Computer systems for laboratory networks and high-performance NMR

Modern computer technology is significantly enhancing the associated tasks of spectroscopic data acquisition and data reduction and analysis. Distributed data processing techniques, particularly laboratory computer networking, are rapidly changing the scientist's ability to optimize results from complex experiments. Optimization of nuclear magnetic resonance spectroscopy (NMR) and magnetic resonance imaging (MRI) experimental results requires use of powerful, large-memory (virtual memory preferred) computers with integrated (and supported) high-speed links to magnetic resonance instrumentation. Laboratory architectures with larger computers, in order to extend data reduction capabilities, have facilitated the transition to NMR laboratory computer networking. Examples of a polymer microstructure analysis and in vivo 31P metabolic analysis are given. This paper also discusses laboratory data processing trends anticipated over the next 5-10 years. Full networking of NMR laboratories is just now becoming a reality.     

(13)C NMR spectral assignment of 1,4-diarylpiperazinones

The piperazinone derivatives have potential application in the pharmaceutical, polymer and textile fields. The present work describes the preparation of a series of new 1,4-diarylsubstituted-2-piperazinones by condensation of substituted N,N'-bis-(2-hydroxyphenyl)-ethylenediamines with glyoxal and the complete (13)C NMR spectral assignment accomplished using APT, HMQC and HMBC techniques. Substituent chemical-shift effects (SCS) were calculated, which showed different values for the lactam- and amine-substituted aromatic rings. The results show that predictions based on SCS effects are not simple for these molecules due to electronic and steric effects. Moreover, in the case of the ortho-substituted derivative 2 g, the NMR spectra reveal a dynamic behavior related to restricted rotation of the phenyl groups (atropisomerism).     

Solid state NMR of a polymer composite and of a polymer blend

Although nuclear magnetic resonance may not seem the technique of choice to study interfaces between components in a polymer composite or polymer blend because of its inherent low sensitivity, for certain systems solid state NMR techniques can emphasize the signals from these interfaces. In case of a composite material with an inorganic filler (particles, fibers) cross-polarization or dipolar dephasing techniques from protons in the organic matrix or in the interphase to nuclei in the filler can be used to selectively observe the nuclei in the surface of the filler. Any changes at the filler surface caused by the presence of the matrix or coupling agent can then be detected. An example of glass reinforced nylon modelcomposites is discussed. The same techniques can also be used to study interphases in polymer blends when one of the components contains a NMR nucleus that is not present in the other component. As an example the blend poly(vinylidene fluoride)-poly(methyl methacrylate) is studied and it is shown that such techniques can provide very detailed information about the miscibility at a molecular scale.     

Suzuki–Miyaura Cross‐Coupling Reaction of Naphthyl Triflate with Indole Boronic Acids Catalyzed by a Recyclable Polymer‐Supported N‐Heterocyclic Carbene–Palladium Complex Catalyst: Synthesis of Naphthalene‐Linked Bis‐Heterocycles

In this study, the Suzuki–Miyaura cross‐coupling reaction of naphthyl triflate with indole boronic acids catalyzed by a recyclable polymer‐supported Pd–NHC complex catalyst is presented. The polymer‐supported catalyst can be reused several times retaining high activity for the transformation. The structures of all the synthesized compounds were established by elemental analysis and from their mass, ¹H‐NMR, and ¹³C‐NMR spectra.     

NMR spectroscopy and free volume analysis of the effects of copolymer composition on the swelling kinetics and chain dynamics of highly crosslinked copolymers of acrylic acid with PEG‐containing multiacrylates

Novel ionizable polymer networks were prepared from oligo(ethylene glycol) (OEG) multiacrylates and acrylic acid (AA), employing bulk radical photopolymerization techniques. The properties of these materials exhibited a complex dependence on the network structure and composition. Penetrant sorption experiments demonstrated that the crosslinked structure of the copolymers depended very strongly on the AA content as well as the number of ethylene glycol groups. The impact of varying the AA content and the oligo(ethylene glycol) chain length on the polymer chain dynamics was examined using diffusion and ¹³C NMR relaxation studies. The penetrant uptake studies indicated a coupling of Fickian and relaxation‐driven contributions to the swelling behavior. The effect of increasing the AA content on the characteristic chain relaxation time was reversed as the oligo(ethylene glycol) chain length was varied, indicating that chain relaxation is controlled by structural considerations, for shorter oligo(ethylene glycol) chains, and by compositional considerations, for longer oligo(ethylene glycol) chains. Measured compositional effects on solid state ¹³C NMR relaxation times supported these conclusions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1953–1968, 1999     

