Comparative 1H NMR study of hydroxy protons in galabioside and its S-linked 4-thiodisaccharide analogue in aqueous solution

The NMR data obtained from hydroxy protons have been used to investigate the presence and absence of intramolecular hydrogen bonding in aqueous solutions of 2-(trimethylsilyl)ethyl galabioside (alpha-D-Galp-(1-->4)-beta-D-Galp-O(CH2)2SiMe3) and the S-linked 4-thiodisaccharide analogue. The data show that there is a weak hydrogen bond interaction between O-6H and O-2'H in galabioside, but not in the thio-analogue. The results are in good agreement with those reported for the substances in a Me2SO-d6 solution. It is also shown that the existence of a hydrogen bond can be quite easily monitored by comparing the NMR data of the hydroxy protons.     

1H- and 13C-NMR studies of solutions of hyaluronic acid esters and salts in methyl sulfoxide: comparison of hydrogen-bond patterns and conformational behaviour.

The 1H- and 13C-NMR spectra of the ethyl and benzyl esters and the tetrabutylammonium and tetraethylammonium salts of hyaluronic acid [[symbol: see text]2)-beta-D-GcpA+-1----3)-beta-D-GlcpNAc-(1[symbol: see text]n] in Me2SO-d6 have been assigned using 1D and 2D techniques. The chemical shifts of the resonance of GlcNAc C-3 suggest that the relative orientations of the monosaccharides at the (1----3) linkage in the esters and salts are different. Small differences in the chemical shifts of the resonance GlcA C-4 suggest only a slight conformational variation around the (1----4) linkage. The 13C-NMR data also suggest similarities in conformation between the esters in Me2SO-d6 and the salts in water. The chemical shifts of the 1H resonances for NH and OH groups and their temperature dependence for the esters and salts in Me2SO reveal markedly stronger inter-residue hydrogen bonds between the carboxyl and NH groups and between HO-4 of GlcA and O-5 of GlcNAc for the salts. The 3J2,NH values indicate a slightly different orientation for the acetamido group. For solutions in Me2SO, the higher segmental flexibility of the esters is supported by the line widths, whereas the reduced viscosity for the tetrabutylammonium salt showed a sigmoidal concentration dependence and suggests association of chains which could contribute to the segmental rigidity. The linear concentration dependence for the benzyl ester suggests a higher overall flexibility without chain association.     

Experimental attempt to simulate receptor site environment. A 500-MHz 1H nuclear magnetic resonance study of enkephalin amides

The amides of Leu5-enkephalin, Met5-enkephalin, and three analogues, D-Ala2,Leu5-enkephalin, (AcO)Tyr1,Met5-enkephalin, and (AcO)Tyr1,D-Ala2,Met5-enkephalin, have been studied by means of 1H NMR spectroscopy in two different solvent systems: Me2SO-d6 and CDCl3. In the latter solvent the peptides were dissolved as complexes with 18-crown-6-ether, a coronand that binds strongly to the NH3+ groups. The crown ether complexation and the apolar solvent were used to simulate the anionic subsite of the receptor and the hydrophobic environment of the receptor cavity, respectively. The very unusual amide proton chemical shifts and their temperature coefficients suggest the presence of folded conformations in CDCl3 for all peptides, consistent with several models of opioid receptors and with the crystal structure of Leu5-enkephalin. The differences among the proposed cyclic conformations of the five peptides may be correlated, in part, with their different biological activity. All peptides in Me2SO-d6 are characterized by complex mixtures of extended fully solvated conformations.     

Crystal structure and n.m.r. analysis of lactulose trihydrate.

