Zero-Dimensional Hybrid Organic-Inorganic Indium Bromide with Blue Emission.

Low-dimensional hybrid organic-inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. Here, we report a new zero-dimensional hybrid organic-inorganic halide, RInBr4, featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R+) cations and nonemissive InBr4- tetrahedral anions. The crystal structure of RInBr4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l'Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications.

PEGylation of Polyethylenimine Lowers Acute Toxicity while Retaining Anti-Biofilm and ß-Lactam Potentiation Properties against Antibiotic-Resistant Pathogens.

Bacterial biofilms, often impenetrable to antibiotic medications, are a leading cause of poor wound healing. The prognosis is worse for wounds with biofilms of antimicrobial-resistant (AMR) bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant S. epidermidis (MRSE), and multi-drug resistant Pseudomonas aeruginosa (MDR-PA). Resistance hinders initial treatment of standard-of-care antibiotics. The persistence of MRSA, MRSE, and/or MDR-PA often allows acute infections to become chronic wound infections. The water-soluble hydrophilic properties of low-molecular-weight (600 Da) branched polyethylenimine (600 Da BPEI) enable easy drug delivery to directly attack AMR and biofilms in the wound environment as a topical agent for wound treatment. To mitigate toxicity issues, we have modified 600 Da BPEI with polyethylene glycol (PEG) in a straightforward one-step reaction. The PEG-BPEI molecules disable ß-lactam resistance in MRSA, MRSE, and MDR-PA while also having the ability to dissolve established biofilms. PEG-BPEI accomplishes these tasks independently, resulting in a multifunction potentiation agent. We envision wound treatment with antibiotics given topically, orally, or intravenously in which external application of PEG-BPEIs disables biofilms and resistance mechanisms. In the absence of a robust pipeline of new drugs, existing drugs and regimens must be re-evaluated as combination(s) with potentiators. The PEGylation of 600 Da BPEI provides new opportunities to meet this goal with a single compound whose multifunction properties are retained while lowering acute toxicity.

Broadband Emission in Hybrid Organic-Inorganic Halides of Group 12 Metals.

We report syntheses, crystal and electronic structures, and characterization of three new hybrid organic-inorganic halides (R)ZnBr3(DMSO), (R)2CdBr4·DMSO, and (R)CdI3(DMSO) (where (R) = C6(CH3)5CH2N(CH3)3, and DMSO = dimethyl sulfoxide). The compounds can be conveniently prepared as single crystals and bulk polycrystalline powders using a DMSO-methanol solvent system. On the basis of the single-crystal X-ray diffraction results carried out at room temperature and 100 K, all compounds have zero-dimensional (0D) crystal structures featuring alternating layers of bulky organic cations and molecular inorganic anions based on a tetrahedral coordination around group 12 metal cations. The presence of discrete molecular building blocks in the 0D structures results in localized charges and tunable room-temperature light emission, including white light for (R)ZnBr3(DMSO), bluish-white light for (R)2CdBr4·DMSO, and green for (R)CdI3(DMSO). The highest photoluminescence quantum yield (PLQY) value of 3.07% was measured for (R)ZnBr3(DMSO), which emits cold white light based on the calculated correlated color temperature (CCT) of 11,044 K. All compounds exhibit fast photoluminescence lifetimes on the timescale of tens of nanoseconds, consistent with the fast luminescence decay observed in π-conjugated organic molecules. Temperature dependence photoluminescence study showed the appearance of additional peaks around 550 nm, resulting from the organic salt emission. Density functional theory calculations show that the incorporation of both the low-gap aromatic molecule R and the relatively electropositive Zn and Cd metals can lead to exciton localization at the aromatic molecular cations, which act as luminescence centers.

Improved Performance of Glucose Bioanodes Using Composites of (7,6) Single-Walled Carbon Nanotubes and a Ferrocene-LPEI Redox Polymer.

