Solution NMR Spectra Research Articles

Structural Requirements for Key Residues and Auxiliary Portions of a BLUF Domain

BlrB in Rhodobacter sphaeroides is a single domain, flavin-based blue light sensor protein in the BLUF family of photoreceptors. Consistent with other members of this family, blue light excitation induces a putative signaling state characterized by a 10 nm red shift in the UV-visible absorbance spectrum. Structural and spectroscopic characterization of truncated BlrB constructs establishes that the C-terminal 50 amino acids of this protein are essential to its structural integrity despite not being part of the canonical BLUF domain architecture. Mutagenesis studies support the critical roles of Tyr9, Asn33, and Gln51 for flavin binding and the integrity of the BLUF domain fold. Comparison of solution NMR spectra of BlrB acquired under dark and light conditions indicates very limited light-dependent conformational changes except for a few interesting residues: Trp92, Met94, and Ile127. Notably, the Ile127 side chain experiences significant chemical shift changes despite the fact that it is far ( approximately 15 A) from the flavin chromophore in the C-terminal extension. These data suggest that the light-induced signal is propagated from the flavin through the beta sheet to the last two alpha helices in the C-terminal extension, potentially providing a mechanism to transmit this change to initiate a cellular response to blue light.

Structural studies of 4,5,6,7-tetrabromobenzimidazole derivatives by means of solid-state 13C, 15N NMR spectroscopy and DFT calculations

Tetrabromobenzimidazole derivatives containing sulfur or nitrogen atom in a five- or six-membered saturated ring were synthesized as potential ligands of casein kinase (CK2). Structural data of these compounds are crucial for understanding their inhibitory activity as inhibitors. Solution and solid-state 13C NMR spectra were recorded for six compounds, and 15N MAS spectra – for two of them. 13C CPMAS spectra were assigned by comparison with solution data and with the aid of dipolar dephasing and variable contact time experiments. The correctness of assignments of 13C and 15N chemical shifts was verified by GIAO DFT calculations of shielding constants. The differences between the solution and solid-state chemical shift values were explained in terms of intermolecular interactions. The doublet resonances occurring in the solid-state 13C and 15N NMR spectra of N 1, N 2-propylene-2-amino-4,5,6,7-tetrabromobenzimidazole indicate the presence of two molecules in crystallographic unit cell. Shielding constants calculated for a dimer with two N1′ H…N3 hydrogen bonds suggest that the association type does not influence carbon shielding. The coexistence of two tautomers with N1′ H and N3 H is less probable.

Substituent Effects in the Solid‐State Assembly of Silver(I) Complexes of 4‐Substituted 3,6‐Di(2‐pyridyl)pyridazines

AbstractThe reactions of one equivalent of silver(I) tetrafluoroborate with one equivalent of 4‐R‐3,6‐di(2‐pyridyl)pyridazine ligands (R = n‐C10H21, 4‐O2NC6H4, 4‐MeOC6H4, 4‐F3CC6H4, 4‐NCC6H4, 3,5‐Br2C6H3, 3,5‐(MeO)2C6H3) in acetonitrile are reported. All complexes have been structurally characterized, and are found to belong to one of four differentsolid‐state structure types: [AgL2][BF4], [Ag2L2][BF4]2, {[Ag3L2][BF4]3}n and {[Ag2(NCMe)2L2][BF4]2}n. For the bulk samples of these compounds, elemental analyses are consistent with formulations of [AgL2][BF4], [Ag2L2][BF4]2, but the two polymeric complexes analyse as 1:1 Ag:L complexes. In solution, 1H and 13C NMR spectra reveal only one ligand environment at room temperature for each product.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 5. Synthesis, Physicochemical and Theoretical Studies of a Novel Pentanuclear Palladium(II) Complex and Related Mononuclear Species

