Nuclear Magnetic Resonance Study of the Protolysis and Ionization of N-Methylacetamide<sup>1</sup>

Berger, Arieh; Loewenstein, A.; Meiboom, S.

doi:10.1021/ja01510a014

Cited by 240 publications

(101 citation statements)

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“…This behaviour agreed with the more acidic character of these protons bordering N-terminal residues [14]. In the pentapeptide an extreme broadening occurred around pH 8.7 for the a protons of the N-terminal LAla and Gly residues.…”

Section: P H Dependence Studiessupporting

confidence: 79%

¹H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

Delbarre

Migliore‐Samour

Gh³

et al. 1981

European Journal of Biochemistry

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The peptides ~A l a -~G l u (L-alanyl-D-glutamic acid), ~Ala-~Glu[~~A2pm(Gly)]NHz, i.e. N2-(L-ahy1-D-yisoglutaminyl)-N6-glycyl-~~-2,6-diaminopimelic acid, and ~A l a -~G h [~~A z p m ( G l y ) -~A l a ] , i.e. N2-(L-alanyl-i)-y glutamyl)-N6-glycyl-~~-a-2,6-diaminopimelyl-u-alanine, extracted from a Streptornyces strain and their immunostimulating synthetic lauroyl derivatives were studied by 'H NMR spectroscopy at 270 MHz. The chemical shift analysis confirms (a) the sequence of these compounds, (b) the occurrence of a y bond between Glu (or GluNH2) and Azpm, (c) the presence of a carboxamide group on the backbone of the tetrapeptide L A I~-D G I u [ I I A z p m (Gly)]. Temperature and pH studies strongly suggest that the tetrapeptide and pentapeptide exist under \cveral folded conformations characterized by a proximity between the NH; group of Gly and the Glu (or GluNH2) residue. The similarity between the chemical shifts of the corresponding protons in ~A l a -~G l u , lauroyl-LAla-oGlu and muramyl-LAla-DGluNHz shows that the coupling of the dipeptide with a lauroyl or a muramyl group does not induce significant changes in the structure of the peptide moiety. In the lipopeptide series the presence of the lauroyl chain leads to amphipathic substances which form micelles in aqueous solution as shown by the large increase of the proton linewidths. The iminunostimulating properties of this kind of peptide manifest themselves at very low concentration and only after their coupling with a susar or lipid moiety. These features can be interpreted by the formation of mixed complexes between the immunoadjuvants and cell membrane constituents.During the last ten years, a large number of studies has been devoted to bacterial and synthetic immunoadjuvants [1,2], mainly in order to determine their possible therapeutic applications. Their mechanism of action still remains unknown however. Recently we described a new family of natural and/or synthetic short lipopeptides which exhibit immunopotentiating activities although they are devoid of a sugar moiety [3,4]. From crude extracts of a Streptomyces strain possessing nonspecific immunopotentiating effects, a tetrapeptide was isolated and its structure established as ~A l a -~G l u [~~A~p m ( G l y ) ]: the presence of an amide group was detected and arbitrarily attributed to the a' COOH of Azpm. This peptide was biologically inactive by itself but its chemical coupling with lauric acid gave a substance endowed with adjuvant activities [3,4]. The synthetic lauroyl tetrapeptide lauroyl-r.Ala-uGlu[~~,~~A~pm(Gly)NH2] possessed immunostimulating properties [3,4] similar in many aspects to those observed with N-acetylmuramyl-L-alanyl-i>-isoglutamine (muramyl dipeptide) thus far considered as the minimal adjuvant-active structure of bacterial cell walls [5,6]. Similar features were found in two related substances, the lipodipeptide lauroyi-LAla-DGlu and the lipopentapeptide ~auroyl-~Ala-~Glu[~~A2pm(Gly)-~A~a]. The biological activity of these amphipathic compounds seems therefore...

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Section: P H Dependence Studiessupporting

confidence: 79%

¹H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

Delbarre

Migliore‐Samour

Gh³

et al. 1981

European Journal of Biochemistry

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“…In the present formamide complex, no evidence was found for a protonated formamide species, such as the IR spectra reported for acetamide cation in hydrogen-and aluminum-exchanged montmorillonites (Tahoun and Mortland, 1966a). The absence of a protonated formamide species is not surprising, inasmuch as protons dissociated from residual water in Na-montmorillonite should not produce an acidity strong enough, i.e., pH <0.8 (Berger et al, 1959), to protonate amides.…”

Section: Hydrolysis Of S-triazinementioning

confidence: 99%

Infrared Spectroscopic Study of the Formamide-Na-Montmorillonite Complex. Conversion of s-Triazine to Formamide

Nguyen

1986

Clays and clay miner.

