Terminal NH2 Groups Research Articles

The Crucial Role of Charge in Thermoresponsive‐Polymer‐Assisted Reversible Dis/Assembly of Gold Nanoparticles

AbstractDynamic control of the spacing between Au nanoparticles using nanoarchitectures incorporating the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) has the capability to induce strong color changes from the plasmon shifts. PNIPAM self‐assembles on the surface of Au nanoparticles regardless of its terminal group. However, in many cases, the collapse of this PNIPAM coating at elevated temperatures fails to cause a color change, due to electrostatic and steric repulsion between the Au nanoparticles. Here, it is shown how tuning the charge repulsion between the nanoparticles is crucial to achieve large, reversible shifts of the plasmon resonances. Using NH2 terminal groups of the PNIPAM is most effective, compared with SH, COOH, and H terminations, due to their synergistic role in citrate stripping and charge neutralization. This detailed understanding of the Au–PNIPAM system is vital to enable temperature‐responsive plasmonic systems with large tuning ranges, suitable for applications such as plasmonic actuators, displays, and Raman switches.

Synthesis of hexahydropyridazin-3-ones by reactions between donor-acceptor cyclopropanes and phenylhydrazine

The nickel perchlorate-initiated reaction between dimethyl esters of 2-aryl- and 2-styryl-substituted cyclopropane-1,1-dicarboxylic acids and phenylhydrazine proceeded with opening of the cyclopropane ring and formation of a mixture containing acyclic and cyclic products: [2-(1-phenylhydrazinyl)alkyl]malonates and 1-phenylhexahydropyridazin-3-ones. Reaction conditions were found for preparative synthesis of polyfunctional hexahydropyridazin-3-ones. Unlike the other starting materials, 2-(p-methoxystyryl)-substituted cyclopropane reacted with the terminal NH2 group of phenylhydrazine, resulting in the formation of 1-(phenylamino)pyrrolidin-2-one.

Hyperbranched poly(amido amine) as an effective demulsifier for oil-in-water emulsions of microdroplets

The destabilization of oil-in-water (O/W) emulsions with average oil droplet sizes of less than 2μm is important. Herein, hyperbranched poly(amido amine) (h-PAMAM) is successfully designed and synthesized by controlling the ratio of methyl acrylate (MA) to ethylenediamine (EDA) to enable the demulsifier to break microdroplets. The investigations on the effects of dosage, temperature, and settling time reveal that the demulsifier h-PAMAM with many NH2 terminal functional groups displays a satisfactory demulsification performance. The oil removal ratio can reach 91% within 30min at the demulsification equilibrium with the addition of h-PAMAM. This ability is primarily ascribed to the hyperbranched topology and abundant amino groups of h-PAMAM. Furthermore, measurements of the rupture rate constants of oil droplets and interfacial tension indicate that h-PAMAM is an excellent demulsifier. Dynamic light scattering (DLS) analysis can provide a new evidence for the exploration of the demulsification mechanism. The effective demulsification performance of h-PAMAM supports its potential applications in petroleum engineering.

Rapid synthesis of g-C3N4 spheres using microwave-assisted solvothermal method for enhanced photocatalytic activity

Abstract Graphitic carbon nitride (g-C3N4), comprising tri-s-triazine (C6N7) units, is a promising visible-light-active photocatalyst and is generally synthesized using thermal condensation. This study reports a time-saving microwave-assisted solvothermal synthesis (MW) in which powders were obtained at temperatures as low as 180 °C within 60–120 min. Images obtained using scanning electron microscopy and transmission electron microscopy demonstrated that the MW g-C3N4 particles had a uniform microspheric shape, whereas g-C3N4 prepared with conventional thermal condensation (TC) and solvothermal (ST) approaches exhibited plate-like layered structures with buckles on their surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy indicated that TC g-C3N4 had terminal NH2 groups on the periphery of its tri-s-triazine units, whereas some cyano moieties were present on MW and ST g-C3N4. In a photocatalytic test, MW g-C3N4 was discovered to have enhanced photocatalytic activity in the degradation of methyl orange dye and phenol solution under visible light irradiation, which can be ascribed to its reduced charge recombination and increased light harvesting in the visible region, as evidenced by UV–vis and photoluminescence spectroscopy. The terminal NH2 groups attached to TC g-C3N4 may have consumed the photoinduced charges, thus reducing the photocatalytic activity and increasing recombination of the sample. The facile and time-saving microwave-assisted solvothermal method presented herein can thus be used for the synthesis of visible-light-active g-C3N4, which has potential photocatalysis applications.

