Number Of Amide Groups Research Articles

Fabrication and characterization of a multi-functional GBR membrane of gelatin-chitosan for osteogenesis and angiogenesis

Guided bone regeneration (GBR) membranes are widely used to treat bone defects. In this study, sequential electrospinning and electrospraying techniques were used to prepare a dual-layer GBR membrane composed of gelatin (Gel) and chitosan (CS) containing simvastatin (Sim)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres (Sim@PLGA/Gel-CS). As a GBR membrane, Sim@PLGA/Gel-CS could act as a barrier to prevent soft tissue from occupying regions of bone tissue. Furthermore, compared with traditional GBR membranes, Sim@PLGA/Gel-CS played an active role on stimulating osteogenesis and angiogenesis. Determination of the physical, chemical, and biological properties of Sim@PLGA/Gel-CS membranes revealed uniform sizes of the nanofibers and microspheres and appropriate morphologies. Fourier-transform infrared spectroscopy was used to characterize the interactions between Sim@PLGA/Gel-CS molecules and the increase in the number of amide groups in crosslinked membranes. The thermal stability and tensile strength of the membranes increased after N-(3-dimethylaminopropyl)-N9- ethylcarbodiimide/N-hydroxysuccinimide crosslinking. The increased fiber density of the barrier layer decreased fibroblast migration compared with that in the osteogenic layer. Osteogenic function was indicated by the increased alkaline phosphatase activity, calcium deposition, and neovascularization. In conclusion, the multifunctional effects of Sim@PLGA/Gel-CS on the barrier and bone microenvironment were achieved via its dual-layer structure and simvastatin coating. Sim@PLGA/Gel-CS has potential applications in bone tissue regeneration.

Effects of the spacer length on the aggregate formation and the gelation of alkylamide amine oxides

Three kinds of alkylamide amine oxides having one, two, and three amides were synthesized, and their solution properties such as the surface tension and the viscosity were examined. The effects of the spacer group length n between amide and dimethyamine oxide group as well as the number of amide groups were examined with respect to the aggregation behavior. For short spacer lengths, amide groups join the hydrophilic head group, while for long spacer lengths, amide groups and a part of the spacer groups are suggested to reside in the micelle palisade layer. In a series of amphiphile having three amide groups, gels formed at a high concentration of 50 mM were tentatively grouped into two types: A and B, depending on the spacer length n. For Gel-A, the gelling temperature T gel increased linearly with n but it was scarcely affected by the protonation of amine oxide (AO) group. For Gel-A, fiber-like aggregates were observed in cryo-TEM images. For Gel-B, values of T gel were higher by 18 ± 2 K than those of Gel-A for a given n. Cryo-TEM images of Gel-B showed wide ribbon-like aggregates. On ionization of AO group, Gel-B transformed into Gel-A.

Highly Efficient Extraction of Rhodium(III) from Hydrochloric Acid Solution with Amide-Containing Tertiary Amine Compounds

Extraction of Rh(III) from a HCl solution with N,N-disubstituted amide–containing tertiary amine (ACTA) compounds (N,N-di-n-hexyl(N-methyl-N-n-octyl-ethylamide)amine (MonoAA), N-n-hexyl-bis(N-methyl-N-n-octyl-ethylamide)amine (BisAA), and tris(N-methyl-N-n-octyl-ethylamide)amine (TrisAA)) was investigated. The ACTAs extract Rh(III) more efficiently than tri-n-octylamine (TOA), and the extraction efficiency increases with increasing number of amide groups: TrisAA > BisAA > MonoAA ≫ TOA. For all ACTAs, the predominant Rh(III) complex extracted from 2 M HCl is probably {[RhCl5(H2O)]·(ACTA·H)2}. The apparent basicity of the ACTAs and TOA varies in the opposite order from that observed for the Rh(III) extraction efficiency. Rh(III) can be readily back-extracted using 10 M HCl solution possessing a high selectivity over similarly loaded Pd(II) and Pt(IV).

