Bond In Side Chain Research Articles

Topological properties of the peptide bond in glycyl-L-threonine dihydrate based on a fast synchrotron/CCD-diffraction experiment at 100 K.

The charge density of glycyl-L-threonine dihydrate is extracted from a synchrotron data set of 98405 reflections collected at 100 K with a Bruker CCD area detector up to a resolution of d=0.38 A (sintheta/lambda = 1.32 A 1). The data are interpreted in terms of the "rigid pseudoatom" model. The topology of the experimental density is analyzed and compared with the topology obtained experimentally for the constituting amino acids and to that derived from Hartree-Fock calculations for the isolated molecule. All critical points of the electron density at the covalent and hydrogen bonds, as well as those of the Laplacian, were located, thereby deriving quantitative topological data for the peptide and side chain bonds. Bond topological indices in the dipeptide compare well with those of the corresponding bonds in the building amino acids, thus suggesting transferability of electronic properties of atoms and functional groups when these are derived by Bader's partitioning. Discrepancies between theoretical and experimental results could be attributed to crystal field effects.

BIOTRANSFORMATION OF ASPEN LIGNIN BY THE FUNGUS Trametes villosus

Quantitative1H and13C NMR spectroscopies demonstrate that biotransformation of aspen wood by the fungusTrametes villosusresults in oxidation and destruction of lignin with cleavage of C-C alkyl-alkyl bonds in side chains and partial demethoxylation in addition to cleavage of lignocarbohydrate bonds. New Car-O-C bonds form while lignin is being destroyed at alkyl-alkyl bonds. Cleavage of rings and destruction of Car-C bonds was not observed.

Crystallization and Cocrystallization in Supramolecular Comb Copolymer-like Systems: Blends of Poly(4-vinylpyridine) and Pentadecylphenol

The solid state of comb copolymer-like systems obtained by blending poly(4-vinylpyridine) with pentadecylphenol was studied by a combination of techniques. Depending on the amount of pentadecylphenol, several regimes are present. For 0.5 ≤ x ≤ 1.0 (x is the ratio between the number of phenol and pyridine groups) the alkyl tails form an interdigitated hexagonally packed crystalline layer. Small-angle X-ray scattering measurements show that for x = 1.5 and 2.0 the excess pentadecylphenol cocrystallizes with the associated pentadecylphenol, with the free phenol groups probably aggregating near the middle of the crystalline layer. For x ≥ 2.0 the orthorhombic crystal modification also appears. Finally for x ≥ 3.0, part of the excess pentadecylphenol macrophase separates on crystallization, forming an additional phase of pure pentadecylphenol with the familiar orthorhombic packing. These findings are similar to results obtained for real comb copolymer systems, i.e., containing covalently bonded side chains. However, our systems are essentially different due to the dynamic hydrogen-bonding equilibrium, which implies that the equilibrium solid state may always involve some form of macrophase separation.

Synthesis of silicon-based polymer films by UV laser ablation deposition of poly(methylphenylsilane)

The deposition of silicon-based polymer film by UV laser ablation of poly(methylphenylsilane) (PMPS) was studied. Deposited films were formed by UV laser ablation deposition of PMPS. The molecular weights of the deposited films were smaller than that of the original polymer. The films exhibited a broad molecular weight distribution ranging from a few hundred to ca. 20 000. The molecular weight distribution of the film depended on the laser fluence and the laser wavelength. The ablation process caused the SiSi bonds in the PMPS to be converted into SiC bonds, at the same time the deposited films contained the same side chain bonds as PMPS. In addition, the deposited films displayed a SiH and an inorganic-like network SiC bond, which was not contained in the original PMPS. The ablation at 351 nm suppressed the formation of both the SiH and the inorganic-like network SiC bond.