The effect of incorporating different types of carbon nanotubes into composite films of a redox polymer (FcMe2-C3-LPEI) and glucose oxidase (GOX) was investigated. The composite films were constructed by first forming a high-surface area network film of either single-walled carbon nanotubes (SWNTs) or multiwalled carbon nanotubes (MWNTs) on a glassy carbon electrode (GCE) by solution casting of a suspension of Triton-X-100 dispersed SWNTs. Next a glucose responsive redox hydrogel was formed on top of the nanotube-modified electrode by cross-linking FcMe2-C3-LPEI with glucose oxidase via ethylene glycol diglycidyl ether (EGDGE). Electrochemical and enzymatic measurements showed that composite films made with (7,6) SWNTs produced a higher response (3.3 mA/cm2) to glucose than films made with (6,5) SWNTs (1.8 mA/cm2) or MWNTs (1.2 mA/cm2) or films made without SWNTs (0.7 mA/cm2). We also show that the response of the composite films could be systematically varied by fabricating SWNT films with different weight ratios of (7,6) and (6,5) SWNTs. Optimization of the (7,6) SWNTs loading and the redox polymer-enzyme film produced a glucose response of 11.2 mA/cm2. Combining the optimized glucose films with a platinum oxygen breathing cathode into a biofuel cell produced a maximum power density output of 343 µW/cm2.

Efficacy of ampicillin against methicillin-resistant Staphylococcus aureus restored through synergy with branched poly(ethylenimine).

ß-Lactam antibiotics kill Staphylococcus aureus bacteria by inhibiting the function of cell wall penicillin-binding proteins (PBPs) 1 and 3. However, ß-lactams are ineffective against PBP2a, used by methicillin-resistant S. aureus (MRSA) to perform essential cell wall crosslinking functions. PBP2a requires teichoic acid to properly locate and orient the enzyme, and thus MRSA is susceptible to antibiotics that prevent teichoic acid synthesis in the bacterial cytoplasm. As an alternative, we have used branched poly(ethylenimine), BPEI, to target teichoic acid in the bacterial cell wall. The result is restoration of MRSA susceptibility to the ß-lactam antibiotic ampicillin with a MIC of 1 µg ml-1, superior to that of vancomycin (MIC=3.7 µg ml-1). A checkerboard assay shows synergy of BPEI and ampicillin. NMR data show that BPEI alters the teichoic acid chemical environment. Laser scanning confocal microscopy images show BPEI residing on the bacterial cell wall, where teichoic acids and PBPs are located.

Electrochemical Characterization of Layer-By-Layer Assembled Ferrocene-Modified Linear Poly(ethylenimine)/Enzyme Bioanodes for Glucose Sensor and Biofuel Cell Applications.

Ferrocenylhexyl- and ferrocenylpropyl-modified linear poly(ethylenimine) (Fc-C6-LPEI, Fc-C3-LPEI) were used with periodate-modified glucose oxidase (p-GOX) in the layer-by-layer assembly of enzymatic bioanodes on gold. Fc-C6-LPEI/p-GOX and Fc-C3-LPEI/p-GOX films of 16 bilayers were capable of generating up to 381 ± 3 and 1417 ± 63 µA cm(-2), respectively, in response to glucose. These responses are greater than those of analogous bioanodes fabricated using conventional cross-linking techniques and are extremely high for planar, low surface area, single-enzyme electrodes. (Fc-C3-LPEI/p-GOX)8 films generated 86 ± 3 µW cm(-2) at pH 7.0 and 149 ± 7 µW cm(-2) at pH 5.0, when poised against an air-breathing platinum cathode in a compartment-less biofuel cell. An increase in power output with decreasing pH was shown to be a result of increases in the platinum cathode performance, indicating it is the rate-limiting electrode in the biofuel cells. The effect of fabrication wash time on the buildup of material at the electrode's surface was probed using cyclic voltammetry (CV) and constant potential amperometry. The use of electrochemical techniques as a diagnostic tool for studying the material deposition process is discussed. CV peak separation (ΔE), surface coverage of the electroactive ferrocene (ΓFc), and amperometric sensitivity of the enzyme to glucose (Jmax), studied as a function of numbers of bilayers, showed that physisorption of materials onto the surface results from initial patchy deposition, rather than in distinctly uniform layers.

Line of Dirac Nodes in Hyperhoneycomb Lattices.

