MOLECULAR DESIGN OF NEW KINDS OF AUXETIC POLYMERS AND NETWORKS

Three new kinds of molecular networks are designed and predicted to exhibit negative Poisson ratios. Molecular mechanics calculations on these networks show that the magnitude of Poisson ratios depends on the relative flexibility of beam and arm structures. Several new kinds of auxetic polymers, whose successful synthesis should be easier than that of the corresponding auxetic networks, are then proposed. It is found that the kabob-like polymers with auxegens lying vertically on the main chain can acquire auxeticity while those with auxegens lying horizontally on the main chain cannot. Besides, a half kabob-like or pseudo-ladder polymer with auxegens linked at the intersection of the beam and the arm does show auxeticity when adopting constrictive conformers. It is, however, worthwhile noting that the origins of auxeticity still await and strongly deserve further experimental and theoretical investigations.

DESIGN AND SYNTHESIS OF NOVEL CHIRAL IONIC LIQUIDS AND THEIR APPLICATION IN FREE RADICAL POLYMERIZATION OF METHYL METHACRYLATE

Two new chiral ionic liquids, 1 -((-)-menthoxycarbonylmethylene)-3-methylimidazolium hexafluorophosphateand 1-((-)-menthoxycarbonylmethylene)-3-hexadecylimidazolium hexafluorophosphate, were designed an d prepared. Theirchemical structures were characterized by ~1H-NMR. Reverse atom transfer radical polymerization of methyl methacrylate(MMA) in these two ionic liquids was carried out using AIBN/CuCl_2/bipy as the initiating system. The resultant well-definedpolymethyl methacrylate (PMMA) was employed as a macroinitiator to induce the atom transfer radical polymerization ofmenthyl methacrylate (MnMA) in chlorobenzene, which yielded a PMMA-b-PMnMA diblock copolymer with narrow polydispersity.

Chelerythrine chloride binding of guanosine in aqueous solution

In this work, the interaction between chelerythrine （CHE） and guanosine is studied using UV-vis and fluorescence measurements at various temperatures. The UV-vis spectra show that the increasing guanosine concentrations result in the decreasing absorption intensity and red shift of CHE E absorption band （267 nm）. The fluorescence spectra are fitted to linear analysis, yielding a binding constant of 1.04×10^4 L/tool at 298.15 K of CHE with guanosine. Besides, with △rHm^θ = - 8.26 kJ/mol, △rGm^θ = -22.90 kJ/mol, and △rSm^θ = 49.38 J/（mol K） the interaction should be entropy-driven and exterothermic.

Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide) synthesized by ATRP

Novel Y-shaped block copolymers of poly（ethylene glycol） and poly（N-isopropylacrylamide）, PEG-b-（PNIPAM）2, were successfully synthesized through atom transfer radical polymerization （ATRP）. A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly（ethylene glycol） monomethyl ether （PEG）. The copolymers were obtained via the ATRP ofN-isopropylacrylamide （NIPAM） at 30℃ with CuCl/Me6TREN as a catalyst system and DMF/H2O （v/v = 3：1） mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography （GPC） and ^1H NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions （PDI 〈 1.15）. Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry （DSC）. As a result, the phase transition temperature of PEG45-b-（PNIPAM55）2 is higher than that of PNIPAM, however, the corresponding enthalpy change is much lower, indicating the significant influence of the macromolecular composition and architecture on the phase transition.

A spectral study of the interaction between chelerythrine chloride and cytidine

To study the possible anticancer mechanisms of chelerythrine (CHE), and its interactions with cytidine were investigated by UV–vis spectrophotometric and spectrofluorimetric measurements and by thermodynamic calculations. The binding of CHE to cytidine could be characterized by the hypochromic and bathochromic effects in the absorption bands, and the quenching of fluorescence intensity. The spectral data were fit by linear analysis, yielding a binding constant of 2.49 × 10(4) L mol(?1)at 25 °C of CHE and cytidine, and a van’t Hoff enthalpy of ?20.02 kJ/mol for the exothermic interaction in the standard state. In addition, with and , the interactions should be entropy-driven.

