“On-water” catalyst-free,one-pot synthesis of quaternary centered and spiro-tetrahydrothiophene-barbiturate hybrids

A green and efficient method have been developed for the synthesis of quaternary centered and spiro-barbiturate-tetrahydrothiophene hybrids via Knoevenagel condensation,1,4-thia-Michael and intramolecular Aldol reactions using “on water” concept under catalyst-free conditions. Systematic studies were carried out to find the role of the water and total reaction concentration (0.086 M) to promote the reaction in two steps (one-pot). The use of water as a reaction medium, catalyst-free conditions, broad substrate scope, one-pot approach for the creation of quaternary centered and spiro molecules are the advantages of this method.     

聚苯胺/贵金属复合纳米材料的可控合成及催化应用

导电高分子/贵金属复合纳米材料因其在催化、传感、表面增强拉曼、光热治疗等诸多领域的应用前景而受到广泛关注.本文主要介绍我们课题组近年来利用可控合成策略制备的负载型和包埋型两种结构聚苯胺/贵金属复合纳米材料,以及利用复合纳米材料的结构和功能特性,对其在多相催化领域的应用、结构与催化性能之间构效关系的探索.     

2-Aminopurine: a probe of structural dynamics and charge transfer in DNA and DNA:RNA hybrids

Spectroscopic techniques are employed to probe relationships between structural dynamics and charge transfer (CT) efficiency in DNA duplexes and DNA:RNA hybrids containing photoexcited 2-aminopurine (Ap). To better understand the variety of interactions and reactions, including CT, between Ap and DNA, the fluorescence behavior of Ap is investigated in a full series of redox-inactive as well as redox-active assemblies. Thus, Ap is developed as a dual reporter of structural dynamics and base-base CT reactions in nucleic acid duplexes. CD, NMR, and thermal denaturation profiles are consistent with the family of DNA duplexes adopting a distinct conformation versus the DNA:RNA hybrids. Fluorescence measurements establish that the d(A)-r(U) tract of the DNA:RNA hybrid exhibits enhanced structural flexibility relative to that of the d(A)-d(T) tract of the DNA duplexes. The yield of CT from either G or 7-deazaguanine (Z) to Ap in the assemblies was determined by comparing Ap emission in redox-active G- or Z-containing duplexes to otherwise identical duplexes in which the G or Z is replaced by inosine (I), the redox-inactive nucleoside analogue. Investigations of CT not only demonstrate efficient intrastrand base-base CT in the DNA:RNA hybrids but also reveal a distance dependence of CT yield that is more shallow through the d(A)-r(U) bridge of the A-form DNA:RNA hybrids than through the d(A)-d(T) bridge of the B-form DNA duplexes. The shallow distance dependence of intrastrand CT in DNA:RNA hybrids correlates with the increased conformational flexibility of bases within the hybrid duplexes. Measurements of interstrand base-base CT provide another means to distinguish between the A- and B-form helices. Significantly, in the A-form DNA:RNA hybrids, a similar distance dependence is obtained for inter- and intrastrand reactions, while, in B-DNA, a more shallow distance dependence is evident with interstrand CT reactions. These observations are consistent with evaluations of intra- and interstrand base overlap in A- versus B-form duplexes. Overall, these data underscore the sensitivity of CT chemistry to nucleic acid structure and structural dynamics.     

Regio- and Diastereoselective Synthesis of β-Lactam-Triazole Hybrids via Passerini/CuAAC Sequence

Passerini (P-3CR) and Passerini-Smiles reactions were investigated in azetidine-2,3-diones, affording the corresponding 3,3-disubstituted-β-lactams with complete diastereoselectivity in high yields. The study has been carried out using different isocyanides, carboxylic acids, and phenols showing the scope of both reactions. In addition, the regioselective synthesis of highly functionalized β-lactam-triazole hybrids has been developed via a Passerini/CuAAC sequence. Interestingly, the use of dialkynes/diazides or trialkynes/triazides as linkers in the CuAAC step has allowed the synthesis of C(2) and C(3) symmetric β-lactam-triazole hybrids, respectively.     

