Quantum scale biomimicry of low dimensional growth: An unusual complex amorphous precursor route to TiO2 band confinement by shape adaptive biopolymer-like flexibility for energy applications

Crystallization via an amorphous pathway is often preferred by biologically driven processes enabling living species to better regulate activation energies to crystal formation that are intrinsically linked to shape and size of dynamically evolving morphologies. Templated ordering of 3-dimensional space around amorphous embedded non-equilibrium phases at heterogeneous polymer-metal interfaces signify important routes for the genesis of low-dimensional materials under stress-induced polymer confinement. We report the surface induced catalytic loss of P=O ligands to bond activated aromatization of C-C C=C and Ti=N resulting in confinement of porphyrin-TiO(2 )within polymer nanocages via particle attachment. Restricted growth nucleation of TiO2 to the quantum scale (˂= 2 nm) is synthetically assisted by nitrogen, phosphine and hydrocarbon polymer chemistry via self-assembly. Here, the amorphous arrest phase of TiO, is reminiscent of biogenic amorphous crystal growth patterns and polymer coordination has both a chemical and biomimetic significance arising from quantum scale confinement which is atomically challenging. The relative ease in adaptability of non-equilibrium phases renders host structures more shape compliant to congruent guests increasing the possibility of geometrical confinement. Here, we provide evidence for synthetic biomimicry akin to bio-polymerization mechanisms to steer disorder-to-order transitions via solvent plasticization-like behaviour. This challenges the rationale of quantum driven confinement processes by conventional processes. Further, we show the change in optoelectronic properties under quantum confinement is intrinsically related to size that affects their optical absorption band energy range in DSSC.This work was supported by the National Research Foundation of Korea (NRF) grant funded by Korea government (MEST) NRF-2012R1A1A2008196, NRF 2012R1A2A2A01047189, NRF 2017R1A2B4008801, 2016R1D1A1A02936936, (NRF-2018R1A4A1059976, NRF-2018R1A2A1A13078704) and NRF Basic Research Programme in Science and Engineering by the Ministry of Education (No. 2017R1D1A1B03036226) and by the INDO-KOREA JNC program of the National Research Foundation of Korea Grant No. 2017K1A3A1A68. We thank BMSI (A*STAR) and NSCC for support. SJF is funded by grant IAF25 PPH17/01/a0/009 funded by A* STAR/NRF/EDB. CSV is the founder of a spinoff biotech Sinopsee Therapeutics. The current work has no conflicting interests with the company. We would like to express our very great appreciation to Ms. Hyoseon Kim for her technical expertise during HRTEM imaging

Summaries of FY 1997 Research in the Chemical Sciences

The objective of this program is to expand, through support of basic research, knowledge of various areas of chemistry, physics and chemical engineering with a goal of contributing to new or improved processes for developing and using domestic energy resources in an efficient and environmentally sound manner. Each team of the Division of Chemical Sciences, Fundamental Interactions and Molecular Processes, is divided into programs that cover the various disciplines. Disciplinary areas where research is supported include atomic, molecular, and optical physics; physical, inorganic, and organic chemistry; chemical energy, chemical physics; photochemistry; radiation chemistry; analytical chemistry; separations science; heavy element chemistry; chemical engineering sciences; and advanced battery research. However, traditional disciplinary boundaries should not be considered barriers, and multi-disciplinary efforts are encouraged. In addition, the program supports several major scientific user facilities. The following summaries describe the programs

Electronic structure, magnetic ordering and phonons in molecules and solids

The present work gives an overview of the authors work in the field of electronic structure calculations. The main objective is to show how electronic structure methods in particular density functional theory (DFT) can be used for the description and interpretation of experimental results in order to enhance our understanding of physical and chemical properties of materials. The recently found superconductor MgB2 is an example where the electronic structure was the key to our understanding of the surprising properties of this material. The experimental confirmation of the predicted electronic structure from first principles calculations was very important for the acceptance of earlier theoretical suggestions. Molecular crystals build from magnetic clusters containing a few transition metal ions and organic ligands show fascinating magnetic properties at the nanoscale. DFT allows for the investigation of magnetic ordering and magnetic anisotropy energies. The magnetic anisotropy which results mainly from the spin-orbit coupling determines many of the properties which make the single molecule magnets interesting

