CONH Groups Research Articles

Partial molar heat capacity of the peptide group in aqueous solutions.

Integral enthalpies of solution at very high dilution of sodium salts of N-acetyl amino acids, N-acetyl peptides, and N-benzoyl glycine have been measured in water at 298.15 and 308.15 K. Standard heat capacities of solution at 303.15 K have been derived from the enthalpy of solution data. The peptide backbone-unit (CH2CONH) contribution toward the limiting partial molal heat capacities derived from these experimental results is compared with those obtained from Cop2 of other model compounds, viz. oligopeptides, pyrrolidones, piperidones, diketopiperazine, and amides. Cop2 of the peptide backbone unit observed in the sodium slats of the N-substituted amino acids and peptides is also correlated with the structural details of the compounds and it is concluded that Cop2 contribution of the whole CH2CONH group, rather than that of CONH group, should be used for predicting the heat capacities of polypeptides and proteins in aqueous solution.

Self‐association of N‐protected α‐amino acids. Optically active and racemic N‐tert‐butyloxycarbonyl‐alanine

AbstractThe ir absorption and x‐ray diffraction analysis of N‐tert‐butyloxycarbonyl‐DL‐alanine (t‐Boc‐DL‐Ala‐OH) in the solid state has revealed a new mode of self‐association for a N‐urethanyl‐α‐amino acid, i.e., ribbons of hydrogen‐bonded cyclic dimers formed through the —COOH groups. In contrast to the recemate, a water molecule, incorporated into the crystal of the chiral t‐Boc‐D‐Ala‐OH, alters in part that hydrogen‐bonding scheme. In the two independent molecules of the unit cell of the optically active alanine derivative, as in that of the racemic derivative: (i) the conformation of the —CONH group is trans, also a new observation for a N‐urethanyl‐α‐amino acid, and (ii) the overall conformation is quasi‐extended. These findings exclude the occurrence of an oxy‐C7 peptide conformation. In solvents of high polarity, strongly solvated species predominate, as shown by ir absorption spectroscopy. In deuterochloroform nonassociated and associated species occur simultaneously. No differences were observed between the optically active and racemic derivatives. The type of self‐association near saturation seems to differ, at least in part, from that found in the anhydrous racemic compound in the crystal state.

Structure of 5-Methyl-4-[(arylamino)methylene]-2,4-dihydro-3H-pyrazol-3-ones

5-Methyl-4-[(arylamino)methylene]-2,4-dihydro-3H-pyrazol-3-ones have been synthesized. Of the 12 possible tautomeric forms it has been shown that they exist as the (ary1amino)methylene tautomerwith intramolecular hydrogen bonding between the CO and exocyclic NH groups.

Synthesis of 6-alk-1′-enyl penicillanic acids; double bond isosteres of the side-chain amide linkage in penicillins

Two penicillin analogues have been prepared which incorporate CC bonds at C 6α and C 6β respectively, in place of the normal side-chain NHCO group.

Heat capacities of transfer of some amino acids and peptides from water to aqueous urea solution

AbstractIntegral enthalpies of solution at low concentrations of several amino acids and peptides in 2 and 6M urea solutions have been determined at 25 and 35°C. These data have been used to derive the enthalpies of transfer (at 25 and 35°C) and heat capacities of transfer (at 30°C) of these amino acids and peptides from water to aqueous urea solutions. Furthermore, the enthalpies of transfer and heat capacities of transfer per CH2 group and per peptide group CONH have also been estimated. These results show that while the enthalpies and heat capacities of transfer per CH2 group are positive and negative, respectively, the reverse is true for CONH group. The implications of these results in the mechanism of the denaturation of proteins by urea are discussed.

Freezing temperatures of aqueous solutions containing formamide, acetamide, propionamide and N,N-dimethylformamide. Free energy of interaction between the CONH and CH2 groups in dilute aqueous solutions

The freezing temperatures of dilute aqueous solutions of formamide, acetamide, propionamide and dimethylformamide have been determined. The data have been used, in association with appropriate enthalpy and heat capacity data, to calculate the pairwise free energy of self interaction coefficients at 298.15 K.The results for the unsubstituted amides are predicted with reasonable accuracy using the group additivity approach developed previously. In contrast to the results for the enthalpies of interaction, the free energies of interaction of the disubstituted amides are not accurately predicted.

