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The crystal structure of Ca2RuD6 has been determined by neutron powder diffraction: space group Fm3m ,K 2PtCl6 structure, as found for other hexahydride salts of group 8 metals with alkaline earth or lanthanide counter ions. No structural phase transition was observed between 340 K and 50 K. The deuterium nuclear quadrupole coupling constant, 54.7 kHz, leads to an ionic character of the Ru–D bond of 76%. The known trends in the behaviour of A2MH6 salts are interpreted in terms of the ionization energies of the cation and the central metal atom. © 2007 Elsevier B.V. All rights reserved.

The 31P CP-MAS NMR spectra of trans-square-planar complexes of dihalonickel(II) complexes with tribenzyl-, tricyclohexyl- and tricyclohexylmethylphosphines have been examined and the chemical shift tensors determined. The spans, δ11–δ33, of the tensor components decrease with change in the halide, Cl > Br > I, for all the tertiary phosphines due principally to the deshielding of the δ33 component.

Deuterium NMR spectroscopy has been used to probe the dynamics of two samples, 2,2-d2-hexadecanoate (HDCA) and perdeuterated HDCA monolayers on nonporous ZrO2 powder (surface area ∼ 40 m2/g) over the temperature range of 180 K to room temperature. The data indicate the presence of a considerable motional gradient in the tethered chain. Line shape simulations were performed on the spectra of 2,2-d2-HDCA to extract detailed information on the dynamic processes involved. These quantitative line shape analyses clearly show that, over the whole temperature range studied, the C2D bonds have substantial motional freedom with respect to the characteristic 2H NMR time scale. In addition, at each temperature, a weighted superposition of several simulated line shapes with different rates and site populations is required to account for the observed spectral features, indicating the presence of considerable motional heterogeneity within the hexadecanoate monolayers. The results will be compared with dynamic behaviors ...

The solid-state119Sn cross-polarization (CP) magic angle spinning (MAS) NMR spectra of a series of triaryltin chlorides of the form Ar3SnCl have been acquired. The indirect spin-spin coupling constants (J(119Sn-35Cl)), quadrupolar-dipolar shifts (d(119Sn-35Cl)), and the119Sn chemical shift tensors were extracted. For the spectrum of triphenyltin chloride (I) the validity of the first-order perturbation approximation was tested by comparing results of both the perturbation and cubic-equation approaches and a variable-temperature NMR study undertaken to investigate the influence of the previously reported molecular motion in the solid. The X-ray crystal structures of the tris(o-tolyl)tin chloride (II) and tris(p-tolyl)tin chloride (IV) complexes have been examined. They belong to the monoclinic and triclinic space groups P21/n and P[Formula: see text], respectively, which are different from the previously reported tris(m-tolyl)tin chloride (III) complex, which crystallizes in the space group R3 and has threefold molecular symmetry. The structures and NMR properties of the complexes with meta-substituents are quite different from those with ortho- or para-substituents having axially symmetric shift tensors with small spans and larger J values.Key words: aryltin chlorides, magic angle spinning NMR, tin-chlorine spin-spin coupling,119Sn chemical shift tensor, crystal structure.

Single-crystal X-ray diffraction studies illustrate that the three title compounds are isomorphous, belonging to the triclinic space group P[Formula: see text], with slightly distorted trigonal bipyramidal geometry about cobalt. The solid-state 29Si, 119Sn, and 207Pb cross-polarization magic angle spinning (CP MAS) NMR spectra are presented. The indirect spin–spin coupling constant (J), quadrupolar–dipolar shift (d), direct dipolar coupling constant (D' ), anisotropy in spin–spin coupling (ΔJ), and the chemical shift tensor were extracted. A plot of the reduced coupling constant vs. s-electron densities at the nucleus indicates that the Fermi contact term may be dominant for the tin and lead complexes; however, the large ΔJ for all complexes indicate that there are also significant anisotropic terms. Trends in the Raman scattering spectra are also discussed.Key words: 29Si, 119Sn, and 207Pb CP MAS NMR, tetracarbonyl cobalt, spin–spin coupling, chemical shift tensor, quadrupole coupling, Fermi contact, cobalt–group 14.

