Mechanistic simulation of batch acetone-butanol-ethanol (ABE) fermentation with in situ gas stripping using Aspen Plus™.

Process simulations of batch fermentations with in situ product separation traditionally decouple these interdependent steps by simulating a separate "steady state" continuous fermentation and separation units. In this study, an integrated batch fermentation and separation process was simulated for a model system of acetone-butanol-ethanol (ABE) fermentation with in situ gas stripping, such that the fermentation kinetics are linked in real-time to the gas stripping process. A time-dependent cell growth, substrate utilization, and product production is translated to an Aspen Plus batch reactor. This approach capitalizes on the phase equilibria calculations of Aspen Plus to predict the effect of stripping on the ABE fermentation kinetics. The product profiles of the integrated fermentation and separation are shown to be sensitive to gas flow rate, unlike separate steady state fermentation and separation simulations. This study demonstrates the importance of coupled fermentation and separation simulation approaches for the systematic analyses of unsteady state processes.

Inverted Micelle-in-Micelle Configuration in Cationic/Carbohydrate Surfactant Mixtures.

Nuclear magnetic resonance is applied to investigate the relative positions and interactions between cationic and non-ionic carbohydrate-based surfactants in mixed micelles with D2 O as the solvent. This is accomplished by using relaxation measurements [spin-lattice (T1 ) and spin-spin (T2 ) analysis] and nuclear Overhauser effect spectroscopy (NOESY). This study focuses on the interactions of n-octyl ß-d-glucopyranoside (C8G1) and ß-d-xylopyranoside (C8X1) with the cationic surfactant hexadecyltrimethylammonium bromide (C16 TAB). Whereas the interactions between carbohydrate and cationic surfactants are thermodynamically favorable, the NOESY results suggest that both of the sugar head groups are located preferentially at the interior core of the mixed micelles, so that they are not directly exposed to the bulk solution. The more hydrophilic sugar headgroups of C8G1 have more mobility than sugar heads of C8X1 owing to increased hydration. Herein, an inverted carbohydrate configuration in mixed micelles is proposed for the first time and supported by fluorescence spectroscopy experiments. This inverted carbohydrate headgroup configuration would limit the use of these mixed surfactants when access to the carbohydrate headgroup is important, but may present new opportunities where the carbohydrate-rich core of the micelles can be exploited.

Lipid Pore-Filled Silica Thin-Film Membranes for Biomimetic Recovery of Dilute Carbohydrates.

Selectively permeable biological membranes containing lipophilic barriers inspire the design of biomimetic carrier-mediated membranes for aqueous solute separation. The recovery of glucose, which can reversibly bind to boronic acid (BA) carriers, is examined in lipid pore-filled silica thin-film composite membranes with accessible mesopores. The successful incorporation of lipids (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) and BA carriers (4-((N-Boc-amino)methyl)phenylboronic acid, BAMP-BA) in the pores of mesoporous silica (∼10 nm pore diameter) through evaporation deposition is verified by confocal microscopy and differential scanning calorimetry. In the absence of BA carriers, lipids confined inside the pores of silica thin films (∼200 nm thick) provide a factor of 14 increase in diffusive transport resistance to glucose, relative to traditional supported lipid bilayers formed by vesicle fusion on the porous surface. The addition of lipid-immobilized BAMP-BA (59 mol % in DPPC) facilitates the transport of glucose through the membrane; glucose flux increases from 45 × 10-8 to 225 × 10-8 mol/m2/s in the presence of BAMP-BA. Furthermore, the transport can be improved by environmental factors including pH gradient (to control the binding and release of glucose) and temperature (to adjust lipid bilayer fluidity). The successful development of biomimetic nanocomposite membranes demonstrated here is an important step toward the efficient dilute aqueous solute upgrading or separations, such as the processing of carbohydrates from lignocellulose hydrolysates, using engineered carrier/catalyst/support systems.

Effect of Pore Confinement of Ionic Liquids on Solute Diffusion within Mesoporous Silica Microparticles.