Nanoparticle Biofunctionalization for Self-Assembly and Energy Transfer Applications

Metal and semiconductor nanocrystals (NCs) have unique optical and physical properties that are dependent on size, composition and morphology. When NCs are coupled to biomolecules, their properties are combined to create unique materials with biomimetic capabilities that can function as biosensors, cellular imaging agents or drug delivery vehicles. Most NCs are synthesized in air free, non-polar conditions, so surface chemistries must be tuned to accommodate hydrophilic biomolecules. This can be achieved through ligand exchange or polymer encapsulation procedures. This work takes advantage of both phase transfer routes to functionalize gold nanoparticles (AuNPs), quantum dots (QDs), and quantum rods (QRs) with DNA and proteins for self-assembly, energy transfer and drug delivery applications. In the first project, we explored the ability to assemble QDs into clusters with a high degree of control through DNA-mediated interactions. The hydrophobic QDs were first transferred to buffers using a polymer encapsulation approach that used an amphiphilic polymer. The polymer encapsulated QDs were successfully functionalized with oligonucleotides through both EDC/NHS coupling and click chemistry. The final QD/DNA conjugates were assembled into multicolor QD clusters through a colloidal stepwise approach. One of the greatest challenges of this project was an inconsistent batch-to-batch QD/DNA coupling efficiency, which was attributed to the presence of excess polymer, QD aggregates and poor stoichiometry. Purifying QDs via ultracentrifugation in a sucrose density gradient removed excess polymer, leading to a decreased optical scattering and increased DNA loading that was beneficial for increasing coupling efficiency. In these clusters, a decrease in the QD donor emission and an increase in the QD acceptor emission indicated that QD-QD FRET occurred. One disadvantage to using QDs as energy acceptors is their broad absorption profile, which causes them to be coexcited with the donor. To overcome this limitation, a bioluminescent protein can be used to generate QD emission through bioluminescence resonance energy transfer (BRET) without external excitation. In the next project, CdSe/CdS quantum rods (QRs) were functionalized with the bioluminescent firefly protein, Photinus pyralis (Ppy). The aim of this project was to improve the long-term stability of the QR/Ppy conjugates. To make these conjugates, hydrophobic CdSe/CdS QRs are rendered hydrophilic through a ligand exchange with histidine (His) followed by an additional ligand exchange to conjugate hexahistagged Ppy proteins to QRs (QR/His/Ppy). In these conjugates, there was a decrease in the stability of the BRET over time. The retention of the BRET signal was significantly improved by changing the QR capping ligand prior to protein conjugation from His to glutathione (GSH). This is because the GSH ligands that remain on the QR surface after Ppy coupling are more highly charged than His, leading to more efficient electrostatic repulsions between QRs. To incorporate the improved QR/Ppy nanoconjugates into the QD/DNA clusters, the QR emission should be a result of non-radiative energy transfer contributions only to prevent simultaneous excitation of the energy donor and acceptor. To investigate the contribution from radiative energy transfer to the BRET signal, control experiments were performed that indicated that most of the BRET signal arises from non-radiative energy transfer from the Ppy to the QR. In the last project, DNA functionalized AuNPs were used as drug carriers for idarubicin (IDA), a clinically approved chemotherapeutic agent. To construct these conjugates, AuNPs are synthesized using a citrate reduction method and a ligand exchange is carried out to exchange the citrate capping molecules with thiol modified DNA and thermoresponsive polymers. Drug binding was investigated using DNA denaturation measurements and kinetic studies. An increase in duplex DNA melting temperature with drug loading verified IDA intercalation at the dsDNA. The kinetics of drug release were investigated at physiological temperature, where the presence of drug outside of a dialysis membrane was monitored through IDA fluorescence. The low drug release, small dissociation rate constant of 0.05 min-1 and high equilibrium constant of 3.0 x 108 M-1 demonstrates that these nanoconjugates can act as efficient vehicles for in vivo drug delivery

