Synthesis and theoretical study of first generation CCK-functional dendrimers

A convenient synthesis and theoretical study of five CCK-functional dendrimers is described.The dendritic cores were linked with the CCK(Trp-Met-Asp(OBn)-PheNH2) fragment by forming amide bonds to give five target molecules.The structures of CCK-functional dendrimers were characterized by NMR,MS spectrum and predicted using molecular mechanics and PM3 semi- empirical molecular orbital theory.     

Synthesis of N-methylene phosphonic chitosan （NMPCS） and its potential as gene carder

N-Methylene phosphoulc chitosan (NMPCS),an amphiphilic macromolecule with powerful chelating ability of Ca~(2 ) ions,was synthesized and characterized.The physicochemical properties of NMPCS and the interactions between NMPCS and plasmid DNA were investigated by FTIR,~(13)C NMR,X-ray,agarose gel electrophorcsis retardation assay,atomic force microscopy (AFM) and circular dichroism (CD).The results suggest that at charge ratio 2:1 or above,DNA could be completely entrapped and spherical complexes with mean size of 80-210 nm were formed.Taking HeLa as host cell,luciferase expression mediated by NMPCS improved about 100 times compared to the expression mediated by chitosan.     

Synthesis of Novel Carbosilane Dendrimers Based on Pentaerythritol

Novel pentaerythritol-based carbosilane dendrimers centered at carbon have been synthesised. Starting from tetraallyl ether based upon pentaerythritol as the core molecule, a succession of alternate Pt-catalyzed hydrosilylation of allyl groups with HSiC13 and allylations of SiC1 groups thus introduced with CH2=CHCH2MgBr in THF provided a divergent synthesis of three generations of carbosilane dendrimers in which the Si atoms are linked by CH2CH2CH2 groups. The reaction conditions for hydrosilylation must be well controlled. After purification by chromatography on silica gel pure products for each generation were obtained. The IR, ^1H and ^13C NMR spectra and elemental analysis data are consistent with the proposed structures. The molecular weights of the resulting carbosilne dendrimers have been determined by vapor pressure osmometry.     

三甲基酰氧基硅烷与环氧氯丙烷的开环反应

Ring cleavage reaction between trimethylacyloxysilances and epichlorohydrin using 5-t-buty 1-2-furanatochromium (IIIe n(TBF)3Cr) as catalyst was studied in detail and the products, various esters of β-trimethylsiloxy-y-chloropropanol, were obtained. Relative reaction rates between various acyloxysilances and epichlorophydrin were compared by determining the half-lives of the acyloxysilances. The direction of ring cleavage was examined with IR, ^1H NMR, ^1^3C NMR and HPLC and comparable to that reported in literature. Toxicity of these products was determined.     

The synthesis and study of the fluorescent probe for sensing Cu2＋ based on a novel coumarin Schiff-base

A novel, fluorescent probe was synthesized from 2,4-dihydroxybenzaldehyde and 8-hydroxyquinoline for sensing Cu2+by the naked eye. The structure was confirmed by IR, MS,1H NMR,13 C NMR and the spectral properties of the probe were investigated. It exhibited strong fluorescence responses toward Cu2+and high selectivity over other metal ions. The binding constant between the probe and Cu2+was calculated using Benesi–Hildebrand equation.     

Low generational polyamidoamine dendrimers to enhance the solubility of folic acid:A‘‘dendritic effect’’investigation

Low generational(G0–G2,G for generation) polyamidoamine(PAMAM) dendrimers were investigated as enhancers to improve the aqueous solubility of folic acid at pH 11 and pH 5.In these two cases,the solubility of folic acid increases with both the dendrimer concentration and generation.However,the solubilization mechanism is different.The electrostatic interaction between the primary amines of dendrimers and the ionized carboxylic groups of folic acid dominates the dissolution process at pH 11 while the increase of the solubility of folic acid at pH 5 is attributed to the hydrophobic encapsulation inside the dendrimer molecules.In addition,for comparison ethylenediamine was used as a small molecule control to examine the ‘‘dendritic effect' in the dendrimer-related solubilization process.Interestingly,PAMAM dendrimers exhibit,at pH 5,a significant superiority over ethylenediamine in enhancing solubility,whereas this ‘‘dendritic effect' cannot be observed under the basic condition.     

Synthesis of ester-capped carbosilane dendrimers via a hybrid divergent–convergent method

A series of novel ester-capped carbosilane dendrimers（G0-COOCH3–G2-COOCH3） were designed and successfully synthesized via a hybrid divergent–convergent method through a facile hydrosilylation reaction. The structures of these dendrimers were confirmed by FTIR,1H NMR, and HRMS analyses.     

A New Maleamide Bridged Carbazole Chromogenic-sensor Based on Proton Transfer Signaling Mode

A Maleamide bridged carbazole receptor was designed and synthesized, the interactions between the receptor and anions, such as Ac-, H2PO4-, OH-, F-, Cl-, Br- and I- in DMSO were investigated by UV-Vis spectroscopy and 1H NMR titration. The results of UV-Vis spectral studies indicate that interactions existed between receptor and anions, which induced remarkable color changes. The 1H NMR titration indicated amide moiety of the receptor was deprontonated first when a small quantity of anions such as Ac-, H2PO4-, F- were added; however, the carbazole N―H was gradually deprontonated upon the addition of anions.     

