Recursos de colección

Caltech Authors (166.781 recursos)

Repository of works by Caltech published authors.

Type = Conference or Workshop Item

Mostrando recursos 1 - 20 de 318

  1. Genomic DNA functionalized 3D printed materials for drug capture

    Yee, Daryl; Schulz, Michael; Blumenfeld, Carl; Grubbs, Robert; Greer, Julia
    Since the discovery of nitrogen mustard as an effective anti-cancer agent in the 1940s, and consequently, the concept of chemotherapy, researchers around the world have been actively developing new and more effective chemotherapeutic agents to better treat cancer. Traditionally, chemotherapeutic agents work by interfering with cell division. However, by virtue of their mechanism of action, healthy normal cells can also be targeted and destroyed. As a result, while chemotherapy is an effective way of managing cancer, the resulting side effects limits its use. One approach currently taken to reduce these side effects is to deliver the chemotherapy drugs directly to the tumor via transarterial chemoembolization,...

  2. Even-handed active space selection in projection-based wavefunction-in-DFT embedding

    Welborn, Matthew; Miller, Thomas F.
    Projection-based embedding offers a simple framework for embedding wavefunction theories in d. functional theory. Underlying this embedding is a heuristic for translating the chem.-intuitive idea of a set of embedded atoms into a set of embedded orbitals on which the embedded wavefunction calcn. will be performed. For single-point calcns., a successful heuristic has been to first localize the occupied Kohn-Sham orbitals, and then assign these localized orbitals to the embedded region based on at. population anal. However, during a large geometry change - such as a chem. reaction - the nature of the localized orbitals, as well as their at. populations can change dramatically. This can...

  3. Operando Raman interrogation of the synthesis and activation of a CoSe HER catalyst

    Rinaldi, Katherine Z.; Carim, Azhar; Lewis, Nathan S.
    A highly active cobalt selenide electrocatalyst for the hydrogen-evolution reaction (HER) in acidic media was electrochem. synthesized using a two-step process consisting of potentiostatic electrodeposition from aq. soln. followed by galvanostatic conditioning in the HER potential regime. Ex-situ Raman spectroscopy and energy-dispersive X-Ray spectroscopy indicated that the initial deposition step generated a material contg. CoSe as well as Se in multiple phases. Operando Raman anal. during the initial galvanostatic operation indicated a structural evolution of the Se phases including the partial elimination of one phase. Despite operating in the HER regime, the faradaic efficiency towards hydrogen evolution was low until this structural change was complete, demonstrating...

  4. Forces on nascent polypeptides during membrane insertion and translocation via the Sec translocon

    Niesen, Michiel J. M.; Miller, Thomas
    Co-translational insertion into and translocation across the cell membrane via the Sec translocon are key steps in the biogenesis of membrane proteins and secreted proteins. However, both exptl. and computational studies of these processes are difficult due to the role of long-timescale non-equil. dynamics during ribosomal translation. We have developed a coarsegrained (CG) simulation approach that is capable of reaching exptl. relevant (i.e. minute) timescales, while retaining the level of detail required to capture the effect of individual amino-acid substitutions. The CG model is applied to uncover the mechanism underlying exptl. obsd. forces acting on hydrophilic, hydrophobic, and charged nascent polypeptides as they are synthesized by...

  5. Photoelectrochemical performance of BiVO_4 photoanodes integrated with [NiFe]-layered double hydroxide water oxidation nanocatalysts

    Mueller, Astrid M.; Sinclair, Timothy S.; Gray, Harry B.
    We integrated laser-made highly active nickel iron layered double hydroxide ([NiFe]-LDH) water oxidn. nanocatalysts, which we developed in our group, with BiVO_4 photoanodes and tested their photoelectrochem. performance under simulated sunlight illumination. We demonstrated decreased aggregation and increased photocurrent generation with nanocatalysts that contain dipos. metals ([NiFe]-LDH and cobalt oxide) as citrate surfactant selectively ligated the catalyst nanoparticles. We also optimized catalyst mass loading, which is a tradeoff between most efficient depletion of photogenerated holes that drive catalytic turnover and parasitic light absorption by the catalyst particles. Integrated [NiFe]-LDH-BiVO_4 photoanodes enhanced photocurrent generation by a factor of 3.3 compared to bare BiVO_4. Comparison of photoelectrochem. performance...

  6. Catalysis of the oxygen evolution reaction in strongly acidic electrolytes with earth-abundant crystalline nickel-manganese antimonate

    Moreno-Hernandez, Ivan A.; MacFarland, Clara A.; Read, Carlos G.; Papadantonakis, Kimberly; Brunschwig, Bruce S.; Lewis, Nathan S.
    Many technologies that store renewable energy in chem. bonds rely on the oxygen evolution reaction (OER) to produce a renewable oxidant. In systems with an alk. electrolyte the OER is catalyzed by earth-abundant oxyhydroxides of the first-row transition metals, whereas systems with acidic electrolytes rely on noble metal oxides such as RuO_2 or IrO_2. The discrepancy in earth-abundance of OER catalysts in alk. and acidic electrolytes corresponds to the thermodn. instability of many first-row transition metal binary oxides in acidic conditions. Understanding how to stabilize first-row transition metals in acidic electrolytes while retaining catalytic activity towards the OER is a key milestone towards the development...

