Combining Modular Ligation and Supramolecular Self‐Assembly for the Construction of Star‐Shaped Macromolecules

A well‐defined random copolymer of styrene (S) and chloromethylstyrene (CMS) featuring lateral chlorine moieties with an alkyne terminal group is prepared (P(S‐co‐CMS), = 5500 Da, PDI = 1.13). The chloromethyl groups are converted into Hamilton wedge (HW) entities (P(S‐co‐HWS), = 6200 Da, PDI = 1.13). The P(S‐co‐HWS) polymer is subsequently ligated with tetrakis(4‐azidophenyl)methane to give HW‐functional star‐shaped macromolecules (P(S‐co‐HWS))₄, = 25 100 Da, PDI = 1.08). Supramolecular star‐shaped copolymers are then prepared via self‐assembly between the HW‐functionalized four‐arm star‐shaped macromolecules ( P(S‐co‐HW )) ₄ and cyanuric acid (CA) end‐functionalized PS (PS–CA, = 3700 Da, PDI = 1.04), CA end‐functionalized poly(methyl methacrylate) (PMMA–CA, = 8500 Da, PDI = 1.13) and CA end‐functionalized polyethylene glycol (PEG–CA, = 1700 Da, PDI = 1.05). The self‐assembly is monitored by ¹H NMR spectroscopy and light scattering analyses.     

Incorporating glycidyl methacrylate into block copolymers using poly(methacrylate‐ran‐styrene) macroinitiators synthesized by nitroxide‐mediated polymerization

Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p‐xylene at 90 °C with 10 mol % of additional SG1‐free nitroxide mediator relative to unimolecular initiator (BlocBuilder^®) to yield methacrylate rich copolymers with polydispersities _w/ _n = 1.23–1.46. k_pK values (k_p = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher k_pK's. Chain extensions with styrene at 110 °C initiated by the methacrylate‐rich macroinitiators (number average molecular weight _n = 12.9–33.5 kg mol^?1) resulted in slightly broader molecular weight distributions with _w/ _n = 1.24–1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 °C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher _w/ _n = 2.01–2.48. P(XMA/S) macroinitiators ( _n = 4.9–8.9 kg mol^?1), polymerized to low conversion and purified to remove “dead” chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with _w/ _n ～ 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (～20%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574–2588, 2009     

Direct Cyclodextrin‐Mediated Ring Opening Polymerization of ϵ‐Caprolactone in the Presence of Yttrium Trisphenolate Catalyst

Unmodified β‐cyclodextrin has been directly used to initiate ring‐opening polymerization of ϵ‐caprolactone in the presence of yttrium trisphenolate. Well‐defined cyclodextrin (CD)‐centered star‐shaped poly(ϵ‐caprolactone)s have been successfully synthesized containing definite average numbers of arms (N_arm = 4–6) and narrow polydispersity indexes (below 1.10). The number‐average molecular weight ( ) and average molecular weight per arm ( ) are controlled by the feeding molar ratio of monomer to initiator. The prepared star‐PCL with of 2.7 × 10³ is in fully amorphous and that with of 13.3 × 10³ is crystallized. In addition, the obtained poly(e‐caprolactone) (PCL) stars with various molecular weights have different solubilities in methanol and tetrahydrofuran, which can be applied for further modifications.     

Macrocyclic and Polymeric Oxaziridine‐Derivatives

Macrocyclic and polymeric imines 5,5′ and 6,6′ are obtained in excellent yields by template‐free polycondensation of 1,6‐bis(4‐formylbenzoyloxy)hexane (1) with commercially available 4,4′‐methylene‐bis(cyclohexylamine) (2) and with bis(2‐amino‐2‐methylprop‐1‐yl)adipate dihydrochloride (4), respectively. The degree of macrocyclization during imine synthesis strongly depends on the diamine. Matrix‐assisted laser desorption–ionization time‐of‐flight (MALDI‐TOF) mass spectrometry analysis and gel permeation chromatography (GPC) measurements show that (2) leads to more macrocyclic adducts than (4). The subsequent meta‐chloroperoxybenzoic acid oxidation of polyimines 5,5′ and 6,6′ ( = 1650–11 200 g mol⁻¹, = 3800–27 350 g mol⁻¹) yields the corresponding polyoxaziridines 7,7′ and 8,8′ consisting of macrocyclic and linear polymeric structures ( = 1750–8050 g mol⁻¹, = 3250–15 800 g mol⁻¹). The synthesized polyoxaziridines are relatively stable and storable at room temperature.     

