Lactic acid, ionization

Under cellular pH conditions, lactic acid ionizes to produce the anion lactate. 

The lactate formed by active skeletal muscles (or by erythrocytes) can be recycled it is carried in the blood to the liver, where it is converted to glucose during the recovery from strenuous muscular activity. When lactate is produced in large quantities during vigorous muscle contraction (during a sprint, for example), the acidification that results from ionization of lactic acid in muscle and blood limits the period of vigorous activity. The best-conditioned athletes can sprint at top speed for no more than a minute (Box 14-1). 

Lactic acid is more acidic than propanoic acid. The measured ionization constants are... 

As pointed out by Heller (2), polymer erosion can be controlled by the following three types of mechanisms (1) water-soluble polymers insolubilized by hydrolytically unstable cross-links (2) water-insoluble polymers solubilized by hydrolysis, ionization, or protonation of pendant groups (3) hydrophobic polymers solubilized by backbone cleavage to small water soluble molecules. These mechanisms represent extreme cases the actual erosion may occur by a combination of mechanisms. In addition to poly (lactic acid), poly (glycolic acid), and lactic/glycolic acid copolymers, other commonly used bioerodible/biodegradable polymers include polyorthoesters, polycaprolactone, polyaminoacids, polyanhydrides, and half esters of methyl vinyl ether-maleic anhydride copolymers (3). 

To what extent the 2-(a do-poly hydroxy alkyl) benzimidazoles can be used in resolving other optically active acids has not been determined. The benzimidazoles are relatively weak bases and do not form stable salts with weakly ionized acids. Haskins and Hudson15 found that when a solution of racemic lactic acid and 2-(D-gluco-D-gulo-hepto-hexa,hydroxy-hexyl)benzimidazole was concentrated, it was the free base that precipitated rather than one of the expected salts. It seems probable, however, that the method will be found useful in other resolutions, especially of the stronger organic acids. 

Figure 7. Ionization constants of acids in ethanol-water mixtures vs. the dielectric constant function at 25°C. A Malonic acid (O), lactic acid (A), succinic acid ( ). (B) Cyanoacetic acid ( ), salicyclic acid ( ), glutaric acid ( ). C Chloroacetic acid (O), glycolic acid (A), isovaleric acia(D).

Enantiomers have identical chemical properties except toward optically active reagents. The two lactic acids are not only acids, but acids of exactly the same strength that is, dissolved in water at the same concentration, bo h ionize to exactly the same degree. The two 2-methyl-1-butanoIs not only form the same products—alkenes on treatment with hot sulfuric acid, alkyl bromides on treatment with HBr, esters on treatment with acetic acid —but also form them at exactly ihe same rate. This is quite reasonable, since the atoms undergoing attack in each case are influenced in their reactivity by exactly the same combination of substituents. The reagent approaching either kind of molecule encounters the same environment, except, of course, that one environment is the mirror image of the other. 

The products were analyzed with a Shimadzu organic acid analyzer (LC-IOAD type) and an Okura SSC-1 steam chromatograph with a flame ionization detector and a Porapak R column. The products were found both in the solution and within the coated film. The samples for these analyses were the distillate that was prepared by evaporating 20 cm of the catholyte until 2 cm under reduced pressure. The products adsorbed on the coated film were released into 25 cm of distilled water under ultrasonic irradiation for 5 min. The identification of lactic acid (product) was performed by liquid chromatograph / electrospray mass spectrometry (LC/MS) examining negative ions. The apparatus used was a Hitachi M-1200 LC/MS. 

Prolonged exercise can temporarily overload the body s capacity for ehrnination of this substance, and the resulting increase in lactic acid concentration in the muscles causes pain and stiffness, (a) Lactic acid has six H atoms, yet it acts as a monoprotic acid in an aqueous environment. Which of the H atoms is ionizable (b) Draw the structural formula of the conjugate base, (c) Write a net ionic equation that illustrates the ionization of lactic acid... 

Lactic acid, C2H4(OF[)COOH, is found in sour milk. It is also formed in muscles during intense physical activity and is responsible for the pain felt during strenuous exercise. It is a weak monoprotic acid and therefore a weak electrolyte. The freezing point of a 0.0100 m aqueous solution of lactic acid is —0.0206°C. Calculate (a) the / value and (b) the percent ionization in the solution. 

Let X = molality of lactic acid that ionizes then... 

Figure 5.9. The Cori cycle. Note that muscle and other tissues can produce excessive lactic acid in early cancer. Some lactate ionizes to H ion and thus lowers local pH. These acid effects are thought to disturb cell-to-cell interactions by ceUnlar water and pH imbalances with chromatin/DNA rearrangements and hence is proposed to initiate neoplastic environments according to the Warburg cancer theory. The Cori cycle repeats many times in advancing cancer and because of the net loss of energy by 2 ATP - 6 ATP = -4 ATPs per each Cori cycle, there is loss in the ability maintain tissne. Hence, there is a wasting of tissne over time. Cachexia is seen in a high percentage of terminal cancer patients.

The use of electrodialysis in food, drug, and chemical industries has been studied quite extensively in recent years. Several applications have considerable economic significance and are already well established today. One is the demineralization of cheese whey [46]. Normal cheese whey contains between 5.5 and 6.5 % of dissolved solids in water. The primary constituents in whey are lactose, protein, minerals, fat and lactic acid. Whey provides an excellent source of protein, lactose, vitamins, and minerals, but in its normal form it is not considered a proper food material because of its high salt content. With the ionized salts substantially removed, whey provides an excellent source for the production of babyfood. The partial demineralization of whey can be carried out quite efficiently by electrodialysis. 

For example, PLA oligomers prepared by direct condensation of D,L-lactic acid have an amphiphilic surfactant similar structure, since the polymers are composed of a hydrophobic polyester chain ended with a carboxylic acid group, which can be ionized to form hydrophilic carboxylate polar heads at neutral pFl in water. 

Garozzo, D., Giuffrida, M., and Montaudo, G., Primary Thermal Fragmentation in Poly(Lactic-Acid) Investigated by Positive and Negative Chemical Ionization Mass Spectrometry, Polym. Deg. Stab., 15,143,1986. 

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