Extracellular polysaccharides production by Arthrobacter viscosus

In this study the production of extracellular polysaccharides by the non-pathogenic soil bacteria Arthrobacter viscosus has been investigated. Different variables affecting extracellular polysaccharide production such as the carbon source (glucose or xylose), the agitation speed and the pH have been analysed.

In a first stage, experiments in shaken conical flasks (250 ml), containing 50 ml of culture medium, were carried out. Using xylose (25 g/l) as the carbon source at an initial pH 8 improved the extracellular polysaccharides levels obtained.

In a second stage, the experiments were scaling in bioreactors. Cultivation was carried out in discontinuous mode and with/without pH control. Polysaccharide production reached a maximum of 10 g of crude product per litre of growth medium after 14 days and the relationship between product formation and cell growth of A. viscosus is 2.7 g polysaccharide per gram biomass. This production was obtained at the optimal conditions determined with pH control at pH 7, xylose as carbon source (25 g/l) and an agitation rate of 800 rpm.     

试谈低pH值元明粉生产技术

从生产实际出发，通过一系列分析研究，找出了低pH值元明粉的生产方法。     

Xylose-lysine model systems: The effect of pH on the volatile reaction products

Aqueous molal solutions of xylose and lysine (initial pH 4–9) were refluxed either with control of the pH at 5–0 or without pH control (final pH 2–6). Analysis by gas chromatography (GC) and GC-mass spectrometry resulted in the identification of 58 and 28 compounds, respectively, from the two systems. Furans were the main reaction products in both systems and 2-furfural alone comprised 522 and 999 g kg^?1 of the volatiles, respectively, from the systems with final pH values of 5–0 and 2–6. Maintaining the pH at 5–0 resulted in a higher yield and greater numbers of nitrogen-containing compounds, and monocyclic pyrroles, pyridines and 2,3-dihydro-l H-pyrrolizines were identified only in that system. Aliphatic compounds, alicyclic compounds, benzene derivatives. l-(2–furfuryl)pyrroles and pyrazines were also identified. This investigation is the first report of the formation of 2.3-dihydro-l H-pyrrolizines in a model system containing lysine as the amino compound; a possible mechanism is proposed.     

土壤因子对植物缺铁失绿的影响

本文主要从土壤 pH ,重碳酸盐 ,和氮素形态等几方面综述了各种土壤因子对土壤缺铁失绿的影响 ,并提出了进一步加强研究的方向     

Sorption of Acid Green 25 on chitosan: Influence of experimental parameters on uptake kinetics and sorption isotherms

Acid Green 25, which is a diazoic dye bearing two sulfonic groups, is efficiently sorbed on chitosan. The protonation of chitosan may explain the electrostatic attraction of this anionic dye and that its optimum pH is close to 3. Preliminary protonation of amine groups (obtained by contact with a sulfuric acid solution) reduced the variation of solution pH following sorbent addition but significantly reduced sorption performance: the maximum sorption capacity of raw chitosan, 525 mg dye/g (0.84 mmol dye/g), was halved by acidic preconditioning. The acidic conditioning also reduced the kinetic rate—the time necessary to reach equilibrium increased up to threefold depending on the experimental conditions. The size of sorbent particles influenced sorption kinetics and equilibrium because of resistance to intraparticle diffusion, but the sorption appeared to occur not only at the surface of the sorbent but also in the intraparticle network of the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1073–1080, 2003     

Synthesis and characterization of chitosan/poly(acrylic acid) polyelectrolyte complex

Polyelectrolyte complex based on chitosan and acrylic acid monomer by photoinitiated free‐radical polymerization in the absence of crosslinker showed a large transition in swelling in response to changes in pH of surrounding medium. Their ability to swell arises from polyelectrolyte interactions and molecular structure of the complex. The main properties of interest that related to the molecular structure, swelling volumes, glass transition temperature, and elastic modulus of the complex were investigated. The effect of water content, the only variable in the sample component, played an important role in molecular structure of the complex and as a consequence, the extent of intermolecular linkage, especially amide bonds which in turn governed the degree of swelling of the polyelectrolyte complex in this study. The decreased degree of swelling and higher temperature shift of glass transition temperature was found with increased water content, whereas increased modulus of elasticity of dry complex was found in lower water content of synthesis component. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1025–1035, 2002     

一种新型硫酸亚铁单液法调剖剂

本文提出用尿素作为ｐⅡ调节剂，加快硫酸亚铁单液法调剖剂中亚铁离子在地层温度下的沉淀，增大沉淀率，提高封堵效能。岩芯流动试验结果表明，１５％ＦｅＳＯ４．７ＩＩ ２Ｏ／５％尿素调剖剂体系的封堵能力比不含尿素的体系增大近一倍。     

超强吸水树脂的吸水性能研究

对自制的超强吸水树脂的吸收性能进行了研究，分别考察了吸水树脂的粒径，溶液的pH值，几种离子如Na^ ,K^ ,Ca^2 ,Mg^2 等的水溶液对吸水树脂吸收性能的影响。实验结果表明，在pH为6－8，树脂粒径为100mesh-120mesh时，树脂的吸水性能最好，各种离子对吸水树脂吸收性能的影响大小顺序为：Na^ ＜K^ ＜Mg^2 ＜Ca^2 。     

Acidity in upland and hill soils: Cation exchange capacity,pH and lime requirement

For 30 acid upland and hill soils, with initial pH from 3.5 to 5.8, and loss on ignition from 14% to 94%, cation exchange capacity varied with pH according to the relationship CEC = m pH+C, where m and C are characteristic of each soil. The slope m depended on loss on ignition (LOI), and is given by: m=Δ CEC/Δ=0.22 LOI+1.92. Because of these relationships, CEC measured at the natural pH of the soil (in 0.025 M MgSO₄ solution) is more relevant to field conditions than a conventional measurement at pH7. An improved method for estimating lime requirement (LR) of these soils was developed, based on the relationship found between LR and the difference in CEC (ΔCEC) between that at the natural pH of the soil and that at the target pH of 5.5: LR=1.12 ΔCEC+1.48. Lime requirement can therefore also be estimated from loss on ignition using the earlier relationships, and is given by: LR=(0.25 LOI+2.15) Δ+1.48, where Δ is the difference between the natural pH (in 0.025 M MgSO₄) and the target pH. Predictions based on this agreed well with results for a further 10 soils.