Α-amino Acid Groups Research Articles

New ampholytic microgels based on N-isopropylacrylamide and α-amino acid: changes in swelling behavior as a function of temperature, pH and divalent cation concentration

Several new microgels based on N-isopropylacrylamide and the amino acid L-ornithine were synthesized by means of surfactant free emulsion polymerization. N-δ-Acryloyl ornithine was copolymerized with N-isopropylacrylamide and N,N′-methylenebisacrylamide, leading to the synthesis of a new ampholytic microgel. The swelling behavior of the obtained microgels with respect to the amount of amino acid incorporated in the polymer network, temperature, concentration of ions and pH was investigated. The pH dependence of the microgel size, measured at a constant temperature, was found to exhibit a minimum; the pH range where the minimum appeared corresponded well with the pH range where zwitterions dominated. The temperature dependence of the swelling process obtained for different pH values showed that for the pH region where zwitterions dominated, the polymer networks collapsed more efficiently. The presence of free α-amino acid groups attached to the polymeric network of the microgels also enabled the complexation of some metal cations. The influence of the presence of two metal ions (Cu2+ and Ca2+), which differ significantly in their ability to form complexes with the α-amino-acid, on the swelling behavior was investigated. It was found that the presence of copper ions that form stable complexes with the α-amino acid strongly influenced the swelling behavior of the investigated microgels.

Polymeric hydrogels modified with ornithine and lysine: Sorption and release of metal cations and amino acids

AbstractA novel, convenient synthesis, using copper ions, is described for the multigram‐scale preparation of acryloyl and methacryloyl ornithine and lysine without the need to use protecting groups and chromatographic purifications. Three methods of removing the copper ions from the amino acid derivatives were examined. The obtained acryloyl and methacryloyl ornithine and lysine were copolymerized with N‐isopropylacrylamide and N,N′‐methylenebisacrylamide as crosslinking agents, resulting in a series of hydrogels with varying incorporated amino acid content. The relative content of a given amino acid was estimated from the 1H NMR data and compared with its molar fraction used in the polymerization process. We investigated the influence of the amount of amino acid groups incorporated into the polymer network on the swelling behavior of the gels in the presence of metal ions of different ability to form complexes (Cu2+, Co2+, and Ca2+) with α‐amino acid groups and the sorption of copper ions. Next, the presence of α‐amino acid groups attached to the polymer network was used to bond the compounds which can cocomplex metal ions. Phenylalanine was selected for examination of its cocomplexation of Cu2+ with the polymer‐network amino acids and its consecutive release from the gel after appropriate change of pH. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Effect of Extraction Temperature on Functional Properties and Antioxidative Activities of Gelatin from Shark Skin

Physico-chemical properties, functional properties, and antioxidative acitivities of gelatin from the skins of brownbanded bamboo shark (BBS; Chiloscyllium punctatum) and blacktip shark (BTS; Carcharhinus limbatus), as affected by extraction temperature, were investigated. α-Amino acid group content and surface hydrophobicity of both gelatins from both species increased as the extraction temperature increased (P < 0.05). Both gelatins had a high solubility (more than 80%) in a wide pH range (1–10). Both gelatins extracted at 60 °C exhibited the highest emulsion activity index (EAI), emulsion stability index (ESI) and foam expansion (FE). The lowest foam stability (FS) was obtained when gelatin was extracted at 75 °C (P < 0.05). The BBS gelatin had lower EAI, ESI, and FE than did BTS gelatin. Nevertheless, a higher FS was found in the former (P < 0.05). Antioxidative activities of both gelatins increased with coincidental increase in α-amino group content as the extraction temperature increased (P < 0.05). The BTS gelatin generally exhibited the higher antioxidative activities, compared with the BBS gelatin (P < 0.05). Gelatin extracted at 60 °C showed the highest interfacial properties, while those extracted at higher temperature (75 °C) had enhanced antioxidative activities. Extraction temperature may therefore be regulated to maximize applications.

ChemInform Abstract: Synthesis and Evaluation of ω-Borono-α-Amino Acids as Active-Site Probes of Arginase and Nitric Oxide Synthases.