The 13C CPMAS n.m.r. spectrum of 4-O-beta-D-galactopyranosyl-D-fructose (lactulose) trihydrate, C12H22O11.3 H2O, identifies the isomer in the crystals as the beta-furanose. This is confirmed by a crystal structure analysis, using CuK alpha X-ray data at room temperature. The space group is P212121, with Z = 4 and cell dimensions a = 9.6251(3), b = 12.8096(3), c = 17.7563(4) A. The structure was refined to R = 0.031 and Rw 0.025 for 1929 observed structure amplitudes. All the hydrogen atoms were unambigously located on difference syntheses. The conformation of the pyranose ring is the normal 4C1 chair and that of the furanose ring is 4T3. The 1----4 linkage torsion angles are O-5'-C-1'-O-1'-C-4 = 79.9(2) degrees and C-1'-O-1'-C-4-C-5 = -170.3(2) degrees. All hydroxyls, ring and glycosidic oxygens, and water molecules are involved in the hydrogen bonding, which consists of infinite chains linked together by water molecules to form a three-dimensional network. There is a three-centered intramolecular, interresidue hydrogen bond from O-3-H to O-5' and O-6'. The n.m.r. spectrum of the amorphous, dehydrated trihydrate suggests the occurrence of a solid-state reaction forming the same isomeric mixture as was observed in crystalline anhydrous lactulose, although the mutarotation of the trihydrate when dissolved in Me2SO is very slow.     

Crystalline structure analysis of cellulose treated with sodium hydroxide and carbon dioxide by means of X-ray diffraction and FTIR spectroscopy

Crystalline structures of cellulose (named as Cell 1), NaOH-treated cellulose (Cell 2), and subsequent CO2-treated cellulose (Cell 2-C) were analyzed by wide-angle X-ray diffraction and FTIR spectroscopy. Transformation from cellulose I to cellulose II was observed by X-ray diffraction for Cell 2 treated with 15-20 wt% NaOH. Subsequent treatment with CO2 also transformed the Cell 2-C treated with 5-10 wt% NaOH. Many of the FTIR bands including 2901, 1431, 1282, 1236, 1202, 1165, 1032, and 897 cm(-1) were shifted to higher wave number (by 2-13 cm(-1)). However, the bands at 3352, 1373, and 983 cm(-1) were shifted to lower wave number (by 3-95 cm(-1)). In contrast to the bands at 1337, 1114, and 1058 cm(-1), the absorbances measured at 1263, 993, 897, and 668 cm(-1) were increased. The FTIR spectra of hydrogen-bonded OH stretching vibrations at around 3352 cm(-1) were resolved into three bands for cellulose I and four bands for cellulose II, assuming that all the vibration modes follow Gaussian distribution. The bands of 1 (3518 cm(-1)), 2 (3349 cm(-1)), and 3 (3195 cm(-1)) were related to the sum of valence vibration of an H-bonded OH group and an intramolecular hydrogen bond of 2-OH ...O-6, intramolecular hydrogen bond of 3-OH...O-5 and the intermolecular hydrogen bond of 6-O...HO-3', respectively. Compared with the bands of cellulose I, a new band of 4 (3115 cm(-1)) related to intermolecular hydrogen bond of 2-OH...O-2' and/or intermolecular hydrogen bond of 6-OH...O-2' in cellulose II appeared. The crystallinity index (CI) was obtained by X-ray diffraction [CI(XD)] and FTIR spectroscopy [CI(IR)]. Including absorbance ratios such as A1431,1419/A897,894 and A1263/A1202,1200, the CI(IR) was evaluated by the absorbance ratios using all the characteristic absorbances of cellulose. The CI(XD) was calculated by the method of Jayme and Knolle. In addition, X-ray diffraction curves, with and without amorphous halo correction, were resolved into portions of cellulose I and cellulose II lattice. From the ratio of the peak area, that is, peak area of cellulose I (or cellulose II)/total peak area, CI(XD) were divided into CI(XD-CI) for cellulose I and CI(XD-CII) for cellulose II. The correlation between CI(XD-CI) (or CI(XD-CII)) and CI(IR) was evaluated, and the bands at 2901 (2802), 1373 (1376), 897 (894), 1263, 668 cm(-1) were good for the internal standard (or denominator) of CI(IR), which increased the correlation coefficient. Both fraction of the absorbances showing peak shift were assigned as the alternate components of CI(IR). The crystallite size was decreased to constant value for Cell 2 treated at >or= 15 wt% NaOH. The crystallite size of Cell 2-C (cellulose II) was smaller than that of Cell 2 (cellulose I) treated at 5-10 wt% NaOH. But the crystallite size of Cell 2-C (cellulose II) was larger than that of Cell 2 (cellulose II) treated at 15-20 wt% NaOH.     

