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ε-Caprolactone (ε-CL) adducts of cationic, amine tris(phenolate)-supported niobium(V) and tantalum(V) ethoxides initiate the ring-opening polymerization of lactones. The Ta(V) species prepared and applied catalytically herein exhibits higher activity in the ring-opening polymerization (ROP) of ε-caprolactone than the previously reported, isostructural Nb(V) complex, contradicting literature comparisons of Nb(V)- and Ta(V)-based protocols. Both systems also initiate the ROP of δ-valerolactone and rac-β-butyrolactone, kinetic studies confirming retention of higher activity by the Ta congener. Polymerizations of rac-β-butyrolactone and δ-valerolactone were previously unrealized under Group V- or Ta-mediated conditions, respectively, although the former has afforded only low molecular weight, cyclic poly-3-hydroxybutyrate. Cationic ethoxo–Nb(V) and −Ta(V) δ-valerolactone adducts are also reported, demonstrating the facility of δ-valerolactone as a ligand and the generality of the synthetic method. Both δ-valerolactone-bearing complexes initiate the ROP of ε-caprolactone, δ-valerolactone, and rac-β-butyrolactone. Accordingly, we have elucidated trends in reactivity and investigated the initiation mechanism for such systems, the insertion event being predicated upon intramolecular nucleophilic attack on the coordinated lactone by the adjacent alkoxide moiety. This mechanism enables quantitative, stoichiometric installation of a single monomer residue distinct from the bulk of the polymer chain, and permits modification of polymer properties via both manipulation of the molecular architecture and tuning of the polymerization kinetics, and thus dispersity, through hitherto inaccessible independent control of the initiation event.

We report three niobium-based initiators for the catalytic ring-opening polymerization (ROP) of ε-caprolactone, exhibiting good activity and molecular weight control. In particular, we have prepared on the gram-scale and fully characterized a monometallic cationic alkoxo-Nb(V) ε-caprolactone adduct representing, to the best of our knowledge, an unprecedented example of a metal complex with an intact lactone monomer and a functional ROP-initiating group simultaneously coordinated at the metal center. At 80 °C, all three systems initiate the immortal solution-state ROP of ε-caprolactone via a coordination–insertion mechanism, which has been confirmed through experimental studies, and is supported by computational data. Natural bond orbital calculations further indicate that polymerization may necessitate isomerization about the metal center between the alkoxide chain and the coordinated monomer. The observations made in this work are expected to inform mechanistic understanding both of amine tris(phenolate)-supported metal alkoxide ROP initiators, including various highly stereoselective systems for the polymerization of lactides and of coordination–insertion-type ROP protocols more broadly.

Small-angle neutron scattering (SANS) experiments were conducted on cyclic and linear polymers of racemic and l-lactides (PLA) with the goal of comparing chain configurations, scaling, and effective polymer–solvent interactions of the two topologies in acetone-d6and THF-d8. There are limited reports of SANS results on cyclic polymers due to the lack of substantial development in the field until recently. Now that pure, well-defined cyclic polymers are accessible, unanswered questions about their rheology and physical conformations can be better investigated. Previously reported SANS experiments have used cyclic and linear polystyrene samples; therefore, our work allowed for direct comparison using a contrasting (structurally and sterically) polymer. We compared SANS results of cyclic and linear PLA samples with various microstructures and molecular weights at two different temperatures, allowing for comparison with a wide range of variables. The results followed the trends of previous experiments, but much greater differences in the effective polymer–solvent interaction parameters between cyclic and linear forms of PLA were observed, implying that the small form factor and hydrogen bonding in PLA allowed for much more compact conformations in the cyclic form only. Also, the polymer microstructure was found to influence polymer–solvent interaction parameters substantially. These results illustrate how the difference in polymer–solvent interactions between cyclic and linear polymers can vary greatly depending on the polymer in question and the potential of neutron scattering as a tool for identification and characterization of the cyclic topology.

