Volumetric,viscometric and acoustic properties of binary mixtures of 2-propanol with n -alkanes (C6, C8, C10) at 298.15 and 308.15 K

Densities (ρ), viscosities (η), and speeds of sound, (u) of the binary mixtures of 2-propanol with n-alkanes (n-hexane, n-octane, and n-decane) were measured over the entire composition range at 298.15 and 308.15 K and at atmospheric pressure. Using the experimental values of density, viscosity and speed of sound, the excess molar volumes (V ^E), viscosity deviations (Δη), deviations in speed of sound (Δu), isentropic compressibility (κ _s), deviations in isentropic compressibility (Δκ _s), and excess Gibbs energies of activation of viscous flow (ΔG* ^E) were calculated. These results were fitted to the Redlich–Kister type polynomial equation. The variations of these excess parameters with composition were discussed from the viewpoint of intermolecular interactions in these mixtures. The excess properties are found to be either positive or negative depending on the molecular interactions and the nature of liquid mixtures.     

Remarkable Effects of External Magnetic Field on Circularly Polarized Luminescence of EuIII(hfa)3 with Phosphine Chirality

Herein, magnetic circularly polarized luminescence (CPL) (MCPL) spectroscopy was conducted to analyze an Eu^III(hfa)₃ complex with three chiral P^III-ligands. Resultantly, (R)-chirality luminophores with S-up orientation and (S)-chirality luminophores with N-up orientation were observed to possess symmetrical mirror image spectra, i. e., they were enantiomers. Similarly, the (R)-chirality luminophores with N-up orientation and the (S)-chirality luminophores with S-up orientation were also enantiomers. Contrarily, (R)-S-up and (S)-S-up were diastereomers and did not possess a mirror-image relationship. Likewise, (R)-N-up and (S)-N-up were diastereomers. The J-dependency of g_MCPL and g_CPL datasets suggested that the N-up/S-up external magnetic field, with the aid of chiral P^III-ligands, increased the g_MCPL values by two- to sixteen-fold and modulated the g_MCPL signs at J=1–4. Additionally, the origins of the nonideal mirror-symmetric CPL and MCPL spectral characteristics of Eu^III(hfa)₃ with three chiral P^III-ligands were discussed in terms of parity (space-inversion, P)-symmetry, time-reversal (T)-symmetry, and PT-symmetry laws.     

Syntheses and radical polymerizations of novel optically active vinyl and isopropenyl carbamates having L-leucine structures

Syntheses and radical polymerizations of vinyl and isopropenyl carbamates having L -leucine methyl ester structures, N-vinyloxycarbonyl-L -leucine methyl ester (VOC-L-M) and N-isopropenyloxycarbonyl-L -leucine methyl ester (IOC-L-M), were carried out. VOC-L-M and IOC-L-M were prepared by the reactions of L -leucine methyl ester with vinyl and isopropenyl chloroformates in the presence of sodium hydrogen carbonate. The radical polymerization of VOC-L-M with AIBN (1 mol %) in bulk, chlorobenzene, methanol, and N,N-dimethylformamide afforded the corresponding polymer (poly(VOC-L-M)) with M _n 7,400–19,000. Meanwhile, IOC-L-M afforded no polymer with AIBN at 60°C but afforded a polymer having low molecular weight with BPO at 80°C. The glass transition temperatures of poly(VOC-L-M) and poly(IOC-L-M) were 53 and 65°C, respectively. The 10% weight loss temperatures of poly(VOC-L-M) and poly(IOC-L-M) under nitrogen were 255 and 173, respectively. The copolymerization parameters of VOC-L-M (M₁) and vinyl acetate (M₂) were evaluated as r₁ = 0.92 and r₂ = 0.63. © 1996 John Wiley & Sons, Inc.     