Consequences of Non-Uniformity in the Stoichiometry of Component Fractions within One and Two Loops Models of α-Helical Peptides

A 3-D electrostatic density map generated using the Wavefront Topology System and Finite Element Method clearly demonstrates the non-uniformity and periodicity present in even a single loop of an α-helix. The four dihedral angles (N-C*-C-N, C*-C-N-C*, and C-N-C*-C) fully define a helical shape independent of its length: the three dihedral angles, φ = -33.5°, ω = 177.3°, and Ψ = -69.4°, generate the precise (and identical) redundancy in a one loop (or longer) α-helical shape (pitch = 1.59 /residue; r = 2.25 ). Nevertheless the pattern of dihedral angles within an 11 and a 22-peptide backbone atom sequence cannot be distributed evenly because the stoichiometry in fraction of four atoms never divides evenly into 11 or 22 backbone atoms. Thus, three sequential sets of 11 backbone atoms in an α-helix will have a discretely different chemical formula and correspondingly different combinations of molecular forces depending upon the assigned starting atom in an 11-step sequence. We propose that the unit cell of one loop of an α-helix occurs in the peptide backbone sequence C-(N-C*-C)3-N which contains an odd number of C* plus even number of amide groups. A two-loop pattern (C*-C-N)7-C* contains an even number of C* atoms plus an odd number of amide groups. Dividing the two-loop pattern into two equal lengths, one fraction will have an extra half amide (N-H) and the other fraction will have an extra half amide C=O, i.e., the stoichiometry of each half will be different. Also, since the length of N-C*-C-N, C*-C-N-C*, and C-N-C*-C are unequal, the summation of the number of each in any fraction of n loops of an α-helix in sequence will always have unequal length, depending upon the starting atom (N, C*, or C).

Solution Properties of Tadpole-type Cationic Amphiphilic Dendrimers Consisting of an Alkyl Chain, a Quaternary Ammonium, and a Poly(amidoamine) Dendron

Tadpole-type amphiphilic dendrimers consisting of an alkyl chain, a quaternary ammonium bromide (qb) and a poly(amidoamine) dendron (den) (CnqbdenGm, where n represents an alkyl chain with a length of 10,14, or 18 carbons; m is the generation number G of dendron taking the value -0.5, 0.5, or 1.5) were synthesized using N, N-dimethylethylenediamine as a central scaffold. Electrical conductivity, surface tension, pyrene fluorescence, and dynamic light scattering measurements were used to characterize the properties of the dendrimers. In addition, the effect of the alkyl chain length and the generation number of a dendron on these properties was evaluated through a comparison with those of the corresponding previously reported amphiphilic dendrimers with lactobionamide sugar terminal groups (CnqbdenGmLac) and conventional cationic monomeric surfactants (CnTAB). Both critical micelle concentration (cmc) and surface tension (except for C18 series) were lower than those of CnqbdenGmLac and CnTAB with the same alkyl chain length, indicating that the synthesized amphiphilic dendrimers have an excellent micelle-forming ability in solution and high adsorption ability at the air/water interface, in spite of the large bulky dendron structure. When the alkyl chain length and the generation number of the amphiphilic dendrimers were increased, the surface tension became high because of the curved long alkyl chain and the bulky structure of dendron. Further, CnqbdenGm formed micelles with a small size in solution, and the micelles of CnqbdenG(-0.5) had almost a constant size despite the changes in the concentration, while those of CnqbdenG0.5 and CnqbdenG1.5 became smaller with increasing concentration. The difference in the behavior results from the difference in the number of amide groups in the low- and high-generation dendrons.

