Amino acids, hydration

J. R. Bruton and H. C. McLaurine. Modified poly-amino acid hydration suppressant proves successful in controlling reactive shales. In Proceedings Volume, pages 127-135. 68th Annu SPE Tech Conf (Houston, TX, 10/3-10/6), 1993. 

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). 

Measurements of model polypeptides were consistent with the non-freezing water being primarily associated with ionic groups of the protein (Kuntz, 1971). A set of amino acid hydration values, constructed to calculate the amount of nonfreezing water according to the amino acid composition of a protein, gave estimates in close agreement with measurement (Kuntz, 1971). 

It is well known that water-mediated interaction stabilizes structure of biomolecules [1, 138, 247-250]. Therefore, several model molecular systems have been chosen to probe the water-mediated interactions in biomolecules and a large amount of experimental and theoretical work has been published over the years on this subject [78, 138, 251-258]. Since phenol is the simplest aromatic alcohol resembling chromophore of an aromatic amino acid, hydration of phenol molecules has been studied to understand H-bonding and solute-solvent interaction in biological systems. Several experimental and theoretical calculations have been made on the phenol-water clusters [259-273]. Recently, we have made a comprehensive analysis on structure, stability, and H-bonding interaction in phenol (P1-4), water (W1-4), and phenol-water (PmW (w = 1-3, n = 1-3, w + n < 4)) clusters using ab initio and DFT methods [245]. In this section, electronic structure calculations combined with AIM analysis on phenol-water clusters are presented. 

The modified procedure involves refluxing the N-substituted phthaUmide in alcohol with an equivalent quantity of hydrazine hydrate, followed by removal of the alcohol and heating the residue with hydrochloric acid on a steam bath the phthalyl hydtazide produced is filtered off, leaving the amine hydrochloride in solution. The Gabriel synthesis has been employed in the preparation of a wide variety of amino compounds, including aliphatic amines and amino acids it provides an unequivocal synthesis of a pure primary amine. 

Also the arene-arene interactions, as encountered in Chapter 3, are partly due to hydrophobic effects, which can be ranked among enforced hydrophobic interactions. Simultaneous coordination of an aromatic oc amino acid ligand and the dienophile to the central copper(II) ion offers the possibility of a reduction of the number of water molecules involved in hydrophobic hydration, leading to a strengthening of the arene-arene interaction. Hence, hydrophobic effects can have a beneficial influence on the enantioselectivity of organic reactions. This effect is anticipated to extend well beyond the Diels-Alder reaction. 

These observations can be extrapolated to the pyrrole series the 2-amino derivatives are very unstable whereas 3-aminopyrroles appear to be more stable. 3-Amino-l-tritylpyr-role (162) appears to exist in solution exclusively in the imino-A -pyrroline form (163) (83JCS(P1)93). 2-Aminoindole (164) is unusual in that it exists mainly as the 3//-tautomer (165). 4-Alkylaminoindoles (166) undergo an unexpected rearrangement to 4-amino-1-alkylindoles (167) when heated with p-toluenesulfonic acid hydrate (82CC1356). 

Reductive alkylation has been used to prepare a-amino acids suitable for lactam formation and further elaboration. In a single step a carbobenzyloxy group was removed, and alkylation with glyoxylic acid hydrate was achieved (18). 

Then, as described in U.S. Patent 3,158,648, the optical isomers may be resolved as follows. 37 g of racemic a-methYl-3,4-dihYdroxYphenylalanine are slurried at 35°C in 100 cc of 1.0 N hydrochloric acid. The excess solids are filtered leaving a saturated solution containing 34.6 g of racemic amino acid of which about 61% is present as the hydrochloride. The solution Is then seeded at 35°C with 7 g of hydrated L-o -methYl-3,4-dihYdroxYphenYlalanine (6.2 g of anhydrous material). The mixture is then cooled to 20°C in 30 minutes and aged one hour at 20°C. The separated material Is isolated by filtration, washed twice with 10 cc of cold water and dried in vacuo. The yield of product is 14.1 g of L-a-methYl-3,4-di-hydroxyphenylalanine in the form of a sesquihydrate of 100% purity as determined by the rotation of the copper complex. 

The amino acid leucine is biosynthesized from n-ketoisocaproate, which is itself prepared from -ketoisovalerate by a multistep route that involves (1) reaction with acetyl CoA, (2) hydrolysis, (3) dehydration, (4) hydration. (5) oxidation, and (6) decarboxylation. Show lhe steps in the transformation, and propose a mechanism for each. 

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

Intravenous replacement solutions are a source of electrolytes and water for hydration (Normosol M Ringer s Injection, Lactated Ringer s, Plasma-Lyte R), and used to facilitate amino acid utilization and maintain electrolyte balance (Lypholyte, Multilyte, TPN Electrolytes). Dextrose and electrolyte solutions such as Plasma-Lyte R and 5% dextrose are used as a parenteral source of electrolytes, calories, or water for hydration. Invert sugar-electrolyte solutions, such as Multiple Electrolytes and Travert 5% and 10%, contain equal parts of dextrose and fructose and are used as a source of calories and hydration. 

The protein that stores iron in the body is called ferritin. A ferritin molecule consists of a protein coat and an iron-containing core. The outer coat is made up of 24 pol3q5eptide chains, each with about 175 amino acids. As Figure 20-27 shows, the pol q5eptides pack together to form a sphere. The sphere is hollow, and channels through the protein coat allow movement of iron in and out of the molecule. The core of the protein contains hydrated iron(HI) oxide, FC2 O3 H2 O. The protein retains its shape whether or not iron is stored on the inside. When filled to capacity, one ferritin molecule holds as many as 4500 iron atoms, but the core is only partially filled under normal conditions. In this way, the protein has the capacity to provide iron as needed for hemoglobin s mthesis or to store iron if an excess is absorbed by the body. 

Certain alkylated ammonium, phosphonium, or sulfonium compounds are effective, in relatively low concentrations, in interfering with the growth of gas hydrate crystals [972] and therefore are useful in inhibiting plugging by gas hydrates in conduits containing low-boiling hydrocarbons and water. For example, tetrabutylammonium bromide will be active. Gas hydrate or ice formation is further inhibited in lines by adding amino acids or amino alcohols [523]. 

Modified amino acids such as N-acyl-dehydroalanine polymers and copolymers with N-vinyl-N-methyl acetamide seem to be particularly effective [396]. The crystallization kinetics in the presence of polyvinylpyrrolidone and tyrosine have been tested by time-resolved experiments [981]. An influence is evident on the particle size distribution of the hydrate [1433]. 

Solid state 13C CPMAS NMR spectra of Wheat High Molecular Weight (W.HMW) subunits show well resolved resonances identical with spectra of dry protein and peptide samples [24], Most of the amino acids side-chain resonances are found in the 0-35 ppm region followed by the alpha resonances of the most abundant amino acids glycine, glutamine and proline at chemical shifts of 42, 52 and 60 ppm, respectively, and the carbonyl carbons show a broad peak in 172-177 ppm region. The CPMAS spectra of hydrated whole HMW provides important information on the structural characteristics. 

FIGURE 88 Dating methods. Shortly after the discovery of radioactivity, at the beginning of the twentieth century, it was found that the decay of radioactive elements could be used to keep track of time. Many of the dating techniques developed since then are, therefore, based on radioactive decay phenomena, but others, such as the hydration of obsidian, amino acid racemization, and dendrochronology, are based on other physical, chemical, or biological phenomena. 

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