Infrared Absorbances of Protein Side Chains

The spectral parameters of amino acid residue side chain and peptide bond absorptions in the region 1800–1440 cm−1have been obtained by using an inverse matrix method applied to the infrared spectra of 42 amino acids, dipeptides, and higher peptides in aqueous solution. In addition the pH-dependent extinction coefficients of the amino acid and peptide COO−/NH+3end groups were derived. It is shown that the secondary structure prediction accuracy of proteins by multivariate data analysis methods increases slightly, if the side chain absorbances of the residues asparagine, glutamine, aspartic acid, glutamic acid, arginine, tyrosine, and lysine are subtracted from the amide I and amide II region.

Structural Requirements of Jasmonates and Mimics for Nicotine Induction inNicotiana sylvestris

Jasmonic acid (JA) is strongly implicated in the long-distance signal transduction cascade increasing nicotine synthesis in the roots of plants after leaf wounding. In order to explore the structural requirements of the inducing signal, we examined jasmonates, mimics, and a biosynthetic precursor for nicotine-inducing activity (NIA). We examine the importance of the keto group on the five-membered ring and the double bond in then-pentenyl chain by comparing the NIA of methyl jasmonate (MJ) with that of cucurbic acid, 1,3-dithiolane-MJ, 1,3-dioxolane-MJ, methyl dihydrojasmonate (DHMJ), 1,3-dioxolane-DHMJ, 1-oxo-indan-4-carboxylic acid ILE-methyl ester, and 1-hydroxyl-indan-4-carboxylic acid ILE-methyl ester. We found that: 1,3-dioxolane MJ, cucurbic acid, and 1,3-dioxolane DHMJ were less active than MJ and that the isoleucine (ILE) conjugates of 1-oxo- and l-hydroxyindanon-4-carboxylic acid had the same NIA as MJ. The activities of these indanon amino acid conjugates may be due to the structural similarity of their keto or hydroxyl groups on the five-membered ring to MJ or to the keto-enolized MJ. These results support the hypothesis that the enolization of the keto group during or prior to its interaction with the putative JA receptor is required for activity. We explore the importance of the esterification of the carboxyl functional group by comparing the NIAs of cucurbic acid and cucurbic acid methyl ester, l-oxo-indan-4-carboxylic acid, 1-oxo-indan-4-carboxylic acid methyl ester, and l-oxo-indan-4-carboxylic acid ILE-methyl ester. In all cases, the esters were more active than the free acids. We compared the NIA of MJ of different epimeric composition (8% and 20% 3R,7S-MJ); 12-oxophytodienoic acid (12-oxo-PDA) methyl ester, an important precursor of JA; and coronatine (a well-known phytotoxin and putative structural mimic of 12-oxo-PDA).We found that: (1) the epimeric composition of MJ did not affect its NIA; (2) 12-oxo-PDA methyl ester had lower NIA than MJ; and (3) coronatine significantly inhibited plant growth but did not increase nicotine biosynthesis. In summary, JA, rather than its biosynthetic precursor, 12-oxo-PDA, is likely the endogenous signal inNicotiana sylvestris, and the keto functional group on the five-membered ring and the double bond in then-pentenyl side chain are crucial components of JA for NIA.

Picosecond to hour time scale dynamics of a "three finger" toxin: correlation with its toxic and antigenic properties.

Toxin alpha from Naja nigricollis (61 amino acids, four disulfide bridges) belongs to the "three finger" fold family, which contains snake toxins with various biological activities and nontoxic proteins from different origins. In this paper, we report an extensive 1H and 15N NMR study of the dynamics of toxin alpha in solution. 15N relaxation, 1H off-resonance ROESY, and H-D exchange experiments allowed us to probe picosecond to hour motions in the protein. Analysis of these NMR measurements demonstrates that toxin alpha exhibits various time scale motions, i.e., particularly large amplitude picosecond to nanosecond motions at the tips of the loops, observable microsecond to millisecond motions around two disulfide bridges, second time scale motions around the C-N bonds of asparagine and glutamine side chains which are more or less rapid depending on their amino acid solvent accessibility, and minute to hour motions in the beta-sheet structure. The less well-defined regions of toxin alpha solution structures are subject to important picosecond to nanosecond motions. The toxic site is organized around residues belonging to the rigid core of the molecule but also comprises residues exhibiting dynamics on various time scales. The Malpha1 epitope is subject to large picosecond to millisecond motions, which are probably modified by the interaction with the antibody. This phenomenon could be linked to the neutralizing properties of the antibody.