Pd-catalyzed orthogonal Knoevenagel/Perkin condensation-decarboxylation-Heck/Suzuki sequences: tandem transformations of benzaldehydes into hydroxy-functionalized antidiabetic stilbene-cinnamoyl hybrids and asymmetric distyrylbenzenes

Tandem reactions that involve chemoselective Knoevenagel/Perkin condensation-decarboxylation-Heck/Suzuki coupling or Heck-aldol sequences have been achieved. This enabled the first concise and efficient synthesis of several important hydroxy-functionalized compound classes, such as stilbene-cinnamoyl hybrids (potent protein tyrosine phosphatase1B inhibitors), cinnamoyl-cinnamic acid hybrids, asymmetric distyrylbenzenes, and biarylstyrenes. Previously reported synthesis require multiple steps and protection/deprotection manipulations.     

Synthesis of novel cinchona-amino acid hybrid organocatalysts for asymmetric catalysis

Three novel subclasses of cinchonidine derivatives coupled to diverse amino acids were prepared in very good overall yield and tested in a benchmark organocatalytic aldol reaction, between acetone and aromatic aldehydes. These subclasses are a family of amino acid-cinchonidine (subclass A), N-formamides-cinchonidine (subclass B) and dipeptide-cinchonidine (subclass C) hybrids. Our main goal, besides obtaining very good yields and enantioselectivities, was to understand the influence of the amino acid side chain residues on the enantioselectivity of the asymmetric aldol reactions. Different amino acid tethered cinchonidine hybrids were compared and their catalytic behaviour was evaluated, allowing good enantioselectivities to be achieved, 92% ee in one case. Other reactions such as Biginelli, Michael addition and ketimine hydrosilylation reactions were screened with these ligands, but the outcome was less successful.     

Rational synthesis of covalently bonded organic-inorganic hybrids

Hybrid materials based on covalently linked inorganic polyoxometalates (POMs) and organic species containing a delocalized pi system have drawn increasing attention. These hybrids, traditionally prepared by cluster assembly approaches that lack predictability and controllability, can now be synthesized through common organic reactions by using organically functionalized POM clusters as building blocks. This minireview highlights some of the most recent advances on a particular type of hybrids where the organic and inorganic components are connected by an imido linkage.     

Carbohydrate-functionalized oligothiophenes for concanavalin A recognition

Versatile synthesis of fluorescent, carbohydrate-functionalized oligothiophene hybrids via Sonogashira-type cross coupling reactions is reported. The mannose derivatives reveal specific binding with the model lectin from Canavalia enisformis (Concanavalin A).     

A new example of a steroid-amino acid hybrid: construction of constrained nine membered D-ring steroids

A new archetype of steroid-amino acid hybrids containing a nine membered D-ring with hetero atoms has been synthesized for the first time from estrone and amino acids by using Yamaguchi coupling reactions.     

Poly(ethylene imine) hybrids containing polyhedral oligomeric silsesquioxanes: Preparation, structure and properties

Both octaglycidyletherpropyl polyhedral oligomeric silsesquioxane and hepta(3,3,3-trifluoropropyl)glycidyletherpropyl polyhedral oligomeric silsesquioxane were synthesized via the hydrosilylation reactions between octahydrosilsesquioxane [and/or hepta(3,3,3-trifluoropropyl)hydrosilsesquioxane] and allyl glycidyl ether. The polyhedral oligomeric silsesquioxane (POSS) macromers were characterized by means of Fourier transform infrared and nuclear magnetic resonance spectroscopy. The inter-component macromolecular reactions between the POSS macromers and poly(ethylene imine) (PEI) were employed to prepare the POSS-containing organic-inorganic PEI hybrids. The inclusion of octaglycidyletherpropyl POSS into PEI results in the formation of the organic-inorganic hybrid networks whereas the introducing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS to PEI affords the linear POSS-grafted PEI copolymers. Differential scanning calorimetry and thermogravimetric analysis show that the POSS-containing PEI hybrids displayed increased glass transition temperatures (T_g’s) and enhanced thermal stability compared to the plain PEI. These PEI hybrid composites can be significantly swollen with water without dissolving, suggesting the formation of hydrogels. The PEI hydrogels containing octaglycidyletherpropyl POSS is in reality the chemically-crosslinked hydrogels whereas the those containing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS displayed the behavior of physical hydrogels. The formation of physical hydrogels is ascribed to the microphase-separated morphology in the hybrids. In addition, the hybrids containing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS exhibited the typical amphiphilicity as evidenced by the increase in surface hydrophobilicity.     