Cyclic polymers have long been reported in the literature, but their development has often been stunted by synthetic difficulties such as the presence of linear contaminants. Research into the synthesis of these polymers has made great progress in the past decade, and this review covers the synthesis, properties, and applications of cyclic polymers, with an emphasis on bio-based aliphatic polyesters. Synthetic routes to cyclic polymers synthesized from bioderived monomers, alongside mechanistic descriptions for both ring closure and ring expansion polymerization approaches, are reviewed. The review also highlights some of the unique physical properties of cyclic polymers together with potential applications. The findings illustrate the substantial recent developments made in the syntheses of cyclic polymers, as well as the progress which can be made in the commercialization of bio-based polymers through the versatility this topology provides.

Titanium(IV) complexes of amino-tris(phenolate) ligands (LTiX, X = chloride, isopropoxide) together with bis(triphenylphosphine)iminium chloride (PPNCl) are active catalyst systems for the ring-opening copolymerization of carbon dioxide and cyclohexene oxide. They show moderate activity, with turnover frequency values of ∼60 h–1(0.02 mol % of catalyst, 80 °C, 40 bar of CO2) and high selectivity (carbonate linkages >90%), but their absolute performances are lower than those of the most active Ti(IV) catalyst systems. The reactions proceed with linear evolution of polycarbonate (PCHC) molar mass with epoxide conversion, consistent with controlled polymerizations, and evolve bimodal molar mass distributions of PCHC (up to Mn= 42 kg mol–1). The stoichiometric reaction between [LTiOiPr] and tetraphenylphosphonium chloride, PPh4Cl, allows isolation of the putative catalytic intermediate [LTi(OiPr)Cl]−, which is characterized using single-crystal X-ray diffraction techniques. The anionic titanium complex [LTi(OR)Cl]−is proposed as a model for the propagating alkoxide intermediates in the catalytic cycle.

The elucidation and prediction of how changes in a protein result in altered activities and selectivities remain a major challenge in chemistry. Two hurdles have prevented accurate family-wide models: obtaining (i) diverse datasets and (ii) suitable parameter frameworks that encapsulate activities in large sets. Here, we show that a relatively small but broad activity dataset is sufficient to train algorithms for functional prediction over the entire glycosyltransferase superfamily 1 (GT1) of the plant Arabidopsis thaliana. Whereas sequence analysis alone failed for GT1 substrate utilization patterns, our chemical–bioinformatic model, GT-Predict, succeeded by coupling physicochemical features with isozyme-recognition patterns over the family. GT-Predict identified GT1 biocatalysts for novel substrates and enabled functional annotation of uncharacterized GT1s. Finally, analyses of GT-Predict decision pathways revealed structural modulators of substrate recognition, thus providing information on mechanisms. This multifaceted approach to enzyme prediction may guide the streamlined utilization (and design) of biocatalysts and the discovery of other family-wide protein functions.

Treatment of [Ti(OiPr)4] with trimethylsilyl triflate results in the formation of [Ti(OiPr)3(OTf)] (2) in high yield. Subsequent treatment of the triflate derivative 2with a series of facially coordinating N3‐donor ligands results in the production of a series of charge‐separated metal alkoxide salts of the general formula [{L}Ti(OiPr)3][OTf] {L = tris(pyrazolyl)methane (3a), 1,3,5‐triethyl‐1,3,5‐triazacyclohexane (3b), 1,3,5‐tribenzyl‐1,3,5‐triazacyclohexane (3c), 1,3,5‐tris(p‐fluorobenzyl)‐1,3,5‐triazacyclohexane (3d), and 1,3,5‐tris[(1S)‐1‐phenylethyl]‐1,3,5‐triazacyclohexane (3e)}. The products were characterized by 1H and 13C NMR spectroscopy and in the case of 3a–cby single‐crystal X‐ray diffraction. Reaction of 2with 1,3,5‐triphenyl‐1,3,5‐triazacyclohexane results in the formation of complex 4[{L′}2Ti(OiPr)2(OTf)2], which contains two 3,4‐dihydroquinazoline ligands (L′), a result of catalytic activation of the triazacyclohexane ligands by [Ti(OiPr)3(OTf)] towards electrophilic aromatic substitution.

