Showing papers by "Nicholas J. Turro published in 2010"

Photoinitiated Polymerization: Advances, Challenges, and Opportunities

Abstract: The use of photoinitiated polymerization is continuously growing in industry as reflected by the large number of applications in not only conventional areas such as coatings, inks, and adhesives but also high-tech domains, optoelectronics, laser imaging, stereolithography, and nanotechnology. In this Perspective, the latest developments in photoinitiating systems for free radical and cationic polymerizations are presented. The potential use of photochemical methods for step-growth polymerization is also highlighted. The goal is, furthermore, to show approaches to overcome problems associated with the efficiency, wavelength flexibility, and environmental and safety issues in all photoinitiating systems for different modes of activation. Much progress has been made in the past 10 years in the preparation of complex and nano-structured macromolecules by using photoinitiated polymerizations. Thus, the new and emerging applications of photoinitiated polymerizations in the field of biomaterials, surface modific...

An Integrated System for DNA Sequencing by Synthesis Using Novel Nucleotide Analogues

Abstract: The Human Genome Project has concluded, but its successful completion has increased, rather than decreased, the need for high-throughput DNA sequencing technologies. The possibility of clinically screening a full genome for an individual's mutations offers tremendous benefits, both for pursuing personalized medicine and for uncovering the genomic contributions to diseases. The Sanger sequencing method, although enormously productive for more than 30 years, requires an electrophoretic separation step that, unfortunately, remains a key technical obstacle for achieving economically acceptable full-genome results. Alternative sequencing approaches thus focus on innovations that can reduce costs. The DNA sequencing by synthesis (SBS) approach has shown great promise as a new sequencing platform, with particular progress reported recently. The general fluorescent SBS approach involves (i) incorporation of nucleotide analogs bearing fluorescent reporters, (ii) identification of the incorporated nucleotide by its fluorescent emissions, and (iii) cleavage of the fluorophore, along with the reinitiation of the polymerase reaction for continuing sequence determination. In this Account, we review the construction of a DNA-immobilized chip and the development of novel nucleotide reporters for the SBS sequencing platform. Click chemistry, with its high selectivity and coupling efficiency, was explored for surface immobilization of DNA. The first generation (G-1) modified nucleotides for SBS feature a small chemical moiety capping the 3'-OH and a fluorophore tethered to the base through a chemically cleavable linker; the design ensures that the nucleotide reporters are good substrates for the polymerase. The 3'-capping moiety and the fluorophore on the DNA extension products, generated by the incorporation of the G-1 modified nucleotides, are cleaved simultaneously to reinitiate the polymerase reaction. The sequence of a DNA template immobilized on a surface via click chemistry is unambiguously identified with this chip-SBS system. The second generation (G-2) SBS system was developed based on the concept that the closer the structures of the added nucleotide and the primer are to their natural counterparts, the more faithfully the polymerase would incorporate the nucleotide. In this approach, the polymerase reaction is performed with the combination of 3'-capped nucleotide reversible terminators (NRTs) and cleavable fluorescent dideoxynucleotides (ddNTPs). By sacrifice of a small amount of the primers permanently terminated by ddNTPs, the majority of the primers extended by the reversible terminators are reverted to the natural ones after each sequencing cycle. We have also developed the 3'-capped nucleotide reversible terminators to solve the problem of deciphering the homopolymeric regions of the template in conventional pyrosequencing. The 3'-capping moiety on the DNA extension product temporarily terminates the polymerase reaction, which allows only one nucleotide to be incorporated during each sequencing cycle. Thus, the number of nucleotides in the homopolymeric regions are unambiguously determined using the 3'-capped NRTs. It has been established that millions of DNA templates can be immobilized on a chip surface through a variety of approaches. Therefore, the integration of these high-density DNA chips with the molecular-level SBS approaches described in this Account is expected to generate a high-throughput and accurate DNA sequencing system with wide applications in biological research and health care.

