Oxidizing agents native oxide

When chromatographic resolution of species based on modifications located at the protein surface is desired, it may be advisable to use conditions that favor retention of native conformation.17 Here, the standard acidic conditions described in the preceding text may be inappropriate, and mobile phases buffered near neutrality may be required. Buffers based on ammonium acetate, ammonium bicarbonate, and triethylammonium phosphate may prove more useful in resolving polypeptide variants with differing posttranslational modifications, amino acid substitutions, or oxidation and deamidation products. The addition of more hydro-phobic ion-pairing agents may be needed to obtain polypeptide retention, and a variety of alkyl sulfonates and alkyl amines have been described for specific applications.17... 

An entirely different property of subtilisin was affected by substituting leucine at the 222 location. Native BPN is extremely sensitive to the presence of oxidation agents, showing rapid inactivation when incubated in the presence of 0.3% H2O2 (Figure 4). The Leu-222 variant, in contrast, was found to be totally stable under the same oxidation conditions. The data clearly show that single amino acid alterations can have dramatic effects upon the activity of the enzyme. Similarly, other changes have been shown to affect catalytic properties, substrate specificities and thermostability (7,2,9). 

The intrinsic viscosity of native ribonuclease is very low. Harrington and Schellman (247) reported 3.3 ml/g at neutral pH in 0.1 M KC1. Buzzell and Tanford (265) found values of 3.3-3.5 ml/g over the entire pH range from 1 to 11 and ionic strengths from 0.05 to 0.25 M. This value increases dramatically on denaturation even without oxidation or reduction of the disulfide bonds to 8.5 ml/g (266). In the presence of reducing agents and 6 M guanidine hydrochloride the value is 16.0 ml/g (267). 

Abstract—This work studies the effects of self-oligomerization of the aminosilane coupling agent 3-aminopropyltriethoxysilane—also called y-aminopropyltriethoxysilane. 3-APS, y-APS, APS or AUOO (Union Carbide)—on the adhesion of thin polyimide films to a native-oxide silica surface under no stress, i.e. T(0) conditions, and after standard 85°C/8I%T H (temperature and humidity) stress. Techniques have been developed using both silicon and hydrogen NMR to control and monitor the degree of oligomerization in aqueous solutions at low concentrations (0.1 vol %). 

The aminosilane coupling agent 3-aminopropyltriethoxysilane or y-amino-propyltriethoxy silane—also abbreviated as 3-APS, y-APS, APS or A1100 (Union Carbide)—is widely used to promote adhesion between polyimide thin films and mineral surfaces such as native-oxide silica, alumina and various glass ceramics [1, 2]. The structure of APS and the hydrolysis reaction sire shown in Fig. 1. Typically, dilute aqueous solutions of 0.1 vol% or approximately 0.080 wt % are employed to prime the mineral surface. The mechanism for the interaction of the bifunctional aminosilane with the mineral surface is the subject of much speculation, although it is conjectured by Linde and Gleason [3] that the amine end initially forms an electrostatic bond with surface hydroxyls. Subsequently, possibly as the result of elevated temperatures, the silanol end of the molecule proceeds to form a siloxane-like bond with the surface and the amine... 

Figure 2. The proposed reaction of the bifunctional APS molecule when serving as an adhesion promoter or coupling agent for polyimide thin films on native-oxide ceramics such as silica and alumina.

As far as passivating film is concerned, in principle as shown in Fig. 8.1, the native copper oxide structures formed in the presence of a strong oxidizer under certain pH conditions can serve the purpose for many applications. For CMP purposes, such a hard surface film does not usually lead to any meaningful material removal under the mechanical forces exerted by a polishing pad. Therefore, there is a need to build a soft passivating layer on a copper film softened by the complexing agent. The most commonly used... 

While a copper-enriched surface has the implication of always causing accelerated electrochemical corrosion, replacing the native, hydroxylated, mixed Al-Mg oxide layer with a thin stable oxide layer seems to allow the plasma films to tightly adhere to the alloy surface. This adhesion, coupled with the barrier properties of the films, appears to provide additional protection of the oxide layer from contact with corrosive agents. 

The two most important sources of uranium are the minerals carnotite, where uranium occurs in the hexavalent oxide or hydrated oxide, and pitchblende, where uranium occurs mostly in the tetravalent state as a compound salt with other metals. It also occurs as a mixed oxide with titanium, thorium, and niobium in the tetravalent form. The tetravalent uranium minerals appear to have been geologically formed in the presence of reducing agents such as hydrocarbon minerals, graphite, native metals, and sulfide minerals, while such association is rarely observed with the hexavalent uranium minerals. 

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