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1.
Two Keplerate‐type macroions, [MoVI72FeIII30O252‐ (CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]?ca. 150 H2O= {Mo72Fe30} and [{Na(H2O)12}?{MoVI72CrIII30O252(CH3COO)19‐ (H2O)94}]?ca. 120 H2O= {Mo72Cr30} , with identical size and shape but different charge density, can self‐assemble into spherical “blackberry”‐like structures in aqueous solution by means of electrostatic interactions. These two macroanions can self‐recognize each other and self‐assemble into two separate types of homogeneous blackberries in their mixed dilute aqueous solution, in which they carry ?7 and ?5 net charges, respectively. Either adjusting the solution pH or raising temperature is expected to make the self‐recognition more difficult, by making the charge densities of the two clusters closer, or by decreasing the activation energy barrier for the blackberry formation, respectively. Amazingly, the self‐recognition behavior remains, as confirmed by dynamic and static light scattering, TEM, and energy dispersive spectroscopy techniques. The results prove that the self‐recognition behavior of the macroions due to the long‐range electrostatic interaction is universal and can be achieved when only minimum differences exist between two types of macroanions.  相似文献   

2.
A polypseudorotaxane (PPR) comprising γ‐cyclodextrin (γ‐CD) as host molecules and poly(N‐isopropylacrylamide) (PNIPAM) as a guest polymer is prepared via self‐assembly in aqueous solution. Due to the bulky pendant isopropylamide group, PNIPAM exhibits size‐selectivity toward self‐assembly with α‐, β‐, and γ‐CDs. It can fit into the cavity of γ‐CD to give rise to a PPR, but cannot pass through α‐CD and β‐CD under the same conditions. The ratio of the number of γ‐CD molecules to entrapped NIPAM repeat units is kept at 1:2.2 or 1:2.4, determined by 1H NMR spectroscopy and TGA analysis, respectively, indicating that there are more than 2 but less than 3 NIPAM repeat units included by one γ‐CD molecule. This finding opens new avenues to PPR‐based supramolecular polymers to be used as solid, stimuli‐responsive materials.  相似文献   

3.
The self‐assembly of semiglobular, positively charged poly(propyleneimine) (PPI) dendrimers with small monovalent counterions (e.g., Cl?) in water/acetone mixtures was investigated. We showed that PPI dendrimers can assemble into hollow, spherical, single‐layered blackberry‐type structures mediated by the presence of monovalent counterions. The effects on the assembly of changing the solvent polarity and adjusting the pH were further investigated to confirm the presence of electrostatic interactions and hydrogen bonding as the driving forces. Results showed that PPI dendrimers form stable, hollow spheres in 5–20 % v/v acetone/water and that the size of the spheres decreases monotonically as the solvent polarity and/or the charge on the dendrimers (i.e., lower solution pH) increases. This is the first example to show that small monovalent counterions can trigger attraction among PPI dendrimers (or broadly defined polyelectrolytes) that is strong enough to bring them together to form large, stable supramolecular assemblies, which indicates that these organic macroions have similar solution behavior to more‐well‐defined inorganic molecular macroions.  相似文献   

4.
In recent years β‐amino acids have increased their importance enormously in defining secondary structures of β‐peptides. Interest in β‐amino acids raises the question: Why and how did nature choose α‐amino acids for the central role in life? In this article we present experimental results of MS and 31P NMR methods on the chemical behavior of N‐phosphorylated α‐alanine, β‐alanine, and γ‐amino butyric acid in different solvents. N‐Phosphoryl α‐alanine can self‐assemble to N‐phosphopeptides either in water or in organic solvents, while no assembly was observed for β‐ or γ‐amino acids. An intramolecular carboxylic–phosphoric mixed anhydride (IMCPA) is the key structure responsible for their chemical behaviors. Relative energies and solvent effects of three isomers of IMCPA derived from α‐alanine (2a–c), with five‐membered ring, and five isomers of IMCPA derived from β‐alanine (4a–e), with six‐membered ring, were calculated with density functional theory at the B3LYP/6‐31G** level. The lower relative energy (3.2 kcal/mol in water) of 2b and lower energy barrier for its formation (16.7 kcal/mol in water) are responsible for the peptide formation from N‐phosphoryl α‐alanine. Both experimental and theoretical studies indicate that the structural difference among α‐, β‐, and γ‐amino acids can be recognized by formation of IMCPA after N‐phosphorylation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 232–241, 2003  相似文献   

