Distortionless Enhancement Polarization Transfer Research Articles

A Cytotoxic Compound from n-Hexane Fraction of Lantana camara Linn Leaves

In this study, one triterpenoid compound from n-hexane fraction of Lantana camaraLinn leaves has cytotoxic activity was isolated. Isolation was carried out using gravity chromatographycolumnand purification by recrystallization method. Isolated compound was obtained white solid with melting point 252-253oC. The structure of isolated compound was elucidated using spectroscopic analysis Ultraviolet (UV), Infrared (IR), 1H-Nuclear Magnetic Resonance (1H-NMR), 13C-Nuclear Magnetic Resonance (13C-NMR) Heteronuclear Multiple Bond Connectivity (HMBC), Heteronuclear Multiple Quantum Correlation (HMQC), Distortionless Enhancement Polarization Transfer (DEPT) and comparative literature data, identified as Lantadene A (22β-angeloyloxy-3-oxoolean-12-en-28-oic-acid) with molecule formula C35H52O5. The Lantadene A compound was evaluated for cytotoxic activity against shrimp larvae Artemia SalinaLeach using Brine Shrimp Lethality Test(BSLT) method, showed strong cytotoxic activity with an LC50value of 48.97 µg/mL.

Scopoletin – an anti-hyperglycemic Coumarin from the fruit of <em>Averrhoa carambola</em> L. (Star fruit)

Purpose: Averrhoa carambola L. has a long history of its use in traditional medicine for the treatment of various diseases such as diabetes, intermittent fevers, intestinal worms, scabies and inflammatory conditions. The fresh fruit of A. carambola is very popular in Sri Lanka for its glucose-lowering effect and is taken as good remedy for diabetes. The present study was carried out to isolate and characterize anti-hyperglycemic principles of the fruit of A. carambola to obtain additional scientific evidence for its usage in traditional medicine in the management of diabetes. Methods: The dried and powdered fruits of A. carambola were successively extracted with n-hexane and CH2Cl2 using soxhlet apparatus. The CH2Cl2 extract was subjected to silica gel column chromatography, eluting in a stepwise gradient with hexane and ethyl acetate (EtOAc) mixtures. The fraction eluted with hexane:EtOAc (60:40) yielded a mixture which with preparative thin-layer chromatography afforded a pure compound designated as JW-AC-3. The structure of JW-AC-3 was elucidated on the basis of its Ultra- violet spectroscopy (UV), Infra-Red spectroscopy (IR), Mass Spectroscopy (MS), and Nuclear Magnetic Resonance spectroscopy (NMR) including Distortionless Enhancement Polarization Transfer (DEPT), Homonuclear Shift-Corrilation Spectroscopy (COSY), Nuclear Overhauser Spectroscopy (NOESY), Hetero Multiple Bond Connectivities (HMBC) and Heteronuclear Multiple-Quantum Coherence (HMQC) experiments and direct comparison with reported data. Results: JW-AC-3 was identified as scopoletin by direct comparison of its spectral data with reported data of scopoletin. To our knowledge, scopoletin has not been reported from A. carambola. Scopoletin has been shown to possess significant anti-hyperglycemic activity by previous workers. The results of this study clearly indicate that the majority of the anti-hyperglycemic activity of the fruits of A. carambola could be attributed to scopoletin. The results also provide for the use of scopoletin as a bio-marker in the standardization and quality control of products derived from the fruits of A. carambola . Conclusion: The results of this study demonstrate potential use of scopoletin in the development of drugs of natural origin in the treatment of diabetes. The results could also be used in the rationalization of ethnomedical use of the fruits of A. carambola .