New palladium(II) complexes of the free-base tetrakis[2,3-(5,6-di-2-pyridylpyrazino)porphyrazine], [Py 8TPyzPzH 2], have been prepared and their physicochemical properties examined. The investigated compounds are the pentanuclear species [(PdCl 2) 4Py 8TPyzPzPd], the monopalladated complex [Py 8TPyzPzPd], and its corresponding octaiodide salt [(2-Mepy) 8TPyzPzPd](I) 8. All three Pd (II) complexes have a common central pyrazinoporphyrazine core and differ only at the periphery of the macrocycle, where the simple dipyridinopyrazine fragments present in [Py 8TPyzPzPd] bear four PdCl 2 units coordinated at the pyridine N atoms in the pentanuclear complex, [(PdCl 2) 4Py 8TPyzPzPd], or carry pyridine-N(CH 3) (+) moieties in the iodide of the octacation [(2-Mepy) 8TPyzPzPd] (8+). The structural features of the pentanuclear complex [(PdCl 2) 4Py 8TPyzPzPd], partly supported by X-ray data and solution (1)H NMR spectra of the [(CN) 2Py 2PyzPdCl 2] precursor, were elucidated through one- and two-dimensional (1)H NMR spectra in solution and density functional theory (DFT) calculations. Structural information on the monopalladated complex [Py 8TPyzPzPd] was also obtained from DFT calculations. It was found that in the complex [(PdCl 2) 4Py 8TPyzPzPd] the peripheral PdCl 2 units adopt a py-py coordination mode and the generated N 2PdCl 2 moieties are directed nearly perpendicular to the plane of the pyrazinoporphyrazine ring, strictly recalling the arrangement found for the palladated precursor [(CN) 2Py 2PyzPdCl 2]. NMR and DFT results consistently indicate that of the four structural isomers predictable for [(PdCl 2) 4Py 8TPyzPzPd], one having all four N 2PdCl 2 moieties pointing on the same side of the macrocyclic framework (i.e., isomer 4:0, plus the 3:1 and the 2:2-cis and 2:2-trans isomers), the 4:0 isomer ( C 4 v symmetry) is the predominant form present. According to cyclic voltammetry and spectroelectrochemical results in pyridine, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF), the monopalladated complex [Py 8TPyzPzPd] undergoes four reversible or quasi-reversible one-electron ligand-centered reductions, similar to the behavior also observed for the pentanuclear complex [(PdCl 2) 4Py 8TPyzPzPd], which shows an additional reduction peak attributable to the presence of PdCl 2. Owing to the electron-withdrawing properties of the PdCl 2 units, the pentanuclear complex is easier to reduce than the mononuclear complex [Py 8TPyzPzPd], some related [Py 8TPyzPzM] complexes, and their porphyrin or porphyrazine analogues, so much so that the corresponding monoanion radical is generated at potentials close to 0.0 V vs SCE in DMSO or DMF. In turn, the monoanion of [(2-Mepy) 8TPyzPzPd](I) 8 is also extremely easy to generate electrochemically. Indeed, because of the eight positively charged N-CH 3 (+) groups in this complex the first reduction occurs at potentials close to +0.10 V in DMSO or DMF. The redox behavior of the mono- and pentapalladated complexes has been rationalized on the basis of a detailed DFT analysis of their ground-state electronic structure.

Synthesis, IR, UV/vis-, 1H NMR and DFT study of chelatophore functionalized 1,3-benzoxazinone spiropyrans

Six novel functionalized spiropyran's derivatives of 2H-1,3-benzoxazinone series were synthesized by introducing the substituents with chelating ability into 2H-chromene part of the 8′-formyl-7′-hydroxy-3-methyl-4-oxo-3,4-dihydro-2H-1,3-benzoxazine-2-spiro-2′-[2H]-chromene (I) by condensation with 2-aminophenol, 2-amino-4-methylphenol, 2-amino-4-nitrophenol, 2-amino-1-methylbenzimidazole, 4-amino-4H-1,2,4-triazole, N-(4-aminophenyl)acetamide. 1H NMR, UV/vis, IR spectroscopy combined with quantum-chemical calculations employing density functional theory (DFT) were used to study their structure. All substances, except 2-amino-4-nitrophenol derivative exist in solid state and in solution solely in closed spiroform, while the mentioned one undergoes partial spiropyran ring opening. In DMSO solution NMR spectra show ratio of 2:1 of closed and opened form, correspondingly.

Investigation of Structural Transition of Regenerated Silk Fibroin Aqueous Solution by Rheo-NMR Spectroscopy

In this study we applied Rheo-NMR to investigate the structural change of Bombyx mori silk fibroin in aqueous solution under shear. Monitoring the time dependence of 1H solution NMR spectra of silk fibroin subjected to constant shear strain, signal intensities of random coil decreased suddenly during shear while peaks from beta-sheet structure did not arise in the solution spectra. After these experiments, an aggregate of silk was found in the Couette flow cell and its secondary structure was determined as beta-sheet by 13C solid-state NMR. In conclusion the moderate shear applied here triggered the change in the secondary structure.