Conformational energy calculations with averaged potential functions: Application to the repeat peptides of elastin

AbstractWe present a method that can reduce conformational energy calculations for an arbitrary peptide consisting of n residues (n‐peptide) to the complexity of a computation for (Gly)n. This reduction, and the concomitant savings in computer time, is accomplished by replacing all side chains, as well as the backbone CαHα and CαH2α groups, by “interaction centers.” The backbone CONH group is left intact in order to preserve its directional character. The interaction centers “see” each other, and the atoms of the CONH group via Boltzmann and space‐averaged effective center‐center and center‐atom potentials, respectively. This averaged‐interaction method is tested on the repeat tetra‐, penta‐, and hexapeptides of elastin, Val‐Pro‐Gly‐Gly (VPGG), Val‐Pro‐Gly‐Val‐Gly (VPGVP), and Ala‐Pro‐Gly‐Val‐Gly‐Val (APGVGV), using the stereoalphabet strategy for the energy calculations. The excellent qualitative and quantitative agreement we obtain with both full atom‐atom calculations and extensive nmr data, coupled with the order‐of‐magnitude reduction in computer time, augurs well for the potential usefulness of the method.

Nuclear-magnetic-resonance study of aggregations and conformations of melanostatin and related peptides.

The 1H and 13C nuclear magnetic resonance spectra of melanostatin (Pro-Leu-Gly-NH2) and related peptides (Pro-Leu-Gly, Z-Pro-Leu-Gly, Z-Pro-Leu-Gly-NH2 and Z-Pro-Leu-Gly-OCH3, where Z = benzyloxycarbonyl) were analysed in a variety of solvents. At physiological pH, the melanostatin molecule is N-protonated in aqueous solution. The concentration dependences of the chemical shifts of amide-proton and carbonyl-carbon resonances and of proton spin-lattice relaxation times were observed in relation to molecular aggregations. In dimethylsulfoxide solution, aggregations were observed for N-protonated melanostatin and Pro-Leu-Gly prepared with HCl and for the Na salt of Z-Pro-Leu-Gly but not for N-protonated melanostatin prepared with HClO4 or HNO3, unprotonated melanostatin, Z-Pro-Leu-Gly-NH2, or Z-Pro-Leu-Gly-OCH3. The leucine NH and glycine CO groups of N-protonated melanostatin are involved in the intermolecular hydrogen bonds of aggregates. The leucine NH group of N-protonated Pro-Leu-Gly also forms the intermolecular hydrogen bond. The solvent and temperature dependences of the chemical shifts of amide-proton and carbonyl-carbon resonances were measured to determine intramolecular hydrogen bonding. In dimethylsulfoxide solution, N-protonated melanostatin molecules in part take the beta-turn structure and the trans carboxamide NH proton and carbonyl oxygen of the proline residue form an intramolecular hydrogen bond.

Synthesis of Furo[2,3‐c]isoquinoline Derivatives

Abstract2‐Methylfuro [2,3‐c] isoquinolin‐5(4H)one (X) and 1‐phenylfuro[2,3‐c] isoquinolin‐5(4H)one (XI) were prepared from thermal cyelization via the Curtius rearrangement of 5‐methyl‐3‐phenyl‐2‐furoyl azide (VI) and 3,4‐diphenyl‐2‐furoyl azide (VII), respectively. Stability against acid, alkylation and conversion of the NHCO group to a C=N double bond of X and XI, which were synthesized, are described. Also, 5‐substituted furo[2,3‐c] isoquinolines (XVIIIa‐c) and (XIXa‐c) were prepared.

Freezing points of aqueous alcohols. Free energy of interaction of the CHOH, CH2, CONH and CC functional groups in dilute aqueous solutions

Download options Please wait... Article information DOI https://doi.org/10.1039/F19787401990 Article type Paper Download Citation J. Chem. Soc., Faraday Trans. 1, 1978,74, 1990-2007 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Freezing points of aqueous alcohols. Free energy of interaction of the CHOH, CH2, CONH and CC functional groups in dilute aqueous solutions B. Y. Okamoto, R. H. Wood and P. T. Thompson, J. Chem. Soc., Faraday Trans. 1, 1978, 74, 1990 DOI: 10.1039/F19787401990 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Byron Y. Okamoto Robert H. Wood Peter T. Thompson

Interactions of the conh group in solution. Interpretation of the infrared and raman spectra in relationship to secondary structures of peptides and proteins

A review is given of the infrared and Raman data which detect interactions of the CONH group through hydrogen bonding (solvent effects, selfassociation, internal chelations) and with ions using the vNH, Amide I, II, III bands of amides, oligopeptides and polypeptides. Examples are given whereby through vibration spectroscopy these various interactions can be related to secondary structure changes. The last part is devoted to critical remarks on tre interpretation of polypeptides and proteins spectra (170 references).