Effect of substitution on the reactivity of some new p-phenylacrylamide derivatives with organotin monomers

Three new monomers of p-phenylacrylamide derivatives were prepared by either the reaction of p-methyl-, p-nitro-, and p-chloroaniline with acryloyl chloride or with acrylic acid in the presence of dicyclohexyl carbodiimide (DCCI). The prepared monomers were copolymerized with each of tri-n-butyltinacrylate and tri-n-butyltinmethacrylate. Copolymerization reactions were carried out in dioxane at 70°C using 1 mol % azobisisobutyronitrile as a free radical initiator. The structure of the new monomers and the prepared copolymers were investigated by IR and ¹H-NMR spectroscopy. The monomer reactivity ratios for the copolymerization of p-chlorophenylacrylamide (M₁) with each of tri-n-butyltinacrylate (TBTA) and tri-n-butyltinmethacrylate (TBTMA) (M₂) were found to be r₁ = 2.6; r₂ = 0.83 and r₁ = 1.3; r₂ = 1.71, respectively. In case of p-tolyacrylamide (M₁) with TBTA and TBTMA (M₂) r₁ = 0.35, r₂ = 1.03 and r₁ = 1.38, r₂ = 0.366 respectively. The Q and e values for the prepared p-tolyl- and p-chlorophenylacrylamide were calculated © 1993 John Wiley & Sons, Inc.     

Herstellung enantiomerenreiner cis- oder trans-konfigurierter 2-(tert-Butyl)-3-methylimidazolidin-4-one aus den Aminosäuren (S)-Alanin, (S)-Phenylalanin, (R)-Phenylglycin, (S)-Methionin und (S)-Valin

Preparation of the Enantiomerically Pure cis- and trans-Configurated 2-(tert-Butyl)-3-methylimidazolidin-4-ones from the Amino Acids (S)-Alanine, (S)-Phenylalanine, (R)-Phenylglycine, (S)-Methionine, and (S)-Valine In contrast to α-hydroxy and α-mercapto carboxylic acids, simple α-amino acids do not form acetal-type derivatives ( 2 , X = NH) with pivalaldehyde. For the generation of amino-acid-derived chiral, nonracemic enolates (cf. 3 ), and hence, for the α-alkylation of amino acids without racemization and without an external chiral auxiliary, the imidazolidinones 12–14 were prepared diastereoselectively. To this end, the methyl or ethyl esters of amino-acid hydrochlorides were first converted to N-methylamides of amino acids which in turn were condensed with pivalaldehyde to give (neopentylidenamino)amides ( 11 ). These Schiff bases could be cyclized either to trans-or to cis-imidazolidinones ( 12, 14 and 13 , respectively), which were obtained in enantiomerically pure form after recrystallization. The enantiomeric purities were confirmed by HPLC with chiral stationary phases or by ¹H-NMR spectroscopy in the presence of chiral shift reagents. The configurations (cis, trans) were assigned by NOE measurements on 300- or 360-MHz ¹H-NMR spectrometers.     

Synthesis,structure and antimicrobial study of two new copper(II) complexes derived from N-(3-aminopropyl) benzylamine ligand (apba) and N-salicylidene-apba

Two new copper(II) complexes were synthesized by reaction of N-(3-aminopropyl)benzylamine (L1: apba, for complex 1) and N-salicylidene-apba (L2: for complex 2) with Cu²⁺. Crystals of complex 1 were orthorhombic, space group pccn, with a?=?15.2149(10), b?=?25.0071(16), c?=?7.6280(5)?Å and α?=?β?=?γ?=?90°. Complex 2 crystals were monoclinic, space group P2₁/c, with a?=?8.688(6), b?=?12.812(9), c?=?16.022(11)?Å and β?=?99.241(10)°. Structures of the two complexes were centro-symmetric and both Cu(II) atoms were four coordinate with a distorted square-planar geometry. The toxicity of the complexes was evaluated by testing antimicrobial activity against bacterial strands.     

Dihydroxyacetone Phosphate Aldolase Catalyzed Synthesis of Structurally Diverse Polyhydroxylated Pyrrolidine Derivatives and Evaluation of their Glycosidase Inhibitory Properties

