Synthesis and Characterization of Amino Acid Modified Chitooligosaccharides

Amino acid modified chitooligosaccharides were synthesized by the new synthetic route. The chloroacetyl-chitooliogosaccharide intermediates were prepared under a mild condition via a reaction between chitooligosaccharide (COS) and chloroacetic anhydride. The intermediates were subsequently reacted with a variety of amino acids, e.g., glycine, aspartic acid, alanine, arginine, and serine, under a basic condition, yielding amino acid modified COS products. The degree of chloroacetylation was calculated based on new ¹H NMR absorption peaks at 3.80 and 3.94 ppm, corresponding to  NH CO CH₂ Cl and  O CO CH₂ Cl, respectively. The degrees of chloroacetylation determined were 0.40, 0.44, 0.62, and 0.93 when the mole ratios of chloroacetic anhydride to COS were 0.5, 1, 2, and 4, respectively. The chemical structures of the COS derivatives were also determined using ¹H NMR spectroscopy. The biological properties of the derivatives were evaluated. Cytotoxicity of the derivatives was assessed by a direct contact, using L929 cells. An MTT assay was a method of choice to evaluate the efficacy of the derivatives to enhance the proliferation of L929 cells.     

1H-NMR Spectroscopy of Gold Drugs. High-Resolution Studies of β-D-Thioglucosetetraacetate Phosphine Complexes of Au(I)

¹H-NMR data (11.74 Tesla) for the gold(I) complexes [R₃P-Au-(2,3,4, 6-tetra-O-acetyl-1-thio-β-D -glucopyranosido-S)] (R = Et, Cyclohexyl, C₆H₅, p-CH₃OC₆H₄) with sulfur coordination to gold, are reported. The resonances associated with the sugar protons have been assigned although these have similar chemical environments. The coordination chemical shifts, Δδ, for the Au? S? C? H proton are ≈? 0.6 ppm, and support S-coordination to gold.     

Laminating resins obtained from 2,2′-(1,4-phenylenedivinylene)bispyridine bismaleimides and maleimide-terminated styrylpyridine prepolymers

A new bismaleimide (2a) , biscitraconimide (2b) , and bisnadimide (4) were synthesized by reacting 2-amino-6-methylpyridine with an equimolar amount of maleic, citraconic, or nadic anhydride, respectively, and then with a half molar amount of 1,4-benzenedicarbaldehyde in the presence of acetic anhydride. They, as well as the intermediate amic acids ( 1a, 1b, and 3 ) were characterized by IR and ¹H-NMR spectroscopy. The DTA thermograms showed that crosslinking of polymer precursors started at 180–212°C. The crosslinked resins obtained from 2a and 2b were stable up to 300–313°C and afforded anaerobic char yield of 53–60% at 800°C. The cured resin of 4 was less thermostable. In addition, end-capping of styrylpyridine prepolymers was accomplished by reacting 2,6-dimethylpyridine (n mol) with 1,4-benzenedicarbaldehyde (n + 1 mol) in acetic anhydride to yield a formyl-terminated styrylopyridine prepolymer. The latter reacted with the maleamic acid 1a (2 mol) to afford a series of maleimide-terminated styrylpyridine prepolymers MTSOs. They showed lower curing temperatures than did the ordinary poly(styrylpyridine). Their cured resins did not lose weight up to 310–344°C both in N₂ or air and afforded anaerobic char yield of 66-72% at 800°C.     

Silicon‐terminated telechelic oligomers by ADMET chemistry: Synthesis and copolymerization

Methoxydimethylsilane and chlorodimethylsilane‐terminated telechelic polyoctenomer oligomers (POCT) have been prepared by acyclic diene metathesis (ADMET) chemistry using Grubbs' ruthenium Ru(Cl₂)(CHPh)(PCy₃)₂ [Ru] or Schrock's molybdenum Mo(CH CMe₂Ph)(N 2,6 C₆H₃ i Pr₂)(OCMe(CF₃)₂)₂ [Mo] catalysts. These macromolecules have been characterized by FTIR, ¹H‐, ¹³C‐, and ²⁹Si‐NMR spectroscopy. The molecular weight distributions of these polymers have been determined by GPC and vapor pressure osmometry (VPO). The number‐average molecular weight (M_n) values of the telechelomers are dictated by the initial ratio of the monomer to the chain limiter. The termini of these oligomers (M_n = 2000) can undergo a condensation reaction with hydroxy‐terminated poly(dimethylsiloxane) (PDMS) macromonomer (M_n = 3300) [HO Si(CH₃)₂ O { Si(CH₃)₂O }_x  Si(CH₃)₃], producing an ABA‐type block copolymer, as follows: (CH₃)₃SiO [ Si(CH₃)₂O ]_x [ CHCH (CH₂)₆ ]_y [ OSi(CH₃)₂ ]_x OSi(CH₃)₃. The block copolymers were characterized by ¹H‐ and ¹³C‐NMR spectroscopy, VPO, and GPC, as well as elemental analysis, and were determined by VPO to have a M_n of 8600. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 849–856, 1999     