Synthesis and Cation Recognition Study of Novel Benzo Crown Ether Functionalized Enamine Derivatives

A novel series of benzo crown ether (dibenzo 18-crown-6 ether, benzo 18-crown-6 ether, and benzo 15-crown-5 ether) functionalized enamines derivatives from amino benzo crown ether (4-amino dibenzo 18-crown-6 ether, 4-amino benzo 18-crown-6 ether, 4-amino benzo 15-crown-5 ether) and substituted 3-(dimethylamino)-1-phenylprop-2-en-1-one compounds have been synthesized. All the synthesized compounds were characterized by infrared, 1H NMR, 13C NMR, distortionless enhancement polarization transfer, and mass and elemental analysis techniques. The cation recognition property for benzo crown ether enamine 8a was studied by absorption and fluorescence spectroscopy.

Studies on 3-Diethyl-aminocarbonyl-1,4;5,6,7,8-hexahydroquinoline Derivatives and their Calcium Channel Antagonistic Activities in vitro

In this study, thirteen 2,6,6-trimethyl-3-carbamoyl-4-aryl-5-oxo-1,4,5,6,7,8-hexahydroquinoline derivatives were synthesized and screened for their calcium channel antagonistic actitivities. The hexahydroquinoline derivatives were synthesized according to Hantzsch reaction. The structures of the compounds were elucidated by IR, 1H-NMR, 13C-NMR, Distortionless Enhancement Polarization Transfer (DEPT), Correlation Spectroscopy (COSY), mass spectroscopy and elemental analyses. The calcium antagonistic activities of the compounds were determined by tests performed on isolated rat ileum and lamb carotid artery. In isolated rat ileum, compounds 8, 12 and 13 were found to be more active than nicardipine (CAS 55985-32-5) at a concentration of 10(-5) mol/L. At the concentration 10(-4) mol/L, compounds 7 and 12 were more active than nicardipine and compounds 5, 8 and 13 were equipotent. In lamb carotid artery studies, at the concentration 10(-5) mol/L all compounds were found to be less active than nicardipine; at the concentration 10(-4) mol/L compounds 5 and 13 showed greater inhibition than nicardipine. At this concentration, compound 9 was found to be as active as nicardipine.

Characterizing Biomass Fast Pyrolysis Oils by 13C NMR and Chemometric Analysis

Several biomass fast pyrolysis oils were characterized by 13C and DEPT (distortionless enhancement polarization transfer) NMR analysis to determine their chemical functional group compositions as related to their energy content. Pyrolysis oils were produced from a variety of feedstocks, including energy crops, woods, animal wastes, and oil seed presscakes, and were also compared with fossil fuels (gasoline and diesel). The 13C and DEPT NMR spectra of the biofuels and the two fossil fuel samples were measured, and each spectrum was divided into distinct regions according to the chemical shift ranges appropriate for various functional groups. The spectral intensities of each region were then quantified, and the carbon proton substitution numbers were determined. This approach provided helpful information on the chemical compositions of the oils, but it was found to oversimplify the information contained in the 13C NMR spectra, resulting in a substantial loss of important details. Hence, a chemometric method...

Preparation and antibacterial activity of Schiff bases from O-carboxymethyl chitosan and para-substituted benzaldehydes

Seven Schiff bases were synthesized from O-carboxymethyl chitosan (CMC) and para-substituted benzaldehydes. The Schiff bases were characterized through Fourier Transform Infrared Spectroscopy, Carbon-13 Nuclear Magnetic Resonance (13C NMR), Distortionless Enhancement of Polarization Transfer (DEPT) 135 NMR, elemental analysis, and acid–base titration. Antibacterial activities of the Schiff bases against Escherichia coli (E. coli, ATCC 35218) and Staphylococcus aureus (S. aureus, ATCC 25923) were measured through the optical density method. Antibacterial activity of the Schiff bases differs from the substituent at the para position of benzaldehyde, and decreases as the sequence OCH3 > CH3 > H > F > Cl > Br > NO2. The IC50 of the Schiff base from 4-methoxylbenzylaldehyde against E. coli and S. aureus is 30 and 34 ppm, respectively, much lower than that of chitosan (53, 48 ppm) and CMC (58, 60 ppm).