The chemoenzymatic synthesis of a collection of pyrrolidine‐type iminosugars generated by the aldol addition of dihydroxyacetone phosphate (DHAP) to C‐α‐substituted N‐Cbz‐2‐aminoaldehydes derivatives, catalyzed by DHAP aldolases is reported. L ‐Fuculose‐1‐phosphate aldolase (FucA) and L ‐rhamnulose‐1‐phosphate aldolase (RhuA) from E. coli were used as biocatalysts to generate configurational diversity on the iminosugars. Alkyl linear substitutions at C‐α were well tolerated by FucA catalyst (i.e., 40–70 % conversions to aldol adduct), whereas no product was observed with C‐α‐alkyl branched substitutions, except for dimethyl and benzyl substitutions (20 %). RhuA was the most versatile biocatalyst: C‐α‐alkyl linear groups gave the highest conversions to aldol adducts (60–99 %), while the C‐α‐alkyl branched ones gave moderate to good conversions (50–80 %), with the exception of dimethyl and benzyl substituents (20 %). FucA was the most stereoselective biocatalyst (90–100 % anti (3R,4R) adduct). RhuA was highly stereoselective with (S)‐N‐Cbz‐2‐aminoaldehydes (90–100 % syn (i.e., 3R,4S) adduct), whereas those with R configuration gave mixtures of anti/syn adducts. For iPr and iBu substituents, RhuA furnished the anti adduct (i.e., FucA stereochemistry) with high stereoselectivity. Molecular models of aldol products with iPr and iBu substituents and as complexes with the RhuA active site suggest that the anti adducts could be kinetically preferred, while the syn adducts would be the equilibrium products. The polyhydroxylated pyrrolidines generated were tested as inhibitors against seven glycosidases. Among them, good inhibitors of α‐L ‐fucosidase (IC₅₀=1–20 μM ), moderate of α‐L ‐rhamnosidase (IC₅₀=7–150 μM ), and weak of α‐D ‐mannosidase (IC₅₀=80–400 μM ) were identified. The apparent inhibition constant values (K_i) were calculated for the most relevant inhibitors and computational docking studies were performed to understand both their binding capacity and the mode of interaction with the glycosidases.     

Toward uniform polymer architecture through stereospecific living polymerization and chromatographic separation technique

Isotactic (it-) and syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) were fractionated into uniform PMMAs (without molecular weight distribution) by supercritical fluid chromatography (SFC). The SFC technique was applied to the isolation of uniform it- and st-PMMAs with a hydroxy group (it- and st-PMMA-OH) at the chain end. Equimolar amounts of uniform it- and st-PMMA-OHs were coupled with sebacoyl dichloride to form uniform stereoblock PMMA. The reaction of uniform st-PMMA-OH with methacryloyl chloride gave uniform PMMA macromonomer with methacryloyl group at the chain end. The resulting uniform macromonomer was polymerized radically and the products were fractionated into uniform comblike polymers (1mer to 4mer) by means of gel-permeation chromatography (GPC). The uniform st-PMMA-OH was reacted with 1, 3, 5-benzenetricarbonyl trichloride to form uniform st-tri-armed star polymer. Some of the properties of these uniform stereoregular polymer architectures were studied.     

Synthesis and cyclopolymerization of novel allyl‐acrylate quaternary ammonium salts

Novel allyl‐acrylate quaternary ammonium salts were synthesized using two different methods. In the first (method 1), N,N‐dimethyl‐N‐2‐(ethoxycarbonyl)allyl allylammonium bromide and N,N‐dimethyl‐N‐2‐(tert‐butoxycarbonyl)allyl allylammonium bromide were formed by reacting tertiary amines with allyl bromide. The second (method 2) involved reacting N,N‐dialkyl‐N‐allylamine with either ethyl α‐chloromethyl acrylate (ECMA) or tert‐butyl α‐bromomethyl acrylate (TBBMA). The monomers obtained with the method 2 were N,N‐diethyl‐N‐2‐(ethoxycarbonyl)allyl allylammonium chloride, N,N‐diethyl‐N‐2‐(tert‐butoxycarbonyl)allyl allylammonium bromide, and N,N‐piperidyl‐N‐2‐(ethoxycarbonyl)allyl allylammonium chloride. Higher purity monomers were obtained with the method 2. Solution polymerizations with 2,2′‐azobis(2‐amidinopropane) dihydrochloride (V‐50) in water at 60–70°C gave soluble cyclopolymers which showed polyelectrolyte behavior in pure water. Intrinsic viscosities measured in 0.09M NaCl ranged from 0.45 to 2.45 dL/g. ¹H‐ and ¹³C‐NMR spectra indicated high cyclization efficiencies. The ester groups of the tert‐butyl polymer were hydrolyzed completely in acid to give a polymer with zwitterionic character. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 901–907, 1999     

