Self-assembled nanocages for hydrophilic guest molecules

Reverse polymeric micelles are obtained following the association of polymeric amphiphiles in apolar media. To this date, reports of pharmaceutical applications for such micelles have been scarce, mainly because these systems have been studied in solvents that are not suitable for medical use. Here, alkylated star-shaped poly(glycerol methacrylate) polymers have been proposed in the design of oil-soluble reverse polymeric micelles. Micellar behavior was studied in various apolar solvents, including ethyl oleate, a pharmaceutically acceptable vehicle. The polymers were shown to assemble into spherical nanostructures (<40 nm) as determined by cryogenic transmission electron microscopy and atomic force microscopy studies. Interestingly, the reverse micelles were able to encapsulate various peptides/proteins (vasopressin, myoglobin, and albumin) in substantial amounts and facilitate their solubilization in oil. The nature of both the polymer used in micelle formation and the guest molecules was found to influence the ability of the micelle to interact with hydrophilic compounds.     

Advancement of light-element neutron depth profiling at the University of Texas

The University of Texas (UT) at Austin has collaborated with the National Institute of Standards and Technology for comparisons of concentration versus depth profiles of samples containing ¹⁰B. Technology sharing from NIST has allowed UT to avoid many initial set backs such that significant advancements in the UT-NDP facility’s experimental and analytical methodology have been achieved. UT has analyzed two samples loaned to them from NIST. The collaborative effort between the two institutions has given the UT-NDP facility the proper tools to begin profiling more advanced samples in hopes of meeting the capabilities set by NIST in the NDP field. The UT-NDP facility was able to profile a borosilicate surface deposit onto silicon such that the concentrations of ¹⁰B at various depths of the deposit were determined and fit well to a Pearson distribution.     

Poly(amidoamine) dendrimers on lipid bilayers II: Effects of bilayer phase and dendrimer termination

The molecular structures and enthalpy release of poly(amidoamine) (PAMAM) dendrimers binding to 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers were explored through atomistic molecular dynamics. Three PAMAM dendrimer terminations were examined: protonated primary amine, neutral acetamide, and deprotonated carboxylic acid. Fluid and gel lipid phases were examined to extract the effects of lipid tail mobility on the binding of generation-3 dendrimers, which are directly relevant to the nanoparticle interactions involving lipid rafts, endocytosis, lipid removal, and/or membrane pores. Upon binding to gel phase lipids, dendrimers remained spherical, had a constant radius of gyration, and approximately one-quarter of the terminal groups were in close proximity to the lipids. In contrast, upon binding to fluid phase bilayers, dendrimers flattened out with a large increase in their asphericity and radii of gyration. Although over twice as many dendrimer-lipid contacts were formed on fluid versus gel phase lipids, the dendrimer-lipid interaction energy was only 20% stronger. The greatest enthalpy release upon binding was between the charged dendrimers and the lipid bilayer. However, the stronger binding to fluid versus gel phase lipids was driven by the hydrophobic interactions between the inner dendrimer and lipid tails.     

Regiospecific photoisomerization of fluorinated (E,E)-1,4-diphenyl-1,3-butadienes

Photoisomerization of five fluorinated E,E-1-(R-phenyl)-4-phenyl-1,3-butadienes in solution (R = 1: p-monofluoro, 2: m,m′-difluoro, 3: m,m′,p-trifluoro, 4: o,o′,m,m′-tetrafluoro, 5: o,o′,m,m′,p-pentafluoro) was investigated via direct irradiation. Our results indicated that cis-trans photoisomerization of the fluorinated 1,4-diphenyl-1,3-butadienes in the excited singlet state took place exclusively at the CC bonds closer to the fluorine substituents.     

Rhodium catalysed tandem conjugate addition-protonation: an enantioselective synthesis of 2-substituted succinic esters

The rhodium catalysed addition of potassium trifluoro(organo)borates to dimethyl itaconate generates an intermediate complex which on protonation provides enantioenriched succinic esters.     

Access to Nitriles from Aldehydes Mediated by an Oxoammonium Salt

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4‐acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl‐imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.     

Probing organization and communication at layered interfaces

We have investigated the local organization intrinsic to a variety of interfacial structures, by both electrochemical and spectroscopic means. Our focus has been on the design and construction of biomimetic interfaces, where a lipid bilayer or a hybrid bilayer membrane can be bound to an interface. The goal of this work is ultimately to create an interface on a transducer surface that can support an enzyme in its active form. To this point, we have examined the extent of organization that is achievable in monolayers that will be used to bind bilayer structures to a transducer surface. Our electrochemical data point to the important role of the substrate surface in determining adlayer organization. We have also investigated the fluidity and structural heterogeneity of lipid bilayers using time-resolved and steady state fluorescence spectroscopy. Our data point to the highly interactive nature of lipid bilayer constituents, where perturbations introduced to one region have significant consequences on other regions of the bilayer. Such information is directly relevant to the existence and properties of lipid raft structures in both model and biological bilayers.     

Magnetic nanoparticle assemblies on denatured DNA show unusual magnetic relaxivity and potential applications for MRI

Denatured (substantially single-stranded) herring sperm DNA acts as a template for the preparation of magnetic nanowires, forming stable aqueous suspensions, which exhibit unprecedentedly high relaxivity at low field, suggesting that the material may be a potentially useful reagent for MRI.     

O-H stretch overtone excitation of ethyl hydroperoxide conformers

We present laser photoacoustic spectra of ethyl hydroperoxide (EHP) for 3-6 quanta of O-H stretch. Spectra are consistent with ab initio spectral simulations that take into account the influence of torsional motion about the O-O bond on O-H stretch overtone excitation. Experimental and simulated spectra share two trends. First, spectral features due to torsional excitation, including hot bands, become more prominent with increasing O-H stretch excitation, as has been shown previously for similar molecules such as methyl hydroperoxide. Second, contributions from the two different EHP conformers become clearly distinguishable at higher O-H stretch excitation, mainly due to the role of torsional motion. Results are consistent with a higher energy separation (330 cm(-1)) between the lower energy anti and the higher energy gauche conformers than predicted by electronic structure calculations (137 cm(-1)). Calculated absorption intensities are consistently higher than experimental values by ~30% but within the experimental uncertainty. With each additional O-H stretch overtone, the dropoff in calculated integrated absorption intensities at room temperature becomes less extreme, with a 14-fold dropoff from 3ν(OH) to 4ν(OH) and an 8-fold decrease from 5ν(OH) to 6ν(OH).