Yuki shiran jiko soshikika tanbunshimaku no kiso bussei oyobi oyo ni kansuru kenkyu

制度:新 ; 報告番号:甲2813号 ; 学位の種類:博士(工学) ; 授与年月日:2009/3/15 ; 早大学位記番号:新503

Carbon Nanodots from an In Silico Perspective

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications

In-situ Gas Phase Catalytic Properties Of Metal Nanoparticles

Recent advances in surface science technology have opened new opportunities for atomic scale studies in the field of nanoparticle (NP) catalysis. The 2007 Nobel Prize of Chemistry awarded to Prof. G. Ertl, a pioneer in introducing surface science techniques to the field of heterogeneous catalysis, shows the importance of the field and revealed some of the fundamental processes of how chemical reactions take place at extended surfaces. However, after several decades of intense research, fundamental understanding on the factors that dominate the activity, selectivity, and stability (life-time) of nanoscale catalysts are still not well understood. This dissertation aims to explore the basic processes taking place in NP catalyzed chemical reactions by systematically changing their size, shape, oxide support, and composition, one factor at a time. Low temperature oxidation of CO over gold NPs supported on different metal oxides and carbides (SiO2, TiO2, TiC, etc.) has been used as a model reaction. The fabrication of nanocatalysts with a narrow size and shape distribution is essential for the microscopic understanding of reaction kinetics on complex catalyst systems ( real-world systems). Our NP synthesis tools are based on self-assembly techniques such as diblock-copolymer encapsulation and nanosphere lithography. The morphological, electronic and chemical properties of these nanocatalysts have been investigated by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Chapter 1 describes briefly the basic principles of the instrumentation used within this experimental dissertation. Since most of the state-of-art surface science characterization tools provide ensemble-averaged information, catalyst samples with well defined morphology and structure must be available to be able to extract meaningful information on how size and shape affect the physical and chemical properties of these structures. In chapter 2, the inverse-micelle encapsulation and nanosphere lithography methods used in this dissertation for synthesizing uniformly arranged and narrow size- and shape-selected spherical and triangular NPs are described. Chapter 3 describes morphological changes on individual Au NPs supported on SiO2 as function of the annealing temperature and gaseous environment. In addition, NP mobility is monitored. Chapter 4 explores size-effects on the electronic and catalytic properties of size-selected Au NPs supported on a transition metal carbide, TiC. The effect of interparticle interactions on the reactivity and stability (catalyst lifetime) of Au NPs deposited on TiC is discussed in chapter 5. Size and support effects on the formation and thermal stability of Au2O3, PtO and PtO2 on Au and Pt NPs supported on SiO2, TiO2 and ZrO2 is investigated in chapter 6. Emphasis is given to gaining insight into the role of the NP/support interface and that played by oxygen vacancies on the stability of the above metal oxides. Chapter 7 reports on the formation, thermal stability, and vibrational properties of mono- and bimetallic AuxFe1-x (x = 1, 0.8, 0.5, 0.2, 0) NPs supported on TiO2(110). At the end of the thesis, a brief summary describes the main highlights of this 5-year research program

Towards single-site heterogeneous catalysts for the hydrogen evolution reaction based on covalent organic frameworks

