Density functional and molecular docking studies towards investigating the role of single-wall carbon nanotubes as nanocarrier for loading and delivery of pyrazinamide antitubercular drug onto pncA protein

The potential biomedical application of carbon nanotubes (CNTs) pertinent to drug delivery is highly manifested considering the remarkable electronic and structural properties exhibited by CNT. To simulate the interaction of nanomaterials with biomolecular systems, we have performed density functional calculations on the interaction of pyrazinamide (PZA) drug with functionalized single-wall CNT (fSWCNT) as a function of nanotube chirality and length using two different approaches of covalent functionalization, followed by docking simulation of fSWCNT with pncA protein. The functionalization of pristine SWCNT facilitates in enhancing the reactivity of the nanotubes and formation of such type of nanotube-drug conjugate is thermodynamically feasible. Docking studies predict the plausible binding mechanism and suggests that PZA loaded fSWCNT facilitates in the target specific binding of PZA within the protein following a lock and key mechanism. Interestingly, no major structural deformation in the protein was observed after binding with CNT and the interaction between ligand and receptor is mainly hydrophobic in nature. We anticipate that these findings may provide new routes towards the drug delivery mechanism by CNTs with long term practical implications in tuberculosis chemotherapy.     

Effects of noncovalently functionalized multiwalled carbon nanotube with hyperbranched polyesters on mechanical properties of epoxy composites

In order to improve the dispersibility and interface properties of multi-walled carbon nanotubes (MWCNTs) in epoxy resin (EP), aromatic hyperbranched polyesters with terminal carboxyl (HBP) and aromatic hyperbranched polyesters with terminal amino groups (HBPN) were used for noncovalent functionalization of MWCNTs. Epoxy composites reinforced by different types of MWCNT were prepared. The effects of noncovalent functionalization of MWCNTs on the dispersibility, wettability, interface properties and mechanical properties of epoxy composites were investigated. The results show that the dispersibility and wettability of MWCNTs are significantly improved after noncovalent functionalization. A large number of terminal primary amines (NH₂) on noncovalently functionalized MWCNT with HBPN (HBPN-MWCNT) form covalent bonds with EP matrix, and thus the interfacial adhesion is enhanced significantly, resulting in high load transfer efficiency and substantial increase in mechanical properties. The interface with covalent bonding formed between the flexible hyperbranched polyester layer on the surface of HBPN-MWCNT and the EP matrix promotes plastic deformation of the surrounding EP matrix. The toughening mechanisms of HBPN-MWCNT are MWCNT pull-out and a large amount of plastic deformation of the surrounding EP matrix.     

"Fingertip"-guided noncovalent functionalization of carbon nanotubes by dendrons

Noncovalent functionalization of carbon nanotubes (CNTs) by dendrons was demonstrated. Certain types of dendrons successfully functionalized CNT surfaces through the noncovalent interactions between the peripheries of the dendrons and the sidewalls of CNTs. Dendrons have a unique anisotropic shape and an orthogonal functional group at their apex, and thus can generate a certain spacing between the functional groups upon immobilization on surfaces. Atomic force microscope (AFM) imaging, dispersion experiments, and MicroRaman spectroscopy were employed for the characterization of the functionalization. The binding was found to be governed by the chemical nature of the terminal groups, namely, the "fingertips", through a comparison study on the adsorption efficiency of the dendron analogs. Functional groups such as the carboxylic acid group and the benzyl amide group were effective for the cooperative binding. AFM analysis showed that the average spacing generated by the dendrons was 14-15 nm at a particular adsorption condition. Assembling streptavidin on the tubes through the dendrons and biotin confirmed the realization of the regulated spacing as well as the elimination of unwanted aggregation. The noncovalent functionalization of CNTs by a dendron can be a new approach toward sensible nanobiodevices, not only by introducing biomolecular probes on CNTs without disruption of the electronic network of the tubes, but also by providing the immobilized probe molecules with a space ample enough to minimize steric hindrance for the unhindered interaction with their target species.     