Outer-Sphere Coordination Chemistry: Amido-Ammonium Ligands as Highly Selective Tetrachloridozinc(II)ate Extractants

Eight new amido functionalized reagents, L(1)-L(8), have been synthesized containing the sequence of atoms R(2)N-CH(2)-NR'-CO-R″, which upon protonation forms a six-membered chelate with a hydrogen bond between the tertiary ammonium N-H(+) group and the amido oxygen atom. The monocationic ligands, LH(+), extract tetrachloridometal(II)ates from acidic solutions containing high concentrations of chloride ions via a mechanism in which two ligands address the "outer sphere" of the [MCl(4)](2-) unit using both N-H and C-H hydrogen bond donors to form the neutral complex as in 2L + 2HCl + MCl(2) ⇌ [(LH)(2)MCl(4)]. The strengths of L(1)-L(8) as zinc extractants in these pH-dependent equilibria have been shown to be very dependent on the number of amide groups in the R(3-n)N(CH(2)NR'COR″)(n) molecules, anti-intuitively decreasing with the number of strong hydrogen bond donors present and following the order monoamides > diamides > triamides. Studies of the effects of chloride concentration on extraction have demonstrated that the monoamides in particular show an unusually high selectivity for [ZnCl(4)](2-) over [FeCl(4)](-) and Cl(-). Hybrid-DFT calculations on the tri-, di-, and monoamides, L(2), L(3), and L(4), help to rationalize these orders of strength and selectivity. The monoamide L(4) has the most favorable protonation energy because formation of the LH(+) cation generates a "chelated proton" structure as described above without having to sacrifice an existing intramolecular amide-amide hydrogen bond. The selectivity of extraction of [ZnCl(4)](2-) over Cl(-), represented by the process 2[(LH)Cl] + ZnCl(4)(2-) ⇌ [(LH)(2)ZnCl(4)] + 2Cl(-), is most favorable for L(4) because it is less effective at binding chloride as it has fewer highly polar N-H hydrogen bond donor groups to interact with this "hard" anion.

Tuning of Thermochromic Properties of Polydiacetylene toward Universal Temperature Sensing Materials through Amido Hydrogen Bonding

Mono- and diamides derivatives of 10,12-pentacosadiynoic acid (PCDA) were synthesized from condensation of PCDA with various aliphatic and aromatic diamines. Polydiacetylenes of the amido-PCDA derivatives were prepared by photopolymerization of their molecular assembly homogeneously dispersed in aqueous media. Thermochromic properties of the resulting polydiacetylene sol were studied by temperature variable UV−vis spectrometry along with photographic recording. The color transition temperatures and thermochromic reversibility of the polymers are varied depended on the number of amide groups and the structure of the aliphatic and aromatic linkers. The phenylenediamide and polymethylenediamide PCDA derivatives give polydiacetylenes with complete thermochromic reversibility, while the polydiacetylenes obtained from 1,2-cyclohexylene and glycolic chain diamide derivatives exhibited irreversible thermochromism, whereas the polymers attained from the aromatic monoamide analogues are partially reversible. The va...

Ab Initio and QM/MM Study of Electron Addition on the Disulfide Bond in Thioredoxin

Thioredoxin controls the intracellular redox potential through a disulfide/dithiol couple. Under conditions of oxidative stress, this protein functions via one-electron exchange, in which formation of the disulfide radical anion occurs. Combined quantum mechanical (QM) and molecular mechanical (MM) calculations using two- and three-level ONIOM schemes were performed on the thioredoxin (Trx) protein of Chlamydomonas reinhardtii in its oxidized-disulfide and one-electron-reduced forms. In both cases, the active site disulfide moiety was described at the MP2(fc)/6-31+G(d) level, and larger regions of varying sizes around the active site were described at the B3LYP/6-31+G(d) level. The remainder of the 112 residues and 33 water molecules of the crystal structure (PDB entry 1EP7) were described by the AMBER force field. Adiabatic electron affinities were calculated for the disulfide bond in all systems. Separate QM or QM/QM calculations were performed on the QM regions to establish the role of the remainder of the protein on the active site properties. The radical anion species becomes more stable as the number of amide groups in the vicinity increases. One-electron reduction potentials were calculated for the small molecule models, and approximated for the protein for which the values are similar to the experimental one (approximately 0 V). This high reduction potential is due to interaction with the charged end of Lys40, as indicated by mutation in silico to norleucine. The inclusion of the protonated Asp30 side chain and a water molecule in the QM region leads to an increase in the electron affinity. Proton transfer from the Asp30 side chain to the Cys39 sulfur in the radical anion species is strongly disfavored. The radical anion is more stable than the protonated form, which is consistent with experimental results.

