True stabilization: A mechanism for the behavior of lead compounds and other primary stabilizers against PVC thermal dehydrochlorination

A free-radical mechanism by which lead compounds are thought to inhibit thermal dehydrochlorination of polyvinyl chloride (PVC) is described. This mechanism is called “true stabilization” in order to distinguish it from simple hydrogen chloride (HCl) scavenging, which is a well-known and sometimes important function of all primary stabilizers used in PVC. In true stabilization, it is thought that stearate or other aliphatic carboxylate groups (initially from lubricants) react with reservoirs of basic lead compound such as the carbonates, dibasic lead phosphite, the phthalates, or the sulfates, to give mobile carboxylates of lead. These latter salts then react with chlorine atoms released by the hot PVC, giving chlorides of lead and aliphatic carboxylate free-radicals. Hence the chlorine atoms are trapped and unable to propagate free-radical dehydrochlorination. Also it is thought that the aliphatic carboxylate free-radicals esterify PVC molecules at methylenic carbon atoms (from which hydrogen atoms have been removed by chlorine atoms giving HCl and free-radical sites in the polymer chain). Thus, unpaired electrons on the carboxylate free-radicals and on these methylenic carbon atoms in the PVC molecules are paired, so that the neighboring chlorine atoms in polymer chloromethylenic groups are stabilized. Hence loss of chlorine atoms in the free-radical dehydrochlorination of PVC is prevented. The pendant aliphatic carboxylate groups dissociate from the PVC molecules taking chloromethylenic hydrogen atoms to form acid molecules, and leaving chlorine atoms in relatively stable vinyl type groups. The aliphatic carboxylic acids react with more of the basic lead compound reservoir, giving mobile carboxylates of lead which can enter further reactions as just described. Thus, the true stabilizing mechanism is continuous and cyclic, while the reservoir of basic lead is available, and the PVC thermal dehydrochlorination will be retarded to almost negligible rates in favorable circumstances. It is thought that the behaviors of metal soaps and of organo-tin stabilizers may be encompassed within the general true stabilization concepts of free-radical exchanges and PVC esterifications described above. In these ways they also would retard PVC thermal dehydrochlorination. However, they are neutral compounds and have no basic reservoir which can react with carboxylic acids in the manner described above for lead stabilizers. Hence they are not able to confer long term stability on PVC in the way that basic lead stabilizing regimes do.     

Mesoscopic coarse‐grained simulations of hydrophobic charge induction chromatography (HCIC) for protein purification

Mesoscopic coarse‐grained simulations are adopted to investigate interfacial mechanisms of hydrophobic charged induction chromatography for protein purification by regulating pH. Simulations results indicate that: (i) lysozyme can be adsorbed mainly with “top end‐on” and “bottom end‐on” orientation on hydrophobic surfaces, dominated by the two hydrophobic regions located at both ends of lysozyme's long axis. Elution from the “top end‐on” orientation is more difficult than that from the “bottom end‐on” orientation; (ii) a higher ligand density can get a faster adsorption rate and stronger adsorption. Interestingly, the effect of ligand density on the desorption is mainly determined by the distribution probability of the positively charged groups of ligands; (iii) a higher ionic strength can lead to a wider orientation distribution, a stronger adsorption and a lower elution rate. This work might provide an efficient way to optimize the operating conditions and designing novel ligands. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2035–2047, 2015     

The role of hindered piperidine (HALS) compounds for the stabilization of polypropylene against oxidation reactions caused by ozone and oxidative products formed during photolysis of ozone

The role of hindered piperidine (HALS) photostabilizers for the photostabilization of polypropylene films against oxidative reactions caused by ozone and oxidative species formed during photolysis of ozone under UV irradiation (i.e., atomic oxygen and singlet oxygen) has been investigated and discussed. It has been found that ozonization and/or photoozonization of 2,2,6,6-tetramethyl-piperidine (I) and piperidinoxy radical (2,2,6,6-tetramethylpiperidino-1-oxy) (II) gives a high yield (91–98%) 2,6-dimethyl-2-hydroxy-6-nitro-heptane. Ozonization and/or photoozonization of HALS probably occur by a similar mechanism as reported for (I) and (II). HALS photostabilizer reacts with ozone and/or photolysis products of ozone (atomic oxygen and/or singlet oxygen) and loses its function in the photostabilization process. For that reason protection of polypropylene against photooxidative degradation and photoozonization is of great commercial importance.     

