Functionalization of carbon nanotubes with biodegradable supramolecular polypseudorotaxanes from grafted-poly(ε-caprolactone) and α-cyclodextrins

Functionalization of multiwalled carbon nanotubes (MWNTs) with biodegradable supramolecular polypseudorotaxanes has been successfully performed by utilizing surface-initiated ring-opening polymerization of ε-caprolactone (CL) to yield poly(ε-caprolactone)-grafted MWNTs (MWNT-g-PCL), followed by forming inclusion complexes between grafted-PCL chains and α-cyclodextrins (α-CDs) to give α-CD-NTPCL hybrids. There are significant differences in the morphology and solubility of MWNTs before and after introduction of α-CD. Some protuberances are clearly observed for α-CD-NTPCL as compared with MWNT-g-PCL. Furthermore, the host-guest stoichiometry (monomeric unit of CL/α-CD molar ratio) for α-CD-NTPCL is much higher than that of polypseudorotaxanes consisted of linear PCL and α-CDs. This observation can be explained by a combination of several reasons including the steric hindrance of grafted-PCL, the competitive exclusion between adjacent PCL chains toward α-CD, and the addition order of α-CD as well as the host-guest feed ratio. The present methodology may open up a new opportunity toward the application of supramolecular chemistry for the chemical manipulation and processing of CNTs. Moreover, such novel supramolecular hybrids provide an entry to extend the applications of CNTs to medicine and biology fields through embedding the functional polymers and heterogeneous components.     

The Mobility of Threaded α-Cyclodextrins in PR Copolymer and Its Influences on Mechanical Properties

The methylated polyrotaxane(Me PR) copolymer was prepared via the methylation of hydroxyl of threaded α-cyclodextrin(α-CDs) in polyrotaxane(PR) copolymer by CH_3I/Na H. Its structure was characterized by GPC, IR and NMR. The WXRD and TGA measurements showed the destruction of channel-like crystalline structure in Me PR copolymer. The sliding of threaded α-CDs along PEG axis in PR and Me PR copolymers was demonstrated by their dielectric spectra that also evidenced the presence of rotating of threaded α-CDs around PEG axis in Me PR copolymer. The frequent and vigorous molecular mobility in Me PR and PR copolymers was also verified by dynamic mechanical analysis(DMA) and rheological measurement, which was possibly assigned to the sliding and rotating of threaded α-CDs. DMA and rheological results showed that the mobility of α-CDs could simultaneously strengthen and toughen PR copolymer proved by stress-stain curves. In this paper, we report the CD mobility in PR and Me PR copolymers. The macroscopic behaviors of PR copolymer, such as mechanical properties in solid state, were also found to be benefited from CD mobility.     

INCLUSION COMPLEX FORMATION BETWEEN α-CYCLODEXTRIN AND BIODEGRADABLE COMBLIKE COPOLYMERS WITH POLY(α,β-MALIC ACID) BACKBONES AND mPEG SIDE CHAINS

Inclusion complexes(ICs) composed ofα-cyclodextrins(α-CD) and biodegradable comblike copolymers with poly(α,β-malic acid)(PMA) backbones and methylated poly(ethylene glycol)(mPEG) side chains were prepared by the host-guest reaction.Two series of ICs with mPEG750 and mPEG2000 were prepared.The stoichiometry(EG/CD) of all the ICs in mPEG2000 series was 3.1,no matter what the graft degree was.While in mPEG750 series,the stoichiometry(EG/CD) was very different:it increased with the amount of mPEG decreasing...     