Insulated Molecular Wires: Dendritic Encapsulation of Poly(triacetylene) Oligomers,Attempted Dendritic Stabilization of Novel Poly(pentaacetylene) Oligomers,and an Organometallic Approach to Dendritic Rods

Multinanometer‐long end‐capped poly(triacetylene) (PTA) and poly(pentaacetylene) (PPA) oligomers with dendritic side chains were synthesized as insulated molecular wires. PTA Oligomers with laterally appended Fréchet‐type dendrons of first to third generation were prepared by attaching the dendrons ( 8 , 13 , and 17 , respectively, Scheme 1) to (E)‐enediyne 18 by a Mitsunobu reaction and subsequent Glaser‐Hay oligomerization under end‐capping conditions (Scheme 2). Whereas first‐generation oligomers up to the pentamer were isolated ( 1a – e ), for reasons of steric overcrowding, only oligomers up to the trimer ( 2a – c ) were formed at the second‐generation level, and only the end‐capped monomer and dimer ( 3a , b ) were isolated at the third‐generation level. By repetitive sequences of hydrosilylation (with the Karstedt catalyst), followed by allylation or vinylation, a series of carbosilane dendrons were also prepared (Schemes 3 and 4). Attachment of the second‐generation wedge 40 to (E)‐enediyne 18 , followed by deprotection and subsequent end‐capping Hay oligomerization, provided PTA oligomers 4a – d with lateral carbosilane dendrons (Scheme 5). UV/VIS Studies (Figs. 5 – 10) demonstrated that the insulating dendritic layers did not alter the electronic characteristics of the PTA backbone, even at the higher‐generation levels. Despite distortion from planarity due to the bulky dendritic wedges, no loss of π‐electron conjugation along the PTA backbone was detected. A surprising (E)→(Z) isomerization of the diethynylethene (DEE) core in the third generation derivative 3a was observed, possibly photosensitized by the bulky Fréchet‐type dendritic wedge. Electrochemical investigations by steady‐state voltammetry and cyclic voltammetry showed that the first reduction potential of the PTA oligomer with Fréchet‐type dendrons is shifted to more negative values as the dendritic coverage increases. With compounds 5a – c , the first oligomers with a poly(pentaacetylene) backbone were obtained by oxidative Hay oligomerization under end‐capping conditions (Scheme 6). The synthesis of dendritic PPA oligomers by oxidative coupling of (E)‐enetetrayne 60 under end‐capping conditions provided oligomers 61a – d , which were formed as mixtures of stereoisomers due to unexpected thermal (E)→(Z) isomerization (Scheme 8). In another novel approach towards dendritic encapsulation of molecular wires with a Pt‐bridged tetraethynylethene (TEE) oligomeric backbone, the trans‐dichloroplatinum(II) complex trans‐ 67 with dendritic phosphane ligands (Fig. 14) was coupled under Hagihara conditions to mono‐deprotected 69 under formation of the extended monomer 65 (Scheme 12). Again, an unexpected thermal (E)→(Z) isomerization, possibly induced by steric strain between TEE moieties and dendritic phosphane ligands in the unstable complex, led to the isolation of 65 as an isomeric mixture only.     

Nitroxide‐mediated controlled statistical copolymerizations of N‐isopropylacrylamide with N‐tert‐butylacrylamide

The copolymerization of N‐isopropylacrylamide (NIPAM) and N‐tert‐butylacrylamide (TBAM) via conventional radical polymerization and nitroxide‐mediated polymerization (NMP) with N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)]nitroxide (SG1) was investigated. The monomer reactivity ratios were determined to be 0.58 and 1.00 for NIPAM and TBAM, respectively. The reactivities were approximately the same at 120 and 60 °C in N,N‐dimethylformamide (DMF) and toluene, respectively, for the conventional copolymerizations and in DMF at 120 °C for NMP. Controlled/living characteristics for NMP were achieved with a 2,2′‐azobisisobutyronitrile/SG1 bimolecular system and a unimolecular polystyrene [poly(STY)]–SG1 macroinitiator in the presence of excess free SG1. Block copolymers of poly(N‐isopropylacrylamide‐stat‐N‐tert‐butylacrylamide) [poly(NIPAM‐stat‐TBAM)] with styrene {poly(N‐isopropylacrylamide‐stat‐N‐tert‐butylacrylamide)‐block‐polystyrene [poly(NIPAM‐stat‐TBAM)‐block‐poly(STY)]} were obtained by chain extension of either poly(NIPAM‐stat‐TBAM)–SG1 with styrene or poly(STY)–SG1 with NIPAM/TBAM. A comparison of the number‐average molecular weight calculated from the end‐group content with the number‐average molecular weight measured by gel permeation chromatography for poly(NIPAM‐stat‐TBAM)‐block‐poly(STY)–SG1 indicated that nearly all poly(NIPAM‐stat‐TBAM) chains were capped by SG1 and were thus living. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6410–6418, 2006     

