Antifouling polymers for nanomedicine and surfaces: recent advances.

Antifouling polymers are materials that can resist nonspecific interactions with cells, proteins, and other biomolecules. Typically, they are hydrophilic polymers with polar or charged moieties that are capable of strong nonbonding interactions with water molecules. This propensity to bind water generates a surface hydration layer that reduces nonspecific interactions with other molecules and is paramount to the antifouling behavior. This property is especially useful for nanoscale applications such as nanomedicine and surface modifications at the molecular level. In nanomedicine, antifouling polymers such as poly(ethylene glycol) and its alternatives play a key role in shielding drug molecules and therapeutic proteins/genes from the immune system within nanoassemblies, thereby enabling effective delivery to target tissues. For coatings, antifouling polymers help to prevent adhesion of cells and molecules to surfaces and are thus valued in marine and biomedical device applications. In this Review, we survey recent advances in antifouling polymers in the context of nanomedicine and coatings, while shining the spotlight on the major polymer classes such as PEG, polyzwitterions, poly(oxazoline)s, and other nonionic hydrophilic polymers.

Visible Light Degradable Acridine-Containing Polyurethanes in an Aqueous Environment.

Light degradable polymers hold significant promise in a wide range of applications including the fabrication of optically recyclable materials, responsive coatings and adhesives, and controlled drug delivery. Here, we report the synthesis of polyurethanes that can be degraded under irradiation of visible light (≤450 nm) from commercial LED (3-15 W) light sources. The photolysis occurs in an aqueous environment via photocleavage of an acridine moiety incorporated within the backbone of the polymer chains. Analysis of the quantum yield as a function of wavelength reveals highly efficient photoreactivity at up to 440 nm activation, which is red-shifted compared to the UV-vis absorbance of the chromophore. The potential of our chemical system in biomaterials is demonstrated by the fabrication of an in situ forming hydrogel that can be degraded by visible light.

Cu(I)/Cu(II) Creutz-Taube Mixed-Valence 2D Coordination Polymers.

Graphene-like 2D coordination polymers (GCPs) have been of central research interest in recent decades with significant impact in many fields. According to classical coordination chemistry, Cu(II) can adopt the dsp2 hybridization to form square planar coordination geometry, but not Cu(I); this is why so far, there has been few 2D layered structures synthesized from Cu(I) precursors. Herein a pair of isostructural GCPs synthesized by the coordination of benzenehexathiol (BHT) ligands with Cu(I) and Cu(II) ions, respectively, is reported. Spectroscopic characterizations indicate that Cu(I) and Cu(II) coexist with a near 1:1 ratio in both GCPs but remain indistinguishable with a fractional oxidation state of +1.5 on average, making these two GCPs a unique pair of Creutz-Taube mixed-valence 2D structures. Based on density functional theory calculations, an intramolecular pseudo-redox mechanism is further uncovered whereby the radicals on BHT ligands can oxidize Cu(I) or reduce Cu(II) ions upon coordination, thus producing isostructures with distinct electron configurations. For the first time, it is demonstrated that using Cu(I) or Cu(II), one can achieve 2D isostructures, indicating an unusual fact that a neutral periodic structure can host a different number of total electrons as ground states, which may open a new chapter for 2D materials.

Guanidinium-Perfunctionalized Polyhedral Oligomeric Silsesquioxanes as Highly Potent Antimicrobials against Planktonic Microbes, Biofilms, and Coronavirus.

Supramolecules have been drawing increasing attention recently in addressing healthcare challenges caused by infectious pathogens. We herein report a novel class of guanidinium-perfunctionalized polyhedral oligomeric silsesquioxane (Gua-POSS) supramolecules with highly potent antimicrobial activities. The modular structure of Gua-POSS Tm-Cn consists of an inorganic T10 or T8 core (m = 10 or 8), flexible linear linkers of varying lengths (n = 1 or 3), and peripherally aligned cationic guanidinium groups as the membrane-binding units. Such Gua-POSS supramolecules with spherically arrayed guanidinium cations display high antimicrobial potency against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, as well as fungus (Candida albicans), with the best showing excellently low minimal inhibitory concentrations (MICs) of 1.7-6.8 µM in media, yet with negligible hemolytic activity and low in vitro cytotoxicity to mammalian cells. More significantly, they can inhibit biofilm formation at around their MICs and near-completely break down preestablished difficult-to-break biofilms at 250 µg mL-1 (∼50 µM). Their strong antiviral efficacy was also experimentally demonstrated against the enveloped murine hepatitis coronavirus as a surrogate of the SARS-CoV species. Overall, this study provides a new design approach to novel classes of sphere-shaped organic-inorganic hybrid supramolecular materials, especially for potent antimicrobial, anti-biofilm, and antiviral applications.