银离子与聚酰胺-胺型树形高分子配位作用的研究

The complexation between poly(amidoamine) (PAMAM) dendrimers and silver ion was studied in this paper. The results showed that generations and surface groups of dendrimers， reaction time， pH value， mole ratio of Ag⁺/PAMAM dendrimers， as well as reaction temperature strongly influence complexation between Ag⁺ and PAMAM dendrimers. The maximum complexing number of Ag⁺ that amino-， hydroxyl- and carboxylate- terminated PAMAM dendrimers could bind has been obtained. It has been found that the measured value of amino- and hydroxyl- ter-minated PAMAM is almost similar to the theory value， but to carboxylate- terminated PAMAM， there is a dis-crepancy between the measured value and theory value because of the electrostatic interaction between the silver ion and carboxyl group.     

SYNTHESIS AND POLYMERIZATION OF 2-OXO-3-METHYLENE-1,4-DIOXANES

A new kind of monomers was successfully synthesized by the reaction between 2-chloro methyl cycloketal and trimethylsilyl cyanide, followed by ring closure and dehaiogenation. Polymerizations of the monomers were carried out in benzene solution at 80℃with benzoyl peroxide as initiator. Both the structures of monomers and polymers were characterized by IR, ~1H NMR, ~(13)C NMR and elemental analysis.     

新型线状-树枝状两亲嵌段共聚物的合成

本文设计合成了一系列由不同链长的聚丙烯酸(PAA)为亲水嵌段和不同代数聚苄醚树枝体(Dendr.PBE)为疏水嵌段的杂化共聚物(PAA-Dendr.PBE)。     

Some structural characteristics of self-associates in the system hydrophobic dendrimer-sodium octanoate-water based on 13C NMR data

Ternary systems hydrophobic dendrimer-surfactant-water were studied by ¹³C NMR spectroscopy in a wide temperature range. The addition of amphiphilic molecules can “dissolve” particles of hydrophobic dendrimers in water due to the formation of supramolecular complexes, because the surface becomes hydrophilic.     

Comparison of facially amphiphilic biaryl dendrimers with classical amphiphilic ones using protein surface recognition as the tool

Facially amphiphilic biaryl dendrimers are compared with the more classical benzyl ether amphiphilic dendrimers for molecular recognition, using protein binding as the probe. The protein used for the proposed study is chymotrypsin (ChT). A generation-dependent binding affinity was observed with the benzyl ether dendrimers, while the affinities were independent of generation in the case of the biaryl dendrimers. Similarly, although the ligands incorporated in both dendrons are the same, the biaryl dendrimers are able to bind more proteins compared to the benzyl ether dendrimers. For example, G3-dendron of biaryl dendrimer can bind six molecules of chymotrypsin, whereas G3-analogue of benzyl ether dendrimers can bind only three molecules of chymotrypsin. This result is consistent with our hypothesis that the internal layers of the facially amphiphilic biaryl dendrons are solvent-exposed and accessible for recognition. In addition, the systematic size differences in dendrons were also used to gain insights into the substrate selectivity that the enzyme gains upon binding to a ligand scaffold.     

两亲性树枝状大分子作为药物缓释载体的研究

利用胆酸对1代聚酰胺-胺树枝状大分子进行修饰,得到两亲性树枝状大分子(PAMAM1-CA6)。采用1H-NMR和酸碱滴定法测得每个1代PAMAM分子上共价键连了6个胆酸分子。PAMAM1-CA6在水相中自组装成纳米粒子,粒径约为273nm。以抗癌药物氨甲喋呤为模型考察了此两亲性树枝状大分子对药物的缓释行为。在碱性条件下(pH=10),PAMAM1-CA6对氨甲喋呤的释放较为缓慢;随着溶液pH的降低,药物的释放速率明显加快。说明PAMAM1-CA6对氨甲喋呤的释放具有环境响应性。体外细胞实验的结果表明,PAMAM1-CA6能够显著地提高氨甲喋呤的疗效。因此,这类由低代树枝状大分子制得的材料有望成为新型的药物控释载体。     

Cu2+对树状大分子PAMAM-FCD荧光性能的影响

以小分子2-芴醛(FCD)修饰树状大分子聚酰胺-氨PAMAM, 合成了1~3代树状大分子PAMAM-FCD, 用IR, 1H NMR和MALDI-TOF-MS等手段表征了化合物结构, 研究了Cu2+浓度对其荧光及紫外性能的影响. 结果表明, Cu2+可使其荧光强度和紫外吸收不同程度地增强. 在紫外光谱中, Cu2+自身的吸收峰消失, 表明Cu2+参与配位. PAMAM-FCD有望成为蓝光区荧光材料及树状大分子-铜杂化材料.     

