Nanomaterials based on phosphorus dendrimers

Dendrimers constitute an increasingly important field of research in chemistry for more than 15 years. After pioneering works concerning synthesis, the interest in dendrimers is now mainly driven by their properties and applications. This Account will emphasize the properties of a special class of dendrimers, that is, phosphorus-containing dendritic macromolecules, as tools for the elaboration of nanomaterials. Indeed, these dendrimers can be considered themselves as materials, or they can be used as an intrinsic constituent of a material or as a modifier of the surface of a material. In this latter case, a fundamental work about surfaces covalently modified by dendrimers recently opened the way to the elaboration of DNA chips.     

Click dendrimers and triazole-related aspects: catalysts, mechanism, synthesis, and functions. A bridge between dendritic architectures and nanomaterials

One of the primary recent improvements in molecular chemistry is the now decade-old concept of click chemistry. Typically performed as copper-catalyzed azide-alkyne (CuAAC) Huisgen-type 1,3-cycloadditions, this reaction has many applications in biomedicine and materials science. The application of this chemistry in dendrimer synthesis beyond the zeroth generation and in nanoparticle functionalization requires stoichiometric use of the most common click catalyst, CuSO(4)·5H(2)O with sodium ascorbate. Efforts to develop milder reaction conditions for these substrates have led to the design of polydentate nitrogen ligands. Along these lines, we have described a new, efficient, practical, and easy-to-synthesize catalytic complex, [Cu(I)(hexabenzyltren)]Br, 1 [tren = tris(2-aminoethyl)amine], for the synthesis of relatively large dendrimers and functional gold nanoparticles (AuNPs). This efficient catalyst can be used alone in 0.1% mol amounts for nondendritic click reactions or with the sodium-ascorbate additive, which inhibits aerobic catalyst oxidation. Alternatively, catalytic quantities of the air-stable compounds hexabenzyltren and CuBr added to the click reaction medium can provide analogously satisfactory results. Based on this catalyst as a core, we have also designed and synthesized analogous Cu(I)-centered dendritic catalysts that are much less air-sensitive than 1 and are soluble in organic solvents or in water (depending on the nature of the terminal groups). These multivalent catalysts facilitate efficient click chemistry and exert positive dendritic effects that mimic enzyme activity. We propose a monometallic CuAAC click mechanism for this process. Although the primary use of click chemistry with dendrimers has been to decorate dendrimers with a large number of molecules for medicinal or materials purposes, we are specifically interested in the formation of intradendritic [1,2,3]-triazole heterocycles that coordinate to transition-metal ions via their nitrogen atoms. We describe applications including molecular recognition of anions and cations and the stabilization of transition metal nanoparticles according to a principle pioneered by Crooks with poly(amido amine) (PAMAM) dendrimers, and in particular, the control of structural and reactivity parameters in which the intradendritic [1,2,3]-triazoles and peripheral tripodal tri(ethylene glycol) termini play key roles in the click-dendrimer mediated synthesis and stabilization of gold nanoparticles (AuNPs). By varying these parameters, we have stabilized water-soluble, weakly liganded AuNPs between 1.8 and 50 nm in size and have shown large differences in behavior between AuNPs and PdNPs. Overall, the new catalyst design and the possibilities of click dendrimer chemistry introduce a bridge between dendritic architectures and the world of nanomaterials for multiple applications.     

Sulphonated “Click” Dendrimer‐Stabilized Palladium Nanoparticles as Highly Efficient Catalysts for Olefin Hydrogenation and Suzuki Coupling Reactions Under Ambient Conditions in Aqueous Media

Water‐soluble 1,2,3‐triazolyl dendrimers were synthesized by “click chemistry” and used to stabilize palladium nanoparticles (PdNPs). These new “click” dendrimer‐stabilized nanoparticles (DSN) are highly stable to air and moisture and are catalytically active for olefin hydrogenation and Suzuki coupling reaction, in aqueous media, under ambient conditions using a low amount of palladium (0.01 mol% Pd). Kinetic studies show high catalytic efficiency and high stability for the new “click” DSN in both reactions. The complexation of potassium tetrachloropalladate (K₂PdCl₄) to the triazole ligands present in the dendritic structures was monitored by UV/vis and, after reduction, the nanoparticles were characterized by transmission electron microscopy (TEM).     