The transport properties of the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) confined within silica microparticles with well-ordered, accessible mesopores (5.4 or 9 nm diameter) were investigated. [BMIM][PF6] confinement was confirmed by using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The transport properties of the confined IL were studied using the neutral and cationic fluorescent probes 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and rhodamine 6G, respectively, through fluorescence recovery after photobleaching (FRAP) in confocal microscopy. The diffusivity of DCM in 9 nm pores is 0.026 ± 0.0091 µm2/s, which is 2 orders of magnitude less than in the bulk ionic liquid. The pore size did not affect the diffusivity of DCM in unmodified silica nanopores. The diffusivity of the cationic probe is reduced by 63% relative to that of the neutral probe. Diffusivity is increased with water content, where equilibrium hydration of the system leads to a 37% increase in DCM diffusivity. The most dramatic impact on diffusivity was caused by tethering an IL-like methylimidazolium chloride group to the pores, which increased the pore hydrophobicity and resulted in 3-fold higher diffusivity of DCM compared to bare silica pores. Subsequent exchange of the chloride anion from the tethering group with PF6- decreased the diffusivity to half that of bare silica. The diffusion of probe molecules is affected most strongly by the pore wall effects on probe interactions rather than by the pore size itself, which suggests that understanding pore wall diffusion is critical to the design of nanoconfined ILs for separations, catalysis, and energy storage.

Metabolic control of Clostridium thermocellum via inhibition of hydrogenase activity and the glucose transport rate.

Clostridium thermocellum has the ability to catabolize cellulosic biomass into ethanol, but acetic acid, lactic acid, carbon dioxide, and hydrogen gas (H(2)) are also produced. The effect of hydrogenase inhibitors (H(2), carbon monoxide (CO), and methyl viologen) on product selectivity was investigated. The anticipated effect of these hydrogenase inhibitors was to decrease acetate production. However, shifts to ethanol and lactate production are also observed as a function of cultivation conditions. When the sparge gas of cellobiose-limited chemostat cultures was switched from N(2) to H(2), acetate declined, and ethanol production increased 350%. In resting cell suspensions, lactate increased when H(2) or CO was the inhibitor or when the cells were held at elevated hyperbaric pressure (6.8 atm). In contrast, methyl-viologen-treated resting cells produced twice as much ethanol as the other treatments. The relationship of chemostat physiology to methyl viologen inhibition was revealed by glucose transport experiments, in which methyl viologen decreased the rate of glucose transport by 90%. C. thermocellum produces NAD(+) from NADH by H(2), lactate, and ethanol production. When the hydrogenases were inhibited, the latter two products increased. However, excess substrate availability causes fructose 1,6-diphosphate, the glycolytic intermediate that triggers lactate production, to increase. Compensatory ethanol production was observed when the chemostat fluid dilution rate or methyl viologen decreased substrate transport. This research highlights the complex effects of high concentrations of dissolved gases in fermentation, which are increasingly envisioned in microbial applications of H(2) production for the conversion of synthetic gases to chemicals.

Complexation of Lignin Dimers with ß-Cyclodextrin and Binding Stability Analysis by ESI-MS, Isothermal Titration Calorimetry, and Molecular Dynamics Simulations.

Lignin derived from lignocellulosic biomass is the largest source of renewable bioaromatics present on earth and requires environmentally sustainable separation strategies to selectively obtain high-value degradation products. Applications of supramolecular interactions have the potential to isolate lignin compounds from biomass degradation fractions by the formation of variable inclusion complexes with cyclodextrins (CDs). CDs are commonly used as selective adsorbents for many applications and can capture guest molecules in their internal hydrophobic cavity. The strength of supramolecular interactions between CDs and lignin model compounds that represent potential lignocellulosic biomass degradation products can be characterized by assessing the thermodynamics of binding stability. Consequently, the inclusion interactions of ß-CD and lignin model compounds G-(ß-O-4')-G, G-(ß-O-4')-truncG (guaiacylglycerol-ß-guaiacyl ether), and G-(ß-ß')-G (pinoresinol) were investigated empirically by electrospray ionization mass spectrometry and isothermal titration calorimetry, complemented by molecular dynamics (MD) simulations. Empirical results indicate that there are substantial differences in binding stability dependent on the linkage type. The lignin model ß-ß' dimer showed more potential bound states including 1:1, 2:1, and 1:2 (guest:host) complexation and, based on binding stability determinations, was consistently the most energetically favorable guest. Empirical results are supported by MD simulations that reveal that the capture of G-(ß-ß')-G by ß-CD is promising with a 66% probability of being bound for G-(ß-O-4')-truncG compared to 88% for G-(ß-ß')-G (unbiased distance trajectory and explicit counting of bound states). These outcomes indicate CDs as a promising material to assist in separations of lignin oligomers from heterogeneous mixtures for the development of environmentally sustainable isolations of lignin compounds from biomass fractions.