Enhanced catalytic activity of methane dry reforming by the confinement of Ni nanoparticles into mesoporous silica

Nickel nanoparticles were immobilized in mesoporous silica by a polyethyleneimine (PEI)-aided route and their catalytic performance was evaluated in dry reforming of methane. NH2 terminal groups of PEI strongly interacted with surface silanol groups of mesoporous silica and then, Ni-chelating PEIs were highly dispersed inside its ordered channel. The steric hindrance of PEI with a long hydrocarbon chain also restricted the aggregation of Ni-PEI complexes anchored in the porous framework. The catalysts prepared by the PEI-aided route showed the stable activity at 750 °C for 40 h because Ni particles were confined inside the pore and therefore, cannot be sintered more than the pore diameter of their parent support. The carbon deposit is much smaller in the catalyst prepared by the PEI-aided route than the reference catalyst synthesized via a traditional impregnation method, suggesting that the sintering of Ni particles is a main contribution to the generation of graphitic carbon.

One-plot Synthesis of AgSbS2 Nanocrystals and Their Photoelectrochemical Properties

This work reports for the first time the use of the modified solvothermal method in the synthesis of AgSbS2 semiconductor nanocrystals, by using oleylamine and oleic acid as complexing agents of Ag+ and Sb3+, respectively. The –NH2 terminal groups of oleylamine and –COOH function groups of oleic acid could combine with the metal cation to form a metal complex. AgSbS2 nanoparticles exhibit a broad absorption in the visible light range and these nanoparticles have great potential in photovoltaic devices.

Half generations magnetic PAMAM dendrimers as an effective system for targeted gemcitabine delivery

Tumor-specific delivery of anticancer drugs by magnetic nanoparticles will maximize the efficacy of the drug and minimize side effects, and reduce systemic toxicity. The magnetic core of these nanoparticles provides an advantage for selective drug targeting as they can be targeted to the tumor site and accumulated in cancer cells by means of an external magnetic field. Magnetic nanoparticles can be coated with Polyamidoamine (PAMAM) dendrimer and loaded with drugs. However, biomedical applications of PAMAM dendrimers are limited due to their toxicity associated with their multiple cationic charges due to terminal NH2 groups. Modifying the positively charged end groups with negatively charged COOH groups, is a satisfactory strategy for obtaining less toxic PAMAM dendrimers. Gemcitabine being an analogue of deoxycytidine, is an effective anticancer drug. However, clinical benefits of Gemcitabine are limited due to its short biological half-life. The aim of this study was to obtain an effective, less toxic targeted delivery system for Gemcitabine. Half generations, between G4.5 and G7.5, of PAMAM dendrimer coated magnetic nanoparticles (DcMNPs) were synthesized and conjugated with Gemcitabine. TEM images showed nanoscale size (12–14nm) of the nanoparticles. The zeta-potential analysis indicated a decreased negativity of surface charge in drug bound dendrimer compared to the empty nanoparticles. Gemcitabine was effectively conjugated successfully onto the surface of half-generations of PAMAM DcMNPs. It was observed Gemcitabine did not effectively bind to Generations G4 and G5. The highest drug loading was obtained for DcMNPs with Generation 5.5. Empty nanoparticles showed no significant cytotoxicity on SKBR-3 and MCF-7 cells. On the other hand, Gemcitabine loaded nanoparticles were 6.0 fold more toxic on SKBR-3 and 3.0 fold more toxic on MCF-7 cells compared to free Gemcitabine. Gemcitabine loaded on Generation 5.5 DcMNPs showed a higher stability than free Gemcitabine. About 94% of the drug was retained over 6 weeks period, at pH 7.2. Due to their targetability under magnetic field, stability, size distribution, cellular uptake and toxicity characteristics the dendrimeric nanoparticles obtained in this study can be useful a delivery system for Gemcitabine in cancer therapy.