Dendritic Polymers – Interdisciplinary Research and Emerging Applications from Unique Structural Properties

Dendritic polymers, i.e., dendrimers and hyperbranched polymers, attract increasing attention due to their unique structures and properties. The step‐wise methodologies for the synthesis of dendrimers allow the tailoring of physical and chemical properties and thus provide a powerful tool to design dendrimers for a wide variety of applications. The complex syntheses of dendrimers often result in expensive products with limited use for large‐scale industrial applications, an area where hyperbranched polymers appear to be promising alternatives. The large body of interdisciplinary research on dendritic polymers is a guarantor for emerging applications. However, the understanding of essential fundamentals such as the phase behavior of dendritic polymer solutions is still in its infancy. Therefore, this review intends to cover the syntheses, properties, and emerging applications of dendritic polymers as well as to discuss the impact of polymer branching on the phase behavior of dendritic polymer solutions within a comprehensive thermodynamic context.     

Poly(amidoamine), polypropylenimine, and related dendrimers and dendrons possessing different 1 → 2 branching motifs: An overview of the divergent procedures

This review presents an overview of 1 → 2 branched dendrimers and dendrons, created by a divergent procedure, from their synthesis to modern day applications. The first members of this branched class of fractal macromolecules were prepared through a cascade synthesis, which was later replaced by the iterative divergent synthetic approach. Most classes of this 1 → 2 N-, Aryl-, C-, Si-, and P-branched families are included and catalogued by their mode of connectivity. Dendritic macromolecules have had significant impact in the field of material sciences and are one of the major starting points for nanotechnology as a result of the numerous modifications that can be conducted, either on the surface or within their molecular infrastructure, thus taking advantage of their unimolecular micelle properties. These host cavities, maintained by the dendritic branches, allow for the incorporation of nanoparticles as well as metal particles, which make these attractive in catalysis and imaging studies. The solubility of these fractal constructs can be tailored depending on their surface modifications. Highly water-soluble, neutral dendrimers appended with, grown from, or acting as hosts to specific molecules give rise to a wide variety of biomedical applications such as drug delivery systems and MRI imaging agents. The inherent supramolecular or supramacromolecular chemistry has been exploited but the design and construction of uniquely tailored macrostructures have just begun. Laser dyes, as well as electron and energy donor and acceptor functionality, have also been paired with these fractal constructs in order to probe their uses in the field of molecular electronics. With their synthetic control, seemingly limitless modifications and wide variety of potential applications, as well as their now commercial availability, these 1 → 2 branched dendrimers have become an important nanostructured tools for diverse utilitarian applications. This review mainly covers 1 → 2 branched non-chiral dendrimers prepared by a divergent process but selected chiral surfaces are considered as well as metal encapsulation and a few hyperbranched routes to related imperfect dendrimers.     

Advances in room temperature curing adhesives and sealants—a review

Room temperature curing adhesives and sealants, defined here as those which cure without a mixing process under the influence of substrates or environmentally available reagents such as daylight, oxygen or moisture, include polyurethane, silicone, anaerobic adhesives, cyanoacrylate and certain acrylic types. Advances in cure chemistry, built-in adhesion promotion, and in formulating techniques have created the scope for significant new properties within all the mentioned systems. In addition, development of resins having two (or more) different functionalities, which respond to substrate and or atmospheric cure agents, has created the potential to achieve new advanced performance levels. Examples of these include compositions which give light curing through acrylic functions while having RTV (room temperature vulcanising) silicone resin chemistry polymerising under the influence of atmospheric moisture. The properties can be tailored by molecular design, formulation and choice of cure accelerators.     

