhenius law with an activation energy of ~50 kJ mol⁻¹. Owing to the thermal adaptability, FPIs demonstrate great malleability, self-healing capability and processing stability at elevated temperatures.     

莫来石抑制钛酸铝材料热分解的机理研究

运用扫描电镜（SEM）、X-射线衍射仪（XRD）、能谱仪（EDS）等现代测试手段,从材质的显微结构、晶界晶相组成分析入手,对莫来石抑制钛酸铝热分解的作用机理作了较为详细的分析研究,探明莫来石抑制钛酸铝热分解的作用机理是：（1）在高温下Si^4 进入钛酸铝晶格或间隙中,形成固溶化的钛酸铝晶体,稳定了晶格;（2）因莫来石与钛酸铝间的热膨胀差异,造成较大的压应力（37.65MPa）,致使固溶化的钛酸铝晶体更趋稳定。     

Evaluation of the adsorption behavior of freeze-dried passion fruit pulp with added carriers by traditional biospeckle laser techniques

This work was aimed to evaluate the potential of the biospeckle laser technique to monitor the sorption behavior of freeze-dried passion fruit pulp. For this purpose, passion fruit pulp with carriers (sucrose, fructose, maltodextrin, and ethanol) was added at different concentrations and combinations were freeze dried, and their sorption behavior was monitored in environments with relative humidities of 0.113, 0.529, 0.753, and 0.903 by gravimetric and biospeckle laser analyses. The thermal and structural stabilities of the powders were evaluated using differential scanning calorimetry and scanning electron microscopy. The biospeckle laser tool was capable of monitoring the water activity present in the passion fruit powders at relative humidities of 0.113, 0.529, and 0.753. In a relative humidity of 0.113, adsorption was slow, and the speckle pattern was altered regardless of the added carrier. Relative humidities of 0.529 and 0.753 resulted in an adsorption behavior and altered speckle pattern, which were variable, i.e., they were dependent upon the added carriers. At a relative humidity of 0.903, the adsorbed mass of water and alterations in the speckle pattern over time were intense. Ethanol furthered the degree of organization of the structures in the crystallization process. Maltodextrin was effective at stabilizing the passion fruit powders, resulting in poorer water adsorption and increased vitreous transition temperature. Fructose promoted typically amorphous freeze-dried powders, due to the high glass transition temperature and the formation of highly sticky tubular and roundish structure.     

Thermal and Morphological Properties of Poly(vinyl alcohol) and Layered Double Hydroxide (LDH) Nanocomposites

Poly(vinyl alcohol) (PVA)/layered double hydroxide (LDH) nanocomposites were synthesized with different compositions: 0, 2, 4, 6, and 8 wt% of LDH by the solution intercalation method. The effects of the layered double hydroxide platelet concentration on the properties of the PVA/LDH films were investigated by thermogravimetric analysis (TGA), optical microscopy, and Fourier transform infrared spectroscopy (FTIR). A reduction in the onset of thermal decomposition temperature was observed in PVA/LDH composites compared to neat PVA. The reduction in the onset of thermal decomposition was likely due to a nucleophilic attack mechanism. The presence of single LDH sheets in form strips in the optical micrographs shows direct evidence of exfoliation, indicating that LDH layers were well-exfoliated and dispersed in the PVA matrix in a disorderly fashion. The FTIR analysis showed good interaction between the continuous PVA matrix and the LDH nanoparticle fillers, by hydrogen bonding through hydroxyl groups. The primary focus of the present investigation was to explore the potential of LDH material as a nanofiller and to improve dispersion of LDH in polar polymers like PVA.     

纳米双羟基复合金属氧化物协同聚磷酸铵阻燃尼龙-6/聚丙烯燃烧及热降解行为的研究

将纳米双羟基复合金属氧化物 (LDH)与聚磷酸铵 (APP)在一定范围内复配 ,用于尼龙 6/聚丙烯 (PA 6/PP)共混体系可产生良好的协同阻燃效果。实验表明 ,LDH参与了共混阻燃体系的热分解反应 ,催化了PA 6/PP/APP体系的交联、成炭 ;LDH协同阻燃体系的残炭形态致密、光滑、残炭微孔呈闭合状态。协同阻燃作用的机理与LDH和APP热降解过程中产物间的化学与物理作用有关。     

Effects of an intercalating agent on the morphology and thermal and flame‐retardant properties of low‐density polyethylene/layered double hydroxide nanocomposites prepared by melt intercalation