SYNTHESIS AND CHARACTERIZATION OF POLYROTAXANES MADE FROM α-CDs THREADED ONTO TRIBLOCK COPOLYMERS WITH PEG AS A CENTRAL AXLE AND FLANKED BY TWO LOW MOLECULAR WEIGHT POLYSTYRENES AS OUTER STOPPERS

A study has been conducted on the synthesis and characterization of a kind of novel polyrotaxanes comprising α cyclodextrins (α-CDs) threaded on triblock copolymers with poly(ethylene glycol) (PEG) as a central axle and flanked by two low molecular weight polystyrenes as outer stoppers.Styrene was allowed to telomerize with polypseudorotaxanes as chain transfer agents made from the self-assembly of a distal thiol-capped PEG with a varying amount of α-CDs in the presence of a redox initiation system at 40℃ in aqueous solutions.The resulting polyrotaxanes were characterized in detail by 1H-NMR,FTIR,XRD,TG and DSC analyses.The findings from the study demonstrated that the low molecular weight polystyrenes were successfully attached to two axle terminals of polypseudorotaxanes,and the number of α-CDs threaded onto the PEG backbone was tunable by varying its molar feeding ratio to some extent,while the polymerization degree of PS nearly remained constant in this radical telomerization process.     

Aerobic biodegradability of hydroxypropyl-β-cyclodextrins in soil

Hydroxylpropyl-β-cyclodextrins (HP-β-CDs), hydroxyalkyl derivatives of β-CD, used in a broad range of applications in food, pharmaceutical, agriculture and bioremediation of soil because of their specific chemical properties. The possibility of varying the biodegradation rate of HP-β-CDs by changing the DS and substitution pattern makes HP-β-CDs suitable for various applications. Therefore, their biodegradation fate has been of great concern. In this study, the biodegradation of various HP-β -CDs, which have different degrees and patterns of substitution in different soil ecosystems, was investigated. The degree and pattern of substitution of HP-β-CDs were determined by the reductive-cleavage method and methylation analysis. Two common soils and a contaminated soil were used in the biodegradation test. All CDs were found to be more or less biodegradable. Increasing the degree of substitution (DS) had negative effect on the biodegradation rate of HP-β-CDs. The substitution pattern affected the biodegradation, too. The biodegradation rates of CDs in the contaminated soil were higher than that obtained in the uncontaminated soils. The contamination removing ability of CDs was highly affected by their own biodegradation fate in soil.     

Cyclodextrin-Based [c2]Daisy Chain Rotaxane Insulating Two Diarylacetylene Cores

A [c2]daisy chain rotaxane with two diarylacetylene cores was efficiently synthesized in 53 % yield by capping a C₂-symmetric pseudo[2]rotaxane composed of two diarylacetylene-substituted permethylated α-cyclodextrins (PM α-CDs) with aniline stoppers. The maximum absorption wavelength of the [c2]daisy chain rotaxane remained almost unchanged in various solvents, unlike that of the stoppered monomer, indicating that the two independent diarylacetylene cores were insulated from the external environment by the PM α-CDs. Furthermore, the [c2]daisy chain rotaxane exhibited fluorescence emission derived from both diarylacetylene monomers and the excimer, which implies that the [c2]daisy chain structure can undergo contraction and extension. This is the first demonstration of a system in which excimer formation between two π-conjugated molecules within an isolated space can be controlled by the unique motion of a [c2]daisy chain rotaxane.     

Synthesis of linked symmetrical [3] and [5]rotaxanes having an oligomeric phenylene ethynylene (OPE) core skeleton as a π-conjugated guest via double intramolecular self-inclusion

Linked symmetrical [3] and [5]rotaxanes consisting of an oligomeric phenylene ethynylene (OPE) framework as a π-conjugated guest moiety and lipophilic permethylated α-cyclodextrins (PM α-CDs), as macrocyclic hosts have been prepared by double intramolecular self-inclusion of an OPE guest unit carrying two PM α-CDs followed by capping with bulky stopper groups using click azide-alkyne Huisgen cycloaddition or Sonogashira coupling. The structures of these linked rotaxanes were determined by MALDI-TOF mass spectrum and two-dimensional NMR spectroscopy.     

A new FRET nanoprobe for trypsin using a bridged β-cyclodextrin dimer-dye complex and its biological imaging applications

A new self-assembly nanoprobe, mercaptoethylamine-modified-gold nanoparticles-Lysine-bridged-bis(β-cyclodextrins)-fluorescein (MGNPs-Lys-bis(β-CDs)-FL), based on fluorescence resonance energy transfer (FRET) was developed for determination of trypsin firstly in biological systems. With the Lys-bis(β-CDs)-FL complex as an energy donor and mercaptoethylamine (MEA)-modified gold nanoparticles (MGNPs) as an energy acceptor, the two parts assemble an efficient FRET nanoprobe through an amide bond. Trypsin is specific for the hydrolysis of amide linkages of lysine. Therefore, in the presence of trypsin, the nanoprobe is cleaved by trypsin on the binding sites of amide with good specificity and sensitivity, resulting in the fluorescence recovery of the quenched FL. The nanoprobe has good biological applicability and provides a potential assay for further clinical research of trypsin in biosystems.     