  7. Sunlight-driven hydrogen formation by membrane-supported photoelectrochemical water splitting

    Lewis, Nathan S.
    We are developing an artificial photosynthetic system that will utilize sunlight and water as inputs and will produce hydrogen and oxygen as outputs using a modular, parallel development approach in which the three distinct primary components-the photoanode, the photocathode, and the product-sepg. but ion-conducting membrane-are fabricated and optimized sep. before assembly into a water-splitting system. The design principles incorporate two sep., photosensitive semiconductor/liq. junctions that will collectively generate the 1.7-1.9 Vat open circuit to support both the oxidn. of H2_O (or OH-) and the redn. of H+ (or H_2O). The photoanode and photocathode will consist of rod-like semiconductor components, with attached heterogeneous multielectron transfer catalysts, needed...

  8. Strategies for controlled bacterial assembly resulting in activation of a quorum-sensing circuit

    Kozlowski, Mark; Silverman, Bradley; Johnstone, Christopher; Tirrell, David
    Bacterial communities show promise in a wide range of applications, such as environmental remediation and multi-step biochem. synthesis. Here we present methods by which bacteria can be assembled in two distinct architectures through controlled surface display of assocg. proteins (SpyTag and SpyCatcher or proteins contg. coiled-coil peptides including SynZip 17 and SynZip 18). We can tune the size of the aggregates by addn. of a "stoichiometric excess" of one type of cell in an interacting pair, as well as by modulating the amt. of protein displayed on the surface. We further demonstrate reversibility of the SynZip-mediated interactions, permanence of the SpyTag-SpyCatcher mediated clustering, and construction...

  9. Nature of the active sites for carbon dioxide reduction on metal nanoparticles: suggestions for optimizing performance

    Cheng, Tao; Wang, Zhijiang; Goddard, William A., III
    Metal nanoparticles exhibit superior carbon dioxide (CO_2) redn. performance due to the existence of unique surface active sites. For example, gold (Au) nanoparticles (NPs) show high efficiency in reducing CO_2 to carbon monoxide (CO), and copper (Cu) NPs efficiently convert CO to C2 productions. However, due to the difficulties in operando measurements, the at. details of these actives site have never been revealed. In this work, we employed multi-scale simulation technologies to "computationally synthesized" the Au NPs and Cu NPs on carbon nanotube (CNT) support by closely simulating the chem. vapor deposition (CVD) expts. The large-scale reactive force field simulations with up to million atoms...

  10. Structured Si/Co-P photocathodes: Designs for efficient light absorption in earth abundant solar fuels devices

    Kempler, Paul; Gonzalez, Miguel; Papadantonakis, Kimberly; Lewis, Nathan S.
    Designs for solar fuels devices frequently employ electrocatalysts integrated directly on the light-absorbing surfaces of semiconductors. Improvements that are gained in catalytic efficiency can be offset by the losses in light-conversion efficiency that result from parasitic absorption by the catalyst. We report two methods of circumventing parasitic absorption in these systems, using silicon light-absorbers decorated with electrodeposited Co-P catalyst as model integrated photocathodes. (1) Co-P catalyst films on planar silicon were restructured during operation to form nanoscale catalyst islands, which led to a doubling of the max. AM1.5 power conversion from 0.56 mW/cm^2 to 1.1 mW/cm^2• (2) Higher loadings of Co-Pon structured n+p-Si photocathodes achieved greater...

  11. Award Address (Herbert C. Brown Award for Creative Research in Synthetic Methods sponsored by the Purdue Borane Research Fund and the Herbert C. Brown Award Endowment). Nucleophilic substitution reactions: A radical alternative to S_N1 and S_N2 reactions

    Fu, Gregory C.
    Classical methods for achieving nucleophilic substitutions of alkyl electrophiles (S_N1 and S_N2) have limited scope and are not generally amenable to enantioselective variants that employ readily available racemic electrophiles. In this presentation, we will describe how the combination of radical chem. and transition-metal catalysis has opened the door to addressing the challenges of reactivity and of enantioselectivity in nucleophilic substitution reactions of secondary and tertiary alkyl electrophiles.

  12. Olefin trimerization and ethylene tandem conversion to linear low density polyethylene

    Bercaw, John E.
    Supporting a titanium catalyst (FI)TiCl_3 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2'-(2"-methoxyphenyl) anilinato) onto MAO/silica affords a more active catalytic system for ethylene and 1-olefin trimerization. Cosupporting the (FI)TiCl_3 catalyst with the ethylene polymn. catalyst (CpSiNR)TiCl_2 (CpSiNR = (C5Me4) SiMe_2NCMe_3), either on sep. or the same MAO/silica particles, affords a catalyst system for producing butyl-branched LLDPE from and ethylene-only feed. Recent expts. aimed at defining the mechanism and LLDPE structure will be described.