Determining the crystal structure of cellulose III(I) by modeling

Recently, a one-chain monoclinic unit cell for cellulose III(I) having P2(1) symmetry and a single glucose in the asymmetric unit was proposed, based on high-resolution diffraction patterns. The new work challenged a two-chain structure that was published 25 years earlier, although it did not provide new three-dimensional coordinates. Our goals were to solve the structure by modeling, find whether modeling would reject the previously determined two-chain unit cell, and compare the model with the anticipated experimental structure. Combinations of three rotamers of the O-2, O-3, and O-6 hydroxyl groups produced 27 'up' and 27 'down' starting structures. Clusters ('minicrystals') of 13 cellotetraose chains terminated by methyl groups for each of the 54 starting structures were optimized with MM3(96). Hydroxyl groups on 16 of these 54 structures reoriented to give very similar hydrogen-bonding schemes in the interiors, along with the lowest energies. Hydrogen bonds included the usual intramolecular O-3H...O-5' linkage, with O-6' also accepting from O-3H. Interchain hydrogen bonds form an infinite, cooperative O-6H...O-2H...O-6 network. Direct comparison of total minicrystal energies for the one- and two-chain unit cell was inappropriate because the two-chain cell's alternate chains are shifted 0.9 A along the z-axis. To get comparable energy values, models were built with both cellotetraose and cellohexaose chains. The differences in their energies represent the energies for the central layers of cellobiose units. The one-chain cell models had much lower energy. The eight best 'up' one-chain models agree reasonably well with the structure newly determined by experiment.     

Structural analysis of two 2-deoxy analogues of alpha- and beta-KDO and the methyl alpha- and beta-glycosides of KDO, and determination of their metal-ion-binding properties

Ammonium 2,6-anhydro-3-deoxy-D-glycero-D-talo-octonate (1), a potent inhibitor of the enzyme CMP-KDO synthetase, its C-2 epimer 2, and the methyl beta- (3) and alpha-glycoside (4) of KDO were studied by 1H- and 13C-n.m.r. spectroscopy. Compound 1 was also analysed by X-ray crystallography. Each compound adopted a 5C2 chair conformation with the side chain equatorial. The preponderant side-chain conformation of 1 in solution was the same as that in the crystal and was stabilised by an intramolecular hydrogen bond from HO-8 to the carboxylate group. This hydrogen bond appeared to be present also in 3. However, the side-chain conformation of 2 and 4 was different from that in 1 and 3. The metal-ion-binding properties, determined on the basis of the line-broadening effects of Mn2+ on the 13C-n.m.r. signals, showed that the carboxylate group was involved in the binding with O-8 in 1 and 3 and with O-6 and O-8 in 2 and 4.     

Conformational features of crystal-surface cellulose from higher plants

Native cellulose in higher plants forms crystalline fibrils a few nm across, with a substantial fraction of their glucan chains at the surface. The accepted crystal structures feature a flat-ribbon 21 helical chain conformation with every glucose residue locked to the next by hydrogen bonds from O-3' to O-5 and from O-2 to O-6'. Using solid-state NMR spectroscopy we show that the surface chains have a different C-6 conformation so that O-6 is not in the correct position for the hydrogen bond from O-2. We also present evidence consistent with a model in which alternate glucosyl residues are transiently or permanently twisted away from the flat-ribbon conformation of the chain, weakening the O-3' - 0-5 hydrogen bond. Previous molecular modelling and the modelling studies reported here indicate that this 'translational' chain conformation is energetically feasible and does not preclude binding of the surface chains to the interior chains, because the surface chains share the axial repeat distance of the 21 helix. Reduced intramolecular hydrogen bonding allows the surface chains to form more hydrogen bonds to external molecules in textiles, wood, paper and the living plant.     