Initiated Chemical Vapor Deposition of Alternating Copolymers of Styrene and Maleic Anhydride

Initiated chemical vapor deposition (iCVD) of alternating copolymer thin films has been achieved for the first time. Copolymerization is desirable for maleic anhydride (Ma) since this monomer does not homopolymerize to an appreciable extent. At conditions where the observed deposition rates for styrene (S) and Ma homopolymers were only 0 and 5.5 nm/min, respectively, combining the two monomers resulted in a much higher deposition rate of 75.4 nm/min. iCVD processes utilize low energy (<30 W) to generate peroxy radicals from initiator molecules while avoiding degradation of functional groups in the monomers. Indeed, full retention of the anhydride functionality from the Ma monomer and avoidance of undesirable side reactions was observed in iCVD of poly(styrene-alt-maleic anhydride) (PSMa) copolymer films. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and 13C nuclear magnetic resonance (NMR) conclusively demonstrate that all of the copolymer films contain 50% styrene and 50% Ma (within experimental error), irrespective of gas feed ratios employed during the deposition. The 13C NMR signal in the 136-140 ppm region from the quaternary carbon in styrene and additional distortionless enhancement polarization transfer experiments confirmed that the copolymers are strictly alternating. Varying the gas feed ratio of Ma to styrene provided control over deposition rates and number-average molecular weights. Number-average molecular weights varied from 1380 to 4680 g/mol, and deposition rates varied from 6.3 to 75.4 nm/min.

High-Temperature Homopolymerization of Ethyl Acrylate and n-Butyl Acrylate: Polymer Characterization

This paper presents a thorough molecular characterization of ethyl acrylate (EA) and n-butyl acrylate (nBA) homopolymers made at high temperature (140−180 °C) to high conversions (50−90%) in xylene isomers without the use of added thermal initiator. Electrospray ionization/Fourier transform mass spectrometry (ESI/FTMS) analysis shows four dominant chain types formed during high-temperature polymerization. Chains initiated by β-scission radicals and by xylol radicals that grow and eventually terminate to form terminally saturated and unsaturated chains. These chain structures suggest the underlying secondary mechanisms in high-temperature acrylate polymerization include β-scission (disproportionation) of the carbon-centered tertiary radical that is most likely formed via intramolecular chain transfer. Additionally, chain transfer to solvent, xylene in this case, also plays an important mechanistic role. Results from 1D NMR using 13C, 1H, and distortionless enhancement polarization transfer (DEPT) corroborate the ESI/FTMS results and additionally predict (i) 2 branch points per chain on average for EA homopolymer with a number-average molecular weight of 4000 and (ii) 1.25 branch points per chain on average for nBA homopolymer with a number-average molecular weight of 3300. The presence of branch points indicates propagation of the midchain tertiary radical does occur to significant extent under the conditions of the experiments. Neither the ESI/FTMS nor NMR results suggest a mechanistic route by which the acrylates initiate polymerization without added thermal initiator.

Polyimides. IV. Synthesis and characterization of fluorinated copolyimides

AbstractA series of new copolyimides were synthesized by the reaction of pyrometallic dianhydride, benzophenone tetracarboxylic acid dianhydride, and 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane (6FDA) with two diamines, 4,4″‐bis(aminophenoxy)‐3,3″‐trifluoromethyl terphenyl and 4,4′‐diaminodiphenyl ether, at a 50:50 ratio by a thermal imidization route. The complete spectral assignment of the copolymer derived from 6FDA was done with the help of distortionless enhancement of polarization transfer 90° and two‐dimensional heteronuclear (C, H) shift correlation spectroscopy. The various types of couplings in the copolymers were assigned with the help of two‐dimensional correlated spectroscopy (COSY) homonuclear correlation spectroscopy. A long‐range connectivity was also observed by a heteronuclear correlation spectroscopy via long‐range coupling experiment. The copolyimides derived from 6FDA were soluble in common organic solvents such as N,N‐dimethyl formamide, N,N‐dimethyl acetamide, dimethyl sulfoxide, N‐methyl pyrrolidone, and chloroform. Water absorption values, after the samples were boiled in water for 72 h, were in the range 0.3–0.7%. These polyimides had low dielectric constants of 2.79–3.01 at 1 MHz, low refractive indices of 1.655–1.705 at 589.3 nm, and high optical transparencies (&gt;90%). The onset temperature for 5% weight loss for these polyimides, as assessed by thermogravimetric analysis, was up to 551°C in air, indicating a very high thermal stability, and the polyimides showed glass‐transition temperatures as high as 316°C. Transparent thin films of these polyimides exhibited tensile strengths up to 93 MPa, moduli of elasticity up to 3.1 GPa, and elongations at break up to 24% depending on the exact repeat unit structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 235–246, 2004

