共查询到20条相似文献,搜索用时 15 毫秒
1.
A. M. Issam 《Research on Chemical Intermediates》2014,40(8):3033-3044
Non-biodegradable polyethylene terephthalate (PET) bottles have attracted increasing attention due to environmental concern in today’s world. In order to reduce the amount of solid wastes generated and the dependency on fossil resources, a new approach has been conducted to prepare Kevlar-49 from PET waste bottles. Terephthalic acid, the main raw material used for preparation of Kevlar, was regenerated from PET waste bottles via subjection to a saponification process, whereas p-phenylenediamine was prepared from PET waste bottles via the Hoffmann rearrangement method. Kevlar was synthesized from the reaction of terephthalic acid and p-phenylenediamine by polycondensation reaction. The structures of terephthalic acid, p-phenylenediamine and Kevlar were characterized by FT-IR, 1H NMR, 13C NMR, and elemental analysis (CHN). In this study, thermogravimetric analysis and differential scanning calorimetry, X-ray diffraction (XRD), as well as the mechanical properties (tensile strength, modulus, and percentage elongation at break) of the synthesized Kevlar-49, were compared with commercial Kevlar-49, prepared from the same raw materials, for better understanding of their properties. 相似文献
2.
A complete 1H and 13C NMR assignment of one of the latrunculins (B) was accomplished with the aid of 2D NMR COSY and CH shift-correlation experiments. The various H-H Coupling constants have been datermined and a conformation of the macrolide and the tetrahydropyran (THP) ring suggested on basis of the J-values and measured NOE's. The absolute configuration of latrunculin-A() was determined on the grounds of its earlier X-Ray analysis, and a chemical degradation to a known compound. Two novel latrunculins, -C() and -D(), were isolated from the Red Sea sponge and their structures elucidated. Starting with L-cysteine a synthon for the latrunculins has been synthesized. 相似文献
3.
《Magnetic resonance in chemistry : MRC》2002,40(12):786-788
The structure of a new bufadienolide glycoside, cinobufagin 3‐O‐β‐D ‐glucoside, was determined by extensive 1D and 2D NMR techniques (1H, 13C, DEPT, COSY, HSQC, g‐HMBC and NOESY). The complete assignments of the 13C and 1H spectral data were also carried out. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
The 13C NMR spectrum of S-peptide (Ribonuclease 19 residue N-terminal fragment) (pH 5.4, 32°C, 12 mM in D2O has been assigned with a basis on characteristic values for 13C signals of amino acids included in short peptides, SFOR multiplicities, 1JCH reduced values and spectral pH variations. The shift vs. temperature changes have been followed in the range 0°C–50°C and the corresponding curves analyzed by using the ΔH° and ΔS° values for the helix-coil transition obtained from 1H NMR spectra. Values for chemical shifts in the coil and in the helix have been obtained in this way. Transition shifts are largest for CO and Cα resonances in the fragment 3–13, confirming that isolated S-peptide folds in a manner closely ressembling the native structure. 相似文献
5.
A procedure of analysis for small-angle X-ray scattering (SAXS) data has been established to obtain density fluctuation of supercritical fluids near the critical point. It is indispensable for the certain analysis to utilize both of high-quality SAXS data measured under stable thermodynamic condition and accurate P–ρ–T data in supercritical region. As a standard example, SAXS measurements have been performed for supercritical CO2, which is a suitable sample satisfying the condition for both experiment and analysis. The measurements were carried out along four isothermal conditions at reduced temperature of Tr = T/Tc = 1.020, 1.022, 1.043 and 1.064. Comparing the experimental density fluctuation with calculated one from the most reliable equation of state, the differences are within 8% at most. 相似文献
6.
Mizuno T Nemoto T Tansho M Shimizu T Ishii H Takegoshi K 《Journal of the American Chemical Society》2006,128(30):9683-9686
(2)H NMR was examined as an approach to determine (1)H chemical shifts in solids. For high-resolution observation, the line width due to (2)H quadrupole interaction and chemical-shift anisotropy was removed by magic-angle spinning and that due to (1)H-(2)H dipolar interactions by (1)H decoupling. Further, we showed that the sensitivity can be enhanced by applying (1)H to (2)H cross polarization and by adding spinning-sideband spectra. These make it possible to obtain (2)H natural-abundance MAS spectra revealing highly resolved (2)H signals. The second-order quadrupole effects of (2)H are also examined. 相似文献
7.