The action of alpha-mannosidase from Oerskovia sp. on the mannose-rich O-linked sugar chains of glycoproteins.

Alpha-mannosidase was isolated from the culture liquid of Oerskovia sp. The purified enzyme had a molecular mass of 480 kDa and comprises four identical subunits. The enzyme cleaves bonds in side chains of yeast mannan (Km = 0.08 mM, k(cat) = 1.02 micromol x min(-1) x mg(-1)) and reveals a low activity towards p-nitrophenyl alpha-D-mannopyranoside. The alpha-mannosidase is a Ca2+-dependent enzyme and is inhibited by EDTA. The enzyme possess no endo-mannosidase activity releasing only mannose in the reaction with the inversion of anomeric configuration and could be classified as exo-alpha-mannanase. The enzyme revealed a high deglycosylating activity towards the short mannose-rich O-linked carbohydrate chains of glycoproteins.

Free energies of amino acid side-chain rotamers in α-helices, β-sheets and α-helix N-caps

Scales have previously been determined for the entropic cost of restricting amino acid side-chain rotations upon protein folding, giving the rule of thumb that the entropic cost of restricting a single side-chain bond is ≈0.5 kcal mol−1. However, this result does not consider the distinct preferences shown by amino acid side-chains for particular side-chain χ1 angles in the folded protein. For example, Glu in an α-helix has χ1 4% gauche− (g−), 39% trans (t) and 58% gauche+ (g+) showing that it is most favourable to restrict Glu χ1 as g+ in a helix while g− is least favoured. The change in side-chain conformational entropy is the same in both cases, but the free energy of each rotamer is different. Here, we determine the energies of every amino acid χ1 rotamer in α-helices, β-sheets and α-helix N-caps and each χ1χ2 rotamer pair in helices and sheets. The calculation uses observed rotamer distributions in secondary structure and the coil state, together with experimentally determined free energy changes for secondary structure formation. The results are sets of rotamer energies within a secondary structure that can be directly compared to each other. For example, we conclude that Tyr is the most stable residue in a β-sheet if only the trans rotamer is accessible; if only the gauche− conformation is available, Thr would be the most stabilising. Previously published scales of amino acid preferences for secondary structure are weighted averages of rotamer energies and therefore imply that Thr is the most stabilising substitution in a β-sheet in any side-chain conformation. Both side-chain conformational entropies and intrinsic secondary structure preferences are subsumed within our data; the results presented here should therefore be used in preference to both side-chain conformational entropies and intrinsic secondary structure preferences when the rotamer occupied in the folded state is known. The results may be useful in protein engineering, simulations of binding and folding, prediction of protein stability and peptide binding energies, and identification of incorrectly folded structures.

Antimutagenic effects of dehydrozingerone and its analogs on UV-induced mutagenesis in Escherichia coli

