Amino acids crystalline solutions

In Parenteral and Enteral Nutrition. Amino acid transfusion has been widely used since early times to maintain basic nitrogen metaboHsm when proteinaceous food caimot be eaten. It was very difficult to prepare a pyrogen-free transfusion from protein hydrolysates. Since the advances in L-amino acid production, the crystalline L-amino acids have been used and the problem of pyrogen in transfusion has been solved. The formulation of amino acid transfusion has been extensively investigated, and a solution or mixture in which the ratio between essential and nonessential amino acid is 1 1, has been widespread clinically. Special amino acid mixtures (eg, branched chain amino acids-enriched solution) have been developed for the treatment of several diseases (93). 

Crystalline amino acid bulk solutions are supplied by various manufacturers in various concentrations (e.g., 3.5%, 5%, 7%, 8.5%, 10%, 15%, and 20%). Different formulations are tailored for specific age groups (e.g., adults and infants) and disease states (e.g., renal and liver disease). Specialized formulations for patients with renal failure contain higher proportions of essential amino acids. Formulas for patients with hepatic encephalopathy contain higher amounts of branched-chain and lower amounts of aromatic amino acids. However, these specialized formulations should not be used routinely in clinical practice because their efficacy has not been clearly demonstrated. Crystalline amino acid solutions have an acidic pH (pH = 5-7) and may contain inherent electrolytes (e.g., sodium, potassium, acetate, and phosphate). 

Properties White, crystalline powder. Bulk d 70 lb/ cu ft, decomposes to monohydrate at 100C. Soluble in water slightly soluble in alcohol insoluble in hydrocarbons. Aqueous solutions are strongly acidic, will precipitate potassium ions and amino acids from solution, are decomposed by bases and heat. 

Much work has been done on the irradiation of amino acids in solution (8, 9, 10, 11, 16, 21) but little information can be found on solid state work (1, 18) despite the advantage of avoiding indirect effects. EPR investigations of irradiated glycine (4, 6, 12, 22) and alanine (17) offer independent results of a physical nature which correlate with the chemical results of this investigation. The qualitative and quantitative effects of alkali metal cations in the crystalline matrix also are helpful in determining the mechanism of irradiation produced decomposition. 

Crystalline solid m.p. 35-36 "C, b.p. 154--156 C, prepared by oxidizing A,A -dicycIo-hexylthiourea with HgO in carbon disulphide solution, also obtained from cyclohexylamine and phosgene at elevated temperatures. Used as a mild dehydrating agent, especially in the synthesis of p>eptides from amino-acids. Potent skin irritant. 

Crystalline derivatives of amino acids are usually produced by reaction at the amino group by treatment with appropriate reagents in alkaline solution ... 

Licjuid Crystals. Ferroelectric Hquid crystals have been appHed to LCD (Uquid crystal display) because of their quick response (239). Ferroelectric Hquid crystals have chiral components in their molecules, some of which are derived from amino acids (240). Concentrated solutions (10—30%) of a-helix poly(amino acid)s show a lyotropic cholesteric Hquid crystalline phase, and poly(glutamic acid ester) films display a thermotropic phase (241). Their practical appHcations have not been deterrnined. 

The enantioselective inverse electron-demand 1,3-dipolar cycloaddition reactions of nitrones with alkenes described so far were catalyzed by metal complexes that favor a monodentate coordination of the nitrone, such as boron and aluminum complexes. However, the glyoxylate-derived nitrone 36 favors a bidentate coordination to the catalyst. This nitrone is a very interesting substrate, since the products that are obtained from the reaction with alkenes are masked a-amino acids. One of the characteristics of nitrones such as 36, having an ester moiety in the a position, is the swift E/Z equilibrium at room temperature (Scheme 6.28). In the crystalline form nitrone 36 exists as the pure Z isomer, however, in solution nitrone 36 have been shown to exists as a mixture of the E and Z isomers. This equilibrium could however be shifted to the Z isomer in the presence of a Lewis acid [74]. 

Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They have large dipole moments, are soluble in water but insoluble in hydrocarbons, and are crystalline substances with relatively high melting points. In addition, amino acids are amphiprotic they can react either as acids or as bases, depending on the circumstances. In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton to yield a cation in aqueous base solution, the zwitterion is an add that loses a proton to form an anion. Note that it is the carboxylate, -C02-, that acts as the basic site and accepts a proton in acid solution, and it is the ammonium cation, -NH3+, that acts as the acidic site and donates a proton in base solution. 