Synthesis of substituted polymethylenes by radical polymerization of N,N,N′,N′-tetraalkylfumaramides and their characterization

Radical polymerization of N,N,N′,N′-tetraalkylfumaramides (TRFAm) bearing methyl, ethyl, n-propyl, isopropyl, and isobutyl groups as N-substituents (TMFAm, TEFAm, TnPFAm, TIPFAm, and TIBFAm, respectively) was investigated. In the polymerization of TEFAm initiated with 1,1′-azobiscyclohexane-1-carbonitrile (ACN) in benzene, the polymerization rate (R_p) was expressed as follows: R_p = k [ACN]^0.28 [TEFAm]^1.26, and the overall activation energy was 102.1 kJ/mol. The introduction of a bulky alkyl group into N-substituent of TRFAm decreased the R_p in the following order: TMFAm > TEFAm > TnPFAm > TIBFAm > TIPFAm ～ 0. The relative reactivities of these monomers were also investigated in radical copolymerization with styrene (St) and methyl methacrylate (MMA). In copolymerization of TRFAm (M₂) with St (M₁), monomer reactivity ratios were determined to be r₁ = 1.07 and r₂ = 0.20 for St–TMFAm, and r₁ = 1.88 and r₂ = 0.11 for St–TEFAm, from which Q₂ and e₂ values were estimated to be 0.35 and 0.44 for TMFAm, and 0.19 and 0.47 for TEFAm, respectively. The other TRFAm were also copolymerized with St, but copolymerization with MMA gave polymers containing a small amount of TRFAm units. The polymer from TRFAm consists of a less-flexible poly(N,N-dialkylaminocarbonylmethylene) structure. The solubility and thermal property of the polymers were also investigated.     

Synthesis and Structure of Linear and Cyclic Oligomers of 3-Hydroxybutanoic Acid with Specific Sequences of (R)- and (S)-Configurations

To study the stereoselectivity of enzymatic cleavage of poly(3-hydroxybutyrates) (PHB) in a well-defined system (purified depolymerase and monodisperse substrate of specific relative configuration), linear and cyclic oligomers of HB (OHBs) containing (R)- and (S)-3-hydroxybutanoate residues were synthesized. The starting material (R)-HB was prepared from natural sPHB, and (S)-HB by enantioselective reduction of 3-oxobutanoate with yeast or with H₂/Noyori-Taber catalyst (Scheme 2). The HB building blocks were then protected (O-benzyl/tert-butyl ester; Scheme 3) and coupled to give dimers 3 , 4 , tetramers 5 – 9 , and octamers 10 – 18 ; for analytical comparison, a 3mer, 5mer, 6mer, and 7mer ( 19 – 22 ) were also prepared. Two of the tetramers were subjected to macrolactonization conditions (Yamaguchi) to give the cyclic tetramers 23 and 25 and octamers 24 and 26 . All new compounds were fully characterized (m.p., [α]_D, CD, IR, ¹H- and ¹³C-NMR, MS, elemental analysis). Single-crystal X-ray structure analyses were performed with oligolides 24 and 25 (Figs. 2 and 4), and the structures, as well as the crystal packing, were compared with those of analogs containing only (R)-HB units or consisting of 3-amino- instead of 3-hydroxybutanoic-acid moieties.     