Neutral Antiaromatic Bis(1,2-dithiolene)-Chelated Nickel Complexes Bearing Multiradical Characters.

Metal-organic complexes with radical characteristics are unique species attracting immense attention in recent years due to their peculiar properties and promising applicability in a wide variety of innovative research fields. However, the reported complexes typically do not exceed diradicality. This study systematically investigates a series of square planar neutral Ni-bis(1,2-dithiolene) and Ni-bis(1,2-dioxolene) complexes with linear, branched, and macrocyclic configurations via ab initio calculations. The linear Ni-complexes display strong singlet diradical characters, while their branched counterparts can also exhibit moderate singlet multiradical characters. Importantly, the macrocyclic Ni-complexes can possess extremely strong singlet multiradical characters up to dodeca-radicality along with their global antiaromaticity and hence strong induced ring current in the presence of an external magnetic field, ascribed to the localization of unpaired α and ß electrons residing in the highest few molecular orbitals at different molecular sites, minimizing their coupling and annihilation. Our work represents the first indication in the rational design of novel multiradical neutral antiaromatic macrocyclic complexes for potential applications in molecular machines and electronic devices.

Titanium compounds containing naturally occurring dye molecules.

A range of titanium compounds containing the naturally occurring dyes quinizarin (QH2) and alizarin (AH2) was synthesized and structurally characterized in the solid state. Among these is the first examples of a discrete metallocyclic arrangement formed exclusively using quinizarin ligands and the first examples of lanthanide containing titanium compounds of the alizarin family of ligands.

The Significance of Metal Coordination in Imidazole-Functionalized Metal-Organic Frameworks for Carbon Dioxide Utilization.

The grafting of imidazole species onto coordinatively unsaturated sites within metal-organic framework MIL-101(Cr) enables enhanced CO2 capture in close proximity to catalytic sites. The subsequent combination of CO2 and epoxide binding sites, as shown through theoretical findings, significantly improves the rate of cyclic carbonate formation, producing a highly active CO2 utilization catalyst. An array of spectroscopic investigations, in combination with theoretical calculations reveal the nature of the active sites and associated catalytic mechanism which validates the careful design of the hybrid MIL-101(Cr).

A Simple Drop-and-Dry Approach to Grass-Like Multifunctional Nanocoating on Flexible Cotton Fabrics Using In Situ-Generated Coating Solution Comprising Titanium-Oxo Clusters and Silver Nanoparticles.

Multifunctional nanocoatings have been of central importance in various technological fields, yet their fabrication, especially on flexible substrates, still remains a persistent challenge to date. We herein demonstrate a mild single-step drop-and-dry approach to the in situ growth of hierarchical grass-like nanostructures on flexible cotton fabrics. A precursor solution comprising titanium-oxo clusters [Ti18MnO30(OEt)20(MnPhen)3] (Phen = 1,10-phenanthroline) and AgNO3 is employed wherein Ag+ cations are in situ-reduced to silver nanoparticles (AgNPs). Drop-casting onto cotton fabrics under mild conditions induces the in situ growth of the heterogeneous grass-like assembly, and each constituent nanofibrous 'grass leaf' incorporates AgNPs both on the surface and embedded in the interior. The hierarchical morphology and heterogeneous composition of these grass-like nanostructures impart the coated cotton fabrics with enhanced antibacterial properties, robust hydrophobicity, and UV-blocking capability, which are features desired in textile materials but lacking in natural cotton.

Suite of Organoplatinum(II) Triangular Metallaprism: Aggregation-Induced Emission and Coordination Sequence Induced Emission Tuning.