The crystal structure of the alpha-cellobiose.2 NaI.2 H(2)O complex in the context of related structures and conformational analysis

The crystal structure of beta-D-glucopyranosyl-(1-->4)-alpha-D-glucopyranose (alpha-cellobiose) in a complex with water and NaI was determined with Mo K(alpha) radiation at 150 K to R=0.027. The space group is P2(1) and unit cell dimensions are a=9.0188, b=12.2536, c=10.9016 A, beta=97.162 degrees. There are no direct hydrogen bonds among cellobiose molecules, and the usual intramolecular hydrogen bond between O-3 and O-5' is replaced by a bridge involving Na+, O-3, O-5', and O-6'. Both Na+ have sixfold coordination. One I(-) accepts six donor hydroxyl groups and three C-H***I(-) hydrogen bonds. The other accepts three hydroxyls, one Na+, and five C-H***I(-) hydrogen bonds. Linkage torsion angles phi(O-5) and psi(C-5) are -73.6 and -105.3 degrees, respectively (phi(H)=47.1 degrees and psi(H)=14.6 degrees ), probably induced by the Na+ bridge. This conformation is in a separate cluster in phi,psi space from most similar linkages. Both C-6-O-H and C-6'-O-H are gg, while the C-6'-O-H groups from molecules not in the cluster have gt conformations. Hybrid molecular mechanics/quantum mechanics calculations show <1.2 kcal/mol strain for any of the small-molecule structures. Extrapolation of the NaI cellobiose geometry to a cellulose molecule gives a left-handed helix with 2.9 residues per turn. The energy map and small-molecule crystal structures imply that cellulose helices having 2.5 and 3.0 residues per turn are left-handed.     

X-ray crystal structure of galabiose, O-alpha-D-galactopyranosyl-(1---4)-D-galactopyranose

O-alpha-D-Galactopyranosyl-(1---4)-D-galactopyranose, C12H22O11, Mr = 342.30, crystallises in the orthorhombic space group P2(1)2(1)2(1), and has alpha = 5.826(1), b = 13.904(3), c = 17.772(4) A, Z = 4, and Dx = 1.579 g.cm-3. Intensity data were collected with a CAD4 diffractometer. The structure was solved by direct methods and refined to R = 0.063 and Rw = 0.084 for 2758 independent reflections. The glycosidic linkage is of the type 1-axial-4-axial with torsion angles phi O-5' (O-5'-C-1'-O-1'-C-4) = 98.1(2) degrees, psi C-3 (C-3-C-4-O-1'-C-1') = -81.9(3) degrees, phi H (H-1'-C-1'-O-1'-C-4) = -18 degrees, and psi H (H-4-C-4-O-1'-C-1') = 35 degrees. The conformation is stabilised by an O-3 . . . O-5' intramolecular hydrogen-bond with length 2.787(3) A and O-3-H . . . O-5' = 162 degrees. The glycosidic linkage causes a folding of the molecule with an angle of 117 degrees between the least-square planes through the pyranosidic rings. The crystal investigated contained 56(1)% of alpha- and 44(1)% of beta-galabiose as well as approximately 70% of the gauche-trans and approximately 30% of the trans-gauche conformers about the exocyclic C-5'-C-6' and C-5-C-6 bonds. The crystal packing is governed by hydrogen bonding that engages all oxygen atoms except the intramolecular acceptor O-5' and the glycosidic O-1' oxygen atoms.     

A crystallographic determination of a chemical structure: 6-amino-10-(beta-D-ribofuranosylamino)pyrimido-[5,4-d]pyrimidine, an example of an unusual D-ribose conformation.