Film Growth and Surface Roughness with Effective Fluctuating Covalent Bonds in Evaporating Aqueous Solution of Reactive Hydrophobic and Polar Groups: A Computer Simulation Model

Summary: A computer simulation model is proposed to study film growth and surface roughness in aqueous (A) solution of hydrophobic (H) and hydrophilic (P) groups on a simple three dimensional lattice of size with an adsorbing substrate. Each group is represented by a particle with appropriate characteristics occupying a unit cube (i.e., eight sites). The Metropolis algorithm is used to move each particle stochastically. The aqueous constituents are allowed to evaporate while the concentration of H and P is constant. Reactions proceed from the substrate and bonded particles can hop within a fluctuating bond length. The film thickness ( ) and its interface width ( ) are examined for hardcore and interacting particles for a range of temperature ( ). Simulation data show a rapid increase in and followed by its non‐monotonic growth and decay before reaching steady‐state and near equilibrium ( ) in asymptotic time step limit. The growth can be described by power laws, e.g., with a typical value of in initial time regime followed by at . For hardcore system, the equilibrium film thickness ( ) and surface roughness ( ) seem to scale linearly with the temperature, i.e., at low and at higher . For interacting functional groups in contrast, the long time (unsaturated) film thickness and surface roughness, and decay rapidly followed by a slow increase on raising the temperature.

Growth of the average film thickness at a temperature .     

Determination of thermodynamic properties of macroporous glycidyl methacrylate‐based copolymers by inverse gas chromatography

Macroporous crosslinked poly(glycidyl methacrylate‐co‐ethylene glycol dimethacrylate) (PGME) was synthesized by suspension copolymerization and modified by ring‐opening reaction of the pendant epoxy groups with ethylene diamine (EDA). Inverse gas chromatography (IGC) at infinite dilution was applied to determine the thermodynamic interactions of PGME and modified copolymer, PGME‐en. The specific surface areas of the initial and modified copolymer samples were determined by the BET method, from low‐temperature nitrogen adsorption isotherms. The specific retention volumes, V, of 10 organic compounds of different chemical nature and polarity (nonpolar, donor, or acceptor) were determined in the temperature range 333–413 K. The weight fraction activity coefficients of test sorbates, , and Flory–Huggins interaction parameters, , were calculated and discussed in terms of interactions of sorbates with PGME and PGME‐en. Also, the partial molar free energy, , partial molar heat of mixing, , sorption molar free energy, ΔG, sorption enthalpy ΔH, and sorption entropy, ΔS, were calculated. Glass transitions in PGME and PGME‐en, determined from IGC data, were observed in the temperature range 373–393 K and 363–373 K, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2524–2533, 2005     

Theoretical study on peroxyl radical additions to methyl‐substituted ethenes

The electrophilic additions of hydroperoxyl (HO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$) and alkylperoxyl (RO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$) radicals to substituted ethenes were studied using the AM1 semiempirical molecular orbital (MO) methods at the self‐consistent field/unrestricted Hartree–Fock (SCF/UHF) level. Reactantlike transition states were predicted for the title additions. The reactivity of an alkylperoxyl radical toward ethenes was found to be decreased as the degree of methyl (Me) substitution on the alkyl group of the radical increased. The relative reactivity and regioselectivity in HO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$ additions to substituted ethenes was suggested to be SOMO (singly occupied)‐HOMO controlled. A good correlation was established between the activation enthalpy $(\Delta H_{f}^{\ast})$ for the studied additions and the Taft polar substituent constants (σ*) of RO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$. The Evans–Polanyi correlation between $\Delta H^{\mbox{\mathversion{bold}$\cdot$}}_{f}$ and $\Delta H^{\circ}_{r}$ was justified and the validity of the Hammond postulate was indicated. The calculated results were compared with the available experimental data. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 761–771, 2000     

Towards Clathrates: Frozen States of Hydration of tert‐Butylamine

The dilution of tert‐butylamine (tBA) with water and subsequent cooling leads to a large series of different crystalline hydrates by an in situ IR laser melting‐zone procedure. The crystal structures were determined for tBA?n H₂O, with n=0, , 1, 7 , 7 , 9 , 11, and 17. For the two lower hydrates (n= , 1), one‐ and two‐dimensional hydrogen‐bonded networks are formed, respectively. The higher hydrates (n>1) exhibit a clathrate‐like three‐dimensional water framework with the tBA molecules as part of, or sitting inside, the cages. In all cases, tBA is hydrogen‐bonded to the H₂O framework. In the intermediate range (1相似文献   