Antimutagenic activities of dehydrozingerone, benzalacetone and its analogs substituted with the hydroxyl, methoxyl or methyl group on the benzene ring were investigated by the post-treatment for UV-induced mutagenesis in Escherichia coli WP2s ( uvrA). In this assay, dehydrozingerone was a poor antimutagen. Among the test compounds except for 2-hydroxybenzalacetone, benzalacetone was the most strong antimutagen, showing that the ring substitutions decrease the antimutagenic activities. 2-Hydroxybenzalacetone was, however, more effective than benzalacetone. The antimutagenicity of 2-hydroxybenzalacetone might be dependent on the property that is known to associate inter-molecularly by hydrogen bonding between the hydroxyl group and the carbonyl group. The effects of the side chain, single, double or triple bond and its adjacent carbonyl group, were further investigated using benzylacetone with saturated carbonyl chain, benzalacetone with double-bonded carbonyl chain, 4-phenyl-3-butyn-2-one with triple-bonded carbonyl chain and trans-β-methyl styrene with only double bond. Benzalacetone and 4-phenyl-3-butyn-2-one suppressed the UV-induced mutagenesis, but benzylacetone and trans-β-methyl styrene scarcely inhibited the mutagenesis: an α,β-double- or triple-bonded carbonyl system was necessary for the antimutagenic activity. 4-Phenyl-3-butyn-2-one showed the potent antimutagenicity at one order lower concentrations than that of benzalacetone. Benzalacetone, 2-hydroxybenzalacetone and 4-phenyl-3-butyn-2-one that were effective on the UV-induced mutagenesis also decreased the γ-induced mutagenesis in Salmonella typhimurium TA2638.

Atomic resolution (1.0 Å) crystal structure of Fusarium solani cutinase: stereochemical analysis

X-ray data have been recorded to 1.0 Å resolution from a crystal of Fusarium solani cutinase using synchrotron radiation and an imaging-plate scanner. The anisotropic treatment of thermal motion led to a fivefold increase in accuracy and to a considerable quality improvement in the electron density maps with respect to an intermediate isotropic model. The final model has an R-factor of 9.4%, with a mean coordinate error of 0.021 Å, as estimated from inversion of the least-squares matrix. The availability of an accurate structure at atomic resolution and of meaningful estimates of the errors in its atomic parameters, allowed an extensive analysis of several stereochemical parameters, such as peptide planarity, main-chain and some side-chain bond distances. The hydrogen atoms could be clearly identified in the electron density, thus providing unambiguous evidence on the protonation state of the catalytic histidine residue. The atomic resolution revealed an appreciable extent of flexibility in the cutinase active site, which might be correlated with a possible adaptation to different substrates. The anisotropic treatment of thermal factors provided insights into the anisotropic nature of motions. The analysis of these motions in the two loops delimiting the catalytic crevice pointed out a “breath-like” movement in the substrate binding region of cutinase.

Glycidyl methacrylate derivatization of α,β-poly( N-hydroxyethyl)- dl-aspartamide and α,β-polyasparthydrazide

α,β-Poly( N-hydroxyethyl)- dl-aspartamide (PHEA) and α,β-polyasparthydrazide (PAHy) are two synthetic macromolecules having many potential applications in the field of biomedical sciences. This paper describes the functionalization of PHEA and PAHy with glycidyl methacrylate (GMA), in order to introduce pendant double bonds in their chains. Derivatized PHEA and PAHy (samples PHG and PAG, respectively) at various GMA content have been obtained and characterized. It has been shown that the derivatization reaction can be controlled by varying some parameters as solvent, catalyst, pH, GMA concentration and reaction time. As expected, PAHy reacted more rapidly and more extensively than PHEA, reasonably because of the higher nucleophilicity of hydrazine groups. Besides, it has been observed that PHG and PAG aqueous solutions easily crosslink by gamma radiation processing and a correlation has been found between gel doses and derivatization degrees of the copolymers. The results of this study demonstrate that introduction of pendant double bonds in side chains of PHEA and PAHy is a suitable method to prepare macromolecular networks.