1H‐ and 13C‐NMR analyses of aqueous polyamideamine–epichlorohydrin resin solutions

AbstractMore accurate signal assignment for 1H‐ and 13C‐NMR spectra of aqueous solutions of polyamideamine‐epichlorohydrin (PAE) resin and its related compounds was achieved by using distortionless enhancement of polarization transfer (DEPT) and C‐H correlation spectroscopy (COSY) methods. On the basis of the assignment, we developed new methods to determine the content of four‐membered azetidinium ring (AZR) and number‐average degree of polymerization (DPn) of the repeating unit of PAE by using NMR. Degree of introduction of epichlorohydrin into polyamideamine chains at the initial stage was 75–80%, and the resultant AZR content per one repeating unit in the PAE sample prepared in this study was about 72%. DPn of the initial polyamideamine was 32, and this value decreased to about 18 during the PAE preparation process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1847–1854, 2004

Copolymerization of Ethylene and 1,7-Octadiene, 1,9-Decadiene with Zirconocene Catalysts

Copolymerizations of ethylene and 1,7-octadiene (OD) and 1,9-decadiene (DD) were investigated with various non-bridged and bridged zirconocene catalysts using methylisobutylaluminoxane as a cocatalyst. The resulting copolymers were extracted with boiling o-dichlorobenzene (ODCB), and the structure of the boiling ODCD-soluble part was studied by 1 H, 13 C NMR and DEPT (distortionless enhancement of polarization transfer) spectroscopy. In the case of ethylene/OD copolymerization, the ligand structure of the zirconocene catalysts strongly affected the propagation mode of OD. The zirconocene catalysts having cyclopentadienyl or pentamethylcyclopentadienyl ligands gave copolymers having 1-hexenyl and 1,3-disubstituted cycloheptane units, derived from 1,2-addition propagation and addition-cyclization propagatin of OD, respectively. On the other hand, the zirconocene catalysts with indenyl ligand produced the copolymers having exclusively 1,3-disubstituted cyclo-heptane units. Furthermore, the copolymer prepared by diphenylmethylene(cyclopentadienyl)(0-fluorenyl)zirconuim dichloride was crosslinked. The diastereostructure of the 1,3-disubstituted cycloheptane units in the copolymers was not influenced by the stereospecificity of the catalysts used, and a cis-structure was preferentially formed. In the case of the copolymerization of ethylene and DD, the C 2v -symmetric zirconocene catalysts produced the copolymers with 1-octenyl branches derived from 1,2-addition propagation of DD. Other C 2 - and C s -symmetric zirconocene catalysts with bulky ligands yielded copolymers with cross-linking structures derived form addition propagation of side-chain unsaturated bond of 1,2-added DD units.

Structure of cyclopentene unit in the copolymer with propylene obtained by stereospecific zirconocene catalysts

Copolymerization of propylene and cyclopentene (CPE) was carried out using as a catalyst isospecific rac-ethylenebis(indenyl)zirconium dichloride (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (2), rac-dimethylsilylenebis(2-methylindenyl)zirconium dichloride (3), or syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (4) with methylaluminoxane as a cocatalyst. Isospecific zirconocene catalysts 1–3 produced copolymers having narrow molecular weight distribution, while syndiospecific catalyst 4 effected propylene homopolymerization. Microstructures of the copolymers were studied by 13C NMR and distortionless enhancement of polarization transfer (DEPT) spectroscopy. CPE was found to be incorporated in the copolymer preferentially via 1,2-insertion mechanism in the copolymerization with the catalyst 3. The catalyst 1 and 2 gave copolymers containing CPE units formed by either 1,2-insertion or 1,3-insertion mechanism. The proportion of 1,3-insertion units increased with increasing CPE content in the copolymers. The isomerization reaction from 1,2-insertion to 1,3-insertion CPE units was discussed on the basis of kinetic parameters.