Precise Molecular Weight Determination and Structure Characterization of End-functionalized Polymers: An NMR Approach via Combination of One-dimensional and Two-dimensional Techniques

We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS).The peaks in 1H-NMR spectra corresponding to main-chain,side-chain and chain-end groups are assigned by 1H-1H gCOSY,1H-13C gHSQC and gHMBC spectra.For the first time,the spin-lattice relaxation time (T1) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW).As a result,a much higher delay time (d1) for chain-ends (d1 ＞ 20T1) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS,which is in accordance with the value estimated by GPC.An improved method for the polymer MW determination is established,by combination of different NMR techniques to distinguish the peaks,and a large dl setting to achieve quantitative NMR analysis.     

Dynamics of polypropene and propene-ethylene copolymers at temperatures above ambient

Several applications of solid-state nuclear magnetic resonance (NMR) spectroscopy to studying polyolefin mobility at temperatures ranging from room temperature to above the polymer melt are described. 13_C NMR can be used with magic-angle spinning and high-power proton decoupling to determine the fraction of mobile polymer in polypropene and to characterize the nature of the polymer chain motions as a function of sample temperature. Similar techniques can be used to characterize the local motions of complex copolymer systems such as heterophasic ethylene-propene copolymers. The practicality of low-speed magic angle spinning to observe quantitative high-resolution NMR spectra of neat, molten polymer samples is also described.     

NMR and x-ray studies on the morphology of thermoreversible polyacrylonitrile gels

The morphology of thermoreversible polyacrylonitrile–propylene carbonate (PAN-PC) gels was examined using solid-state carbon-13 nuclear magnetic resonance (NMR) spectroscopy and x-ray diffraction. Following complete dissolution of the polymer at elevated temperature and cooling of the concentrated PAN-PC solutions, a gel was formed. The PAN-PC gels consisted of regions of mobile polymer chains, rich in PC, “cross-linked” by regions of rigid polymer. The mobile regions of the gels showed solution-type NMR spectra with resolution of tacticity effects. The rigid component detected by NMR would correspond to the crysttallites detected previously by x-ray diffraction. Wide-angle x-ray diffractograms of the gels showed different peaks when compared with the dry polymer powder. After solvent extraction and drying of the gel, the diffractogram reverted to that of the original dry powder. This new result is the strongest evidence to support the view advanced earlier that the new peaks found in the diffraction pattern of the wet gels arises from solvated polymer crystallites rather than from ordinary polymer crystallites. © 1993 John Wiley & Sons, Inc.     

Polymer‐supported half‐titanocene catalysts for the syndiospecific polymerization of styrene

Monocyclopendienyltitanium trichloride (CpTiCl₃) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n‐butanone and characterized by carbon nuclear magnetic resonance (¹³C NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n‐butanone‐insoluble part and high melting temperatures, but ¹³C NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. ¹³C NMR analysis showed that the polymerization mechanism of the supported active sites was an active‐site controlled mechanism instead of a chain‐end controlled mechanism of the unsupported active sites. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 127–135, 2000     

Synthesis and properties of novel aliphatic polycarbonate from carbon dioxide with 1,2-butylene oxide and ε-caprolactone

A new degradable aliphatic poly(butylene-co-e-caprolactone carbonate) (PBCL) was synthesized through the terpolymerization of carbon dioxide, 1,2-butylene oxide (BO) and e-caprolactone (CL), a polymer supported bimetallic complex (PBM) was used as a catalyst. The terpolymers prepared were characterized by FT-IR,1H NMR, 13C NMR, WXRD and DSC. The hydrolysis tests were carried out to appraise the degradability of the copolymers.     

Colour formation in poly(ethylene terephthalate) during melt processing

The discolouration, that occurs in virgin poly(ethylene terephthalate) - PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (¹H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.     

硅取代聚烷硅的合成与表征

硅取代聚烷硅的合成与表征;聚甲基硅烷;高分子反应     

Surfactant/Nonionic polymer interaction. A NMR diffusometry and NMR electrophoretic investigation

The interaction between the nonionic polymer poly(ethylene oxide) (PEO) of molecular weight 20,000 and surfactants of various types [sodium dodecyl sulfate (SDS), dodecyl trimethylammonium bromide, octyl beta-D-glucoside, and potassium laurate] has been investigated in an aqueous solution at 25 degrees C by 1H NMR pulsed-gradient spin-echo self-diffusion techniques. The SDS/PEO study was further complemented by component-resolved 1H NMR-based studies of the electrophoretic mobility of PEO and the alkyl part of SDS under the same measurement conditions. Through such combined studies, a much more complete picture of the binding and aggregation processes becomes accessible.     

