Low molecular weight organic acids

Oxidation first produces soluble oxygenated compounds of molecular weights between 500 and 3000 that increase the viscosity of oil then they polymerize, precipitate, and form deposits. Oxidation also causes formation of low molecular weight organic acids which are very corrosive to metals. 

Direct Metal Reaction. The DMR process is carried out over a catalyst with fatty acids ia a melted state or dissolved ia hydrocarbons. The acid reacts directiy with the metal, suppHed ia a finely divided state, produciag the metal soap and ia some cases hydrogen. Catalysts iaclude water, aUphatic alcohols, and low molecular-weight organic acids. 

Short-chain and low molecular weight organic acids, such as acetic acid and formic acid, can be formed by certain bacteria. The resulting organic acid salts are not easily detected without specialized analytical equipment in a laboratory. 

Acidolysis is a similar weathering reaction to hydrolysis in that is used to weather minerals, but in this case the source of is not water but organic or inorganic acids. Humic and fulvic acids (discussed in Section 8.3.2), carbonic acid, nitric or sulfuric acid, and low-molecular-weight organic acids such as oxalic acid can all provide H to weather minerals. All of these acids occur naturally in soils in addition nitric and sulfuric acid can be added to soil by acid pollution. The organic acids are prevalent in the... 

Del Nozal, M. J., Bernal, J. L., Diego, J. C., Gomez, L. A., and Higes, M. (2003a). HPLC determination of low molecular weight organic acids in honey with series-coupled ion-exdusion columns. /. Liq. Chromatogr. Relat. Technol. 26,1231-1253. 

F. S. Zhang, J. Ma, and Y. P, Cao, Phosphorus deficiency enhances root exudation of low-molecular weight organic acids and utilization of sparingly soluble inorganic phosphates by radish (Raphanus. sativus L.) and rape Bra.ssica napus L.) plants. 

L. Strom, T. Olsson, and G. Tyler, Differences between calcifuge and acidifuge plants in root exudation of low molecular weight organic acids. Plant Soil 167 239 (1994). 

G. Cieslinski, K. C. J. Van Rees, A. M. Szmigielska, G. S. R. Krishnamurti, and P. M. Huang. Low-molecular-weight organic acids in rhizosphere soils of durum wheat and their effect on cadmium bioaccumulation. Plant Soil 203 109 (1998). 

Gross differences have been ob.served in the amounts of fixed carbon released by annuals and perennials (47), with annuals releasing much less C than perennials. This effect may in part be due to perennials having to invest more of their assimilates to survive year round. Between more closely related plants, several studies have reported that both the quantity and quality of root exudates vary between plant species (39,48,49). In addition, it is also recognized that different cultivars of the same species may vary in their root exudation patterns. For example, Cieslinski et al. (50) quantified low-molecular-weight organic acids released... 

Renella G., Landi L., Nannipieri P. Degradation of low molecular weight organic acids complxed with heavy metals in soil. Geoderma 2004 122 311-315. 

Kwong KF Ng Kee, Huang PM (1981) Comparison of the influence of tannic acid and selected low-molecular-weight organic acids on precipitation products of aluminum. Geoderma 26 179... 

Thermal and catalytically cracked gasoline fractions can contain significant concentrations of phenols, low-molecular-weight organic acids, and alkyl and aryl mercaptans. All of these compounds can initiate gum formation in gasoline. Caustic treatment readily removes these compounds. 

By-products of anaerobic microbial metabolism include H2S, H2, CH4 and low molecular weight organic acids. Also the formation of FeS and the accumulation of microbial cell decomposition products can complicate the contamination problem. 

Isoelectric focusing is a procedure used to determine the isoelectric point (pi) of a protein (Fig. 3-21). A pH gradient is established by allowing a mixture of low molecular weight organic acids and bases (ampholytes p. 81) to distribute themselves in an electric field generated across the gel. When a protein mix-... 