A series of triangular metallaprisms with a kinetically inert Pt-N bond have been synthesized from the stepwise assembly of a Pt-corner, linear linker 4,4'-bipy (4,4'-bipy = 4,4'-bipyridine) and triangular ligand [tpb or tpt, tpb = tris(4-pyridyl)benzene, tpt = tris(4-pyridyl)triazine]. The use of an unsymmetrical [Pt(HL)]-corner (H2L = 2,6-diphenylpyridine) leads to novel isostructural products. Phenyl rotation at the metal-corners endows these complexes with good aggregation-induced emission (AIE) function, with varied activities across the isostructural complexes. The coordination sequence of electron-deficient ligand tpt also imparts significant influence on the complex emission. These organoplatinum triangular metallaprisms thus provide a good model to study the influence of building blocks and coordination sequence on the luminescence of supramolecules.

Metal-salen molecular cages as efficient and recyclable heterogeneous catalysts for cycloaddition of CO2 with epoxides under ambient conditions.

A salen based molecular cage, salen@cage, was synthesized and complexed with Co and Al to yield metal-salen molecular cages, Co(ii)@cage, Co(iii)@cage and Al(iii)@cage. These cages were demonstrated to be efficient heterogeneous catalysts for the cycloaddition of CO2 with styrene oxide, achieving full conversion at 25 °C and 1 atm CO2. Good to excellent yields of various cyclic carbonates were also achieved under mild conditions. Al(iii)@cage can be reused up to five times without any significant loss of its high catalytic activity. The capability to access a variety of heterogeneous organometallic catalysts with salen@cage offers new prospects for practical CO2 utilization and chemical manufacturing.

Energy transfer and photoluminescence properties of lanthanide-containing polyoxotitanate cages coordinated by salicylate ligands.

Polyoxotitanate (POT) cages have attracted considerable attention recently; much of this from the fact that they can be considered to be structural models for the technologically important semiconductor TiO2. Among the reported POT cages, lanthanide-containing (Ln-POT) cages are of particular interest owing to the fascinating luminescence properties of Ln3+ ions and the versatile coordination environments that they can adopt. In the present study, we report the energy transfer mechanism and photoluminescence properties of a series of isostructural Ln-POT cages coordinated by salicylate ligands, of general formula [LnTi6O3(OiPr)9(salicylate)6] (Ln-1, Ln = La to Er excluding Pm). Both visible (for Pr-1, Sm-1, Eu-1, Ho-1 and Er-1) and near-infrared (for Nd-1 and Er-1) Ln3+-centred photoluminescence can be sensitised in solution, and most importantly, their excitation bands all extend well into the visible region up to 475 nm. With the assistance of steady-state and time-resolved photoluminescence spectroscopy, an energy-transfer mechanism involving the salicylate-to-Ti4+ charge-transfer state is proposed to account for the largely red-shifted excitation wavelengths of these Ln-1 cages. The photoluminescence quantum yield of Nd-1 upon excitation via the charge-transfer state reaches 0.30 ± 0.01% in solution, making it among the highest reported values for Nd3+-complexes in the literature.

Self-assembled [2]catenane in trapezoidal metallacycles with [Cp*Ir]-corners.

A series of trapezoidal metallacycles were synthesized by the selective combination of a rigid with a flexible arm. [2]Catenane 3 was obtained by self-assembly when the cavity size of the trapezoidal rings was optimised.

IrIII -based Octahedral Metalloligands Derived Primitive Cubic Frameworks for Enhanced CO2 /N2 Separation.

We developed a metalloligand strategy to construct porous frameworks, viz. the combined use of IrIII -based octahedral metalloligands and the linear unit [Ni(cyclam)] easily afforded two isostructural complexes 1 and 2 with primitive cubic frameworks. Both complexes show good CO2 /N2 separation property.

Synthesis, structure and paramagnetic NMR analysis of a series of lanthanide-containing [LnTi6O3(OiPr)9(salicylate)6] cages.

The influence of paramagnetic Ln3+ ions on the NMR behaviour is investigated via a series of new isostructural lanthanide-containing cages with the general formula [LnTi6O3(OiPr)9(salicylate)6] (Ln-1, Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er). Compared to conventional coordination compounds containing Ln3+ ions, the peripheral ligands in Ln-1 are separated from the paramagnetic lanthanide centres by oxo-Ti4+ linkages, and therefore experience a weaker paramagnetic influence. As a result, all of the 1H and 13C NMR signals of these Ln-1 cages (except for Gd-1) are observed and can be unambiguously assigned, which provides an excellent platform for the in-depth study of the NMR behaviour of paramagnetic Ln3+ ions. Further analysis of the fully assigned paramagnetic signals suggests that the pseudo-contact component dominates the 1H NMR shifts, whereas both the pseudo-contact and Fermi-contact contributions affect the 13C shifts, although the majority of the resonance environments are at least four bonds distant from the central Ln3+ ion. Our results also show that the use of Bleaney's factors to describe the pseudo-contact shift is inadequate for this Ln-1 cage series.

