Amino-terminated poly(ethylene glycol) as the initiator for the ring-opening polymerization of 3-methylmorpholine-2,5-dione

Block copolymers with poly[3-methylmorpholine-2,5-dione] (PMMD) and poly[ethylene glycol] (PEG) blocks, PMMD-b-PEG-b-PMMD, were synthesized via ring-opening polymerization of 3-methylmorpholine-2,5-dione with amino-terminated PEG as the initiator at 140 °C within 10 h. Three kind of amino terminated PEG with different average molecular weight were used. The block copolymer was amorphous and the glass transition temperature decreased with increase of PEG block in the copolymer.     

吗啉-2,5-二酮衍生物及其聚合物的研究进展

吗啉-2,5-二酮衍生物是一类制备可生物降解材料的环状单体,本文综述了吗啉-2,5-二酮衍生物及其聚合物的合成方法,以及其在生物医用领域的应用前景。首先介绍了吗啉-2,5-二酮衍生物的三种合成方法,以及采用吗啉-2,5-二酮衍生物均聚反应制备聚缩肽的方法,其次介绍了吗啉-2,5-二酮衍生物与ε-己内酯和丙交酯开环共聚制备基于氨基酸的共聚物。最后,总结了吗啉-2,5-二酮衍生物嵌段共聚物的制备,及其在药物释放和基因载体应用研究中的最新进展。     

A new method for simultaneous determination of Co(II), Ni(II) and Pd(II) as morpholine-4-carbodithioate complex by SPME-HPLC-UV system

A new approach for the analysis of Co(II), Ni(II) and Pd(II) as morpholine-4-carbodithioate (MDTC) complexes in aqueous medium by using solid phase microextraction (SPME)-high performance liquid chromatography (HPLC)-UV has been developed. The method involves sorption of metal complexes on PDMS fiber from aqueous solution followed by desorption in the desorption chamber of SPME-HPLC interface using acetonitrile:water (60:40) as mobile phase. A good separation of metal complexes is achieved on C₁₈ column. The detection limits of Co(II), Ni(II) and Pd(II) are 0.17, 0.11 and 0.06 ng ml⁻¹, respectively. These can be determined by the proposed method without interference from other common metal ions such as Mo(VI), V(V), Ag(I), Sn(IV), Cd(II), Pb(II), Zn(II), Ag(I), Sn(II), Cr(III) and Cr(VI). The method was applied to the determination of these metals in different alloy samples and drinking water sample.     

氨基酸改性聚乳酸

为了改善聚乳酸降解速度慢、细胞亲和性差等方面的不足,氨基酸对聚乳酸的改性工作正在得到人们越来越多的关注.本文综述了氨基酸对聚乳酸改性的各种方法,以及各种氨基酸改性聚乳酸材料的性能与应用.其中,较为常见的改性方法是合成聚(乳酸-氨基酸).展望氨基酸改性聚乳酸类生物降解材料的未来,降低合成成本是广泛应用的关键.因此,虽然目前广泛应用的聚(乳酸-氨基酸)合成途径是氨基酸环状衍生物(尤其是吗啉-2,5-二酮)开环聚合法,但经济有效地以氨基酸、乳酸等为原料的直接聚合法值得关注.     

Synthesis of (+)-pechueloic acid and (+)-aciphyllene. Revision of the structure of (+)-aciphyllene

1αH,7αH,10αH-Guaia-4,11-dien-3-one and its 1βH,10βH diastereomer, easily obtained from (+)-dihydrocarvone, are good starting materials for the synthesis of natural guaiane derivatives. Allylic oxidation of the 1αH,10αH isomer gave as main product its 13-hydroxy derivative and a small amount of (+)-7β-hydroxy-1αH,10αH-guaia-4,11-dien-3-one, whereas the 1βH,10βH diastereomer afforded selectively the (−)-7α-hydroxy-1βH,10βH enantiomer in excellent yield. From the 13-hydroxy derivative (+)-pechueloic acid and (+)-methyl pechueloate were synthesized. Deoxygenation at C₃ of the 1βH,10βH guaiadienone afforded a guaiadiene with the reported structure for aciphyllene but its spectral data did not agree with those reported for the natural diene. The structure of natural (+)-aciphyllene has been corrected to 1αH,7αH,10αH-guaia-4,11-diene obtained by deoxygenation of the 1αH,10αH guaiadienone.     