Mode of Membrane Interaction and Fusogenic Properties of a de Novo Transmembrane Model Peptide Depend on the Length of the Hydrophobic Core

Model peptides composed of alanine and leucine residues are often used to mimic single helical transmembrane domains. Many studies have been carried out to determine how they interact with membranes. However, few studies have investigated their lipid-destabilizing effect. We designed three peptides designated KALRs containing a hydrophobic stretch of 14, 18, or 22 alanines/leucines surrounded by charged amino acids. Molecular modeling simulations in an implicit membrane model as well as attenuated total reflection-Fourier transform infrared analyses show that KALR is a good model of a transmembrane helix. However, tryptophan fluorescence and attenuated total reflection-Fourier transform infrared spectroscopy indicate that the extent of binding and insertion into lipids increases with the length of the peptide hydrophobic core. Although binding can be directly correlated to peptide hydrophobicity, we show that insertion of peptides into a membrane is determined by the length of the peptide hydrophobic core. Functional studies were performed by measuring the ability of peptides to induce lipid mixing and leakage of liposomes. The data reveal that whereas KALR14 does not destabilize liposomal membranes, KALR18 and KALR22 induce 40 and 50% of lipid-mixing, and 65 and 80% of leakage, respectively. These results indicate that a transmembrane model peptide can induce liposome fusion in vitro if it is long enough. The reasons for the link between length and fusogenicity are discussed in relation to studies of transmembrane domains of viral fusion proteins. We propose that fusogenicity depends not only on peptide insertion but also on the ability of peptides to destabilize the two leaflets of the liposome membrane.

Acylation of Amines with Carboxyethyl Dextran Azides

The stability and reactivity of carboxyethyl dextran azides toward amines, and also the influence exerted by the pH of the reaction medium and pKa of the amine on the number of amide groups in acylation products were studied.

The γ-Radiolysis of Nylons: Molecular Rearrangement and Gas Production

The γ-radiolysis of nylons 12, 11, 6/12, 6/9, 6/6, and 6 were investigated. The IR spectra of film samples before and after the γ-irradiation show the formation of amines, aldehydes, and ketones, and suggest that the cleavage of amide group is one of the major processes of radiolysis. The yields of gaseous products and their evolution from the bulk were measured with a quadrupole mass spectrometer. Four gases were determined as the major radiolytic products and their yields were found to be in the order H2 > CO > CO2 > CH4 for all the nylons. The relationship between the gas yields and the chemical composition of the monomer unit shows that the H2 yield increases with the relative number of H atoms. The results suggest a random distribution of energy leading to H2 production. It was found that the yields of CO and CO2 decrease with an increase in the relative number of amide groups on the nylon monomer unit. Since these later products must be derived from the amide group, chain scission and fragmentation ...

Effect of Mixed Pendent Groups on the Solution and Catalytic Properties of Europium(III) Macrocyclic Complexes: Bifunctional and Monofunctional Amide and Alcohol Pendents in Septadentate or Octadentate Ligands