Strategy for Conjugating Oligopeptides to Mesoporous Silica Nanoparticles Using Diazirine-Based Heterobifunctional Linkers.

Successful strategies for the attachment of oligopeptides to mesoporous silica with pores large enough to load biomolecules should utilize the high surface area of pores to provide an accessible, protective environment. A two-step oligopeptide functionalization strategy is examined here using diazirine-based heterobifunctional linkers. Mesoporous silica nanoparticles (MSNPs) with average pore diameter of ~8 nm and surface area of ~730 m2/g were synthesized and amine-functionalized. Tetrapeptides Gly-Gly-Gly-Gly (GGGG) and Arg-Ser-Ser-Val (RSSV), and a peptide comprised of four copies of RSSV (4RSSV), were covalently attached via their N-terminus to the amine groups on the particle surface by a heterobifunctional linker, sulfo-succinimidyl 6-(4,4'-azipentanamido)hexanoate (sulfo-NHS-LC-diazirine, or SNLD). SNLD consists of an amine-reactive NHS ester group and UV-activable diazirine group, providing precise control over the sequence of attachment steps. Attachment efficiency of RSSV was measured using fluorescein isothiocyanate (FITC)-tagged RSSV (RSSV-FITC). TGA analysis shows similar efficiency (0.29, 0.31 and 0.26 mol peptide/mol amine, respectively) for 4G, RSSV and 4RSSV, suggesting a generalizable method of peptide conjugation. The technique developed here for the conjugation of peptides to MSNPs provides for their attachment in pores and can be translated to selective peptide-based separation and concentration of therapeutics from aqueous process and waste streams.

Mechanism of Mesoporous Silica Nanoparticle Interaction with Hairy Root Cultures during Nanoharvesting of Biomolecules.

Cellular uptake and expulsion mechanisms of engineered mesoporous silica nanoparticles (MSNPs) are important in their design for novel biomolecule isolation and delivery applications such as nanoharvesting, defined as using nanocarriers to transport and isolate valuable therapeutics (secondary metabolites) out of living plant organ cultures (e.g., hairy roots). Here, temperature-dependent MSNP uptake and recovery processes in hairy roots are examined as a function of surface chemistry. MSNP uptake into hairy roots and time-dependent expulsion are quantified using Ti content (present for biomolecule binding) and fluorescence spectroscopy of fluorescently tagged MSNPs, respectively. The results suggest that functionalization and surface charge (regulated by amine group attachment) play the biggest role in the effectiveness of uptake and recovery. Comparison of MSNP interactions with hairy roots at 4 and 23 °C shows that weakly charged MSNPs functionalized only with Ti are taken up and expelled by thermally activated mechanisms, while amine-modified positively charged particles are taken up and expelled mainly by direct penetration of cell walls. Amine-functionalized MSNPs move spontaneously in and out of plant cells by dynamic exchange with a residence time of 20 ± 5 min, suggesting promise as a biomolecule nanoharvesting platform for plant organ cultures.

Interaction of lignin dimers with model cell membranes: A quartz crystal microbalance and molecular dynamics simulation study.

A study of the interaction between cell membranes and small molecules derived from lignin, a protective phenolic biopolymer found in vascular plants, is crucial for identifying their potential as pharmacological and toxicological agents. In this work, the interactions of model cell membranes [supported 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers] are compared for three ßO4 dimers of coniferyl alcohol (G lignin monomer): guaiacylglycerol guaiacol ester with a hydroxypropenyl (HOC3H4-) tail (G-ßO4'-G), a truncated GG dimer without HOC3H4- (G-ßO4'-truncG), and a benzylated GG dimer (benzG-ßO4'-G). The uptake of the lignin dimers (per mass of lipid) and the energy dissipation (a measure of bilayer disorder) are higher for benzG-ßO4'-G and G-ßO4'-truncG than those for G-ßO4'-G in the gel-phase DPPC bilayer, as measured using quartz crystal microbalance with dissipation (QCM-D). A similar uptake of G-ßO4'-truncG is observed for a fluid-phase bilayer of 1,2-dioleoyl-sn-glycero-3-phosphocholine, suggesting that the effect of the bilayer phase on dimer uptake is minimal. The effects of increasing lignin dimer concentration are examined through an analysis of density profiles, potential of mean force curves, lipid order parameters, and bilayer area compressibilities (disorder) in the lipid bilayers obtained from molecular dynamics simulations. Dimer distributions and potentials of mean force indicate that the penetration into bilayers is higher for benzG-ßO4'-G and G-ßO4'-truncG than that for G-ßO4'-G, consistent with the QCM-D results. Increased lipid tail disorder due to dimer penetration leads to a thinning and softening of the bilayers. Minor differences in the structure of lignin derivatives (such as truncating the hydroxypropenyl tail) have significant impacts on their ability to penetrate lipid bilayers.

