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Transition of polymers from rubbery elastic state to fluid state
Renyuan QIAN, Yansheng YU
Front Chem Chin. 2009, 4 (1): 1-9.
https://doi.org/10.1007/s11458-009-0014-y
On increasing the temperature of a polymer, the transition of the polymer from a rubbery elastic state to a fluid state could occur. The transition temperature is termed the fluid temperature of the polymer, Tf, which has a direct relationship with the polymer molecular weight. As one of polymer parameters, Tf is as important as the glass transition temperature of a polymer, Tg. Moreover, special attention to Tf should be paid for polymer processing. In research on the transition of a polymer from a rubbery elastic state to a fluid state, the concept of Tf would be more reasonable and more effective than the concept of Tl,l because it is neglected in the concept of Tl,l in that the molecular weight of a polymer may affect the transition of the polymer. In this paper the discussion on the fluid temperature involves the characters of polymers, such as the deformation–temperature curve, the temperature range of the rubbery state and the shear viscosity of polymer melt. From the viewpoint of the cohesional state of polymers, the transition of a polymer from a rubbery elastic state to a fluid state responds to destruction and construction of the cohesional entanglement network in the polymer. The relaxing network of polymer melt would be worthy to be considered as an object of study.
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Denaturation study of bovine serum albumin induced by guanidine chloride or urea by microcalorimetry
Xiangrong LI, Wei GUO, Yan LU
Front Chem Chin. 2009, 4 (1): 32-38.
https://doi.org/10.1007/s11458-009-0009-8
The denaturation of bovine serum albumin (BSA) induced by guanidine chloride or urea at different pH values was studied by isothermal microcalorimetry measurements at 30°C. The simple bonding model, which was developed by Privalov, was employed to obtain the apparent bonding constant K, the apparent singular bonding Gibbs bonding energy ΔG and the total Gibbs energy ΔG(a) between the protein and denaturant, from analysis of the calorimetric data. Furthermore, linear extrapolation at the midpoint of transition was employed to determine the apparent denaturation enthalpy ΔHd. The results showed that for guanidine chloride, the bonding between BSA and guanidine chloride could proceed more easily in an alkaline condition, and the apparent denaturation enthalpy ΔHd of BSA due to guanidine chloride was 350 kJ·mol–1 at pH 6.97 and 7.05, while it was 275 kJ·mol–1 at pH 9.30, which indicated that BSA was more stabilized in a neutral condition. However, for urea, the bonding between BSA and urea could proceed more easily in an acidic condition, and the apparent denaturation enthalpy ΔHd of BSA due to urea was 295 kJ·mol–1 at pH 6.97, while it was 230 kJ·mol–1 at pH 7.05 and 9.30. The results indicate that the degree of expansion of BSA in the two denaturants is different.
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Photocatalytic hydrogen generation using glycerol wastewater over Pt/TiO2
Min LI, Yuexiang LI, Shaoqin PENG, Gongxuan LU, Shuben LI
Front Chem Chin. 2009, 4 (1): 39-43.
https://doi.org/10.1007/s11458-009-0019-6
Using glycerol as electron donor, photocatalytic hydrogen generation over Pt/TiO2 was investigated. The results show that glycerol can not only improve the efficiency of photocatalytic hydrogen generation but can also be decomposed effectively. The factors which affect photocatalytic hydrogen generation, such as irradiation time, initial concentration of the glycerol solution, pH-value of the suspensions and the coexisting substances were studied. The final oxidation products of glycerol were H2O and CO2. Glyceraldhyde, glycoladehyde, glycolic acid and formaldehyde were identified as the intermediates. A possible reaction mechanism was discussed.
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Synthesis and shapes of gold nanoparticles by using transition metal monosubstituted heteropolyanions as photocatalysts and stabilizers
Caihong NIU, Ying WU, Zhenping WANG, Zheng LI, Rong LI
Front Chem Chin. 2009, 4 (1): 44-47.
https://doi.org/10.1007/s11458-009-0005-z
Gold nanoparticles were prepared via a simple photoreduction technique in the presence of transition metal monosubstituted Keggin heteropolyanions (PW11M, M= Cu2+, Ni2+, Zn2+, Fe3+), in which PW11M acted as reducing agent, photocatalyst and stabilizer. The results indicated that the formation rate and morphology of the nanoparticles strongly depended on the kind of transition metal substituted in heteropolyacid and the preparation conditions, such as irradiation time and propan-2-ol amount. The photoreduction rates of PW11Zn and PW11Fe were faster than those of PW11Ni and PW11Cu. The shapes of the nanoparticles synthesized in the presence of PW11Fe and PW11Zn were nearly uniform spheres, whereas the morphologies of the nanoparticles synthesized in the presence of PW11Ni and PW11Cu were found to contain a mixture of flat triangular/hexagonal structures as well as spheres. Increases in the irradiation time and the propan-2-ol amount could make the morphology of nanoparticles uniform and shorten the formation time of the nanoparticles.
