带有端烷烃链的超支化聚酯的受限结晶及动态黏弹行为

以三羟甲基丙烷(TMP)为核,二羟甲基丙酸(DMPA)为支化单体,通过熔融缩聚法合成了第3代端羟基脂肪族超支化聚酯,并用十八酸对其进行端基改性,采用广角X射线衍射(WAXD)、示差扫描量热分析(DSC)及红外光谱(FTIR)研究了不同端基改性程度的超支化聚酯的结晶熔融行为及端烷烃链的构象和堆积结构随温度的变化,采用旋转流变仪研究了端烷烃链对脂肪族超支化聚酯熔体动态黏弹行为的影响.结果表明,这类改性超支化聚酯的结晶归因于长链端烷烃的有序排列,改性程度越高,衍射峰强度越大.受限结晶的端烷烃链在升温后并不能完全转变为无序的结构状态,改性超支化聚酯在"熔点"以上仍有部分有序结构存在.超支化聚酯的线性黏弹区随着端基改性程度的增大而逐渐变短,超支化聚酯的弹性逐渐增大,剪切变稀越明显.动态流变测试中所出现的现象与改性超支化聚酯中端烷烃链的受限密切相关.     

Maleimidophenyl isocyanates as postpolymerization modification agents and their applications in the synthesis of block copolymers

The maleimide structure is highly reactive, exemplified by thiol–ene click reactions with thiols and Diels–Alder reactions with furans. Although postpolymerization modifications and macromolecular conjugations involving maleimide units have been widely studied, mostly due to their selectivity and high reactivity, little has been reported on the one‐pot postpolymerization introduction of maleimides in polymer chains. Herein, we report p‐maleimidophenyl isocyanate and its derivatives as modification agents to introduce maleimide moieties by reaction with hydroxy groups into polymer chains. The high reactivity of the resulting modification agents and of the corresponding maleimide structures once inserted in the polymer chains was examined by studying their reaction kinetics. Furthermore, these modification agents were successfully applied to the synthesis of macromonomers for graft polymerization and various block copolymers, with, for example, AB‐type, star‐shaped, and H‐shaped architectures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2396–2406     

Effect of Side Chain Substituent Volume on Thermoelectric Properties of IDT-Based Conjugated Polymers

A p-type thermoelectric conjugated polymer based on indacenodithiophene and benzothiadiazole is designed and synthesized by replacing normal aliphatic side chains (P1) with conjugated aromatic benzene substituents (P2). The introduced bulky substituent on P2 is detrimental to form the intensified packing of polymers, therefore, it hinders the efficient transporting of the charge carriers, eventually resulting in a lower conductivity compared to that of the polymers bearing aliphatic side chains (P1). These results reveal that the modification of side chains on conjugated polymers is crucial to rationally designed thermoelectric polymers with high performance.     

Dissecting Ubiquitin Signaling with Linkage‐Defined and Protease Resistant Ubiquitin Chains

Ubiquitylation is a complex posttranslational protein modification and deregulation of this pathway has been associated with different human disorders. Ubiquitylation comes in different flavors: Besides mono‐ubiquitylation, ubiquitin chains of various topologies are formed on substrate proteins. The fate of ubiquitylated proteins is determined by the linkage‐type of the attached ubiquitin chains, however, the underlying mechanism is poorly characterized. Herein, we describe a new method based on codon expansion and click‐chemistry‐based polymerization to generate linkage‐defined ubiquitin chains that are resistant to ubiquitin‐specific proteases and adopt native‐like functions. The potential of these artificial chains for analyzing ubiquitin signaling is demonstrated by linkage‐specific effects on cell‐cycle progression.     

DNA‐Catalyzed Lysine Side Chain Modification

Catalyzing the covalent modification of aliphatic amino groups, such as the lysine (Lys) side chain, by nucleic acids has been challenging to achieve. Such catalysis will be valuable, for example, for the practical preparation of Lys‐modified proteins. We previously reported the DNA‐catalyzed modification of the tyrosine and serine hydroxy side chains, but Lys modification has been elusive. Herein, we show that increasing the reactivity of the electrophilic reaction partner by using 5′‐phosphorimidazolide (5′‐Imp) rather than 5′‐triphosphate (5′‐ppp) enables the DNA‐catalyzed modification of Lys in a DNA‐anchored peptide substrate. The DNA‐catalyzed reaction of Lys with 5′‐Imp is observed in an architecture in which the nucleophile and electrophile are not preorganized. In contrast, previous efforts showed that catalysis was not observed when Lys and 5′‐ppp were used in a preorganized arrangement. Therefore, substrate reactivity is more important than preorganization in this context. These findings will assist ongoing efforts to identify DNA catalysts for reactions of protein substrates at lysine side chains.     

