As reported in Biomaterials, secondary amine-functionalized chitosan oligosaccharides of different molecular weights have been synthesized by the Schoenfisch Group. The process involved grafting 2-methyl aziridine from the primary amines on chitosan oligosaccharides, followed by reaction with nitric oxide, NO, gas under basic conditions to yield N-diazeniumdiolate NO donors. The total NO storage, maximum NO flux, and half-life of the resulting NO-releasing chitosan oligosaccharides were controlled by the molar ratio of 2-methyl aziridine to primary amines and the functional group surrounding the N-diazeniumdiolates respectively.
The secondary amine-modified chitosan oligosaccharides greatly increased the NO payload over existing biodegradable macromolecular NO donors. In addition, the water-solubility of the chitosan oligosaccharides enabled their penetration across the extracellular polysaccharides matrix of Pseudomonas aeruginosa biofilms and association with embedded bacteria. The effectiveness of these chitosan oligosaccharides at biofilm eradication was shown to depend on both the molecular weight and ionic characteristics. Low molecular weight and cationic chitosan oligosaccharides exhibited rapid association with bacteria throughout the entire biofilm, leading to enhanced biofilm killing. At concentrations resulting in 5-log killing of bacteria in Pseudomonas aeruginosa (P. aeruginosa) biofilms, the NO-releasing and control chitosan oligosaccharides elicited no significant cytotoxicity to mouse fibroblast L929 cells in vitro.
In a collaborative effort initiated by Jillian Tyrrell, a graduate student in the Biological Division, and funded by the National Science Foundation, the groups of Gary Pielak and Kevin Weeks tackled the challenging problem of understanding how the authentic cellular environment affects RNA structure. To date, essentially all biophysical studies performed on RNA have employed highly simplified conditions in dilute solution in vitro. Biologists simply had no idea how RNA structures in cells might be different from that in simple solution.
The collaborators, as published in Biochemistry, showed that the cytoplasm of healthy living bacterial cells has large effects on the structure of the aptamer domain of a riboswitch RNA and stabilizes, or pre-organizes, a highly structured form of the RNA. Importantly, the in-cell structure cannot be mimicked using simple in vitro conditions.
In work published in PNAS, the Redinbo Group, in collaboration with the Tarran Group at UNC's Cystic Fibrosis Center, contributed the first crystal structure of SPLUNC1, the most abundantly secreted protein in human lungs. The structure lead the team to make specific electrostatic predictions regarding the surface of the SPLUNC1 protein, which were shown to be correct with respect to how SPLUNC1 controls the proper level of fluid in the lungs.
Cystic fibrosis, CF, is caused by mutations in the cystic fibrosis transmembrane conductance regulator, CFTR, gene, which codes for a chloride/bicarbonate channel whose absence leads to dehydration and acidification of CF airways. A contributing factor to CF lung disease is dysregulation of the epithelial Na+ channel, ENaC, which exacerbates mucus dehydration.
In the image above, healthy lung cells are on the right. The finger-like cilia point up into the proper fluid level because the blue SPLUNC1 proteins are "plugging" the ENaC channels (orange) which otherwise would remove Na (yellow) along with a lot of water. In CF lungs, left, the pH of the liquid is low, SPLUNC1 cannot bind to ENaC and plug that drain, so the Na and water flow into the cells, and the lungs become dehydrated. This work suggests that future CF therapy be directed toward raising the pH of CF airways.
Nanoparticle (NP) drug loading is one of the key defining characteristics of an NP formulation. However, the effect of NP drug loading on therapeutic efficacy and pharmacokinetics has not been thoroughly evaluated. Published in Biomaterials, researchers in the DeSimone Group, characterize the efficacy, toxicity and pharmacokinetic properties of NP docetaxel formulations that have differential drug loading but are otherwise identical.
Particle Replication in Non-wetting Templates, PRINT®, a soft-lithography fabrication technique, was used to formulate NPs with identical size, shape and surface chemistry, but with variable docetaxel loading. The lower weight loading (9%-NP) of docetaxel was found to have a superior pharmacokinetic profile and enhanced efficacy in a murine cancer model when compared to that of a higher docetaxel loading (20%-NP). The 9%-NP docetaxel increased plasma and tumor docetaxel exposure and reduced liver, spleen and lung exposure when compared to that of 20%-NP docetaxel.