Controlling Cellular Uptake and Toxicity of Polyphenylene Dendrimers by Chemical Functionalization

Polyphenylene dendrimers (PPDs) represent a unique class of macromolecules based on their monodisperse and shape‐persistent nature. These characteristics have enabled the synthesis of a new genre of “patched” surface dendrimers, where their exterior can be functionalized with a variety of polar and nonpolar substituents to yield lipophilic binding sites in a site‐specific way. Although such materials are capable of complexing biologically relevant molecules, show high cellular uptake in various cell lines, and low to no toxicity, there is minimal understanding of the driving forces to these characteristics. We investigated whether it is the specific chemical functionalities, relative quantities of each moiety, or the “patched” surface patterning on the dendrimers that more significantly influences their behavior in biological media.     

Click synthesis of glycosylated porphyrin-cored PAMAM dendrimers with specific recognition and thermosensitivity

Glycoporphyrin dendrimers have received increasing attentions due to their distinct physical and chemistry properties, such as fluorescence and water solubility. They also acted as a promising photodynamic therapy (PDT) sensitizer and used in the study of carbohydrate-protein interaction. In this study, different generations of porphyrin-cored dendrimers consisting of glycosylated siloxane-poly (amido amine) typed dendron (PP-Si-PAMAM-D_m-Lac, m?=?1, 2, and 3), multifunctional specific-targeting sensitizers, had been synthesized via click reaction. The structure of PP-Si-PAMAM-D_m-Lac was characterized by ¹H NMR, GPC, FT-IR, UV-vis and fluorescence analyses. This glycoporphyrin dendrimers, not only obtained high fluorescence quantum yield and singlet oxygen production efficiency, but also showed specific recognition of lectin and remarkable temperature-responsive property (20–80 °C). These properties proved a facile click synthetic strategy of glycosylated siloxane-poly (amido amine) typed dendrimers with multiple functions as a promising tumor-selective photsensitizer (PS) for PDT and also allow applications in highly sensitive fluorescent probes over a larger temperature window.     

Ferrocenyl-terminated Dendrimers: Design for Applications in Molecular Electronics, Molecular Recognition and Catalysis

This micro-review shows how a simple but powerful organometallic C–H activation could be made very useful for the construction of a large variety of stars, dendritic cores, dendrons and dendrimers of variable sizes including giant dendrimers and gold-nanoparticle-cored dendrimers. The synthesis of ferrocenyl-terminated dendrimers was then achieved by reactions of chlorocarbonylferrocene with polyamino dendrimers, ferrocenylsilylation of polyolefin dendrons and dendrimers and “click” reactions of ferrocenyl acetylene with azido-terminated dendrimers. The functions of these metallodendrimers include molecular electronics (molecular batteries), molecular redox recognition and sensing and catalysis using dendritic stabilization of nanoparticle catalysts.     

Complex Adaptable Systems based on Self-Assembling Dendrimers and Dendrons: Toward Dynamic Materials

Self-assembling dendrons are biologically inspired complex systems that can form self-organized periodic arrays in the bulk state. Here we adopt the point of view of Constitutional Dynamic Chemistry (CDC) to discuss the design and properties of self-assembling dendrimers and dendronized structures. Among other objectives, CDC seeks to generate chemical diversity through constitutional dynamics, and to improve the design of dynamic materials using adaptive systems. Can we address these issues with dendrimer chemistry? We will show that generational and co-assembly approaches in the synthesis of self-assembling dendritic systems lead to a remarkable collection of periodic lattices and quasi-periodic arrays. Moreover, in some cases the morphological properties of the resulting supramolecular structures can be tuned by external signals. These dendron-based adaptive systems find applications in various fields such as nano-machines and switches or porous protein mimics.     