Monocytes and T helper (TH) cells rapidly infiltrate inflamed tissues where monocytes differentiate into inflammatory dendritic cells (DCs) through undefined mechanisms. Our studies indicate that THcells frequently interact with monocytes in inflamed skin and elicit the differentiation of specialized DC subsets characteristic of these lesions. In psoriasis lesions, TH1 and TH17 cells interact with monocytes and instruct these cells to differentiate into TH1- and TH17-promoting DCs, respectively. Correspondingly, in acute atopic dermatitis, TH2 cells interact with monocytes and elicit the formation of TH2-promoting DCs. DC formation requires GM-CSF and cell contact, whereas THsubset specific cytokines dictate DC function and the expression of DC subset specific surface molecules. Moreover, the phenotypes of T cell–induced DC subsets are maintained after subsequent stimulation with a panel of TLR agonists, suggesting that TH-derived signals outweigh downstream TLR signals in their influence on DC function. These findings indicate that THcells govern the formation and function of specialized DC subsets.

Monocytes and T helper (TH) cells rapidly infiltrate inflamed tissues where monocytes differentiate into inflammatory dendritic cells (DCs) through undefined mechanisms. Our studies indicate that TH cells frequently interact with monocytes in inflamed skin and elicit the differentiation of specialized DC subsets characteristic of these lesions. In psoriasis lesions, TH1 and TH17 cells interact with monocytes and instruct these cells to differentiate into TH1- and TH17-promoting DCs, respectively. Correspondingly, in acute atopic dermatitis, TH2 cells interact with monocytes and elicit the formation of TH2-promoting DCs. DC formation requires GM-CSF and cell contact, whereas TH subset specific cytokines dictate DC function and the expression of DC subset specific surface molecules. Moreover, the phenotypes of T cell–induced DC subsets are maintained after subsequent stimulation with a panel of TLR agonists, suggesting that TH-derived signals outweigh downstream TLR signals in their influence on DC function. These findings indicate that TH cells govern the formation and function of specialized DC subsets.

Tetraamine Me6TREN has been used as a scaffold support to provide coordinative saturation in the complexes PhCH2M⋅Me6TREN (M=Li, Na, K). The Li derivative displays a LiC σ interaction with a pyramidalized CH2both in the solid state and in solution, and represents the first example of η4coordination of Me6TREN to lithium. In the sodium derivative, the metal cation slips slightly towards the delocalized π electrons whilst maintaining a partial σ interaction with the CH2group. For the potassium case, coordinative saturation successfully yields the first monomeric benzylpotassium complex, in which the anion binds to the metal cation exclusively through its delocalized π system resulting in a planar CH2group.

An air and moisture stable C3‐symmetric titanium(IV) triflate, supported by a tripodal amine‐(tris‐phenolate) ligand, has been synthesized and characterized by X‐ray crystallography and shown to be a good Lewis acid catalyst for a range of aza‐Diels–Alder, Diels–Alder, synaldol, allylation, and alkylation reactions.

Protein-based vaccines have been explored as a safer alternative to traditional weakened or killed whole organism based vaccination strategies and have been investigated for their ability to activate the immune system against certain cancers. For optimal stimulation of T lymphocytes, protein-based vaccines should deliver protein antigens to antigen presenting cells in the context of appropriate immunostimulatory signals, thus mimicking actual pathogens. In this report, we describe the synthesis, characterization, and biological evaluation of immunostimulatory acid-degradable microparticles, which are suitable delivery vehicles for use in protein-based vaccines and cancer immunotherapy. Using a 3′ conjugation strategy, we optimized the attachment of immunostimulatory CpG DNA to our vaccine carriers and demonstrated that under acidic conditions similar to those found in endosomal compartments, these new particles were capable of simultaneously releasing a model protein antigen and a CpG DNA adjuvant. We found in an in vivocytotoxicity assay that the co-encapsulation of ovalbumin, a model antigen, and immunostimulatory agent in the same particle led to superior cytotoxic T lymphocyte activity compared to particles coadministered with adjuvant in an unbound form. In addition, we investigated the ability of these acid-degradable particles to induce protective immunity in the MO5 murine melanoma model and found that they were effective until tumor escape, which appeared to result from a loss of antigen expression by the cancer cells due to in vivoselection pressure.