Researchers in the Moran Group, as published in the Journal of Physical Chemistry A, are using femtosecond laser spectroscopies to examine a thymine family of systems chosen to expose the interplay between excited state deactivation and two distinct vibrational energy transfer (VET) pathways. One from the base to the deoxyribose ring, the second between neighboring units in a dinucleotide. They report that relaxation in the ground electronic state accelerates markedly as the molecular sizes increase from the nucleobase to the dinucleotide.
Overall, the researchers conclude that the transfer of vibrational quanta from thymine to the deoxyribose ring couples significantly to the internal conversion rate, whereas the neighboring unit in the dinucleotide serves as a secondary heat bath. In natural DNA, it follows that (local) thermal fluctuations in the geometries of subunits involving the base and deoxyribose ring are most important to this subpicosecond relaxation process.
Published in JACS, researchers in the Nicewicz Group report on a metal-free method for the direct anti-Markovnikov hydroamination of unsaturated amines.
Irradiation of the amine substrates with visible light in the presence of catalytic quantities of easily synthesized 9-mesityl-10-methylacridinium tetrafluoroborate and thiophenol as a hydrogen-atom donor furnished the nitrogen-containing heterocycles with complete regiocontrol. The article also discloses two examples of intermolecular anti-Markovnikov alkene hydroamination.
An organic/inorganic hybrid solar cell, if engineered properly, can combine the advantages of both organic and inorganic materials. Organic materials typically have good light absorption coefficient, tunable energy levels and band gaps, and can be processed at low cost. On the other hand, inorganic materials offer high carrier mobility and good air stability. Subsequently, the concept of organic/inorganic hybrid solar cells has recently gained much ground. Studies have spanned from a variety of inorganic semiconductors to organic materials, and efficiency of the hybrid solar cell have reached above 10%. However, the mechanism of the hybrid solar cell is still unclear.
As published in ACS Nano, the You Group has systematically investigated GaAs/polymers hybrid solar cells in a simple planar junction, aiming to fundamentally understand the function of semiconducting polymers in GaAs/polymers based heterojunction solar cells. A library of semiconducting polymers with different band gap and energy levels were evaluated in GaAs/polymers planar heterojunctions. The optimized thickness of active polymer layer was discovered to be ultrathin (~ 10 nm). Further, the open circuit voltage (Voc) of such GaAs/polymers planar heterojunctions was fixed around 0.6 V, regardless of the HOMO energy level of the polymer employed. Based on this and other evidence, it was concluded that n-type GaAs/polymer planar heterojunctions are not type II heterojunctions but Schottky barrier junctions with its corresponding anode, while the semiconducting polymer of appropriate energy levels can function as hole transport layer (HTL) and/or electron blocking layer (EBL). This discovery will help researchers to further design hybrid solar cell with increasingly high efficiency.
Nitric oxide, NO, a reactive free radical, has proven effective in eradicating bacterial biofilms with reduced risk of fostering antibacterial resistance. Published in ACS Applied Materials & Interfaces, researchers in the Schoenfisch Group have evaluated the efficacy of NO-releasing silica nanoparticles against Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus biofilms as a function of particle size and shape.
Three sizes of NO-releasing silica nanoparticles with identical total NO release were utilized to study antibiofilm eradication as a function of size. To observe the role of particle shape on biofilm killing, the group varied the aspect ratio of the NO-releasing silica particles from 1 to 8 while maintaining constant particle volume and NO-release totals. Nitric oxide-releasing particles with decreased size and increased aspect ratio were more effective against both P. aeruginosa and S. aureus biofilms, with the Gram-negative species exhibiting the greatest susceptibility to NO.
To further understand the influence of these nanoparticle properties on NO-mediated antibacterial activity, the group visualized intracellular NO concentrations and cell death with confocal microscopy. Smaller NO-releasing particles exhibited better NO delivery and enhanced bacteria killing compared to the larger particles. Likewise, the rod-like NO-releasing particles proved more effective than spherical particles in delivering NO and inducing greater antibacterial action throughout the biofilm.