The crystal and molecular structure of 6-amino-10-(beta-D-ribofuranosylamino)-pyrimido[5,4-d]pyrimidine has been determined by single crystal X-ray diffraction methods. The crystals are triclinic, of noncentric space group Pl, with cell dimensions a equals 5.434 (5), b equals 12.269 (19), c equals 4.574 (4) A, alpha equals 92.3 (1), beta equals 94.0 (1), gamma equals 95.3 degrees (1) and Z equals 1. The structure has been refined to an R value of 0.049 (Rw equals 0.063), by use of counter measured intensity data for 1063 observed reflections. The pyrimidopyrimidine ring is planar. The sugar moiety is in the envelope conformation with O-1'-endo (0E), and there is an intramolecular hydrogen bond (2.58 A) (O-3'-H-O3'...O-2'). All oxygen atoms except O-1' ring oxygen-atom are involved in hydrogen bonding. The pyrimidopyrimidine rings lie in planes 3.4 A apart.     

Solution conformation of enkephalin. A nuclear magnetic resonance study of 13C-enriched carbonyl carbons in [Leu5]-enkephalin.

By using 13C enrichment in [Leu5]-enkephalin, it has been possible to improve the assignment of carbonyl resonances in the nuclear resonance spectrum and to remove some of the ambiguities in the derived phi and chi dihedral angles, thereby providing information about the conformation of this molecule in solution. The combined use of 13C and 1H nuclear magnetic resonance experiments leads to the conclusion that [Leu5]0enkephalin contains a type I beta bend at residues Gly3-Phe4 in dimethyl-d6 sulfoxide (Me2SO0d6) solution. Furthermore, the side chains of Tyr1, Phe4, and Leu5 exist predominantly in one conformation (tg-) in this solvent. A comparison is made between the conformation found in Me2SO-d6 and those determined by X-ray diffraction and conformational energy calculations.     

A new crystal form of beta-cyclodextrin-ethanol inclusion complex: channel-type structure without long guest molecules

A new crystal form of beta-cyclodextrin (beta-CD)[bond]ethanol[bond]dodecahydrate inclusion complex [(C(6)H(10)O(5))(7).0.3C(2)H(5)OH.12H(2)O] belongs to monoclinic space group C2 (form II) with unit cell constants a=19.292(1), b=24.691(1), c=15.884(1) A, beta=109.35(1) degrees. The beta-CD macrocycle is more circular than that of the complex in space group P2(1) [form I: J. Am. Chem. Soc. 113 (1991) 5676]. In form II, a disordered ethanol molecule (occupancy 0.3) is placed in the upper part of beta-CD cavity (above the O-4 plane) and is sustained by hydrogen bonding to water site W-2. In form I, an ethanol molecule located below the O-4-plane is well ordered because it hydrogen bonds to surrounding O-3[bond]H, O-6[bond]H groups of the symmetry-related beta-CD molecules. In the crystal lattice of form I, beta-CD macrocycles are stacked in a typical herringbone cage structure. By contrast, the packing structure of form II is a head-to-head channel that is stabilized at both O-2/O-3 and O-6 sides of each beta-CD by direct O(CD)...O(CD) and indirect O(CD)...O(W)...(O(W))...O(CD) hydrogen bonds. The 12 water molecules are disordered in 18 positions both inside the channel-like cavity of beta-CD dimer (W-1[bond]W-6) and in the interstices between the beta-CD macrocycles (W-7[bond]W-18). The latter forms a cluster that is hydrogen bonded together and to the neighboring beta-CD O[bond]H groups.     

Synthetic receptor analogues: the conformation of methyl 4-O-alpha-D-galactopyranosyl-beta-D-galactopyranoside (methyl beta-D-galabioside) and related derivatives, determined by n.m.r. and computational methods

The conformations of galabiose and its methyl and ethyl beta-glycosides as well as the 3-deoxy, 3-O-methyl, 3-deoxy-3-C-methyl, 3-deoxy-3-C-ethyl, and 6-deoxy analogues were investigated by n.m.r. (1H, 13C, n.O.e.) and computational (HSEA) methods. A good correlation was found between the computational data and the n.m.r. data for aqueous solutions. The conformations in aqueous solution were similar, whereas crystalline galabiose or methyl beta-D-galabioside in solution in methyl sulfoxide adopted different conformations that showed intramolecular hydrogen bonds (O-5'. . . O-3 and O-2'. . . O-6, respectively).     