Interaction between poly(ethylene oxide) and sodium dodecyl sulfonate as studied by surface tension, conductivity, viscosity, electron spin resonance and nuclear magnetic resonance

The aggregation of sodium dodecyl sulfonate (AS) in aqueous solution containing various amounts of poly(ethylene oxide) (PEO) has been investigated by different experimental techniques. The experimental techniques include surface tension, conductivity, viscosity, electron spin resonance (ESR) and nuclear magnetic resonance (NMR). The critical aggregate concentration of AS on polymer strands as well as the concentration where the polymer becomes saturated with surfactant has been determined. Both ESR and NMR results indicate that the AS–PEO complex forms a more “open” structure and that PEO may penetrate into the interior of the micelles. Received: 22 October 1998 Accepted in revised form: 1 April 1999     

Mechanistic study of enzyme catalyzed polymerization of 8-hydroxyquinoline-5-sulfonate using nuclear magnetic resonance spectroscopy

Horseradish peroxidase catalyzed polymerization of 8-hydroxyquinoline-5-sulfonate (HQS) has been studied by in-situ NMR spectroscopy. The 2, 4 and 7 positions of the HQS are involved in oxidative free radical coupling with other HQS molecules with the order of reactivity being 7 ≥ 2 > 4. A mechanism for the oxidative free radical coupling and structure of the resulting polymer is proposed, which is supported by ¹³C NMR spectroscopy.     

NMR elucidation of novel SQ109 derivatives

The NMR elucidation of five novel SQ109 analogues including SQ109 is reported herein. These derivatives were synthesized as potential anti-tuberculosis candidates. One-dimensional NMR (¹H and ¹³C) techniques show a series of overlapping signals from the methine and methylene groups of these compounds, thereby making it extremely difficult to assign all NMR signals. Two-dimensional (2D) NMR techniques were instrumental in overcoming these challenges. This paper appears to be a rare report on the complete structure elucidation of mono-substituted adamantane moieties.     

Novel Cellulose Ethers: Synthesis and Structure Characterization of 3-Mono-O-(3′-hydroxypropyl) Cellulose

Summary: The synthesis of 3-mono-O-(3′-hydroxypropyl) cellulose via 3-mono-O-allyl-2,6-di-O-thexyldimethylsilyl cellulose was studied. Conversion of the double bond with 9-borabicyclo[3.3.1]nonane and subsequent alkaline oxidation lead to the 3′-hydroxypropyl group. Finally, the treatment with tetrabutylammonium fluoride trihydrate yields the complete cleavage of the protecting groups. The structure of the polymer was confirmed by one- and two dimensional NMR spectroscopic techniques. 3-mono-O-(3′-hydroxypropyl) cellulose is soluble in water and aprotic-dipolar organic media.     

NMR Studies of polymeric materials - an overview

NMR has been used extensively in studies of synthetic polymers. The approaches employed may require solution NMR, solid state NMR, or NMR imaging. In each case, different techniques and analytical methodologies have been devised to facilitate experimentation or to maximize information output. These techniques are not mutually exclusive and often provide complementary information. A selective review is made herewith of polymer/NMR studies, with emphasis on the contributions made at NMR symposia held in Detroit in October, 1993 as part of the 20th FACSS meeting.     

Efficient synthesis of piperidine derivatives using dendrimer based catalytical pockets

The synthesis of highly functionalized piperidine derivatives using amine functionalized maltitol-cored dendritic polymer (MAL-G0) in acetonitrile as the reaction medium is reported. A variety of piperidine derivatives were synthesized and the reaction gave an excellent yield of 89%–95%. The highly functionalized nature of the catalyst provided large number of active sites which resulted in good yield within a short period of time. Maltitol is a carbohydrate polyol system which was chosen here as the core for the synthesis of the dendritic catalyst; it was an effective approach for the preparation of piperidine like medicinal compounds. Maltitol-cored dendritic polymer was effectively synthesized and characterized using GPC, TG, UV–Visible, IR, and NMR techniques and also all the synthesized piperidine derivatives were characterized using LCMS, IR, and NMR techniques.     

Quality control of solid-phase synthesis: C PST/MAS NMR analysis on non-destructed SynPhase lantern

Pulse saturation transfer (PST)/MAS was highly effective for enhancing a magic angle spinning (MAS) ¹³C NMR of the inter-mobile region of polymer supported organic compounds. Direct monitoring of solid-phase synthesis on non-destructed SynPhase lantern was demonstrated using a 7 mm probe on the ¹³C PST/MAS NMR study.