Enantiomerically pure ω-borono-α-amino acids of various chain lengths have been synthesized according to a general methodology involving condensation of alkenyl and alkynyl bromides with NiII complex of the Schiff base derived from glycine and (S)-2-[N′-(N-benzylprolyl)amino]benzophenone, hydroboration of the intermediate ω-unsaturated α-amino acids with diisopinocampheylborane, and oxidation with acetaldehyde. Some of these compounds act as potent inhibitors of rat liver and murine macrophage arginases, demonstrating that distance between the B(OH)2 and α-amino acid groups is a key determinant for their interaction with arginase. In contrast, they are without effect on neuronal and inducible NO synthases.

New poly(N-δ-acryloyl ornithine) gels cross-linked with N,N′-methylenebisacrylamide. Sorption properties

To make a polymer from ornithine the acryloyl group was added to δ-amino group of the amino acid and N-δ-acryloyl ornithine was polymerized. The presence of α-amino acid groups attached to the polymeric network of the gels enables the complexation of some di- and trivalent metal cations. Copper ions, which can form two complexes of different stoichiometry (1:1 and 1:2) with amino acids, were used to investigate the influence of the complexation process on the swelling behavior and sorption properties of the obtained gels. The swelling ratio decreased as copper ion concentration increased. The poly(N-δ-acryloyl ornithine) gel was most sensitive to the copper ions in the concentration range of 1–100 mg/mL. The obtained UV–Vis spectra indicated that the copper ions mainly formed complexes of stoichiomery 1:2 with the α-amino acid group. Copper ion uptake was found to exceed 94% in a wide pH range (4–10). The maximum sorption capacity calculated by applying the Langmuir equation was 18.0 mg/g. Kinetic data showed that the sorption process reached equilibrium within 30 min and indicated the importance of the intraparticle diffusion step.

Influence of polymer network-metal ion complexation on the swelling behaviour of new gels with incorporated α-amino acid groups

New gels based on N-isopropylacrylamide and amino acid L-ornithine were prepared by free radical polymerization in aqueous solutions. To make the amino acid attachable to the polymer chain the acrylic group was added to the δ-amino group of ornithine, to obtain N-δ-acrylic ornithine. After the polymerization process the α-amino acid groups were unbound. The relative content of amino acid incorporated into the polymeric network of the gels was estimated from 1HNMR spectra, then compared with the molar fraction used for the polymerization process. The presence of free α-amino acid groups attached to the polymeric network of the gels enabled the complexation of some di- and trivalent metal cations. Copper ions, which can form two complexes of different stoichiometry (1 : 1 and 1 : 2) with amino acids, were used to investigate the influence of the complexation process on the swelling behavior of the gels. The influence of amino acid content, temperature and copper ion concentration on the swelling process was also examined. The gels were found to be most sensitive to concentrations of copper ions in the range 10−6–10−5 M. As the amount of amino acid in the polymer network increases the gels gradually lose their temperature-sensitivity and become more sensitive to copper ion concentration. The volume-phase-transition temperature decreases significantly after the addition of copper ions. Analysis of the UV-Vis spectra and the swelling behavior indicates that both 1 : 1 and 1 : 2 complexes are present in the swollen state of the gels, whereas the latter complex is more dominant in the shrunken state.

Drug Design, in Vitro Pharmacology, and Structure−Activity Relationships of 3-Acylamino-2-aminopropionic Acid Derivatives, a Novel Class of Partial Agonists at the Glycine Site on the N-Methyl-d-aspartate (NMDA) Receptor Complex

Retaining agonistic activity at the glycine coagonist site of the NMDA receptor in molecules derived from glycine or d-serine has proven to be difficult because in the vicinity of the alpha-amino acid group little substitution is tolerated. We have solved this problem by replacing the hydroxy group of d-serine with an amido group, thus keeping the hydrogen donor function and allowing for further substitution and exploration of the adjacent space. Heterocyclic substitutions resulted in a series of 3-acylamino-2-aminopropionic acid derivatives, with high affinities in a binding assay for the glycine site. In a functional assay assessing the activation of the glycine site, these compounds displayed a wide range of intrinsic efficacies, from antagonism to a high degree of partial agonism. Structure-activity relationships reveal that lipophilic substituents, presumably filling an additional hydrophobic pocket, are accepted by the glycine site, provided that they are separated from the alpha-amino acid group by a short linker.