Sulfonic and Phosphonic Acid and Bifunctional Organic–Inorganic Hybrid Membranes and Their Proton Conduction Properties

Hybrid organic–inorganic approaches are used for the synthesis of bifunctional proton exchange membrane fuel cell (PEMFC) membranes owing to their ability to combine the properties of a functionalized inorganic network and an organic thermostable polymer. We report the synthesis of both sulfonic and phosphonic acid functionalized mesostructured silica networks into a poly(vinylidenefluoride‐co‐hexafluoropropylene) (poly(VDF‐co‐HFP) copolymer. These membranes, containing different amounts of phosphonic acid and sulfonic acid groups, have been characterized using FTIR and NMR spectroscopy, SA‐XRD, SAXS, and electrochemical techniques. The proton conductivity of the bifunctional hybrid membranes depends strongly on hydration, increasing by two orders of magnitude over the relative humidity (RH) range of 20 to 100 %, up to a maximum of 0.031 S cm⁻¹ at 60 °C and 100 % RH. This value is interesting as only half of the membrane conducts protons. This approach allows the synthesis of a porous SiO₂ network with two different functions, having  SO₃H and  PO₃H₂ embedded in a thermostable polymer matrix.     

Nitrene Insertion into C?C and C?H Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

The impact of redox non‐innocence (RNI) on chemical reactivity is a forefront theme in coordination chemistry. A diamide diimine ligand, [{‐CHN(1,2‐C₆H₄)NH(2,6‐iPr₂C₆H₃)}₂]ⁿ (n=0 to −4), (dadi)ⁿ, chelates Cr and Fe to give [(dadi)M] ([ 1 Cr(thf)] and [ 1 Fe]). Calculations show [ 1 Cr(thf)] (and [ 1 Cr]) to have a d⁴ Cr configuration antiferromagnetically coupled to (dadi)²⁻*, and [ 1 Fe] to be S=2. Treatment with RN₃ provides products where RN is formally inserted into the C C bond of the diimine or into a C H bond of the diimine. Calculations on the process support a mechanism in which a transient imide (imidyl) aziridinates the diimine, which subsequently ring opens.     

Über das fluktuierende Verhalten von triphenylmethylsubstituierten Cyclopentadienyl-Metallverbindungen

The fluxional behaviour of triphenylmethyl substituted cyclopentadienyl metal compounds ¹H-NMR. spectroscopy has been used to study the influence of the triphenylmethyl substituent on the metallotropic rearrangement in C₅H₄(CPh₃)Si(CH₃)₃ and C₅H₄ (CPh₃)Sn(CH₃)₃. The most likely mechanism corresponds to a degenerate metal exchange between two neighbouring ring positions. The AA'XX' spectrum of the cyclopentadienyl ring protons in C₅H₄(CPh₃)Sn(CH₃)₃ has been analysed under rapid exchange conditions. The free energy of activation for the sigmatropic [1,5]-Sn shift has been measured by comparison with computer simulated spectra for slow exchange.     

Characterization of polybenzoxazine and its electrochemical polymerization mechanism

Poly(3-(p-methyl)benzyl-3,4-dihydro-6-methyl-2H-1,3-benzoxazine) (poly(pCpT)), which was obtained from electrochemical polymerization in acetonitrile/alkali aqueous solution, was characterized by FT-IR, UV-Vis and ¹H-NMR. The results indicate a ring-opening structure of the polymer. By using a rotating-ring disc electrode (RRDE), the electrochemical behaviors of polymerization were studied and the polymerization mechanism was proposed.     