The cell cytoplasm contains a complex array of macromolecules at concentrations exceeding 300 g/L. The natural, most relevant state of a biological macromolecule is thus a "crowded" one. Moving quantitative protein chemistry from dilute solution to the inside of living cells represents a major frontier that will affect not only our fundamental biological knowledge, but also efforts to produce and stabilize protein-based pharmaceuticals.
Published in PNAS, researchers in the Pielak Group show that the bacterial cytosol actually destabilizes a test protein, contradicting most theoretical predictions, but in agreement with a novel Escherichia coli model.
Researchers in the Allbritton Group have developed a novel photoresist composite incorporating poly(methyl methacrylate-co-methacrylic acid), the epoxy resin 1002F, and colloidal maghemite nanoparticles to produce a stable, transparent and biocompatible photoresist. As described in the Journal of Micromechanics and Microengineering, the composite photoresist was prepared in a scalable fashion in batches up to 1 kg with the particles remaining dispersed during room-temperature storage for at least six months.
The ability to manipulate microstructures formed from the composite was demonstrated by magnetically collecting clonal colonies of HeLa cells from a micropallet array. The transparency, biocompatibility, scalable synthesis and superparamagnetic properties of the novel composite address key limitations of existing magnetic composites.
Published in Molecular Pharmaceutics, scientists in the DeSimone Group report on the development of a nonviral lipid-complexed PRINT, Particle Replication in Nonwetting Templates, protein particle system, LPP particle, for RNA replicon delivery with a view toward RNA replicon-based vaccination. Cylindrical bovine serum albumin, BSA, particles with a diameter, d, of 1 μm, height, h, 1 μm, loaded with RNA replicon and stabilized with a fully reversible disulfide cross-linker were fabricated using PRINT technology.
Highly efficient delivery of the particles to Vero cells was achieved by complexing particles with a mixture of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) lipids. Our data suggest that (1) this lipid-complexed protein particle is a promising system for delivery of RNA replicon-based vaccines and (2) it is necessary to use a degradable cross-linker for successful delivery of RNA replicon via protein-based particles.
A water-soluble Iridium PCP-type pincer catalyst has been developed in a collaboration between the Brookhart and Meyer groups. As published in Chemical Science, the catalyst was developed to reduce CO2 to formate electrocatalytically in water with high efficiency and selectivity. Formate is the only reduced carbon product, formed in 93% Faradaic yield with no formation of CO. A small fraction of "background" H2, circa 7%, is directly produced at the electrode by solvent reduction.
Detailed kinetic information relevant to the catalysis was obtained. The high selectivity for formate production over H2 originates from the aqueous stability of Ir dihydride species, the active species for hydride reduction of CO2. Under neutral pH, the Ir pincer complex does not catalyze the reduction of protons to H2 making water a viable solvent for use with this catalyst system. Addition of small amounts, circa 1%, of acetonitrile reduces the over-potential and renders the catalysis sustainable. Mechanistic studies suggest that acetonitrile is a key ancillary ligand that ionizes formate effectively preventing catalyst deactivation.
Nonlinear laser spectroscopies in the deep UV spectral range are motivated by studies of biological systems and elementary processes in small molecules. In an invited perspective article published in Chemical Physics, the Moran Group discusses recent technical advances in this area with a particular emphasis on diffractive optic based approaches to four-wave mixing spectroscopies.
Applications to two classes of systems illustrate present experimental capabilities. First, experiments on DNA components at cryogenic temperatures are used to uncover features of excited state potential energy surfaces and vibrational cooling mechanisms. Second, sub-200 fs internal conversion processes and coherent wavepacket motions are investigated in cyclohexadiene and α-terpinene. Finally, the group members propose new experimental directions that combine methods for producing few-cycle UV laser pulses in noble gases with incoherent detection methods, for example photoionization, in experiments with time resolution near a single femtosecond. These measurements are motivated by knowledge of extremely fast non-adiabatic dynamics and the resolution of electronic wavepacket motions in molecules.