We propose a family of structures that have "Dirac loops," closed lines of Dirac nodes in momentum space, on which the density of states vanishes linearly with energy. Those lattices all possess the planar trigonal connectivity present in graphene, but are three dimensional. We show that their highly anisotropic and multiply connected Fermi surface leads to quantized Hall conductivities in three dimensions for magnetic fields with toroidal geometry. In the presence of spin-orbit coupling, we show that those structures have topological surface states. We discuss the feasibility of realizing the structures as new allotropes of carbon.

Application of the compensated Arrhenius formalism to explain the dielectric constant dependence of rates for Menschutkin reactions.

The dependence of the reaction rate on solvent dielectric constant is examined for the reaction of trihexylamine with 1-bromohexane in a series of 2-ketones over the temperature range 25-80 °C. The rate constant data are analyzed using the compensated Arrhenius formalism (CAF), where the rate constant assumes an Arrhenius-like equation that also contains a dielectric constant dependence in the exponential prefactor. The CAF activation energies are substantially higher than those obtained using the simple Arrhenius equation. A master curve of the data is observed by plotting the prefactors against the solvent dielectric constant. The master curve shows that the reaction rate has a weak dependence on dielectric constant for values approximately less than 10 and increases more rapidly for dielectric constant values greater than 10.

Effect of surfactant type and redox polymer type on single-walled carbon nanotube modified electrodes.

Electrodes modified with single-walled carbon nanotubes (SWNTs) offer a number of attractive properties for developing novel electrochemical sensors. A common method to immobilize SWNTs onto the electrode surface is by placing a droplet of a SWNT suspension onto the electrode surface and allowing the solvent to evaporate. In order to maximize the properties of individual SWNTs, surfactants are normally present in these suspensions to provide stable and homogeneous SWNT dispersions. In this study we investigated the effect of different surfactants on the electrochemical and enzymatic performance of SWNT modified glassy carbon electrodes (GCEs). Amperometic biosensors for glucose were fabricated by a two-step procedure. In the first step, SWNT films were deposited onto GCEs by solution casting suspensions of SWNTs in water, Triton X-100, Tween 20, sodium cholate or sodium dodecylbenzenesulfonate (NaDDBS). In the second step, hydrogels containing a redox polymer and the enzyme, glucose oxidase (GOX), were deposited and cross-linked onto the SWNT-modified GCE. Three different redox polymers were tested: 3-ferrocenylpropyl-modified LPEI, (Fc-C3-LPEI), 6-ferrocenylhexyl-modified LPEI, (Fc-C6-LPEI), and poly[(vinylpyridine)Os(bipyridyl)2Cl](2+/3+)(PVP-Os). Biosensors constructed with SWNT films from suspensions of Triton X-100 or Tween 20 generally produced the highest electrochemical and enzymatic responses, with Triton X-100 films producing current densities of ~1.7-2.1 mA/cm(2) for the three different redox polymers. In contrast, biosensors constructed with SWNT films from sodium cholate suspensions resulted in significant decreases in the electrochemical and enzymatic response and in some cases showed no enzymatic activity. The results with SWNT films from NaDDBS suspensions were dependent upon the specific redox polymer used, but in general gave reduced enzymatic responses (~0.05-0.4 mA/cm(2)). These results demonstrate the importance of surfactant type in fabricating SWNT-modified electrode films.

Layer-by-layer assembly of ferrocene-modified linear polyethylenimine redox polymer films.