Absorption methods are currently being used to collect polar air contaminants that are soluble in water. Low-molecular-weight organic acids and peroxides are examples of species that can be removed from ambient air that contacts a water surface. Formic and acetic acid can be collected by... 

The discovery of the TCA cycle began with a series i of biochemical experiments performed in the early 1900s on anaerobic suspensions of minced animal tissues. The experiments established that the suspensions contained enzymes that could transfer hydrogen atoms from various low-molecular-weight organic acids to other reducible compounds, such as the dye, methylene blue (methylene blue was a convenient indicator in these experiments because it is converted from a blue to a colorless form by... 

Gero, L., Smyrl, T.G. Behavior of low molecular weight organic acids during freeze-drying. J. Food Sci. 47, 954-957, 1982... 

Fox, T. R. 1995. The influence of low-molecular-weight organic acids on properties and processes in forest soils. In Carbon Forms and Functions in Forest Soils (W. W. McFee and J. M. Kelly, Eds.). Soil Science Society of America, Madison, WI. 

Fox, T. R., and N. B. Comerford. 1990. Low molecular weight organic acids in selected forest soils of the southeastern USA. Soil Science Society of America Journal 54 1139-1144. 

FIGURE 1 DOM pie diagram based on distribution of DOC in a typical river with a DOC concentration of 5 mg C/L (adapted from Thurman, 1985). Fulvic acids typically constitute the largest percentage of DOC, followed by low-molecular-weight organic acids. 

Brinkman, T., C. Zwiener, and F. H. Frimmel. 2000. Trace level determination of low molecular weight organic acids in humic substances by ion exchange chromatography. Vom Wasser 94 41—50. 

Karlsson, S., H. Wolrath, and J. Dahlen. 1999. Influence of filtration, preservation and storing on the analysis of low molecular weight organic acids in natural waters. Water Research 11 2569-2578. 

Jahnel, J. B., Brinkmann, T., Abbt-Braun, G., and Frimmel, F. H. (2002). Occurence of amino acids, carbohydrates, and low-molecular-weight organic acids in refractory organic substances. In Refractory Organic Substances (ROS) in the Environment, Frimmel, F. H., Abbt-Braun, G., Heumann, K. G., Hock, B., Ltidemann, H.-D., and Spiteller, M., eds., Wiley-VCH, Weinheim, pp. 264-281. 

Figure 13.3. Appearance of non-size-exclusion effects on SEC-elution curves of polyelectrolytes and other charged analytes including low-molecular-weight organic acids. Kd is the distribution coefficient and Ve, V0, and Vt are elution volume of the analyte, column void volume, and total column volume, respectively.

P. A. W. van Hees, S. I. Vinogradoff, A. C. Edwards, D. L. Godbold, and D. L. Jones, Low molecular weight organic acid adsorption in forest soils effects on soil solution concentrations and biodegradation rates, Soil Biol. Biochem. 35, 1015-1026 (2003). 

P. A. W. van Hees, U. S. Lundstrom, and R. Giesler, Low molecular weight organic acids and their Al-complexes in soil solution—composition, distribution and seasonal variation in three podzolized soils, Geoderma 94, 173-200 (2000). 

Adsorbed films of ethykriethoxysilane and vinyltriethoxy-silane were formed on silica and alumina by retraction from hydrocarbon solution and their wettabilities and water-stabilities determined. The vinyltriethoxysilane films were generally more oleophobic, more hydrophobic and more resistant to contact with water than the films formed by the ethyl analog. Neither adsorbate formed stable films on a-alumina. The addition of low molecular weight organic acids or bases to the adsorbate solution resulted in both the ethyl and vinyl compound forming hydrophobic and water-stable films on silica and ot-alumina. Films of p-chloro-phenyl-ft-ethyltrichloro, -trimethoxy, and -triethoxysilane were also studied and found to be water-stable and to have wettabilities characteristic of a surface comprised of closely-spaced p-chlorophenyl groups. 

---