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Abstract--The adsorption and degradation on montmorillonite of s-triazine, the parent compound of a major group of triazine-based herbicides, were studied by Fourier-transform infrared spectroscopy. The original s-triazine appeared to hydrolyze with residual bound water in montmorillonite at 20"C to produce formamide, which formed an intercalate with the clay. A mechanism for the conversion of s-triazine to formamide was proposed which does not support earlier reports that formic acid and ammonia are the reaction products. The infrared spectrum of the formamide-Na-montmorillonite intercalate suggests that formamide reacted with the exchangeable Na cation and that the NH2 group hydrogen bonded with the clay. Assuming the intercalated formamide molecule to be planar, the molecular plane was found to be inclined at ~33 ~ with respect to the plane of the silicate sheet. C-N and C-O bonds were also found to be tilted at the same angle with respect to the clay surface. The proposed orientation is in good agreement with the measured value of d (001) for the formamide-Na-montmorillonite complex. The proposed model of the formamide-montmorillonite complex serves as a basis for comparison of other clay-amide complexes that are important in protein-clay interactions.

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“…Under most conditions, amide HX is catalyzed by hydroxide ions (26,27) at a rate that is influenced by inductive and steric effects from adjacent side chains (28). For unstructured peptides, HX is a slow process simply because the hydroxide concentration is low.…”

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confidence: 99%

How amide hydrogens exchange in native proteins

Persson

Halle

2015

Proc. Natl. Acad. Sci. U.S.A.

127

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Amide hydrogen exchange (HX) is widely used in protein biophysics even though our ignorance about the HX mechanism makes data interpretation imprecise. Notably, the open exchange-competent conformational state has not been identified. Based on analysis of an ultralong molecular dynamics trajectory of the protein BPTI, we propose that the open (O) states for amides that exchange by subglobal fluctuations are locally distorted conformations with two water molecules directly coordinated to the N-H group. The HX protection factors computed from the relative O-state populations agree well with experiment. The O states of different amides show little or no temporal correlation, even if adjacent residues unfold cooperatively. The mean residence time of the O state is ∼100 ps for all examined amides, so the large variation in measured HX rate must be attributed to the opening frequency. A few amides gain solvent access via tunnels or pores penetrated by water chains including native internal water molecules, but most amides access solvent by more local structural distortions. In either case, we argue that an overcoordinated N-H group is necessary for efficient proton transfer by Grotthuss-type structural diffusion.protein dynamics | hydration | proton transfer | MD simulation | BPTI B efore the tightly packed and densely H-bonded structure of globular proteins had been established, Hvidt and Linderstrøm-Lang (1) showed that all backbone amide hydrogens of insulin exchange with water hydrogens, implying that all parts of the polypeptide backbone are, at least transiently, exposed to solvent. In the following 60 y, hydrogen exchange (HX), usually monitored by NMR spectroscopy (2) or mass spectrometry (3), has been widely used to study protein folding and stability (4-10), structure (11, 12), flexibility and dynamics (13-15), and solvent accessibility and binding (16,17), often with single-residue resolution. However, because the exchange mechanism is unclear, HX data from proteins can, at best, be interpreted qualitatively (18)(19)(20)(21)(22)(23)(24)(25).Under most conditions, amide HX is catalyzed by hydroxide ions (26, 27) at a rate that is influenced by inductive and steric effects from adjacent side chains (28). For unstructured peptides, HX is a slow process simply because the hydroxide concentration is low. For example, at 25°C and pH 4, HX occurs on a time scale of minutes. Under similar conditions, amides buried in globular proteins exchange on a wide range of time scales, extending up to centuries. HX can only occur if the amide is exposed to solvent, so conformational fluctuations must be an integral part of the HX mechanism (18).Under sufficiently destabilizing conditions HX occurs from the denatured-state ensemble, but under native conditions few amides exchange by such global unfolding (9, 29-31). For example, in bovine pancreatic trypsin inhibitor (BPTI), 8 amides in the core β-sheet exchange by global unfolding under native conditions (7, 32), whereas the remaining 45 amides require less extensive conforma...

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Nuclear Magnetic Resonance Study of the Protolysis and Ionization of N-Methylacetamide¹

Cited by 240 publications

References 0 publications

¹H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

¹H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

Infrared Spectroscopic Study of the Formamide-Na-Montmorillonite Complex. Conversion of s-Triazine to Formamide

How amide hydrogens exchange in native proteins

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Nuclear Magnetic Resonance Study of the Protolysis and Ionization of N-Methylacetamide1

Cited by 240 publications

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1H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

1H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

Infrared Spectroscopic Study of the Formamide-Na-Montmorillonite Complex. Conversion of s-Triazine to Formamide

How amide hydrogens exchange in native proteins

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Nuclear Magnetic Resonance Study of the Protolysis and Ionization of N-Methylacetamide¹

¹H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution

¹H NMR Studies of Natural and Synthetic Immunostimulating Peptides in Aqueous Solution