Stereochemistry in cationic polymerization of alkenyl ethers. I. 1H- and 13C-NMR spectra of poly(propenyl ethers)

Benzyl, ethyl, and deuterated ethyl propenyl ethers (BzPE, EPE, and EPE-d₅, respectively) with different cis/trans isomer ratios were polymerized by BF₃O(C₂H₅)₂ at ?78°C in toluene, methylene chloride, and nitroethane solvents. Poly(propenyl alcohol) [poly(PA)] was also prepared by treating poly(BzPE) with HBr gas. The steric structure of these polymers was studied by ¹H- and ¹³C-NMR spectroscopy. The poly(EPE-d₅) obtained from a trans-rich monomer mixture was crystalline, while one from a cis-rich monomer mixture was amorphous. Poly(BzPE) was always amorphous. Poly(BzPE), poly(PA), and poly(EPE-d₅) gave ¹H-NMR spectra with two β-methine peaks, relative intensities of which depended on the geometric structure of the monomers. Their spectra of β-methyl protons decoupled from β-methine proton were also split into two peaks, relative intensities of which corresponded to those of the two α-methine peaks. ¹³C-NMR spectra of α-OCH₂ and β-CH₃ of poly(EPE), respectively, consisted of two peaks. These observations show that the poly(propenyl ethers) examined, whether crystalline or amorphous, have only two dyad structures (probably threo or erythro-meso and racemic), and that their α- and β-carbons have the same dyad structure, irrespective of the kind of the alkoxyl groups.     

Synthesis and Properties of Silphenylene-containing Epoxy Resins with High UV-stability

Two novel silphenylene-containing cycloaliphatic epoxy resins, 1,4-di [2-(3, 4-epoxycyclohexylethyl) dimethylsilyl] benzene (DEDSB) and 1,3,5-tri [2-(3, 4-epoxycyclohexylethyl) dimethylsilyl] benzene (TEDSB) were synthesized through in situ Grignard reaction and hydrosilylation, and characterized by FT-IR and ¹H-NMR. They were colorless transparent viscous liquids. Methyhexahydrophthalic anhydride (MeHHPA) was used to cure the epoxy resins to give glassy solids with high optical clarity. Differential scanning calorimetry (DSC) results indicated that DEDSB and TEDSB showed similar curing reactivity. The cured TEDSB had a higher glass transition temperature, a higher storage modulus and a lower coefficient of linear thermal expansion than the cured DEDSB due to a higher crosslink density. The cured silphenylene-containing epoxy resins exhibited a much higher resistance to discoloration under UV irradiation than the commonly used epoxy resins diglycidyl ether of bisphenol-A (DGEBA). XPS analysis revealed that they were much less susceptible to photo-oxidation than DGEBA.     

Olefin polymerization and copolymerization with soluble transition‐metal complex catalysts

Olefin polymerizations catalyzed by Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 1 – 5 ; Cp′ = cyclopentadienyl group), RuCl₂(ethylene)(pybox) { 7 ; pybox = 2,6‐bis[(4S)‐4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine}, and FeCl₂(pybox) ( 8 ) were investigated in the presence of a cocatalyst. The Cp*TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 5 )–methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and 1‐hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1‐hexene incorporation and a lower r_E · r_H value with 5 than with [Me₂Si(C₅Me₄)(N^tBu)]TiCl₂ ( 6 ) were obtained, despite the rather wide bond angle of Cp Ti O (120.5°) of 5 compared with the bond angle of Cp Ti N of 6 (107.6°). The 7 –MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1‐hexene copolymerization, and the resultant copolymer incorporated 1‐hexene. The 8 –MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1‐hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring‐opened poly(norbornene) substituent was accomplished by ringopening metathesis polymerization with the well‐defined Mo(CHCMe₂Ph)(N‐2,6‐ⁱPr₂C₆H₃)[OCMe(CF₃)₂]₂ ( 10 ). The key step for the macromonomer synthesis was the exclusive end‐capping of the ring‐opened poly(norbornene) with p‐Me₃SiOC₆H₄CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4613–4626, 2000     

Supramolecular hexagonal structure of a segmented liquid crystalline polyester with allyl group as lateral substituent

The molecular structure of the phase—stable at room temperature—for the polymer with formula [ p C₆H₄ COO p C₆H₃(R) p C₆H₃(R) OOC p C₆H₄ O (CH₂)₁₀O ]_x, with R =  CH₂ CHCH₂, is reported. The cell is hexagonal (a = b = 13.43 Å, c = 33.3 Å, γ = 120°), space group P6₃, six chains per unit cell (d_calcd = 1.23 g cm⁻³). The six chains are packed together to give a bundle with the center of mass set at the origin of the unit cell. The allyl groups are placed inside the bundle, thus explaining the unexpected reactivity of the double bonds to give crosslinking when fiber samples are annealed in the solid state. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1601–1607, 1999     

