Negative ion fragmentations of deprotonated peptides containing post‐translational modifications. An unusual cyclisation/rearrangement involving phosphotyrosine; a joint experimental and theoretical study

The characteristic fragmentations of a pTyr group in the negative ion electrospray mass spectrum of the [M–H]^? anion of a peptide or protein involve the formation of PO (m/z 79) and the corresponding [(M‐H)^?–HPO₃]^? species. In some tetrapeptides where pTyr is the third residue, these characteristic anion fragmentations are accompanied by ions corresponding to H₂PO and [(M‐H)^?–H₃PO₄]^? (these are fragmentations normally indicating the presence of pSer or pThr). These product ions are formed by rearrangement processes which involve initial nucleophilic attack of a C‐terminal ‐CO [or ‐C(?NH)O^?] group at the phosphorus of the Tyr side chain [an S_N2(P) reaction]. The rearrangement reactions have been studied by ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory. The study suggests the possibility of two processes following the initial S_N2(P) reaction. In the rearrangement (involving a C‐terminal carboxylate anion) with the lower energy reaction profile, the formation of the H₂PO and [(M‐H)^?–H₃PO₄]^? anions is endothermic by 180 and 318 kJ mol^?1, respectively, with a maximum barrier (to a transition state) of 229 kJ mol^?1. The energy required to form H₂PO by this rearrangement process is (i) more than that necessary to effect the characteristic formation of PO from pTyr, but (ii) comparable with that required to effect the characteristic α, β and γ backbone cleavages of peptide negative ions. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Selective Detection of Multicarboxylate Anions based on “Turn on” Electron Transfer by Self‐Assembled Molecular Rectangles

Two new large molecular rectangles ( 4 and 5 ) were obtained by the reaction of two different dinuclear arene ruthenium complexes [Ru₂(arene)₂(O O)₂Cl₂] (arene=p‐cymene; O O=2,5‐dihydroxy‐1,4‐benzoquinonato ( 2 ), 6,11‐dihydroxy‐5,12‐naphthacene dionato ( 3 )) with the unsymmetrical amide (N‐[4‐(pyridin‐4‐ylethynyl)phenyl]isonicotinamide) donor ligand 1 in methanol in the presence of AgO₃SCF₃, forming tetranuclear cations of the general formula [Ru₄(arene)₄( )₂(O O)₂]⁴⁺. Both rectangles were isolated in good yields as triflate salts and were characterized by multinuclear NMR, ESI‐MS, UV/Vis, and photoluminescence spectroscopy. The crystal structure of 5 was determined by X‐ray diffraction. Luminescent rectangle 5 was used for anion sensing with an amide ligand as a hydrogen‐bond donor and an arene–ruthenium acceptor as a signaling unit. Rectangle 5 strongly bound multicarboxylate anions, such as oxalate, tartrate, and citrate, in UV/Vis titration experiments in 1:1 ratios, in contrast to monoanions, such as F^?, Cl^?, NO₃^?, PF₆^?, CH₃COO^?, and C₆H₅COO^?. The fluorescence titration experiment showed a large fluorescence enhancement of 5 upon binding to multicarboxylate anions, which could be attributed to blocking of the photoinduced electron transfer process from the arene–ruthenium moiety to the amidic donor in 5 ; this was likely to be a result of hydrogen bonding between the ligand and the anion. On the other hand, rectangle 5 was not selective towards any other anions. To the naked eye, multicarboxylate anions in a solution of 5 in methanol appear greenish upon irradiation with UV light.     