8-Chloroguanosine: solid-state and solution conformations and their biological implications

The three-dimensional structure of 8-chloroguanosine dihydrate was determined by X-ray crystallography. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), and the cell dimensions are a = 4.871 (1) A, b = 12.040 (1) A, and c = 24.506 (1) A. The structure was determined by direct methods, and least-squares refinement, which included all hydrogen atoms, converged at R = 0.031 for 1599 observed reflections. The conformation about the glycosidic bond is syn with chi CN = -131.1 degrees. The ribose ring has a C(2')-endo/C-(1')-exo (2T1) pucker, and the gauche+ conformation of the -CH2OH side chain is stabilized by an intramolecular O-(5')-H...N(3) hydrogen bond. Conformational analysis by means of 1H NMR spectroscopy showed that, in dimethyl sulfoxide, the sugar ring exhibits a marked preference for the C(2')-endo conformation (approximately 70%) and a conformation about the glycosidic bond predominantly syn (approximately 90%), hence similar to that in the solid state. However, the conformation of the exocyclic 5'-CH2OH group exhibits only a moderate preference for the gauche+ rotamer (approximately 40%), presumably due to the inability to form the intramolecular hydrogen bond to N(3) in a polar medium. The conformational features are examined in relation to the behavior of 8-substituted purine nucleosides in several enzymatic systems, with due account taken of the steric bulk and electronegativities of the 8-substituents.     

Metadynamics modelling of the solvent effect on primary hydroxyl rotamer equilibria in hexopyranosides

Accurate modelling of rotamer equilibria for the primary hydroxyl groups of monosaccharides continues to be a great challenge of computational glycochemistry. The metadynamics technique was applied to study the conformational free energy surfaces of methyl α-d-glucopyranoside and methyl α-d-galactopyranoside, employing the glycam06 force field. For both molecules, seven to eight conformational free-energy minima, differing in the ω (O-5–C-5–C-6–O-6) and χ (C-3–C-4–O-4–HO-4) dihedral angles, were identified in vacuum or in a water environment. The calculated rotamer equilibrium of the primary hydroxyl group is significantly different in vacuum than in water. The major effect of a water environment is the destabilisation of a hydrogen bond between O-4–HO-4 and O-6–HO-6 groups. It was possible to calculate the free-energy differences of individual rotamers with an accuracy of better than 2 kJ/mol. The calculated gg, gt and tg rotamer populations in water are in close agreement with experimental measurements, and therefore support the theoretical background of metadynamics.     

The crystal structures of Man(alpha1-3)Man(alpha1-O)Me and Man(alpha1-6)Man(alpha1-O)Me in complex with concanavalin A.

The crystal structures of concanavalin A in complex with Man(alpha1-6)Man(alpha1-O)Me and Man(alpha1-3)Man(alpha1-O)Me were determined at resolutions of 2.0 and 2.8 A, respectively. In both structures, the O-1-linked mannose binds in the conserved monosaccharide-binding site. The O-3-linked mannose of Man(alpha1-3)Man(alpha1-O)Me binds in the hydrophobic subsite formed by Tyr-12, Tyr-100, and Leu-99. The shielding of a hydrophobic surface is consistent with the associated large heat capacity change. The O-6-linked mannose of Man(alpha1-6)Man(alpha1-O)Me binds in the same subsite formed by Tyr-12 and Asp-16 as the reducing mannose of the highly specific trimannose Man(alpha1-3)[Man(alpha1-6)]Man(alpha1-O)Me. However, it is much less tightly bound. Its O-2 hydroxyl makes no hydrogen bond with the conserved water 1. Water 1 is present in all the sugar-containing concanavalin A structures and increases the complementarity between the protein-binding surface and the sugar, but is not necessarily a hydrogen-bonding partner. A water analysis of the carbohydrate-binding site revealed a conserved water molecule replacing O-4 on the alpha1-3-linked arm of the trimannose. No such water is found for the reducing or O-6-linked mannose. Our data indicate that the central mannose of Man(alpha1-3)[Man(alpha1-6)]Man(alpha1-O)Me primarily functions as a hinge between the two outer subsites.     