Deuterium NMR spectroscopy has been used to probe the dynamics of deuterated octadecylphosphonate (−1,1−d2) (ODPA−d2) monolayers on nonporous ZrO2 powder (surface area ≈ 40 m2/g) over the temperature range of 200−340 K. At 200 K, a broadened Pake doublet with distinct nonrigid characteristics and a horn splitting of approximately 120 kHz was observed. With increasing temperature, the 2H spectrum gradually transforms into a relatively narrow and featureless peak. Spectral simulations are performed with the help of plausible motional models, and the results show that, over the whole temperature range studied, the C1−D bonds have substantial motional freedom with respect to the characteristic 2H NMR time scale. In addition, at each temperature, a weighted superposition of several simulated line shapes with different rates and site populations is required to account for the observed spectral features, indicating the presence of considerable motional heterogeneity within the ODPA monolayers. The results are fu...

A new polymer-stabilized nematic liquid crystal has been characterized for the measurement of biomolecular residual dipolar couplings. Filamentous Pf1 phage were embedded in a polyacrylamide matrix that fixes the orientation of the particles. The alignment was characterized by the quadrupolar splitting of the 2H NMR water signal and by the measurement of 1H-15N residual dipolar couplings (RDC) in the archeal translation elongation factor 1β. Protein dissolved in the polymer-stabilized medium orients quantitatively as in media without polyacrylamide. We show that the quadrupolar splitting and RDCs are zero in media in which the Pf1 phage particles are aligned at the magic angle. This allows measurement of J and dipolar couplings in a single sample.

Solid-state nuclear magnetic resonance and vibrational spectroscopic studies are reported for bis(pentacarbonylmanganese)diphenyltin(IV) and bis(pentacarbonylmanganese)diphenyllead(IV). The solid-state, CP-MAS, 119 Sn and 207 Pb NMR spectra of these complexes each reveal a single asymmetric undecet due to the 1 J 119 Sn‐ 55 Mn and 207 Pb‐ 55 Mn spin‐spin couplings and second-order quadrupole‐dipole effects. The 1 JSn‐Mn and 1 JPb,-Mn values are 139 ^ 1a nd 228^ 1H z; respectively. The 119 Sn and 207 Pb chemical shift anisotropies have been determined. The crystal structure of the tin compound has been re-examined. q 2001 Elsevier Science B.V. All rights reserved.

The solid-state CP MAS (29Si, 119Sn, and 207Pb) NMR spectra of the triphenylsilyl-, triphenyltin-, and triphenyllead(pentacarbonyl)manganese(I) complexes, (Ph3E)Mn(CO)5 (E = Si, Sn, Pb), have been analyzed to give the chemical shifts, one-bond spin-spin coupling constants, 1JE-Mn, the "effective-dipolar" coupling constants (D - ΔJ/3), the chemical shift tensors, and the spin-spin anisotropy (ΔJ), where the analysis permits. For the tin and lead compounds, three and four sets of chemical shifts, respectively, were observed, and two different polymorphs occur for the lead complex, depending on the solvent used for recrystallization. The average values of the reduced coupling constants, 1KMn-Si (2.64 × 1020 T2 J-1), 1KSn-Mn (1.25 × 1020 T2 J-1), and 1KPb-Mn (4.18 × 1020 T2 J-1) showed a linear correlation with the s-electron densities at the respective metal nuclei. The principal components of the chemical shift tensors have been determined for the tin and lead compounds.Key words: manganese-group-14 compounds, solid-state 29Si, 119Sn, and 207Pb CP MAS NMR, spin-spin coupling, chemical shift anisotropy, quadrupole coupling.

The 31P chemical shift tensor components and anisotropies of the trimethyl- and triphenylphosphine complexes of the group 6 metal pentacarbonyls, M(CO)5PR3 (M = Cr, Mo, W and R = Me, Ph), have been measured using solid-state CP-MAS 31P NMR spectroscopy. For the trimethylphosphine derivatives, the chemical shift tensors have near axial symmetry and the shift tensor components are in reasonable agreement with the calculated values for the chromium and molybdenum complexes. In the triphenylphosphine complexes, the tensors are asymmetric due to the different torsion angles of the phenyl rings. The trend to higher shielding of the isotropic 31P chemical shifts on descending group 6 arises from changes in the perpendicular components of the shift tensor. The one-bond coupling constants, 1J(95/97Mo-31P), for the trimethyl- and triphenylphosphine complexes are 129 and 133 Hz, respectively.Key words: chemical shift anisotropy, phosphines, chromium, molybdenum, tungsten.