Reactivity at the interface of chiral amphiphilic dendrimers. High asymmetric reduction by NaBH(4) of various prochiral ketones.

New amphiphilic dendrimers derived from PAMAM and D-gluconolactone were found to induce chirality in the reduction of prochiral ketones by NaBH(4), in heterogeneous (THF) and homogeneous (water) conditions. The third generation of these amphiphilic dendrimers, G(3)G, was found to be a good chiral ligand for the reduction of various prochiral ketones in heterogeneous conditions. Even with substrates well-known to give poor results (especially linear ketones), good enantioselectivities were obtained. It is also important to notice that under heterogeneous conditions (THF) the dendrimer could be recovered by filtration, regenerated, and recycled (up to 10 times), leading to reproducible results in asymmetric reduction of ketones. We have also discussed the reduction of acetophenone in water. Evidence is presented that the selectivity is dominated by the architecture of the dendrimer and some supramolecular ordering in the position of the ketone at the chiral solvating interface. The results obtained showed a correlation between stereoselectivity of the reduction and the compact character of the dendritic particles.     

Novel amphiphilic linear polymer/dendrimer block copolymer: Synthesis of poly(2-methyl-2-oxazoline)-block-poly(amido amine) dendrimer

Novel linear polymer/dendrimer block copolymers, poly(2-methyl-2-oxazoline)-block-poly(amido amine) dendrimers (water-soluble full-generation type 4 (G = 4.0 and 5.0) and amphiphilic half-generation type 5 (G = 3.5, 4.5, and 5.5)), were synthesized by divergent-growth dendrimer construction with ω-ethylenediamine-terminated poly(2-methyl-2-oxazoline), which was prepared by living ring-opening polymerization of 2-methyl-2-oxazoline. Assembly of the amphiphilic dendrimer-based block copolymer (G = 5.5) was investigated by surface tension measurements (critical micelle concentration, 0.49 wt.-%) and by small-angle neutron scattering analysis (spherical particles; assembled number, ca. 10³).     

Cinnamoyl shell‐modified poly(amidoamine) dendrimers

Poly(amidoamine)(PAMAM) dendrimers with a cinnamoyl shell were prepared by reacting full generation PAMAM dendrimers (G=3.0) with 2‐chloroethanol and cinnamoyl chloride, which resulted in densely packed polymerizable unsaturated groups on the periphery. The cinnamoyl shell of the dendrimers dimerized when irradiated under a UV light by using 5‐nitroacenaphthylene as an initiator in dilute dimethylformamide (DMF). FTIR, ¹H NMR, UV‐Vis, SEC, and a viscosity test certified that the photocycloaddition of the cinnamoyl shell of the dendrimers took place within the molecules with the disappearance of double bond signals in the FTIR. ¹H NMR spectra as well as the intrinsic viscosity and polydispersity value of the products both before and after irradiation showed no difference. It was further found that the cinnamoyl shell‐modified dendrimers possessed fluorescence property, and the fluorescence intensity became stronger when the shell was photocyclized under UV‐ irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4147–4153, 2000     

External electrostatic interaction versus internal encapsulation between cationic dendrimers and negatively charged drugs: which contributes more to solubility enhancement of the drugs?

Relationships of electrostatic interaction and encapsulation between poly(amidoamine) (PAMAM) dendrimers and negatively charged drug molecules have been investigated by aqueous solubility and NMR ( (1)H NMR and two-dimensional nuclear Overhauser effect spectroscopy (2D-NOESY)) studies. PAMAM dendrimers significantly increased the solubilities of phenobarbital and sulfamethoxazole, but scarcely influenced those of primidone and trimethoprim. Moreover, (1)H NMR and 2D-NOESY measurements indicated that few phenobarbital or sulfamethoxazole molecules were entrapped in the cavities of low-generation dendrimers (generation 3, G3). These results suggest that external electrostatic interaction contributes more to the solubility enhancement of drugs than internal encapsulation.     

Specific binding structures of dendrimers on lipid bilayer membranes

Dissipative particle dynamics simulations are used to study the specific binding structures of polyamidoamine (PAMAM) dendrimers on amphiphilic membranes and the permeation mechanisms. Mutually consistent coarse-grained (CG) models both for PAMAM dendrimers and for dimyristoylphosphatidylcholine (DMPC) lipid molecules are constructed. The PAMAM CG model describes correctly the conformational behavior of the dendrimers, and the DMPC CG model can properly give the surface tension of the amphiphilic membrane. A series of systematic simulations is performed to investigate the binding structures of the dendrimers on membranes with varied length of the hydrophobic tails of amphiphiles. The permeability of dendrimers across membranes is enhanced upon increasing the dendrimer size (generation). The length of the hydrophobic tails of amphiphiles in turn affects the dendrimer conformation, as well as the binding structure of the dendrimer-membrane complexes. The negative curvature of the membrane formed in the dendrimer-membrane complexes is related to dendrimer concentration. Higher dendrimer concentration together with increased dendrimer generation is observed to enhance the permeability of dendrimers across the amphiphilic membranes.