The Spin Chemistry and Magnetic Resonance of H2@C60. From the Pauli Principle to Trapping a Long Lived Nuclear Excited Spin State inside a Buckyball

Abstract: One of the early triumphs of quantum mechanics was Heisenberg’s prediction, based on the Pauli principle and wave function symmetry arguments, that the simplest molecule, H2, should exist as two distinct species—allotropes of elemental hydrogen. One allotrope, termed para-H2 (pH2), was predicted to be a lower energy species that could be visualized as rotating like a sphere and possessing antiparallel (↑↓) nuclear spins; the other allotrope, termed ortho-H2 (oH2), was predicted to be a higher energy state that could be visualized as rotating like a cartwheel and possessing parallel (↑↑) nuclear spins. This remarkable prediction was confirmed by the early 1930s, and pH2 and oH2 were not only separated and characterized but were also found to be stable almost indefinitely in the absence of paramagnetic “spin catalysts”, such as molecular oxygen, or traces of paramagnetic impurities, such as metal ions. The two allotropes of elemental hydrogen, pH2 and oH2, may be quantitatively incarcerated in C60 to form e...

Inelastic neutron scattering of a quantum translator-rotator encapsulated in a closed fullerene cage: Isotope effects and translation-rotation coupling in H 2 @C 60 and HD@C 60

Abstract: We report an inelastic neutron-scattering (INS) investigation of coupled quantum translation and rotation of hydrogen molecules trapped inside the closed isotropic cages of ${\text{C}}_{60}$. The low-lying states that characterize the translation-rotation manifold of the hydrogen molecules are accurately determined in our study of the INS peak energies. A comparison between the spectra of ${\text{H}}_{2}$ and HD isotopomers provides quantitative insight into the coupling between rotational and translational angular momentum with HD exhibiting the strongest effects due to mixing of the rotational eigenstates.

Hydrogen molecules inside fullerene C70: Quantum dynamics, energetics, maximum occupancy, and comparison with C60

Abstract: Recent synthesis of the endohedral complexes of C70 and its open-cage derivative with one and two H2 molecules has opened the path for experimental and theoretical investigations of the unique dynamic, spectroscopic, and other properties of systems with multiple hydrogen molecules confined inside a nanoscale cavity. Here we report a rigorous theoretical study of the dynamics of the coupled translational and rotational motions of H2 molecules in C70 and C60, which are highly quantum mechanical. Diffusion Monte Carlo (DMC) calculations were performed for up to three para-H2 (p-H2) molecules encapsulated in C70 and for one and two p-H2 molecules inside C60. These calculations provide a quantitative description of the ground-state properties, energetics, and the translation−rotation (T−R) zero-point energies (ZPEs) of the nanoconfined p-H2 molecules and of the spatial distribution of two p-H2 molecules in the cavity of C70. The energy of the global minimum on the intermolecular potential energy surface (PES) ...

Distance-Dependent Paramagnet-Enhanced Nuclear Spin Relaxation of H2@C60 Derivatives Covalently Linked to a Nitroxide Radical

Abstract: A series of H2@C60 derivatives covalently linked to a nitroxide radical has been synthesized. We report distance-dependent nuclear spin relaxivity of H2 in these derivatives. The results clearly indicate that the relaxivity of H2 is distance-dependent and in good agreement with the Solomon−Bloembergen equation, which predicts a 1/r6 dependence.

Guest rotations within a capsuleplex probed by NMR and EPR techniques.

Abstract: With the help of 1H NMR and EPR techniques, we have probed the dynamics of guest molecules included within a water-soluble deep cavity cavitand known by the trivial name octa acid. All guest molecules investigated here form 2:1 (host/guest) complexes in water, and two host molecules encapsulate the guest molecule by forming a closed capsule. We have probed the dynamics of the guest molecule within this closed container through 1H NMR and EPR techniques. The timescales offered by these two techniques are quite different, millisecond and nanosecond, respectively. For EPR studies, paramagnetic nitroxide guest molecules and for 1H NMR studies, a wide variety of structurally diverse neutral organic guest molecules were employed. The guest molecules freely rotate along their x axis (long molecular axis and magnetic axis) on the NMR timescale; however, their rotation is slowed with respect to that in water on the EPR timescale. Rotation along the x axis is dependent on the length of the alkyl chain attached to t...

A magnetic switch for spin-catalyzed interconversion of nuclear spin isomers.

Abstract: The interconversion of ortho-hydrogen (oH2) and para-hydrogen (pH2), the two nuclear spin isomers of dihydrogen, requires a paramagnetic spin catalyst such as a nitroxide. We report the design and demonstration of spin catalysis of the interconversion of oH2 and pH2 incarcerated in an endofullerene based on a reversible nitroxide/hydroxylamine system. The system is an example of a reversible magnetic spin catalysis switch that can increase the rate of interconversion of the nuclear spin isomers of H2 by a factor of ∼104.