Oxodesmosine and Isooxodesmosine, Candidates of Oxidative Metabolic Intermediates of Pyridinium Cross-Links in Elastin

We isolated two new dihydrooxopyridine cross-links, oxodesmosine (OXD) and isooxodesmosine (IOXD) from the acid hydrolysates of the bovine aortic elastin. OXD and IOXD were identified to have N-substituted 1,2-dihydro-2-oxopyridine and N-substituted 1,4-dihydro-4-oxopyridine skeletons, respectively, with three α-amino acid groups and mass of 495 (C23H37N5O7). These structures and distribution indicated that OXD and IOXD are oxidative metabolites generated from desmosine (DES) and isodesmosine (IDE), respectively, by reactive oxygen species (ROS). Effects of ROS derived from divalent metal (Fe2+, Cu2+)/H2O2 on DES, IDE, OXD, and IOXD in elastin were investigated. Changes in the contents of these cross-links in elastin were observed by using reverse-phase HPLC with UV detection. The time- and pH-dependent formation of OXD and reduction of DES and IDE in elastin by Cu2+/H2O2 and Fe2+/H2O2 were observed. OXD was found to be formed from DES by Fe2+/H2O2. No formation of IOXD was observed under the conditions of oxidation examined. By using a model compound of IDE, however, we found that 4-pyridone could be formed by Fe2+/H2O2. Elastin incubated in Cu2+/H2O2 was also solubilized dependent on solution pH and the concentration of H2O2. These results suggest that oxidative degradation of elastin with cross-links results in its weakening, followed by its solubilization. Pyridinium cross-links, such as DES and IDE, may be oxidatively metabolized by ROS, further changing to dihydrooxopyridine cross-links such as OXD and IOXD, respectively.

Synthesis and evaluation of ω-borono-α-amino acids † as active-site probes of arginase and nitric oxide synthases

Enantiomerically pure ω-borono-α-amino acids of various chain lengths have been synthesized according to a general methodology involving condensation of alkenyl and alkynyl bromides with NiII complex of the Schiff base derived from glycine and (S)-2-[N′-(N-benzylprolyl)amino]benzophenone, hydroboration of the intermediate ω-unsaturated α-amino acids with diisopinocampheylborane, and oxidation with acetaldehyde. Some of these compounds act as potent inhibitors of rat liver and murine macrophage arginases, demonstrating that distance between the B(OH)2 and α-amino acid groups is a key determinant for their interaction with arginase. In contrast, they are without effect on neuronal and inducible NO synthases.

Oxidation of functional olefines: Synthesis of protected amino acids bearing a terminal α-hydroxyketo group

The osmium trichloride-catalyzed oxidation with peracetic acid of olefinic compounds bearing a protected α-amino acid group leads to α-ketol amino acid precursors related to the 5-Hydroxy-4-Oxo-Norvaline antibiotic.

Covalent Protein Crosslinks: General Detection, Quantitation, and Characterization via Modification with Diphenylborinic Acid

Progressive crosslinking of proteins appears to be a general phenomenon in aging cells and tissues. Crosslinked proteins can form insoluble aggregates which become increasingly resistant to proteolysis as more crosslinks form. However, most evidence for progressive crosslinking with age is indirect, and little is known about the chemical mechanisms involved. We have therefore developed a method for detection and isolation of any type of stable covalent crosslink from protein hydrolysates which requires no prior knowledge of the molecular structure of whatever crosslink(s) may be present. It utilizes the specificity of the diphenylborinic acid reagent for α-amino acid groups and the chromatographic properties and uv absorbance of the crosslink derivatives. The method is demonstrated using eight different crosslinks from collagen and fibrin, and a general procedure is given for detection of any type of crosslink in a protein hydrolysate.