Kristallin-flüssige Aldoximester

Liquid-crystalline Aldoxime Esters Benzaldoxime-benzoates were prepared by the acylation of aromatic aldoximes with benzoylchlorides. By substitution of the 4- and 4′-positions with suitable linear-chain substituents a new class of substances with liquid-crystalline properties has been made accessible. In several series 1–6 the influence of different „wing”︁-groups on the mesomorphic behaviour and resulting anomalies in the clearing-point curves was investigated.     

Dendrimers: a review of their appeal and applications

Dendrimer chemistry is one of the most fascinating and rapidly expanding areas of modern chemistry. This review attempts to uncover the appeal of these structurally‐perfect branched macromolecules. The three intriguing regions of a dendritic molecule are discussed: the multifunctional surface, the tailored sanctuary within the branches, and the encapsulated core. The advantages of dendritic structures for property modification, and their potential applications in very diverse areas are illustrated. The exciting merger of dendrimer chemistry with self‐assembly offers new, stimulating avenues for exploration. Consequently, self‐assembling dendrimers comprise a major section of this article. © 2001 Society of Chemical Industry     

Synthesis and incorporation in Langmuir films of oligophenylenevinylene dendrimers bearing a polar head group and different dendritic poly(benzyl ether) branches

Oligophenylenevinylene (OPV) units containing a hydroxyl polar head group and different dendritic poly(benzyl ether) branches bearing aliphatic chains (n-propyl and n-dodecyl) have been synthesized. The obtained dendrimers were characterized by ¹H and ¹³C NMR, FTIR and absorption spectroscopies. Optical properties of the dendrimers have been studied in toluene and dichloromethane solutions. Changes in the maximum absorption wavelength were observed for the dendrimers OPV core. Increasing the dendron branches generation gave rise to a hypsochromic shift of the maximum absorption band of the OPV core. The ability of all dendrimers to form Langmuir films at the air-water interface was also investigated; the obtained films were characterized by surface pressure versus molecular area isotherms, and by compression-expansion cycles (hysteresis curves). All dendrimers were able to form stable Langmuir monolayers in the air-water interface, and exhibited a good reversible behavior upon successive compression/expansion cycles. The terminal alkyl chains length of the dendritic branches has a remarkable influence on the packing of highest generation dendrimers in the monolayers. These dendrimers can be promising prospects for the preparation of Langmuir-Blodgett films, in view of optical and electronic potential applications.     

Industrielle Bedeutung der Vilsmeier–Haack-Reaktion in der Farbstoffchemie

Vilsmeier–Haack Formylation Reaction – Importance in Colour Industry The Vilsmeier-Haack reaction which has been discovered in 1927 is being used in industry to formylate alkylated aromatic amines and related compounds. Roughly 2000 tons of formylation products are yearly produced in the world. Preferably they are used as building blocks in dye chemistry. Many classes of dyes like cyanines, coumarin dyes, merocyanines, cationic dyes, color formers or dyes for non linear optical applications are being obtained from „Vilsmeier”︁ products. Different conditions of the Vilsmeier-Haack reaction and alternative routes for the introduction of a formyl group are discussed in this progress report.     

简述功能树状聚合物的合成与应用

树状聚合物是一种极具发展前景的功能性材料,由于其特殊的空间结构,可广泛应用于药物载体、生物传感器、有机发光二极管、太阳能电池、催化剂等多个领域。目前主要的合成树状聚合物的方法大致分为三种:分枝歧化法、收敛法、点击化学。文章结合一些典型的树状聚合物对这些合成方法做了分析,并例举了部分树状聚合物的性能及应用。     

Electronegativity Effects in Organic Synthesis: Differences in stability of isomeric substituted alkanes