Autoxidation of a 4-iminoimidazolidin-2-one with a tertiary 5-hydrogen to its 5-hydroxy derivative

Chemoselective autoxidation of 4-imino-1,5-dimethyl-3-(4-nitrophenyl)imidazolidin-2-one (1b) to its 5-hydroxy derivative 2 occurred in solutions of DMSO-d6, acetonitrile-d3 or refluxing ethanol. Also bis(imidazolidin-5-yl) peroxide 5 was isolated as a minor product. It crystallizes as a 1:1 mixture of R*, R* and R*, S* diastereomers, whereas the NMR spectra of the reaction solution in DMSO-d6 showed unequal amounts of the two isomers. Molecular mechanics modeling studies with the MM3 force field indicate the R*,S* diastereomer as the more stable one. The 5-unsubstituted and the 5,5-dimethyl substituted imines 1a and 1c, respectively, were found stable against autoxidation; the difference in reactivity of 1b is attributed to the single 5methyl group enhancing the population of the enamine tautomer. The 5-hydroxy-4-imino-1,5dimethylimidazolidin-2-one (2) underwent acid hydrolysis to form 5-hydroxyhydantoin 4.

Progress in C13 and H1 solid-state nuclear magnetic resonance for paramagnetic systems under very fast magic angle spinning

High-resolution solid-state NMR (SSNMR) of paramagnetic systems has been largely unexplored because of various technical difficulties due to large hyperfine shifts, which have limited the success of previous studies through depressed sensitivity/resolution and lack of suitable assignment methods. Our group recently introduced an approach using "very fast" magic angle spinning (VFMAS) for SSNMR of paramagnetic systems, which opened an avenue toward routine analyses of small paramagnetic systems by (13)C and (1)H SSNMR [Y. Ishii et al., J. Am. Chem. Soc. 125, 3438 (2003); N. P. Wickramasinghe et al., ibid. 127, 5796 (2005)]. In this review, we discuss our recent progress in establishing this approach, which offers solutions to a series of problems associated with large hyperfine shifts. First, we demonstrate that MAS at a spinning speed of 20 kHz or higher greatly improves sensitivity and resolution in both (1)H and (13)C SSNMR for paramagnetic systems such as Cu(II)(DL-alanine)(2)H(2)O (Cu(DL-Ala)(2)) and Mn(acac)(3), for which the spectral dispersions due to (1)H hyperfine shifts reach 200 and 700 ppm, respectively. Then, we introduce polarization transfer methods from (1)H spins to (13)C spins with high-power cross polarization and dipolar insensitive nuclei enhanced by polarization transfer (INEPT) in order to attain further sensitivity enhancement and to correlate (1)H and (13)C spins in two-dimensional (2D) SSNMR for the paramagnetic systems. Comparison of (13)C VFMAS SSNMR spectra with (13)C solution NMR spectra revealed superior sensitivity in SSNMR for Cu(DL-Ala)(2), Cu(Gly)(2), and V(acac)(3). We discuss signal assignment methods using one-dimensional (1D) (13)C SSNMR (13)C-(1)H rotational echo double resonance (REDOR) and dipolar INEPT methods and 2D (13)C(1)H correlation SSNMR under VFMAS, which yield reliable assignments of (1)H and (13)C resonances for Cu(Ala-Thr). Based on the excellent sensitivity/resolution and signal assignments attained in the VFMAS approach, we discuss methods of elucidating multiple distance constraints in unlabeled paramagnetic systems by combing simple measurements of (13)C T(1) values and anisotropic hyperfine shifts. Comparison of experimental (13)C hyperfine shifts and ab initio calculated shifts for alpha- and beta-forms of Cu(8-quinolinol)(2) demonstrates that (13)C hyperfine shifts are parameters exceptionally sensitive to small structural difference between the two polymorphs. Finally, we discuss sensitivity enhancement with paramagnetic ion doping in (13)C SSNMR of nonparamagnetic proteins in microcrystals. Fast recycling with exceptionally short recycle delays matched to short (1)H T(1) of approximately 60 ms in the presence of Cu(II) doping accelerated 1D (13)C SSNMR for ubiquitin and lysozyme by a factor of 7.3-8.4 under fast MAS at a spinning speed of 40 kHz. It is likely that the VFMAS approach and use of paramagnetic interactions are applicable to a variety of paramagnetic systems and nonparamagnetic biomolecules.

