Precise molecular weight determination and structure characterization of end-functionalized polymers: An NMR approach <Emphasis Type="Italic">via</Emphasis> 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 (T ₁) 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 > 20T ₁) 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 d1 setting to achieve quantitative NMR analysis.     

Effects of protonation and co-anion on the 1H and 13C chemical shifts of 2r,6c- diphenylpiperidin-4-ones: evidence for the formation of ion pair

(1)H and (13)C NMR spectra have been recorded for 2r,6c-diphenylpiperidin-4-one (1a), 3t-alkyl-2r,6c-diphenylpiperidin-4-ones 1b-d, 3t-alkyl-2r,6c-diphenyl-4-oxopiperidinium nitrates 2b and 2d, 3t-alkyl-2r,6c-diphenylpiperidin-4-one hydrochlorides 3a-c and 3t-methyl-2r,6c-diphenyl-4-oxopiperidinium picrate 4b in DMSO-d(6). For 1b, 2b and 3b, (1)H and (13)C NMR spectra have been recorded in CH(3)OD also. For 1b, 1d, 2b, 2d, 3b and 4b, 2D spectra have also been recorded. In DMSO-d(6) the protons of the piperidine ring and the ortho protons of the phenyl groups are markedly deshielded due to protonation. Protonation shields all the carbons of the piperidine ring and the ipso carbons of the phenyl groups markedly but deshields the other aromatic carbons slightly. The deshieldings on H-3a, H-5a and the ortho protons of the phenyl groups are less in the nitrate and picrate than in the corresponding hydrochloride. The effects on (13)C chemical shifts are not influenced by the co-anion. These observations suggest that the nitrates and pictrate exist as ion pairs in DMSO-d(6) and the nitrate and picrate ions shield, H-3a, H-5a and the ortho protons by magnetic anistropic effect. In CH(3)OD for 2b and 3b in addition to the ion-pair containing free ions two ion-pairs containing solvated ions are also present. The effects of protonation in the ion pairs containing the solvated ions are significantly different from those in the ion-pair containing free ions.     

2D NMR Investigation of Dynamic Equilibrium of Tautomers of Gossypol

Gossypol was obtained as an yellow platelike crystal with m.p. 210-214 . In CDCl3 there were three tautomers of gossypol: Ⅰ aldehyde, Ⅱ lactol, Ⅲ ketal, in equilibrium .Their total 1H NMR spectra were assigned by means of 1D and 2D NMR techniques including 1H-1H cosy ,DEPT, HMQC (1H Detected Heteronuclear Multiple Quantum Coherence) and HMBC (1H Detected Heteronuclear Multiple Bond Connectivity) experiments.This paper first reported that we took use of the 2D NMR techniques to assign all of 1H NMR chemical shifts of each tautomer , through the assignments of each peaks we investigated the tautomerism of gossypol . We concluded that when gossypol ( Ⅰ ) was put into CDCl3 , it would tautomerized three tautomers, they stable existed and attained tautomeric equilibrium in a molar ratio of 6:2:1 according to peaks intensity ratios in CDCl3. The result listed in table 1.Table 1. The 1H spectroscopy chemical shifts (ppm) for gossypol (Ⅰ), (Ⅱ) and (Ⅲ)All spectra were recorded at room tempreture in CDCl3 using TMS as an internal standard reported in δ units,hydroxyl protons were identified by D2O exchange.     

Complete 1H and 13C assignments of 8-C-beta-D-[2-O-(E)-p-coumaroyl]glucopyranosyl-2-(2-hydroxy)propyl-7-methoxy-5-methylchromone

1H and 13C NMR spectra of 8-C-beta-D-[2-O-(E)-p-coumaroyl] glucopyranosyl-2-(2-hydroxy)propyl-7-methoxy-5-methylchromone were completely assigned by 2D NMR observations. Especially the 1H assignments of the glucosyl and hydroxyl protons were achieved by utilizing HMQC, HMBC, 1H-1H COSY and DEPT techniques together with a heavy water exchange 1H NMR experiment.     

变温核磁共振对壳聚糖/磷酸甘油盐温敏性水凝胶的初步研究

采用变温核磁共振技术对壳聚糖/磷酸甘油盐温敏性水凝胶体系的凝胶化过程进行跟踪研究. 实验结果表明, 壳聚糖中氢和磷酸甘油盐中磷的化学位移均随着温度的升高而变化, 其中壳聚糖中氢的化学位移向高场移动而磷酸甘油盐中磷的化学位移向低场移动. 在凝胶温度附近, 壳聚糖中H-2(D)的化学位移变化出现转折点, 表明其所处的化学环境发生了突变. 随着体系中磷酸甘油盐含量的增加或者pH值的增大, 壳聚糖中H-2(D)的化学位移愈加偏向高场, 体系的凝胶温度则越低. 由此, 我们提出如下壳聚糖/磷酸甘油盐温敏性水凝胶的凝胶机理: 随着温度的升高, 壳聚糖通过氨基正离子与磷酸甘油盐形成的静电吸引被破坏, 随之由于壳聚糖分子链间形成大量氢键而发生凝胶化.     