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent

The ¹H chemical shifts of 48 amides in DMSO solvent are assigned and presented. The solvent shifts Δδ (DMSO‐CDCl₃) are large (1–2 ppm) for the NH protons but smaller and negative (?0.1 to ?0.2 ppm) for close range protons. A selection of the observed solvent shifts is compared with calculated shifts from the present model and from GIAO calculations. Those for the NH protons agree with both calculations, but other solvent shifts such as Δδ(CHO) are not well reproduced by the GIAO calculations. The ¹H chemical shifts of the amides in DMSO were analysed using a functional approach for near ( ≤ 3 bonds removed) protons and the electric field, magnetic anisotropy and steric effect of the amide group for more distant protons. The chemical shifts of the NH protons of acetanilide and benzamide vary linearly with the π density on the αN and βC atoms, respectively. The C=O anisotropy and steric effect are in general little changed from the values in CDCl₃. The effects of substituents F, Cl, Me on the NH proton shifts are reproduced. The electric field coefficient for the protons in DMSO is 90% of that in CDCl₃. There is no steric effect of the C=O oxygen on the NH proton in an NH…O=C hydrogen bond. The observed deshielding is due to the electric field effect. The calculated chemical shifts agree well with the observed shifts (RMS error of 0.106 ppm for the data set of 257 entries). Copyright © 2014 John Wiley & Sons, Ltd.     

Fire- and heat-resistant adhesive resins based on maleimido and citraconimido substituted 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes

A novel class of fire- and heat-resistant bisimide resins was prepared by thermal polymerization of maleimido or citraconimido derivatives of 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes (1). The neat bisimide resin prepared by curing 1-[di(2-chloroethoxyphosphinyl)methyl]-2,4- and -2,6-bismaleimidobenzene exhibited a limiting oxygen index 75% higher and smoke evolution about 30 times lower compared with the parent polymer obtained by curing m-phenylenebismaleimide. The char yield of cured bisimide resins at 700°C was 58–70% in a nitrogen atmosphere and 35–60% in air. An increase in formula weight between the imide groups slightly reduced the char yield. The polymer precursors were synthesized by reacting the phosphorus-containing diamines (1) (1 mol) with maleic anhydride/citraconic anhydride (2 mol) or by reacting the monomaleimido derivative of (1) with benzophenone tetracarboxylic dianhydride/methylenebis(4-phenylisocyanate) in a 2:1 mole ratio. The monomers were characterized by elemental analysis, Fourier-transform–infrared (FT-IR), proton nuclear magnetic resonance (¹H-NMR) spectroscopy, and gas chromatography–mass spectroscopy (GC-MS). Direct cleavage of the P? C bond and inversion of the synthesis reaction may occur during their pyrolysis. The thermal polymerization of the monomers was investigated by differential scanning calorimetry (DSC). Biscitraconimides are thermally polymerized at a relatively lower temperature than the corresponding bismaleimides.     

1H-NMR of the esterification of syndiotactic poly(methacrylic acid) with carbodiimides—II. Esterification with benzylalcohol and trifluoroethanol

The partial esterification of syndiotactic poly(methacrylic acid) with benzyl alcohol or trifluoroethanol and dicyclohexylcarbodiimide as a condensing agent has been studied, evaluating triad and pentad probabilities by ¹H-NMR. The mechanism of this esterification leads to a tendency toward alternation for esterified and unesterified monomer units along the chain and to a limiting conversion. Only a moderate approximation of triad and pentad probabilities by conditional probabilities of first and second order was possible. The esterification of poly(methacrylic acid) with trifluoroethanol has been carried out also in conc H₂SO₄ and leads to a random distribution of monomer units.     

1H-NMR study of polyisoprenes

¹H-NMR spectra of polyisoprene were assigned using polymers of isoprene-1,1,4,4-d₄, isoprene-1,1,5,5,5-d₅, and isoprene-4,4-d₂ polymerized with various catalysts. The methylene-proton signal at 2.1 ppm in cis-1,4 - and trans-1,4-polyisoprenes was divided into H₄- and H₁-proton signals; H₄ resonated at 2.21 ppm in both cis-1,4 and trans-1,4 units whereas H₁ resonated at 2.05, 2.21, and 2.15 ppm. Splitting due to the dyad sequences of 1,4 and 3,4 units was apparent. The methine-proton (H₃) in a 3,4 unit showed a broad peak centered around 1.5 ppm in C₆D₆. The overlapping of this signal with the methyl-proton signals at 1.73 and 1.63 ppm resulted in some uncertainty in the determination of the microstructure of polyisoprene which contained a considerable amount of 3,4 unit.     