On an Unexpected 2D‐linked Rare Earth 1,2,4‐Triazolate Network: Synthesis,Crystal Structure,Spectroscopic and Thermal Properties of $_{\infty}^{2}\rm [Ho(Tz)_{3}(TzH)_{2}]TzH$

The network compound , (Tz^? = 1,2,4‐triazolate anion, C₂H₂N₃^?, TzH = 1,2,4‐1H‐triazole, C₂H₃N₃), was obtained as pink single crystals by the reaction of the holmium metal with a melt of the amine 1,2,4‐1H‐triazole. No additional solvent was used. The compound is an unexpected example of a 2D‐linked network structure as other lanthanides give 3D‐frameworks and MOFs with 1,2,4‐1H‐triazole instead. This illustrates that the series of lanthanides yields very different results in attempts to create MOF structures. In the triazolate ligands Tz^? function both as μ‐η¹:η² linkers as well as η¹ end on ligands. The latter coordination mode is also found for additional triazole molecules. C.N. is nine for holmium(III). The layers exhibit a system of intra and inter layer hydrogen bonding and to triazole molecules from the melt reaction intercalated in‐between the layers. The product was investigated by X‐ray single crystal analysis, Mid IR, Far IR and Raman spectroscopy, and with DTA/TG regarding its thermal behaviour.     

The gas phase ion chemistry of the acetyl cation and isomeric [C2H3O]+ ions. On the structure of the [C2H3O]+ daughter ions generated from the enol of acetone radical cation

Methods are described for the unequivocal identification of the acetyl, [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} ?O] (a), 1-hydroxyvinyl, [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] (b), and oxiranyl, (d), cations. They involve the careful examination of metastable peak intensities and shapes and collision induced processes at very low, high and intermediate collision gas pressures. It will be shown that each [C₂H₃O]⁺ ion produces a unique metastable peak for the fragmentation [C₂H₃O]⁺ → [CH₃]⁺+CO, each appropriately relating to different [C₂H₃O]⁺ structures. [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] ions do not interconvert with any of the other [C₂H₃O]⁺ ions prior to loss of CO, but deuterium and ¹³C labelling experiments established that [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] (b) rearranges via a 1,2-H shift into energy-rich leading to the loss of positional identity of the carbon atoms in ions (b). Fragmentation of b to [CH₃]⁺+CO has a high activation energy, c. 400 kJ mol^?1. On the other hand, , generated at its threshold from a suitable precursor molecule, does not rearrange into [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH], but undergoes a slow isomerization into [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] via [CH₂\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HO]. Interpretation of results rests in part upon recent ab initio calculations. The methods described in this paper permit the identification of reactions that have hitherto lain unsuspected: for example, many of the ionized molecules of type CH₃COR examined in this work produce [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] ions in addition to [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] showing that some enolization takes place prior to fragmentation. Furthermore, ionized ethanol generates a, b and d ions. We have also applied the methods for identification of daughter ions in systems of current interest. The loss of OH^˙ from [CH₃COOD]^+˙ generates only [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OD]. Elimination of CH₃^˙ from the enol of acetone radical cation most probably generates only [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] ions, confirming the earlier proposal for non-ergodic behaviour of this system. We stress, however, that until all stable isomeric species (such as [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{\rm + } $\end{document}?C:]) have been experimentally identified, the hypothesis of incompletely randomized energy should be used with reserve.     

Ferrocene‐based derivative bearing phenol group recognitive sites: efficient H2PO4− receptor

Two artificial receptors, bearing ferrocene and phenol groups, were synthesized and their anion‐binding properties were evaluated for F^?, Cl^?, Br^?, I^?, AcO^? and by UV–vis, ¹H NMR titration and cyclic voltammetry experiments in order to research the effect of different substituents on anion‐recognition properties. Results indicate that the anion binding abilities can be effectively tuned by introducing a nitro group in the ortho position of the phenyl ring of the receptors, and the most obvious effect is for . Copyright © 2007 John Wiley & Sons, Ltd.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. X. Effect of hydrogen and catalytic site deactivation