Sobre uma degenerescência acidental nos deslocamentos químicos de RMN de 31P{¹H} em complexos difosfínicos de rutênio

The [RuCl(bipy)(dppb)(4-pic)]PF6 complex was prepared and fully characterized. The X-ray crystal structure of this complex was determined in order to make an unambiguous distinction between the two possible positions of the 4-methylpyridine ligand (4-pic) in the compound: trans to phosphorus atom or trans to nitrogen atom. The [RuCl(bipy)(dppb)(4-pic)]PF6 complex exhibits an unusual temperature-dependent accidental degeneracy of the 31P chemical shifts in its solution NMR spectrum.

Synthesis and Structure of Permethylcyclopentadienyltitanium Diisopropoxide Zwitterionic Complex

Half-sandwich pentamethylcyclopentadienyltitanium chloroisopropoxides [Ti(η5-C5Me5)-Ti(Oi-Pr)nCl3-n] (n = 1 (1) or 2 (2)) and methylisopropoxides [Ti(η5-C5Me5)Ti(Oi-Pr)nMe3-n] (n = 1 (3) or 2 (4)) were prepared and characterized by spectroscopic methods, and compound 1 by single crystal X-ray diffraction analysis. Compounds 3 and 4 were reacted with an equimolar quantity of B(C6F5)3, however, only compound 4 afforded a crystalline product of limited stability at ambient temperature. Its single crystal X-ray diffraction analysis revealed that it is the zwitterionic complex [(η5-C5Me5)Ti(Oi-Pr)2]+[(μ-Me)B(C6F5)3]- (5) and its crystal structure is very similar to the recently reported tert-butoxy complex [(η5-C5Me5)-Ti(Ot-Bu)2]+[(μ-Me)B(C6F5)3]- (6). The 1H, 13C, and 19F NMR spectra in C6D6 solution also showed the features analogous to those of 6. 1D NOESY experiments proved a close through space interaction of irradiated C5Me5 or OCHMe2 protons with the bridging Ti···Me-B group. The NMR data indicate the inner sphere ion pair structure of 5 in C6D6, like for 6. The crystal structure geometry of the C-H bonds of the Ti···Me-B group fulfils conditions for their agostic interaction with the titanium centre. Although structurally similar to 6, compound 5 is less thermally stable apparently due to a lower bulkiness of Oi-Pr group compared to that of Ot-Bu group.

Structural Analyses of Anaphe Silk Fibroin and Several Model Peptides Using 13C NMR and X-ray Diffraction Methods

The Thaumetopoeid silkmoth Anaphe reticulata is highly abundant in equatorial and southern Africa and a potential commercial source of silk. In this paper, we report detailed structural characteristics of the silk fibroins. Comparison of the 13C solution NMR spectra of Anaphe silk fibroin and several model peptides with Ala and Gly residues indicates that (AAG)n1 and (AG)n2 are the main sequences. In addition this analysis also indicates that the sequence contains (A)m (where m > 2) such as (AAAG)n3, (AAGAG)n4, and (AAAGAG)n5. GG sequences were absent at a level that could be detected by our NMR method. The 13C CP/MAS NMR study shows that the fiber structure is heterogeneous, but predominantly β-sheet structure and the length of (AG)n2 is too short to form the Silk I structure detected in Bombyx mori silk fibroin. X-ray diffraction analyses gave information on the higher order structure and hydrogen-bonding character of Anaphe silk fiber.

Structure discrimination for the C-terminal domain of Escherichia coli trigger factor in solution