Biorational synthesis of iridomyrmecin diastereomers from catnip oil

4S,4aS,7S,7aR; 4R,4aS,7S,7aR; 4S,4aS,7S,7aS, and 4R,4aS,7S,7aS diastereomers of iridomyrmecin have been prepared in 5 steps from 4aS,7S,7aR and 4aS,7S,7aS-nepetalactones, major components of catnip oil. 4S,4aS,7S,7aR and 4R,4aS,7S,7aR-iridomyrmecin have been identified as defensive compounds from Iridomyrmex ants.     

Reaction modes of oxidative dimerization of epoxycyclohexenols

Of the 16 possible modes of the oxidation-6π-electrocylization-Diels-Alder reaction cascade for an epoxyquinone, and eight for a 2-alkenyl-3-hydroxymethyl-2-cyclohexen-1-one, only the endo-anti(epoxide)-anti(Me)-hetero and endo-anti(Me)-hetero are respectively observed, while both the endo-anti(epoxide)-anti(Me)-hetero and exo-anti(epoxide)-anti(Me)-homo reaction modes occur with epoxy-4-hydroxycyclohexenones owing to a hydrogen-bonding interaction.     

Studies of non-isothermal crystallization and melting of ultra high molecular weight polyethylene

The non-isothermal crystallization and melting of ultra high molecular weight polyethylene (UHMWPE) were observed by means of differential scanning calorimetry and compared with those of ordinary high-density polyethylene (HDPE). The crystallization temperature (T _c ) and melting point (T _m ) of UHMWPE were found to be higher thanT _c andT _m of HDPE, and the latent heat of crystallization (δH _c ) and fusion (δH _m ) of UHMWPE are smaller thanδH _c andδH _m of HDPE. The results were explained in terms of the theory of polymer crystallization and the structure characteristics of UHMWPE. The relationships between the parameters (T _c ,T _T ,δH _c andδH _m ) and the molecular weight (M) of UHMWPE are discussed. Processing of the experimental data led to the establishment of four expressions describing the above relationships.     

Genetic characterization of Escherichia coli RecN protein as a member of SMC family of proteins

The proteins of SMC family are characterized by having Walker A and B sites. The Escherichia coli RecN protein is a prokaryotic member of SMC family that involved in the induced excision of Tn10 and the repair of the DNA double strand breaks. In this work, the Walker A nucleotide binding site of the E. coli RecN protein was mutated by changing the highly conserved lysine residue 35 to the aspartic acid (D), designated as recN_K35D. Reverse genetics was utilized to delete the entire recN gene (ΔrecN108) or introduce the recN_K35D gene into the E. coli chromosomal DNA. The recN_K35D cells showed decrease in the frequency of excision of Tn10 from gal76::Tn10 after treatment with mitomycin C compared to recN⁺ cells. The ΔrecN108 cells showed an un-induced increase in the frequency of Tn10 excision from gal76::Tn10 in rec⁺ background while, recBC sbcBC ΔrecN108 cells are completely deficient in Tn10 excision. The recombination proficiency is reduced in cells carrying recBC sbcBC cells in addition recN_K35D mutation. We observed that the Walker A nucleotide binding site is important for the RecN protein. Strains that deleted recN gene are recombination deficient and more sensitive to mitomycin C than strains carrying recN_K35D.     

Synthesis of novel optical isomers of α-methylpolyamines

Earlier unknown (R)- and (S)-α-methylspermidine, (R)- and (S)-α-methylspermine, (R,R)-, (S,S)-, and (R,S)-α,ω-dimethylspermine were synthesized in gram scale from readily available (R)- and (S)-2-aminopropanols in high overall yields.     