Patterning dewetting in thin polymer films by spatially directed photocrosslinking

Abstract: In this report we examine the dewetting of spin-cast poly (styrene) films in a confined geometry. We designed a platform for laterally confining PS by photo-patterning crosslinks in spin-coated thin films. Heating the patterned film above the glass transition temperature of PS results in localized dewetting patterns in regions that were not crosslinked, while the crosslinked pattern serves as a rigid barrier that confines the retraction of the uncrosslinked polymer in micron-sized domains. The barriers also provide a favorable surface that the liquid PS wets onto, forming a rim at the boundary of crosslinked and uncrosslinked polymer. The resulting patterns are shown to be dependent on the irradiation and annealing time, the dimensions of the uncrosslinked region and the thickness of the film.

Electron Spin Polarization Transfer from a Nitroxide Incarcerated within a Nanocapsule to a Nitroxide in the Bulk Aqueous Solution

Abstract: A thioxanthone derivative containing a covalently attached 15N-labeled nitroxide was incarcerated into an octaacid nanocapsule. Photoexcitation of the thioxanthone chromophore generated electron spin polarization of the nitroxide. This spin polarization of the 15N-labeled nitroxide was transferred through the walls of the carcerand to a 14N-labeled nitroxide in external bulk solvent, a process that was directly observed by time-resolved EPR spectroscopy. The efficiency of the communication between the incarcerated guest and molecules in the bulk solvent was shown to be controlled by supramolecular factors such as Coulombic attraction and repulsion between the guest@host complex and charged molecules in the bulk solvent phase.

Closed Nanocontainer Enables Thioketones to Phosphoresce at Room Temperature in Aqueous Solution

Abstract: Thiocarbonyl compounds possess unusual photophysical properties: they fluoresce from S(2), phosphoresce from T(1) only at extremely low concentrations in solution at room temperature, have unit quantum yield of intersystem crossing from S(1) to T(1), undergo self-quenching at diffusion-controlled rates, and are quenched by ground-state oxygen leading to self-destruction. In this article, we are concerned with finding a new method to observe phosphorescence from thioketones at room temperature in aqueous solution at high concentrations. To achieve this goal, one needs to find ways to eliminate diffusion-limited self-quenching and oxygen quenching. We present here a general strategy that has allowed us to record phopshorescence from a number of thioketones in aqueous solution at room temperature. The method involves encapsulation of thioketone molecules within a "closed nanocontainer" made up of two cavitand molecules known by its trivial name as octa acid. In these supramolecular complexes, despite two thiocarbonyl compounds being present in close proximity, no self-quenching occurs within the confined space due to curtailment of their rotational freedom. Although phosphorescence could also be observed when these thioketones are included in open containers, such as cucurbiturils and cyclodextrines, the closed container made up of octa acid is found to be the best medium to observe phosphorescence from thioketones whose excited state chemistry is essentially controlled by self-quenching.

A New Strategy to Photoactivate Green Fluorescent Protein

Abstract: Photoactivatable fluorescent proteins have become an important addition to the set of molecular probes used to understand cellular function. Known as “molecular highlighters”, their fluorescence is switched on by irradiation, thereby enabling non-invasive tracking of protein trafficking and dynamics. They are also the basis for the imaging technique called photoactivated light microscopy (PALM) in which multiple emitted photons are observed from individual active fluorophores which are sequentially activated from a large pool of inactive proteins and then photobleached. By locating the center of the point spread function for these emitted photons, it is possible to determine the location of the active fluorophore at better resolution than the theoretical diffraction limit. Previous green fluorescent protein (GFP) mutants exhibiting photomodulatory behavior have been reported including Kaede and KikGR whose emission wavelength change irreversibly, Dronpa whose fluorescence can be reversibly activated with light, and photoactivatable GFP (paGFP), whose excitation wavelength can be irreversibly changed with light. For Kaede, KikGR, and Dronpa, the precise three-dimensional structure of the fluorophore must be preserved to maintain photoswitching behavior. In paGFP, the shift in excitation wavelength is mediated by a light dependent decarboxylation of Glu222. The loss of this carboxy group is believed to cause reorientation of an internal hydrogen bond network, which changes the protonation state of the fluorophore and leads to an irreversible shift in the excitation maximum from 397 nm to 475 nm. This mechanism of GFP photoactivation requires the preservation of active-site residues His203, His148, Ser205, and Glu222. Unfortunately, the sequence restrictions necessary to maintain photomodulatory behavior are not always compatible with the mutations necessary to produce other fluorescent protein variants including YFP and RFP. In addition, Kaede, KikGR, and paGFP exist in two forms with differing excitation and emission wavelengths, precluding the simultaneous use of these wavelengths for other purposes. To address these problems, we have developed a general strategy for photoactivating GFP based upon nonnatural amino acid mutagenesis with the photocaged tyrosine analogue o-nitrobenzyl-O-tyrosine (ONBY). Replacing the fluorophore tyrosine 66 with ONBY yields a GFP molecule that is non-fluorescent as observed for other onitrobenzyl appended fluorophores including fluoresceine, Texas Red, and quantum dots. An earlier nonnatural variant of GFP was produced using a similar strategy, however, the high pre-irradiation background fluorescence and low protein yield made this unsuitable for use as a molecular marker. Fast, time-resolved UV/Vis spectroscopy measurements indicate that the fluorescence quenching likely occurs through photo-induced electron transfer (PET). Irradiation at 365 nm is sufficient to remove the o-nitrobenzyl