NMR measurements can give important information on solution structure, without the necessity for a full-scale solution structure determination. The C-terminal protein binding domain of the ribosome-associated chaperone protein trigger factor is composed of non-contiguous parts of the polypeptide chain, with an interpolated prolyl isomerase domain. A construct of the C-terminal domain of Escherichia coli trigger factor containing residues 113-149 and 247-432, joined by a Gly-Ser-Gly-Ser linker, is well folded and gives excellent NMR spectra in solution. We have used NMR measurements on this construct, and on a longer construct that includes the prolyl isomerase domain, to distinguish between two possible structures for the C-terminal domain of trigger factor, and to assess the behavior of the trigger factor C-terminal domain in solution. Two X-ray crystal structures, of intact trigger factor from E. coli (Ferbitz et al., Nature 431:590-596, 2004), and of a truncated trigger factor from Vibrio cholerae (Ludlam et al., Proc Natl Acad Sci USA 101:13436-13441, 2004) showed significant differences in the structure of the C-terminal domain, such that the two structures could not be superimposed. We show using NMR chemical shifts and long range nuclear Overhauser effects that the secondary and tertiary structure of the E. coli C-terminal domain in solution is consistent with the crystal structure of the E. coli trigger factor and not with the V. cholerae protein. Given the similarity of the amino acid sequences of the E. coli and V. cholerae proteins, it appears likely that the structure of the V. cholerae protein has been distorted as a result of truncation of a 44-amino acid segment at the C-terminus. Analysis of residual dipolar coupling measurements shows that the overall topology of the solution structure is completely inconsistent with both structures. Dynamics analysis of the C-terminal domain using T1, T2 and heteronuclear NOE parameters show that the protein is overall rather flexible. These results indicate that the structure of this domain in solution resembles the X-ray crystal structure of the E. coli protein in secondary structure and at least some tertiary contacts, but that the overall topology differs in solution, probably due to structural fluctuation.

Preparation and structural characterization of [RuCl 2(CO) 2{Te(CH 2SiMe 3) 2} 2] and [RuCl 2(CO){Te(CH 2SiMe 3) 2} 3

The objective of the present work was to synthesize mononuclear ruthenium complex [RuCl 2(CO) 2{Te(CH 2SiMe 3) 2} 2] ( 1) by the reaction of Te(CH 2SiMe 3) 2 and [RuCl 2(CO) 3] 2. However, the stoichiometric reaction affords a mixture of 1 and [RuCl 2(CO){Te(CH 2SiMe 3) 2} 3] ( 2). The X-ray structures show the formation of the cis(Cl), cis(C), trans(Te) isomer of 1 and the cis(Cl), mer(Te) isomer of 2. The 125Te NMR spectra of the complexes are reported. The complex distribution depends on the initial molar ratio of the reactants. With an excess of [RuCl 2(CO) 3] 2 only 1 is formed. In addition to the stoichiometric reaction, a mixture of 1 and 2 is observed even when using an excess of Te(CH 2SiMe 3) 2. Complex 1 is, however, always the main product. In these cases the 125Te NMR spectra of the reaction solution also indicates the presence of unreacted ligand.

Structure of polycondensates from hydroxymethylphenols

AbstractThe structure of oligomers obtained from mono‐hydroxymethylphenols in melt condensation at 120°C was determined using 13C NMR spectra in CD3OD solution. Alongside of methylene region of spectrum, valuable information was obtained from signals of aromatic carbons. Noncatalytic conditions promote the formation of dihydroxydibenzyl ethers in equilibrium with ortho‐ and para‐benzoquinones of oxymethylene derivatives. The final methylene linked oligomers are formed, mainly, by splitting the ether intermediates with free aromatic positions. In alkaline conditions, highly nucleophilic phenoxide ions of ortho‐hydroxymethyl compounds are responsible for substitution in free aromatic positions. The most favored reaction in the mixture of both hydroxymethylphenols is the formation of p,p′‐methylene. In condensation of para‐hydroxymethylphenol, formation of p,p′‐methylene groups occurs with simultaneous release of formaldehyde. High content of alkali stabilized ortho‐hydroxymethyl groups of fully substituted methylene linked oligomers determines the curing behavior of resol phenol–formaldehyde resins. The role of hemiformals in reactions was insignificant. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

A simple two-step automatic assignment procedure for complicated NMR spectra of solutes in liquid crystals using genetic algorithms

The complexity of 1H NMR spectra of solutes in partially ordered solvents such as liquid crystals increases rapidly with the number of spins. Spectra of simple solutes with sufficient symmetry and containing not too many spins (typically ⩽6) are readily analysed. The analysis of larger spin systems is more difficult, and often impossible. In this Letter, we present the application of a general automated genetic algorithm to solving highly complex spin systems with minimal operator intervention. The robustness of the method is demonstrated for the nine-spin system p-bromo-biphenyl, a solute interconverting between two symmetry-related conformations.