Probing high order structure of proteins by fast-atom bombardment mass spectrometry

During the past decade, numerous investigations have demonstrated that the rate at which amide hydrogens located at peptide linkages undergo isotopic exchange is a sensitive probe of the high order structure and dynamics of proteins. The present investigation demonstrates that microbore high-performance liquid chromatography (HPLC) continuous-flow fast-atom bombardment mass spectrometry (FABMS) can be used to accurately quantify deuterium located at peptide linkages in short segments of large proteins. This result is important because it demonstrates the feasibility of using mass spectrometry as a tool for studying the high order structure and dynamics of large proteins. Following a period of deuterium exchange-in, a protein was placed into slow-exchange conditions and fragmented into peptides with pepsin. The digest was analyzed by continuous-flow HPLC FABMS to determine the molecular weights of the peptides, from which the number of deuterons located at the peptide linkages could be deduced. The HPLC step was used both to fractionate the peptides according to their hydrophobicities and to remove through back-exchange all deuterium except that located at peptide amide linkages. This approach has been applied to α-crystallin, a lens protein composed of two gene products with monomer molecular weights of 20 kDa and an aggregate molecular weight approaching 1000 kDa. Results from this study show that some of the peptide amide hydrogens in αA-crystallin exchange very rapidly (k > 10 h^?1) while others exchange very slowly (k < 10^?3 h^?1). The ability not only to detect that a conformational change has occurred, but also to identify the specific regions within the protein where the change occurred, was demonstrated by measuring changes in the exchange rates within these regions as the deuterium exchange-in temperature was increased from 10 to 80 ° C.     

SYNTHESIS AND CHARACTERIZATION OF POLYROTAXANES MADE FROM α-CDs THREADED ONTO TRIBLOCK COPOLYMERS WITH PEG AS A CENTRAL AXLE AND FLANKED BY TWO LOW MOLECULAR WEIGHT POLYSTYRENES AS OUTER STOPPERS

A study has been conducted on the synthesis and characterization of a kind of novel polyrotaxanes comprisingα- cyclodextrins (α-CDs) threaded on triblock eopolymers with poly(ethylene glycol) (PEG) as a central axle and flanked by two low molecular weight polystyrenes as outer stoppers.Styrene was allowed to telomerize with polypseudorotaxanes as chain transfer agents made from the self-assembly of a distal thiol-capped PEG with a varying amount ofα-CDs in the presence of a redox initiation system at 40~C in aqueous solutions.The resulting polyrotaxanes were characterized in detail by ~1H-NMR,FTIR,XRD,TG and DSC analyses.The findings from the study demonstrated that the low molecular weight polystyrenes were successfully attached to two axle terminals of polypseudorotaxanes,and the number ofα-CDs threaded onto the PEG backbone was tunable by varying its molar feeding ratio to some extent,while the polymerization degree of PS nearly remained constant in this radical telomerization process.     

LA PHOTOOXYDATION DU GROUPE PEPTIDE—I. PROTÉINES FIBREUSES*

Abstract— The determination of the α-ketoacids, glyoxylic and pyruvic in partial hydrolysates of fibrous proteins (keratin and fibroin) after exposition to u.v. light has allowed us to suggest a photooxydation mechanism for the α-aminoacid residues of glycine and alanine in proteins. The primary reaction is believed to be the formation of the peptide radical -NH-CR-CO-, and the breakdown of polypeptide chains is explained by the formation of α-ketoacyl peptide linkages.     

