农业供应链金融能有效缓解企业的融资约束？——涉农企业参与精准扶贫的实证研究

农业供应链金融为涉农企业融资难问题提供了新思路。本文以上市涉农上市企业2016~2018年的财务数据为样本,探讨了农业供应链金融对缓解企业融资约束的影响,以及涉农企业参与精准扶贫对缓解融资约束的调节作用。研究发现:涉农企业普遍面临融资约束问题,而农业供应链金融显著缓解了涉农企业的融资约束,且对参与精准扶贫企业的融资约束缓解更为显著。本文揭示了:农业供应链金融能有效缓解涉农企业的融资约束问题,再次证明了农业供应链金融缓解涉农企业融资约束的重要性和必要性,拓展了供应链金融研究的领域,同时对企业参与精准扶贫,响应新时期涉农企业社会责任的具体要求,形成政府、企业等共同承担社会责任的多元化减贫治理机制,助力乡村振兴提供相应借鉴。     

Ground-state energy of a quantum chain with competing interactions

We show rigorously that the ground state of a quantum chain with competing ferromagnetic nearest and antiferromagnetic next nearest interactions undergoes a transition from ferromagnetic to helical type, in the isotropic case, for a certain value of the relevant ratio of coupling constants. Boundaries of the phase diagram are also determined in the anisotropic case. The stability of a special quantum state (corresponding to a classical modulated phase of =/3) is analyzed by an extension of Holstein-Primakoff arguments, along a line of constant ratio of couplings, showing in particular a sequence of (instability) gaps. Finally, a natural adaptation of a variational wave function due to Huse and Elser is used to study several portions of the phase diagram, with very good agreement with previous theoretical results.     

ISOLATION,CHARACTERIZATION AND EXPRESSION OF THE COMPLEMENTARY DNA FOR HUMAN TUMOR NECROSIS FACTOR (TNF-α)

A cDNA for human TNF-α (615bp) was isolated by means of polymerase chain reaction (PCR) using first strand cDNA from PMA-induced HL-60 cells as template. The result from sequencing the 615 bp cDNA fragment indicated that it corresponded to the entire sequence of mature human TNF coding region. Direct expression of mature human TNF was achieved using a plasmid pHT-1 constructed by ligation of the cDNA and a synthetic DNA. The IPTG-induced bacterial product (hTNF) showed cytotoxicity to mouse L-929 cells. The TNF activity was further identified by neutralization of a specific monoclonal antibody against human TNF-α. Approximately 80,000 units of activity were detected per ml of culture at A600=2.     

Designed Syntheses of Three {Ni6PW9}-Based Polyoxometalates,from Isolated Cluster to Cluster-Organic Helical Chain

Three new hexa-Ni-substituted Keggin-type polyoxometalates (POMs), [Ni₆(OH)₃- (DACH)₃(H₂O)₆(PW₉O₃₄)]·31H₂O (1), [Ni(DACH)₂][Ni₆(OH)₃(DACH)₃(HMIP)₂(H₂O)₂(PW₉O₃₄)]·56 H₂O (2), and [Ni(DACH)₂][Ni₆(OH)₃(DACH)₂(AP)(H₂O)₅(PW₉O₃₄)]·2H₂O (3) (DACH = 1,2-Diami- nocyclohexane, MIP = 5-Methylisophthalate, AP = Adipate) were successfully made in the presence of DACH under hydrothermal conditions. 1 is an isolated hexa-Ni-substituted Keggin unit decorated by DACH. In order to further construct POM cluster-organic frameworks (POMCOFs) on the basis of 1, by analyzing the steric hindrances and orientations of the POM units, the rigid HMIP and flexible AP ligands were successively incorporated, and another anionic monomeric POM 2 and the new 1D POM cluster organic chain (POMCOC) 3 were obtained. HMIP ligand still acts as a decorating group on the Ni₆ core of 2 but results in the different spatial arrangement of the {Ni₆PW₉} units. AP ligands in 3 successfully bridge adjacent isolated POM cluster units to 1D POMCOC with left-hand helices. The AP in 3 is the longest aliphatic carboxylic acid ligand in POMs, and the 1D POM cluster-AP helical chain represents the first 1D POMCOC with a helical feature.     

Influence of Aliphatic Chain Length on Structural,Thermal and Electrochemical Properties of n-alkylene Benzyl Alcohols: A Study of the Odd–Even Effect

The century-old, well-known odd–even effect phenomenon is still a very attractive and intriguing topic in supramolecular and nano-scale organic chemistry. As a part of our continuous efforts in the study of supramolecular chemistry, we have prepared three novel aromatic alcohols (1,2-bis[2-(hydroxymethyl)phenoxy]butylene (Do4OH), 1,2-bis[2-(hydroxymethyl)phenoxy]pentylene (Do5OH) and 1,2-bis[2-(hydroxymethyl)phenoxy]hexylene (Do6OH)) and determined their crystal and molecular structures by single-crystal X-ray diffraction. In all compounds, two benzyl alcohol groups are linked by an aliphatic chain of different lengths (CH₂)_n; n = 4, 5 and 6. The major differences in the molecular structures were found in the overall planarity of the molecules and the conformation of the aliphatic chain. Molecules with an even number of CH₂ groups tend to be planar with an all-trans conformation of the aliphatic chain, while the odd-numbered molecule is non-planar, with partial gauche conformation. A direct consequence of these structural differences is visible in the melting points—odd-numbered compounds of a particular series display systematically lower melting points. Crystal and molecular structures were additionally studied by the theoretical calculations and the melting points were correlated with packing density and the number of CH₂ groups. The results have shown that the generally accepted rule, higher density = higher stability = higher melting point, could not be applied to these compounds. It was found that the denser packaging causes an increase in the percentage of repulsive H‧‧‧H interactions, thereby reducing the stability of the crystal, and consequently, the melting points. Another interesting consequence of different molecular structures is their electrochemical and antioxidative properties—a non-planar structure displays the highest oxidation peak of hydroxyl groups and moderate antioxidant activity.     