Chemical inequivalence behavior of the protons attached to the same carbon in ethylene-propylene copolymer（EPC）

Six ethylene-propylene copolymer samples with different structural parameters were analyzed by ^1H NMR,^13C NMR and ^1H-^13C COSY in this paper.With the aid of the ^1H-^13C COSY spectra of ethylene-propylene copolymer,the chemical inequivalence behavior of the protons attached to the same carbon in the ethylene-propylene copolymer could be observed. Four basic types of chemical bonds were divided,and two kinds of main conformations were proposed to explain this phenomenon. Based on the calculation of conformation distribution,it can be proved that the explanation of this phenomenon was reasonable.     

NMR Investigations of Inclusion Complexes between β-Cyclodextrin and Naphthalene/Anthraquinone Derivatives

A ¹H and ¹³C NMR study on the inclusion complex between β-cyclodextrin and naphthalene, 1,5-dichloronaphthalene and 9,10-anthraquinone was carried out in order to define the stoichiometry of the association and the possible conformations. The upfield variation of the chemical shifts from the protons locate inside the cavity (H-3, H-5) coupled with the downfield variation of the other protons which locate outer sphere of the β-CD (H-1, H-2, H-4 and H-6,6′) provided clear evidence of the inclusion phenomena. The NMR spectra revealed the formation of 1:1 inclusion complex in which aromatic ring of the guest is tightly held by the host cavity. The signal degeneration of ¹H & ¹³C NMR spectra still exist for naphthalene and 1,5-dichloronaphthalene upon complexation revealed a symmetrical conformation of the guest molecules in the cavity of β-cyclodextrin, respectively. However, in 9,10-anthraquinone, the signal degeneration of ¹H & ¹³C NMR spectra was removed upon complexation which revealed an unsymmetrical conformation of the guest molecule inside the cavity. According to theoretical calculations and NMR studies, the possible conformations of the inclusion complexes are given here.     

Complete assignments of 1H and 13C NMR data for ten phenylpiperazine derivatives

Ten phenylpiperazine derivatives were designed and synthesized. The first complete assignments of (1)H and (13)C NMR chemical shifts for these phenylpiperazine derivatives were achieved by means of 1D and 2D NMR techniques, including (1)H-(1)H COSY, HSQC and HMBC spectra.     

苯并咪唑萘酰亚胺类化合物的合成与结构确证

本文合成并分离提纯了1位和4位单取代的苯并咪唑萘酰亚胺(NBI)类化合物1~4,对化合物1的紫外-可见光谱、红外光谱、质谱、核磁共振谱(包括1H NMR、13C NMR、DEPT、1H-13C HSQC、1H-13C HMBC、1H-1HCOSY多种NMR技术)进行了详细解析,对其所有的1H和13C NMR信号进行了归属,并使用了GIAO和CSGT两种方法量化计算核磁位移,通过多种波谱学技术确证了化合物的结构。     

一种金属洗涤剂的NMR分析

由于精细化工行业的迅速发展,作为“工业味精”的表面活性剂,已广泛进入日化、轻工、纺织、建筑、石化、金属加工等生产领域,对其的分析也显得日益重要。表面活性剂的分析历来是比较困难的课题之一,而通过核磁共振(NMR)进行定性和定量的文献则更少[1]。本文利用NMR为多种表面活     