Relating Mobility of dsRNA in Nanoporous Silica Particles to Loading and Release Behavior.

Nanoparticle delivery of polynucleic acids traditionally relies on the modulation of surface interactions to achieve loading and release. This work investigates the additional role of confinement in mobility of dsRNA (84 and 282 base pair (bp) sequences of Spodoptera frugiperda) as a function of silica nanopore size (nonporous, 3.9, 8.0, and 11.3 nm). Amine-functionalized nanoporous silica microspheres (NPSMs, ∼10 µm) are used to directly visualize the loading and exchange of fluorescently labeled dsRNA. Porous particles are fully accessible to both lengths of dsRNA by passive diffusion, except for 282 bp dsRNA in 3.9 nm pores. The stiffness of dsRNA suggests that encapsulation occurs by threading into nanopores, which is inhibited when the ratio of dsRNA length to pore size is large. The mobility of dsRNA at the surface and in the core of NPSMs, as measured by fluorescence recovery after photobleaching, is similar. The mobility increases with pore size (from 0.0002 to 0.001 µm2/s for 84 bp dsRNA in 3.9-11.3 nm pores) and decreases with the length of dsRNA. However, when the dsRNA is unable to load into the pores (on nonporous particles and for 282 bp dsRNA in 3.9 nm pores), surface mobility is not detectable. The pore structure appears to serve as a "source" to provide a mobile network of dsRNA at the particle surface. The importance of mobility is demonstrated by exchange experiments, where NPSMs saturated with mobile dsRNA can exchange dsRNA with the surrounding solution, while immobile dsRNA is not exchanged. These results indicate that nanoparticle synthesis techniques that provide pores large enough to take up polynucleic acids internally (and not simply on the external surface of the particle) can be harnessed to design polynucleic acid/nanoporous silica combinations for controlled mobility as a path forward toward effective nanocarriers.

Fluorophilicity of Alkyl and Polyfluoroalkyl 1 Nicotinic Acid Ester Prodrugs.

The fluorophilicity of a series of hydrocarbon and fluorocarbon-functionalized nicotinic acid esters (nicotinates) is measured from their partitioning behavior (log K(P)) in the biphasic solvent system of perfluoro(methylcyclohexane) (PFMC) and toluene. The chain length of the hydrocarbon or fluorocarbon alkyl group of the ester ranges from one to twelve carbon atoms. Knowledge of the fluorophilicity of these solutes is relevant to the design of these prodrugs for fluorocarbon-based drug delivery. The experimental log K(p) values range from -1.72 to -3.40 for the hydrocarbon nicotinates and -1.64 to 0.13 for the fluorinated nicotinates, where only the prodrug with the longest fluorinated chain (2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl nicotinic acid ester) partitions preferentially into the fluorinated phase (log K(p) = 0.13). Predictions of the partition coefficients using solubility parameters calculated from group contribution techniques or molecular dynamics simulation are in reasonable agreement for the perhydrocarbon nicotinates and short chained perfluorinated nicotinates (≈ 0.3%-39% deviation). Significant deviations from experimental partition coefficients (greater than 100%) are observed for the longest chain perfluoroalkyl nicotinates.

Interaction of lignin-derived dimer and eugenol-functionalized silica nanoparticles with supported lipid bilayers.