Daniel J. Kenny Kenneth R. Worthington John B. Hoyes 《Journal of the American Society for Mass Spectrometry》2010,21(6):1061-1069
A new type of mass analyzer is described, which allows lowresolution axial ion ejection to be obtained from a traveling wave
based, stacked ring collision cell. Linking this ejection temporally with the scanning of the second quadrupole of a tandem
quadrupole mass spectrometer provides an improvement in sampling duty cycle, which results in significant signal intensity
improvements for scanning acquisitions such as product ion spectra. A near 100% storage efficiency is enabled by a split cell
design, which allows ion fragmentation and accumulation to be performed in one section of the collision cell whilst previously
accumulated ions are simultaneously ejected from the rear of the cell. These characteristics combine to give an m/z-dependent signal gain of 7–20X over a conventional scanning quadrupole for a 1000 Th scan. The ability to swap very rapidly
from a non-enhanced mode of operation to an enhanced mode whilst retaining the existing sensitivity, speed, and functionality
of a conventional tandem quadrupole mass spectrometer is also described. 相似文献
8.
A new approach to near-infrared spectral data analysis using independent component analysis 总被引:8,自引:0,他引:8
This paper presents a new approach to near-infrared spectral (NIR) data analysis that is based on independent component analysis (ICA). The main advantage of the new method is that it is able to separate the spectra of the constituent components from the spectra of their mixtures. The separation is a blind operation, since the constituent components of mixtures can be unknown. The ICA based method is therefore particularly useful in identifying the unknown components in a mixture as well as in estimating their concentrations. The approach is introduced by reference to case studies and compared to other techniques for NIR analysis including principal component regression (PCR), multiple linear regression (MLR), and partial least squares (PLS) as well as Fourier and wavelet transforms. 相似文献
9.
The phytochemical investigation of extracts from the branch wood and branch barks of Andira surinamensis yielded a novel isoflavone dimer, 4'-methoxyisoflavone-(7-O-7')-3',4'-methylenedioxyisoflavone (surinamensin), along with the triterpene lupeol and the known isoflavones 5,7-dihydroxy-4'-methoxyisoflavone (biochanin A), 5,4'-dihydroxy-7-methoxyisoflavone (prunetin), 7,3'-dihydroxy-4'-methoxyisoflavone (calycosin), and 5,7,3'-trihydroxy-4'-methoxyisoflavone (pratensein). The structure of the new isoflavone was elucidated by 1D and 2D homonuclear and heteronuclear NMR spectroscopy and by comparison with published data for closely related compounds. 相似文献
10.
A new chlorotryptamine alkaloid, N-chloromethyl-N,N-dimethyltryptamine, was isolated from a methanol extract of the Chinese shrub Acacia confusa Merr., together with its known hallucinogenic analogues, N-methyltryptamine, N,N-dimethyltryptamine and N,N-dimethyltryptamine-N-oxide. The new compound was an artefact of the isolation conditions. The complete (1)H and (13)C NMR assignments for these compounds were carried out using (1)H, (13)C, DEPT, gCOSY, gHSQC and gHMBC NMR experiments. 相似文献
11.
Wolfgang Vautz Bertram Bödeker Jörg Ingo Baumbach Sabine Bader Michael Westhoff Thorsten Perl 《International Journal for Ion Mobility Spectrometry》2009,12(2):47-57
Ion mobility spectrometry is increasingly in demand for medical applications and its potential for implementation in food
quality and safety or process control suggest rising use of instruments in this field as well. All those samples are commonly
extremely complex and mostly humid mixtures. Therefore, pre-separation techniques have to be applied. As ion mobility spectrometers
with gas-chromatographic pre-separation acquire a huge amount of data, effective data processing and automated evaluation
by comparison of detected peak pattern with data bases have to be utilised. This requires accurate on-line calibration of
the instruments to guarantee reproducible results, in particular with respect to identification of an analyte by determination
of its ion mobility and retention time. To reduce environmental and instrumental influence, the reduced ion mobility is used.