5614339 Object recycling by laser of coating material: Tankovich Nikolai San Diego, CA, United States assigned to Lumedics Ltd

n-Pentylbenzene and 2-phenylpentane were reacted over a series of catalysts covering a wide range of acidic and dehydrogenation activities.Acid-catalyzed cyclization favors the formation of six-membered rings provided that the same type of carbonium ion intermediate is involved in both six- and five-membered cyclization processes. Side-chain branching increases the rate of acid-catalyzed cyclization. Dehydrogenation of the alkylbenzene could be the rate-controlling step in acid-catalyzed cyclizations.Pt-catalyzed cyclization of n-alkylbenzenes forms about equal amounts of five- and six-membered rings. Five-membered ring cyclization is favored with secondary alkylbenzenes. The Pt does not function as an acid when catalyzing cyclization of alkylbenzenes.Isomerization may be catalyzed by acids or by the Pt metal. Pt-catalyzed isomerizations proceed either via cyclic intermediates or through 1,3-diadsorbed intermediates. In certain Pt-catalyzed isomerizations, a 1,4-diadsorbed intermediate might also be involved.At 371 °C, acid-catalyzed cracking rates of a secondary side chain are about an order of magnitude higher than that of a normal side chain. Pt-catalyzed hydrogenolysis affects the side-chain bonds of n-alkylbenzenes at an approximately equal rate. In secondary alkylbenzenes, cleavage of the bond between the tertiary carbon atom and the ring is preferred.This work completely confirmed the reaction mechanisms suggested by our earlier n-butylbenzene work; namely, (a) in addition to its dehydrogenation activity, Pt has considerable cyclization, isomerization, and hydrogenolysis activities; (b) cyclization occurs on both acid and metal sites; and (c) in the acid-catalyzed cyclization process, the stability of the carbonium ion intermediate determines whether cyclization forms five- or six-membered ring products.

Experimental early-stage coalification of a peat sample and a peatified wood sample from Indonesia

Experimental coalification of a peat sample and a buried wood sample from domed peat deposits in Indonesia was carried out to examine chemical structural changes in organic matter during early-stage coalification. The experiment (125°C, 408 atm lithostatic pressure, and 177 atm fluid pressure for 75 days) was designed to maintain both lithostatic and fluid pressure on the sample, but allow by-products that may retard coalification to escape. We refer to this design as a geologically open system. Changes in the elemental composition, and 13C NMR and FTIR spectra of the peat and wood after experimental coalification suggest preferential thermal decomposition of O-containing aliphatic organic compounds (probably cellulose) during early-stage coalification. The elemental compositions and 13C NMR spectra of the experimentally coalified peat and wood were generally similar to those of Miocene coal and coalified wood samples from Indonesia. Yields of lignin phenols in the peat and wood samples decreased following experimental coalification; the wood sample exhibited a larger change. Lignin phenol yields from the experimentally coalified peat and wood were comparable to yields of lignin phenols from Miocene Indoesian lignite and coalified wood. Changes in syringyl/vanillyl and p-hydroxy/vanillyl ratios suggest direct demethoxylation as a secondary process to demethylation of methoxyl groups during early coalification, and changes in lignin phenol yields and acid/aldehyde ratios point to a coupling between demethoxylation processes and reactions in the alkyl side chain bonds of the α-carbon in lignin phenols.

Synthesis of novel poly(ethylene glycol) derivatives having pendant amino groups and aggregating behavior of its mixture with fatty acid in water.

Novel poly(ethylene glycol) (PEG) derivatives having pendant amino groups were prepared by copolymerization of allyl glycidyl ether with ethylene oxide followed by chemical modification of the double bond side chains. Dropwise addition of the mixture of monomers to the anionic initiator gave an almost monodisperse (Mw/Mn = 1.05) random copolymer. 1H NMR spectra showed that addition of 2-aminoethanethiol to the pendant allyl groups of the copolymer was completely carried out in methanol without catalyst, and an aminated PEG derivative with a definite structure was obtained. Acetylation of the pendant amino groups was readily performed by acetic anhydride with triethylamine. A gel permeation chromatogram of the acetylated polymer showed a very narrow molecular weight distribution (Mw/Mn = 1.06) of the polyamine. These cationic PEG derivatives make amphiphilic polyion complexes with fatty acids, and then aggregate in water. A fluorescence study using pyrene as a microenvironment probe revealed that the aminated PEG-lauric acid ion complex could take up the hydrophobic fluorescence probe into the lipophilic field inside, and they also had a critical aggregation concentration at [lauric acid] = 0.7 mM. It is much lower than the critical micelle concentration of the corresponding fatty acid sodium salts, indicating high stability of the polymer-fatty acid aggregate.