Fe(CN)$\rm{ {_{6}^{4-}}}$‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Electrode. Part 1: Electrochemical Characterization and Its Electrocatalytic Activity Towards Oxidation of Ascorbic Acid

The present work describes preparation, characterization, and electrocatalytic behavior of a hexacyanoferrate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Fe(CN) film modified glassy carbon electrode. The modified electrode has been successfully prepared by electrostatically binding negatively charged Fe(CN) mediator into cross‐linked poly‐L ‐lysine cationic film. The dependence of the peak current of the modified electrode in pure supporting electrolyte (pH 6.8 phosphate buffer solution; PBS) shows that the charge transport in the film is fast and relatively unimpeded at lower scan rates. Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic activity of modified electrode towards oxidation of ascorbic acid. The rate constant (k), of catalytic reaction between electrogenerated Fe(CN) ions and ascorbic acid, obtained from RDE analysis was found to be 5.53×10⁵ cm³ mol^?1 s^?1. Finally, the PLL‐GA‐Fe(CN) film electrodes are successfully used for the individual estimation of ascorbic acid in the concentration range of physiological interest.     

Multilayer Assemblies Consisting of Tri‐Vanadium‐Substituted Heteropolyanions and Its Electrocatalytic Properties

We describe the controlled fabrication of ultrathin multilayer films consisting of tri‐vanadium‐ substituted heteropolytungstate anions (denoted as P₂W₁₅V₃) and a cationic polymer of quaternized poly (4‐vinylpyridine) partially complexed with osmium bis(2,2′‐bipyridine) (denoted as QPVP‐Os) on the 4‐aminobenzoic acid (4‐ABA) modified glassy carbon electrode (GCE) surface based on layer‐by‐layer assembly. Cyclic voltammetry and UV‐vis absorption spectrometry have been used to easily monitor the thickness and uniformity of thus‐formed multilayer films. The V‐centered redox reaction of P₂W₁₅V₃ in the multilayer films can effectively catalyze the reduction of BrO and NO . The resulting P₂W₁₅V₃/QPVP‐Os multilayer film modified electrode behaves as a much promising electrochemical sensor because of the low overpotential for the catalytic reduction of BrO and NO , and the catalytic oxidation of ascorbic acid.     

Palladium(II) and platinum(II) complexes of (1R,2R)‐(−)‐1,2‐diaminocyclohexane (DACH) with various carboxylato ligands and their cytotoxicity evaluation

Several palladium(II) and platinum(II) complexes analogous to oxaliplatin, bearing the enantiomerically pure (1R,2R)‐(?)‐1,2‐diaminocyclohexane (DACH) ligand, of the general formula {MX₂[(1R,2R)‐DACH]}, where M = Pd or Pt, X (COO)₂, CH₂(COO)₂, , , {1,1′‐C₅H₈(CH₂COO)₂}, [1,1′‐C₆H₁₀(CH₂COO)₂], [1,1′‐(COO)₂ferrocene], , , , MeCOO and Me₃CCOO, were synthesized. All the complexes prepared were characterized physicochemically and spectroscopically. Some selected complexes were screened in vitro against several tumor cell lines and the results were compared with reference standard drug, oxaliplatin. Copyright © 2009 John Wiley & Sons, Ltd.     

One‐Step Pyrolysis Preparation of 1.1.1 Oriented Gold Nanoplatelets Supported on Graphene and Six Orders of Magnitude Enhancement of the Resulting Catalytic Activity

Pyrolysis of chitosan films containing Au³⁺ renders 1.1.1 oriented Au nanoplatelets (20 nm lateral size, 3–4 nm height) on a few layers of N‐doped graphene ( /fl‐G), while the lateral sides were 0.0.1 oriented. Comparison of the catalytic activity of /fl‐G films with powders of unoriented Au NPs supported on graphene showed that /fl‐G films exhibit six orders of magnitude enhancement for three gold‐catalyzed reactions, namely, Ullmann‐like homocoupling, C? N cross coupling, and the oxidative coupling of benzene to benzoic acid. This enhancement is the result of the defined morphology, facet orientation of Au nanocrystals, and strong gold‐graphene interaction.     