It is derived from the drift time normalised to electric field, length of the drift region and to temperature and pressure
of the drift gas (traditional method). All data required for this normalisation are afflicted with a particular error and
thus leading to a deviation of the calculated ion mobility value. Furthermore, this traditional method enables a calculation
of the reduced ion mobility only after the measurement. To avoid those errors and to enable on-line calibration of ion mobility,
an instrument specific factor is implemented generally representing all relevant variables. This factor can be determined
from an initial measurement of few spectra and can thereafter be applied on the following measurement. The application of
this approach obtained reproducible reduced ion mobility values for positive and negative ions over a broad drift time range
and for common variation of ambient conditions as well for varying instrument conditions such as electric fields respectively
drift times and in different drift gases. Moreover, the reduced ion mobility is available already during the measurements
with a significantly higher reliability and accuracy which was increased to a factor of 5 compared to the traditional ion
mobility determination and enables an on-line identification of analytes for the first time. 相似文献
12.
Pascal Palmas Coralie Nyffenegger Eric Pasquinet Gérald Guillaumet 《Magnetic resonance in chemistry : MRC》2009,47(9):752-756
Mesomeric heteropentalene betaines are conjugated fused polyheterocyclic structures that represent interesting intermediates for organic synthesis. Five such structures, containing at least four nitrogen atoms and various substituents, have been characterized by 1H, 13C and 15N NMR. We report, apparently for the first time, nitrogen NMR data and coupling information on such systems. Inter‐ring long‐range correlations across five bonds with 15N (5JHN) and up to seven bonds with 13C (6JHC and 7JHC) were observed in HSQC experiments. The incorporation of an electron‐withdrawing substituent such as NO2 was observed to cause an increase in the magnitude of the remote couplings and deshielding of nearby protons, carbons and on all nitrogen atoms of the structure, including remote ones situated on other cycles. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
13.
A new benzoxazolinone glucoside, 4-O-beta-D-glucopyranosyl-benzoxazolin-2(3H)-one, was isolated from Acanthus ilicifolius, a medicinal plant from south China. The complete (1)H and (13)C NMR assignments of the compound were carried out by using DEPT, HMBC, HMQC, NOESY and (1)H--(1)H COSY spectra. 相似文献
14.
Joakim Riikonen Jarno Salonen Vesa-Pekka Lehto 《Journal of Thermal Analysis and Calorimetry》2011,105(3):811-821
Thermoporometry is a relatively new method of characterising porous properties of nanostructured materials based on observation
of solid–liquid phase transitions of materials confined in pores. It provides several advantages over the conventional characterisation
methods, mercury porosimetry and gas sorption. The advantages include possibility of using short measurement times, non-toxic
chemicals and wet samples. In addition, complicated sample preparation and specialised instruments are not required. Therefore,
it has a great potential of becoming a widely utilised characterisation method, although its potential has not yet been widely
realised. In recent years, there has been a significant increase in research activities regarding the method. In the first
part of the review, we introduce thermoporometry and review related results of the confinement effects on materials and their
solid–liquid phase transition. 相似文献
15.
Thermoporometry is a relatively new method of characterising porous properties of nanostructured materials based on observation
of solid–liquid phase transitions of materials confined in pores. It provides several advantages over the conventional characterisation
methods, mercury porosimetry and gas sorption. The advantages include possibility of using short measurement times, non-toxic
chemicals and wet samples. In addition, complicated sample preparation and specialised instruments are not required. Therefore,
it has a great potential of becoming a widely utilised characterisation method, although its potential has not yet been widely
realised. In recent years, there has been a significant increase in research activities regarding the method. In the second
part of the review, results and conclusions of the recent studies about thermoporometry are surveyed and discussed focusing
on the application of thermoporometry in extracting various structural information from the porous materials. 相似文献
16.
A new approach has been developed for discriminating at the dropping mercury electrode (DME) between currents controlled by various types of rate processes, including diffusion and chemical kinetics of reactions coupled with electron transfer. The crux of time scanning pulse polarography (t.s.p.p.) is a combination of chronoamperometry with pulse polarography. Typically, pulses of 200 ms were used and applied instantaneously (i.e. with the aid of a potentiostat whose rise-time was 2 ms) at a time, t0 (on the order of 1 s) which corresponded to an appreciable fraction of the total drop time of the DME. Limiting currents, (i) were subsequently “sampled” on successive drops as function of a time-shift, 1<θ<200 ms. These current measurements were taken at times (t0+θ) using sampling “time-windows” of 5 ms or less. Diagnostic plots of log i versus long θ were obtained whose slopes were characteristic of the controlling rate process, viz, ? log i/? log θ=?0.47, for a diffusion controlled electrode reaction; ? log i/? log θ=zero, for an electrode process whose kinetics are controlled by a preceding first order chemical reaction. Similar diagnostic plots were found to characterize “catalytic current” sequences. The significance of t.s.p.p. is inherent in the feature that it is applicable to trace concentration levels (10μM or less) which are intractable by classical polarography. 相似文献
17.