Deuterium NMR spectroscopy has been used to probe the dynamics of deuterated cholate (-2,2,4,4-d 4 ) ions bound to two strong anion exchange resins: a poly(acrylamide)-based resin (-[CH 2 CH(CONH-(CH2)12N+(CH3)3Cl - )-In) and cholestyramine (Dowex 1X2-100). For the poly(acrylamide)-cholate system a nearly rigid Pake doublet with a horn splitting of 119 ± 1 kHz was observed between 0 and 20°C, indicating that the bound ions experience a highly restricted environment. At higher temperatures, the spectra show an additional, relatively narrow and featureless peak superimposed onto the broader Pake doublet. An increase in temperature also causes the relative intensity of the narrow peak to grow at the expense of the broader signal, which disappears completely above 50 °C. Line-shape simulations show that, over the whole temperature range, the cholate ions execute slow reorientation motions with correlation times in the range of 10 -4 - 10 -6 rad/s. The spectra observed for the Dowex-cholate system display similar variations with temperature; however, a Pake doublet is only observed near 0 °C. These results suggest the presence of strong hydrophobic, possibly cooperative, interactions in the cholate -resin systems. To further probe the dynamics ofbound ions in these systems the spin-lattice relaxation times were measured as a function of temperature. Analyses of the relaxation data with various motional models revealed small amplitude librations, with rates near the Larmor frequency. The difference observed between the poly(acrylamide) and Dowex systems is also discussed.

Alginic acid, obtained from Sargassum brown algae that drift from the Sargasso Sea to beaches in Cuba, has been examined as an aqueous solution by 1H and 13C NMR spectroscopy, and also in the solid state by MAS 13C NMR spectroscopy. Its composition is distinctive, relative to that for alginic acid from most other brown algae, in having a lower content of β-D-mannopyranosyluronic acid residues (M) than of α-L-gulopyranosyluronic acid residues (G). That is, M/G is ~0.6, whereas ratios of >1 have been reported for many other species, including Macrocystispyrifera, which was examined here as well. In acquiring the high-resolution spectra, partial depolymerization was used to give solutions of reduced viscosity; as is well known, this procedure may cause separation into fractions and the formation of sediments, examples of which are cited. Proton resonances of the reducing end units of chain-shortened segments of the polymers exhibited unusual, marked, line broadening at elevated temperature, which may reflect thermal dehydration. MAS 13C experiments offered the advantage of information about the intact alginate samples. Although the spectra consisted of broad, heavily overlapping peaks, curve-fitting analysis afforded qualitative and quantitative data that supplement those obtained with solutions of the polymers. Keywords: Sargassum alginate, 1H NMR of fractions, M/G constituent ratios, MAS 13C NMR, curve-fitting analysis.

The effect of the chain length and temperature on ordering of alkylphosphonate, (CnH2n+1)PO3H2, n = 8−18, monolayers on ZrO2 was characterized by solid-state 13C NMR. Alkylphosphonate monolayers wi...

Dense, highly ordered monolayers can be prepared by the adsorption of octadecylphosphonic acid (ODPA) onto nonporous ZrO2, TiO2, and zirconated silica powders. ODPA reacts strongly with Al2O3 to form a bulk (aluminoalkyl)phosphonate. The infrared spectra of the ODPA monolayers indicate a degree of conformational order comparable to self-assembled monolayers on planar substrates. From the solid-state 31P and 13C NMR spectra, the strength of the surface interaction and the degree of conformational order decrease in the following order: zirconated silica > ZrO2 > TiO2. Although the inner methylenes are primarily in an all-trans conformation, the chain termina are highly disordered. In the case of zirconated silica, there is evidence for the formation of some bulk zirconium alkylphosphonate. Proton line width measurements from 2D WISE NMR experiments reveal that considerable chain mobility is present in the ODPA monolayers on ZrO2 and TiO2, in contrast to bulk crystalline phases.

