Small but bright: origin of the enhanced luminescence of ultrasmall ZnGa2O4:Cr3+ in mesoporous silica nanoparticles.

Chromium(III)-doped zinc gallate (CZGO) is one of the representative persistent luminescent phosphors emitting in the near-infrared (NIR) region. The emission wavelength it covers falls in the tissue-transparent window, making CZGO a promising optical probe for various biomedical applications. The PersL mechanism dictates that such a phenomenon is only profound in large crystals, so the preparation of CZGO with sizes small enough for biological applications while maintaining its luminescence remains a challenging task. Recent attempts to use mesoporous silica nanoparticles (MSN) as a template for growing nanosized CZGO have been successful. MSN is also a well-studied drug carrier, and incorporating CZGO in MSN further expands its potential in imaging-guided therapeutics. Despite the interest, it is unclear of how the addition of MSN would affect the luminescence properties of CZGO. In this work, we observed that forming a CZGO@MSN nanocomposite could enhance the luminescence intensity and extend the PersL lifetime of CZGO. X-ray absorption fine structure (XAFS) analysis was conducted to investigate the local structure of Zn2+, and an interaction between Zn2+ in CZGO and the MSN matrix was identified.

Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π-Donating Imidazolin-2-iminato Ligand.

Synthesis and characterization of new P(III) and P(V) bis(azido)phosphines/phosphoranes supported by an N,N'-bis(2,6-diisopropylphenyl) imidazolin-2-iminato (IPrN) ligand and their reactivity with various secondary and tertiary phosphines result in the formation of chiral and/or asymmetric mono(phosphinimino)azidophosphines via the Staudinger reaction. The reaction of IPrNP(N3)2 (2) or IPrNP(S)(N3)2 (4S) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP(N3)(NPMe3) (7) or IPrNP(S)N3(NPR3) (5R), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy2) to produce IPrNP(S)N3[NP(H)Cy2] (6a), which exists in equilibrium with a tautomeric IPrNP(S)N3[N(H)PCy2] form (6b), as confirmed by 31P-31P nuclear Overhauser effect spectroscopy (NOESY). Density functional theory (DFT) calculations point to a combination of energetically unfavorable lowest unoccupied molecular orbitals (LUMOs) and the accumulation of increasing negative charge at the terminal azido-nitrogen upon a single azide-to-phosphinimine conversion that gave rise to the observed chemoselectivity.

Mesoionic carbene-based self-assembled monolayers on gold.

N-Heterocyclic carbenes (NHC) have been widely studied as ligands for surface chemistry, and have shown advantages compared to existing ligands (e.g. thiols). Herein, we introduce mesoionic carbenes (MICs) as a new type of surface ligand. MICs exhibit higher σ-donor ability compared to typical NHCs, yet they have received little attention in the area of surface chemistry. The synthesis of MICs derived from imidazo[1,2-a]pyridine was established and fully characterized by spectroscopic methods. The self-assembly of these MICs on gold was analyzed by X-ray photoelectron spectroscopy (XPS). Additionally, XPS was used to compare bonding ability in MICs compared to the typical NHCs. These results show that MIC overlayers on gold are robust, resistant to replacement by NHCs, and may be superior to NHCs for applications that require even greater levels of robustness.

Multicomponent Synthesis of Poly(α-aminophosphine chalcogenide)s and Subsequent Depolymerization.

Multicomponent reactions of primary phosphines (R-PH2), diimines (R'-N═C(H)-R-(H)C═N-R'), and chalcogens (O2, S8) generate poly(α-aminophosphine chalcogenide)s (4-7) through step-growth polymerization. Characterization of the linear polymers using 31P{1H} diffusion-ordered NMR spectroscopy (DOSY) experiments aided in determining the molecular weight (Mw) of the material. Subjecting the polyphosphine oxide or sulfide to reducing conditions in the presence of a Lewis acid resulted in complete depolymerization of the polymers, quantitatively releasing the 1° phosphine and diimine (2) starting materials, with concomitant reduction of diimine to diamine (9).

UV induced hydrophosphination of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate towards phosphine chalcogenides.

Dimethyl 2-vinylcyclopropane-1,1-dicarboxylate underwent a hydrophosphination reaction with either a primary or secondary phosphine under photolytic conditions. Notably, a free radical initiator was not required. The resulting tertiary phosphines were derivatized using S8 to afford moisture and air stable yellow or colorless oils in a 27%-73% isolated yield. A series of control reactions were performed, and we propose that this UV induced hydrophosphination reaction proceeds through a radical mechanism.