Experimental analysis of the grafting products of diethyl maleate onto linear and branched polyethylenes

This paper is focused on establishing the grafting products of diethylmaleate onto ethylene–α-olefin copolymers of varying comonomer contents. Several commercial ethylene/α-olefin copolymers ranging in comonomer contents from 0.35 to 3.70mol% were used, as well as a hydrogenated polybutadiene (HPB) with a 1,2 unit content of 13.9mol%. The polymers were functionalized with DEM in solution. The experimental techniques employed to verify the grafting and to ascertain the exact positioning of the insertion with respect to the branching points were: Fourier transform infra red spectroscopy (FTIR), carbon 13 nuclear magnetic resonance (13C NMR) and Distortionless enhancement polarization transfer NMR (13C NMR-DEPT). Thermal fractionation was performed by Differential Scanning Calorimetry (DSC) employing the successive self-nucleation and annealing technique (SSA).The results obtained show that the DEM insertion onto polyethylene chains occurs in secondary carbons of the main chain regardless of the copolymer branch type and content. The reasons for this behavior may be related to a statistical factor being involved in the peroxide radical attack since there is an excess of secondary carbons as compared to tertiary ones per PE chain. Also, steric effects produced by the size of the DEM molecules are probably involved in the DEM insertion step. Our 13C NMR-DEPT results suggest that DEM not only avoids the tertiary carbons where the branches are located but also, in polyethylenes with less than 4mol% branch content, it prefers to insert in the secondary carbons that are at least 5 carbon atoms away from the branch point. In those cases where unsaturations are present in PE chain ends, FTIR shows that they can also be depleted by DEM grafting. However, in the HPB case where no unsaturations are present and the branching content is very high, the insertion still occurs only in the secondary carbons of the main chain. The thermal fractionation performed by SSA corroborated the aforementioned results since the fractions with the longest linear chains were always the first to be depleted by the grafting reactions.

Dihydroxy-Terminated Poly(l-lactide) Obtained by Controlled Ring-Opening Polymerization: Investigation of the Polymerization Mechanism

Hydroxy telechelic poly(l-lactide)s of different molecular weight have been synthesized by controlled ring-opening polymerization using cyclic tin alkoxides. NMR analysis showed that the propagation proceeded through an insertion mechanism. No free hydroxyl or carboxyl end groups were detected in the polymerization mixture. Complete reaction of the initiator was observed over the entire range of compositions studied. Both tin−oxygen bonds were reactive and participated in the propagation reaction. Peak assignments were obtained by 1H, 13C, distortionless enhancement polarization transfer (DEPT), and heteronuclear multiple quantum coherence−gradient selected (hmqc-gs) nuclear magnetic resonance spectroscopy. The kinetics of the solution polymerization of l-lactide has been investigated and showed a first order in monomer. The external order in initiator has been determined to be 3/4 for initiator concentrations above 5 mmol/L and to 2 below 2 mmol/L. The molecular weight could easily be adjusted by the mon...