Nascent and melt-crystallized ultrahigh molecular weight polyethylene (PE) have been studied using solid-state 13 C NMR spectroscopy. Significant differences between the two materials are observed in the CPMAS spectra particularly at elevated temperatures. Three separate resonances are observed in nascent samples when the temperature is raised to near the melting point, the third peak being of an intermediate chemical shift between the crystalline and amorphous resonances that are observed in the spectra of melt-crystallized samples. Based on this chemical shift, the third resonance is likely due to polymer chains which undergo conformational averaging which is intermediate between the rigid all-trans crystalline polymer and very mobile amorphous chains. Evidence is reported which shows that this is material that is present in nascent PE below the melting point and is not created during the melting process. These observations are confirmed by the measurement of 2D wide-line separation (WISE) experiments where the 1 H line width of the amorphous component of melt-crystallized PE is much narrower than that of a nascent sample. Numerous nascent PE samples, including those of low molecular weight, display similar spectral features

The proton spin-lattice relaxation times (T 1 ) for a series of progressively sulphonated black spruce pulps were measured at two static magnetic fields and at a variety of temperatures. These determinations showed that the frequency of the anisotropic molecular motions of carbohydrates and lignin responsible for spin relaxation on wood and pulps is of the order of 10 -9 s. For cross-polarization measurements with a 300 MHz solid state NMR spectrometer, room temperature seems to be close to the T 1 versus correlation time minimum

Chitosan is composed primarily of 2-amino-2-deoxy-o-glucose residues and is produced by the deacetylation of chitin (2acetamido-2-deoxy-o-glucose) by methods that include alkaline hydrolysis’ and thermo-mechano-chemical technology’. This biopolymer has applications in industries ranging from cosmetics to water clarification and waste management. Accurate determination of the degree of deacetylation of chitosan is essential when studying structure-properties relations and possible industrial uses3. Infrared4 and NMR spectroscopy’, potentiometric5, argentometric5 and colloid titration6, mass spectrometry’, ultraviolet spectrometry’, and gel-permeation chromatography7 have been proposed as methods for the determination of the acetyl content of chitosan samples. For low acetyl contents, such methods as the IR technique, which depend on deconvoluting the amide I band (1655 cm-‘), show inherent resolution difficulties4. The need for a reliable technique to determine low acetyl contents, which are typical of commercial chitosan, is evident. Conductometric titration is a well known analytical tool for quantifying acidic functional groups. It was popularized by the well known text “pH and Electra Titrations” by Kolthoff and Laitinen8. Numerous applications, such as measuring the number of carboxylic and sulfonic acid groups in wood pulps’, quantifying strong and weak acids bound to latexes”, and characterizing heparin” are known. In fact, it is probably the most accurate technique for analyzing multifunctional polysaccharides and should prove invaluable for characterizing glycosaminoglycans. In this study, the degree of deacetylation of chitosan samples was determined by the conductometric approach and solid-state NMR. The results were compared to those obtained by ultraviolet spectrophotometry, a frequently used technique for these determinations. Also included in this study are results on a water-insoluble film of chitin crystallites (hydrochitin)‘2T13, which exemplifies a high level of acetyl content.

Polymer blends of polyamide-6 (PA6) with polystyrene at 5.4% and 9.7% sulfonation levels (SPS5 and SPS10) were investigated. NMR data showed that in 70:30 LiSPS5/PA6 and LiSPS10/PA6 70:30 blends, the two polymers are highly miscible and the separated domains, if present, are smaller than 20 A, while for PS/PA6 and NaSPS10/PA6 at the same ratio; the txo components in the blends are not miscible with separated phase dimensions larger than 200 A. The misciblity of LiSPS5 or LiSPS10 with PA6 in these blends depends significantly on the ratio of the two polymers

A thermal elastomer poly(β-hydroxyalkanoate) produced by Pseudomonas oleovorans from sodium octanoate as substrate, containing 85 % n-pentylside chains and with about 25-33 % crystallinity was studied. Variable temperature NMR spectra showed that there is significantly different dynamics for the side chains and backbone.

On a traite des pâtes a haut rendement par du nitrosodisulfonate de potassium pour produire des groupes ortho-quinone, par de l'hydrosulfite de sodium pour reduire les groupes quinone, et par du peroxyde d'hydrogene alcalin pour oxyder les groupes quinone. On a fait reagir ces pâtes et des composes modeles selectionnes avec du phosphite de trimethyle. On etudie les spectres 31 P CP/MAS NMR des composes d'addition resultants, ainsi que les spectres FTIR et UV/visible des pâtes traitees.