Since these investigations could be carried out only in the crystalline state, the question of the dynamics of the triple-helix formation and of the correlation of its stability with the amino acid sequence could be answered only with the help of other methods working in solution. 

A substrate is a substance that is the basic component of an organism. Protein substrates are amino acids, which are essential to life Protein substrates are amino acid preparations that act to promote the production of proteins (anabolism). Amino acids are necessary to promote synthesis of structural components, reduce the rate of protein breakdown (catabolism), promote wound healing, and act as buffers in the extracellular and intracellular fluids. Crystalline amino acid preparations are hypertonic solutions of balanced essential and nonessential amino acid concentrations that provide substrates for protein synthesis or act to conserve existing body protein. 

Patient case A patient s daily nutritional requirements have been estimated to be 100 g protein and 2,000 total kcal. The patient has a central venous access and reports no history of hyperlipidemia or egg allergy. The patient is not fluid restricted. The PN solution will be compounded as an individualized regimen using a single-bag, 24-hour infusion of a 2-in-1 solution with intravenous fat emulsion (IVFE) piggybacked into the PN infusion line. Determine the total PN volume and administration rate by calculating the macronutrient stock solution volumes required to provide the desired daily nutrients. The stock solutions used to compound this regimen are 10% crystalline amino acids (CAA), 70% dextrose, and 20% IVFE. 

Silk type Function Proteins (ratio )a Predicted structure from sequence Amino acid (%Y Structure in solution Conformational change in solutione Fiber degree of crystallinity mf Fiber extensibility (%)e... 

Infants treated before 1979 received protein hydrolysates containing high concentrations of phosphate which limited the concentration of calcium that could be used without causing precipitation. Beginning in 1979 crystalline amino acid solutions which contained less obligatory phosphate became available these allowed greater latitude in the concentrations of calcium and phosphate that could be achieved. The data in Table I suggest that the severity of demineralization and the incidence of fractures and rickets will decrease if more calcium is added to the parenteral alimentation solution. 

Activated esters of A-alkoxycarbonylamino acids are prepared by two approaches, activation of the acid followed by reaction with the hydroxy compound, and trans-esterification. Most of the products are stable enough to be purified by washing a solution of the ester in an organic solvent with aqueous solutions. A few that are not crystalline are purified by passage through a column of silica. The commonly used method for their preparation is addition of dicyclohexylcarbodiimide to a cold mixture of the reactants in dimethylformamide or ethyl acetate. The first Boc-amino acid nitrophenyl esters were obtained using pyridine as solvent. Pyridine generates the nitrophenoxide ion that is more reactive. For one type of ester, 2-hydroxypyridino... 

Biochemistry and chemistry takes place mostly in solution or in the presence of large quantities of solvent, as in enzymes. As the necessary super-computing becomes available, molecular dynamics must surely be the method of choice for modeling structure and for interpreting biological interactions. Several attempts have been made to test the capability of molecular dynamics to predict the known water structure in crystalline hydrates. In one of these, three amino acid hydrates were used serine monohydrate, arginine dihydrate and homoproline monohydrate. The first two analyses were by neutron diffraction, and in the latter X-ray analysis was chosen because there were four molecules and four waters in the asymmetric unit. The results were partially successful, but the final comments of the authors were "this may imply that methods used currently to extract potential function parameters are insufficient to allow us to handle the molecular-level subtleties that are found in aqueous solutions" (39). 

The amino acid is recrystallized by dissolving all the crude material in 12.5 1. of water heated to 950 on a steam cone. The hot solution is treated with 20 g. of Norite for thirty minutes and filtered hot. An equal volume of 95 per cent alcohol is added immediately, and the flask is placed in the icechest overnight. The crystalline material is collected on a filter and washed with 200 cc. of 95 per cent alcohol. The yield of pure leucine in this fraction is 290-300 g. An additional crop is obtained by evaporating the mother liquors under reduced pressure until considerable solid separates (liquid volume about 1 1.), adding an equal volume of alcohol, and cooling. This crop is washed with 100 cc. of cold water and then with 200 cc. of alcohol it amounts to 60-65 g- The total yield of pure leucine is 350—365 g. (43-45 per cent of the theoretical amount). It decomposes at 290-292° (uncorr.) in a sealed capillary (Note 4). 

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