Selectivity is such an intellectually, economically, and ecologically important matter in organic synthesis that it is highly desirable to know all the factors, both kinetic and thermodynamic, which influence it. We were surprised by the high selectivity obtained in an equilibration of isomeric β-thioalkyl trifluoroacetates, because the thermodynamic difference implied by this and other, similar, rearrangements did not appear to have been explained. It now appears that this difference is due to the thermochemical effect whereby polar substituents bind more strongly to alkyl groups of complementary polarity; in other words electronegative atoms prefer more „procationic”︁ tertiary and secondary alkyl groups, electropositive ones prefer the more „proanionic”︁ primary alkyl and methyl groups. This small but significant (1 to 7 kcal·mol⁻¹) effect is well documented by thermochemical data, and has been described several times; it can be predicted qualitatively by Pauling's formula relating bond energy, bond polarisation, and electronegativity. We first describe how the electronegativity effect explains our observations: they are due to the higher electronegativity of oxygen and chlorine relative to that of sulfur. We then go on to show that it is useful for the interpretation of many other literature reports, ranging from the acid-catalysed isomerization of alkyl halides, to the carbocyclization of organozinc reagents, and the isomerization of alkyltransition metal complexes (a key step for the selectivity of important industrial processes such as alkene hydroformylation).     

Dendritic Molecular Nanobatteries and the Contribution of Click Chemistry

This article is a mini-review mostly based on the work of the authors’ laboratory on the redox chemistry of metallodendrimers and gold nanoparticles, with emphasis on “click” chemistry. Late transition-metal sandwich complexes possess a rather unique ability to withstand two or three oxidation states without breakdown, especially with permethylated π-cyclopentadienyl or arene ligands. When they are linked to dendritic cores, the assembled nano-systems undergo chemically and electrochemically reversible transfer of a large number of electrons (up to 14,000). These multiple redox processes are useful for nanodevices behaving as nanobatteries for redox sensing, modified electrode surfaces and redox catalysis. Click chemistry was recently disclosed as one of the most powerful means to form such assemblies including both arene-cored and gold nanoparticle-cored dendrimers.     

Dendrimers for fluorescence‐based bioimaging

Dendrimer science is a relatively new branch of nanotechnology focused on non‐linear macromolecules called dendrimers. These hyperbranched polymers are characterized by monodispersity, highly defined structure and – depending on specific type of dendrimer – good biocompatibility. Due to the possibility of encapsulation or surface conjugation of guest molecules on a dendrimer it can serve as delivery agent in life sciences. For bioimaging based on fluorescence dendritic polymers were extensively studied as conventional fluorophore carriers. Complexing of organic dyes with these macromolecules improves their solubility and enhances cellular uptake. Moreover, it helps overcome other limitations in using them for photobleaching, and their lack of specificity or cytotoxicity. Protective properties of dendrimers are especially valuable for use with quantum dots, which have great optical potential but contain heavy metals that can adversely affect biological objects. Dendrimer based fluorescent probes have been widely applied in vitro and in vivo bioimaging. An interesting phenomenon is non‐traditional intrinsic fluorescence (NTIF) of dendrimers. Some of them show pH‐ and oxygen‐dependent fluorescence without conjugation with other particles. NTIF is not fully understood, but attempts to take advantage of it for bioimaging have been made. This phenomenon has great potential since it enables dendrimers to serve simultaneously as delivery and diagnostic tool. © 2017 Society of Chemical Industry     

含硅树枝状聚合物

简述了近年来在高分子化学领域内十分活跃的树枝状聚合物的基本概况，着重介绍了含硅树枝状聚合物的特点、合成方法及其应用，指出了树枝状聚合物在实际应用中的局限性。     

树形聚合物的合成和结构及应用研究进展

树形聚合物为纳米级单分散性大分子 ,它独特的核 -壳结构、表面端基的高密度及高反应活性 ,使其易于组装或修饰为功能化树形聚合物 ,用于催化体系、细胞识别及基因治疗、光学分子开关及光获体系等 ,而成为引人注目的 2 1世纪新材料