Synthesis and characterisation of novel chemical conjugates based on α,β-polyaspartylhydrazide and β-cyclodextrins

A new family of supramolecular systems based on a synthetic polyaminoacid and cyclic oligosaccharides such as β-cyclodextrins (β-CDs) was synthesised. The pharmaceutical potential of these systems arises from the proper combination between the complexing properties of cyclodextrins and the particular pharmacokinetic profile that can be obtained by using macromolecular conjugates with a biocompatible backbone. Five supramolecular conjugates were synthesised by using α,β-polyaspartylhydrazide (PAHy) as a polymeric component and various amounts of two β-CD derivatives. In particular, by reaction of PAHy with β-CD monoaldehyde, samples named as A₁, A₂ and A₃, bearing, respectively, 4.0, 7.5 and 10.7 mol% of β-CDs were obtained. The reaction of PAHy with 6-[aminoethyl(4′-carboxybutanamide)]-β-CD afforded samples named as B₁ and B₂, bearing, respectively, 1.8 and 2.6 mol% of β-CDs linked to the polymer. The occurrence of the conjugation reactions as well as the evaluation of the amount of oligosaccharides conjugated to the polymeric backbone were confirmed by FT-IR, ¹H NMR, DSC, SEC analyses and viscosimetric measurements. Molecular weight values obtained by SEC analysis were in good agreement with the theoretical increase of molecular weight of PAHy due to the β-CD moieties linked to the polymeric backbone. Fluorescence studies on the conjugate A₃ evidenced an interaction of a probe molecule with β-CDs linked to PAHy greater than that found with β-CDs alone and even in both cases the formation of a 1:1 host-guest complex occurs.     

Branched Multifunctional Polyether Polyketals: Variation of Ketal Group Structure Enables Unprecedented Control over Polymer Degradation in Solution and within Cells

Multifunctional biocompatible and biodegradable nanomaterials incorporating specific degradable linkages that respond to various stimuli and with defined degradation profiles are critical to the advancement of targeted nanomedicine. Herein we report, for the first time, a new class of multifunctional dendritic polyether polyketals containing different ketal linkages in their backbone that exhibit unprecedented control over degradation in solution and within the cells. High-molecular-weight and highly compact poly(ketal hydroxyethers) (PKHEs) were synthesized from newly designed α-epoxy-ω-hydroxyl-functionalized AB(2)-type ketal monomers carrying structurally different ketal groups (both cyclic and acyclic) with good control over polymer properties by anionic ring-opening multibranching polymerization. Polymer functionalization with multiple azide and amine groups was achieved without degradation of the ketal group. The polymer degradation was controlled primarily by the differences in the structure and torsional strain of the substituted ketal groups in the main chain, while for polymers with linear (acyclic) ketal groups, the hydrophobicity of the polymer may play an additional role. This was supported by the log?P values of the monomers and the hydrophobicity of the polymers determined by fluorescence spectroscopy using pyrene as the probe. A range of hydrolysis half-lives of the polymers at mild acidic pH values was achieved, from a few minutes to a few hundred days, directly correlating with the differences in ketal group structures. Confocal microscopy analyses demonstrated similar degradation profiles for PKHEs within live cells, as seen in solution and the delivery of fluorescent marker to the cytosol. The cell viability measured by MTS assay and blood compatibility determined by complement activation, platelet activation, and coagulation assays demonstrate that PKHEs and their degradation products are highly biocompatible. Taken together, these data demonstrate the utility this new class of biodegradable polymer as a highly promising candidate in the development of multifunctional nanomedicine.     

Diffusions of β-cyclodextrins in mucus studied by <Superscript>19</Superscript>F diffusion NMR

β-Cyclodextrin (β-CD) based materials have been widely used as drug carriers for pharmaceutical applications. To understand the diffusion of β-CDs in mucus is important for selecting β-CD based drug carriers for applications targeting mucosal absorption because the surfaces of many biological membranes are covered with a highly viscous aqueous mucus layer which forms relatively effective diffusion barriers for drugs. In this study, ¹⁹F self-diffusion NMR technique has been applied to study the self-diffusions of β-CDs in mucus. The ¹⁹F NMR signals arose from 1-fluoroadamantane molecules entrapped in the cavities of β-CDs. The diffusive abilities of different β-CDs in mucus were assessed through analyzing the diffusion coefficients using the presented kinetic model, and Ogston’s and Renkin’s diffusion models for hydrogel systems. The kinetic results show that 2-hydroxypropyl-β-CD and 2-Carboxyethyl-β-CD have the smallest binding affinities to bovine submaxillary mucin and human nasal mucin among five tested β-CDs. The mesh sizes of the bovine submaxillary mucus at different concentrations and that of the human nasal mucus were evaluated using the diffusion models. We hope that this ¹⁹F diffusion method will be useful to study the diffusion of β-CD based materials in other biological systems.     