Synthesis,characterization, and in vitro antimicrobial and antitumor activities of some tetraphenylstibonium(V) carboxylates

Several hitherto unreported pentacoordinated tetraphenylstibonium(V) carboxylates of general formula (C₆H₅)₄SbL, where L = o‐OHC₆H₅COO , (C₆H₅)₂C(OH)COO , 2‐(6‐OCH₃C₁₀H₆)CH(CH₃)COO , ArCH(OH)COO (Ar = C₆H₅, p‐CF₃C₆H₄, and p OCH₃C₆H₄), have been prepared and characterized by elemental analysis, solid state IR, ¹H NMR, and ¹³C NMR spectra, conductivity, and molecular weight measurements. Spectroscopic data together with solution phase studies conform to the requirement of triagonal‐bipyramidal configuration for these compounds. They were tested for in vitro antifungal (against Aspergillus flavus and Aspergillus niger) and antibacterial (against Staphylococcus aureus and Klebsiella pneumoniae) activities. The in vitro antitumor activity of all stibonium carboxylates was examined against MCF‐7 cell line. A few of them were found to exhibit moderate to significant biological activity. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:688–693, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20498     

Synthesis and characterization of novel bisphthalonitrile resins linked by different molecular weight main-chain polybenzoxazines

A series of novel type bisphthalonitriles with different molecular weight main-chain polybenzoxazines as linkages have been successfully synthesized using 4, 4′-diaminodiphenyl methane, paraformaldehyde, bisphenol A and 4-nitrophthalonitrile as initial materials. The structures were characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (¹H-NMR). The formation of benzoxazine and the existence of nitrile groups were confirmed by the absorbance at 950cm^?1 of benzene attached with oxazine ring and 2231 cm^?1 of nitrile groups. The characteristic resonance peaks observed at about 4.52 (C-CH₂-N) and 5.28 ppm (N-CH₂-O) also determined the structure of benzoxazine ring. The curing behaviors were monitored by differential scanning calorimetry (DSC) and FT-IR. Two-stage polymerization mechanisms were observed according to the ring-opening of benzoxazine and the polymerization of nitrile groups catalyzed by phenolic hydroxyl groups, which generated during the curing reaction of benzoxazine. The polymerization of these bisphthalonitriles exhibited self-promoted curing behaviors. The completion of polymerization was proved by the disappearance of the band located at 950 cm^?1 in FT-IR. Thermogravimetric analysis (TGA) was used to investigate the thermal stability, and the results showed that the cured polymers achieved extremely high char yield from 61.1% up to 74.2% at 800°C under nitrogen and exhibited increasing decomposition temperature as the contents of phthalonitrile groups increased, which indicated that the polymerization of phthalonitriles could improve the thermal stability.     

A new synthetic procedure for the preparation of pyridinium tetrafluoroborate and hexafluorosilicate

Pyridinium tetrafluoroborate (C₅H₅NHBF₄) and pyridinium hexafluorosilicate [(C₅H₅NH)₂SiF₆] have been prepared in good yields and high purity by the reaction of pyridinium poly(hydrogen fluoride) with oxides and acids of boron and silicon respectively. The salts have been characterised by melting points, IR, ¹H and ¹⁹F NMR spectroscopy and chemical analysis.     

Synthesis, curing kinetics and thermal properties of bisphenol-AP-based benzoxazine

A novel bisphenol-AP-aniline-based benzoxazine monomer (B-AP-a) was synthesized from the reaction of 4,4′-(1-phenylethylidene) bisphenol (bisphenol-AP) with formaldehyde and aniline. The chemical structures were identified by FT-IR, ¹H and ¹³C NMR analyses. The polymerization behavior of the monomer and the types of hydrogen bonding species were monitored by differential scanning calorimetry (DSC) and FT-IR. The curing kinetics was studied by isothermal DSC and the isothermal kinetic parameters were determined. The thermal properties of cured benzoxazine were measured by DSC and thermogravimetric analysis (TGA). The bisphenol-AP-aniline-based polybenzoxazine (poly(B-AP-a)) exhibited higher glass transition temperature (T_g) and better thermal stability than corresponding bisphenol A-aniline-based polybenzoxazines (poly(BA-a)). The T_g value of poly(B-AP-a) is 171 °C. The temperatures corresponding to 5% and 10% weight loss is 317 and 347 °C, respectively, and the char yield is 42.2% at 800 °C. The isothermal curing behavior of B-AP-a displayed autocatalysis and diffusion control characteristics. The modified autocatalytic model showed good agreement with experimental results.