Herein, both electrostatic and covalent layer-by-layer assembly were used for the construction of multicomposite thin films using a ferrocene-modified linear poly(ethylenimine) redox polymer (Fc-C6-LPEI) as the cationic polyelectrolye, and poly(acrylic acid) (PAA), poly(glutamic acid) (PGA), or glucose oxidase (GOX) as the negative polyelectrolyte. The assembly of the multilayer films was characterized by cyclic voltammetry (CV), UV/Vis spectroscopy, and ellipsometry with the enzymatic response of the films containing GOX being characterized via constant potential amperometry. CV measurements suggested that the successful buildup of multilayer films was dependent upon the nature of the anionic polyelectrolyte used. Electrostatic assembly of films composed of Fc-C6-LPEI and either PAA or PGA produced large oxidation peak current densities of 630 and 670 µA cm(-2), respectively, during cyclic voltammetry. Increased measured absorbance by UV/Vis spectroscopy and increased measured film thicknesses (400-600 nm) by ellipsometry provided additional evidence of successful film formation. In contrast, the films incorporating GOX that were electrostatically assembled surprisingly produced significantly lower electrochemical responses (12 µA cm(-2)), low absorbance values, and reduced film thicknesses (~15 nm), and glucose electro-oxidation current densities less than 1 µA cm(-2), which all suggested unstable or minimal film formation. Subsequently, we developed a covalent layer-by-layer approach to fabricate films of Fc-C6-LPEI/GOX by covalently linking the amine groups of Fc-C6-LPEI to the aldehyde groups of periodate-oxidized glucose oxidase. Covalent assembly of the Fc-C6-LPEI/GOX films produced oxidation peak current densities during cyclic voltammetry of 40 µA cm(-2) and glucose electro-oxidation current densities of 220 µA cm(-2). These films also showed an increase in their thicknesses (~140 nm) relative to the electrostatic GOX films. For the films containing either PAA or PGA, the pH of the polymer solutions used for construction was found to have a significant effect on the response of the multilayer films, and the electrochemical response of the Fc-C6-LPEI/PAA, Fc-C6-LPEI/PGA, or covalently assembled Fc-C6-LPEI/GOX films could be tuned by varying the number of bilayers (n=1-16) in the film. These results are important because this is the first report of the use of the novel Fc-C6-LPEI redox polymer in the successful development of multicomposite layer-by-layer films. The electrochemical response achieved with the covalently assembled Fc-C6-LPEI/GOX films demonstrates that this redox polymer and layer-by-layer assembly technique can be used for possible biosensor and biofuel applications, and the success of multiple anionic polyelectrolytes could lead to additional applications with other enzyme systems.

Mass and charge transport in cyclic carbonates: implications for improved lithium ion battery electrolytes.

The compensated Arrhenius formalism (CAF) is applied to conductivity and diffusion data for a family of cyclic carbonates composed of octylene carbonate, decylene carbonate, undecylene carbonate, and dodecylene carbonate. The strong intermolecular interactions in these liquids lead to diffusion activation energies that are higher than those for typical aprotic solvents. The conductivity results show that activation energies are similar between TbaTf and LiTf cyclic carbonate electrolytes. However, the conductivities of the TbaTf solutions are higher than those for the LiTf solutions, and this is attributed to the greater number of charge carriers in the TbaTf electrolytes. These CAF results are then used to give a possible explanation of why the ionic conductivity in lithium ion battery electrolytes is often optimized by mixing a cyclic carbonate with a lower viscosity liquid.

Molecular and system parameters governing mass and charge transport in polar liquids and electrolytes.

Onsager's model of the dielectric constant is used to provide a molecular-level picture of how the dielectric constant affects mass and charge transport in organic liquids and organic liquid electrolytes. Specifically, the molecular and system parameters governing transport are the molecular dipole moment µ and the solvent dipole density N. The compensated Arrhenius formalism (CAF) writes the temperature-dependent ionic conductivity or diffusion coefficient as an Arrhenius-like expression that also includes a static dielectric constant (ε(s)) dependence in the exponential prefactor. The temperature dependence of ε(s) and therefore the temperature dependence of the exponential prefactor is due to the quantity N/T, where T is the temperature. Using the procedure described in the CAF, values of the activation energy can be obtained by scaling out the N/T dependence instead of the ε(s) dependence. It has been previously shown that a plot of the prefactors versus ε(s) results in a master curve, and here it is shown that a master curve also results by plotting the prefactors against N/T. Therefore, the CAF can be applied by using temperature-dependent density data instead of temperature-dependent dielectric constant data. This application is demonstrated for diffusion data of n-nitriles, n-thiols, n-acetates, and 2-ketones, as well as conductivity data for dilute tetrabutylammonium triflate-nitrile electrolytes.

Incorporation of single-walled carbon nanotubes into ferrocene-modified linear polyethylenimine redox polymer films.