Schiff base ligands L1H–L8H have been prepared and complexed to ZnIIcentres. All eight complexes have been characterised by singlecrystal Xray diffraction methods, multinuclear NMR spectroscopy and elemental analysis. It was shown that for L1H and L2H trimetallic complexes of the form Zn3OAc4L1–22were isolated. However, for L3H to L7H monometallic complexes were formed, ZnL3–72. For L8H a trimetallic complex was also isolated with the same stoichiometry as Zn3OAc4L1–22but a different coordination motif was detected. The Schiff base ligand L1H was anchored to silica and treated with ZnOAc2·2H2O to form the heterogeneous ZnIIsystem. This was characterised by 13C{1H} CPMAS NMR spectroscopy. All homogeneous and heterogeneous catalysts were assessed for the ringopening polymerisation of raclactide at 130 °C in the absence of solvent, using unsublimed monomer. All catalysts offered good conversions and a moderate degree of control.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

Summary:Surfactant‐free honeycomb‐structured Poly(DLlactide) (PDLLA) and Poly‐(DLlactide‐co‐glycolide) PDLLGA thin films were fabricated by water droplet templating methods. Thin films with uniform pore structure were obtained after controlled evaporation of solvents in a humid atmosphere. Solvent, polymer concentration and humidity were found to be important factors in the formation of honeycomb‐structured thin films. Preliminary cell culture studies with MG‐63 osteoblast‐like cell lines showed promising degrees of cell attachment and proliferation on these films, suggesting that they are applicable as scaffolds for tissue engineering.

The coordination modes of various azines (C=N–N=C) and hydrazones (C=N–NR2) with titanium(IV) are investigated. Five ligands were studied, two hydrazones 1H–2H and three azines 3H2–5H2, and it was found that hydrazones form monomers and azines form dimers in the solid state. The hydrogen-bonded arrays observed for the hydrazones were significantly different for the two ligands, with one forming a ribbon like structure and the other a chain. For the azines the supramolecular structures are also discussed. A pronounced twist is observed in the azine ligand upon complexation to the metal centre, which is rationalised in terms of the favourable interactions observed in the solid-state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

This paper reports the reaction of Ti(OiPr)4 with a series of Schiff-base ligands. The Schiff-base proligands 1a–l are synthesised by the condensation of salicylaldehyde with a range of primary alkylamine and aniline derivatives. The treatment of 1a–f with Ti(OiPr)4 yields the octahedral bis(aryloxy–imine)Ti(OiPr)2 complexes 2a–f. X-ray crystal structure analysis of 2c, 2d and 2e reveals complexes with a trans-aldiminato oxygen atom and cis-N,cis-alkoxide ligand arrangement about the central metal atom. The reactions of Ti(OiPr)4 with the ligands 1g and 1h result in a sterically induced ligand rearrangement to form the octahedral complexes 2g and 2h, also characterised by X-ray diffraction experiments, in which the nitrogen atoms of the O,N-chelate are now trans-orientated at the titanium centre. 1H NMR analysis reveals significant deshielding of the isopropoxide methine proton, induced by this coordination mode. In contrast, reactions of 1i and 1j with Ti(OiPr)4 result in the formation and isolation of the complexes 2i and 2j. X-ray crystal structure analysis shows complex 2j to have a previously unobserved ligand orientation, in which both ligands are trans-orientated, with respect to the aldiminato oxygen atoms, about the titanium centre, but steric bulk of the ligand inhibits the bidentate coordination of both O,N-ligands. Further increase in thesteric bulk of the imine substituent results in a reduced reactivity for ligands 1k and 1l, such that Ti(OiPr)4 reacts with 1k to form the dimeric mono(Schiff-base) complex 2k (characterised by X-ray analysis). No reaction is observed for 1l. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The structures of derivatives of phenyl-ortho-carborane bearing on the second cage hypercarbon atom a π-donor substituent (F, OH, O−, NH₂, NH− and CH₂−) were investigated by NMR, X-ray crystallography and computational studies. The molecular structures of these compounds, notably their cage C1–C2 distances and the orientations of their π-donor substituents (OH, NH₂, NH− and CH₂−) show remarkable and systematic variations with the degree of exo π-bonding, which varies as expected with the π-donor characteristics of the substituent.

The structures of derivatives of phenyl-ortho-carborane bearing on the second cage hypercarbon atom a π-donor substituent F, OH, O−, NH2, NH−and CH2− were investigated by NMR, X-ray crystallography and computational studies. The molecular structures of these compounds, notably their cage C1–C2 distances and the orientations of their π-donor substituents OH, NH2, NH−and CH2− show remarkable and systematic variations with the degree of exoπ-bonding, which varies as expected with the π-donor characteristics of the substituent.