Hybrid polyoxometalates: Keggin and Dawson silyl derivatives as versatile platforms

A new series of polyoxometalate-based hybrids has been synthesized. These covalently linked organic-inorganic materials represent valuable elementary building blocks ready for postfunctionalization, using classical organic reactions and couplings. This approach is exemplified by the grafting of an organic chromophore via a Sonogashira coupling.     

对羟基二联苯诱导的表面金属-有机键断裂

金属-有机杂化结构是表面在位反应过程中常见的中间体. 金属-有机杂化结构中金属-有机键的断裂需要克服较高的活化能垒, 往往会引起一系列竞争副反应以及分子的脱附. 本文利用扫描隧道显微镜研究了 4,4′-二羟基联苯分子在金属表面与预先制备的金属-有机链的作用, 发现其氧端能有效地降低金属有机杂化体系断键的能垒, 使得金属-有机键的断键反应能在较低的温度下进行. 该结果提供了一种调控表面反应中间物的新手段.     

Reaction kinetics and network characterization of UV-curing polyester acrylate inorganic/organic hybrids

Polyester acrylate inorganic/organic hybrids were prepared using a sol-gel precursor, coupling agent, and reactive diluent. The hybrids were cured via a UV-free radical initiator. Design of experiments (DOE) was utilized to investigate reaction kinetics and complex variable interactions. The effects of the silicate groups on the free radical photo-curing reaction kinetics were investigated utilizing a time-resolved Fourier transform infrared (FT-IR) spectroscopy and a differential scanning calorimeter equipped with a photocalorimetric accessory (photo-DSC). Microgel and inorganic network formation during the UV-initiated free radical crosslinking reactions was suggested to describe the complex gel-point behavior. It was proposed that the formation of the inorganic silicate groups retarded the organic crosslinking reactions. The UV-cured inorganic/organic hybrid films exhibited more homogeneous film morphology compared to the organic counterparts. In the hybrid films, a core-shell like inorganic/organic particle morphology was observed. The UV-crosslinked organic phase forms the core, whereas, the inorganic silicate forms the surrounding shell.     

Highly Stereoselective Synthesis of Natural‐Product‐Like Hybrids by an Organocatalytic/Multicomponent Reaction Sequence

In an endeavor to provide an efficient route to natural product hybrids, described herein is an efficient, highly stereoselective, one‐pot process comprising an organocatalytic conjugate addition of 1,3‐dicarbonyls to α,β‐unsaturated aldehydes followed by an intramolecular isocyanide‐based multicomponent reaction. This approach enables the rapid assembly of complex natural product hybrids including up to four different molecular fragments, such as hydroquinolinone, chromene, piperidine, peptide, lipid, and glycoside moieties. The strategy combines the stereocontrol of organocatalysis with the diversity‐generating character of multicomponent reactions, thus leading to structurally unique peptidomimetics integrating heterocyclic, lipidic, and sugar moieties.     

Effect of a modification site on the electron-transfer reaction of glucose oxidase hybrids modified with phenothiazine via a poly(ethylene oxide) spacer

Glucose oxidase [GOx-(PT-PEONH2)] hybrids are synthesized by attaching phenothiazine (PT) groups to aspartic and glutamic acid residues on the enzyme surface via poly(ethylene oxide) (PEO) spacers of different molecular weights. A fast oxidation of FADH2/FADH by PT+ with the aid of the local motion of a hydrophilic, long, flexible PEO spacer is achieved for the GOx-(PT-PEONH2) hybrids and yields greater electron-transfer (ET) rates than that for GOx-(PTNH2) hybrids, in which the PT groups are directly bonded to the GOx surface. The ET rate of GOx-(PT-PEONH2) hybrids depends on the molecular weight of PT-PEONH2, and the maximum is obtained at a molecular weight of 3000. The ET rates of GOx hybrids are compared in terms of the location of the PT modification and the length and structure of the spacer chain connection of the PT mediator to a surface amino acid residue. Greater ET rates are obtained for the modification at aspartic and glutamic acid residues than for the lysine modification when the PT groups are bonded directly or via a short PEO spacer chain. In contrast, no advantage of aspartic and glutamic acid residues over lysine residues in generating a fast oxidation of FADH2/FADH by PT+ is observed for GOx hybrids in which the PT groups are attached via longer PEO spacers. The long PEO spacer is able to compensate the disadvantage of lysine residues locating far from the FAD center in GOx hybrids whose mediation reactions are based on the so-called wipe mechanism.     