In this study, we describe the effects of incorporating single-walled carbon nanotubes (SWNTs) into redox polymer-enzyme hydrogels. The hydrogels were constructed by combining the enzyme glucose oxidase with a redox polymer (Fc-C(6)-LPEI) in which ferrocene was attached to linear poly(ethylenimine) by a six-carbon spacer. Incorporation of SWNTs into these films changed their morphology and resulted in a significant increase in the enzymatic response at saturating glucose concentrations (3 mA/cm(2)) as compared to films without SWNTs (0.6 mA/cm(2)). Likewise, the sensitivity at 5 mM glucose was significantly increased in the presence of SWNTs (74 µA/cm(2)·mM) as compared to control films (26 µA/cm(2)·mM). We demonstrate that the increase in the electrochemical and enzymatic response of these films depends on the amount of SWNTs incorporated and the method of SWNT incorporation. Furthermore, we report that the presence of SWNTs in thick films allows for more of the ferrocene redox centers to become accessible. The high current densities of the hydrogels should allow for the construction of miniature biosensors and enzymatic biofuel cells.

High-sensitivity amperometric biosensors based on ferrocene-modified linear poly(ethylenimine).

Amperometric biosensors for glucose and hydrogen peroxide have been built by immobilizing glucose oxidase (GOX) and horseradish peroxidase (HRP) in cross-linked films of ferrocene-modified linear poly(ethylenimine). At pH 7, the glucose sensors generated limiting catalytic current densities of 1.2 mA/cm2. These current densities are approximately 4 times higher than those with other ferrocene-based redox polymers and are comparable to the highest reported values for osmium-based redox polymers with GOX. Because of the high sensitivity of these films (73 nA/cm2.microM), glucose concentrations in the micromolar range could be detected. Similarly, sensors were constructed with HRP-generated current densities of 0.9 mA/cm2 under saturation conditions and sensitivities of 500 nA/cm2.microM. The results show that the ability of Fc-LPEI to effectively communicate with a variety of enzymes has potential applications in measuring low substrate concentrations in implantable biosensors and producing high current outputs in enzymatic biofuel cells.

Effects of electrolyte and pH on the behavior of cross-linked films of ferrocene-modified poly(ethylenimine).

Ferrocene redox polymers based on the coupling of ferrocenecarboxaldehyde to both linear and branched poly(ethylenimine) (PEI) have been prepared to investigate the effects of pH, electrolyte, and cross-linking on electron charge transport and film swelling. The redox behavior of both ferrocene-modified linear PEI and ferrocene-modified branched PEI was investigated by cyclic voltammetry, while electron diffusion coefficients reported for PEI-based redox polymers were determined by electrochemical impedance spectroscopy. In phosphate solutions at pH>7, cross-linked films of both redox polymers exhibited multiple redox wave behavior and were unstable. In contrast, in non-phosphate solutions, cross-linked films exhibited stable electrochemical behavior and fast electron transfer in solutions with pH<11. Gel swelling experiments suggested that the multiple wave behavior and instability exhibited in either phosphate solutions or at high pH in non-phosphate solutions were related to a combination of film collapse and electrolyte binding within the hydrogel. The electron diffusion coefficients for these polymers are on the order of 10-8 (mol cm(-2) s(-1/2)), which are approximately 40 times greater than other ferrocene-modified polymers. Incorporation of the enzyme, glucose oxidase, into these films demonstrated that these redox polymers were able to electrically communicate with the enzyme's flavin adenine dinucleotide (FAD) redox centers. Glucose sensors based on these films exhibited enzyme saturation current densities that ranged from 240 to 480 microA/cm2 in response to glucose, which were dependent upon the supporting electrolyte and pH. The sensitivity of these sensors at 5 mM glucose ranged from 10 to 48 microA.cm(-2).mM(-1).

Conversion of N-aromatic amides to O-aromatic esters.

[reaction: see text] N-Aromatic secondary amides can be transformed into O-aromatic esters in high yield via N-nitrosamide intermediates. The amides can be generated in situ from the corresponding aromatic amines or nitro compounds, and phenols can easily be made from the esters. The reaction can be modified by addition of methyl methacrylate or toluene at 0 degrees C to give polymerization or deamination, respectively. The rearrangement mechanism may involve radical formation and recombination.