Study of the oxidation of 3-hydroxypyrroloindoles to pyrrolobenzoxazine alkaloids

This report describes a detailed study of the oxidation-Meisenheimer rearrangement of N-methyl-3-hydroxy-7-chloropyrroloindoline ethyl ester and the corresponding O-Boc and N-Boc derivatives. Experimental conditions were found, which allowed the selective Boc protection of either the tertiary alcohol substituent or the NH group of the aminal function. It was shown that both the parent compound and its O-Boc derivative yielded a mixture of oxazines and, in some cases, N-oxides upon treatment with m-CPBA. MS fragmentation (APCI) clearly differentiates formation of N-oxides and oxazines. The N-Boc derivatives exclusively yielded the N-oxides showing that the Meisenheimer rearrangement requires the presence of a high energy lone pair on the neighbouring nitrogen atom. Both the parent compound and the O-Boc derivative gave a mixture of rearranged products and N-oxide depending on the reaction conditions.     

Moderate generation of sulfenylnitrenes from novel N-sulfenylsulfodiimides

N-Sulfenylated sulfodiimides were first prepared by the reaction of S,S-diphenyl-N-tosylsulfodiimide with arenesulfenyl chlorides under the basic conditions. Thermolysis of S,S-diphenyl-N-(2-nitrophenylsulfenyl)- and S,S-diphenyl-N-(2,4-dinitrophenylsulfenyl)sulfodiimides in the presence of olefins proceeded at 50-80 °C to give the corresponding deiminated S,S-diphenyl-N-tosylsulfimide and N-sulfenylaziridines in very good yields. 2,4-Dinitrophenyl-sulfenylnitrene was trapped by trans- and cis-1-phenylpropenes stereospecifically. The thermolysis temperature of the N-sulfenylsulfodiimides was found to be lower than N-sulfenylsulfoximide and higher than N-sulfenyliminosulfonium salt and very effective to trap the sulfenylnitrene to give the N-sulfenylaziridines in very good yields.     

Regioselectivity in the formation of norbornene-fused pyrazoles: preparation of 1-substituted derivatives of 4,5,6,7-tetrahydro-1H-4,7-methanoindazole

The structural characteristics of (±)-(exo,exo)-3-(hydroxymethylene)-5,6-(isopropylidenedioxy)bicyclo[2.2.1]heptan-2-one make the reactions between this β-diketone and hydrazines particularly interesting for elucidating the mechanism of pyrazole formation. The isolation and X-ray structure determination of two 5-hydroxy substituted Δ²-pyrazolines [(±)-(3aR*,4R*,5R*,6S*,7R*,7aR*)-7a-hydroxy-5,6-(isopropylidenedioxy)-3a,4,5,6,7,7a-hexahydro-4,7-methano-1H-indazole] and [(±)-(3aS*,4R*,5R*,6S*,7R*,7aR*)-7a-hydroxy-5,6-(isopropylidene-dioxy)-1-phenyl-3a,4,5,6,7,7a-hexa-hydro-4,7-methano-1H-indazole] has been determinant for proposing a mechanism. Besides B3LYP/6-31G* calculations have been carried out on all intermediate dihydroxypyrazolidines and 5-hydroxypyrazolines. Finally, the annular tautomerism of the NH-methanotetrahydroindazoles has been studied both experimentally (¹³C NMR) and theoretically: the Mills-Nixon effect favours the 2H-tautomer.     

Thermodynamics of fluorinated derivatives of carbosilane dendrimers of high generations

The temperature dependences of the heat capacities of fluorinated derivatives of carbosilane dendrimers of high (4.5 and 7.5) generations were studied by adiabatic vacuum calorimetry in the range from 6 to 340 K for the first time. The standard thermodynamic characteristics of devitrification were estimated. The experimental results were used to calculate the standard thermodynamic functions C _p °(T), H°(T)?H°(0), S°(T)?S°(0), and G°(T)-H°(0) over the range from T??0 to 340 K and standard entropies of formation of dendrimers at T = 298.15 K. The low-temperature (T ?? 50 K) heat capacity was analyzed by using Debye??s heat capacity theory of solids and the multifractal model. The values of fractal dimensionality D were determined, and some conclusions about topology of the studied structures were made. The standard thermodynamic characteristics of the studied fluorinated derivatives of carbosilane dendrimers were compared.     