Five new Eu(III) macrocyclic complexes have been prepared and their solution and catalytic properties studied. The Eu(III) complexes with septadentate ligands TRED and NB-TRED dissociate rapidly at pH 7.4, 37 degrees C (TRED = 1,4,7-tris(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, NB-TRED = 1-(nitrobenzyl)-4,7,10-tris(hydroxyethyl)-1,4,7,10-tetraazacyclododecane). Dissociation rates as determined in the presence and absence of strongly binding competing ligands suggest that under most conditions the Eu(III) complexes of ATHC, ABHC, and CNPHC are more kinetically inert to dissociation than is the Eu(III) complex containing all hydroxyethyl groups (ATHC = 1-(carbamoylmethyl)-4,7,10-tris(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, ABHC = 1,7-bis(carbamoylmethyl)-4,10-bis(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, CNPHC = 1-(1-carboxamido-3-(4-nitrophenyl)propyl)-4,7,10-tris(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane). Laser-induced luminescence excitation spectra of Eu(III) complexes of ABHC, ATHC, CNPHC, THED, and S-THP suggest that there is a single major species in solution at pH 6.3 and a second species that appears at more basic pH values (THED = 1,4,7,10-tetrakis(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, S-THP = 1S,4S,7S,10S-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). The species present at basic pH is proposed to be an alkoxide or hydroxide complex; pK(a) values as determined by potentiometric titrations are 7.5 and 8.1 for Eu(CNPHC)(3+) and Eu(ABHC)(3+), respectively. Eu(CNPHC)(3+), Eu(ATHC)(3+), and Eu(ABHC)(3+) promote transesterification of the hydroxypropyl ester of 4-nitrophenyl phosphate with pseudo-first-order rate constants at pH 7.3, 37 degrees C, and 1.00 mM complex of 1.4 x 10(-)(5), 9.3 x 10(-)(6), and 1.0 x 10(-)(6) s(-)(1), respectively. Both Eu(CNPHC)(3+)and Eu(ABHC)(3+) promote attack of an hydroxyethyl group of the macrocycle on bis(4-nitrophenyl) phosphate with pseudo-first-order rate constants at pH 7.3, 37 degrees C, and 1.00 mM complex of 1.5 x 10(-)(4) and 3.5 x 10(-)(5) s(-)(1), respectively. In general, an increase in the number of amide groups on the macrocycle of the Eu(III) complex decreases the rate of both intramolecular or intermolecular phosphate diester transesterification reactions.

Peptide-mediated chiral discrimination in bilipeptides: biliverdin di- and tri-peptides

Synthetic biliverdin di- and tri-peptides (1)–(26) have been investigated by c.d. and u.v.–visible absorption spectroscopy with regard to the influence of their peptide chains on chiral discrimination of the helical, optically labile bilatriene backbone. In general, chiral discrimination increases with the number of amide groups per sidechain; the excess of population in bilitripeptides may exceed 85%. The preferred helicity of the bilatriene moiety is primarily determined by the presence of chiral centres between amide groups while the extent of discrimination depends on the steric requirements of all amino acid constituents present. In biliverdin bis(peptides) intramolecular interchain interactions may occur, lowering discriminatory efficiencies. Chiral discrimination is monitored by c.d. and its origin discussed in terms of intramolecular amide–bilatriene hydrogen bonding.

Quantitative estimation of the contribution of pyrrolcarboxamide groups of the antibiotic distamycin A into specificity of its binding to DNA AT pairs

Interaction of DNA with the analogs of the antibiotic distamycin A having different numbers of pyrrolcarboxamide groups and labeled with dansyl was studied. The binding isoterms of the analogs to synthetic polydeoxyribonucleotides were obtained. Analysis of the experimental data leads to the following conclusions: (1) the free energy of binding of the analogs to poly(dA).poly(dT) depends linearly on the number of amide groups in the molecule of the analog whereas attachment of each pyrrolcarboxamide group produces changes of 2 kcal/mole in the free energy; (2) attachment of a pyrrolcarboxamide unit to the GC pair results in the free energy change of 0.95 kcal/mole; (3) the binding of analogs to poly(dA).poly(dT) is a cooperative process, presumbly, dependent on conformational changes induced by the binding of analogs to DNA.