类蜘蛛丝聚合物结构及分子运动的固体核磁共振研究

运用固体核磁共振(NMR)技术研究了聚丙氨酸多肽片段(Ala)5与高分子齐聚物聚苯乙烯(PS, 分子量2000)及聚异戊二烯(PI, 分子量2210)共聚而成的类蜘蛛丝蛋白聚合物——聚苯乙烯-co-聚丙氨酸聚合物(PS-co-PAL)和聚异戊二烯-co-聚丙氨酸聚合物(PI-co-PAL)的结构及分子运动. 聚合物13C CP/MAS NMR(交叉极化/魔角旋转核磁共振)谱及其旋转坐标系中自旋-晶格弛豫时间(T1ρ(13C))的结果表明, 此两种聚合物中多肽片段(Ala)5具有相同的化学位移, 即相似的化学环境和二级结构, 并具有相近的T1ρ(13C), 即类似的聚集态结构. 聚合物的宏观力学性质明显不同: 常温下, PS-co-PAL呈硬颗粒状, PI-co-PAL呈橡胶状且易拉伸. 结果说明聚合物力学性质与高分子链段的性质密切相关. PI-co-PAL聚合物的PI链段, 其骨架—CH2CH—的T1ρ为(5.3±0.4) ms, 而PS-co-PAL聚合物的PS链段, 其骨架—CH2CH—的T1ρ为(47.0±5.5) ms, 说明二聚合物中PI链段较PS链段更为柔软. 另外, 基于密度泛函理论(DFT)的化学位移计算证明, 聚合物PS-co-PAL和PI-co-PAL中多肽片段(Ala)5的二面角均为(-131°, 142°), 说明它们以β-折叠构象存在.     

High-resolution solid-state 19F-NMR spectroscopy of the sorption and diffusion of fluorine-containing aromatic molecules in polymeric media

High-resolution ¹⁹F solid-state NMR spectroscopy was employed to study the sorption properties of hexafluorobenzene (HFB) and 3,5-bis (trifluoromethyl) aniline (TFMA) in polystyrene (PS) and butyl rubber (BR). The NMR spectra indicate that the penetrants undergo dual-mode sorption in the glassy polymer (PS), but are highly mobile in the rubbery polymer (BR). In addition, the NMR method was utilized in the experimental determination of diffusion coefficients for the HFB/PS, TFMA/PS, and HFB/BR systems through desorption studies. The diffusion results for the TFMA/PS case agree very well with those previously obtained via resonance nuclear reaction analysis. © 1993 John Wiley & Sons, Inc.     

Branched polyphenylenes and phenylene dendrimers: NMR and optical studies

Two branched polyphenylenes with 1,3,5-triphenylbenzene as branching centers were synthesized together with a family of phenylene cyclotrimers as model compounds. On the basis of the NMR analysis, specifically ¹H NMR, ¹³C NMR and 2D heteronuclear correlation experiments (HSQC and HMBC) of model compounds, the huge number of overlapping signals in the polymer spectra are attributed to aromatic protons and carbon atoms of the branched phenylene structure. The comparison with absorption spectra of linear model compounds clearly shows that the polymer optical properties depend on the length of the segments between the branching cores. This result strongly supports the proposed NMR assignment proving that the combination of the two techniques is a powerful tool for unveiling complex branched structures.     

SEC‐MR‐NMR: Online Coupling of Size Exclusion Chromatography and Medium Resolution NMR Spectroscopy

Online coupling of size exclusion chromatography together with medium resolution nuclear magnetic resonance (SEC‐MR‐NMR) might be one solution to the problem of chemically sensitive detection in liquid polymer chromatography. By use of a combination of SEC with a table‐top, specially designed 20 MHz NMR spectrometer, based on a permanent magnet, online ¹H NMR spectra of SEC fractions can be obtained. The integration of digital filters, mechanical shims and electronic shims led to substantially improved sensitivity and chemical selectivity compared to former TD (time domain) 20 MHz instruments. ¹H NMR spectra of PMMA and PS homopolymers as well as PS‐PMMA block copolymers were of sufficient quality to enable detection and de‐formulation of unknown polymer compounds. ¹H NMR spectra of acceptable resolution and S/N ratio were collected online during the chromatography. The SEC separation online with the NMR measurements performed well and resulted in the proof of principle of the SEC‐MR‐NMR combination.

     

Complete 1H and 13C NMR assignment of trans,trans-2,3-divinylfuran derivatives

1H and 13C NMR spectra of trans, trans-2,3-divinylfuran derivatives (1-4) in CDCl3 were fully assigned using one- and two-dimensional NMR techniques. The 1H NMR resonances of ethylenic protons in position 2 with regard to the corresponding protons in position 3 of the furan ring are discussed.     

1H and 13C NMR spectral study of some 3-aryl-5r-aryl-6t-carbethoxycyclohex-2-enones-a study of four-bond 1H-1H couplings

Nine 3-aryl-5r-aryl-6t-carbethoxycyclohex-2-enones 2a-2i have been synthesized. For all these compounds, (1)H and (13)C NMR spectra have been recorded. For two compounds, 2D spectra have been recorded. The spectral data suggest that these compounds adopt sofa conformation in solution with H-5, H-6 and H-4t occupying axial-like positions and H-4c occupying equatorial-like positions. In 3-phenyl-5r-(o-chlorophenyl)-6t-carbethoxycylohex-2-enone (2b), the o-chlorophenyl group is oriented such that the chlorine atom is in between H-4c and H-5. Allylic coupling of H-2 is observed only with H-4t. Evidence has been obtained for four-bond coupling between 1,3-diaxial and 1,3-axial-equatorial protons.     