Encapsulation and sustained release of a model drug, indomethacin, using CO(2)-based microencapsulation

A carbon dioxide (CO(2))-based microencapsulation technique was used to impregnate indomethacin, a model drug, into biodegradable polymer nanoparticles. Compressed CO(2) was emulsified into aqueous suspensions of biodegradable particles. The CO(2) plasticizes the biodegradable polymers, increasing the drug diffusion rate in the particles so that drug loading is enhanced. Four types of biodegradable polymers were investigated, including poly(d,l-lactic acid) (PLA), poly(d,l-lactic acid-co-glycolic acid) (PLGA) with two different molar ratios of LA to GA, and a poly(d,l-lactic acid-b-ethylene glycol) (PLA-PEG) block copolymer. Biodegradable nanoparticles were prepared from polymer solutions through nonsolvent-induced precipitation in the presence of surfactants. Indomethacin was incorporated into biodegradable nanoparticles with no change of the particle size and morphology. The effects of a variety of experimental variables on the drug loadings were investigated. It was found that the drug loading was the highest for PLA homopolymer and decreased in PLGA copolymers as the fraction of glycolic acid increased. Indomethacin was predicted to have higher solubility in PLA than in PLGA based on the calculated solubility parameters. The drug loading in PLA increased markedly as the temperature for impregnation was increased from 35 to 45 degrees C. Drug release from the particles is a diffusion-controlled process, and sustained release can be maintained over 10 h. A simple Fickian diffusion model was used to estimate the diffusion coefficients of indomethacin in the biodegradable polymers. The diffusion coefficients are consistent with previous studies, suggesting that the polymer properties are unchanged by supercritical fluid processing. Supercritical CO(2) is nontoxic, easily separated from the polymers, can extract residual organic solvent, and can sterilize biodegradable polymers. The CO(2)-based microencapsulation technique is promising for the production of drug delivery devices without the use of harmful solvents.     

分子动力学模拟Cu2+对α-突触核蛋白(1-17)肽段构象变化的影响

利用分子动力学模拟研究铜离子(Cu2+)对α-突触核蛋白1-17号氨基酸肽段(α-synuclein(1-17))构象变化的影响,采用GROMOS 43A1力场对Cu2+-α-synuclein(1-17)复合体和α-synuclein(1-17)肽段单体分别进行了6组独立的分子动力学模拟,每组模拟时间为500ns,总模拟时间为3μs.研究结果表明:Cu2+与α-synuclein(1-17)肽段结合使其更易向β折叠片结构折叠,促进了其二级结构的形成,增强了构象的稳定性;Cu2+增大了α-synuclein肽段疏水残基的溶剂可及表面积,增强了其疏水残基的暴露程度.自由能分析指出,Cu2+-α-synuclein(1-17)复合体的自由能比α-synuclein(1-17)肽段低,构象稳定,采样空间紧密,其自由能极小构象为β折叠片结构.构象聚类分析进一步表明,Cu2+使得α-synuclein(1-17)肽段构象趋于稳定.总之,Cu2+诱导固有无序蛋白α-synuclein(1-17)肽段由无序向有序转变,降低了构象的自由能,同时Cu2+增强了α-synuclein(1-17)肽段的疏水性,使得α-synuclein肽段因疏水作用更倾向于形成β折叠片结构,加速其疏水性聚集.     