New Signal Amplification Strategy Using Semicarbazide as Co-reaction Accelerator for Highly Sensitive Electrochemiluminescent Aptasensor Construction

A highly sensitive electrochemiluminescent (ECL) aptasensor was constructed using semicarbazide (Sem) as co-reaction accelerator to promote the ECL reaction rate of CdTe quantum dots (CdTe QDs) and the co-reactant of peroxydisulfate (S2O8(2-)) for boosting signal amplification. The co-reaction accelerator is a species that when it is introduced into the ECL system containing luminophore and co-reactant, it can interact with co-reactant rather than luminophore to promote the ECL reaction rate of luminophore and co-reactant; thus the ECL signal is significantly amplified in comparison with that in which only luminophore and co-reactant are present. In this work, the ECL signal probes were first fabricated by alternately assembling the Sem and Au nanoparticles (AuNPs) onto the surfaces of hollow Au nanocages (AuNCs) via Au-N bond to obtain the multilayered nanomaterials of (AuNPs-Sem)n-AuNCs for immobilizing amino-terminated detection aptamer of thrombin (TBA2). Notably, the Sem with two -NH2 terminal groups could not only serve as cross-linking reagent to assemble AuNPs and AuNCs but also act as co-reaction accelerator to enhance the ECL reaction rate of CdTe QDs and S2O8(2-) for signal amplification. With the sandwich-type format, TBA2 signal probes could be trapped on the CdTe QD-based sensing interface in the presence of thrombin (TB) to achieve a considerably enhanced ECL signal in S2O8(2-) solution. As a result, the Sem in the TBA2 signal probes could accelerate the reduction of S2O8(2-) to produce the more oxidant mediators of SO4(•-), which further boosted the production of excited states of CdTe QDs to emit light. With the employment of the novel co-reaction accelerator Sem, the proposed ECL biosensor exhibited ultrahigh sensitivity to quantify the concentration of TB from 1 × 10(-7) to 1 nM with a detection limit of 0.03 fM, which demonstrated that the co-reaction accelerator could provide a simple, efficient, and low-cost approach for signal amplification and hold great potential for other ECL biosensors construction.

Ab initio kinetics and thermal decomposition mechanism of mononitrobiuret and 1,5-dinitrobiuret

Mononitrobiuret (MNB) and 1,5-dinitrobiuret (DNB) are tetrazole-free, nitrogen-rich, energetic compounds. For the first time, a comprehensive ab initio kinetics study on the thermal decomposition mechanisms of MNB and DNB is reported here. In particular, the intramolecular interactions of amine H-atom with electronegative nitro O-atom and carbonyl O-atom have been analyzed for biuret, MNB, and DNB at the M06-2X/aug-cc-pVTZ level of theory. The results show that the MNB and DNB molecules are stabilized through six-member-ring moieties via intramolecular H-bonding with interatomic distances between 1.8 and 2.0 Å, due to electrostatic as well as polarization and dispersion interactions. Furthermore, it was found that the stable molecules in the solid state have the smallest dipole moment amongst all the conformers in the nitrobiuret series of compounds, thus revealing a simple way for evaluating reactivity of fuel conformers. The potential energy surface for thermal decomposition of MNB was characterized by spin restricted coupled cluster theory at the RCCSD(T)/cc-pV∞ Z//M06-2X/aug-cc-pVTZ level. It was found that the thermal decomposition of MNB is initiated by the elimination of HNCO and HNN(O)OH intermediates. Intramolecular transfer of a H-atom, respectively, from the terminal NH2 group to the adjacent carbonyl O-atom via a six-member-ring transition state eliminates HNCO with an energy barrier of 35 kcal/mol and from the central NH group to the adjacent nitro O-atom eliminates HNN(O)OH with an energy barrier of 34 kcal/mol. Elimination of HNN(O)OH is also the primary process involved in the thermal decomposition of DNB, which processes C2v symmetry. The rate coefficients for the primary decomposition channels for MNB and DNB were quantified as functions of temperature and pressure. In addition, the thermal decomposition of HNN(O)OH was analyzed via Rice-Ramsperger-Kassel-Marcus/multi-well master equation simulations, the results of which reveal the formation of (NO2 + H2O) to be the major decomposition path. Furthermore, we provide fundamental interpretations for the experimental results of Klapötke et al. [Combust. Flame 139, 358-366 (2004)] regarding the thermal stability of MNB and DNB, and their decomposition products. Notably, a fundamental understanding of fuel stability, decomposition mechanism, and key reactions leading to ignition is essential in the design and manipulation of molecular systems for the development of new energetic materials for advanced propulsion applications.