Modulating the propeller-like shape of a tripodal C(CH 2PPh 2) 3 fragment by the size of the substituent at the pivotal carbon atom in macrobicyclic tri-λ 5-phosphazenes

The chiral macrobicyclic tri-λ 5-phosphazenes formed by tripod–tripod coupling of tris(3-azidobenzyl)amines and 1,1,1-tris[(diphenylphosphino)methyl]methanes present helical topologies as a result of combining two propeller-shaped tripodal fragments with the same sense of twist. The introduction of a series of R piv substituents of increasing size at the pivotal carbon of the lower tert-butane fragment R piv–C(CH 2PPh 2) 3 causes a gradual decrease of the helicity in the lower propeller. This phenomenon is revealed in their CDCl 3 solution NMR spectra, and the activation energies for the racemization process of the tri-λ 5-phosphazenes were calculated by coalescence VT-NMR experiments.

Synthesis, NMR and crystallographic studies of 2-substituted dihydroquinazolinones derived from (S)-phenylethylamine.

2,3-Dihydro-3-[(S)-1-phenethyl]quinazolinone and some new 2-substituted derivatives bearing isopropyl, o-nitrophenyl and p-nitrophenyl groups were prepared in 40-90% yield by amidation of isatoic anhydride with (S)-phenylethylamine, followed by condensation with triethyl orthoformate, isopropylaldehyde, o-nitro- and p-nitro-benzaldehyde, respectively. The two 2-subtituted dihydroquinazolinones obtained either by using isopropylaldehyde, o-nitro- or p-nitrobenzaldehyde, were separated and purified before their NMR spectra in CDCl3 solutions were recorded. The detection of the low energy conformation of O=C-N-phenethyl segment in solution allowed the correlation of the NMR data with the configuration of newly stereogenic carbon C-2; thus, one diastereomer was labeled SS while the other was RS. Configurations determined by the NMR method were corroborated by X-ray diffraction analysis. X-ray structures of each diastereomeric series showed characteristic conformational types: a propeller-like for the SS and a hairpin for the RS series. Interatomic distances of the hairpin conformation suggest the existence of intramolecular face-to-face interactions between two aromatic rings.

1H and 13C NMR Spectral Studies on N-(j, k-Dichlorophenyl)- and N-(j, k-Dimethylphenyl)-acetamides and Substituted Acetamides

70 N-( j,k-Dichlorophenyl / j,k-dimethylphenyl)-acetamides and substituted acetamides of the general formula j,k-X′2C6H3NH-CO-CH3−iXi ( j,k = 2,3; 2,4; 2,5; 3,4 or 3,5; X, X′ = Cl or CH3; i = 0, 1, 2 or 3) have been synthesized and their 1H and 13C NMR spectra in solution were studied. The influence of Cl and methyl substitution in the side chain as well as in the aryl group was ystematically investigated and discussed in detail. Chemical shifts of all aromatic protons and carbon atoms were computed by adding the substituent contributions in three different ways to those of the unsubstituted molecules. The agreement with the experimental values is discussed in detail for the three different methods of calculation.

Direct dissolution of cellulose in NaOH/thiourea/urea aqueous solution

Untreated cellulose was directly and quickly dissolved in NaOH/thiourea/urea aqueous solution. The mechanism of dissolution was investigated by SEM, WXRD and 13C NMR. The components of this solvent cannot dissolve cellulose on their own, and the interactions between NaOH and urea, as well as between NaOH and thiourea, play an important role in improving the dissolution of cellulose. Moreover, 13C NMR spectra proved that NaOH, thiourea, and urea were bound to cellulose molecules, which brings cellulose molecules into aqueous solution to a certain extent and prevents cellulose macromolecules from associating. 13C NMR spectra of the cellulose solution show that this novel mixture is a direct solvent. Optical microscopy and CP MAS 13C NMR were used to study the process of dissolution. The results reveal that cellulose is dissolved completely and that cellulose I (cotton linter) first changes to amorphous cellulose chains in solution, and then to cellulose II during regeneration. Moreover, a new, more effective dissolution method is proposed, as confirmed by dynamic rheology measurements.

Solid-state vibrational spectra and theoretical study of alaninamide acetate

AbstractSolid-state IR and Raman spectroscopic elucidation of alaninamide acetate is preformed by means of the possibilities of linear-polarized IR and Raman methods. The experimental assignment is compared with theoretical vibrational analysis with the intention to explain the influence of intermolecular interactions in solid phase on the spectroscopic properties of the compound studied. The 1H and 13C NMR spectra in solution are compared with the corresponding ones of alanine, studying the amidation effect on the chemical shift signals in the alanine moieties.