Calorimetric study of electron-donor properties of compounds of (CH3)n [(CH3)2N]3-nPO series

1. The calorimetric titration method was used to determine the composition and enthalpy of formation of the complexes of a number of phosphoric, dialkylphosphonic, and alkylphosphonic acid amides with SnCl4 and alkyltin chlorides. The donor capacity of the phosphoryl compounds changes nonmonotonic ally with increase in the number of amide groups, while the character of the change depends on the strength of the acceptor. 2. It is postulated that the ability of the discussed phosphoryl compounds to form complexes is determined by the competition of the inductive and conjugation effects of the substituents on the phosphorus atom, and also by the steric accessibility of the oxygen atom of the phosphoryl group.

Glycoenzymes: Structure and properties of the two forms of glucoamylase from Aspergillus niger

Aspergillus niger produces two forms (isoenzymes) of glucoamylase that are separable by electrophoresis or by chromatography on DEAE-cellulose and that are designated glucoamylase I and II. The molecular weight of glucoamylase I is 99,000, and that of glucoamylase II is 112,000. Both forms of the glucoamylase contain covalently linked carbohydrate (containing d-mannose, d-glucose, and d-galactose residues) and are therefore glycoenzymes. The carbohydrate-protein linkage in the glycoenzyme is primarily glycosidic to the hydroxyl group of l-serine and l-threonine residues, but glycosylamine linkages to l-asparagine and l-glutamine may also be present. Glucoamylase I and II possess identical amino acid compositions and, presumably, identical amino acid sequences. However, the two glycoenzymes differ in carbohydrate content, glucoamylase II containing nearly twice as many carbohydrate residues per molecule as glucoamylase I. Accordingly, it is suggested that the two forms of glucoamylase are isoglycoenzymes. The difference in electrophoretic and chromatographic properties of the isoglycoenzymes is probably due to a difference in the number of amide groups or glycosylaminically linked carbohydrate units in the polypeptide chains.

Studies on Two Physiological Forms of the Human Retinol-binding Protein Differing in Vitamin A and Arginine Content

Abstract The human retinol-binding protein (RBP) is shown to exist in two main physiological forms each of which displays electrophoretic heterogeneity. Only one of the two RBP components contains vitamin A. The retinol-containing RBP species is under physiological conditions firmly bound to thyroxine-binding prealbumin. The protein complex thereby formed is the actual vitamin A carrier normally encountered in plasma. The vitamin A-free form of RBP is unable to bind prealbumin. The difference in the affinity of the two RBP species for prealbumin made it possible to separate them by chromatography on a Sepharose gel to which prealbumin had been covalently attached. Differences in conformation between the two RBP components were established by physical-chemical, chemical, and immunological techniques. On polyacrylamide gel electrophoresis both species of RBP exhibited multiple bands. The studies revealed that the variations in electrophoretic mobility could be ascribed to differences in the content of vitamin A, in the number of amide groups, and in the sequence of the COOH-terminal amino acid residues. Hence, it was found that the vitamin A-containing form of RBP had an additional residue of arginine compared to the form lacking the vitamin. This result, obtained by amino acid analysis, was confirmed by peptide mapping, which revealed an arginine-stainable spot present only in the vitamin A-containing species. The COOH-terminal amino acid sequences in the two RBP species were -Lys-Arg-OH and -Lys-OH, respectively. The loss of 1 amino acid residue from the vitamin A-free species obviously causes a conformational change which is not compatible with the binding to prealbumin. Vitamin A per se is not a prerequisite for the binding of RBP to prealbumin since it was shown that RBP from which the vitamin had been extracted retained its affinity for prealbumin. The data obtained in this study strongly suggest that the species devoid of both vitamin A and the COOH-terminal arginine is a catabolite of RBP.

Electron donor capacity of certain compounds of trivalent phosphorus, containing P-O and P-N bonds

1. The electron donor capacity with respect to H-acid increases in the series from the complete amide of phosphorous acid. 2. The frequency shift and intensity of the absorption bands of H-complexes of derivatives of trivalent phosphorus are lower than for the corresponding esters and amines. 3. The change in the rate of alcoholysis and phenolysis was characterized quantitatively as a function of the strength of the H-acid and the number of amide groups in the molecule.