Effect of arginine methylation on the RNA recognition and cellular uptake of Tat-derived peptides

Arginine (Arg) methylation is a common post-translational modification that regulates gene expression and viral infection. The HIV-1 Tat protein is an essential regulatory protein for HIV proliferation, and is methylated in the cell. The basic region (residues 47–57) of the Tat protein contains six Arg residues, and is responsible for two biological functions: RNA recognition and cellular uptake. In this study, we explore the effect of three different methylation states at each Arg residue in Tat-derived peptides on the two biological functions. The Tat-derived peptides were synthesized by solid phase peptide synthesis. TAR RNA binding of the peptides was assessed by electrophoresis mobility shift assays. The cellular uptake of the peptides into Jurkat cells was determined by flow cytometry. Our results showed that RNA recognition was affected by both methylation state and position. In particular, asymmetric dimethylation at position 53 decreased TAR RNA binding affinity significantly, but unexpectedly less so upon asymmetric dimethylation at position 52. The RNA binding affinity even slightly increased upon methylation at some of the flanking Arg residues. Upon Arg methylation, the cellular uptake of Tat-derived peptides mostly decreased. Interestingly, cellular uptake of Tat-derived peptides with a single asymmetrically dimethylated Arg residue was similar to the native all Arg peptide (at 120μM). Based on our results, TAR RNA binding apparently required both guanidinium terminal NH groups on Arg53, whereas cellular uptake apparently required guanidinium terminal NH2 groups instead. These results should provide insight into how nature uses arginine methylation to regulate different biological functions, and should be useful for the development of functional molecules with methylated arginines

Novel magnetic cross-linked lipase aggregates for improving the resolution of (R, S)-2-octanol.

Novel magnetic cross-linked lipase aggregates were fabricated by immobilizing the cross-linked lipase aggregates onto magnetic particles with a high number of -NH2 terminal groups using p-benzoquinone as the cross-linking agent. At the optimal fabrication conditions, 100% of immobilization efficiency and 139% of activity recovery of the magnetic cross-linked lipase aggregates were achieved. The magnetic cross-linked lipase aggregates were able to efficiently resolve (R, S)-2-octanol, and retained 100% activity and 100% enantioselectivity after 10 cycles of reuse, whereas the cross-linked lipase aggregates only retained about 50% activity and 70% enantioselectivity due to insufficient cross-linking. These results provide a great potential for industrial applications of the magnetic cross-linked lipase aggregates.

A microporous cationic metal–organic framework constructed from metallamacrocycle-based nanocages: structures and luminescence properties

A novel metal–organic framework (MOF) {[CuI13(L1)10]·(OH)3(H2O)3}∞ (1) has been fabricated through in situ copper-mediated ring conversions of 2,5-bis(4-amidophenyl)-1,3,4-oxadiazoles into 3,5-bis(4-amidophenyl)-1,2,4-triazolate under hydrothermal conditions. The most aesthetically fascinating structural feature of 1 is the host cationic microporous metal–organic framework constructed from unique indiscrete polyhedral [Cu32(L1)28] nanocages. Interestingly, the cage is composed of three different kinds of two-fold symmetry related polynuclear metallamacrocycles (MMCs): octanuclear rhombus-like, dodecanuclear boat-shaped, and dodecanuclear square-like MMCs. These cages are arranged into 1-D square-like channels with an effective dimension of ~5.9 × 4.4 A, viewed along the a-axis, occupied by uncoordinated water molecule and OH− anions, hydrogen bonded to the terminal NH2 groups of the L1 ligands. Additionally, from the topology views, considering the propeller-shaped [Cu3(L1)5] moiety as a secondary building unit (SBU1), it adopts a non-interpenetrating 5-connected uninodal 3-D network; but if regarding the [Cu8(L1)10] as a SBU2 generated from two SBU1 connected by two Cu5, it adopts a non-interpenetrating 6-connected uninodal α-Po 3-D network. Moreover, the luminescence spectra show that it exhibits yellow-green fluorescence with a broad emission band peaked at 536 nm upon photoexcitation at 389 nm.

Intramolecular hydrogen bonding motifs in deprotonated glycine peptides by cryogenic ion infrared spectroscopy.