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Structural and electrochemical properties of high-capacity Ml-Mg-Ni-based hydrogen storage alloys
Shumin HAN, Yuan LI, Zhong ZHANG, Xilin ZHU, Jinhua LI, Lin HU
Front Chem Chin. 2009, 4 (1): 48-51.
https://doi.org/10.1007/s11458-009-0007-x
The Ml-Mg-Ni-based (Ml= La-rich mixed lanthanide) hydrogen storage alloy Ml0.88Mg0.12Ni3.0Mn0.10Co0.55Al0.10 was prepared by inductive melting. The micro-structure was analyzed by XRD and SEM. The alloy consists mainly of CaCu5-type phase, Ce2Ni7-type phase and Pr5Co19-type phase. The electrochemical measurements show that the maximum discharge capacity is 386 mAh/g, 16.3% higher than that of the commercial AB5-type alloy (332 mAh/g). At discharge current density of 1 100 mA/g, high rate dischargeability is 62%, while that of the AB5-type alloy is only 45%. The discharge capacity decreases to 315 mAh/g after 300 charge/ discharge cycles, 81.5% of the maximum discharge capacity.
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Synthesis, characterization and crystal structure of 1-ferrocenesulfonyl-2-long carbon chain alkyl benzimidazole
Junzhen ZHANG, Bingqin YANG, Yating YANG, Binglin ZHANG
Front Chem Chin. 2009, 4 (1): 52-57.
https://doi.org/10.1007/s11458-009-0008-9
Six new 1-ferrocenesulfonyl-2-benzimidazole derivatives were prepared by the reaction of ferrocenesulfonyl chloride with benzimidazole derivatives in the presence of dichloromethane and n-tetrabutylammonia bromide. The yields of these six new ferrocenesulfonyl benzimidazole derivatives were about 80%. The structures characteristic were confirmed by IR, 1H-NMR, Elemental analysis and MS. The crystal structure of compound a2 was determined via X-ray single crystal diffraction and it belongs to monoclinic system with space group C2/c, and the unit cell parameters are α = 2.8252(2) nm, b = 0.97696(7) nm, c = 1.64828(12) nm, α = 90°, β = 92.053(2)°, γ = 90°, V = 4.5466(6) nm3, Z = 8, F (000) = 2024, Mr =481.40, Dc = 1.407 g/cm3, μ = 0.784 mm–1, R1 = 0.0495, wR2 = 0.1517. The results show that the reactions of 2-alkylbenzimidazoles containing active hydrogen with ferrocenesulfonyl chloride gave 1-ferrocenesulfonyl-2-alkylbenzimidazoles in good yields.
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Synthesis and antiemetic activity of 1,2,3,9-tetrahydro-9-methyl-3-(4-substituted-piperazin-1-ylmethyl)-4H-carbazol-4-one derivatives
Qigui XU, Tianyu LIU, Rui TIAN, Qingeng LI, Deyin MA
Front Chem Chin. 2009, 4 (1): 63-68.
https://doi.org/10.1007/s11458-009-0017-8
5-HT3 receptor antagonists, such as Ondansetron, are used for anti-emesis after chemotherapy, radiotherapy and operations. Some Ondansetron analogs possessing piperazine ring as side chains were synthesized in our lab. Thus, one of the two carbonyl groups of starting material 1,3-cyclohexandione (1) was condensed with phenylhydrazine hydrochloride to form monophenylhydrazone (2). 1,2,3,9-Tetrahydro-4H-carbazol-4-one (3) was prepared from 2via cyclization and rearranged in the presence of ZnCl2. Through a methylation reaction, compound 3 was converted to 1,2,3,9-tetrahydro-9-methyl-4H-carbazol-4-one (4). 3-Dimethylaminomethyl substituted compound (5) was synthesized from 4 by a Mannich reaction in glacial acetic acid. Nine novel 1,2,3,9-tetrahydro-9-methyl-3-(4-substituted-piperazin-1-ylmethyl)- 4H-carbazol-4-one derivatives (6a-6i) were synthesized through nucleophilic substitution reaction of 5 with piperazines. The structures of all the target compounds were determined by elemental analysis, IR, MS, 1H NMR and 13C NMR spectra. The results of preliminary pharmacological test show that part of the novel compounds have antiemetic activity comparable to that of the control Ondansetron.