The topological analysis of the experimentally determined charge density distribution in the semi-stabilized ylide Ph₃PCHPh revealed the multiple character and high ionicity of the ylide bond and a different role of the phenyl groups in charge delocalisation in the PPh₃ fragment. The analysis of intra- and inter-molecular contacts located the interactions which are responsible for the conformation of the molecule and determine the packing of the molecules in the crystal.

Ab initio calculations have been used to determine the possible structure of lithium derivatives of phosphine oxides in THF: extension of these calculations to the docking of a carbonyl compound onto such a lithium derivative suggests an explanation for the anti selectivity of the Horner—Wittig reaction.

A series of amine bis(phenolate) ligand precursors and their group 4 metal complexes have been prepared, characterised by single-crystal X-ray diffraction, and tested for ring opening polymerisation of -caprolactone.

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Two unprecedented hydrogen bondswere observed in the adducts obtained by the reactions of an N‐heterocyclic carbene with a bulky phenol and with diphenylamine. In the former case, proton transfer yields an imidazolium aryloxide (1) containing the shortest C−H⋅⋅⋅O interaction seen to date and in the latter, the hydrogen atom remains bound to the organic acid but forms a unique N−H⋅⋅⋅C hydrogen bond (2).

A bis(bora)calixarene, 3, the first lower-rim boron derivatised calixarene to be structurally characterised, is synthesised by the reaction of PhBCl2with 4-tert-butylcalix[4]arene, and is demonstrated to be a sensitive and selective fluorescent fluoride sensor.

A bis(bora)calixarene, 3, the first lower-rim boron derivatised calixarene to be structurally characterised, is synthesised by the reaction of PhBCl₂ with 4-tert-butylcalix[4]arene, and is demonstrated to be a sensitive and selective fluorescent fluoride sensor.

Reaction of ZrOiPr4or SnNSiMe322with the tris-phenol amine ligand H3LMeMeresults in the formation of zirconium or tin complexes containing the new C3-symmetric zwitterionic ammonium-trisphenolate ligand HL2−, while increasing the steric bulk of the ligand results in the isolation of a zirconium complex containing the known trianionic ligand L3−.

An air- and moisture-stable titaniumiv triflate, 3, supported by a C3-symmetric amine trisphenolate ligand has been synthesised, characterised by X-ray crystallography and demonstrated to be an excellent catalyst for formal aza-Diels–Alder reactions.

An air- and moisture-stable titanium(iv) triflate, 3, supported by a C₃-symmetric amine tris(phenolate) ligand has been synthesised, characterised by X-ray crystallography and demonstrated to be an excellent catalyst for formal aza-Diels–Alder reactions.

Reaction of Zr(OiPr)₄ or Sn[N(SiMe₃)₂]₂ with the tris-phenol amine ligand H₃L(Me/Me) results in the formation of zirconium or tin complexes containing the new C₃-symmetric zwitterionic ammonium-trisphenolate ligand HL2−, while increasing the steric bulk of the ligand results in the isolation of a zirconium complex containing the known trianionic ligand L3−.

The structures of the adduct nido-C₂B₁₀H₁₂·HNP(NMe₂)₃ and the borenium salt [(Me₂N)₃PNHBNP(NMe₂)₃]₂O²⁺(C₂B₉H₁₂⁻)₂, both obtained from 1,2-C₂B₁₀H₁₂ and HNP(NMe₂)₃, were determined by X-ray crystallography; the adduct represents the first structurally determined carborane of its type, a possible intermediate in the well known conversion of closo-1,2-C₂B₁₀H₁₂ into the nido-7,8-C₂B₉H₁₂⁻ anion by bases.

Tetralithiation of tert-butylcalix[4]arene in the presence of hmpa (hexamethylphosphoramide) results in the isolation of either a monomeric complex in which LiOH is incorporated into an Li₅O₅ core based on an isolated square pyramid of Li atoms, or a dimeric LiOH-free species containing an Li₈O₈ core in which the same structural motif is maintained by edge-sharing of two square pyramids of Li atoms.