The infrared spectra of deprotonated glycine peptides, (Gn-H)(-) with n = 1-4, in the 1200-3500 cm(-1) spectral region are presented. Comparisons between the experimental and calculated spectra reveal the chain length dependent hydrogen bonding motifs that define the geometries of these species. First, an interaction between the terminal carboxylate and the neighboring amide N-H is present in all the peptide structures. This interaction is strong enough to align this amide group in the same plane as the carboxylate. However, we found that the vibrational frequency shift of this hydrogen bonded N-H group is not well reproduced in the calculations. Second, in the longer (G3-H)(-) and (G4-H)(-) species, the peptide chain folds such that the terminal NH2 group also interacts with the carboxylate. Both of these folded structures display an interaction between the terminal NH2 and the neighboring N-H as well. Lastly, an amide-amide interaction is observed in the longest (G4-H)(-) structure. Analysis of the N-H peak positions reveals the interplay among the different hydrogen bonds, especially around the negatively charged carboxylate moiety.

Assessing the critical concentration of NH2 terminal groups on the surface of MWNTs towards chain scission of PC in PC/SAN blends: effect on dispersion, electrical conductivity and EMI shielding

The localization and dispersion quality of as received NH2 terminated multiwall carbon nanotubes (MWNT-I) and ethylene diamine (EDA) functionalized MWNTs in melt mixed blends of polycarbonate (PC) and poly(styrene-co-acrylonitrile) (SAN) were assessed in this study using rheo-electrical and electromagnetic interference (EMI) shielding measurements. In order to improve the dispersion quality and also to selectively localize MWNTs in the PC phase of the blends, EDA was grafted onto MWNTs by two different strategies like diazonium reaction of the para-substituted benzene ring of MWNTs with EDA (referred to as MWNT-II) and acylation of carboxyl functionalized MWNTs with thionyl chloride (referred to as MWNT-III). By this approach we could systematically vary the concentration of NH2 functional groups on the surface of MWNTs at a fixed concentration (1 wt%) in PC/SAN blends. XPS was carried to evaluate the % concentration of N in different MWNTs and was observed to be highest for MWNT-III manifesting in a large surface coverage of EDA on the surface of MWNTs. Viscoelastic properties and melt electrical conductivities were measured to assess the dispersion quality of MWNTs using a rheo-electrical set-up both in the quiescent as well as under steady shear conditions. Rheological properties revealed chain scission of PC in the presence of MWNT-III which is due to specific interactions between EDA and PC leading to smaller PC grafts on the surface of MWNTs. The observed viscoelastic properties in the blends were further correlated with the phase morphologies under quiescent and annealed conditions. Electromagnetic interference (EMI) shielding effectiveness in X and Ku-band frequencies were measured to explore these composites for EMI shielding applications. Interestingly, MWNT-II showed the highest electrical conductivity and EMI shielding in the blends.

Synthesis and characterization of ferrocenyl camphor compounds

Several ferrocene camphor compounds of the general formula FcCONHR, where Fc = ferrocenyl and R is N(C10H13NSO2) (2), N(C10H14O) (3), N(C10H16) (4) or NLiCO(C10H14O) (6), were synthesized by the reaction of FcCONHNH2 (1) with the respective camphor derivatives. In the resulting compounds, the ferrocene and camphor units are connected via a hydrazone link formed through condensation of the terminal NH2 group in 1 and the carbonyl group of the camphor derivative. The characterization of the complexes is based mostly on analytical data and on NMR and IR spectra. Additional insight into the structural characteristics of complex (E)-FcCONHN(C10H14O) (3) was obtained from variable temperature and 2D NMR measurements while computational calculations were used to assign the bands in IR spectra of FcCONHN(C10H13NSO2) isomers. X-ray diffraction analysis has shown that the molecules of (E)-FcCONHN(C10H13NSO2) associate into symmetric dimers in the solid state via N–H⋯O hydrogen bonds between the hydrazone moieties.