The effects of an intercalating agent on the morphology and thermal and flame‐retardant properties of low‐density polyethylene (LDPE)/layered double hydroxide (LDH) nanocomposites were studied with Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, microscale combustion calorimetry, thermogravimetric analysis, and mechanical property measurements. X‐ray diffraction and transmission electron microscopy demonstrated that after intercalation with stearate anion (SA) or dodecyl sulfate anion (DS), organo‐LDH could be nanodispersed in an LDPE matrix with exfoliated structures or intercalated structures simultaneously with partially exfoliated structures, respectively, via melt intercalation. However, the unmodified LDH composites yielded only microcomposites. Microscale combustion calorimetry, thermogravimetric analysis, and dynamic Fourier transform infrared spectra showed the following order for the flame‐retardant and thermal properties: LDPE/SA‐modified LDH > LDPE/DS‐modified LDH > LDPE/NO₃‐modified LDH > LDPE. The higher performance of the LDPE/LDH nanocomposites with respect to flame retardance and thermal stability could be attributed to the better dispersion state of the LDH layers in the LDPE matrix and the greater hindrance effect of LDH layers on the diffusion of oxygen and volatile products throughout the composite materials when they were exposed to burning or thermal degradation. The tensile strength and elongation at break of the LDPE/LDH nanocomposites decreased to some extent because of the decrease in the crystallinity of the LDPE matrix. A transmittance test showed that the transparency of the exfoliated LDPE/SA‐modified LDH nanocomposite was very close to that of neat LDPE. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Evaluation of the phase composition of amylose by FTIR and isothermal immersion heats

Amylose, a linear component of starch, has been shown to be directly responsible for many of starch's physical properties. In this study isothermal DSC assisted by FTIR spectroscopy was used to determine the phase composition of amylose under various pH conditions and while shear was used to disrupt chain-chain interactions. The analysis was based on a three-phase model consisting of crystalline (type B and single helices), amorphous, and network (physical entanglements and hydrogen bonds related) environments. Varying the pH of the water present in the samples enables the detection of the presence of the networks. Such networks, preferentially located in the amorphous phase, were found to be more reactive to chemical and probably thermal modifications. However, when chain entanglements or hydrogen bond networks are found near or in the helix of the crystalline phase, the polymer becomes more resistant to chemical and physical modification. Furthermore, it was observed that pH and shear could be used to control the morphology, orientation and phase content of amylose, which had a significant impact on the biodegradability of the treated samples.     

Polyanion/gelatin complexes as pH‐sensitive gels for controlled protein release

Polyanion/gelatin complexes including poly(methacrylic acid) (PMAA)/gelatin, poly(acrylic acid) (PAA)/gelatin, and heparin/gelatin are investigated as pH‐sensitive gels for controlled protein release. Polyanions can interact with gelatin and form amorphous precipitates within a certain pH range, which is affected by the polyanion nature. The entrapment efficiency of model proteins (myoglobin, cytochrome c, and pepsin) into the complexes is rather high (>80%). By using a modified colloid titration that mixes a solution of gelatin and model proteins titrated with polyanion solution, myoglobin and cytochrome c are found to interact with polyanions by electrostatic forces at low pH, while pepsin either interacts with the polyanion when the pH is below its isoelectric point (IEP) or complexes with gelatin at a pH above IEP_pepsin. At pH 7.4 all the complexes dissociate and proteins are rapidly released within a few hours. The complexes are stable and the proteins are retained within a certain pH range, which is related to the polyanion type (e.g., 5.0–2.0 for PMAA, 4.6–1.2 for PAA, and <4.3 for heparin). The three processes of complex formation, dissociation, and protein release have a good correlation. In addition, the protein release transition takes place within a rather narrow pH range (ca. 0.5 units) and the protein nature has little effect on the protein release profile. The high protein entrapment efficiency and good pH sensitivity of the protein release can be mainly attributed to the electrostatic attractive interactions between proteins and polyanion or gelatin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1416–1425, 2001     

Thermal,mechanical, and rheological characterization of polypropylene/layered double hydroxide nanocomposites

Polypropylene (PP)/organomodified layered double hydroxide (LDH) nanocomposites were prepared in order to examine the influence of LDH content on thermal, mechanical, and rheological properties. The nanostructure examinations by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the exfoliated/intercalated dispersion of LDH. Incorporation of the LDH resulted in a noteworthy improvement in the thermal stability of PP. It was shown that the addition of LDH contributed to the reinforcement effect by increasing the elastic modulus. The mechanical performance, as evaluated by stress–strain curves, reveal that PP/LDH hybrid materials showed significant contribution toward increment in elastic modulus, tensile strength but at the expense of impact strength. The rheological response showed a strong influence of LDH particles on the flow behavior of the PP/LDH melt which resulted in enhancement of storage, loss of moduli, and complex viscosity of nanocomposites. Therefore, the nanocomposites have higher moduli but better processibility compared with pure PP. Overall, the results indicated that the LDH particles in nanometer size might act as potential reinforcing agent for polypropylene. POLYM. ENG. SCI., 52:2006–2014, 2012. © 2012 Society of Plastics Engineers     

Thermal Degradation of Poly (vinyl chloride)-Stabilization Effect of Dichlorotin Dioxine

Abstract

Thermal degradation of polyvinyl chloride (PVC) and the effect of dichlorotin dioxine (DCTD) on this process have been investigated using dehydrochlorination (DHCl) and thermogravimetric techniques. A significant decrease in the rate of degradation was observed when PVC was mixed with a small amount which was maximum with 0.25 pph of DCTD and thermal decomposition temperature with DCTD was found to be higher than that of pure PVC. The value of apparent activation energy of the dehydrochlorination process has been calculated and a suitable mechanism for the stabilizing action of DCTD on PVC has been purposed.