Relaxation Phenomena of Thermo-Shrinkage of Methacryloyl Polymer Gels with Pendant α-Amino Acid Groups

Swelling of methacryloyl polymer gels [CH 2 C(CH 3 )(CONHCHRCOOR')] n (R= CH 3 , R'= H, Me, Et, t-Bu, CH 2 Ph; R'= Me, R= H, Me, i-Pr, CH(Me)Et) was investigated as a function of temperature and time

A new temperature-sensitive hydrogel with α-amino acid group as side chain of polymer

New thermo-responsive hydrogels with α-amino acid groups as side chains, e.g. methacryloylglycine methyl ester, methacryloyl- l-proline [MA-( l)Pro] and methacryloyl- l-phenylalanine methyl ester, were synthesized by copolymerizing a hydrophobic monomer viz. 2-hydroxypropyl methacrylate (HPMA) and a crosslinking monomer viz. polyethylene glycol No. 600 dimethacrylate (14G), using γ-rays from a 60Co source. Of these hydrogels, the MA-( l)Pro-containing copolymer gels gave the strongest reversible thermo-response; the swelling-deswelling mechanisms can be classified into two types according to the kind of copolymer, viz. the surface regulating system for the MA-( l)Pro/HPMA copolymer and matrix pumping system for the MA-( l)Pro/14G copolymer. Thus, when raising the temperature, the copoly[MA-( l)Pro/HPMA] gel in the swollen state undergoes initial rapid shrinkage of the outer layer of the sample in contact with water, followed by a gradual deswelling. From microscopic observation, it was found that there are many micropores in the swollen gel but they disappear immediately after treating at high temperature, especially at the surface of the gel. In contrast, the swollen copoly[MA-( l)Pro/14G] gel undergoes rapid shrinkage of the whole sample without the disappearance of micropores. In addition, the control of drug release from such thermo-responsive copolymer formulations was investigated.

Antithrombic activity of some polysaccharide resins

Crosslinked dextrans (Sephadex®) bearing essentially car☐ymethyl, benzylsulphonate and α-amino acid groups have been synthesized. The antithrombic activity of the resins may be the result of a cooperative effect between the functional groups. The binding of benzylsulphonate to car☐ymethylated Sephadex endows these materials with activity. However the highest activity is obtained when the resins contain simultaneously benzylsulphonate, α-amino acid and car☐ylic acid groups.

Structure of ristocetin A.

Acid hydrolysis of ristocein A yields a number of amino acids of unusual structure. One set of diastereoisomeric pairs has a molecular weight of 362 and an empirical formula of C(17)H(18)N(2)O(7). Mass spectral and nuclear magnetic resonance (NMR) evidence suggest a diphenyl ether with hydroxyl and alpha-amino acid [-CH-(NH(2))COOH] groups on one ring, and methyl, hydroxyl and alpha-amino acid groups on the other ring. Coupling in the NMR and nuclear Overhauser effect experiments favor certain substitution patterns, which are shown. Another set of diastereoisomers seems to be a lower homolog of the previous set, without the aromatic methyl group.

Presence of N-acetyl group in hyaluronidase

Our previous investigations, concerning some of the chemical characteristics of hyaluronidase, have indicated leucine as its C-terminal amino acid, but, at the same time, have failed to reveal an N-terminal amino acid when fluorodinitrobenzene was used. The question thus arises as to whether or not this amino acid is masked because its α-amino acid group is blocked by an acyl residue. Our present investigation demonstrated the presence of an acetyl group in the hyaluronidase molecule. The method used was hydrazinolysis at 100 ° (18 hours), followed by coupling with 1-fluoro-2,4-dinitrobenzene and identification of DNP-acetylhydrazide ( N-2,4-dinitrophenylacetylhydrazide) by thin-layer chromatography on silica gel. The acetyl group is an N-acetyl group and not an O-acetyl group since DNP-hydrazide was not formed at room temperature. By chromatography on a Dowex 50W-X2 column and further purification by paper chromatography of a proteolytic digest of the hyaluronidase, a single ninhydrin-negative peptide, which reacted with the Rydon-Smith reagent, was identified among the many peptides so isolated, and demonstrated the blockage of the N-terminal amino acid. The following amino acids were identified after acid hydrolysis of this peptide: tyrosine, leucine, phenylalanine, alanine, and glutamic acid.