Photochemical reaction of magnesium tetraphenyl porphyrin with sulfur dioxide

The photochemical reaction of magnesium tetraphenyl porphyrin（MgTPP） with sulfur dioxide（SO_2） was investigated in dichloromethane（CH_2Cl_2） by steady-state fluorescence,UV-vis absorption,MS,and XRD spectroscopic techniques.These spectra showed that under irradiation MgTPP reacted with SO_2 to form 1：1 molecular adduct at first step.During the process of keeping irradiation and maintaining the flow of SO_2,SO_2 was reduced into S^（2-） by MgTPP and the results were detected using MS and XRD techniques.Understanding the photochemical reaction of MgTPP with SO_2 is of key interest in elucidating fundamental photochemical reaction mechanisms associated with this class of chlorophyll in the presence of SO_2.

EFFECT OF HEATING RATE ON THERMO-INDUCED AGGREGATION OF POLY(ETHYLENE OXIDE)-b-POLY(N-ISOPROPYLACRYLAMIDE) IN AQUEOUS SOLUTIONS

The effects of heating rate on the aggregate behavior of poly（ethylene oxide）-b-poly（N-isopropylacrylamide） in aqueous solutions were investigated in detail by laser light scattering and TEM. By employing two separate heating protocols, step-by-step heating at 〈 5 K/step and one-step jump, to heat the sample from 15℃ to the selected temperature, we found that the heating rate only showed significant effect on the aggregates above the cloud point. The aggregate formed by step-by-step heating exhibited a much larger size and a broader size distribution than those formed by one-step jump heating. Moreover, neither of the aggregates were ideal micellar structures as indicated by the size and the Rg/Rh values. On the contrary, at temperatures below the cloud point where the block copolymer formed core-shelled micelles, the heating rate showed negligible effect on the size and size distribution of the micelles. Since the system underwent a phase separation above the cloud point, the heating rate effect could be reasonably explained by the phase separation mechanisms： the nucleation-and-growth mechanism in the metastable region and the spinodal decomposition mechanism in the unstable region.

REGULATING FUNCTION OF COENZYMIZATION AND DECOENZYMIZATION OF THE LACTATE DEHYDROGENASE ISOZYMES IN THE MOUSE TISSUES DURING HYPOXIA

Objective. To study the characteristics of changes of LDH enzyme patterns of mice under slight hypoxia. Methods. Mice treated with artificial hypoxia, various tissues were made for the test of LDH enzymatic activity by the specific staining technique. LDH(1-5) relative percentage enzymatic activity (RPEA) were measured with CS-910 dual-wavelength thin layer chromatography scanner. Results. The RPEA of LDH isozymes of various tissues after slight hypoxia shifted to the isozymes LDH1 and LDH2, whose principal subunits are H subunits, and be RPEA of LDH1(H4), LDH2(H3M) increased, while RPEA of LDH5(M4) in various tissues decreased prominently except the cardiac muscle, and that of LDH4(HM3) decreased as well. After polyacrylamide gel electrophoresis (PAGE) of the hypoxia treated cardiac muscle specimen was made, activity subbands originated regularly in the isozyme patterns of LDH, with the regularity of LDH1 (0 subband), LDH2 (0-1 subbands), LDH3(0-2 subbands), LDH4(1-3 subbands), LDH5(2-4 subbands). After adding appropriate amount of NAD^+ to the hypoxia treated cardiac muscle specimen, PAGE showed the subbands of four isozymes (LDH2-LDH5) reduced or even totally disappeared in the isozyme patterns. Conclusions. The negative feedback regulation of coenzymization and decoenzymization of LDH isozymes is one of the mouse stress responses to slight hypoxia.

Millimeter observations of organic molecules toward high-mass star formation region G34.26+0.15

To investigate the chemical origination of organic molecules CH3OH, CH3OCH3, C2H5OH, CH3OCH, CH3CN, C2HaCN and C2H5CN in the hot core associated with high-mass star formation re- gion G34.26＋0.15, Submillimeter Array observations were made with its 230 GHz receiver. The molecular gas distribution has shown that the oxygen- and nitrogen-containing molecules peak at different positions. Comparing the spatial distributions with rotational temperatures and fractional abundances of the observed molecules, we discuss the possible chemical origination of these organic molecules.