Cross-Linked ``Matrix-Free'' Nanocomposites from Reactive Polymer-Silica Hybrid Nanoparticles

Abstract: Nanoparticles have been used to reinforce polymers for at least 150 years, beginning perhaps with the development of carbon black filled elastomers for the tire industry. The incorporation of nanoparticles generally brings about significant improvements in a number of important polymer properties. Silica nanoparticles dispersed homogeneously within polymer matrices, for example, have been reported to enhancemechanical properties including modulus, flexural, tensile, and impact strength up to a silica content of about 2.5%. As a result, fracture toughness and thermal stability were also improved. More recently, the advent of strategies for the synthesis of nanoparticles with unique photonic, magnetic, electrical, and catalytic properties has brought excitement and promise for new nanoparticle applications in a broad range of emergent areas including sensors, optics, membranes, biology, medicine, and microelectronics. While these new properties and applications have garnered great interest, it has not been widely appreciated that these nanoparticles must generally be combined with some organic material, usually polymeric in nature, in order to realize macroscopic materials with useful properties. The direct dispersion of nanoparticleswithin a polymermatrix, however, is a process prone to aggregation, a phenomenon that cannot be readily overcome by more intensive mixing and that negates many desired property enhancements. Much effort has therefore focused on the modification of nanoparticlenanoparticle interactions to improve dispersion quality. For example, decorating the nanoparticle surface with a polymer brush screens particle-particle interactions and creates a polymer-inorganic hybrid that disperses more readily into a homopolymermatrix.Unfortunately, nanoparticle aggregation, a deleterious effect that negates many of the desirable nanocomposite properties, is only avoided when the brush molecular weight exceeds that of the polymermatrix, a condition that does not lead to optimal physical properties. We report herein a supramolecular building block approach for the preparation of a new family of nanocomposites that comprise nanoparticles cross-linked by polymer bridges but that do not require a polymer matrix. These “matrix-free” nanocomposites (MFNs) are not prone to the nanoparticle aggregation effects that plague conventional nanocomposites and hold promise to provide exceptionally high strength and toughness owing to the formation of covalent polymer bridges linking nanoparticles. Our novel modular approach is based upon the construction of complementary reactive supramolecular building blocks: nanoparticles decorated with heterobifunctional polymer brushes that provide reactive functionality at their periphery as depicted in Figure 1. These hybrid building blocks are somewhat analogous to block copolymers, specifically star block copolymers, wherein covalent bonding between different polymer sequences of the block copolymer prevents the aggregation or phase separation that usually occurs in the physical blend of the corresponding two homopolymers. In a similar fashion, covalent bonding between the polymer and a nanoparticle can prevent nanoparticle aggregation in aMFN. In the present case, nanoparticles with covalently bound azide-terminated polymer brushes and nanoparticles with covalently bound alkyne-terminated polymer brushes constitute hybrid building blocks that are simply “clicked” together like molecularLegos orTinkerToys to formcross-linkednanoparticle assemblies as shown in Figure 1. Reinforcement is provided by polymer bridges joining adjacent nanoparticles, yet aggregation is avoided because a polymer matrix is not employed. “Click” chemistry, specifically the 1,3-dipolar cycloaddition of alkyne and azide end groups to produce triazole cross-links, is chosen as the curing chemistry because its quantitative and chemoselective nature allows nanoparticles to be decoratedwith virtually any polymer. Polymer brushes on the azideand alkyne-functional supramolecular building blocks need not be the same polymer species (two different polymers are illustrated inFigure 1), and the nanoparticles may also differ in chemical nature (identical nanoparticles are shown). MFNs offer unique gelation behavior because the supramolecular building blocks from which they are formed provide exceptionally high reactive functionality. Conventional gels, typically based on cross-linkers with a functionality of 3-4, require a reaction conversion in the range of 50-75% to reach the gel point. The cross-linkers in MFNs, in contrast, are hybrid nanoparticles decorated with hundreds of end-functional polymer brushes, potentially lowering the conversion required for gelation to 1%or less andminimizing the formationof any sol fraction. While cross-linked nanoparticle assemblies have been prepared previously, e.g., by adding bifunctional cross-linkers