The potential to impart surfaces with specific lignin-like properties (i.e. resistance to microbes) remains relatively unexplored due to the lack of well-defined lignin-derived small molecules and corresponding surface functionalization strategies. Here, allyl-modified guaiacyl ß-O-4 eugenol (G-eug) lignin-derived dimer is synthesized and attached to mesoporous silica nanoparticles (MSNPs) via click chemistry. The ability of G-eug lignin-dimer functionalized particles to interact with and disrupt synthetic lipid bilayers is compared to that of eugenol, a known natural antimicrobial. Spherical MSNPs (∼150 nm diameter with 4.5 nm pores) were synthesized using surfactant templating. Post-synthesis thiol (SH) attachment was performed using (3-mercaptopropyl) trimethoxysilane and quantified by Ellman's test. The resultant SH-MSNPs were conjugated with the G-eug dimers or eugenol by a thiol-ene reaction under ultraviolet light in the presence of a photo initiator. From thermogravimetric analysis (TGA), attachment densities of approximately 0.22 mmol eugenol/g particle and 0.13 mmol G-eug dimer/g particle were achieved. The interaction of the functionalized MSNPs with a phospholipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (representing model cell membranes) supported on gold surface was measured using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D). Eugenol-grafted MSNPs in PBS (up to 1 mg/mL) associated with the bilayer and increased the mass adsorbed on the QCM-D sensor. In contrast, MSNPs functionalized with G-eug dimer show qualitatively different behavior, with more uptake and evidence of bilayer disruption at and above a particle concentration of 0.5 mg/mL. These results suggest that bio-inspired materials with conjugated lignin-derived small molecules can serve as a platform for novel antimicrobial coatings and therapeutic carriers.

Nanoharvesting of bioactive materials from living plant cultures using engineered silica nanoparticles.

Plant secondary metabolites are valuable therapeutics not readily synthesized by traditional chemistry techniques. Although their enrichment in plant cell cultures is possible following advances in biotechnology, conventional methods of recovery are destructive to the tissues. Nanoharvesting, in which nanoparticles are designed to bind and carry biomolecules out of living cells, offers continuous production of metabolites from plant cultures. Here, nanoharvesting of polyphenolic flavonoids, model plant-derived therapeutics, enriched in Solidago nemoralis hairy root cultures, is performed using engineered mesoporous silica nanoparticles (MSNPs, 165 nm diameter and 950 m2/g surface area) functionalized with both titanium dioxide (TiO2, 425 mg/g particles) for coordination binding sites, and amines (NH2, 145 mg/g particles) to promote cellular internalization. Intracellular uptake and localization of the nanoparticles (in Murashige and Skoog media) in hairy roots were confirmed by tagging the particles with rhodamine B isothiocyanate, incubating the particles with hairy roots, and quenching bulk fluorescence using trypan blue. Nanoharvesting of biologically active flavonoids was demonstrated by observing increased antiradical activity (using 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay) by nanoparticles after exposure to hairy roots (indicating general antioxidant activity), and by the displacement of the radio-ligand [3H]-methyllycaconitine from rat hippocampal nicotinic receptors by solutes recovered from nanoharvested particles (indicating pharmacological activity specific to S. nemoralis flavonoids). Post-nanoharvesting growth suggests that the roots are viable after nanoharvesting, and capable of continued flavonoid synthesis. These observations demonstrate the potential for using engineered nanostructured particles to facilitate continuous isolation of a broad range of biomolecules from living and functioning plant cultures.

Lignin-graft-PLGA drug-delivery system improves efficacy of MEK1/2 inhibitors in triple-negative breast cancer cell line.

Aim: Few targeted therapies are available for triple-negative breast cancer (TNBC) patients. Here, we propose a novel alkaline-lignin-conjugated-poly(lactic-co-glycolic acid) (L-PLGA) nanoparticle drug delivery system to improve the efficacy of targeted therapies. Materials & methods: L-PLGA nanoparticles (NPs) loaded with the MEK1/2 inhibitor GDC-0623 were characterized, tested in vitro on MDA-MB-231 TNBC cell line and compared with loaded PLGA NPs. Results: Loaded L-PLGA NPs were less than half the size of PLGA NPs, had slower drug release and improved the efficacy of GDC-0623 when tested in vitro. We demonstrated that GDC-0623 reversed epithelial-to-mesenchymal transition in TNBC. Conclusion: Our findings indicate that L-PLGA NPs are superior to PLGA NPs in delivering GDC-0623 to cancer cells for improved efficacy in vitro.

Effect of Confinement in Nanopores on RNA Interactions with Functionalized Mesoporous Silica Nanoparticles.