Polyrotaxane-based triblock copolymers synthesized via ATRP of N-isopropylacrylamide initiated from the terminals of polypseudorotaxane of Br end-capped pluronic 17R4 and β-cyclodextrins

Thermo-responsive polyrotaxane (PR)-based triblock copolymers were synthesized via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide initiated with self-assemblies made from a distal 2-bromoisobutyryl end-capped Pluronic 17R4 (PPO14-PEG24-PPO14) with a varying amount of β-cyclodextrins (β-CDs) in the presence of Cu(I)Cl/PMDETA at 25 °C in aqueous solution. The molecular structure was characterized by means of H NMR, FTIR, WXRD, GPC, TGA and 1 DSC analyses. About half of β-CDs are still entrapped on the Pluronic 17R4 chain while the number of incorporated NIPAAm monomers is nearly a double feed value in the resulting copolymers. The aggregate morphologies in aqueous solution were evidenced by TEM observations. A two-step thermo-responsive transition arising from a combination of a polypseudorotaxane middle block with poly(N-isopropylacrylamide) flanking blocks was also demonstrated by turbidity measurements. Given their thermo-responsive behavior in aqueous solution, these PR-based triblock copolymers show the potential to be used as smart materials for the controlled drug delivery systems, biosensors, and the like.     

Synthesis of novel cyclodextrin derivatives by aromatic spacer insertion and their inclusion ability

Novel cyclic host molecules were synthesized by the insertion of three types of aromatic spacers into the skeleton of permethylated α-cyclodextrin. These host molecules formed a 1:1 complex with sodium 3- and 4-nitrobenzenesulfonates (3- and 4-NBS), and sodium 2,4-dinitrobenzenesulfonate (DNBS) in D₂O/CD₃OD (4:1) solution. The type of spacer inserted remarkably affected the inclusion ability of the hosts toward DNBS. The p-xylylene-inserted CDs showed greater inclusion ability toward DNBS than permethylated α- and β-CDs.     

Reversible α-helix formation controlled by a hydrogen bond surrogate

Strategically placed covalent linkages have been shown to stabilize helical conformations in short peptide sequences. Here we report the synthesis of a stabilized α-helix that utilizes an internal disulfide linkage. Structural analysis indicates that the dynamic nature of the disulfide bridge allows for the reversible formation of an α-helix through oxidation and reduction reactions.     

Double-threaded dimer and supramolecular oligomer formed by stilbene modified cyclodextrin: effect of acyl migration and photostimuli

We observed changing supramolecular structures of stilbene-α-cyclodextrin (StiO-α-CD) by photoirradiation and migration. Stilbene derivatives show photoinduced isomerization under irradiation with λ = 340 nm to give 2-cis-StiO-α-CD and with λ = 254 nm to give 2-trans-StiO-α-CD. Photoisomerization of StiO-α-CD shows the photostationary state during 30 min. 2D NMR and diffusion coefficient studies revealed that 2-trans-StiO-α-CD forms a double-threaded dimer but 2-cis-StiO-α-CD changes to a supramolecular oligomer by photoirradiation. We found that the mutual migration of a stilbene group (StiO) on α-CD occurs under neutral conditions. The StiO group of α-CD (StiO-α-CD) moves between the C2 and C3 positions on the secondary hydroxyl group of StiO-α-CD (the wider rim of α-CD) to give 3-trans-StiO-α-CD. 3-trans-StiO-α-CD forms a supramolecular oligomer, whereas 3-cis-StiO-α-CD changes to a double-threaded dimer, indicating that 3-StiO-α-CDs gives the opposite results in the supramolecular structures of 2-StiO-α-CDs. The thermal isomerization (migration) is very slow. It takes about 300 h to reach the equilibrium state. Moreover, the migration rate constant (k(trans3→2)) of the trans-StiO group from the C3 position to the C2 position of α-CD is faster than k(trans2→3) from the C2 position to the C3 position of α-CD. On the other hand, k(cis2→3) of the cis-StiO group from the C2 position to the C3 position of α-CD is faster than k(cis3→2) from the C3 position to the C2 position, meaning k(cis2→3) > k(cis3→2), which is the opposite result for k(trans3→2) > k(trans2→3). The formation of a stable double-threaded dimer would suppress the migration of the StiO group of StiO-α-CDs in aqueous solutions.