摘要:

AbstractTwo‐dimensional (2D) NMR is a versatile technique which exists in many versions. Two broad classes of 2D techniques are (1)correlatedspectroscopy and (2)J‐resolvedspectroscopy. The first of these may be divided into two further subdivisions: COSY, which permits correlations of resonancesviaJ‐coupling, and NOESY, which allows direct measurement of intenuclear (usually interproton) distances by the nuclear Overhauser effect. COSY greatly facilitates the interpretation of complex spectra and spectral interpretation in terms of stereochemical sequences is placed on a firmer foundation. NOESY provides direct information concerning the local conformations of polymers in solution. By use of J‐resolved 2D NMR, we can separate J‐couplings and chemical shifts on different axes and thus achieve a degree of resolution of both these parameters far beyond what is attainable in the 1D spectrum. Finally, we may combine correlated and J‐resolved spectroscopy and achieve the benefits of both in3D NMR, in which the 2D cross peaks exhibit J‐coupling fine structure. These techniques are illustrated for a variety of polymers includingpoly(methyl methacrylate), poly(vinyl fluoride), poly‐y‐benzyl L‐glutamate, and po

ISSN:0258-0322    

DOI:10.1002/masy.19900340102

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractRecent developments in high resolution multidimensional NMR spectroscopy are discussed. Emphasis is laid on the extraction of structural information especially of 3D spectra. A novel 2D experiment is proposed to measure cross relaxation induced by correlated motion in macromolecules.

ISSN:0258-0322    

DOI:10.1002/masy.19900340103

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe possibility of extending NMR methods for structure determination to larger proteins (MW>10 kD) depends on the development of isotopic labeling protocols for the simplification of their NMR spectra (isotopic spectral editing). We describe here the successful use of selective deuteration to obtain sequence specific assignments for (thus far) more than 50% of the residues of thetrprepressor protein (25 kD). This is the largest protein for which detailed sequence specific assignments have been attempted to‐dat

ISSN:0258-0322    

DOI:10.1002/masy.19900340104

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance spectroscopy (NMR) has become the most frequently used technique for the investigation of the structure of biomacromolecules in solution. In particular, selective relaxation techniques have been used in the analysis of homonuclear dipolar connectivities (selective and biselective proton spin‐lattice relaxation experiments) and heteronuclear couplings (selective {H} C‐NOE, biselective carbon R1experiments). An accurate determination of selected i‐j internuclear distances has made it possible to identify the preferred solution structure. A different experimental technique based on two‐dimensional NOE spectra has made it possible to define the complex network of dipolar interactions that exists in biomacromolecules and hence the conformational properties in s

ISSN:0258-0322    

DOI:10.1002/masy.19900340105

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractUsing 26 NMR spectrometers, the Research Group on NMR, the Society of Polymer Science, Japan observed the1H NMR chemical shift, resolution, and signal intensity;13C NMR chemical shift, resolution, and signal intensity; the effect from initiator fragment signal;1H spin‐lattice relaxation times;13C spin‐lattice relaxation times; and13C nuclear Overhauser enhancement of radically polymerized poly(methyl methacrylate). Excellent reliability was found after comparison between the data from different spectrometers. Molecular motion of this polymer was analyzed with a term of 3τ m

ISSN:0258-0322    

DOI:10.1002/masy.19900340106

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSome applications of nuclear magnetic relaxation in the investigation of aqueous polyelectrolyte solutions are discussed. The main topics are solvent dynamics, counterion ‐ polymer interaction, main chain mobility and diffusio

ISSN:0258-0322    

DOI:10.1002/masy.19900340107

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractCarbon‐13 spin‐lattice relaxation time measurements have been performed at two experimental frequencies on a series of amorphous polymers in the bulk state at temperatures well above the glass‐transition temperatures and in solution. The high experimental values of the T1minimum as a function of temperature cannot be accounted for only by the specific orientation autocorrelation functions developed for polymers. They indicate the existence of an additional fast anisotropic motion, which we have assigned to librations of limited but significant extent of the internuclear CH vectors about their rest position. Moreover, in most cases, the temperature dependence of the segmental motions proves that they are involved in the glass‐rubber transition ph