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Synthesis, characterization and quantum chemistry study of 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine
Bozhou WANG, Weipeng LAI, Qian LIU, Peng LIAN, Yongqiang XUE
Front Chem Chin. 2009, 4 (1): 69-74.
https://doi.org/10.1007/s11458-009-0001-3
3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) was synthesized by the condensation of triaminoguanidinium nitrate with 2,4-pentanedione, followed by oxidation and substitution reaction. The product was characterized by elemental analysis, IR, NMR spectrometry and DSC analysis. Instead of nitrogen dioxide/N-methylpyrrolidone, acetic acid/sodium nitrite was used as the oxidizer during the oxidation. Thus, the cost was reduced and the process was simplified. The theoretical properties of BTATz were estimated by a B3LYP method based on a 6-31G(d,p) basis set, and the stable geometric configuration and bond order were obtained. The vibrational frequencies, IR spectrum and thermodynamic properties under different temperatures were obtained from vibrational analysis and the relationship between temperature and thermodynamics properties was deduced. Pyrolysis mechanism of BTATz was discussedand the transition state and activation energy of ring opening reaction of the tetrazole were deduced.
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Effect of unsaturated hydroxyl-fatty acid modified nano-CaCO3 on the morphological and rheological behavior of PP
Ju GU, Qiang XIONG, Demin JIA, Yuanfang Luo, Rongshi Cheng
Front Chem Chin. 2009, 4 (1): 75-82.
https://doi.org/10.1007/s11458-009-0013-z
A modified nano-calcium carbonate (R-CCR) was prepared by coating a layer of unsaturated hydroxyl-fatty acid on the surface of CCR powders using a solid state method; the latter were commercial nano-CaCO3 modified with stearic acid. FTIR studies indicate that the modifier is combined on the surface of CaCO3. PP/EPDM/nano-CaCO3 ternary composites were prepared by a melt-mixing method. SEM and TEM were utilized to examine the morphology of the composites. The tensile fractured surface of PP/EPDM/R-CCR showed a fibroid morphology and large-scale yield deformation. The impact fractured surface showed that the amount of cavities in the PP/EPDM/R-CCR system was increased, however their size diminished obviously. R-CCR particles were dispersed uniformly in the PP matrix, and their compatibility was distinctly improved as compared to CCR when the amount of R-CCR was 15 h-1. The tensile strength remained nearly constant (reduced from 27.6 MPa to 27.5 MPa), while the impact strength increased from 9.6 kJ/m2 to 15.4 kJ/m2 as CCR was replaced by R-CCR. Meanwhile, the bending strength and bending modulus also increased correspondingly. Furthermore, the impact strength of PP/EPDM/R-CCR was maintained at a high level (15.4 kJ/m2), which was more than the sum of that of PP/EPDM and PP/R-CCR (6.6 kJ/m2 and 6.1 kJ/m2 respectively). This indicates that the R-CCR and EPDM have a significant synergistic toughening effect on PP while maintaining the strength and modulus of virgin PP. Both the storage modulus G¢ and loss modulus G¢¢ of PP/EPDM and PP/EPDM/R-CCR composites increase with increasing frequency, but the values of G¢ and G¢¢ of the tertiary composite are relatively higher than those of the binary system. The loss factor and viscosity decrease with increasing frequency, but there is little difference between tertiary and binary composites. The apparent viscosity η of the tertiary system containing R-CCR is lower than that of the tertiary system containing CCR and virgin PP. The viscosity of the composites significantly decreases with increasing shear rate. The measured mechanical properties of the composites indicate that replacing CCR with R-CCR for binary composites could simultaneously enhance the toughness and strength of PP.