戊型肝炎病毒重组蛋白P179抗原单克隆抗体及抗原检测试剂盒的制备

目的制备戊型肝炎病毒(Hepatitis E virus,HEV)重组蛋白P179抗原单克隆抗体及抗原检测试剂盒。方法以4型HEV ORF2重组蛋白P179免疫BALB/c小鼠,取免疫小鼠脾细胞与SP2/0骨髓瘤细胞进行融合,间接ELISA法筛选阳性杂交瘤细胞株,有限稀释法进行克隆化培养,制备腹水,并对杂交瘤细胞进行染色体计数,鉴定单抗亚类及特异性、并检测稳定性;经SDS-PAGE分析抗体纯度,以兔抗179抗原多抗作为包被抗体,HRP标记P179单抗作为酶标抗体,建立双抗体夹心ELISA法,制备试剂盒,并进行最佳线性范围测定、准确性、精密性和稳定性验证。结果获得4株能稳定分泌抗P179抗原单抗的杂交瘤细胞株,分别命名为3A10、3F8、4E9和5G6,腹水抗体效价分别为1∶10-7、1∶10-6、1∶10-6和1∶10-7,染色体数分别为96、98、101和99条;亚类分别为IgG2a、IgG2a、IgG1和IgG2b;4株单抗连续传代3个月,液氮冻存1年抗体效价未发生变化;制备的试剂盒有良好的线性(R2>0.950 0)、准确性、精密性,试验内变异系数为4.17%～6.26%,回收率在87.9%～114.8%之间,试验间变异系数为5.82%～8.01%,回收率在90.8%～108.9%之间;于37℃及4℃放置3 d,仍具有良好的稳定性。结论成功制备了戊型肝炎病毒P179抗原单克隆抗体及抗原检测试剂盒,可用于戊型肝炎疫苗生产中定量检测疫苗抗原。     

Increasing the hydrophobic interaction between terminal W-motifs enhances the stability of Salmonella typhimurium sialidase. A general strategy for the stabilization of {beta}-propeller protein fold

Protein engineering of the ß-propeller protein aimedat enhancing the structural stability of the protein was carriedout using a monomeric single domain ß-propeller protein,Salmonella typhimurium sialidase, as a model. Ala53 and Ala69each located at strands B and C of the W1 motif were mutatedto Leu and Val, respectively, to increase the hydrophobic interactionbetween W1 and W6 motifs. The mutants showed enhanced stabilitytowards guanidine hydrochloride and thermal unfolding. Ala53Leushowed higher stability, probably owing to the capability ofthe mutated Leu to interact extensively with more residues involvedin the hydrophobic interactions between the terminal W-motifs.The mutations, which are located far from the active site, haveno significant effect on the enzymatic properties. The strategyto enhance the stability proposed here might be applied to theother ß-propeller proteins.     

Prediction-based protein engineering of domain I of Cry2A entomocidal toxin of Bacillus thuringiensis for the enhancement of toxicity against lepidopteran insects

Issues relating to sustenance of the usefulness of genetically modified first generation Bt crop plants in the farmer's field are of great concern for crop scientists. Additional biotechnological strategies need to be in place to safeguard the possibility for yield loss of Bt crop by other lepidopteran insects that are insensitive to the Cry1A toxin, and also against the possibility for emergence of resistant insects. In this respect, Cry2A toxin has figured as a prospective candidate to be the second toxin to offer the required protection along with Cry1A. In the present study, the entomocidal potency of Cry2A toxin was enhanced through knowledge-based protein engineering of the toxin molecule. Deletion of 42 amino acid residues from the N-terminal end of the peptide followed by the replacement of Lys residues by nonpolar amino acids in the putative transmembrane region including the introduction of Pro resulted in a 4.1-6.6-fold increase in the toxicity of the peptide against three major lepidopteran insect pests of crop plants.