Covalent organic frameworks (COFs) have emerged as a new class of materials for applications ranging from gas storage and adsorption to optoelectronics and catalysis. They feature crystallinity, high chemical stability and at the same time almost unrestricted diversity due to their molecular tunability. The growing energy challenges of the 21st century require new solutions from today’s scientists. During the last years, photocatalytic hydrogen evolution enabled by COF photosensitizers has emerged as a new field of research. After the seminal discovery of COF photocatalysis in 2014, many different COFs were explored, while only a few proved capable. Skillful organic chemistry allowed the rational design of COF materials to study the mechanism of photocatalytic hydrogen evolution with COFs in more detail. During this work, variables were defined that need to be adjusted to create an optimized COF photocatalysis system. Those variables range from structural factors (crystallinity, porosity, robustness and stability of the linkages, COF-catalyst interactions) to optoelectronics (light harvesting ability, charge separation and transport, stability of the radical reaction intermediates). In state-of-the-art COF photocatalysis systems, Pt nanoparticles are used as hydrogen evolution co-catalysts. In this thesis, the utilization of molecular cobaloxime co-catalysts was explored with different azine- and hydrazine-based COFs as photosensitizers. Physisorption of the cobaloximes to the COFs proved the compatibility of the components. The best performing system showed a hydrogen evolution rate of 782 µmol g 1 h 1 and a turnover number of 54.4 in a water/acetonitrile mixture with triethanolamine as electron donor. In a further step, the cobaloxime catalysts were covalently attached to the COFs. The as-created heterogeneous, but fully single-site photocatalytic system proved double as active than the respective physisorbed system. This could be the foundation for a modular leaf-like architecture leading to a full-water-splitting system. Additionally, the COFs’ molecular tunability was used to create a platform with enhanced CO2 interactions. Tertiary amines were integrated into different COF systems and their CO2 and water adsorption properties were investigated. The synergy of amine content, COF polarity and wettability were found crucial for the performance of the COF system leading to very high heats of adsorption at zero coverage (72.4 kJ mol-1) in the best case

Applications of Nanoporous Materials in Gas Separation and Storage

Past decades in the field of gas separation and storage utilized the concepts of both cryogenic distillation and non-cryogenic methods such as high-pressure cylinders but few concerns – efficiency, energy intensiveness, cost associated, risk of failure always existed. Recent advances in the field focuses on using porous materials especially nanoporous materials. Nanoporous materials, due to their well-defined structure, range of pore diameters, and striking surface chemistry hold over traditional porous materials for gas separation and storage. With pore diameter less than 2 nm and abundance of energetically favorable sites (such as unsaturated metal sites, channels, cages, cavities etc.), these materials can also undergo various surface decorations to enhance the adsorbate-adsorbent interactions making them suitable for the applications using the principles of pressure swing adsorption. The objective of this study is to show the potential these materials hold in gas separation and storage studies and we provide four different nanoporous materials dedicated to deal with certain gas mixtures. Out of the wide class of nanoporous materials, in first part of this work we show screening of 229 zeolitic frameworks in separation of radiochemically relevant noble gases mixture of Kr/Xe by Grand Canonical Monte Carlo simulations by benchmarking the model by measuring adsorption isotherms at various temperatures. Zeolites with narrow pore system and zig-zag or elliptical cross sections were found to be more selective for Xe. To separate one of the lightest gas mixture of D2/H2 we examine the adsorption into a nanoporous nickel phosphate, VSB-5, which on the basis of gas sorption analysis gives one of the highest heats of adsorption (HOA) for hydrogen (16 kJ/mol). A much higher HOA for D2 with calculated selectivities above 4 for D2 at 140 K suggests that VSB-5 is a promising adsorbent for separations of hydrogen isotopes. iv To understand the storage aspect of nanoporous materials, we utilize the principles of Inelastic Neutron Scattering (INS) to examine the lightest gas (H2) on one of the simplest yet exciting surface of graphene where the H2 gas corresponds to a 2D rotor with a rotational barrier of around 4 meV. This also helps in checking the validity of the model of H2 in an anisotropic potential and thereby provides more insight on the concept of hydrogen storage. A hand-in-hand comparison with a much stronger interaction potential provided by Ni2+ sites in VSB-5 is also studied. A huge shift in the rotational line of hydrogen in VSB-5 represents itself as a case of Kubas complex indicating the strong affinity of the unsaturated metal sites towards H2. To capture a different system of toxic gas of ammonia (NH3), we functionalize a well-studied metal organic framework, HKUST-1 (copper trimesate) containing bound sulfuric acid tethered to the framework through terminal oxygen coordination to the accessible Cu(II) sites. Presence of sulfuric acid in the framework and the NH3 sorption is examined by INS. Here acid modified HKUST-1 shows three times more uptake of NH3 compared with pristine HKUST-1. A series of DFT simulation reveals adsorption of ammonia at the acid -OH site leading to a partial transfer of H + and giving an elongated O-H-N bond rather than a full transfer of H+ and explaining the observed reversibility of adsorption without the destruction of framework