5.
Multistimuli‐responsive precise morphological control over self‐assembled polymers is of great importance for applications in nanoscience as drug delivery system. A novel pH, photoresponsive, and cyclodextrin‐responsive block copolymer were developed to investigate the reversible morphological transition from micelles to vesicles. The azobenzene‐containing block copolymer poly(ethylene oxide)‐b‐poly(2‐(diethylamino)ethyl methacrylate‐co‐6‐(4‐phenylazo phenoxy)hexyl methacrylate) [PEO‐b‐P(DEAEMA‐co‐PPHMA)] was synthesized by atom transfer radical polymerization. This system can self‐assemble into vesicles in aqueous solution at pH 8. On adjusting the solution pH to 3, there was a transition from vesicles to micelles. The same behavior, that is, transition from vesicles to micelles was also realizable on addition of β‐cyclodextrin (β‐CD) to the PEO‐b‐P(DEAEMA‐co‐PPHMA) solution at pH 8. Furthermore, after β‐CD was added, alternating irradiation of the solution with UV and visible light can also induce the reversible micelle‐to‐vesicle transition because of the photoinduced trans‐to‐cis isomerization of azobenzene units. The multistimuli‐responsive precise morphological changes were studied by laser light scattering, transmission electron microscopy, and UV–vis spectra. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   

6.
A new type of amphiphilic macromolecule was synthesized through the attachment of a poly(ethylene glycol) chain to a permethyl‐amino‐β‐cyclodextrin ring. The structure of the product was studied with 1D and 2D NMR experiments and with MALDI‐TOF MS. The resulting comet‐shaped molecule showed self‐assembly behavior in polar solvents. The presence of supramolecular structures in aqueous media was detected with dynamic light scattering and proven also by 2D NOESY and DOSY experiments. The supramolecular structures that formed could serve as starting materials for new types of drug delivery bioconjugates containing two independent dopable sites, that is, the cyclodextrin ring and the core of the supramolecular structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5149–5155, 2007  相似文献   

7.
The solution properties of low‐charge‐density ampholytic terpolymers of acrylamide, sodium 3‐acrylamido‐3‐methylbutanoate, and (3‐acrylamidopropyl)trimethylammonium chloride were studied as functions of the solution pH, ionic strength, and polymer concentration. Terpolymers with low charge densities, large charge asymmetries, or both exhibited excellent solubility in deionized (DI) water, and higher charge density terpolymers were readily dispersible in DI water; however, the higher charge density terpolymer solutions separated into polymer‐rich and polymer‐poor phases upon standing over time. Charge‐balanced terpolymers exhibited antipolyelectrolyte behavior at pH values greater than or equal to the ambient pH (6.5 ± 0.2); the same terpolymers behaved increasingly as cationic polyelectrolytes with decreasing solution pH because of the protonation of the 3‐acrylamido‐3‐methylbutanoate (AMB) repeat units. Unbalanced terpolymers generally exhibited polyelectrolyte behavior, although the effects of intramolecular electrostatic attractions (i.e., polyampholyte effects) on the hydrodynamic volume of the unbalanced terpolymer coils were evident at certain values of the solution pH and salt concentration. The dilute‐solution behavior of the terpolymers correlated well with the behavior predicted by several polyampholyte solution theories. In the semidilute regime, solution viscosities increased with increasing terpolymer charge density, and this indicated a significant enhancement of the solution viscosity by intermolecular electrostatic associations. Upon the addition of NaCl, semidilute‐solution viscosities tended to decrease because of the disruption of the intermolecular electrostatic associations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3252–3270, 2004  相似文献   

8.
Double helices are not common in polypeptides and proteins except in the peptide antibiotic gramicidin A and analogous l,d ‐peptides. In contrast to natural polypeptides, remarkable β‐double‐helical structures from achiral γ‐peptides built from α,β‐unsaturated γ‐amino acids have been observed. The crystal structures suggest that they adopted parallel β‐double helical structures and these structures are stabilized by the interstrand backbone amide H‐bonds. Furthermore, both NMR spectroscopy and fluorescence studies support the existence of double‐helical conformations in solution. Although a variety of folded architectures featuring distinct H‐bonds have been discovered from the β‐ and γ‐peptide foldamers, this is the first report to show that achiral γ‐peptides can spontaneously intertwine into β‐double helical structures.  相似文献   

9.
Multi‐micelle aggregation (MMA) mechanism is widely acknowledged to explicate large spherical micelles self‐assembly, but the process of MMA during self‐assembly is hard to observe. Herein, a novel kind of strong, regular microspheres fabricated from self‐assembly of amphiphilic anthracene‐functionalized β‐cyclodextrin (CD‐AN) via Cu(I)‐catalyzed azide‐alkyne click reactions is reported. The obtained CD‐AN amphiphiles can self‐assemble in water from primary core–shell micelles to secondary aggregates with the diameter changing from several tens nm to around 600–700 nm via MMA process according to the images of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy as well as the dynamic light scattering measurements, followed by further crosslinking through photo‐dimerization of anthracene. What merits special attention is that such photo‐crosslinked self‐assemblies are able to disaggregate reversibly into primary nanoparticles when changing the solution conditions, which is benefited from the designed regular structure of CD‐AN and the rigid ranging of anthracene during assembly, thus confirming the process of MMA.