Amine-functionalized mesoporous silica nanoparticles (MSNPAs) are ideal carriers for oligonucleotides for gene delivery and RNA interference. This investigation examines the thermodynamic driving force of interactions of double-stranded (ds) RNA with MSNPAs as a function of RNA length (84 and 282 base pair) and particle pore diameter (nonporous, 2.7, 4.3, and 8.1 nm) using isothermal titration calorimetry, extending knowledge of solution-based nucleic acid-polycation interactions to RNA confined in nanopores. Adsorption of RNA follows a two-step process: endothermic interactions driven by entropic contribution from counterion (and water) release and an exothermic regime dominated by short-range interactions within the pores. Evidence of hindered pore loading of the longer RNA and pore size-dependent confinement of RNA in the MSPAs is provided from the relative contributions of the endothermic and exothermic regimes. Reduction of endothermic and exothermic enthalpies in both regimes in the presence of salt for both lengths of RNA indicates the significant contribution of short-range electrostatic interactions, whereas ΔH and ΔG values are consistent with conformation changes and desolvation of nucleic acids upon binding with polycations. Knowledge of the interactions between RNA and functionalized porous nanoparticles will aid in porous nanocarrier design suitable for functional RNA delivery.

Analysis of composition and structure of Clostridium thermocellum membranes from wild-type and ethanol-adapted strains.

Clostridium thermocellum is a candidate organism for consolidated bioprocessing of lignocellulosic biomass into ethanol. However, commercial use is limited due to growth inhibition at modest ethanol concentrations. Recently, an ethanol-adapted strain of C. thermocellum was produced. Since ethanol adaptation in microorganisms has been linked to modification of membrane lipids, we tested the hypothesis that ethanol adaptation in C. thermocellum involves lipid modification by comparing the fatty acid composition and membrane anisotropy of wild-type and ethanol-adapted strains. Derivatization to fatty acid methyl esters provided quantitative lipid analysis. Compared to wild-type, the ethanol-adapted strain had a larger percentage of fatty acids with chain lengths >16:0 and showed a significant increase in the percentage of 16:0 plasmalogens. Structural identification of fatty acids was confirmed through mass spectral fragmentation patterns of picolinyl esters. Ethanol adaptation did not involve modification at sites of methyl branching or the unsaturation index. Comparison of steady-state fluorescence anisotropy experiments, in the absence and presence of ethanol, provided evidence for the effects of ethanol on membrane fluidity. In the presence of ethanol, both strains displayed increased fluidity by approximately 12%. These data support the model that ethanol adaptation was the result of fatty acid changes that increased membrane rigidity that counter-acted the fluidizing effect of ethanol.

Preparation and characterization of multimodal hybrid organic and inorganic nanocrystals of camptothecin and gold.

We demonstrate a novel inorganic-organic crystalline nanoconstruct, where gold atoms were imbedded in the crystal lattices as defects of camptothecin nanocrystals, suggesting its potential use as simultaneous agents for cancer therapy and bioimaging. The incorporation of gold, a potential computed tomography (CT) contrast agent, in the nanocrystals of camptothecin was detected by transmission electron microscope (TEM) and further quantified by energy dispersive X-ray spectrometry (EDS) and inductively coupled plasma-optical emission spectrometers (ICP-OES). Due to gold's high attenuation coefficient, only a relatively small amount needs to be present in order to create a good noise-to-contrast ratio in CT imaging. The imbedded gold atoms and clusters are expected to share the same biological fate as the camptothecin nanocrystals, reaching and accumulating in tumor site due to the enhanced permeation and retention (EPR) effect.

Experimental and Molecular Dynamics Simulation Study of the Effects of Lignin Dimers on the Gel-to-Fluid Phase Transition in DPPC Bilayers.

