Time-dependent binding mode of a cationic porphyrin dimer to poly[d(G-C)2] and Poly[d(A-T)2

The time-dependent binding mode of a porphyrin dimer to poly[d(G-C)2] and poly[d(A-T)2] was investigated by spectroscopic methods including absorption and circular and linear dichroism (CD and LD) spectroscopy. Immediately after mixing with poly[d(G-C)2], the porphyrin dimer exhibited red-shift and hypochromism in the absorption spectrum and negative CD and LD spectra. With further red-shift in absorption, the CD and LD magnitude in the Soret region became increasingly negative over time. After it was stabilized, the magnitude of the reduced LD (LDr) in the Soret region was larger than that in the DNA absorption region, indicating that the second porphyrin was also intercalated. Following the rapid intercalation of the first porphyrin, the very slow intercalation of the second followed with first-order kinetics. In the poly[d(A-T)2] case, a bisignate CD spectrum was observed in the Soret region suggesting stacking of the porphyrins. The small alteration in the CD spectrum and increased absorbance, which followed the initial rapid spectral change, was of the second order. This alteration in the spectral properties was attributed to the conformational change of poly[d(A-T)2] near the binding site because the overall shape of the CD spectrum was conserved in spite of the changes in the absorption spectrum.     

Surface-initiated enzymatic polymerization of DNA

We describe a technique to synthesize DNA homopolymers on a surface using surface-initiated enzymatic polymerization (SIEP) with terminal deoxynucleotidyl transferase (TdTase), an enzyme that repetitively adds mononucleotides to the 3'-end of oligonucleotides. The thickness of the synthesized DNA layer was found to depend on the deoxymononucleotide monomer, in the order of dATP > dTTP > dGTP approximately dCTP. In addition, the composition and the surface density of oligonucleotide initiators were also important in controlling the extent of DNA polymerization. The extension of single-stranded DNA chains by SIEP was further verified by their binding to antibodies specific to oligonucleotides. TdTase-mediated SIEP can also be used to grow spatially defined three-dimensional DNA structures by soft lithography and is a new tool for bioinspired fabrication at the micro- and nanoscale.     

Detection of mismatched caspase-3 DNA oligonucleotides with an SPR biosensor following amplification by Taq polymerase

We demonstrate that base mismatches of caspase-3 DNA sequences can be detected by surface plasmon resonance (SPR) following signal amplification by polymerase from Thermus aquaticus (Taq). The concentration of magnesium ions and the respective dNTPs for polymerase binding to the oligonucleotides on the sensing surface were optimized. Taq polymerase binds to double-stranded DNA that is self-assembled on the gold surface of the biosensor to induce an SPR signal. Experiments are presented on the effect of Mg(II) and dNTP concentrations on the activity of the polymerase on the sensing surface. The detection limits are 50 pM, 0.1 nM, 0.7 nM, 7 nM, and 20 nM for correctly matched, single-base mismatched, two-base mismatched, three-base mismatched and four-base mismatched DNA of caspase-3, respectively. This is attributed to the optimized experimental conditions, with samples containing 2 μM of Mg(II) and 0.3 mM of dNTP.

Surface-initiated atom transfer radical polymerization on poly(vinylidene fluoride) membrane for antibacterial ability

Surface-active microporous membranes were prepared from the poly(vinylidene fluoride)-graft-poly(2-(2-bromoisobutyryloxy)ethyl acrylate) copolymer (PVDF-g-PBIEA copolymer) by phase inversion in water. The PBIEA side chains could function as initiators for the atom transfer radical polymerization (ATRP) of 2-(N,N-dimethylamino)ethyl methacrylate on the membrane surfaces to give rise to the PVDF-g-PBIEA-ar-PDMAEMA membranes. N-alkylation with hexyl bromide and nitromethane gave rise to the quanternized PVDF-g-PBIEA-ar-QPDMAEMA membranes with polycation chains chemically tethered on the membrane surface, including the pore surfaces. The changes in the surface morphology and the surface chemical composition were confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. The scanning electron microscopy revealed that, in comparison to the pristine PVDF-g-PBIEA membranes, not only could the PVDF-g-PBIEA-ar-QPDMAEMA membranes remove the Gram-negative bacterium Escherichia coli but also inhibited the bacterial reproduction on the membranes to a significant extent.     