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10.
A facile and green approach is reported to construct pixantrone/poly(γ‐glutamic acid) nanoparticles (PIX/γ‐PGA NPs) as an oral drug delivery system through the complex self‐assembly of polyelectrolyte γ‐PGA and the anticancer drug pixantrone dimaleate (PDM). The complex self‐assembly behavior is investigated in detail. The results demonstrate that PDM can interact with γ‐PGA to conveniently form NPs and the size of NPs can be controlled by adjusting the solution volume ratio of PDM to γ‐PGA. These NPs illustrate their pH‐dependent release behavior, efficient cellular uptake and enhanced drug efficacy through an in vitro release study, flow cytometry, CLSM analysis and the MTT assay. In summary, PIX/γ‐PGA NPs may serve as a promising oral drug delivery system for cancer therapy.

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11.
Molecular motions of single polycarbonate (PC) chains threaded into crystalline γ‐cyclodextrin (γ‐CD) channels were examined using solid‐state 13C NMR and molecular dynamics simulations. The location of PC within the channels was confirmed by spin diffusion from a PC 13C label to natural‐abundance 13C of the γ‐CD. Rotor‐encoded longitudinal magnetization (RELM) (under 7‐kHz magic‐angle sample‐spinning conditions) was combined with multiple‐pulse 1H‐1H dipolar decoupling to detect large‐amplitude phenyl‐ring motion in both bulk PC and polycarbonate γ‐cyclodextrin inclusion compound (PC‐γ‐CD). The RELM results indicate that the phenyl rings in PC‐γ‐CD undergo 180° flips faster than 10 kHz just as in bulk PC. The molecular dynamics simulations show that the frequency of the phenyl‐ring flips depends on the cooperative motions of PC atoms and neighboring atoms of the γ‐CD channel. The distribution of protonated aromatic‐carbon laboratory and rotating‐frame 13C spin‐lattice relaxation rates for bulk PC and PC‐γ‐CD are similar but not identical. The distributions for both systems arise from site heterogeneities. For bulk PC, the heterogeneity is attributed to variations in local chain packing, and for PC‐γ‐CD the heterogeneity arises from variations in the location of the PC phenyl rings in the γ‐CD channel. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1271–1282, 2007  相似文献   

12.
The controlled secondary self‐assembly of amphiphilic molecules in solution is theoretically and practically significant in amphiphilic molecular applications. An amphiphilic β‐cyclodextrin (β‐CD) dimer, namely LA‐(CD)2, has been synthesized, wherein one lithocholic acid (LA) unit is hydrophobic and two β‐CD units are hydrophilic. In an aqueous solution at room temperature, LA‐(CD)2 self‐assembles into spherical micelles without ultrasonication. The primary micelles dissociates and then secondarily form self‐assemblies with branched structures under ultrasonication. The branched aggregates revert to primary micelles at high temperature. The ultrasound‐driven secondary self‐assembly is confirmed by transmission electron microscopy, dynamic light scattering, 1H NMR spectroscopy, and Cu2+‐responsive experiments. Furthermore, 2D NOESY NMR and UV/Vis spectroscopy results indicate that the formation of the primary micelles is driven by hydrophilic–hydrophobic interactions, whereas host–guest interactions promote the formation of the secondary assemblies. Additionally, ultrasonication is shown to be able to effectively destroy the primary hydrophilic–hydrophobic balances while enhancing the host–guest interaction between the LA and β‐CD moieties at room temperature.  相似文献   