A possible mechanism of chain extension in nylon-6 during crystallization under pressure

The effect of pressure on crystallization from the melt and annealing of nylon-6 fractions has been investigated. Pressures exceeding 5 kbar and temperatures 40°C below the final melting temperature of the fractions under pressure, were sufficient to produce the extended-chain crystals by an isothermal crystallization from the melt as well as by annealing of the chain-folded material. Crystalline structure and the thermal characteristics of the extended-chain crystals formed from the fractionated nylo̧n-6, were identical to those of unfractionated polymer. G.p.c. analysis of the extended-chain material formed from the fractions of narrow molecular weight distribution showed that this material most probably had a wide molecular weight distribution, similar to that of unfractionated nylon-6. Based on a change in the molecular weight distribution and decrease in the molecular weight, concurrent with the extended-chain crystallization it is suggested that on the thermal treatment of polyamides under pressure a transamidation reaction occurs between the CONH groups of the broken folds of adjacent lamellae, which may lead to the chain extension.

Calorimetric studies of elastin solvation.

The interaction of ox ligamentum nuchae elastin (native, purified and soluble) with four different solvents was investigated by Differential Scanning Calorimetry. The freezable solvent content was determined, at different total solvent contents, from the melting endotherms, and the amount of unfreezable solvent was obtained by extrapolation. For two bifunctional solvents, water and ethylene glycol, the molar ratio "bound solvent/elastin residue" was the same for all the elastin samples investigated, and very close to 1.5. This result is identical to that obtained by other workers for the "water/CO-NH group" of synthetic amorphous polyamides, and it can suggest that the hydration of elastin is interpretable on the basis of a similar model. The model is based on a direct interaction of water with the peptide group, and suggests that 0.5 moles of water are strongly bound, and 1.0 moles are loosely bound to the CO-NH group. The ratio "bound water/elastin residue" is larger for the soluble beta elastin. Different molar ratios are also obtained for monofunctional solvents such as methanol and trifluoroethanol.

Infrared spectra in the vNH region and structures of associated species of acetamide

The IR spectra of a series of binary (1:1) and ternary (1:2) acetamide—base H-complexes are reported. Complicated v NH and v ND patterns observed in those spectra, as well as in the spectra of self-associated acetamide, are accounted for by Fermi perturbations and by the revealed cis— trans isomerism of the H-bonds. The two protons in the CONH 2-group are shown to be highly different with respect to hetero- and self-association processes and the cyclic structure of the acetamide dimer is proved. Frequencies and intensities of the v NH stretching vibrations in H-complexes, and corresponding H-bond strengths are evaluated.

Enthalpy of dilution of aqueous mixtures of amides, sugars, urea, ethylene glycol, and pentaerythritol at 25�C: Enthalpy of interaction of the hydrocarbon, amide, and hydroxyl functional groups in dilute aqueous solutions

The enthalpy of dilution of all one-and two-solute aqueous mixtures of a series of compounds were measured from about 0.2 to 2.0 mole-kg−1 at 25°C. The compounds included in the study wereN-methylformamide,N-methylacetamide,N-methylpropionamide,N-butylacetamide, urea, ethylene glycol, pentaerythritol, glucose, and sucrose. The results of the enthalpy measurements were used to calculate the pairwise enthalpy of interaction for each compound with all the other compounds. A simple additivity principle is used to correlate the data. The principle assumes that each functional group on one molecule interacts with every functional group on the other molecule and that each of these interactions has a characteristic effect on the enthalpy that is independent of the positions of the functional groups in the two molecules. The resulting equation gives a rough but useful correlation of the results. Of the six interactions between the CH2, CONH, and CHOH functional groups, the CONH−CONH interaction is the strongest, the CHOH−CHOH interaction is the weakest, and the CH2−CH2 interaction is about equal in magnitude to the rest of the interactions. Thus, the CH2−CH2 and CONH−CONH are not the only interactions making important contributions to the enthalpy of a wide variety of systems.

Solution conformation of a retro-D analogue of tocinamide.