The crystal structure of Ca2RuD6 has been determined by neutron powder diffraction: space group Fm3m ,K 2PtCl6 structure, as found for other hexahydride salts of group 8 metals with alkaline earth or lanthanide counter ions. No structural phase transition was observed between 340 K and 50 K. The deuterium nuclear quadrupole coupling constant, 54.7 kHz, leads to an ionic character of the Ru–D bond of 76%. The known trends in the behaviour of A2MH6 salts are interpreted in terms of the ionization energies of the cation and the central metal atom. © 2007 Elsevier B.V. All rights reserved.

Bacterial copolyesters of poly(beta-hydroxyalkanoates) (PHA) with average side-chain lengths between C5 and C7 crystallize as a 21 helix in an orthorhombic lattice with two molecules per unit cell. The fibre repeat, or c dimension, is 4.55 A on average, compared with 5.96 and 5.56 A for poly(beta-hydroxybutyrate) (PHB) and poly(beta-hydroxyvalerate) (PHV), respectively. This collapse of the c dimension while maintaining the 21 helical symmetry may be thought of as crystallization driven by side-chain packing influences. This class of PHA with homologous hydrocarbon side-chains must form ordered sheets with the extended alkane branches in polyethylene-like domains. The melting point, glass transition temperature and fibre repeat change regularly as a function of average number of side-chain carbons for the whole family of PHA. X-ray diffraction of a melt-crystallized PHA indicated a maximum crystallinity of about 25%, achieved only after several hours at room temperature. Compared with P(HB-co-HV) polyesters, the stress-strain curves of PHA polyesters studied are typical of elastomers. 13C-n.m.r. spectra and relaxation times of the bulk phase amorphous regions of these polymers demonstrate the high degree of motional freedom of the side-chains and the significantly slower motion for the backbone carbons. 13C n.m.r. was also used to estimate the percentage crystallinity which is in agreement with the X-ray diffraction results. Modelling and conformational analysis of single chains using the virtual bond approach lead to two possible models for the crystalline helix: 'herringbone' versus 'comb-like'.

The deuterium NMR spectra of the ternary metal deuterides (TMDs) Ca(2)RhD(5) and Ca(2)IrD(5) show that the disorder is dynamic at room temperature, with barriers to the motion of 31.8 and 39.0 kJ mol(-1), respectively. At low temperatures, splittings equivalent to quadrupole coupling constants of 50.9 and 24.5 kHz were obtained for Ca(2)RhD(5) and 68.3 and 41.7 kHz for Ca(2)IrD(5) and are assigned to the planar and apical deuterium positions, respectively. Differential scanning calorimetric study of the transition in Ca(2)IrH(5) located a reversible phase transition at 284 K with an enthalpy change of 650 J mol(-1) and entropy change of 2.3 J K(-1) mol(-1).

Hydrogels present an attractive alternative to nanoscale block copolymer aggregates and microscale resin beads as potential asystemic serum cholesterol reduction materials. Not only would the oral delivery of these materials be more pleasant than the sand-like bile salt anion sequestrant beads but also the hydrogel preparation is much simpler than the copolymer aggregate analogues [Cameron, N. S.; Eisenberg, A.; Brown, G. R. Biomacromolecules 2002, 3, 116-123. Cameron, N. S.; Eisenberg, A.; Brown, G. R. Biomacromolecules 2002, 3, 124-132]. Our goal was to explore these materials building on our experience with bulk resins and self-assembled copolymers. In this paper, following a brief introduction to hydrogels and their application to hypercholesterolemia, the synthesis, characterization, and preliminary glycocholate binding properties of poly(N,N,N-trimethylammoniumalkyl acrylamide chloride)gel are presented [Cameron, N. S.; Eisenberg, A.; Brown, G. R. Polym. Preprints 2002, 43, 771-772].

Synthetic biodegradable poly(butylene adipate-co-butylene terephthalate), P(BA-co-BT), with 56 mol % butylene adipate, BA, was characterized by solid-state NMR spectroscopy, thermal analysis, X-ray diffraction, computer modeling, and polarization microscopy. The NMR study showed the presence of BA and butylene terephthalate, BT. T(1C) NMR measurements proved that some BA and BT units were in crystalline regions. Thermal analysis showed one glass-transition temperature and a single diffuse melting endotherm corresponding to a large melting-point depression of about 100 degrees C compared with poly(butylene terephthalate), PBT. These results suggest that there is only one crystalline phase. An X-ray fiber diagram of a stretched film could be indexed with the same unit cell as that for PBT. Computer modeling showed that the adipate unit fits into the crystal structure of PBT by adopting a TTGTG dihedral angle sequence in the crystalline conformation proposed for the cocrystallization model. The predicted fiber diagram from the proposed model qualitatively agrees with the experimental one. Polarization microscopy revealed that the spherulite growth rate of P(BA-co-BT) was similar to that for poly(butylene adipate), PBA.