Controlled Synthesis of a Chitosan‐Based Graft Copolymer Having Polysarcosine Side Chains Using the NCA Method with a Carboxylic Acid Additive

Summary: A novel chitosan derivative with polysarcosine side chains, i.e., chitosan‐graft‐polysarcosine [chitosan‐graft‐poly(N‐methylglycine)], was synthesized by ring‐opening polymerization of sarcosine N‐carboxyanhydride (NCA) with chitosan as a macroinitiator in the presence of carboxylic acids in dimethyl sulfoxide at 27 °C. Degree of substitution ( ) for polysarcosine side chains introduced to chitosan was controlled successfully by the feed amount of the additive nicotinic acid ( = 0.21–0.71). Independent of control, degree of polymerization ( ) for polysarcosine side chains was controlled by adjusting feed ratios of NCA monomer to chitosan ( = 14–43). Kinetic analysis of the propagation of sarcosine NCA was conducted by measuring CO₂ evolution. Apparent k_p values decreased with increased feed amounts of nicotinic acid, supporting the theory that propagation of NCA in the presence of nicotinic acid proceeds via equilibrium between active amine and dormant ammonium species.

Propagation mechanism of carboxylic acid‐mediated polymerization of sarcosine N‐carboxyanhydride.     

Lewis acid‐base properties of cellulose acetate butyrate by inverse gas chromatography

The dispersive component of the surface‐free energy, , of cellulose acetate butyrate (CAB) has been determined using the net retention volume, V_N, of n‐alkanes (C₅? C₈) probes in the temperature range 323.15–393.15 K. The values decrease nonlinearly with increase in temperature, and the temperature coefficients of are ? 0.32 (mJ/m²K) and ? 0.10 (mJ/m²K) in the range 323.15–353.15 K and 353.15–393.15 K, respectively. This variation in has been attributed to the structural changes that take place on the surface of CAB at ～353.15 K. The specific components of the enthalpy of adsorption, , and entropy of adsorption, , calculated using V_N of polar solutes are negative. The values are used to evaluate Lewis acidity constant, K_a, and Lewis basicity constant, K_b, for the CAB surface. The K_a and K_b values are found to be 0.126 and 1.109, respectively, which suggest that the surface is predominantly basic. The K_a and K_b results indicate for the necessary surface modifications of CAB which act as biodegradable adsorbent material. Copyright © 2010 John Wiley & Sons, Ltd.     

Iodostannate(II) mit kettenförmigen [SnI3]–‐Anionen – der Übergang von fünffach zu sechsfach koordinierten SnII‐Zentralatomen

Iodostannates(II) with Anionic [SnI₃]^– Chains – the Transition from Five to Six‐coordinated Sn^II The iodostannates (Me₄N) [SnI₃] ( 1 ), [Et₃N–(CH₂)₄–NEt₃] [SnI₃]₂ ( 2 ), [EtMe₂N–(CH₂)₂–NEtMe₂] [SnI₃]₂ ( 3 ), [Me₂HN–(CH₂)₂–NH–(CH₂)₂–NMe₂H] [SnI₃]₂ ( 4 ), [Et₃N–(CH₂)₆–NEt₃] [SnI₃]₂ ( 5 ) and [Pr₃N–(CH₂)₄–NPr₃]‐ [SnI₃]₂ · 2 DMF ( 6 ) with the same composition of the anionic [SnI₃]^– chains show differences in the coordination of the Sn^II central atoms. Whereas the Sn atoms in 1 and 2 are coordinated in an approximately regular octahedral fashion, in compounds 3 – 6 the continuous transition to coordination number five in (Pr₄N) [SnI₃] ( 7 ) or [Fe(dmf)₆] [SnI₃]₂ ( 8 ) can be observed. Together with the shortening of two or three Sn–I bonds, the bonds in trans position are elongated. Thus weak, long‐range Sn…I interactions complete the distorted octahedral environment of SnI₄ groups in 3 and 4 and SnI₃ groups in 5 and 6 . Obviously the shape, size and charge of the counterions and the related cation‐anion interactions are responsible for the variants in structure and distortion.     

Subgroup‐chain symmetry‐adapted irreducible matrices and CG coefficients of point groups

The irreducible matrices and Clebsch–Gordan coefficients of any crystallographic point group adapted to all possible canonical subgroup chains are calculated ab initio for both single‐valued and double‐valued representations and tabulated with exact values in the form of or and with components labeled by the irrep labels of the group chain in Koster notation. The phases and ordering of the components of irreducible bases for the cubic point groups are properly chosen so that irreducible matrices for all subgroup chains of G=T_d, O, O_h obey the associated relations D(G)=D(G)D(G), i=4, 6, and the complex conjugation relation for the group T, D(T)=D(T)*. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 67–80, 1999     

Electrochemical Detection of ClO$\rm{ {_{3}^{-}}}$, BrO$\rm{ {_{3}^{-}}}$, and IO$\rm{ {_{3}^{-}}}$ at a Phosphomolybdic Acid Linked 3‐Aminopropyl‐Trimethoxysilane Modified Electrode