High resolution differential scanning calorimetry (DSC) and molecular dynamics (MD) simulations were used to investigate the effect of three lignin dimers on the gel to fluid phase transition in DPPC lipid bilayers. The goal of this research is to begin to understand the partitioning of model lignin dimers into lipid bilayers and its effects on the gel to fluid transition temperature (Tm). The long-term objective is to establish structure-function relationships for well-defined lignin derivatives at biologically relevant surfaces. This work uses a newly synthesized guiacylglycerol guaiacol ester with a hydroxypropenyl (HOC3H4-) group resembling natural lignin (GG dimer), compared with a truncated GG dimer without the HOC3H4- and benzyl-modified GG dimers. The DSC results show that the dimer most like natural lignin (with a hydroxypropenyl tail) has log K = 2.72 ± 0.05, and MD simulations show that it associates with the headgroups of the lipid but does not penetrate strongly into the interior of the bilayer. Therefore, this dimer has little effect on the Tm value. In contrast, the truncated dimer, which has been used as a representative GG dimer in prior studies, partitions into the bilayer, as seen in MD simulations, and shifts Tm because of its increased lipophilicity (DSC log K = 3.45 ± 0.20). Similarly, modification of the natural GG dimer by benzylation of the phenol makes it lipophilic (DSC log K = 3.38 ± 0.28), causing it to partition into the bilayer, as seen in MD simulations and shift Tm. In MD, we capture the transition from gel to fluid phase by defining and analyzing a normalized deuterium order parameter averaged over all carbon atoms located in the middle of the lipid tails. In this way, the phase transition can be clearly observed and, importantly, MD results show the same trend of transition temperature shifts as the DSC results. Furthermore, we compare partition coefficients estimated from free energy profiles calculated in MD to those obtained from experiment and they are in qualitative agreement. The success at predicting the structural effects of lignin dimers on lipid bilayers suggests that MD simulations can be used in the future to screen the interactions of lignin oligomers and their derivatives with lipid bilayers.

Synthesis, physicochemical properties and in vitro cytotoxicity of nicotinic acid ester prodrugs intended for pulmonary delivery using perfluorooctyl bromide as vehicle.

This study explores perfluorooctyl bromide (PFOB) as a potential vehicle for the pulmonary delivery of a series of prodrugs of nicotinic acid using cell culture studies. The prodrugs investigated have PFOB-water (logK(p)=0.78 to >2.2), perfluoromethylcyclohexane-toluene (logK(p)=-2.62 to 0.13) and octanol-water (logK(p)=0.90-10.2) partition coefficients spanning several orders of magnitude. In confluent NCI-H358 human lung cancer cells, the toxicity of prodrugs administered in culture medium or PFOB depends on the medium of administration, with EC20's above 8 mM and 2.5 mM for culture medium and PFOB, respectively. Short-chain nicotinates administered both in PFOB and medium increase cellular NAD/NADP levels at 1mM nicotinate concentrations. Long-chain nicotinates, which could not be administered in medium due to their poor aqueous solubility, increased NAD/NADP levels if administered in PFOB at concentrations > or =10 mM. These findings suggest that even highly lipophilic prodrugs can partition out of the PFOB phase into cells, where nicotinic acid is released and converted to NAD. Thus, PFOB may be a novel and biocompatible vehicle for the delivery of lipophilic prodrugs of nicotinic acid and other drugs directly to the lung of laboratory animals and humans.

Tuning the position of head groups by surfactant design in mixed micelles of cationic and carbohydrate surfactants.

HYPOTHESIS: Emerging applications of carbohydrate/cationic surfactant mixtures require not only synergistic mixing, but also accessible sugar headgroups at the exterior of micelles. A previous study showed that the glucoside headgroups of octyl-ß-d-glucopyranoside aggregate at the interior of mixed micelles with equimolar cetyltrimethylammonium bromide rather than mixing with trimethylammonium groups at the corona. The current study tests the hypothesis that structural characteristics of the surfactants (the relative lengths of the alkyl tails and the type of linker) can be tuned to shift the carbohydrate groups to micelle surfaces. EXPERIMENTS: The structural arrangement of 30 mM equimolar mixed micelle solutions in D2O is investigated using NMR. The dynamics in different regions are probed using 1H spin-lattice (T1) and spin-spin (T2) relaxation measurements, and relative positioning by nuclear Overhauser effect spectroscopy (NOESY). Additional micellar properties are determined using solvatochromic fluorescent probes. FINDINGS: Matching surfactant alkyl tail lengths is found ineffective at "pushing out" the carbohydrate headgroups due to a large mismatch in interactions between the headgroups and D2O. However, inserting a novel polar triazole group between the carbohydrate head group and the hydrophobic tail (e.g. in n-octyl-ß-d-xylopyranoside) using click chemistry is able to "pull out" the carbohydrate, thus giving accessible sugar moieties at the surface of mixed micelles.