Solid-State NMR Approaches to Internal Dynamics of Proteins: From Picoseconds to Microseconds and Seconds

Solid-state nuclear magnetic resonance (NMR) spectroscopy has matured to the point that it is possible to determine the structure of proteins in immobilized states, such as within microcrystals or embedded in membranes. Currently, researchers continue to develop and apply NMR techniques that can deliver site-resolved dynamic information toward the goal of understanding protein function at the atomic scale. As a widely-used, natural approach, researchers have mostly measured longitudinal (T1) relaxation times, which, like in solution-state NMR, are sensitive to picosecond and nanosecond motions, and motionally averaged dipolar couplings, which provide an integral amplitude of all motions with a correlation time of up to a few microseconds. While overall Brownian tumbling in solution mostly precludes access to slower internal dynamics, dedicated solid-state NMR approaches are now emerging as powerful new options. In this Account, we give an overview of the classes of solid-state NMR experiments that have expanded the accessible range correlation times from microseconds to many milliseconds. The measurement of relaxation times in the rotating frame, T1ρ, now allows researchers to access the microsecond range. Using our recent theoretical work, researchers can now quantitatively analyze this data to distinguish relaxation due to chemical-shift anisotropy (CSA) from that due to dipole-dipole couplings. Off-resonance irradiation allows researchers to extend the frequency range of such experiments. We have built multidimensional analogues of T2-type or line shape experiments using variants of the dipolar-chemical shift correlation (DIPSHIFT) experiment that are particularly suited to extract intermediate time scale motions in the millisecond range. In addition, we have continuously improved variants of exchange experiments, mostly relying on the recoupling of anisotropic interactions to address ultraslow motions in the ms to s ranges. The NH dipolar coupling offers a useful probe of local dynamics, especially with proton-depleted samples that suppress the adverse effect of strong proton dipolar couplings. We demonstrate how these techniques have provided a concise picture of the internal dynamics in a popular model system, the SH3 domain of α-spectrin. T1-based methods have shown that large-amplitude bond orientation fluctuations in the picosecond range and slower 10 ns low-amplitude motions coexist in these structures. When we include T1ρ data, we observe that many residues undergo low amplitude motions slower than 100 ns. On the millisecond to second scale, mostly localized but potentially cooperative motions occur. Comparing different exchange experiments, we found that terminal NH2 groups in side chains can even undergo a combination of ultraslow large-angle two-site jumps accompanied by small-angle fluctuations that occur 10 times more quickly.

DNA probe modified with 3-iron bis(dicarbollide) for electrochemical determination of DNA sequence of Avian Influenza Virus H5N1

In this work, we report on oligonucleotide probes bearing metallacarborane [3-iron bis(dicarbollide)] redox label, deposited on gold electrode for electrochemical determination of DNA sequence derived from Avian Influenza Virus (AIV), type H5N1. The oligonucleotide probes containing 5'-terminal NH2 group were covalently attached to the electrode, via NHS/EDC coupling to 3-mercaptopropionic acid SAM, previously deposited on the surface of gold. The changes in redox activity of Fe(III) centre of the metallacarborane complex before and after hybridization process was used as analytical signal. The signals generated upon hybridization with targets such as complementary or non-complementary 20-mer ssDNA or various PCR products consisting of 180–190bp (dsDNA) were recorded by Osteryoung square-wave voltammetry (OSWV). The developed system was very sensitive towards targets containing sequence complementary to the probe with the detection limit estimated as 0.03fM (S/N=3.0) and 0.08fM (S/N=3.0) for 20-mer ssDNA and for dsDNA (PCR product), respectively. The non-complementary targets generated very weak responses. Furthermore, the proposed genosensor was suitable for discrimination of PCR products with different location of the complementarity region.

Adsorption and detection of Escherichia coli using an Au substrate modified with a catecholate-type artificial siderophore–Fe3+ complex

A catecholate-type artificial siderophore with a terminal-NH2 group (1) and its Fe(3+) complex (2) were prepared. Siderophore 1 was characterized by (1)H NMR, FT-IR, and ESI-TOF MS spectroscopy. The corresponding Fe(3+) complex 2 was obtained by reaction of 1 with Fe(acac)3. The absorption band at 500 nm (ε = 4670 M(-1) cm(-1) at pH 7.0) of the electronic absorption spectrum of 2 is assignable as the LMCT (O(catecholate) → Fe(3+)) absorption band. This band indicates the formation of the Fe(3+) complex of 1. The biological activity of 2 with respect to Escherichia coli was clearly confirmed by observing that it permeates into the cell membrane. The self-assembled monolayer of 2 on an Au substrate, 2/Au, was prepared and its preparation was confirmed by FT-IR reflection-absorption spectroscopy (IR-RAS) and cyclic voltammetry (CV). Furthermore, a quartz crystal microbalance (QCM) chip modified with 2 effectively adsorbed E. coli. M. flavescens, an organism which is incapable of synthesizing siderophores and must therefore use exogenous hydroxamate-type siderophores for growth, did not adsorb on 2/Au. In contrast, E. coli did not adsorb on the hydroxamate-type artificial siderophore-Fe(3+) complex (3)-modified Au substrate, 3/Au. These results provide preliminary evidence that microbes recognized Fe(3+) ion-bound siderophores on the surface. The detection limit of 2/Au was ∼10(4) CFU mL(-1).