A composite film modified electrode containing a Keggin‐type heteropolyanion, H₃(PMo₁₂O₄₀)?H₂O, was fabricated with 3‐aminopropyltrimethoxysilane (APMS) attached on an electrochemically activated glassy carbon (GC) electrode through the formation of C? O? Si bond. PMo₁₂O was then complexed with APMS through the electrostatic interaction between the phosphate groups of PMo₁₂O and amine groups of APMS (PMo₁₂O ‐APMS). XPS and cyclic voltammetry were employed for characterization of the composite film. The PMo₁₂O ‐APMS modified electrode showed three reversible redox pairs with smaller peak‐separation and was stable in the larger pH range compared with that in a solution phase. The catalytic properties of the modified electrode for the reduction of ClO , BrO , and IO were studied and the modified electrode exhibited good electrocatalytic activities for the three anions. The experimental parameters, such as pH, temperature, and the applied potential were optimized. The detection limits were determined to be 7.0±0.35 μM, 4.0±0.17 μM, and 0.1±0.04 μM for ClO , BrO , and IO , respectively. The modified electrode was applied to natural water samples for the detection of ClO , BrO , and IO .     

A Helical Poly(macromonomer) Consisting of a Polyacetylene Main Chain and Polystyrene Side Chains

A novel helical poly(macromonomer) [poly(M‐PS): absolute = 82 800–252 000, determined by GPC/RALLS] with a polyacetylene main chain and polystyrene (PS) side chains was synthesized by the polymerization of acetylene‐terminated M‐PS [ = 2 000, / = 1.20, = 18] with an Rh catalyst. M‐PS was prepared by ATRP of styrene using the acetylene‐containing initiator 2‐bromo‐2‐methylpropionic acid (S)‐1‐methylpropargyl ester ( l ). In solutions, poly(M‐PS) exhibited an intense CD signal at 345–355 nm, indicating that it possessed a predominantly one‐handed helical conformation. Poly(M‐PS) had a stable helical conformation irrespective of solvents and temperature.

     

Amphiphilic Poly(4‐acryloylmorpholine)/Poly[2‐(N‐carbazolyl)ethyl acrylate] Random and Block Copolymers Synthesized by NMP

A series of random copolymers and block copolymers containing water‐soluble 4AM and fluorescent VAK are synthesized by NMP. The homopolymerizations of 4AM and VAK and 4AM/VAK random copolymerization are performed in 50 wt% DMF using 10 mol% SG1, resulting in a linear increase in versus conversion, and final polymers with narrow molecular weight distributions ( < 1.4). Reactivity ratios r_VAK = 0.64 ± 0.52 and r_4AM = 0.86 ± 0.66 are obtained for the 4AM/VAK random copolymerization. In addition, a poly(4AM) macroinitiator is used to initiate a surfactant‐free suspension polymerization of VAK. After 2.5 h, the resulting amphiphilic block copolymer has = 12.6 kg · mol^?1, = 1.48, molar composition F_VAK = 0.38 with latex particle sizes between 270 and 475 nm.

     

Study on the Indirect Electrochemical Detection of Ammonium Ion with In Situ Electrogenerated Hypobromous Acid

The electrochemical oxidation of bromide in the presence of ammonium ion (NH ) was studied by cyclic voltammetry and UV‐vis spectroscopy. The experimental results suggested that the anodically generated bromine (Br₂) would be hydrolyzed to hypobromous acid (HBrO) at the pH range of 5–7 and was further disproportionate to hypobromite anion (BrO^?) when pH was larger than 7. Both HBrO and BrO^? were confirmed to be participated in the following homogeneous chemical reaction with the coexisted ammonium ion. However, HBrO is electroactive whereas BrO^‐ is electroinactive at carbon electrode. Based upon the reaction of HBrO with NH , an indirect electrochemical method was proposed for determination of NH with dual‐electrode configuration in phosphate buffer solution (pH 7), where HBrO was produced at a generator electrode and the excess HBrO was subsequently detected at a collector electrode after a reaction with NH in a batch solution or in a micro flow injection analytical (micro‐FIA) system by using an interdigitated array (IDA) Pt microelectrode and a carbon film ring‐disk electrode (CFRDE), respectively. The decreasing of reduction current at the collector electrode was proportional to the concentration NH in both systems, with the detection limit below 3.0 μM. This approach shows the advantage of highly selectivity even in presence of a large amount of coexisted cations, and was successfully applied for the determination of NH in environmental water samples.