Comparative NMR properties of H2 and HD in toluene-d8 and in H2/HD@C60.

Abstract: Spin-lattice relaxation times, T(1), have been measured from 200-340 K for the protons in H(2) and HD molecules dissolved in toluene-d(8) and incarcerated in C(60). It is found that HD relaxes more slowly than H(2) in both environments and at all temperatures, as expected from the smaller values of the spin-rotation and dipole-dipole coupling in HD compared to H(2). More detailed analysis using models developed to describe relaxation in both condensed media and the gas phase indicates that transitions among the rotational states of H(2) occur at a rate similar to those of HD in both toluene-d(8) solution and in C(60), in contrast to the situation in gas phase collisions between hydrogen and He or Ar, where the lifetimes of rotational states of HD are markedly shorter than those for H(2). Measurements of the relative (1)H chemical shifts of H(2) and HD, the coupling constant J(HD), and the widths of the HD peaks at various temperatures revealed only small effects with insufficient accuracy to warrant more detailed interpretation.

Aliphatic β-Nitroalcohols for Therapeutic Corneoscleral Cross-linking: Chemical Mechanisms and Higher Order Nitroalcohols

Abstract: PURPOSE. The recent tissue cross-linking studies indicate that aliphatic ! -nitroalcohols (BNAs) may be useful as pharmacologic corneoscleral cross-linking agents. The present study was performed to identify the specific chemistry involved under physiologic conditions, with the intent of identifying more effective agents. METHODS. The mechanism of chemical cross-linking at pH 7.4 and 37°C was studied using three techniques. The colorimetric Griess assay was used to follow the release of nitrite from three mono-nitroalcohols (2-nitroethanol [2ne], 2-nitro-1-propanol [2nprop]), and 3-nitro-2-pentanol [3n2pent]). Second, the evolution of 2nprop in 0.2 M NaH2PO4/Na2HPO4/D2O was studied using 1 H-NMR. Third, thermal shrinkage temperature analysis (Ts), a measure of tissue cross-linking, was used to support information from the 1 H-NMR studies. RESULTS. A time-dependent release of nitrite was observed for all three mono-nitroalcohols studied. The maximum levels were comparable using either 2ne or 2nprop (! 30%). However, much less (! 10%) was observed from 3n2pent. Using 1 H-NMR, 2nprop evolved into a unique splitting pattern. No match was observed with reference spectra from three possible products of denitration. In contrast, 2-methyl-2-nitro-1,3propanediol (MNPD), a nitro-diol, was identified, implying the formation of formaldehyde from a retro-nitroaldol (i.e., reverse Henry) reaction. In support of this mechanism, Ts shifts induced by the nitro-triol 2-hydroxymethyl-2-nitro-1,3-propanediol (HNPD) were superior to the nitro-diol MNPD which were superior to the mono nitroalcohol 2nprop. CONCLUSIONS. BNAs function as both formaldehyde and nitrite donors under physiologic conditions to cross-link collagenous tissue. Higher order BNAs are more effective than mono nitroalcohols, raising the possibility of using these agents for

Solvation Dynamics at the Air/Water Interface with Time-Resolved Sum-Frequency Generation