Synthesis and oxygenation of selenophosphate dendrimers

The backbone of a selenophosphate-based dendrimer of generation 3 having three and four carbon chains is flexible enough to allow its chemical modification by means of partial or complete oxygenation with bulky peroxide.     

聚芴类电致发光材料

聚芴与其衍生物是一类重要的电致发光聚合物,它们具有较高的光致发光效率,并且易于进行结构修饰,因此受到材料化学家们的高度关注。本文叙述的线索是聚合物结构与其电致发光性能之间的构效关系。通过化学修饰,可以调节材料的前线分子轨道、热和光谱稳定性,进而开发新的发光材料。文中首先简单介绍了聚芴类发光材料的聚合方法,然后把这些聚合物按结构不同分成两个部分介绍：一部分是主链仅含有共轭芴单元的聚合物,它们的化学修饰依赖于芴9位的活性碳原子;另一部分是通过共聚方法得到的主链含有芴和其它基团的聚合物。     

Catalytic protein modification with dirhodium metallopeptides: specificity in designed and natural systems

In this study, we present advances in the use of rhodium(II) metallopeptides for protein modification. Site-specific, proximity-driven modification is enabled by the unique combination of peptide-based molecular recognition and a rhodium catalyst capable of modifying a wide range of amino-acid side chains. We explore catalysis based on coiled-coil recognition in detail, providing an understanding of the determinants of specificity and culminating in the demonstration of orthogonal modification of separate proteins in cell lysate. In addition, the concepts of proximity-driven catalysis are extended to include modification of the natural Fyn SH3 domain with metallopeptides based on a known proline-rich peptide ligand. The development of orthogonal catalyst-substrate pairs for modification in lysate, and the extension of these methods to new natural protein domains, highlight the capabilities for new reaction design possible in chemical approaches to site-specific protein modification.     

Orientation control of ferroelectric polymer molecules using contact-mode AFM

We have developed an orientation control technique for polymer molecules utilizing contact-mode atomic force microscopy (AFM). In this technique, the molecular chains were directly modified by scanning an AFM cantilever tip in contact with the film surface at the temperature just below its melting point. We call this process “modification scan”. Here, we applied this technique to poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) thin films on graphite and glass. We prepared a 75-nm thick copolymer crystalline film on graphite whose lamellar plane was perpendicular to the substrate (edge-on), and also prepared a film of the same thickness on glass whose lamellar plane was parallel to the substrate (flat-on). After applying this technique on both films, molecular chains were stretched and aligned to the modification scan direction, and new edge-on crystals were obtained, whose lamellar planes were well-aligned perpendicular to the modification scan direction.     

The molecular origin of lamellar branching in the α (monoclinic) form of isotactic polypropylene

The specific lamellar branching characteristic of isotactic polypropylene (iPP) in its α monoclinic modification, first investigated in detail by Khoury, is analyzed in molecular terms on the basis of the geometrical and structural models of Padden and Keith and of Binsbergen and de Lange, respectively. As suggested by these authors the branching corresponds, structurally, to an homoepitaxy of the daughter lamellae on the lateral (010) faces of the parent lamellae; the epitaxy is favored by a satisfactory interdigitation of the molecular subgroups (methyl side chains) of facing planes and by the near identity of a and c parameters of the α monoclinic unit cell of iPP. On a molecular basis, the branching is initiated on a lateral (010) face made up of chains of a given hand by the deposition of chains of the same hand, whereas the crystal structure of the α modification would call for chains of opposite hand. Favorable interactions of side chains of helices of the same hand is realized only when the helix axes are at a substantial angle (in the present case, 100°) to one another. Related behavior is observed for the packing of α helices in the structure of globular proteins, in which molecular interactions, but no crystallographic interactions, are involved. On the basis of this molecular picture, the widespread occurrence of lamellar branching in the crystallization of the α form of isotactic polypropylene is accounted for, especially for high growth rates. At the same time, the specificity of the branching (only observed for the α crystal modification of this polymer) is explained by stringent geometrical and structural requirements that must be fulfilled at the contact plane.     