Simultaneous binding of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin and 4',6-diamidino-2-phenylindole at the minor grooves of poly(dA).poly(dT) and poly[d(A-T)(2)]: fluorescence resonance energy transfer between DNA bound drugs

The spectral properties of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) bound to poly(dA).poly(dT) and poly[d(A-T)(2)] in the presence and in the absence of 4',6-diamidino-2-phenylindole (DAPI) have been studied. DAPI fits deeply into the minor groove of both poly(dA).poly(dT) and poly[d(A-T)(2)], and TMPyP is also situated at the minor groove. The nature of the absorption, circular dichroism (CD), and flow linear dichroism (LD) spectra of the TMPyP-poly(dA).poly(dT) and -poly[d(A-T)(2)] complexes in the Soret band is essentially unaffected whether the minor groove is blocked by DAPI or not, although small variations been noticed in the presence of DAPI. Furthermore, a close analysis of the reduced LD spectrum in the Soret band results in angles of approximately 80 degrees and 55 degrees between transition moments of the TMPyP and DNA helix axes in the absence of DAPI. All these observations indicate that the side of TMPyP whose structure resembles that of classical minor groove binding drugs does not fit deeply into the minor groove. This suggests that TMPyP binds across the minor groove: two positively charged pyridiniumyl rings interact electrostatically with negatively charged phosphate groups of DNA. When DAPI and TMPyP are simultaneously bound to poly(dA).poly(dT) or poly[d(A-T)(2)], the fluorescence intensity of DAPI decreases as TMPyP concentration increases, indicating that the excited energy of DAPI is transferred to TMPyP.     

Surface-initiated synthesis of poly(3-methylthiophene) from indium tin oxide and its electrochemical properties

Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications.     

Surface-initiated living radical polymerization from silica particles functionalized with poly(ethylene glycol)-carrying initiator

A novel yet versatile approach is described for surface-initiated living radical polymerization (SI-LRP) from silica particles (SiPs). Monodisperse SiPs were surface-modified with a newly designed surface-fixable initiator (BPEGE) having three components: a triethoxysilane moiety, a poly(ethylene glycol) (PEG) unit, and an initiation site for atom transfer radical polymerization (ATRP) in the form of a 2-bromoisobutyryl group. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the BPEGE-fixed SiPs. The polymerization proceeded in a living manner, producing SiPs coated with well-defined poly(MMA) of a target molecular weight with a graft density as high as 0.5 chains/nm². Thanks to the amphiphilic property of PEG, the system was successfully applied for SI-ATRP of PEG methacrylate and sodium p-styrenesulfonate in aqueous media in which the BPEGE-fixed SiPs were highly dispersed without causing any aggregations. The formation of colloidal crystals with the polymer brush-afforded SiPs demonstrated the high uniformity and perfect dispersibility of the hybrid particles.     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.     

表面活性(可控)接枝聚合研究进展

表面是材料与外界接触的窗口,材料的众多性质,如耐磨性、耐腐蚀性、生物相容性等均在很大程度上取决于表面的构成.可通过在材料表面接枝不同的聚合物链使之满足不同的需要.表面引发的活性(可控)聚合可得到分布均匀、厚度可控的接枝层,因而成为表面改性中的重要方法.本文介绍了一系列表面引发的活性(可控)聚合技术及其应用举例,对这一领域所取得的研究进展及现状作一综述.     

Hole polarons in poly(G)-poly(C) and poly(A)-poly(T) DNA molecules

The polaron might play an important role in the process of charge migration through duplex DNA stack. In the present work, we investigate properties of hole polarons in DNA molecules containing identical base pairs, such as poly(G)-poly(C) and poly(A)-poly(T), An extended tight-binding model (extended Su-Schrieffer-Heeger model), which involves the effect of an electric field in the direction of DNA stack, will be introduced. The transfer integral and electron-phonon coupling parameters in this model are obtained according to ab initio calculation for different base pair dimers. Calculations reveal that the polaron in poly(A)-poly(T) has a wider shape and a higher mobility under a specific electric field than that in poly(G)-poly(C) DNA stack.     

Different crystallinity of poly(d,l-lactide-co-p-dioxanone) copolymers acquired by control of chain microstructure

Poly(d,l-lactide-co-p-dioxanone)(P(LA-co-PDO)) copolymers with different chain microstructures were synthesized by one-step or two-step bulk ring-opening polymerizations of d,l-lactide(LA) and p-dioxanone(PDO) monomers using stannous octoate [Sn(Oct)_2]/n-dodecanol as the initiating system.The average sequence lengths of the lactidyl(L_(LA)) and dioxanyl(L_(PDO)) units were calculated from the ~1H NMR spectra.It was found that both L_(LA) and L_(PDO) values from the two-step syntheses were significantly ...     

DNA adsorption onto polyethylenimine-attached poly(p-chloromethylstyrene) beads

In this study, DNA adsorption properties of polyethylenimine (PEI)-attached poly(p-chloromethylstyrene) (PCMS) beads were investigated. Spherical beads with an average size of 186 microm were obtained by the suspension polymerization of p-chloromethylstyrene conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, PCMS beads had a specific surface area of 14.1 m2/g. PEI chains could be covalently attached onto the PCMS beads with equilibrium binding capacities up to 208 mg PEI/g beads, via a direct chemical reaction between the amine and chloromethyl groups. After PEI adsorption with 10% (w/w) initial PEI concentration, free amino content of PEI-attached PCMS beads was determined as 0.91 mequiv./g. PEI-attached PCMS beads were utilized as sorbents in DNA adsorption experiments conducted at +4 degrees C in a phosphate buffer medium of pH 7.4. DNA immobilization capacities up to 290 mg DNA/g beads could be achieved with the tried sorbents. This value was approximately 50-times higher relative to the adsorption capacities of previously examined sorbents.     