运用功能化修饰的碳纳米管针尖测量配体-受体的作用力

电弧法自制碳纳米管原子力显微镜针尖,对其末端进行功能化修饰,然后测量配体-受体之间的作用力。运用没有功能化修饰的碳纳米管针尖与修饰有亲和素分子的基底进行接触测量时,没有粘滞力出现;而运用末端修饰生物素分子的碳纳米管针尖测量时,有粘滞力产生。功能化的碳纳米管针尖直接测得的粘滞力均大约200pN,此值符合一对配体生物素和受体亲和素之间的作用力。这一结果很难用传统的针尖获得,功能化修饰的碳纳米管针尖能够克服传统针尖在力测量中的局限,在生物学和化学领域有着广泛的应用前景。     

DFT study of SiO2 nanoparticles as a drug delivery system: structural and mechanistic aspects

Structural Chemistry - Adsorption and reaction mechanisms for the noncovalent and covalent functionalization of SiO2 nanoparticle (SiNP) with gemcitabine (GEM) anticancer drug have been...     

Multipurpose organically modified carbon nanotubes: from functionalization to nanotube composites

We show that covalent functionalization of carbon nanotubes (CNTs) via 1,3-dipolar cycloaddition is a powerful method for enhancing the ability to process CNTs and facilitating the preparation of hybrid composites, which is achieved solely by mixing. CNTs were functionalized with phenol groups, providing stable dispersions in a range of polar solvents, including water. Additionally, the functionalized CNTs could easily be combined with polymers and layered aluminosilicate clay minerals to give homogeneous, coherent, transparent CNT thin films and gels.     

NHS-ester functionalized poly(PEGMA) brushes on silicon surface for covalent protein immobilization

Poly(PEGMA) homopolymer brushes were developed by atom transfer radical polymerization (ATRP) on the initiator-modified silicon surface (Si-initiator). Through covalent binding, protein immobilization on the poly(PEGMA) films was enabled by further NHS-ester functionalization of the poly(PEGMA) chain ends. The formation of polymer brushes was confirmed by assessing the surface composition (XPS) and morphology (atomic force microscopy (AFM), scanning electronic microscopy (SEM)) of the modified silicon wafer. The binding performance of the NHS-ester functionalized surfaces with two proteins horseradish peroxidase (HRP) and chicken immunoglobulin (IgG) was monitored by direct observation. These results suggest that this method which incorporates the properties of polymer brush onto the binding surfaces may be a good strategy suitable for covalent protein immobilization.     

Characterization of carbonyl chloride-terminated aromatic polyamide nanoparticles with carboxyl groups and their reaction

Aromatic polyamide nanoparticles with carbonyl chloride (COCl) and carboxyl (COOH) groups were obtained using a precipitation polymerization method. The morphology, number of COCl groups incorporated, and degree of polymerization of the resulting particles depended on the reaction system. The COOH group of diamine used decreased the reactivity of NH₂ groups and chemically stabilized the COCl groups existing at the ends of the molecular chains. Also, the COCl groups were retained in particles by the rapid formation of particles. Thus, the chemical structures and formation mechanism were found to play an important role in the formation of particles with COCl groups.     

Functionalization of multi-walled carbon nanotubes by epoxide ring-opening polymerization

In this study, covalent functionalization of carbon nanotubes (CNTs) was accomplished by surface-initiated epoxide ring-opening polymerization. FT-IR spectra showed that polyether and epoxide group covalently attached to the sidewalls of CNTs. TGA results indicated that the polyether was successfully grown from the CNT surface, with the final products having a polymer weight percentage of ca. 14-74 wt%. The O/C ratio of CNTs increased significantly from 5.1% to 29.8% after surface functionalization of CNTs. SEM and TEM images of functionalized CNTs exhibited that the tubes were enwrapped by polymer chains with thickness of several nanometers, forming core-shell structures with CNTs at the center.     

Pyrene‐Anderson‐Modified CNTs as Anode Materials for Lithium‐Ion Batteries

An organo‐functionalized polyoxometalate (POM)–pyrene hybrid (Py‐Anderson) has been used for noncovalent functionalization of carbon nanotubes (CNTs) to give a Py‐Anderson‐CNT nanocomposite through π–π interactions. The as‐synthesized nanocomposite was used as the anode material for lithium‐ion batteries, and shows higher discharge capacities and better rate capacity and cycling stability than the individual components. When the current density was 0.5 mA cm^?2, the nanocomposite exhibited an initial discharge capacity of 1898.5 mA h g^?1 and a high discharge capacity of 665.3 mA h g^?1 for up to 100 cycles. AC impedance spectroscopy provides insight into the electrochemical properties and the charge‐transfer mechanism of the Py‐Anderson‐CNTs electrode.     