The effect of H₂ on propylene polymerization initiated by a MgCl₂/EB/PC/AlEt₃/TiCl₄–3 AlEt₃/MPT catalyst was studied. Hydrogen increases significantly the initial rate during the early stage of the polymerization to give a higher yield of polymer than reactions without H₂. But H₂ reduces the yield toward the latter stages so that the net effect on the total yield can be quite small. There is no appreciable effect of H₂ on either the isotacticity index or polydispersity of the products. It decreases molecular weight proportional to (p_H2)^1/2. The chain transfer by H₂ resulted in a decrease of total metal polymer bond concentration with time of polymerization. The rate constants of hydrogen chain transfer for the two kinds of isospecific and nonspecific sites are = 5.1 × 10^?3, = 2.7 × 10^?3, = 7.5 × 10^?3, = 4.4 × 10^?3, in units of torr^1/2 sec^?1 at 50°. Hydrogen assists in the deactivation of the catalytic sites as does propylene; rates of the former and the latter vary with (p_H2)^1/2 and [C₃H₆]^1/2, respectively, with k = (12.1 ± 0.9) M^?1 torr^?1/2 sec^?1 and k = (65.3 ± 3.3) M^?3/2 sec^?1 at 50° and A/T = 167. The mechanism for deactivation of catalytic sites are discussed.     

Temperature and shear dependencies of rheology of poly(acrylonitrile‐co‐itaconic acid) dope in DMF

Poly(acrylonitrile‐co‐itaconic acid) (poly(AN‐co‐IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN‐co‐IA) polymer solutions in N,N‐dimethylformamide (DMF), in the range of 1 × 10⁵–1 × 10⁶ g mol^?1, has been investigated in the shear rate (γ′) range of 1 × 10¹–5 × 10⁴ min^?1. The zero shear viscosity (η₀) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius–Frenkel–Eyring model. The free energy of activation of viscous flow (ΔG_V) values were in the range 5–32 kJ mol^?1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔG_V value of the polymer solution of any and concentration (c) is suggested. The power law fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and was found to exist at constant shear rate, concentration and temperature. For each , the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.     

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     

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.     

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.     

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.     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

Molecular Recognition in Anion Coordination Chemistry. Structure,Binding Constants and Receptor-Substrate Complementarity of a Series of Anion Cryptates of a Macrobicyclic Receptor Molecule

The crystal structures of four anion cryptates [X^? ? BT -6H⁺] formed by the protonated macrobicyclic receptor BT -6H⁺ with F^?, Cl^?, Br^? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F^?-ion is tetracoordinated, while Cl^? and Br^? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H⁺ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H⁺ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP^2?, ADP^3?, ATP^4?, P₂O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F^?, Cl^?, Br^?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H⁺ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered.     

Supramolecular Arrays of Cationic Complexes Containing Pyrazole Ligands and Tetrafluoroborate,Trifluoromethanesulfonate, or Nitrate as Counterions. Crystal Structure of Bis(3,5‐dimethyl‐4‐nitro‐1H‐pyrazole‐κN2)silver(1+) Nitrate ([Ag(HpzNO2)2](NO3))

The structures of [Pd(η³‐C₃H₅)(Hpz^R2)₂](BF₄) (Hpz^R2=Hpz^bp2=3,5‐bis(4‐butoxyphenyl)‐1H‐pyrazole, 1 ; Hpz^R2=Hpz^NO2=3,5‐dimethyl‐4‐nitro‐1H‐pyrazole=Hdmnpz, 2 ) and [Ag(Hpz^R2)₂](A) (Hpz^R2=Hpz^bp2, A= , 3 ; Hpz^R2=Hpz^NO2, A= , 4 ) were comparatively analyzed to determine the factors responsible for polymeric assemblies. In all cases, the H‐bonding interactions between the pyrazole moieties and the appropriate counterion and, in particular, the orientation of the NH groups of the pyrazole ligands are determinant of one‐dimensional polymeric arrays. In this context, the new compound [Ag(Hpz^NO2)₂](NO₃) ( 5 ) was synthesized and its structure analyzed by X‐ray diffraction (Fig. 4). The Hpz^NO2 serves as N‐monodentate ligand, which coordinates to the Ag^I center through its pyrazole N‐atom giving rise to an almost linear N Ag N geometry. The planar NO counterion bridges two adjacent Ag^I centers to form a one‐dimensional zigzag‐shaped chain which is also supported by the presence of N H⋅⋅⋅O bonds between the pyrazole NH group of adjacent cationic entities and the remaining O‐atom of the bridging NO (Fig. 5). The chains are further extended to a two‐dimensional layer‐like structure through additional Ag⋅⋅⋅O interactions involving the NO₂ substituents at the pyrazole ligands (Fig. 6).     