聚合物-锂改性蒙脱石复合材料离子迁移

以聚合物（ＰＥＯ,ＰＥＯ－ＰＭＭＡ）和锂改性蒙脱石作为主要原料,采用聚合物粉末直接熔融嵌入的方法,制备聚合物－蒙脱石复合材料．利用ＮＭＲ、ＡＣ阻抗等分析方法探讨了复合材料中聚合物链对 Ｌｉ＋离子迁移的影响．结果表明,聚合物（ＰＥＯ）嵌入蒙脱石层间,层间聚合物链的无序度增大,有利于Ｌｉ＋离子迁移．ＰＭＭＡ引入对ＰＥＯ链的改性,进一步加大聚合物链的无序度,更易于层间Ｌｉ＋离子迁移;复合材料的常温离子电导率接近１０－２Ｓ·ｃｍ－１,且具有良好的温度稳定性．     

Integrated surface modification of fully polymeric microfluidic devices using living radical photopolymerization chemistry

Surface modification using living radical polymerization (LRP) chemistry is a powerful technique for surface modification of polymeric substrates. This research demonstrates the ability to use LRP as a polymer substrate surface‐modification platform for covalently grafting polymer chains in a spatially and temporally controlled fashion. Specifically, dithiocarbamate functionalities are introduced onto polymer surfaces using tetraethylthiuram disulfide. This technique enables integration of LRP‐based grafting for the development of an integrated, covalent surface‐modification method for microfluidic device construction. The unique photolithographic method enables construction of devices that are not substrate‐limited. To demonstrate the utility of this approach, both controlled fluid flow and cell patterning applications were demonstrated upon modification with various chemical functionalities. Specifically, poly(ethylene glycol) (375) monoacrylate and trifluoroethyl acrylate were grafted to control fluidic flow on a microfluidic device. Before patterning, surface‐functionalized samples were characterized with both goniometric and infrared spectroscopy to ensure that photografting was occurring through pendant dithiocarbamate functionalities. Near‐infrared results demonstrated conversion of grafted monomers when dithiocarbamate‐functionalized surfaces were used, as compared to dormant control surfaces. Furthermore, attenuated total reflectance/infrared spectroscopy results verified the presence of dithiocarbamate functionalities on the substrate surfaces, which were useful in grafting chains of various functionalities whose contact angles ranged from 7 to 86°. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1404–1413, 2006     

糖类相关基因芯片的设计与制备

随着糖组学的发展,研究表明某些疾病如肿瘤等的发生伴随着体内糖蛋白表面糖链结构的变化,而糖链结构的形成与修饰经过糖基转移酶、糖苷酶和磺基转移酶的参与.本研究从Genebank等数据库中选取人类糖基转移酶基因127条、糖苷酶基因34条和磺基转移酶34条以及管家基因10条.通过对每个基因的mRNA序列进行探针设计,制备出一款糖类相关基因芯片,用于研究糖类相关基因的表达谱,旨在揭示疾病发生与糖类相关基因表达变化的关联性.制备的芯片应用于人肝癌细胞系SMMC-7721与正常肝细胞系Chang’s liver的研究,筛选出差异表达的基因34个,其中上调基因19个、下调基因15个.通过对2个上调基因和2个下调基因进行Realtime-PCR验证,得到了一致的实验结果.     

Density functional approach to adsorption of simple fluids on surfaces modified with a brush-like chain structure

A density functional theory to describe adsorption of a simple fluid from a gas phase on a surface modified with pre-adsorbed chains is proposed. The chains are bonded to the surface by one of their ends, so they can form a brush-like structure. Two models are investigated. According to the first model all but the terminating segment of a chain can change the configuration during the adsorption of fluid species. The second model assumes that the chains remain "frozen", and the system is considered as a nonuniform quenched-annealed mixture. We apply simple form of interactions to study adsorption phenomena, microscopic structure, and layering transitions. Our principal findings show that new layering phase transitions can occur because of a chemical modification of the substrate under certain conditions, in comparison with nonmodified surfaces. However, opposite trends, that is, smoothing the adsorption isotherms, can also be observed, depending on the surface density of the grafted chains.     