Heterocyclic Phosphenium Cations and Their Divergent Coordination Chemistry.

While they are often encountered as reaction intermediates, phosphenium cations are not commonly incorporated into π-conjugated systems. We report the synthesis and characterization of donor-stabilized phosphenium cations supported by pyridylhydrazonide ligands. The preparation of these cations relies on precise control of ligand E-Z isomerism. The heterocycles were treated with a variety of transition metals, with [Rh(COD)Cl]2 yielding the only well-defined organometallic products. The optoelectronic properties of the phosphenium heterocycles and their transition-metal complexes were examined using UV-vis absorption spectroscopy, cyclic voltammetry, and modeling by density functional theory (DFT). Computations support the description of these compounds as phosphenium cations and corroborate our observation of a weak P-Npyridine bond, which was manifested experimentally as the Rh adducts undergo selective insertion of Rh into the P-Npyridine bond, depending on the substituent at phosphorus. The reported compounds provide a framework for further study of π-conjugated, N,N'-chelated phosphenium cations and their transition-metal adducts.

Reactivity of Primary Phosphines and Primary Phosphine Sulfides towards Imines.

Reactivity of primary phosphines with two stoichiometric equivalents of imine results in the formation of bis-α-aminophosphines (2 a-e), which can be subsequently oxidized in the presence of S8 or H2 O2 to generate air stable bis-α-aminophosphine sulfides (2 b-m(S/O)). To elucidate the mechanism of this three-component reaction, Hammett analysis, kinetic isotope effect (KIE), and trapping experiments were performed. Ultimately a P(V)-P(III) tautomerization is invoked, followed by nucleophilic attack by the P(III) species to generate the desired products.

"Lignophines": lignin-based tertiary phosphines with metal-scavenging ability.

Methacrylated lignin was reacted with PH3(g) to prepare a phosphorus rich bio-based polymer containing PH/PH2 functional groups, which were converted to tertiary phosphine units via the phosphane-ene reaction. This represents a straightforward method for the upconversion of low-value biomass waste to useful inorganic polymer with potential utility in metal scavenging applications.

Phosphonium versus Ammonium Compact Polyelectrolyte Complex Networks with Alginate-Comparing Their Properties and Cargo Encapsulation.

Phosphonium and ammonium polymers can be combined with polyanions to form polyelectrolyte complex (PEC) networks, with potential application in self-healing materials and drug delivery vehicles. While various structures and compositions have been explored, to the best of our knowledge, analogous ammonium and phosphonium networks have not been directly compared to evaluate the effects of phosphorus versus nitrogen cations on the network properties. In this study, we prepared PECs from sodium alginate and poly[triethyl(4-vinylbenzyl)phosphonium chloride], poly[triethyl(4-vinylbenzyl)ammonium chloride], poly[tri(n-butyl)(4-vinylbenzyl)phosphonium chloride], poly[tri(n-butyl)(4-vinylbenzyl)ammonium chloride], and poly[tris(hydroxypropyl)(4-vinylbenzyl)phosphonium chloride]. These networks were ultracentrifuged to form compact PECs (CoPECs), and their physical properties, chemical composition, and self-healing abilities were studied. In phosphate-buffered saline, the phosphonium polymer networks swelled to a higher degree than their ammonium salt-containing counterparts. However, the viscous and elastic moduli, along with their relaxation times, were quite similar for analogous phosphoniums and ammoniums. The CoPEC networks were loaded with anions including fluorescein, etodolac, and methotrexate, resulting in loading capacities ranging from 5 to 14 w/w % and encapsulation efficiencies from 29 to 93%. Anion release occurred over a period of several days to weeks, with the rate depending largely on the anion structure and polycation substituent groups. Whether the cation was an ammonium or a phosphonium had a smaller effect on the release rates. The cytotoxicities of the networks and polycations were investigated and found to depend on both the network and polycation structure.

Metallized Phosphane-Ene Polymer Networks as Precursors for Ceramics with Excellent Shape Retention.