13.
We report on the synthesis of an H‐shaped polymer bonding β‐cyclodextrin (β‐CD) at branch points and influences of attached β‐CD on physical properties. First, a poly(ethylene glycol)(PEG)‐based functional macroinitiator bearing two azidos and four chlorines at chain‐ends (PEG‐2N3(‐4Cl)) was prepared via terminal modification reactions. Then, PEG‐2N3(‐4Cl) was applied to initiate the atom transfer radical polymerization of N‐isopropylacrylamide, leading to the synthesis of an H‐shaped block polymer with PEG as the central chain and poly(N‐isopropylacrylamide) (PNIPAM) as side‐arms (PEG‐2N3(‐4PNIPAM)). Azido groups were at the branch points of the polymer. Finally, the click reaction between PEG‐2N3(‐4PNIPAM) and alkynyl monosubstituted β‐cyclodextrin (β‐CD) afforded another H‐shaped polymer with two β‐CDs bonding at the polymer branch points (PEG‐2CD(‐4PNIPAM)). The glass transition temperature (Tg) and lower critical solution temperature (LCST) of the H‐shaped polymer increased after the attachment of β‐CD. The self‐assembly and thermal responsive behaviors, as well as the encapsulation behaviors of PEG‐2CD(‐4PNIPAM) were also altered. When temperature was below the LCSTs, PEG‐2N3(‐2PNIPAM) dissolved in water molecularly, whereas PEG‐2CD(‐4PNIPAM) could self‐assemble into nano‐sized micelles. After the LCST transitions, PEG‐2N3(‐4PNIPAM) aggregated into micron‐sized unstable particles, whereas PEG‐2CD(‐4PNIPAM) transformed into PNIPAM‐cored nanomicelles. Besides, PEG‐2CD(‐4PNIPAM) can encapsulate doxorubicin below its LCST due to the formation of micelles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013  相似文献   

14.
Three newly synthesized chiral selectors, namely, 2IO‐, 3IO‐, and 6IO‐carboxymethyl‐γ‐cyclodextrin, native γ‐cyclodextrin, and commercially available carboxymethylated γ‐cyclodextrin with degree of substitution of 3–6 were used as additives in a background electrolyte composed of phosphate buffer at 20 mmol/L concentration and pH 2.5. This system was used for the analysis of several biologically significant low‐molecular‐mass chiral compounds by capillary electrophoresis. The results confirmed that the position of carboxymethyl group influences the enantioseparation efficiency of all the studied analytes. The 2IO‐ and 3IO‐ regioisomers provide a significantly better resolution than native γ‐cyclodextrin, while the 6IO‐regioisomer gives only a slightly better enantioseparation than native γ‐cyclodextrin. The application of γ‐cyclodextrin possessing higher number of carboxymethyl groups led to the best resolution for the majority of the compounds analyzed.  相似文献   

15.
The hydrophilic polyoxotungstate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- ({Cu20P8W48}) self-assembles into single-layer, hollow, spherical "blackberry"-type structures in aqueous solutions, as studied by dynamic light scattering (DLS), static light scattering (SLS), zeta potential analysis, and scanning electron microscopy (SEM) techniques. This represents the first report of blackberry formation for a non-Mo-containing polyoxometalate. There is no obvious change in the shape and size of the blackberries during the slow blackberry formation process, neither with macroionic concentration nor with temperature. Our results suggest that the blackberry-type structure formation is most likely a general phenomenon for hydrophilic macroions with suitable size and charge in a polar solvent, and not a specific property of polyoxomolybdates and their derivatives. The {Cu20P8W48} macroions are thus far the smallest type of macroions to date (equivalent radius < 2 nm) showing the unique self-assembly behavior, helping us to move one step closer toward identifying the transition point from simple ions (can be described by the Debye-Hückel theory) to macroions in very dilute solutions. Moreover, by using {Cu20P8W48} blackberry-type structures as the model system, the electrophoretic properties of macroionic supramolecular structures are studied for the first time via zeta-potential analysis. The mobility of blackberry-type structures is determined and used for understanding the state of small cations in solution. We notice that the average charge density on each {Cu20P8W48} macroanion in a blackberry is much lower than that of discrete "free" {Cu20P8W48} macroions. This result suggests that some small alkali counterions are closely associated with, or even incorporated into, the blackberry-type structures and thus do not contribute to solution conductivity. This model is fully consistent with our speculation that monovalent counterions play an important role in the self-assembly of macroions, possibly providing an attractive force contributing to blackberry formation.  相似文献   