Synthesis and characterization of poly(d,l-lactide-co-glycolide) modified by maleic anhydride and 1,4-butanediamine

Bone tissue engineering is sought to apply strategies for bone defects healing biodegradable porous scaffolds without limitations and shortcomings. In this work, we have developed a novel maleic anhydride (MAH) and 1,4-butanediamine modified poly(lactide-co-glycolide) polymer (BMPLGA). The synthesized polymer was characterized by Fourier transform infrared spectrometry (FTIR), Nuclear magnetic resonance spectra (¹H NMR), gel permeation chromatography (GPC) and contact angle measurements. In addition, cell morphologies in the extracts and cell cytotoxity were also studied. The results showed that the BMPLGA was successfully obtained by introducing MAH and 1,4-butanediamine into PLGA in bulk. The introduction of anhydride and amino groups improved the hydrophilicity of PLGA. Fibroblastic cells showed normal morphologies in BMPLGA extracts, and the BMPLGA materials showed no cell cytotoxicity. The synthetic BMPLGA material may have potentials for biomedical applications due to improving hydrophilicity.     

Synthesis and drug controlled release of block copolymers of poly(l-lactide) with poly(d,l-lactide) and related monomers

Four types of new biodegradable block copolymers AB, ABA, AC and AD, where A is poly(L-lactide) (PLLA), B is poly(D, L-lactide) (PDLLA), C is poly(p-dioxanone) (PDON) and D is poly(ϵ-caprolactone) (PCL) with different block lengths were synthesized and characterized by GPC, IR, ¹H-NMR and DSC. There are phase-separated and biodegradable block copolymers. Their in vitro biodegradation rates with the change of composition ratio were studied as well as the biodegradation rates of homopolymers with the series as PDON > PDLLA > PLLA in parallel with their crystallinities, i.e. from amorphous to semicrystalline. All these block copolymers were used as matrix to test their controlled release behavior of levo-norgestrel (LNG) in the form of microspheres through solvent evaporation preparation with thoroughly long-time washing to minimize the generally occurring bursting effect. As a result all of them showed almost constant rate of release even from the initial stage,     

Effective form of sulfoquinovosyldiacyglycerol (SQDG) vesicles for DNA polymerase inhibition

Sulfoquinovosyldiacyglycerol (SQDG) has a wide range of biological activities that make it an attractive compound for the development of new drugs. Chemically synthesized beta-SQDG-C(18:0) (1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-beta-d-glucopyranosyl)-sn-glycerol), for example, has a potent inhibitory effect on DNA polymerases. We investigated the properties of the vesicle form of beta-SQDG-C(18:0) as the monomer has low solubility in water. The structure of the beta-SQDG-C(18:0) vesicles are highly influenced by NaCl concentration in preparation process. At low NaCl concentrations, the beta-SQDG-C(18:0) vesicles have high surface curvature and form small unilamellar vesicles. Increases in NaCl concentration, resulted in decreased surface curvature and a tendency for beta-SQDG-C(18:0) to form large multilamellar vesicles. The small unilamellar vesicles showed a potent inhibitory effect on DNA polymerase beta, whereas the large multilamellar vesicles had no such effect. We investigated further the relationship between vesicle size and activity by preparing smaller vesicles (262, 99 and 43 nm in diameter) using an extrusion technique. These smaller vesicles had a greater inhibitory effect on DNA polymerase beta activity than non-extruded vesicles. beta-SQDG-C(18:0) vesicles, especially those of small size, were effective in DNA polymerase inhibition and are expected to have high applicability in DNA polymerase study.     

Species-specific polymerase chain reaction amplification of camel (Camelus) DNA extracts

A sensitive polymerase chain reaction (PCR) method based on amplification of a specific DNA fragment was established for the identification of camel (Camelus) materials. The species-specific primer pair L183/H372 was designed based on the nucleotide sequence of the mitochondrial cytochrome b gene, and its specificity was confirmed by amplification of 3 camel (domestic double-humped camel, wild double-humped camel, wild one-humped camel) samples and 11 non-Camelus animal (sheep, goat, pig, chicken, cattle, fish, dog, horse, donkey, deer, and rabbit) materials. An expected 208 base pair fragment was amplified from camel materials; no cross-reactive or additional fragments were generated from other animal materials. Taq I restriction endonuclease digestion of the unpurified PCR product can be used routinely to confirm the camel origin of the amplified sequence.