Adsorption of Sodium Cyanide on Pyrite Particle Surface

Adsorption of sodium cyanide on pyrite particle surface was studied. And influences of adsorbing time, dosage of pyrite, and pH on adsorbing effect were investigated. IR spectra, SEM, EDS and Element Area Scanning of samples before and after adsorption were measured. Results showed that adsorption of sodium cyanide on pyrite particle surface is a fast adsorbing process. As soon as adsorbing time is 1 min, adsorbing equilibrium is reached. At the condition of concentration of NaCN 24mg/L, adsorbing time 5min, and stirring rate 2000r/min, when dosage of pyrite particles is 5g/L, adsorbing rate is up to 80%, and at the time adsorbing capacity is the largest, 381.4mg/g. When pH is within 8.0-11.0, pH has little influence on adsorbing effect. IR and EDS results showed that at the particle range of-45μm is 93%, the surface of pyrite particles is easy to be oxidized and hydroxylated. S atoms on the surface of pyrite lattice are oxidized, while Fe atoms on the surface of pyrite lattice are hydroxylated. There exists hydrogen bond function between CN-and OH-, and there exists monomolecular chemical bond function between CN-and pyrite. And-Fe (CN)nm-(n<6) is produced on the surface of pyrite, thus the superficial properties of pyrite is changed.

Disulfide Bond in Pseudomonas aeruginosaLipase Stabilizes the Structure but Is Not Required for Interaction with Its Foldase

ABSTRACT Pseudomonas aeruginosa secretes a 29-kDa lipase which is dependent for folding on the presence of the lipase-specific foldase Lif. The lipase contains two cysteine residues which form an intramolecular disulfide bond. Variant lipases with either one or both cysteines replaced by serines showed severely reduced levels of extracellular lipase activity, indicating the importance of the disulfide bond for secretion of lipase through the outer membrane. Wild-type and variant lipase genes fused to the signal sequence of pectate lyase from Erwinia carotovora were expressed inEscherichia coli, denatured by treatment with urea, and subsequently refolded in vitro. Enzymatically active lipase was obtained irrespective of the presence or absence of the disulfide bond, suggesting that the disulfide bond is required neither for correct folding nor for the interaction with the lipase-specific foldase. However, cysteine-to-serine variants were more readily denatured by treatment at elevated temperatures and more susceptible to proteolytic degradation by cell lysates of P. aeruginosa. These results indicate a stabilizing function of the disulfide bond for the active conformation of lipase. This conclusion was supported by the finding that the disulfide bond function could partly be substituted by a salt bridge constructed by changing the two cysteine residues to arginine and aspartate, respectively.

A NOTE ON RISKY BOND VALUATION

This paper develops a corporate bond valuation model that incorporates a default barrier with dynamics depending on stochastic interest rates and variance of the corporate bond function. Since the volatility of the firm value affects the level of leverage over time through the variance of the corporate bond function, more realistic default scenarios can be put into the valuation model. When the firm value touches the barrier, bondholders receive an exogenously specified number of riskless bonds. We derive a closed-form solution of the corporate bond price as a function of firm value and a short-term interest rate, with time-dependent model parameters governing the dynamics of the firm value and interest rate. The numerical results show that the dynamics of the barrier has material impact on the term structures of credit spreads. This model provides new insight for future research on risky corporate bonds analysis and modelling credit risk.