NMR elucidation of a novel (S)-pentacyclo-undecane bis-(4-phenyloxazoline) ligand and related derivatives

The NMR elucidation of a novel ligand (S)-pentacyclo-undecane bis-(4-phenyloxazoline) and related pentacyclo-undecane (PCU) derivatives is reported. Two-dimensional NMR proved to be a powerful technique in overcoming the difficulties associated with the elucidation of these compounds when only one-dimensional NMR data is utilized. A chiral substituent was introduced to both 'arms' of the PCU skeleton to produce derivatives 1-3. These derivatives display C(1) symmetry with all thecage atoms being nonequivalent. Owing to overlapping of peaks in the (1)H spectra, identification of these diastereomeric protons was very difficult. The (13)C spectra gave rise to clear splitting of the nonequivalent carbons. This is unusual compared to similar PCU derivatives with chiral substituents as splitting of all the diastereomeric cage carbons has not yet been reported. Nuclear Overhauser enhancement spectroscopy (NOESY) correlations of derivatives 1-3 confirm the different conformations of the molecule in which the side 'arms' occupy different orientations with respect to cage moiety.     

NMR characterization of the host-guest inclusion complex between beta-cyclodextrin and doxepin

The interaction between doxepin, a member of the tricyclic antidepressant (TCA) class of drugs, with beta-cyclodextrin (beta-CD) was investigated using NMR. Several TCAs have been reported to form a complex with beta-CD having 1:1 stoichiometry. Previous results from UV-visible spectroscopy, fluorescence measurements, and molecular modeling indicated that for imipramine, desipramine, and amitriptyline, the TCA aliphatic tail is included in the cyclodextrin cavity with apparently no interaction of the tricyclic ring. An alternative view of the doxepin-beta-CD complex is presented in this work using analysis of complexation-induced chemical shifts (CICSs), the method of continuous variation (Job's analysis), and analysis of ROESY spectra. The Job's plot derived from the NMR spectral data confirms that the complex formed has 1:1 stoichiometry. The largest changes in the CICS data were observed for the aromatic protons of one of the doxepin rings, with much smaller chemical shift changes observed for the protons of the other aromatic ring and the doxepin tail. Perhaps the most significant evidence for inclusion of the doxepin tricyclic ring is the strong ROESY cross peaks between the doxepin aromatic resonances and the protons located inside the beta-CD cavity. Changes in the doxepin (1)H NMR spectrum and the behavior of ROESY exchange cross peaks suggest that inclusion complex formation decreases the rate of internal motions of doxepin.     

Quantitative 2D HSQC (Q-HSQC) via suppression of J-dependence of polarization transfer in NMR spectroscopy: application to wood lignin

A quantitative method to record (1)H-(13)C correlation NMR spectra (Q-HSQC) is presented. The suppression of (1)J(CH)-dependence is achieved by modulating the polarization transfer delays of HSQC. In addition, the effect of homonuclear couplings, as well as relaxation during the pulse sequence are discussed. We developed the Q-HSQC approach for the quantitative analysis of wood lignin, a complex polymer where it has been difficult to obtain reliable data on the relative amounts of different structural units. The current method is applicable to a variety of complex mixtures, where normal 1D (1)H- and (13)C-NMR methods fail.     

Differential protonation and dynamic structure of doxylamine succinate in solution using 1H and 13C NMR

A protonation and dynamic structural study of doxylamine succinate, a 1:1 salt of succinic acid with dimethyl-[2-(1-phenyl-1-pyridin-2-yl-ethoxy)ethyl]amine, in solution using one- and two-dimensional 1H and 13C NMR experiments at variable temperature and concentration is presented. The two acidic protons of the salt doxylamine succinate are in 'intermediate' exchange at room temperature, as evidenced by the appearance of a broad signal. This signal evolves into two distinct signals below about -30 degrees C. A two-dimensional 1H-1H double quantum filtered correlation experiment carried out at -55 degrees C shows protonation of one of the acidic protons to the dimethylamine nitrogen. A two-dimensional rotating frame 1H-1H NOE experiment at the same temperature reveals that the other proton remains with the succinate moiety. Comparison of the 1H and 13C chemical shifts and the 13C T1 relaxation times of the salt with those of the free base further substantiate the findings.