Supramolecular binding of amines with functional magnesium tetraphenylporphyrin for CO_2 capture

In this work, magnesium tetraphenylporphyrin （MgTPP） was used as a new supramolecular amine-fixing agent. Once introduced, C02 easily competes with MgTPP for amines, leading to the release of MgTPP. The processes can be explained by the fact that the association constant （Kassoc） values of MgTPP with amines were in the range of 0.6 （ethanolamine） to 3.9 （ethylenediamine）, which are lower than the Kassoc values of C02 with these amines. MgTPP interacted with aniline, ethanolamine, pyrrolidine, or ethylenediamine to form 1：1 adducts. Ethylenediamine presents a stronger Kassoc value for MgTPP, so it was considered an optimal agent for C02 capture.

NEW INITIATION SYSTEMS FOR ATOM TRANSFER RADICAL POLYMERIZATION

This review summarizes our achievements in designing new initiation systems for atom transfer radical polymerization (ATRP). First-order kinetics and extension experiments revealed the living nature of these reactions. Tailor- made vinyl polymers with functional end groups were characterized by 1H-NMR and UV-vis spectroscopic analyses. Replacing traditional radical initiators AIBN and BPO, carbon-carbon bond compounds, 1,1,2,2-tetraphenyl-1,2-ethanediol, diethyl 2,3-dicyano-2,3-diphenylsuccinate and diethyl 2,3-dicyano-2,3-di(p-tolyl)succinate, were utilized in reverse ATRP to produce the initiating radical. Sulfur-sulfur bond iniferter, tetraethylthiuram disulfide (TD), in conjunction with CuBr/bpy or NiCl2/PPh3 complex could control the styrene polymerization via redox reaction. Pseudo-halogen transfer reaction was demonstrated to maintain the dormant-active species equilibrium in normal and reverse ATRP with Cu(S2CNEt2), Cu(S2CNEt2)Cl and Fe(S2CNEt2)3 as catalysts. The organic halide initiator and reduced transition metal compound that started the living polymerization were produced in situ from the components of TD/FeCl3/PPh3, TD/CuBr2/bpy and Fe(S2CNEt2)3/FeCl3/PPh3 systems. Accurate control of UV irradiation time favored the radical generation process in photo ATRP with the 2,2-dimethoxy-2-phenylacetophenone/Fe(S2CNEt2)3 initiation system.

Simultaneous determination of dihydroxybenzene isomers utilizing a thiadiazole film electrode

The present study reports a sensitive electro-analytical method for the simultaneous determination of dihydroxybenzene isomers by using a thiadiazole film electrode, which was readily prepared by electropolymerization of 2,5-dimercapto-1,3,4-thiadiazole on a glassy carbon electrode with cyclic voltammetry. The functionalized electrode has a distinguishable and sensitive response to dihydroxybenzene isomers. Under the optimized conditions, the linear stripping peak currents showed good linear relationships with hydroquinone, catechol and resorcinol at concentration ranges 0.50-120, 0.50-110 and 1.00-110 μmol/L, and the detection limits are 0.1, 0.1 and 0.3 μmol/L, respectively. The proposed method is applicable to the simultaneous determination of dihydroxybenzene isomers in real samples with the relative standard deviations of less than 5.7% and the recovery rates of 95.6%-106%. The constructed electrode is characterized by simple preparation, good selectivity, and high sensitivity advantages.

Interaction between human serum albumin and cholesterol-grafted polyglutamate as the potential carriers of protein drugs