Abstract: The dynamics of molecular solvation at the air/water interface has been monitored with femtosecond time-resolved pump-sum frequency generation (TR-SFG), a technique that has been shown to be feasible in the study of ultrafast rotional motions. In the work reported here, the solvation process was monitored by femtosecond photoexcitation of interfacial coumarin 314 (C314) molecules. In these experiments, the SFG signal is brought into a vibrational resonance with the carbonyl symmetric stretch of C314 by tuning the IR pulse to the carbonyl frequency by using a pump-TR-SFG probe. Two solvation time constants were obtained, 230 ± 40 fs and 2.17 ± 0.3 ps. These results are the same within experimental error as those measured in time-resolved second-harmonic generation (TR-SHG) experiments. This suggests that the solvent response is due to solvation-induced shifts of the electronic-state energies in the SFG hyperpolarizability and not significantly to solvation effects on the energy of the carbonyl vibration no...

Cage Effect Dynamics under Photolysis of Photoinitiators

Abstract: The efficiency of photoinitiators depends upon the quantum yield of photogeneration of reactive free radicals and the cage effect value. Only radicals that escape the cage can initiate free radical polymerization. The modern concept of the cage effect is presented. Dependencies of the cage effect upon increasing of solvent viscosity in the course of polymerization are discussed. Cage effect dynamics or kinetics of geminate recombination is of special interest. Results of a kinetic study on the cage effect using ns laser flash photolysis are described. © Koninklijke Brill NV, Leiden, 2010

Stearic acid delivery to corneum from a mild and moisturizing cleanser.

Abstract: Summary Objective A mild moisturizing body wash with stearic acid, a key component of corneum lipids, and emollient soybean oil has been introduced in the market place. The objectives of this study are to determine the amount and the location of the stearic acid in the corneum after in vivo cleansing by the formulation. Method Clinical cleansing studies for one and five consecutive days were carried out with the formulation containing soybean oil or petroleum jelly (PJ). The free stearic acid in it was replaced by the fully deuterated variant. The amounts of stearic acid in 10 consecutive corneum tape strips were measured by liquid chromatograph‐mass spectroscopy. Separately, electron paramagnetic resonance (EPR) measurements were taken with a porcine skin after a wash by the soybean oil formulation with its free fatty acid replaced by its spin probe analogue, 5-doxyl stearic acid. Results Deuterated stearic acid was detected in all 10 consecutive layers of stratum corneum and the total amount after five washes with the soybean oil formulation was 0.33 lg ⁄cm 2 . The spin probe in cleanser-treated skin was incorporated in a partially ordered hydrophobic region similar to corneum lipids. The probe mobility increased in the temperature region where lipid disorder was expected. Conclusions The estimated total fatty acid delivered to skin from cleansing is comparable to the amount of fatty acid in a corneum layer. The delivered fatty acid is most likely incorporated in the corneum lipid phase.

Modification of surfaces with nanoparticles

Abstract: Methods for functionalizing a surface of a substrate with nanoparticles are described. In certain embodiments, the method can include attaching a plurality of photoactive linker to nanoparticles to obtain photoactive nanoparticles, wherein each photoactive linker comprises a binding group that attaches to the nanoparticles and a photoactive group; depositing the photoactive nanoparticles to the surface of the substrate, wherein the surface of the substrate comprises reactive groups that are capable of reacting with the photoactive groups; and irradiating the photoactive nanoparticles with radiation to react the photoactive group with the reactive group and to functionalize the surface of the substrate with nanoparticles. In certain embodiments, the method can include attaching a plurality of photoactive linker to a surface of a substrate to obtain a photoactive surface, wherein each photoactive linker comprises a photoactive group and a binding group that attaches to the surface of the substrate; depositing nanoparticles to the photoactive surface, wherein the nanoparticles comprise reactive groups that are capable of reacting with the photoactive groups; and irradiating the photoactive surface with radiation to react the photoactive group with the reactive group to functionalize the surface of the substrate with nanoparticles.