Molar excess enthalpies of ternary mixtures of non-electrolytes

Molar excess enthalpies, H^E_ijk(T₁, x_i, x_j), for methylenebromide (i)+pyridine (j)+β-picoline (k); pyridine (i)+β-picoline (j)+cyclohexane (k); benzene (i)+toluene (j)+1,2-dichloroethane (k); benzene (i)+o-xylene (j)+1,2-dichloroethane (k); and benzene (i)+p-xylene (j)+1,2-dichloroethane (k) mixtures have been measured calorimetrically as a function of temperature and composition. The data have been analysed in terms of the Sanchez and Lacombe theory and using an approach employing the “graph theoretical” concept of connectivity parameters to characterize its pure components. It has been observed that the H^E_ijk (T, x_i, x_j) data calculated from the “graph theoretical” approach using ³ξ values based on δ^v considerations (that take into consideration the valency of individual atoms of the molecular graph constituent components) best reproduces the corresponding experimental H^E_ijk data.     

Synthesis of oligomers including eight P-chiral centers and the construction of the 12-phosphacrown-4 skeleton

The stepwise oxidative coupling reaction from (S,S)-1 gave optically active oligomers, (S,R,R,S)-2 and (S,R,S,R,R,S,R,S)-3, having four and eight chiral phosphorus atoms, respectively. The behaviors of these oligomers in the solid state and in solution were investigated in detail. The first construction of a 12-phosphacrown-4 skeleton was also reported.     

Synthesis of the repeating trisaccharide unit of the cell wall lipopolysaccharide of Escherichia coli type 8

NIS/TfOH mediated glycosidation of methyl 3,4,6-tri-O-benzyl-α-d-mannopyranoside with phenyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-α-d-mannopyranoside furnished the corresponding disaccharide derivative in excellent yield and α-selectivity. Zémplen deacetylation of the same followed by reaction with BSP/Tf₂O-preactivated phenyl 4,6-O-benzylidene-2,3-di-O-benzyl-1-thio-α-d-mannopyranoside generated methyl 4,6-O-benzylidene-2,3-di-O-benzyl-β-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranoside in very good yield and excellent β-selectivity. Pd/C catalyzed hydrogenation of the latter finally afforded the repeating trisaccharide of Escherichia coli 8 O-antigen as its methyl glycoside.     

Identification of new lines in the beam-foil spectrum of B II–IV

Ten, six, and twenty-one new lines appearing in the beam-foil spectra of boron (30–200 nm) have been identified in B II, B III, and B IV, respectively. Energies have been determined with higher accuracy than obtained before for the 2p3s ¹ P ⁰, 2s6d ³ D, 2p3p ³ D, 2p3p ³ S, 2p3p ³ P, and 2p3p ¹ D terms in B II. First energy values are also reported for the 2s6d ¹ D and 2s7d ³ D terms in B II.     

Photoisomerization of octyl methoxycinnamate

The octyl-p-methoxy-trans-cinnamate (E-OMC) was exposed to sunlight to induce the E to Z transformation. Octyl-p-methoxy-cis-cinnamate (Z-OMC) was then purified from the mixture of the E- and the Z-OMC using C-18-semi-preparative HPLC. The UV absorption of the Z configuration at various concentrations in various solvents was measured. Molar absorption coefficient of the compound was then calculated. By using the obtained molar absorption coefficient of Z-OMC and of E-OMC, E to Z photoisomerization of octyl methoxycinnamate (OMC) in various solvents at various concentrations could be monitored by C-18 HPLC using UV detector. The result indicates that equilibrium of photoisomerization depends upon concentration and polarity of the solvent used.