Copolymerization of Propene and Nonconjugated Diene Involving Intramolecular Cyclization with Metallocene/Methylaluminoxane

Copolymerizations of propene with 1,5-hexadiene and 1,7-octadiene were carried out with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride (1) and syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (2) combined with methylaluminoxane. Microstructures of the copolymers were determined by 1H NMR, 13C NMR, and DEPT (distortionless enhancement of polarization transfer) spectroscopies. Incorporation of nonconjugated dienes in the copolymer was higher with 2 than with 1. Intramolecular cycloaddition of the nonconjugated dienes proceeded regardless of the catalysts. Stereoselectivity in cycloaddition of 1,5-hexadiene was investigated based on the structures of isolated methylene-1,3-cyclopentane units. It was found that 1,5-hexadiene was inserted stereospecifically by enantiomorphic site control with both catalysts. The diastereoselectivity of the cyclization step of 1,2-inserted 1,5-hexadiene was, however, found to be independent of stereospecificity of the catalyst. The cyclization selectivity of 1,5-hexadiene copolymerization was higher than that of 1,7-octadiene copolymerization. 1 gave the copolymers with higher selective in cyclization than 2 in the propene/1,5-hexadiene copolymerization, while the opposite tendency was observed in the propene/1,7-octadiene copolymerization. Decrease of cyclization selectivity was observed with the increases of 1,5-hexadiene and 1,7-octadiene concentration in both copolymerizations. Propene insertion could disturb the cyclization of 1,2-inserted dienes, which declined the cyclization selectivity of the copolymers, except propene/1,5-hexadiene copolymerization with 2.

Molecular Weight of Heparin Using 13C Nuclear Magnetic Resonance Spectroscopy

Heparin is a polydisperse, heterogeneous polysaccharide that has been used as an anticoagulant for the past 50 years. The molecular weight determination of this important drug has traditionally relied on gel permeation chromatography, which requires the use of well‐defined molecular weight standards that are not easily obtained. We have investigated the use of13C‐NMR spectroscopy for measuring the number average molecular weight of heparin. The signal intensities of the reducing end and internal anomeric carbons, having distinctive chemical shifts in the13C‐NMR spectrum, were used to determine the molecular weight. Distortionless enhancement polarization transfer was found to provide a better quantitation of signal intensities of anomeric carbons than broad band decoupling or selective decoupling of anomeric protons. Signal averaging over 300 000 transients, requiring approximately 48 h on a 360 MHz NMR spectrometer, resulted in the measurement of the number average molecular weight (˜10 000 Da) of heparin.13C‐NMR spectroscopy does not require the use of difficult to obtain molecular weight standards and thus is particularly well‐suited for workers in the pharmaceutical industry.

Molecular weight of low molecular weight heparins by 13C nuclear magnetic resonance spectroscopy

Heparin and low molecular weight heparins are polydisperse polysaccharides with a degree of polymerization ranging from 4 to ∼ 40. The determination of their average molecular weights has traditionally relied on size exclusion chromatography involving the use of oligosaccharides of known size and molecular weight as standards. 13C NMR spectroscopy is applied for the first time to obtain the molecular weights of low molecular weight heparins. The signal intensities of the reducing end and internal anomeric carbons, having distinctive chemical shifts in the 13C NMR spectrum, are measured to determine the molecular weight. Compared to techniques utilizing broad band decoupling or selective decoupling of anomeric protons, distortionless enhancement polarization transfer pulse sequence gave better quantitation of signal intensities of anomeric carbons. Molecular weight was calculated from the calibrated ratio of signal intensities of the anomeric carbons of reducing end groups and internal residues, and the disaccharide compositional analysis. The calibrated signal intensity ratio is determined using the T 1 relaxation rates of anomeric carbons of model oligosaccharides. The disaccharide composition of low molecular weight-heparins is obtained using capillary electrophoresis. Signal averaging over 40 000–90 000 transients, requiring a total of 12–18 h on a 360-MHz NMR spectrometer was adequate to measure molecular weights in the range of 3000–7000. The measured molecular weights of twelve low molecular weight heparins, analyzed by this 13C NMR spectroscopic technique, correlated well with the number average molecular weights obtained using high performance-gel permeation chromatography and gradient polyacrylamide gel electrophoresis. In addition to establishing the number average molecular weight, the 13C NMR spectra helped distinguish the structural properties of different commercially prepared low molecular weight heparins.