Currently there is no successful platform technology for the sustained release of protein drugs.It seems inevitable to specifically develop new materials for such purpose, and hence the understanding of protein–material interactions is highly desirable. In this study, we synthesized cholesterol-grafted polyglutamate(PGA-g-Chol) as a hydrophobically-modified polypeptide, and thoroughly characterized its interaction with a model protein(human serum albumin) in the aqueous solution by using circular dichroism, fluorescence methods, and light scattering. With the protein concentration fixed at 5 μmol/L,adding PGA-g-Chol polymers into the solution resulted in continuous blue shift of the protein fluorescence(from 339 to 332 nm), until the polymer molar concentration reached the same value as the protein. In contrast, the un-modified polyglutamate polymers apparently neither affected the protein microenvironment nor formed aggregates. Based on the experimental data, we proposed a physical picture for such protein–polymer systems, where the polymer first bind with the protein in a 1:1 molar ratio via a fraction of their hydrophobic pendant cholesterol resides along the polymer chain. In this protein/polymer complex, there are excess unbound cholesterol residues. As the polymer concentration increases, the polymers form multi-polymer aggregates around 200 nm in diameter via the same hydrophobic cholesterol residues. The protein/polymer complex also participate in the aggregation via their excess cholesterol residues, and consequently the proteins are encapsulated into the nanoparticles. The encapsulation was also found to increase the thermal stability of the model protein.

Halogen effects on phenylethynyl palladium(Ⅱ) complexes for living polymerization of isocyanides

Polyisocyanides belong to one of the most important artificial helical polymers. The rigid-rod helical conformation makes them to exhibit wide potential applications in chiral recognition, enantioseparation, asymmetrical catalysis, and liquid crystals [1]. Up to now, quite a few metal-promoted polymerization methods have been developed to synthesize polyisocyanides. Especially, it is a great challenge for synthetic chemists to synthesize polyisocyanides in living/controllable fashion that afford well-defined and high isotactic helical polymers.

Synthesis and fluorescence behavior of 2,5-diphenyl-l,3,4- oxadiazole-containing bismaleimides and bissuccinimides

Bismaleimides bearing 2,5-diphenyl-l,3,4- oxadiazole chromophores at para, meta, ortho position and corresponding saturated bissuccinimides were synthe- sized. Several synthetic strategies for these bismaleimides were discussed in detail. Almost no or very weak fluorescence was observed for these bismaleimides, however, the bissuccinimides show a strong fluorescence. The effect of molecular geometry on optical behavior and fluorescence quenching mechanism were investigated by UV-vis absorption and fluorescence emission spectro- scopy. The electron coupling of ground state of p- bismaleimide is stronger than those of m- and o- bismaleimides.p-Bissuccinimide displays increasing fluor- escence quantum yields with red shifts of 22-24 nm, compared to m-bissuccinimide. Polymerizable C=C bonds play a key role in the intramolecular fluorescence quenching.

Preconcentration and separation of trace Pd(II) and Pt(IV) with silica gel bonded by aminopropyl-benzoylazo-4-(2-pyridyl-azo)-resorcinol

This paper reports a simple and highly selective method for preconcentrating and separating of trace Pd(II) and Pt(IV) with silica gel bonded by aminopropyl-benzoylazo-4-(2-pyridylazo)-resorcinol (ABPR·SG). ABPR·SG is stable in solution from 6 mol/L HCl to pH 7.0 and in common organic solvents. The maximum adsorptive capacity of Pd(II) on ABPRSG is 362 μmol/g. After preconcentrating and separation by using ABPR·SG column, Pd(II) and Pt(IV) of μg/L level in artificial water samples can be measured reliably by common spectrophotometer. The maximum concentration factors of Pd(II) and Pt(IV) on ABPR·SG column are 143 and 125 respectively. The chromatographic column packed with ABPR·SG can be reused. The method is simple and efficient.

A red-emitting water-soluble fluorescent probe for biothiol detection with a large Stokes shift

In this work, we presented a fluorescent probe(MCQ-DNBS) for selective and sensitive detection of biothiols based on a methylated chromenoquinoline(MCQ) derivative. Probe MCQ-DNBS was constructed by masking the OH group in MCQ with a common sensing unit, 2,4-dinitrobezensulfonate group(DNBS) for biothiols. Due to the photo-induced electron transfer(PET) process between MCQ and DNBS, this probe was weekly fluorescent. Upon the addition of biothiols(Cys, Hcy and GSH), this probe emitted a strong red fluorescence(λ_(em max)=613 nm) with a large Stokes shift(115 nm). In addition,fluorescence imaging of biothiols in living cells was successfully realized using MCQ-DNBS as a detector.