Surface plasmon resonance study on binding interactions of multivalent cyclophane hosts with immobilized guests

Guest‐binding affinities of water‐soluble cyclophane heptadecamer (1) and pentamer (2) with immobilized guests such as 1‐pyrenylmethylamine (PMA) and 2‐(1‐ naphthyl)ethylamine (NEA) were investigated by surface plasmon resonance (SPR) measurements. As a typical example, the binding constants (K) for 1 and 2 with the immobilized PMA as a guest were evaluated to be 2.5 × 10⁷ and 2.7 × 10⁶ M^?1, respectively, and were much larger than that of a monocyclic reference cyclophane (K, 2.5 × 10⁴ M^?1). Interestingly, in the complexation of 1 and 2 with the immobilized guests, more favorable association and dissociation rate constant values (k_a and k_d, respectively) were observed in comparison with those for the monocyclic cyclophane, reflecting multivalent effects in macrocycles. The multivalent effects in macrocycles as well as molecular recognition abilities of the cyclophane oligomers were confirmed even when the guest molecules were immobilized on SPR sensor chip surfaces. Copyright © 2009 John Wiley & Sons, Ltd.     

m‐Methoxy Substituents in a Tetraphenylethylene‐Based Hole‐Transport Material for Efficient Perovskite Solar Cells

Three tetrapheynlethylene derivatives (N,N‐di(4‐methoxyphenyl)aminophenyl‐substituted tetraphenylethylene; TPE‐4DPA) with different methoxy positions (pp‐, pm‐, and po‐) have been synthesized and characterized. The methoxy groups can control the oxidation potential of the materials, and the electronic properties of the derivatives were affected by the position of the methoxy substituents. These compounds were synthesized in a facile and cost‐effective way, and were applied as hole‐transport materials in perovskite solar cells. The corresponding cell performances were compared with respect to their structure modifications, and it was found that the derivative with m‐OMe substituents showed the highest power conversion efficiency (PCE) of 15.4 %, with a J_sc value of 20.04 mA cm^?2, a V_oc value of 1.07 V, and a fill factor (FF) value of 0.72, which is higher than the p‐OMe and o‐OMe substituents. Moreover, the PCE of pm‐TPE‐4DPA is comparable with that of the state‐of‐the‐art 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene under identical conditions.     

Carbocyclische Verbindungen aus Monosacchariden. I. Umsetzungen in der glucosereihe

Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose Series A method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23 , see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5-enoses (such as 11 and 24 , see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N-methyl- or N-(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano-isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano-isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62 . The configuration of the cyclization products were established by pyrolysis of the N-oxide 65 to the enol ether 67 (Scheme 10).     

邻-甲氧基苯酚和α-,β-环糊精包合现象的理论与实验研究

通过紫外可见光谱法考察了水溶液中邻-甲氧基苯酚(o-Mop)和α-与β-环糊精(CD)的分子间相互作用, 利用Hildebrand-Benesi方程给出了两个包合物的稳定常数(K_s). 采用半经验PM3方法研究了α-,β-CD和o-Mop及其类似物苯酚(Phe)、丁香酚(Eug)之间的包络作用, 阐述了这些主客体包合作用过程中体系能量随主客体相对位置改变而变化的细节, 据此推断出主-客体包合物可能的分子结构, 计算了包合物的稳定化能(ΔE_s). 研究结果表明, 本文所选主客体体系而言, 当客体和同一种主体分子作用时, 超分子包合物的ΔE_s随着客体分子苯环上取代基团数目的增多而增加. 基于PM3方法优化得到的主-客体包合物在真空中的分子结构和通过实验方法在水溶液中测定的结构一致.     

Chiral Heterospirocyclic 2H‐Azirin‐3‐amines as Synthons for 3‐Amino‐2,3,4,5‐tetrahydrofuran‐3‐carboxylic Acid and Their Use in Peptide Synthesis