Preparation and structural characterisation of O-aminopropyl starch and amylose

O-aminopropyl starch was prepared by Michael addition of acrylonitrile and subsequent reduction with freshly prepared cobalt boride and sodium borohydride. In a second approach, the aminopropyl group was introduced via Williamson etherification with N-phthalyl-protected 3-bromo-1-propylamine. The protecting group was removed by borohydride reduction and subsequent hydrolysis in acetic acid. The DS of all samples and the degree of reduction of the cyanoethyl groups were estimated from the 1H NMR spectra. Total monomer composition was determined after methanolysis or hydrolysis and trimethylsilylation by GLC and GCMS. While the regioselectivity in the thermodynamically controlled reaction was O-6 > O-2 > O-3 (50:37:13), the kinetically controlled process showed strongly preferred O-2-etherification (up to 94%) followed by O-6- and O-3-substitution. It could be influenced by choice of solvent (water, Me(2)SO) and base (NaOH, Li-dimsyl).     

Two-dimensional correlation spectroscopy and principal component analysis studies of temperature-dependent IR spectra of cotton-cellulose

The FTIR spectra were measured for raw Uplands Sicala-V2 cotton fibers over a temperature range of 40-325 degrees C to explore the temperature-dependent changes in the hydrogen bonds of cellulose. These cotton-cellulose spectra exhibited complicated patterns in the 3800-2800 cm(-1) region and thus were analyzed by both the exploratory principal component analysis (PCA) and two-dimensional (2-D) correlation spectroscopy methods. The exploratory PCA showed that the spectra separate into two groups on the basis of thermal degradation of the cotton-cellulose and the consequent breakage of intersheet H-bonds present in its structure. Frequency variables, which strongly contributed to each principal component highlighted in its loadings plot, were linked to the frequencies assigned to vibrations of the OH groups involved in different kinds of H-bonds, as well as to vibrations of the CH groups. Deeper insights into reorganization of the temperature-dependent hydrogen bonding were obtained by 2-D correlation spectroscopy. Synchronous and asynchronous spectra were analyzed in the temperature ranges of 40 to 150 and 250 to 320 degrees C, the ranges indicated by PCA. Detailed band assignments of the OH stretching region and changes in the patterns of the hydrogen bonding network of the cotton-cellulose were proposed with the aid of the 2-D correlation spectroscopy analysis. Below 150 degrees C, distinctly different bands assigned to the less stable Ialpha and the more stable Ibeta interchain H-bonds O-6-H-6...O-3' were observed at about 3230 and 3270 cm(-1), respectively. Evaporation of water entrapped in the cellulose network was examined by means of the band at about 3610 cm(-1). The cooperativity of hydrogen bonds, which play a key role in the cellulose conformation, was monitored by frequencies assigned to intrachain H-bonds. It was possible to separate the frequencies assigned to the O-2-H-2...O-6 and O-3-H-3...O-5 intrachain H-bonds into two separate ranges, the spread of which was controlled by the cooperativity effect. The temperature dependence of the asynchronous spectra indicated that the less stable O-3-H-3...O-5 bonds gave rise to an absorption extending from 3300 to 3384 cm(-1), while the more stable O-2-H-2...O-6 bonds were characterized by the absorption between 3400 and 3470 cm(-1). The final breaking of the inter- and intrachain H-bonds, which occurs at the higher temperatures, was monitored by the asynchronous peaks at 3533 and 3590 cm(-1), respectively. On the basis of both the exploratory PCA and 2-D correlation spectroscopy investigations, it was possible to extract well-defined wavenumber ranges assigned to different kinds of intra- and interchain hydrogen bonds, as well as to the free OH groups of the cotton-cellulose.