A new polymer-stabilized nematic liquid crystal has been characterized for the measurement of biomolecular residual dipolar couplings. Filamentous Pf1 phage were embedded in a polyacrylamide matrix that fixes the orientation of the particles. The alignment was characterized by the quadrupolar splitting of the 2H NMR water signal and by the measurement of 1H-15N residual dipolar couplings (RDC) in the archeal translation elongation factor 1beta. Protein dissolved in the polymer-stabilized medium orients quantitatively as in media without polyacrylamide. We show that the quadrupolar splitting and RDCs are zero in media in which the Pf1 phage particles are aligned at the magic angle. This allows measurement of J and dipolar couplings in a single sample.

Crosslinked polystyrene (Ps) bearing functional side groups Ps-CH 2 CH 2 SR (R= CH 2 CH 2 COOH, Ph, -tBu, COCH 3 , H, CH 2 CH 2 OH, n-Bu, (CH 2 ) n SH (n= 2,3,4)) were investigated. Solid state 13 C NMR spectroscopy was shown to be a powerful technique to characterize structure and mobility these polymers. Results indicate that the polymer backbone generally behaves as a rigid network, while certain spacer-supported functionalities can show significant flexibility

A controlled release excipient based on sodium trimetaphosphate (STMP) crosslinked high amylose starch has been examined by 13C CP/MAS NMR. The dry excipient powder is pressed to a hard tablet whose volume increase in H2O runs parallel to the STMP concentration used. The known polymorph resonances of single helix ‘V’ starch (hydrated) and double helix ‘B’ starch (hydrated) both contribute to the spectrum corresponding to the swollen tablet. The wet tablet when loaded with a pharmaceutical agent provides a near zero-order release profile for up to 20 h. The swelling and drug release behaviour is explained in terms of self-assembly of the STMP treated starch nanomolecular particles. These particles are drawn together by “self-assembly” due to formation of amylose double helices as water penetrates the tablet. An optimum level of chemical crosslinking ensures the integrity of the swollen tablet whose sponge-like structure enclosed by a membranous surface is responsible for sustained release.

Solid-state, CP-MAS, 119Sn NMR spectra were measured for a series of para-substituted triaryltin(pentacarbonyl)manganese(I) complexes. All the spectra show an asymmetric sextet due to spin-spin coupling and second-order quadrupolar effects, transmitted by dipolar coupling between the 119Sn and 55Mn nuclei, which are not suppressed by magic-angle rotation. The solid-state 1JMn-Sn spin-spin and nuclear quadrupole coupling constants range from 130 to 250 Hz and -8 to 21 MHz, respectively, and show an inverse linear correlation, which is attributed to the dominance of the Fermi contact contribution to the 1JMn-Sn coupling. The tris(p-methylthiophenyl)tin derivative is an exception, attributed to a difference in crystal structure from the other complexes. The magnitudes of the principal elements of the 119Sn chemical shift tensors were determined and appear to be strongly influenced by the ring torsion angles and the para-substituents of the phenyl rings. Solid-state 119Sn NMR spectroscopy provides a useful method of probing the electronic environment around the tin and manganese nuclei in transition metal complexes. Copyright 1998 Academic Press.

Summary By measuring the proton spin-lattice relaxation times (T~) in the solid state, for a series of progressively sulphonated and methylated black spruce pulps, the molecular mobilities of carbohydrates and lignin have been evaluated as a function of chemical treatment. These measurements were made possible only after the paramagnetic metal ion impurities were removed from the samples. For untreated wood the proton T, values of carbohydrates and lignin were virtually undistinguishable, irrespective of the applied magnetic field strength. The introduction of sodium salts of carboxylic and sulphonic acid groups in softwood pulps and the introduction of methoxyl groups, seem to very significantly increase the molecular mobilities of carbohydrates and lignin. The opposite was true when calcium were the counterions of the acidic groups. These observations have been attributed to the disruption of associative lignin-carbohydrate hydrogen bonding interactions otherwise operating within untreated wood. 19