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Preparation of polyvinylpyrrodione microspheres by dispersion polymerization
Linfeng ZHAI, Tiejun SHI, Hualin WANG
Front Chem Chin. 2009, 4 (1): 83-88.
https://doi.org/10.1007/s11458-009-0003-1
The preparation of polyvinylpyrrolidone (PVP) microspheres in ethyl acetate by dispersion polymerization with N-vinylpyrrolidone (NVP) as initial monomer, poly(N-vinylpyrrolidone-co-vinyl acetate) (P(NVP-co-VAc)) as dispersant, and 2,2¢- azobisisobutyronitrile(AIBN) as initiator is reported. The influences of monomer concentration, dispersant concentration and initiator concentration on the size of PVP microspheres as well as the monomer conversion were studied. The structure and properties of PVP microspheres were analyzed. The results show that the prepared PVP microspheres have a mean diameter of 3–4 mm. With an increase in NVP concentration, the size and the molecular weight of the PVP microspheres as well as the monomer conversion all increase. With increasing P(NVP-co-VAc) concentrations, the PVP molecular weight and monomer conversion both increase while the size of the microspheres becomes smaller. As the concentration of AIBN increases, the microsphere size and monomer conversion increase whereas the PVP molecular weight decreases. The PVP prepared by dispersion polymerization has a crystal structure, and its molecular weight is lower compared to that prepared by solution polymerization.
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Designed synthesis and chiroptical properties of regioregular poly(p-phenyleneethynylene-alter-m-phenyleneethynylene) bearing (-)-trans-myrtanoxyl side groups
Xiangfeng LI, Chusheng LI, Jiang LU, Hui LIANG
Front Chem Chin. 2009, 4 (1): 93-103.
https://doi.org/10.1007/s11458-009-0018-7
Two regioregular poly(p-phenyleneethynylene-alter-m-phenyleneethynylene)s bearing (-)-trans-myrtanoxyl side groups with different substitution patterns were designed and synthesized, e.g. Myr-PMPE-1 and Myr-PMPE-2. In Myr-PMPE-1, the side chiral groups are distributed uniformly along the backbone. In Myr-PMPE-2, the distribution of the side chiral groups is alternatively crowded and loose. Both of these two polymers show no CD signal in solutions because of their good solubility. The investigations of chiroptical properties of these two polymers were carried out in the form of spin-coated films. The films were annealed above the glass temperature of the corresponding polymer, and the effects of annealing temperature and time on the properties of the films were investigated by UV-Vis absorption, fluorescence and circular dichroism spectra. The results show that annealing treatment had no significant effect on the properties of Myr-PMPE-1, including UV-Vis absorption, fluorescence and optical activity. The maximum absolute value of dissymmetry factor (|gmax|) was 1.62 × 10-4. On the other hand, annealing treatment significantly affected the properties of Myr-PMPE-2. Without annealing or being annealed below 100°C, Myr-PMPE-2 films show almost no Cotton effect. In contrast, when annealed above 120°C, the absorption and emission of Myr-PMPE-2 films slightly red shifted with increasing annealing temperature and annealing time. Most importantly, the intensity of CD signals increased significantly and the optical activity of Myr-PMPE-2 films markedly increased. After annealing at 140°C for 4 h, the |gmax| of Myr-PMPE-2 films was increased up to 3.07 × 10-3, about one order of magnitude higher than that of Myr-PMPE-1 films.
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Micellization and controlled release properties of methoxy poly(ethylene glycol)-b-poly(D,L-lactide-co-trimethylene carbonate)
Jieming GAO, Yingzhi GUO, Zhongwei GU, Xingdong ZHANG
Front Chem Chin. 2009, 4 (1): 104-109.
https://doi.org/10.1007/s11458-009-0006-y
Amphiphilic block copolymers composed of D,L-lactide, trimethylene carbonate and methoxy poly(ethylene glycol) (PETLA) were synthesized with ring-opening copolymerization. Studies on the micellization and drug-controlled release behavior of PETLA were performed. Both of the copolymers and the micelles were characterized with the methods of 1H nuclear magnetic resonance (1H-NMR), fluorescence spectroscopy, gel permeation chromatographic (GPC), dynamic light scattering (DLS), transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV). As a result, the critical micelle concentration of the copolymer was decreased with the increase of the hydrophobic chain length. DLS resulys indicated the diameters of the micelle were increased with increasing of hydrophobic length. TEM photographs illustrated that micelles MT1 were regularly spherical with the diameter from 30 nm to 40 nm. Taking 9-nitro-20(S)-camptothecin (9-NC) for the model drug, the release profiles in vitro show that the release behavior from micelles was controllable and nearly in zero order after the initial burst release.
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