5480625 Enhancing carbon dioxide sorption rates using hygroscopic additives

n-Pentylbenzene and 2-phenylpentane were reacted over a series of catalysts covering a wide range of acidic and dehydrogenation activities.Acid-catalyzed cyclization favors the formation of six-membered rings provided that the same type of carbonium ion intermediate is involved in both six- and five-membered cyclization processes. Side-chain branching increases the rate of acid-catalyzed cyclization. Dehydrogenation of the alkylbenzene could be the rate-controlling step in acid-catalyzed cyclizations.Pt-catalyzed cyclization of n-alkylbenzenes forms about equal amounts of five- and six-membered rings. Five-membered ring cyclization is favored with secondary alkylbenzenes. The Pt does not function as an acid when catalyzing cyclization of alkylbenzenes.Isomerization may be catalyzed by acids or by the Pt metal. Pt-catalyzed isomerizations proceed either via cyclic intermediates or through 1,3-diadsorbed intermediates. In certain Pt-catalyzed isomerizations, a 1,4-diadsorbed intermediate might also be involved.At 371 °C, acid-catalyzed cracking rates of a secondary side chain are about an order of magnitude higher than that of a normal side chain. Pt-catalyzed hydrogenolysis affects the side-chain bonds of n-alkylbenzenes at an approximately equal rate. In secondary alkylbenzenes, cleavage of the bond between the tertiary carbon atom and the ring is preferred.This work completely confirmed the reaction mechanisms suggested by our earlier n-butylbenzene work; namely, (a) in addition to its dehydrogenation activity, Pt has considerable cyclization, isomerization, and hydrogenolysis activities; (b) cyclization occurs on both acid and metal sites; and (c) in the acid-catalyzed cyclization process, the stability of the carbonium ion intermediate determines whether cyclization forms five- or six-membered ring products.

Hydrogen Exchange and Protein Hydration: The Deuteron Spin Relaxation Dispersions of Bovine Pancreatic Trypsin Inhibitor and Ubiquitin

Water deuteron ( 2H) spin relaxation was used to study hydrogen exchange hydration, and protein dynamics in aqueous soltuions of the globular proteins bovine pancreatic trypsin inhibitor (BPTI) and ubiquitin. The frequency dispersion of the longitudinal 2H relaxation rate was measured in the pD range 2 to 11 at 27°C. In contrast to the previously reported water 17O relaxation dispersion from the same samples, the 2H dispersion depends strongly on pD. This pD dependence is due to labile protein deuterons in acidic side-chains and surface peptide groups, which exchange rapidly with water deuterons. The pD dependence of the 2H relaxation in BPTI solutions could be quantitatively accounted for in terms of known p Kvalues and hydrogen exchange rate constants. For ubiquitin, labile protein deuterons contribute importantly to the 2H relaxation dispersion even in the neutral pD range. The 2H relaxation data also provided information about the orientational order and internal motion of OD and ND bonds in side-chains and surface peptides. A comparison of the water contribution to the 2H dispersion with the 17O dispersion indicates that one of the four internal water molecules of BPTI, presumably the deeply buried water molecule W122, exchanges more slowly (10 −6to 10 −4second) than the other three (10 −8to 10 −6second).