Quantum Dynamics of a Hydrogen Molecule Inside an Anisotropic Open-Cage Fullerene: Coupled Translation-Rotation Eigenstates and Comparison with Inelastic Neutron Scattering Spectroscopy

Abstract: We report rigorous quantum five-dimensional (5D) calculations of the translation-rotation (T-R) energy levels and wave functions of H(2) inside aza-thia-open-cage fullerene (ATOCF). Translational and rotational excitations of this endohedral complex have been measured in a recent inelastic neutron scattering (INS) study, enabling direct comparison between theory and experiment. ATOCF has no symmetry, and therefore the intermolecular potential energy surface (PES) governing the T-R dynamics of H(2) is strongly anisotropic. A pairwise additive PES is employed in the calculations. Inspection of the wave functions shows three regular quasi-1D translational modes aligned with the Cartesian x, y, and z axes, respectively. These and other translational excitations can be assigned with the Cartesian quantum numbers v(x), v(y), and v(z). The radial anisotropy of the cage environment causes the splitting of the translational fundamental into three excitations whose frequencies differ substantially; the z mode directed toward the ATOCF orifice has the lowest frequency and is the most anharmonic. All three translational modes exhibit negative anharmonicity. The j = 1 rotational level of H(2) is also split into a triplet, due to the angular anisotropy of the cage. The complete lifting of the degeneracies of the translational fundamental and the j = 1 triplet of the encapsulated H(2) molecule that emerges from the calculations is also observed in the INS spectra of H(2)@ATOCF. The calculated magnitudes of both splittings, as well as the energies of the individual sublevels, rotational and translational, are in good agreement with the INS data.

Magnetic Interaction of Solution-State Paramagnets with Encapsulated H2O and H2

Abstract: The bimolecular contribution, R1 (M−1 s−1), to the T1 of isolated H2 and H2O protons, as well as free H2O in organic solution, by paramagnetic metal complexes was determined. Isolation was achieved by encapsulation in a fullerene: H2 was trapped in pristine C60 or in C60 with a 13-atom opening, and H2O in an open-C60 with a 19-atom opening. The R1 values in the presence of the various M(acac)x complexes [M = Fe(III), Cr(III), Cu(II), Co(III)] scale with μeff2 of the metal complex. The R1 values were significantly smaller for the trapped species than the free H2O. Surprisingly, R1 was nearly identical for the all three endohedral proton pairs, even in different solvents. This suggests that the magnetic isolation effects of the carbon cage are not significantly affected by the solvent, the completeness of the carbon cage, or separation of the hydrogens by an oxygen atom.

Nitroalcohol Induced Hydrogel Formation in Amine-Functionalized Polymers

Abstract: Certain β-nitroalcohols degrade under basic conditions or upon heating to form formaldehyde. This reaction provides an elegant approach to generate formaldehyde within a system at a desired time using the stimulus of pH or temperature. Using β-nitroalcohols as a delivery agent for formaldehyde, polymer crosslinking can be induced via stimulus. Such an approach is akin to those used to prepare “self-healing” polymers, which have received much attention recently. Herein, we describe the use of certain β-nitroalcohols as a masked formaldehyde delivery system and demonstrate its use as a crosslinking agent of amine functionalized polymers to form hydrogels. We examine the temperature and pH dependence of 2-nitro-1,3-propanediol and 2-(hydroxymethyl)-2-nitro-1,2-propanediol on the rate and extent of gelation and characterize the resulting gel by swelling and FTIR experiments.

Photobase Generator Assisted Pitch Division

Abstract: The drive to sustain the improvements in productivity that derive from following Moore’s law has led the semiconductor industry to explore new technologies that enable production of smaller and smaller features on semiconductor device. Pitch division techniques and double exposure lithography are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by modifying the lithographic process. This paper presents a new technique that enables pitch division in the printing of gratings using only a single exposure that is fully compatible with the current manufacturing tools. This technique employs a classical photoresist polymer together with a photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator (PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the low dose regions. This photoactive system can be exploited in the design of both positive tone and negative tone resist formulations that provide a developed image of a grating that is twice the frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half pitch relief image after development. Through this new technique, a 45 nm half pitch line and space pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This corresponds to a k1 factor of 0.13. The principles, the materials design and the first lithographic evaluations of this system are reported.

Functionalization of organic surfaces

Abstract: The present invention relates to functionalizing a surface of an organic material. For example, surfaces of materials having C—H bonds, such as polymers having C—H bonds, can be functionalized. In certain embodiments, a heterobifunctional molecule having a photoactive anchor, a spacer, and a terminal functional group is applied to the surface of an organic material that contains one or more C—H bonds. The heterobifunctional molecule can be bound to any surface having C—H bonds as the photoactive anchor can react with C—H bonds upon irradiation. The terminal functional group has a “click” functionality which can be utilized to functionalize the surface of the organic material with any desired functionalizing moiety having the orthogonal click functionality.