The heterospirocyclic N‐methyl‐N‐phenyl‐5‐oxa‐1‐azaspiro[2.4]hept‐1‐e n‐2‐amine (6 ) and N‐(5‐oxa‐1‐azaspiro[2.4]hept‐1‐en‐2‐yl)‐(S)‐proline methyl ester ( 7 ) were synthesized from the corresponding heterocyclic thiocarboxamides 12 and 10 , respectively, by consecutive treatment with COCl₂, 1,4‐diazabicyclo[2.2.2]octane, and NaN₃ (Schemes 1 and 2). The reaction of these 2H‐azirin‐3‐amines with thiobenzoic and benzoic acid gave the racemic benzamides 13 and 14 , and the diastereoisomeric mixtures of the N‐benzoyl dipeptides 15 and 16 , respectively (Scheme 3). The latter were separated chromatographically. The configurations and solid‐state conformations of all six benzamides were determined by X‐ray crystallography. With the aim of examining the use of the new synthons in peptide synthesis, the reactions of 7 with Z‐Leu‐Aib‐OH to yield a tetrapeptide 17 (Scheme 4), and of 6 with Z‐Ala‐OH to give a dipeptide 18 (Scheme 5) were performed. The resulting diastereoisomers were separated by means of MPLC or HPLC. NMR Studies of the solvent dependence of the chemical shifts of the NH resonances indicate the presence of an intramolecular H‐bond in 17 . The dipeptides (S,R)‐ 18 and (S,S)‐ 18 were deprotected at the N‐terminus and were converted to the crystalline derivatives (S,R)‐ 19 and (S,S)‐ 19 , respectively, by reaction with 4‐bromobenzoyl chloride (Scheme 5). Selective hydrolysis of (S,R)‐ 18 and (S,S)‐ 18 gave the dipeptide acids (R,S)‐ 20 and (S,S)‐ 20 , respectively. Coupling of a diastereoisomeric mixture of 20 with H‐Phe‐O^tBu led to the tripeptides 21 (Scheme 5). X‐Ray crystal‐structure determinations of (S,R)‐ 19 and (S,S)‐ 19 allowed the determination of the absolute configurations of all diastereoisomers isolated in this series.     

Hydroxy-terminated poly(ε-caprolactone-co-δ-valerolactone) oligomers: Synthesis,characterization, and polyurethane network formation

Difunctional hydroxy-terminated poly(ε-caprolactone-co-ε-valerolactone) (PCV) oligomers were synthesized by the diol-initiated bulk copolymerization of ε-caprolactone (C) and δ-valerolactone (V). The two homopolymers were semicrystalline, with almost identical melting temperatures; copolymerization significantly lowered the melting point (T_m) compared to either homopolymer. Copolymer melting points were found to decrease with decreasing molecular weight and to be dependent on composition, i.e., the incorporation of a comonomer into either homopolymer resulted in a decrease in T_m, with the maximum decrease occurring at a copolymer composition of about 60 mol % ε-caprolactone. The molar compositions of the copolyesters were determined from ¹³C-NMR spectra. The reactivity ratios of the two monomers (M₁ = C, M₂ = V) were determined to the r₁ = 0.25 and r₂ = 0.49. Number average molecular weight (M?_n) of the PCV diols was inversely proportional to the initial diol concentration within the studied molecular weight range of 900 to 11,100 g/mol. Crosslinked polyurethane networks were prepared by reacting PCV diols with triphenylmethane triisocyanate. Network characterization included determination of sol content by solvent extraction, glass transition (T_g) and T_m by DSC, and tensile properties by stress-strain measurements. Completely amorphous networks resulted from PCV diols of M?_n ≤ 2,400; semicrystalline networks resulted from PCV diols of M?_n ≥ 3,600.     

Synthesis and properties of liquid crystalline polyurethanes

1,4-Bis(p-hydroxybenzoate)phenylene was prepared using 1,4-bis(trimethylsiloxy)benzene and p-hydroxybenzoyl chloride as starting materials. A series of novel 1,4-bis(p-hydroxyalkoxybenzoate)phenylene were synthesized by reaction of 1,4-bis(p-hydroxybenzoate) phenylene with 3-brompropanol and 4-bromobutanol, respectively. The liquid crystal polyurethanes were prepared by 1,4-bis(p-hydroxyalkoxybenzoate)phenylene with MDI (p-methylene diphenylenediisocyanate) and 2,4-TDI(2,4-toluenediisocyanate), respectively. The thermotropic properties, the melting point (T _m) and the isotropization temperature (T _i) of the synthesized polyurethanes were characterized by DSC, IR and POM. It showed that all of the polyurethane polymers exhibited thermotropic liquid crystalline properties between 144°C and 260°C. The transition temperature (T _m and T _i) decreased with an increase in the length of the methylene spacer. __________ Translated from Journal of Qingdao University of Science and Technology, 2006, 27(1) (in Chinese)