《Magnetic resonance in chemistry : MRC》2003,41(8):633-635
A new diterpenoid, 12β,13α‐dihydroxytriptonide, was obtained from the transformed culture of triptonide by Catharanthus roseus cell suspension cultures. The complete 1H and 13C NMR assignments of the compound were carried out by using DEPT, COSY, HSQC, g‐HMBC and NOESY techniques. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
18.
Mutual Diffusion Driven NMR: a new approach for the analysis of mixtures by spatially resolved NMR spectroscopy
下载免费PDF全文
![点击此处可从《Magnetic resonance in chemistry : MRC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Christian F. Pantoja Jose A. Bolaños Andrés Bernal Julien Wist 《Magnetic resonance in chemistry : MRC》2017,55(6):519-524
We introduce a new approach for resolving the NMR spectra of mixtures that relies on the mutual diffusion of dissolved species when a concentration gradient is established within the NMR tube. This is achieved by cooling down a biphasic mixture of triethylamine and deuterated water below its mixing temperature, where a single phase is expected. Until equilibrium is reached, a gradient of concentration, from ‘pure’ triethylamine to ‘pure’ water, establishes within the tube. The amount of time required to reach this equilibrium is controlled by the mutual diffusion coefficient of both species. Moreover, a gradient of concentration exists for each additional compound dissolved in this system, related to the partition coefficient for that compound in the original biphasic state. Using slice selective experiments, it was possible to measure these concentration gradients and use them to separate signals from all the present species. We show the results acquired for a mixture composed of n‐octanol, methanol, acetonitrile and benzene and compare them with those obtained by pulse field gradient NMR. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
19.
Vieil E 《Physical chemistry chemical physics : PCCP》2007,9(29):3877-3896
The creation of a purely graphic language called Formal Graphs for modelling many physical and physico-chemical systems is described. It represents an improvement over traditional equivalent circuits used for modelling systems made of individual components and over bond graphs used mainly in physico-chemistry. In contradistinction with these graphs, which represent graphically only mounting equations and maintain algebraic equations for describing components behaviour, a formal graph is an oriented graph incorporating all the information contained in a usual algebraic model. Combination of paths considerably extends use to domains that were not accessible to quantitative graphs, such as relaxation processes, chemical reactivity or mass-transfer. Moreover, inclusion of space derivation allows representing graphically every physical law describing a process involving energy conservation or dissipation, such as particle diffusion. Physical meaning can be deduced from paths in a graph that can be followed by processes, as illustrated by the exponent of fractional derivation, which appears as bearing the information on the proportion of conserved versus dissipated energy. The numerous examples given in this introduction address several domains, electrodynamics, mechanics, thermodynamics, and physico-chemistry. They show common graph structures that reveal a striking unity of our classical formalism, bringing transversal insight and opening a new route towards unification. Differences also appear that are subjects of interrogation. 相似文献
20.
A new approach to NMR chemical shift additivity parameters using simultaneous linear equation method
Shahab YA Khalil RA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(2):265-270
A new approach to NMR chemical shift additivity parameters using simultaneous linear equation method has been introduced. Three general nitrogen-15 NMR chemical shift additivity parameters with physical significance for aliphatic amines in methanol and cyclohexane and their hydrochlorides in methanol have been derived. A characteristic feature of these additivity parameters is the individual equation can be applied to both open-chain and rigid systems. The factors that influence the (15)N chemical shift of these substances have been determined. A new method for evaluating conformational equilibria at nitrogen in these compounds using the derived additivity parameters has been developed. Conformational analyses of these substances have been worked out. In general, the results indicate that there are four factors affecting the (15)N chemical shift of aliphatic amines; paramagnetic term (p-character), lone pair-proton interactions, proton-proton interactions, symmetry of alkyl substituents and molecular association. 相似文献