新型耐甲醇氧还原电催化剂——氮掺杂中空碳微球@铂纳米粒子复合材料

通过模板法制备了一种新型耐甲醇氧还原电催化剂——氮掺杂中空碳微球@铂纳米粒子复合材料(HNCMS@PtNPs)。首先,将铂纳米粒子负载于氨基化二氧化硅微球上,获得PtNPs/SiO₂复合材料。然后通过多巴胺自聚合反应在PtNPs/SiO₂复合材料上包裹聚多巴胺(PDA)膜,将其在氮气气氛中直接进行碳化处理并通过氢氟酸溶液刻蚀去除SiO₂,获得了内嵌有PtNPs的氮掺杂中空碳微球,标记为HNCMS@PtNPs复合材料。采用扫描电子显微镜、透射电子显微镜、X射线衍射仪、拉曼光谱仪、比表面积分析仪和X射线光电子能谱仪对HNCMS@PtNPs复合材料的形貌和结构进行了表征。采用循环伏安法和线性扫描伏安法研究了HNCMS@PtNPs复合材料的电催化氧还原性能。结果表明：HNCMS@PtNPs催化剂的Pt载量高达11.9%(w,质量分数),对氧还原反应具有高电催化活性、高稳定性和优良的抗甲醇性能,是一种具有应用潜力的直接甲醇燃料电池(DMFCs)阴极电催化剂。     

Morphology controls of the melt blending in a novel highly crosslinked bismaleimide system

A novel bismaleimide of 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMIP) with a broad working-temperature-range for the melt blending was successfully synthesized. BMIP possesses a considerably broad working-temperature-range from 75 °C to 250 °C, prior to undergoing cure reactions to form a highly crosslinked network. The morphology types of cured BMIP/clay hybrids can be controlled by varying the shearing temperatures and the contents of the clay. The conditions necessary for achieving an exfoliated or an intercalated BMIP/clay hybrid were thoroughly investigated via X-ray diffractometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All the uncured samples prepared at different shearing temperatures and with an adequate amount of MMT-C (above 3 phr) exhibited an intercalated form of morphology. However, the crosslinking reactions for specified samples prepared at relatively elevated shearing temperatures (above 120 °C) and with a relatively low content of clay (below 15 phr) resulted in morphology changes from the intercalated form to the exfoliated form of morphology. There exists an isotropically mechanical property for the cured matrix of the exfoliated hybrids whereas there exists an anisotropically mechanical property for the cured matrix of the intercalated hybrids.     

Functional aqueous assemblies of linear-dendron hybrids

Linear-dendron (LD) hybrids are macromolecules comprising a linear polymer or oligomer conjugated at one or both termini with branched macromolecules called dendrons. Since their introduction approximately 2 decades ago, tremendous progress has been made in their synthesis, the study of their self-assembly, and toward their application in a variety of fields. This highlight is focused on aqueous assemblies of LD hybrids where function is imparted by the dendron, linear component, or both. These functions include the encapsulation and release of drug molecules, enhancement of cell uptake and targeting of specific tissues, and the stabilization of enzymes for catalysis. In addition, many stimuli-responsive LD hybrids that undergo changes in response to light, enzymes, pH, temperature, redox potential, or even multiple stimuli have been developed. LD hybrids can also be used to form networks via cross-linking reactions. Described here are the structure–property relationships underlying the functions of these materials, along with their potential applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 148–172     

Polyoxometalate-organic hybrid molecules as amphiphilic emulsion catalysts for deep desulfurization

So emulsional: Two hexavanadate-organic hybrids were synthesized and their amphiphilic properties were confirmed by forming emulsions in mixtures of water and nonpolar organic solvents, and were utilized as "emulsion catalysts" in deep desulfurization reactions (see figure). Their catalytic activities show a pH-dependent behavior, which can be explained by the size-change of emulsions and the appearance of reverse emulsions.     

Synthesis of a mitomycin C–lexitropsin hybrid

We have constructed hybrid drugs where mitomycin C is linked to the N-methylpyrrole carboxamide framework present in lexitropsins. The coupling reactions leading to these products are efficient and the yields are very high. An interesting spectroscopic feature of these hybrids is the red shift observed in the UV–vis spectrum. Although DFT calculations indicate the possible existence of complexes formed during the coupling reactions, these complexes were not detected. The only species produced and isolated were the mitomycin C-mono- and bis-N-methyl pyrrole conjugates.