13C chemical shifts and 13C–31P couplings are reported for 11 cyclic phosphoramidates of ring sizes from four to nine. Vicinal couplings are compared with those of carbocyclic analogs and provide insight regarding the degree of nitrogen lone pair derealization into the N—P bond. For six-membered and larger rings, there appears to be nearly complete lone pair delocalization, i.e., a trigonal planar nitrogen atom. In azetidine derivatives the nitrogen lone pair remains localized, giving rise to a highly puckered ring conformation. Pyrrolidine derivatives are viewed as having a nitrogen with a partially delocalized electron pair.

The conformational analysis of DL-, L- and D-methionine was studied by solid-state 13C NMR with the help of cross-polarization and magic-angle spinning techniques. The spectrum of commercial crystalline DL-methionine showed two chemical shifts (18.7 and 15.8 ppm) for the methyl carbon. Crystallization from water or water-ethanol (95 : 5) allowed the separation of two crystalline forms (α and β), of which one had δ (CH3) 18.7 ppm and the other δ (CH3) 15.8 ppm. Therefore, each crystalline form of DL-methionine consists of a single conformer, a result in agreement with x-ray diffraction data. This conformational difference of the two crystalline forms was also reflected in the carbon resonances of C-β and C-γ. When L- and D-methionine were crystallized from water-ethanol (3 : 2), the solid-state 13C NMR spectra showed that each isomer displayed two methyl carbon peaks at 18.1 and 16.2 ppm of equal intensities, while the α-carbon resonances showed a broad peak due to two unresolved doublets. These results suggest that the L- or D-methionine crystal contains two different conformers in one unit cell, a conclusion that is also supported by the x-ray data.

13C nmr chemical shifts and 13C–31P couplings through one, two, and three bonds are reported for twelve carbocyclic hydroxyphosphonates and alkyl derivatives with all ring sizes from four to twelve, except the cyclodecyl system. On the basis of the vicinal couplings and carbon shieldings, inferences regarding preferred conformations are drawn. Evidence for ring flattening in some cyclohexyl compounds is presented. For a given ring size, it is demonstrated that 1Jcp becomes less positive as the degree of steric congestion about the C—P bond increases.

Natural abundance 13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high-power decoupling, cross-polarization and magic angle spinning. Solid-state NMR of aspirin had excellent sensitivity compared with liquid-state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non-protonated carbons. The solid-state 13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic. The solid-state 13C NMR spectra of several commercial aspirin tablets, some of them containing buffer components, indicated that there were no interactions among the aspirin and the buffer components; only after dissolving the tablets and lyophilization did the 13C NMR spectra of the dry lyophilized powders show strong interactions between aspirin and the buffer components.

A series of macrocyclic polyether-diester ligands containing a proton-ionizable triazole subcyclic unit has been prepared. The crystal structure of one ligand shows that it forms a hydrate with the water molecule located in the macrocyclic cavity. The water is coordinated by hydrogen bonding to two oxygen atoms of the macrocycle and to the NH group of the triazole moiety. These macrocycles also form complexes with amines. These amine complexes are kinetically more stable than complexes formed by the triazole ligands with the corresponding alkylammonium perchlorate salts. The crystal structure of one of these complexes shows that the triazole ring has donated a proton to the amine group. 41 references, 4 figures, 2 tables.

A series of chiral diphenyl-substituted macrocyclic polyether-diester ligands have been prepared from the chiral diphenyl-substituted tetraethylene glycol. Enantiomeric recogntion by the chiral diphenyl-substituted pyridino-diester-18-crown-6 compound (7) was studied by temperature dependent 1H NMR spectroscopy in deuteriodichloromethane. This ligand exhibited chiral recognition when complexed with the hydrogen per-chlorate salts of (R)- and (S)-α-(1-naphthyl)ethylamine and (R)- and (S)-methyl phenylalaninate.

13C nmr chemical shifts and 13C—31P couplings through one, two, and three bonds are reported for eleven carbocyclic phenylaminephosphonates with ring sizes from four to seven. On the basis of these data, inferences regarding preferred conformations are drawn. Low temperature spectra of the 4-methylcyclohexyl derivative show the existence of two conformers, populated in the ratio of approximately 2:1 at 183 K.