巯基棉预浓集—中子活化法测定水泥及其浸出水中的微量汞

在不同酸度下巯基棉可以从溶液中富集和分离Au、As、Ag、Br、Cu、Ca Co、InHg、Ni、Se、Sb、Sn、Pb、W、Fe和In等30多种元素。由于用巯基棉吸附待测元素后不必洗脱,因此大大提高了富集能力,可用于海水、地下水、地表水及工业废水中一些元素的测量。本文用巯基棉富集后进行中子活化分析测定水泥及其浸出水中的汞。     

巯基活性炭分离富集发射光谱法同时测定金、铂、钯和铊

研究了巯基活性炭在盐酸介质中对金、铂、钯和铊的吸附能力。该法具有吸附速度快、吸附容量大、在一定条件下，普通金属不被吸附的特点，可用于分离富集各类矿物中微量贵金属。吸附后巯基活性炭低温灰化，与缓冲剂混合发射光谱法同时测定金、铂、钯和铊，选择锆作内标线，直接压样于杯形的石墨电极中，该方法简便、快速、准确。对测定条件、干扰因素进行了研究，从而建立测定金、铂、钯和铊的新方法。金、铂、钯和铊的分析线分别为312.3nm，306．5nm，311．4nm和313．1nm，内标线选择为310．7nm的锆，金、铂、钯和铊的线性范围(原子百分数)分别为0～0．20％，0～0．40％，0～0．20％和0～0．40％。金、铂、钯和铊的检测限分别0．01％，0．003％，0．003％和0．001％。用于样品的测定获得满意结果。     

Effect of lipids on soy protein isolate solubility

Reduced-lipid soy protein isolate (SPI), prepared from soy flour treated so that most of the polar lipids have been removed, exhibited an increase in protein solubility of 50% over that of the control SPI prepared from hexane-defatted flour. Adding lipids from a commercial SPI during processing of reduced-lipid SPI decreased SPI solubility by 46%. The 19% decreased solubility caused by the lipids (primarily phospholipids) was largely recovered by treating the protein with a reducing agent (2-mercaptoethanol). The balance of protein insolubility, caused by the lipids, was attributed to a smaller lipid fraction (approximately 5% of the total lipids). Adding lipids during SPI processing contributed to both the formation of oxidized protein sulfhydryls, incapable of being reduced by 2-mercaptoethanol, and to oxidative deterioration of protein as determined by protein carbonyl contents.     

原子荧光光谱法测定茶叶中微量硒的研究

采用原子荧光光谱法对茶叶中硒的含量进行了分析,用巯基棉富集和硫脲抗坏血酸掩蔽Pb2 、Cu2 、Ag 的干扰.讨论并确定了最佳测定条件,硒的检出限为0.57 ng·mL-1,线性范围为0.00～100.00 ng·mL-1,回收率为99.0%～106.3%,相对标准偏差小于1.71 %.     

基于两种双硫键自修复聚氨酯制备及性能

以异佛尔酮二异氰酸酯(IPDI)和双(2-羟基乙基)二硫醚(DTBO)为硬段,聚四氢呋喃(PTMG)为软段,β-巯基乙醇(ME)为封端剂,制备巯基封端且含双硫键的聚氨酯(PUR)预聚物,利用巯基易氧化的特点,用H2O2/NaI进行氧化,合成分子链内和分子链端均含有双硫键的自修复交联PUR.采用傅立叶变换红外光谱仪、差示...     

热处理对扇贝闭壳肌肌动球蛋白生化性质的影响

肌动球蛋白是扇贝闭壳肌中的主要功能蛋白质,对贝类制品的品质起关键的作用。文中以虾夷扇贝(Patinopecten yessoensis)闭壳肌为原料,提取其肌动球蛋白,并考察了热处理温度和时间对肌动球蛋白的α-螺旋含量、表面疏水性、活性-SH含量和浊度的影响。结果表明:在热处理过程中,扇贝闭壳肌肌动球蛋白的α-螺旋发生解旋,肽链展开,疏水性氨基酸残基暴露,蛋白表面疏水性增强;同时热处理使活性-SH氧化生成二硫键,蛋白聚集,使得扇贝闭壳肌肌动球蛋白的浊度增加。加热温度越高,这些指标变化越快。由此推断,扇贝闭壳肌肌动球蛋白在热处理过程中伴随着肽链的解旋和蛋白的无规则聚集。     