Our research group has reported the synthesis of phosphane-ene photopolymer networks, where the networks are composed of cross-linked tertiary alkyl phosphines. Taking advantage of the rich coordination chemistry of alkyl phosphines and the material's susceptibility to solution chemistry, we were able to generate Co, Al, and Ge macromolecular adducts. The metallized polymer networks can be pyrolyzed to make metal-doped carbon, commodity materials in the areas of battery, and fuel cell research. The polymer precursors can also be shaped by spin coating and lithography, before being metallized and pyrolyzed to give patterned ceramics, which display excellent shape retention of the original patterns.

Orthogonally Bimetallized Phosphane-ene Photopolymer Networks.

The development of batteries and fuel cells has brought to light a need for carbon anode materials doped homogeneously with electrocatalytic metals. In particular, combinations of electrocatalysts in carbon have shown promising activity. A method to derive functional carbon materials is the pyrolysis of metallopolymers. This work describes the synthesis of a bifunctional phosphonium-based system derived from a phosphane-ene network. The olefin functionality can be leveraged in a hydrogermylation reaction to functionalize the material with Ge. Unaffected by this radical addition, the bromide counterion of the phosphonium cation can be used to subsequently incorporate a second metal in an ion-complexation reaction with CuBr2 . The characterization of the polymers and the derived ceramics are discussed.

Phosphonium Polyelectrolyte Complexes for the Encapsulation and Slow Release of Ionic Cargo.

Polyelectrolyte complexation, the combination of anionically and cationically charged polymers through ionic interactions, can be used to form hydrogel networks. These networks can be used to encapsulate and release cargo, but the release of cargo is typically rapid, occurring over a period of hours to a few days and they often exhibit weak, fluid-like mechanical properties. Here we report the preparation and study of polyelectrolyte complexes (PECs) from sodium hyaluronate (HA) and poly[tris(hydroxypropyl)(4-vinylbenzyl)phosphonium chloride], poly[triphenyl(4-vinylbenzyl)phosphonium chloride], poly[tri(n-butyl)(4-vinylbenzyl)phosphonium chloride], or poly[triethyl(4-vinylbenzyl)phosphonium chloride]. The networks were compacted by ultracentrifugation, then their composition, swelling, rheological, and self-healing properties were studied. Their properties depended on the structure of the phosphonium polymer and the salt concentration, but in general, they exhibited predominantly gel-like behavior with relaxation times greater than 40 s and self-healing over 2-18 h. Anionic molecules, including fluorescein, diclofenac, and adenosine-5'-triphosphate, were encapsulated into the PECs with high loading capacities of up to 16 wt %. Fluorescein and diclofenac were slowly released over 60 days, which was attributed to a combination of hydrophobic and ionic interactions with the dense PEC network. The cytotoxicities of the polymers and their corresponding networks with HA to C2C12 mouse myoblast cells was investigated and found to depend on the structure of the polymer and the properties of the network. Overall, this work demonstrates the utility of polyphosphonium-HA networks for the loading and slow release of ionic drugs and that their physical and biological properties can be readily tuned according to the structure of the phosphonium polymer.

A Comprehensive Investigation of a Zwitterionic GeI Dimer with a 1,2-Dicationic Core.

The reductive dehalogenation of a zwitterionic GeII species to make a zwitterionic GeI dimer with a 1,2-dicationic core is reported herein. To the root of the stability of this compound, the molecular and electronic structures were comprehensively characterized and investigated using crystallographic, spectroscopic, and computational methods. It was determined that the Ge centers are attracted because they are both electron-rich and positively charged. A comparison to the electronic structure in triphosphenium cations revealed varying degrees of covalent bonding and that this difference can be distinguished spectroscopically.

Antibacterial Activity of Polymers: Discussions on the Nature of Amphiphilic Balance.

The purpose of this Viewpoint is to discuss the molecular design principles that guide development of synthetic antimicrobial polymers, especially those intended to mimic the structure of host defense peptides (HDPs). In particular, we focus on the principle of "amphiphilic balance" as it relates to some recently developed polyphosphoniums with somewhat atypical structure. We find that the fundamental concept of amphiphilic balance is still applicable to these new polymers, but that the method to achieve such balance is somewhat unique. We then briefly outline the future challenges and opportunities in this field.

Phosphonium hydrogels for controlled release of ionic cargo.