Rapid and sensitive amperometric determination of hydrogen peroxide with a biosensor based on a carboxyphenyl functionalised boron-doped diamond electrode

In the present work, a mediator-free biosensor for hydrogen peroxide (H2O2) based on a surface carboxyphenyl functionalised boron-doped diamond (BDD) electrode has been constructed via a simple electrochemical way in an aryl diazonium salt. The BDD surface was primarily interfacial, designed by grafting an aromatic ‘bridge’ of 4-carboxyphenyl (4-CP) groups by single-stepped electrochemical reduction of 4-CP diazonium cations. A locked-in carboxyl-terminated BDD interface was thus produced. Then the model biomolecule, cytochrome c (Cyt c) was attached to the interface through the ‘bridge’ by covalent combination between –NH2 terminal groups of Cyt c and –COOH groups of 4-CP, obtaining a Cyt c/4-CP/BDD biosensor. Well-defined peaks attributed to the FeIII/FeII couple of Cyt c were clearly observed on the biosensor which could not be obtained direct on BDD without carboxyphenyl functionalisation. The Cyt c/4-CP/BDD biosensor further exhibited remarkable biosensor features in the rapid and sensitive amperometric sensing of H2O2. The steady-state reduction current response to the addition of H2O2 could be achieved within 4 s. In the range from 4.0 × 10−6 to 3.6 × 10−5 M, the reduction current indicated good linear dependence with the concentration of H2O2. The detection limit was estimated to be as low as 6.1 × 10−7 M based on the signal to noise ratio of 3 and the apparent Michaelis constant was evaluated to be 1.02 ± 0.25 × 10−5 M according to the Lineweaver-Burke equation. All the results indicated that the covalent graft 4-carboxyphenyl group played an important role in BDD surface function to help the direct electron transfer of Cyt c with favourable biocompatibility and good bio-electrocatalytic affinity. A promising biosensor for hydrogen peroxide has thus been provided.

Hydroxyapatite–poly(l-lactide) nanohybrids via surface-initiated ATRP for improving bone-like apatite-formation abilities

It is important to improve the compatibility of hydroxyapatite (HA) nanoparticles in biodegradable polyesters to obtain desirable nanocomposites for bone tissue engineering applications. Polymer grafting has been proven an efficient way to get nanohybrids with good dispersibility in polymeric matrixes. In this paper, a new strategy to prepare HA–poly(l-lactide) (PLLA) nanohybrids was developed, where PLLA oligomers were grafted from HA nanoparticle surfaces via surface-initiated atom transfer radical polymerization (ATRP) of methylacrylate group terminated PLLA macromonomers (PLLA-MA). HA with the derived ATRP initiators was obtained by (1) preparation of HA from precursors in the presence of 3-aminopropyl-triethoxysilane (APTS) to produce the HA surface with terminal NH2 groups (HA–NH2) and (2) reaction of the NH2 groups of the HA–NH2 nanoparticles with 2-bromoisobutyryl bromide (BIBB) to produce the 2-bromoisobutyryl-immobilized nanoparticles (HA–Br). The obtained HA–PLLA nanohybrids demonstrated good dispersibility in chloroform. With the good dispersion of HA–PLLA nanohybrids in PLLA matrix, the resultant PLLA/HA–PLLA nanocomposites could much faster induce bone-like apatite-formation in simulated body fluids (SBF) than the PLLA/HA counterparts where the HA nanoparticles aggregated heavily. With the versatility of ATRP, properly, grafting oligomeric PLLA chains from HA nanoparticle surfaces is an effective means for the design of novel HA–polymer biohybrids for future bone tissue engineering applications.