  13. What Bob Parr has wrought: Quantum mechanics based reaction mechanisms for electrocatalysis

    Goddard, William A.
    Bob Parr, along with major contributions by Levy and Perdew, provided the key advances in understanding the foundation of D. Function Theory that underlies the major advances in theory and computation in predicting the mechanisms of complex electrocatalytic reactions, which is now leading to new in silica design that is being validated exptl. We will highlight some recent advances in such methodologies including: Grand canonical QM calcns. of electrochem. catalysis at canst. potential (instead of canst. nos. of electrons), QM Metadynamics calcns. of free energies of electrocatalysis at operational temp. and potential which we will illustrate with recent applications to catalytic systems including:...

  14. Embedded mean-field theory for high-efficiency electronic structure

    Ding, Feizhi; Manby, Frederick; Miller, Thomas
    Quantum embedding has emerged as a powerful strategy for electronic structure calcns., in which the total system is divided into a small, chem. active subsystem described by a high level of theory, while the surrounding subsystem is treated with a lower level of theory. However, popular realizations of the approach, such as ONIOM, can exhibit drawbacks that include the need to specify fixed particle no. and spin state for each subsystem and uncontrolled errors assocd. with subsystem interactions. Here, we present embedded mean-field theory (EMFT), a quantum embedding approach that alleviates these restrictions by describing the subsystems at different levels...

  15. Award Address (ACS Award for Creative Work in Synthetic Organic Chemistry sponsored by MilliporeSigma). Complex natural products as a driving force for discovery in organic chemistry

    Stoltz, Brian
    Our lab. is deeply interested in the discovery and development of new reaction methodol. en route to the chem. synthesis of complex bioactive mols. Over the course of the past seventeen years, research in our group at the California Institute of Technol. has been initiated in the general area of synthetic chem., with a focus on the development of new strategies for the prepn. of complex mols., including natural products that possess interesting structural, biol., and phys. properties. Concurrent to this program of target driven synthesis is a strong effort directed toward the development of new techniques and reaction methods, which are...

  16. Hubbert analysis for coal

    Rutledge, David
    Global coal prodn. based on the phys. multi-cycle Hubbert anal. of historical prodn. data and compared with carbon dioxide emissions in a business-as-usual scenario are utilized in this overview.

  17. Necessity is the mother of invention: Natural products and the chemistry they inspire

    Reisman, Sarah
    The chem. synthesis of natural products provides an exciting platform from which to conduct fundamental research in chem. and biol. Our group is currently pursuing the synthesis of a no. of structurally complex natural products, including the diterpenoids ryanodine and talatisamine, and the antibiotic pleuromutilin. The densely-packed arrays of heteroatoms and stereogenic centers that constitute these polycyclic targets challenge the limits of current technol. and inspire the development of new synthetic strategies and tactics. This seminar will describe the latest progress in our methodol. and target-directed synthesis endeavors.

  18. Integrated wearable sensors for in situ sweat analysis

    Gao, Wei
    The rising clin. and basic research interest in personalized and precision medicine promises to revolutionize traditional medical practices. This presents a tremendous opportunity for developing wearable devices toward predictive analytics and treatment. In this talk, I will introduce fully-integrated biosensors for multiplexed in-situ perspiration anal., which can selectively measure a wide spectrum of sweat analytes (e.g. metabolites, electrolytes, heavy metals and other small mols.) and allow us to gain real-time insight into the sweat-secretion and gland physiol. I will also demonstrate an intergrated wearable sweat extn. and sensing system which can be programmed to induce sweat on demand with various...

  19. Synthesis of chiral molecular sieves: A 30 year journey

    Davis, Mark
    Recently, my co-workers and I synthesized an enantiomerically enriched, polycryst. mol. sieve that has the STW framework topol. My journey to prep. a chiral mol. sieve began 30 years ago, and in this presentation, I will chronicle the progress made from start to finish. Over that period of time, advances in synthetic methods, characterization techniques and computer simulations have greatly advanced, and all these advances were used to design, prep. and conclusively prove that an enantiomerically enriched, polycryst. mol. sieve was indeed obtained. Addnl., I will make a few comments about what may be possible with chiral mol. sieves in the...

  20. Molecular recognition of DNA: From discovery to oncology

    Kurmis, Alexis; Dervan, Peter
    Pyrrole-imidazole polyamides are synthetic mols. programmed to read the DNA double helix by a set of simple chem. principles. These small mols. achieve affinities comparable to DNA-binding proteins and are cell permeable. Research efforts are focused on the modulation of gene expression pathways by disruption of transcription factor-DNA interfaces. The oversupply or overactivity of one or more transcription factors may be required for the survival, growth, and metastatic behavior of all human cancers. The efficacy of Py-Im polyamide oligomers targeted against therapy resistant prostate cancer xenografts will be discussed.

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.