16.
Host–guest interactions between α‐, β‐ and γ‐cyclodextrins and vanadocene dichloride (Cp2VCl2) have been investigated by a combination of thermogravimetric analysis, differential scanning calorimetry, powder X‐ray diffraction and solid‐state and solution electron paramagnetic resonance (EPR) spectroscopy. The solid‐state results demonstrated that only β‐ and γ‐cyclodextrins form 1:1 inclusion complexes, while α‐cyclodextrin does not form an inclusion complex with Cp2VCl2. The β‐ and γ‐CD–Cp2VCl2 inclusion complexes exhibited anisotropic electron‐51V (I = 7/2) hyperfine coupling constants whereas the α‐CD–Cp2VCl2 system showed only an asymmetric peak with no anisotropic hyperfine constant. On the other hand, solution EPR spectroscopy showed that α‐cyclodextrin (α‐CD) may be involved in weak host–guest interactions in equilibrium with free vanadocene species. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
Self‐assembled, noncovalent polymeric biodegradable materials mimicking proteoglycan aggregates were synthesized from inclusion complexes of cationic surfactants with γ‐cyclodextrin and the natural anionic polymer hyaluronan. The amorphous structure of this ternary system was proven by X‐ray diffraction and thermal analysis. Light‐scattering measurements showed that there was a competition between hyaluronic acid and the surfactant for the cyclodextrin cavity. These self‐assembled supramolecular matrices were loaded with both hydrophilic and lipophilic drug substances for dissolution studies. The release of the entrapped drugs was found to be controlled by cations in the surrounding media and by biodegradation. Slow drug release in an ion‐free medium became faster in physiological salt solution in which the macroscopic polymer matrix was disassembled. In contrast, the enzymatic degradation of hyaluronan was hindered in the polymeric matrix. The supramolecular systems consisting of γ‐cyclodextrin as a macrocyclic host, a cationic surfactant guest, and hyaluronic acid as the anionic polymer electrostatically cross‐linked by the inclusion complex of the first two was found to be a novel drug‐delivery system for the controlled release of traditional drugs such as curcumin and ketotifen and proteins such as bovine serum albumin.  相似文献   

18.
Enantiomers of Tröger's base were separated by capillary electrophoresis using 2IO‐, 3IO‐, and 6IO‐carboxymethyl‐α‐, β‐, and γ‐cyclodextrin and native α‐, β‐, and γ‐cyclodextrin as chiral additives at 0–12 mmol/L for β‐cyclodextrin and its derivatives and 0–50 mmol/L for α‐ and γ‐cyclodextrins and their derivatives in a background electrolyte composed of sodium phosphate buffer at 20 mmol/L concentration and pH 2.5. Apparent stability constants of all cyclodextrin–Tröger's base complexes were calculated based on capillary electrophoresis data. The obtained results showed that the position of the carboxymethyl group as well as the cavity size of the individual cyclodextrin significantly influences the apparent stability constants of cyclodextrin–Tröger's base complexes.  相似文献   

19.
《Electroanalysis》2006,18(15):1463-1470
The gold electrode is functionalized by sequential self‐assembly of a monolayer of the title thiolated cyclodextrin with and without dopamine included in the cavities. The structure of α‐cyclodextrin modified gold electrode is carefully characterized using STM and AFM. Surface complexation of dopamine is examined and its association constant is evaluated. Chemical reactions accompanying the electrode process of dopamine, which interfere in the electrochemical dopamine determination, are described and the conditions to avoid them are proposed. Dopamine incorporated in the α‐cyclodextrin sites anchored to the electrode surface was found to provide electrochemical contact of the electrode with the solution‐resident dopamine. Dopamine present in the α‐cyclodextrin cavities has different properties compared to dopamine in the bulk buffer solution and can act as a mediator for the dopamine molecules diffusing to the electrode. This unique mediation effect leads to improvement of the sensitivity of dopamine determination using the α‐cyclodextrin modified electrode and a procedure for the determination of dopamine in large excess of ascorbate is proposed.  相似文献   

20.
The rod‐coil molecules with n‐shaped rod building block, consisting of an anthracene unit and two biphenyl groups linked together with acetylenyl bonds at the 1,8‐position of anthracene as a rigid rod segment, and the alkyl or alkyloxy chains with various length (i.e., methoxy‐ ( 1 ), octyl‐ ( 2 ), hexadecyl‐ ( 3 )) at the 10‐position of anthracene and poly(ethylene oxide) with the number of repeating units of 7 connected with biphenyl as coil segments were synthesized. The molecular structures were characterized by 1H NMR and MALDI‐TOF mass spectroscopy. The self‐assembling behavior of new type of molecules 1–3 was investigated by means of DSC, POM, and SAXS at the bulk state. These molecules with a n‐shaped rod building block segment self‐assemble into supramolecular structures through the combination of π–π stacking of rigid rod building blocks and microphase separation of the rod and coil blocks. SAXS studies reveal that molecules 1 and 2 show hexagonal columnar and rectangular columnar structures in the liquid crystalline phase, respectively; meanwhile, molecules 1–3 self‐organize into lamellar structures in the crystalline state. In addition, self‐assembling studies of molecules 1–3 by DLS and TEM indicated that these molecules self‐assemble into elongated nanofibers in aqueous medium. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1415–1422, 2010  相似文献   

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