Synthesis of well‐defined side chain fullerene polymers and study of their self‐aggregation behaviors

Monoalkynyl‐functionalized fullerene was precisely synthesized starting with pristine fullerene (C₆₀) and characterized by multiple techniques. Methyl methacrylate and 6‐azido hexyl methacrylate were then randomly copolymerized via reversible addition fragmentation chain transfer polymerization to build polymer backbones with well‐controlled molecular weights and copolymer compositions. Finally, these two moieties were covalently assembled into a series of well‐defined side chain fullerene polymers (SFPs) via the copper‐mediated click reaction which was verified by Fourier transform infrared spectroscopy and ¹H NMR. The fullerene loadings of the resultant polymers were estimated by thermogravimetric analysis and UV–vis spectroscopy, demonstrating consistent and high conversions in most of the samples. The morphology studies of the SFPs were performed both in solution and on solid substrates. Very intriguing self‐aggregation behaviors were detected by both gel permeation chromatography and dynamic light scattering analyses. Furthermore, the scanning electron microscopic images of these polymers showed the formation of various supramolecular nanoparticle assemblies and crystalline‐like clusters depending on the fullerene contents and polymer chain lengths. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3572–3582     

Twin liquid crystals and segmented thermotropic polyesters containing azobenzene—effect of spacer length on LC properties

We report systematic studies on a homologous series of twin liquid crystalline (LC) molecules based on phenyl and naphthyl azobenzene ( PnP and NpnNp ) as well as segmented copolyesters based on them. The twin series had the structure azobenzene–oligooxyethylene–azobenzene, where the ethyleneoxy length was varied from 2 to 6 units. The LC properties of the twin series depended on the chemical structure of the azochromophore and also the length of the central oligooxyethylene segment. The PnP series exhibited smectic LC properties for n > three oligooxyethylene units. Conversely, NpnNp series exhibited spherulitic phases only for the shortest member – Np2Np . One non‐LC short spacer twin ( P2P ) and one LC long spacer twin ( P6P ) were incorporated as part of a main chain polyester composed of fully aliphatic segments of sebacate and di or tetraethylene glycol (DEG/TEG) units by melt polycondensation. Non‐LC P2P formed LC polymers even at low (5 mol %) incorporation in DEG‐based copolymers, whereas the LC‐ P6P could do so only at 30 mol % incorporation. The LC properties of the twin molecules as well as copolymers were studied using differential scanning calorimetry, polarized light microscopy (PLM) along with variable temperature wide angle X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tuning the sugar‐response of boronic acid block copolymers

A detailed study of the pH‐ and sugar‐responsive behavior of poly(3‐acrylamidophenylboronic acid pinacol ester)‐b‐poly(N,N‐dimethylacrylamide) (PAPBAE‐b‐PDMA) block copolymers is presented. Reversible addition‐fragmentation chain transfer (RAFT) polymerization of the pinacol ester of 3‐acrylamidophenylboronic acid resulted in homopolymers with molecular weights between 12,000 and 37,000 g/mol. The resulting homopolymers were employed as macro‐chain transfer agents during the polymerization of N,N‐dimethylacrylamide (DMA). Successful chain extension and removal of the pinacol protecting groups to yield poly(3‐acrylamidophenylboronic acid)‐b‐PDMA (PAPBA‐b‐PDMA) with free boronic acid moieties resulted in pH‐ and sugar‐responsive block copolymers that were subsequently investigated for their behavior in aqueous solution. The PAPBA‐b‐PDMA block copolymers were capable of solution self‐assembly due to the PAPBA block being water‐insoluble below its pK_a. The resulting aggregates were demonstrated to solubilize and release model hydrophobic compounds, as demonstrated by fluorescence studies. Dissociation of the aggregates was induced by raising the pH above the pK_a of the boronic acid residues or by adding sugars capable of forming boronate esters. Aggregate size, dissociation kinetics, and the effect of various sugars were considered. The critical sugar concentration needed to induce aggregate dissociation was tuned by incorporation of hydrophilic DMA units within the PAPBA responsive segment to yield PDMA‐b‐poly(3‐acrylamidophenylboronic acid‐co‐DMA) block copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Single‐pulse pulsed laser polymerization–electron paramagnetic resonance investigations into the termination kinetics of n‐butyl acrylate macromonomers

The termination of model mid‐chain radicals (MCRs), which mimic radicals that occur in acrylate polymerization over a broad range of reaction conditions, has been studied by single‐pulse pulsed laser polymerization (SP‐PLP) in conjunction with electron paramagnetic resonance spectroscopy. The model radicals were generated by initiator‐fragment addition to acrylic macromonomers that were preformed prior to the kinetic experiments, thus enabling separation of termination from the propagation reaction, for these model radicals propagate sparingly, if at all, on the timescale of SP‐PLP experiments. Termination rate coefficients of the MCRs were determined in the temperature range of 0–60°C in acetonitrile and butyl propionate solution as well as in bulk macromonomer over the range of 0–100 °C. Termination rate coefficients slightly below those of the corresponding secondary radicals were deduced, demonstrating the relatively high termination activity of this species, even when undergoing MCR–MCR termination. For chain length of 10, a reduction by a factor of 6 is observed. Unusually high activation energies were found for the termination rate coefficient in these systems, with 35 kJ mol^?1 being determined for bulk macromonomer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012