We describe the synthesis of three different phosphonium salts and their reaction with poly(ethylene glycol) dimethacrylate to create cationic hydrogels. The hydrogels were loaded with an anionic dye and an anionic anti-inflammatory drug through ionic interactions and compared with an analogous ammonium gel. The release rates of these anions depended on their structure and pKa values, as well as the pH and ionic strength of the release medium.

Antimony-Functionalized Phosphine-Based Photopolymer Networks.

The synthesis of phosphane-ene photopolymer networks, where the networks are composed of crosslinked tertiary alkyl phosphines are reported. Taking advantage of the rich coordination chemistry of alkyl phosphines, stibino-phosphonium and stibino-bis(phosphonium) functionalized polymer networks could be generated. Small-molecule stibino-phosphonium and stibino-bis(phosphonium) compounds have been well characterized previously and were used as models for spectroscopic comparison to the macromolecular analogues by NMR and XANES spectroscopy. This work reveals that the physical and electronic properties of the materials can be tuned depending on the type of coordination environment. These materials can be used as ceramic precursors, where the Sb-functionalized polymers influence the composition of the resulting ceramic.

Surprising Antibacterial Activity and Selectivity of Hydrophilic Polyphosphoniums Featuring Sugar and Hydroxy Substituents.

There is currently an urgent need for the development of new antibacterial agents to combat the spread of antibiotic-resistant bacteria. We explored the synthesis and antibacterial activities of novel, sugar-functionalized phosphonium polymers. While these compounds exhibited antibacterial activity, we unexpectedly found that the control polymer poly(tris(hydroxypropyl)vinylbenzylphosphonium chloride) showed very high activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus and very low haemolytic activity against red blood cells. These results challenge the conventional wisdom in the field that lipophilic alkyl substituents are required for high antibacterial activity and opens prospects for new classes of antibacterial polymers.

Icephobic Behavior of UV-Cured Polymer Networks Incorporated into Slippery Lubricant-Infused Porous Surfaces: Improving SLIPS Durability.

Ice accretion causes damage on power generation infrastructure, leading to mechanical failure. Icephobic materials are being researched so that ice buildup on these surfaces will be shed before the weight of the ice causes catastrophic damage. Lubricated materials have imposed the lowest-recorded forces of ice adhesion, and therefore lubricated materials are considered the state-of-the-art in this area. Slippery lubricant-infused porous surfaces (SLIPS) are one type of such materials. SLIPS are initially very effective at repelling ice, but the trapped fluid layer that affords their icephobic properties is easily depleted by repeated icing/deicing cycles, even after one deicing event. UV-cured siloxane resins were infused into SLIPS to observe effects on icephobicity and durability. These UV-cured polymer networks enhanced both the icephobicity and longevity of the SLIPS; values of ice adhesion below 10 kPa were recorded, and appreciable icephobicity was maintained up to 10 icing/deicing cycles.

Preparation and Characterization of P2 BCh Ring Systems (Ch=S, Se) and Their Reactivity with N-Heterocyclic Carbenes.

Four-membered rings with a P2 BCh core (Ch=S, Se) have been synthesized by the reaction of phosphinidene chalcogenide (Ar*P=Ch) and phosphaborene (Mes*P=BNR2 ). The mechanistic pathways towards these rings are explained by detailed computational work that confirmed the preference for the formation of P-P, not P-B, bonded systems, which seems counterintuitive given that both phosphorus atoms contain bulky ligands. The reactivity of the newly synthesized heterocycles, as well as that of the known (RPCh)n rings (n=2, 3), was probed by the addition of N-heterocyclic carbenes, which revealed that all investigated compounds can act as sources of low-coordinate phosphorus species.

Addressing the Nature of Phosphinidene Sulfides via the Synthesis of P-S Heterocycles.

The phosphorus-sulfur heterocycles 1,2-thiaphosphetenes and phosphirene sulfides have been prepared, and represent the first structurally characterized derivatives for either class of compound. These strained P-S ring systems are formed by the reaction of a phosphinidene sulfide and alkyne. Using an internal alkyne, only the 3-membered PV , phosphirene sulfide was produced, whereas a terminal alkyne yielded a mixture of phosphirene sulfide and 1,2-thiaphosphetene (PIII ). Detailed computational analysis revealed that for numerous derivatives of alkynes, the corresponding 4-membered rings are always more stable than the 3-membered isomers. The electronic nature of "free" phosphinidene sulfides (R-P=S) is discussed based on computational results.