The influence of halides in polyoxotitanate cages; dipole moment, splitting and expansion of d-orbitals and electron-electron repulsion.

Metal-doped polyoxotitanate (M-POT) cages have been shown to be efficient single-source precursors to metal-doped titania [TiO2(M)] (state-of-the-art photocatalytic materials) as well as molecular models for the behaviour of dopant metal ions in bulk titania. Here we report the influence halide ions have on the optical and electronic properties of a series of halide-only, and cobalt halide-'doped' POT cages. In this combined experimental and computational study we show that halide ions can have several effects on the band gaps of halide-containing POT cages, influencing the dipole moment (hole-electron separation) and the structure of the valance band edge. Overall, the band gap behaviour stems from the effects of increasing orbital energy moving from F to I down Group 17, as well as crystal-field splitting of the d-orbitals, the potential effects of the Nephelauxetic influence of the halides and electron-electron repulsion.

Correction: A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide.

Correction for 'A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide' by Chee Koon Ng et al., Chem. Commun., 2016, 52, 11842-11845.

A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide.

Binary catalyst systems comprising a cationic Ru-CNC pincer complex and an alkali metal salt were developed for selective hydroboration of CO2 utilizing pinacolborane at r.t. and 1 atm CO2, with the combination of [Ru(CNCBn)(CO)2(H)][PF6] and KOCO2tBu producing formoxyborane in 76% yield. A bicyclic catalytic mechanism was proposed and discussed.

Novel properties and potential applications of functional ligand-modified polyoxotitanate cages.

Functional ligand-modified polyoxotitanate (L-POT) cages of the general type [TixOy(OR)z(L)m] (OR = alkoxide, L = functional ligand) can be regarded as molecular fragments of surface-sensitized solid-state TiO2, and are of value as models for studying the interfacial charge and energy transfer between the bound functional ligands and a bulk semiconductor surface. These L-POTs have also had a marked impact in many other research fields, such as single-source precursors for TiO2 deposition, inorganic-organic hybrid material construction, photocatalysis, photoluminescence, asymmetric catalysis and gas adsorption. Their atomically well-defined structures provide the basis for the understanding of structure/property relationships and ultimately for the rational design of new cages targeting specific uses. This highlight focuses on recent advances in L-POTs research, with emphasis on their novel properties and potential applications.

How Does Substitutional Doping Affect Visible Light Absorption in a Series of Homodisperse Ti11 Polyoxotitanate Nanoparticles--A Comment on the Band Gap Determination of the Fe(II) Cages (Chem. Eur. J. 2015, 21, 11538).

There is no experimental support for the conclusion by Coppens and Chen in a recent paper that the (HOMO-LUMO) band gaps in a series of Fe(II) polyoxotitanate cages are in the range 1.43-1.59 eV.

Synthesis, structure and properties of the manganese-doped polyoxotitanate cage [Ti18MnO30(OEt)20(MnPhen)3] (Phen = 1,10-phenanthroline).

The novel heterometallic polyoxotitanate cage [Ti18MnO30(OEt)20(MnPhen)3] (1), obtained by solvothermal reaction of Ti(OEt)4 with Mn(AcO)3·(H2O)2 and 1,10-phenanthroline (Phen) in EtOH, has a C3 symmetric core structure containing an interstitial tetrahedral Mn(II) ion and is surrounded by three Mn(II)(Phen) fragments. The molecular structure is retained in thin film electrodes of 1 deposited by solution drop-casting onto fluorinated tin oxide (FTO). Both solid state and solution phase electrochemical measurements show dual redox couples, consistent with the two distinct Mn coordination environments in the cage structure. Sintering of 1 in air at 600 °C produces a black crystalline solid which consists of Mn-doped TiO2 (mainly in the rutile phase) together with α-Mn2O3. Such a composite semiconductor has an optical band gap of ca. 1.80 eV, similar to that of α-Mn2O3.