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

The dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) ( 3 ) and lithium‐benzo[b]fluorenide(tmeda) ( 4 ) using CP/MAS solid‐state ¹³C‐ and ¹⁵N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the ¹³C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH^?=42.7 kJ mol^?1, ΔS^?=?5.3 J mol^?1 K^?1, and =44.3 kJ mol^?1 for 3 , and ΔH^?=36.8 kJ mol^?1, ΔS^?=?17.7 J mol^?1 K^?1, and =42.1 kJ mol^?1 for 4 , respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T_1ρ, the ¹³C spin‐lattice relaxation time in the rotating frame, and led to ΔH^?=24.8 kJ mol^?1, ΔS^?=?49.2 J mol^?1 K^?1, and =39.5 kJ mol^?1 for 3 , and ΔH^?=18.2 kJ mol^?1, ΔS^?=?65.3 J mol^?1 K^?1, and =37.7 kJ mol^?1 for 4 , respectively. For (D₁₂)‐ 3 , the rotation of the CD₃ groups has also been studied, and a barrier E_a of 14.1 kJ mol^?1 was found.     

Thermodynamics of Formation of Binary and Ternary Nitrides in the System Ce/Mn/N

Drop solution calorimetry in high‐temperature oxide melts has been shown to be very useful to study the energetics of nitride formation. This methodology was used to determine the enthalpies of formation from the elements of binary and ternary nitrides in the Ce/Mn/N system. The resulting values in kJ mol^–1 are; δH (CeN) = –340.19 ± 6.80, δ(H (Mn₃N_1.95, η‐Mn₃N₂ type) = –192.68 ± 7.57, δH (Mn₆N_5.40, θ‐Mn₆N₅ type) = –430.80 ± 10.93 and δH (Ce₂MnN₃) = –928.18 ± 9.46. The results show the role of inductive effects in Ce₂MnN₃ leading to a higher energetic stability compared to binary components.     

Colorimetric naked‐eye recognizable anion sensors synthesized via RAFT polymerization

A polymeric sensor (PTH) containing naphthalimide signal moiety and thiourea recognition moiety for the detection of anions was synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization, which can guarantee controllable molecular weight, narrow molecular weight distribution, and precise polymer structure. Both PTH and its corresponding monomer (TH) showed naked‐eye recognizable yellow‐to‐orange changes upon addition of fluoride (F^?), acetate (AcO^?), and dihydrogen phosphate (H₂PO) of low concentration. However, only F^? can result in orange‐to‐purple change when the aforementioned anions were added at high concentrations, which was attributed to the deprotonation of the thiourea N? H groups and the mechanism was supported by the UV‐Vis absorption spectra and ¹H NMR titration. The effect of these anions on thin PTH films was also investigated, and the addition of F^? led to obvious spectra change. It was found that other halide anions (Cl^?, Br^?, and I^?) could hardly induce any variation of absorption spectra. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1551–1556, 2010     

A chiral polymer‐based turn‐on fluorescent sensor for specific recognition of hydrogen sulfate

A new kind of polymeric chemosensor containing chiral naphthaldimine moiety in the side chain was synthesized by the reversible addition‐fragmentation chain transfer polymerization of N‐{[2‐(4‐vinylbenzyloxy)‐1‐naphthyl]‐methylene}‐(S)‐2‐phenylglycinol (VNP). The resulting polymers (PVNP) showed high selectivity for hydrogen sulfate relative to other anions including F^?, Cl^?, Br^?, H₂PO, CH₃CO, and NO in tetrahydrofuran (THF) solution as judged from UV?vis, fluorescence, and circular dichroism spectrophotometric titrations. Compared with its monomer, the polymer has proven to be more attractive for detection of HSO in terms of sensitivity and reproducibility. Upon addition of the anion it gives remarkable spectral responses concomitant with detectable color change from colorless to pale yellow. Furthermore, the HSO‐induced CD or fluorescence signal can be totally reversed with addition of base and eventually recovered the initial state, leading to a reproducible molecular switch with two distinguished “on” and “off” states. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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.