The solution conformation of a retro-D analogue of tocinamide H-D-Cys-D-Asn-D-Gln-D-aIle-D-Tyr-NHCH2CH2S was examined using proton magnetic resonance and circular dichroism spectroscopy. The observations support major contributions to the conformational distribution from structures with a type I beta turn in the sequence D-Asp-D-Gln-D-aIle-D-Tyr. This is topologically similar to the beta turn proposed for oxytocin, L-Tyr-L-Ile-L-Gln-L-Asn, but with the polarity of the CONH groups reversed along the chain; the peptide is, however, hormonally inert. In conjuction with nuclear magnetic resonance data, the circular dichroism spectra are interpreted to indicate that the region of the peptide ring near the disulfide occurs in at least two different conformations. One of the side-chain carboxamides, probably that of asparagine, appears to be intramolecularly associated rather than freely exposed to solvent.

Relaxation Behavior of Poly(N-monosubstituted Methacrylamides)

Abstract A free-oscillating torsional pendulum was used to investigate the effect of substituents R on the dynamic mechanical relaxation behavior of poly(N-monosubstituted methacrylamides) in the temperature interval from –196 to 130°C. A comparison with the corresponding polymethacrylates shows that the relaxation motion of the side groups R, which gives rise to the low temperature dispersion (below – 130°C), is virtually independent of whether R is attached to COO or CONH groups. On the other hand the obtained data give evidence that a strong intermolecular interaction and high steric hindrances suppress the onset of the motion of CONH–R side chains as a whole. For the same reason the glass transition temperature of the poly(N-monosubstituted methacrylamides) is about 100°C higher than that of the corresponding polymethacrylates. The incorporation of low molecular weight substances leads to reduction of the low-temperature dispersion and to formation of a new secondary dispersion at a temperature of abo...

WATER SORPTION FOR ACRYLONITRILE/ACRYLAMIDE COPOLYMERS AND POLYACRYLONITRILE/POLYACRYLAMIDE BLENDS

Equilibrium water sorption isotherms for acrylonitrile (AN)/acrylamide (AAm) random copolymers and polyacrylonitrile (PAN)/polyacrylamide (PAAm) blend polymers were obtained and the sorptive capacity of these polymers was discussed.At low humidities, the sorptive capacity of random copolymers was higher than that of blend polymers. With increasing relative humidities the sorptive capacity of blend polymers approached that of random copolymers. BET sorption mechanism could be applied to these cases in the relative humidities 10% to 45%. Nm, water content per a CONH2 group, was constant at every composition of polymer. Moreover, Nm of blend polymers was not different from that of random copolymers.Clustering function showed that polyacrylonitrile had no clustering water over the whole range of humidity, while on polyacrylamide water molecules began to cluster at about 40% relative humidity. On random copolymers there was no clustering at low humidities, and the more acrylamide groups presented in the polymer matrix, the higher was its clustering tendency towards water. Whereas blend polymers had much clustering water even at low humidities for their strong hydrogen bonds between CONH2 groups, its clustering function showed a minimum at about 30% relative humidity where the polymer sorbed the water required to form monolayer.

Dilute solution properties of polylaurolactam

For a number of fractions and unfractionated samples of polylaurolactam, molecular weights ( M w = 1 × 10 4−12·5 × 10 4 ) were measured by the light-scattering method in a mixed solvent of m-cresol with 60 vol. % 2,2,3,3-tetrafluoropropanol; intrinsic viscosities were determined in m-cresol and 96% H 2SO 4, and the constants of the Mark-Houwink equation were calculated. The calculated values of the characteristic ratio of unperturbed dimensions (virtually identical for m-cresol and 96% H 2SO 4) were compared with the respective values for polypyrrolidone and polycaprolactam. It was found that the higher frequency of the CONH-groups reduces the rigidity of the polyamide chain.

Structure of poly- m-phenyleneisophthalamide

The unit cell of crystalline poly- m-phenyleneisophthalamide has been analysed. The cell is a triclinic, three dimensional PI group. The cell parameters are: a=b =5·36 A ̊ , c=11·3 A ̊ , α=β=112°40′, γ=87°35′ . The crystalline phase density is 1·465 g/cm 3. The planes of CONH groups make angles of 45 and 155° with benzene ring planes. H bonds are positioned alternately in the 010 and 100 planes. Dichroism values calculated for the vibrations of CO and CN are in good agreement with the values based on the IR spectra.