Characterization of maleuric acid derivatives on transgenic human monoclonal antibody due to post-secretional modifications in goat milk

A fully human antibody to tumor necrosis factor-alpha was expressed in the mammary glands of transgenic goats. The goat expressed antibody (gAb) is heterogeneous and has several isoforms due to typical cellular post-translational modifications. In addition, one post-secretional modification on gAb was discovered by high-resolution cation exchange chromatography (CIEX). The presence of these variants in the final product was shown to be dependent upon the initial milk storage and traditional purification methodologies used. These observations allow for the development of new sample recovery and purification processes to eliminate these variants. Various enzymatic treatments were used to characterize different gAb heavy chain C-terminal lysine and sialic acid variants. In addition, an unknown derivative with the additional mass of 140 Da was found in transgenic gAb using mass spectrometry (MS). The modification sites were identified as the N-termini of gAb light chains and heavy chains using Q-TOF MS. Characterization of transgenic gAb isoforms was facilitated by utilizing different enzymes, CIEX and MS techniques. A maleuric acid modification on the N-terminal portion of gAb was shown to be consistent with the available data characterizing this new derivative of transgenic gAb isoforms in goat milk.     

Modification of ethylene-propylene-diene elastomers to improve the ozone resistance of their covulcanizates with butadiene-nitrile rubbers

The modification of ethylene-propylene-diene elastomers via the addition of fragments of an accelerating agent or chlorine atoms to improve their compatibility with butadiene-nitrile rubbers and to reduce the rate of ozone degradation of the polydiene matrix is efficient only in the case of low stereoregularity of propylene units in the ethylene-propylene-diene copolymers when the crosslinking system is added to butadiene-nitrile rubber. When the isotacticity of propylene fragments in the chains of ethylene-propylene-diene elastomers is high, their modification leads to a reduction in the ozone resistance of the crosslinked blend independently of the mode of introduction of the crosslinking system.     

The Length of a Ubiquitin Chain: A General Factor for Selective Recognition by Ubiquitin‐Binding Proteins

The attachment of ubiquitin (Ub) chains of various length to proteins is a prevalent posttranslational modification in eukaryotes. The fate of a modified protein is determined by Ub‐binding proteins (UBPs), which interact with Ub chains in a linkage‐selective manner. However, the impact and functional consequences of chain length on the binding selectivity of UBPs remain mostly elusive. We have generated Ub chains of defined length and linkage by using click chemistry and GELFrEE fractionation. These defined polymers were used in affinity‐based enrichment assays to identify length‐ and linkage‐selective interaction partners on a proteome‐wide scale. For the first time, it is revealed that the length of a Ub chain generally has a major impact on its ability to be selectively recognized by UBPs.     

Covalent attachment of alkene and alkyne groups on carbon surfaces by electrochemical oxidation of unsaturated aliphatic carboxylates

The covalent modification of glassy carbon electrodes by oxidation of unsaturated aliphatic carboxylates is reported in this work. It is shown that the presence of π-bonds on the hydrocarbon structure is essential to develop the grafting process, which does not occurs with totally saturated carboxylates. In this way, the glassy carbon surface modification with aliphatic chains containing alkene and alkyne groups was performed and the presence of such groups was demonstrated through a Heck and a Click reaction, allowing respectively a further functionalization with nitrobenzene and ferrocene groups.     

Synthesis and functionalization of a highly fluorescent and completely water-soluble poly(para-phenyleneethynylene) copolymer for bioconjugation

Bioconjugation of a highly fluorescent water-soluble poly(para-phenyleneethynylene) (PPE) copolymer with ionic and non-ionic side chains is achieved by means of chain-end modification, providing a design principle for biosensor development.     

Synthesis and surface modification of mesoporous mcm-41 silica materials

Surface modification offers a great opportunity to adjust both the pore diameter and surface properties of MCM-41 type organic–inorganic hybrid materials which result in materials of improved hydrothermal and mechanical stability. Therefore, MCM-41 silica, surface modified with organic ligands, are promising systems with engineered properties and attractive for advanced applications. In the present study, after optimization of the reaction conditions highly ordered MCM-41 silica spheres with uniform mesopores were prepared by the pseudomorphic transformation route. The effect of functionality and alkyl chain length of the alkyl ligands during surface modification was probed by using butyl and octylsilanes with two different functionalities. Due to steric hindrance, the longer chains are assumed to bind only on the outer silica surface and near the entrance of the pores, while the shorter chains are also able to bind to the interior mesopore walls. The resulting materials were comprehensively characterized before and after surface modification using nitrogen sorption techniques, XRD, SEM, solid-state NMR spectroscopy and FTIR spectroscopy. From chromatographic test measurements it was found that the separation power primarily depends on surface coverage and alkyl chain length. On the basis of the present data, surface modified mesoporous silica of MCM-41 type are very promising candidates for future chromatographic applications.