Chain Segmental Motion and Side-Chain Internal Rotations of Poly(1-naphthylalkyl acrylate)s in Solution Studied by 13C Nuclear Magnetic Relaxation

C longitudinal relaxation times and nuclear Overhauser enhancements were measured as a function of temperature in three magnetic fields for a series of poly(1-naphthylalkyl acry1ate)s in 1,1,2,2- tetrachloroethane-dz. Variable-temperature 13C transverse relaxation time measurements at 75.4 and 125.7 MHz also were undertaken. The relaxation data have been described by using various models for main-chain segmental motion and side-chain internal rotations. Among these, the Dejean-Laupretre-Monnerie (DLM) model offered the best description of segmental motion for the poly(1-naphthylalkyl acrylate) chains. Internal rotations about the side-chain bonds, including naphthyl internal motion, were described by hindered rotations superimposed on segmental motions, the latter being described by the DLM model. An attempt was made to correlate rates and activation energies associated with the various modes of reorientation in the aforementioned polymers with the rates of excimer formation between the side-chain naphthalene chromophores.

High temperature stable photopatternable copolymers: Synthesis, optical properties, and photopatterning process studies

AbstractPhotopatternable copolymers and photopatterning processes for high temperature stable optical elements have been studied. The photopatternable copolymers were synthesized from methyl methacrylate and methacrylic ester comprising a nonconjugate carbon–carbon double bond side chain and epoxy side chain. Their optical properties were investigated on film samples doped with m‐benzoylbenzophenone (BBP). After irradiating with UV light, insoluble polymer was formed in a high yield at higher temperature, resulting in changes in thickness and refractive index, which were precisely controlled by the exposure energy of UV light. The two step photopatterning processes were carried out by means of UV irradiations with and without a photomask bearing a grating pattern followed by removal of unreacted BBP to draw an optical pattern on the polymer material with cross‐linking. Further photoreaction was also performed to cure the polymer by exposure with a high energy UV lamp containing shorter wavelength light after the patterning process. By a combination of the patterning process and the postcuring process, an optical grating fabricated from these copolymers showed a heat stability up to 160°C. © 1994 John Wiley & Sons, Inc.

1H NMR studies on an Asn-linked glycopeptide. GlcNAc-1 C2-N2 bond is rigid in H2O.

The conformation of an Asn-linked glycopeptide in H2O was studied by two-dimensional 1H NMR. Nonexchangeable proton and exchangeable amide (NH) proton resonances were assigned for the hen ovomucoid glycopeptide 1, Ser-Ile-Glu-Phe-Gly-Thr-Asn Ile-Ser-Lys, with pentasaccharide Man alpha 1-3 (Man alpha 1-6)Man beta 1-4GlcNAc beta 1-4GlcNAc beta 1-NH attached to the Asn7 gamma-carboxamide. The pentasaccharide increases the local correlation times of amino acid residues near the N-glycosylation site. Nuclear Overhauser effect (NOE) measurements on 1 and the corresponding Man3-GlcNAc2 pentasaccharide 3 show that the attached peptide does not perturb O-glycoside conformation. Sequential dNN (i, i + 1) NOEs in the Thr6-Ser9 region indicate populations of folded structure near the N-glycosylation site of both glycopeptide 1 and aglycosyl peptide 2. However, the Man3GlcNAc2 pentasaccharide does not dramatically affect the average conformation of either the peptide backbone or the Asn7 side chain. GlcNAc NH protons were studied at pH 3.0; and NOE and 3JNH data were used to constrain the glycopeptide's GlcNAc-1 side chain dihedral angle (tau) (C1-C2-N2-C7(Ac)). The glycopeptide's core GlcNAc-1 C2-N2 side chain bond is not flexible in H2O. A strong GlcNAc-1 NH2-H3 NOE, a medium strength NH2-H1 NOE, and a weak NH2-H2 interaction suggest that GlcNAc-1 has a rigid C2-N2 bond, with tau between 95 and 115 degrees. No evidence was found for intramolecular hydrogen bonds restricting this C2 side chain torsion. It may be that GlcNAc-1's rigid planar N-glycosidic linkage limits the conformational space available to the adjacent C2 acetamido side chain.