Improving the dispersion and flexural strength of multiwalled carbon nanotubes-stiff epoxy composites through β-hydroxyester surface functionalization coupled with the anionic homopolymerization of the epoxy matrix

Multiwalled carbon nanotubes (MWNTs) were functionalized in a two-step acid-epoxy functionalization process, in which suitable surface condition and reactivity compatible with the DGEBA epoxy resin was introduced. The use of (4-dimethylamino)-pyridine as an initiator for DGEBA homopolymerization produced covalent bonds between the functionalized MWNTs and the epoxy matrix through chain transfer reactions involving the secondary hydroxyls. This process yielded uniform MWNTs-stiff epoxy composites with significant enhancement in flexural strength without sacrificing the elastic modulus when compared to the neat resin.     

Electronic structures of hydrogen functionalized carbon nanotube: Density functional theory (DFT) study

Electronic structures and formation mechanism of hydrogen functionalized carbon nanotube (CNT) have been investigated by means of density functional theory (DFT) method. The mechanism of hydrogen addition reaction to the CNT surface was also investigated. Pure and boron-nitrogen (BN) substituted CNT (denoted by CNT and BN-CNT, respectively) were examined as the carbon nanotubes. It was found that the additions of hydrogen atom to B (boron atom) and C (carbon atom) sites of BN-CNT proceed without activation barrier, whereas the hydrogenation of N (nitrogen atom) site needs the activation energy. The electronic states of hydrogen functionalized CNT and BN-CNT were discussed on the basis of theoretical results.     

Perfluorophenyl azide functionalization of electrospun poly(para‐dioxanone)

Strategies to surface‐functionalize scaffolds by covalent binding of biologically active compounds are of fundamental interest to control the interactions between scaffolds and biomolecules or cells. Poly(para‐dioxanone) (PPDO) is a clinically established polymer that has shown potential as temporary implant, eg, for the reconstruction of the inferior vena cava, as a nonwoven fiber mesh. However, PPDO lacks suitable chemical groups for covalent functionalization. Furthermore, PPDO is highly sensitive to hydrolysis, reflected by short in vivo half‐life times and degradation during storage. Establishing a method for covalent functionalization without degradation of this hydrolyzable polymer is therefore important to enable the surface tailoring for tissue engineering applications. It was hypothesized that treatment of PPDO with an N‐hydroxysuccinimide ester group bearing perfluorophenyl azide (PFPA) under UV irradiation would allow efficient surface functionalization of the scaffold. X‐ray photoelectron spectroscopy and attenuated total reflectance Fourier‐transformed infrared spectroscopy investigation revealed the successful binding, while a gel permeation chromatography study showed that degradation did not occur under these conditions. Coupling of a rhodamine dye to the N‐hydroxysuccinimide esters on the surface of a PFPA‐functionalized scaffold via its amine linker showed a homogenous staining of the PPDO in laser confocal microscopy. The PFPA method is therefore applicable even to the surface functionalization of hydrolytically labile polymers, and it was demonstrated that PFPA chemistry may serve as a versatile tool for the (bio‐)functionalization of PPDO scaffolds.     

Electrochemical Characterization of the Interaction of Multiwalled Carbon Nanotubes with Doxorubicin

It has been suggested that multiwalled carbon nanotubes (MWCNTs) interacting with pharmaceutics may be introduced into the body as nanocarriers. To deliver the anticancer drugs, covalent or noncovalent functionalization of MWCNTs is required. In this study, the influence of oxidation on MWCNTs in the interaction with chemotherapeutic drug, doxorubicin, was characterized. The binding of doxorubicin with MWCNTs decreased rapidly with the increasing oxidation period with sulfuric acid. However, with nitric acid, the interaction increased initially and slowly decreased with time. The best results were obtained for sulfuric and nitric acid following 1 and 3?h of oxidation, respectively. The results show that sulfuric acid provided more favorable interaction for MWCNTs with doxorubicin than nitric acid.     

Computer simulation of the binding of quinocarcin to DNA. Prediction of mode of action and absolute configuration

Summary Computer-based models were derived for the covalent and noncovalent binding of the antitumor antibiotic quinocarcin to a representative DNA segment, d(ATGCAT)₂. They showed that a mode of action, involving opening of the oxazolidine ring to give an iminium ion, followed by initial noncovalent binding in the minor groove and subsequent alkylation of the 2-amino group of guanine, was rational and attended by favorable interaction energies in each step. The best model had the aryl ring of quinocarcin lying in the 3 direction from the covalent binding site and anR configuration at the carbon involved in covalent bond formation. It also showed that the preferred absolute configuration for quinocarcin was the reverse of that arbitrarily assigned in the literature.