不同形式壳聚糖基水凝胶的微观结构与控释性能对比

本文采用离子交联和巯基化两种不同方式改性壳聚糖,制备载有活性蛋白的壳聚糖水凝胶。通过红外光谱、粒径/zeta电位分析、透射电镜、扫描电镜、模拟消化实验等手段,探讨了其微观结构和控释性能。实验结果发现,由于分子间氢键作用,p H值、CS:TPP质量比以及BSA浓度等对交联壳聚糖水凝胶的蛋白包载率影响明显,而由于巯基的引入,使得巯基化壳聚糖水凝胶在酸性环境下具有较小的粒径(平均409.61 nm)和较低的表面电势(平均-0.67 mV)。壳聚糖基材料微观结构的变化进而影响其水凝胶的控释性能。模拟消化实验显示,交联壳聚糖水凝胶在模拟胃液中出现突释现象,在运送至结肠前,已有44.76%的活性蛋白释放,而巯基化壳聚糖水凝胶在模拟上消化道环境中释放缓慢,仅有8.42%的活性蛋白释放,运转至模拟结肠,活性蛋白释放速度逐渐增加,呈现持续释放的效果,约有34.53%的BSA逐渐释放在结肠中。因此,巯基化壳聚糖基水凝胶具有更好的控释性能,这对活性蛋白的生物利用改善具有重要作用。     

Antifeedant effects of proteinase inhibitors on feeding behaviors of adult western corn rootworm (Diabrotica virgifera virgifera)

Low-molecular-weight peptidyl proteinase inhibitors (PIs) including leupeptin, calpain inhibitor I, and calpeptin were found to be potent antifeedants for adult western corn rootworm (WCR) against the phagostimulation of cucurbitacin B (Cuc B) or a corn pollen extract (CPE). Leupeptin was the strongest (ED₅₀ = 0.36 and 0.55 nmol/disk for Cuc B and CPE, respectively) among PIs tested with an antifeedant potency much stronger than the steroid progesterone (ED₅₀ = 2.29 and 5.05 nmol/disk for Cuc B and CPE, respectively), but slightly less than the reference alkaloid, strychnine (ED₅₀ = 0.17 and 0.37 nmol/disk for Cuc B and CPE, respectively). All active PIs contain a di- or tripeptidyl aldehyde moiety, indicating that PIs exert their antifeedant effects by covalent interaction with putative sulfhydryl (SH) groups on taste receptors as do these PIs with cysteine proteinases. However, opposite inhibition potency against Cuc B versus CPE by two thiol-group reducing agents, DTT and L-cysteine, and the results with other cysteine-modifying reagents obscure the net functional role of SH groups at WCR taste chemoreceptors. Surprisingly, the model phagostimulant for diabroticites, Cuc B, was more easily counteracted by these feeding deterrents than the stimulants present in CPE. Three-dimensional structure–antifeedant relationships for the PIs suggest that a novel taste chemoreception mechanism exists for these peptidyl aldehydes or that they fit partially into a strychnine binding pocket on protein chemoreceptors. Favorable economic benefit may be achieved if PIs are discovered to be useful in adult WCR control, since both pre- and postingestive sites would be targeted.     

Tensile, Solubility, and Electrophoretic Properties of Egg White Films as Affected by Surface Sulfhydryl Groups

Films plasticized with polyethylene glycol were cast from alkaline (pH 10.5, 11.0, or 11.5), aqueous egg white (EW) solutions with or without heating (40°C for 30 min). Prior to casting, concentration of surface sulfhydryl (SH) groups was determined and they increased (P < 0.05) (3.81–19.45 μM/g protein) with both pH and heating, presumably due to protein denaturation and cleavage of disulfide (S-S) bonds. Concentration of surface SH groups correlated (P < 0.05) with film tensile strength (r = 0.70), elongation at break (r = 0.86), and film total soluble matter (r =−0.94). Most likely, surface SH groups formed S-S bonds through air oxidation and/or sulfhydryl/disulfide interchange, thus contributing to EW film formation. SDS-PAGE patterns in presence or absence of 2-mercaptoethanol confirmed occurrence of S-S bonding in dried EW films.     

Effect of Hydrostatic Pressure on Molecular Conformation of Tilapia (Orechromis niloticus) Myosin

ABSTRACT: Change in tilapia myosin molecular conformation due to pressurization at 50 to 200 MPa for 0 to 60 min was investigated. After a 50-MPa treatment, tilapia myosins slightly decreased their total sulfhydryl contents and exposed their hydrophobic residues. Experimental results indicated that 100- and 150-MPa treatments caused an apparent unfolding of myosins and a 1-fold increase of their surface hydrophobicity ( S _o). Myosins mainly formed intermolecular disulfide bonds with pressures of 100 to 200 MPa. In addition, increasing pressures altered the myosin conformation and decreased its Ca-ATPase activity. Myosin apparently unfolded and formed disulfide bonds and hydrophobic interactions with pressurizing at 150 MPa.