ISSN:0258-0322    

DOI:10.1002/masy.19900340108

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractProton spin diffusion studies for characterizing minimum domain dimensions have been carried out on three blends: a 40/60 blend of nylon 6,6 with the aromatic rigid rod polymer poly(benzo[a,d]dithiazol‐2,6‐diyl‐1,4‐phenylene), PBZT, a 47/53 blend of an amorphous nylon with PBZT, and a 50/50 blend of a polyetherimide (PEI) and a polybenzimidazole (PBI). Polarization gradients necessary for these experiments were generated using both chemical shift differences (via multiple pulse techniques) and linewidth differences. Polarization readout techniques included proton lineshape deconvolution, multiple pulse proton lineshapes and13C CPMAS spectra utilizing short CP times. The two nylon/PBZT blends are expected to phase separate from thermodynamic arguments; however, kinetic considerations, more than thermodynamics, determine domain size. In the 40/60 blend, the minimum domain dimensions of each of the nylon and the PBZT phases were about 4 nm with some scattered larger crystals of nylon. In the 47/53 blend, mixing in some regions indicated domain dimensions similar to the 40/60 blend. In contrast to the 40/60 blend, however, the 47/53 blend was still far from internal spin polarization equilibrium after spin diffusion times of 140 ms. The implication is that the sample‐average composition is not found over dimensions like 40 nm; the problem is that the possible morphological explanations are manifold. By investigating the proton rotating frame relaxation, T1p, the possibility that some of the PBZT domains are isolated from the nylon, in a spin diffusion sense, was eliminated. It is more likely that about half of the nylon protons are isolated by spin diffusion from the PBZT protons on a 140 ms timescale. The PEI/PBI blend is a compatible blend of two aromatic polymers where mixing on a molecular scale is expected. We were interested in a measurement of the lower limit of domain size using proton spin diffusion. This lower limit turned out to be about 2.5 nm based on low temperature T1pmeasurements as opposed to room temperature multiple pulse methods. The latter measurements monitored the disappearance of a polarization gradient between the PEI methyl protons and all the remaining protons. The superiority of the T1pmeasurements over the multiple pulse method for establishing the smaller minimum domain dimension is not a general result and reasons are discussed. Finally, some general remarks about characterizing polymer blends by solid state NMR, particularly blends which have undergone spinodal phase separation, are

ISSN:0258-0322    

DOI:10.1002/masy.19900340109

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe1H NMR laboratory‐ and rotating‐frame (LF,RF) spin‐lattice relaxation (SLR) behaviour in solid polyethylenes is reviewed in light of the two region spin diffusion coupled model. Highly crystalline high‐density materials show single T1values indicative of the fast diffusion limit whilst RFSLR is close to the slow diffusion limit, allowing direct determination of the dimensions of the crystalline and disordered regions. The LFSLR and RFSLR of the HDPE's suggest the existence of an interfacial material which the SLR behaviour includes as part of the crystalline region in contrast to XRD and DSC.13C CPMAS measurements of1H RFSLR in a LLDPE provide an additional insight into this problem. The1H RFSLR is best represented by a superposition of two exponentials, measured by either1H or13C NMR. The1H RFSLR, measured at different chemical shifts in the13C NMR spectrum, provides direct evidence of the interfacial material. The possible use of spin‐locking at angles other than 90° in the rotating frame to scale the spin diffusion rates is reviewed and its possible utility for LLDPE material

ISSN:0258-0322    

DOI:10.1002/masy.19900340110

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe phase behavior of poly(dialkylsiloxane)s which are symmetrically substituted with ethyl,n‐propyl, andn‐butyl side groups has been investigated by solid state NMR and differential scanning calorimetry. All polymers exhibit disordering transitions before isotropization. The observation of conformational and motional changes is correlated to the different thermal transitions. Diffusive rotation of the chain segments around the molecule long axis is indicated by29Si‐NMR below the isotropization transition. The remarkably fluid character is explained in part by the coexistence of anisotropic and isotropic motional states of the ‐OSiEt2‐ segments. Molecular motion below the upper disordering transition is restricted but still fast with respect to the29Si‐NMR time scale. Long range reorganization processes have to be considered to explain the difference between α2‐PDES and β2‐PDES. The stepwise disordering at the onset of different motional processes, which results in the formation of a columnar liquid crystalline phase of these highly flexible chain molecules, is discussed with respect to the amphiphilic constitution of the molecules having an inorganic backbone substituted by or

ISSN:0258-0322    

DOI:10.1002/masy.19900340111

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY