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- Volume 66, 2015
Annual Review of Physical Chemistry - Volume 66, 2015
Volume 66, 2015
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Low-Temperature Kinetics and Dynamics with Coulomb Crystals
Vol. 66 (2015), pp. 475–495More LessCoulomb crystals—as a source of translationally cold, highly localized ions—are being increasingly utilized in the investigation of ion-molecule reaction dynamics in the cold regime. To develop a fundamental understanding of ion-molecule reactions, and to challenge existing models that describe the rates, product branching ratios, and temperature dependence of such processes, investigators need to exercise full control over the experimental reaction parameters. This requires not only state selection of the reactants, but also control over the collision process (e.g., the collisional energy and angular momentum) and state-selective product detection. The combination of Coulomb crystals in ion traps with cold neutral-molecule sources is enabling the measurement of state-selective reaction rates in a diverse range of systems. With the development of appropriate product detection techniques, we are moving toward the ultimate goal of examining low-energy, state-to-state ion-molecule reaction dynamics.
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Early Events of DNA Photodamage
Vol. 66 (2015), pp. 497–519More LessUltraviolet (UV) radiation is a leading external hazard to the integrity of DNA. Exposure to UV radiation triggers a cascade of chemical reactions, and many molecular products (photolesions) have been isolated that are potentially dangerous for the cellular system. The early steps that take place after UV absorption by DNA have been studied by ultrafast spectroscopy. The review focuses on the evolution of excited electronic states, the formation of photolesions, and processes suppressing their formation. Emphasis is placed on lesions involving two thymine bases, such as the cyclobutane pyrimidine dimer, the (6-4) lesion, and its Dewar valence isomer.
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Physical Chemistry of Nanomedicine: Understanding the Complex Behaviors of Nanoparticles in Vivo
Vol. 66 (2015), pp. 521–547More LessNanomedicine is an interdisciplinary field of research at the interface of science, engineering, and medicine, with broad clinical applications ranging from molecular imaging to medical diagnostics, targeted therapy, and image-guided surgery. Despite major advances during the past 20 years, there are still major fundamental and technical barriers that need to be understood and overcome. In particular, the complex behaviors of nanoparticles under physiological conditions are poorly understood, and detailed kinetic and thermodynamic principles are still not available to guide the rational design and development of nanoparticle agents. Here we discuss the interactions of nanoparticles with proteins, cells, tissues, and organs from a quantitative physical chemistry point of view. We also discuss insights and strategies on how to minimize nonspecific protein binding, how to design multistage and activatable nanostructures for improved drug delivery, and how to use the enhanced permeability and retention effect to deliver imaging agents for image-guided cancer surgery.
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Time-Domain Ab Initio Modeling of Photoinduced Dynamics at Nanoscale Interfaces
Vol. 66 (2015), pp. 549–579More LessNonequilibrium processes involving electronic and vibrational degrees of freedom in nanoscale materials are under active experimental investigation. Corresponding theoretical studies are much scarcer. The review starts with the basics of time-dependent density functional theory, recent developments in nonadiabatic molecular dynamics, and the fusion of the two techniques. Ab initio simulations of this kind allow us to directly mimic a great variety of time-resolved experiments performed with pump-probe laser spectroscopies. The focus is on the ultrafast photoinduced charge and exciton dynamics at interfaces formed by two complementary materials. We consider purely inorganic materials, inorganic-organic hybrids, and all organic interfaces, involving bulk semiconductors, metallic and semiconducting nanoclusters, graphene, carbon nanotubes, fullerenes, polymers, molecular crystals, molecules, and solvent. The detailed atomistic insights available from time-domain ab initio studies provide a unique description and a comprehensive understanding of the competition between electron transfer, thermal relaxation, energy transfer, and charge recombination processes. These advances now make it possible to directly guide the development of organic and hybrid solar cells, as well as photocatalytic, electronic, spintronic, and other devices relying on complex interfacial dynamics.
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Toward Design Rules of Directional Janus Colloidal Assembly
Vol. 66 (2015), pp. 581–600More LessBurgeoning interest in supracolloidal assembly has reached the point at which the field can seek so-called intelligent design rather than solely rely on evolution. Emphasizing Janus and triblock particles, this review presents a progress report on formulating design rules for the assembly of interesting structures. We discuss how to design building blocks, bearing in mind that patchy particles embody not just geometric shape but also chemical shape, that chemical shape determines particle–particle interactions, and that the assembly process can be designed to proceed in hierarchical stages. Remarks are included about the potential of kinetic and nonequilibrium control, as well as the potential for the augmented use of soft building blocks. Whereas the reverse design problem, in which arbitrarily selected structures can be designed from the bottom up, still stands as a grand challenge, the field has reached the point of understanding necessary, although not always sufficient, conditions.
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Charge Transfer–Mediated Singlet Fission
N. Monahan, and X.-Y. ZhuVol. 66 (2015), pp. 601–618More LessSinglet fission, the splitting of a singlet exciton into two triplet excitons in molecular materials, is interesting not only as a model many-electron problem, but also as a process with potential applications in solar energy conversion. Here we discuss limitations of the conventional four-electron and molecular dimer model in describing singlet fission in crystalline organic semiconductors, such as pentacene and tetracene. We emphasize the need to consider electronic delocalization, which is responsible for the decisive role played by the Mott-Wannier exciton, also called the charge transfer (CT) exciton, in mediating singlet fission. At the strong electronic coupling limit, the initial excitation creates a quantum superposition of singlet, CT, and triplet-pair states, and we present experimental evidence for this interpretation. We also discuss the most recent attempts at translating this mechanistic understanding into design principles for CT state–mediated intramolecular singlet fission in oligomers and polymers.
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Upconversion of Rare Earth Nanomaterials
Vol. 66 (2015), pp. 619–642More LessRare earth nanomaterials, which feature long-lived intermediate energy levels and intraconfigurational 4f-4f transitions, are promising supporters for photon upconversion. Owing to their unique optical properties, rare earth upconversion nanomaterials have found applications in bioimaging, theranostics, photovoltaic devices, and photochemical reactions. Here, we review recent advances in the photon upconversion processes of these nanomaterials. We start by considering energy transfer models involved in the study of upconversion emissions, as well as well-established synthesis strategies to control the size and shape of rare earth upconversion nanomaterials. Progress in engineering energy transfer pathways, which play a dominant role in determining upconversion emission outputs, is then discussed. Lastly, representative optical applications of these materials are considered. The aim of this review is to provide inspiration for researchers to explore novel upconversion nanomaterials and extended optical applications.
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Computational Studies of Protein Aggregation: Methods and Applications
Vol. 66 (2015), pp. 643–666More LessProtein aggregation involves the self-assembly of normally soluble proteins into large supramolecular assemblies. The typical end product of aggregation is the amyloid fibril, an extended structure enriched in β-sheet content. The aggregation process has been linked to a number of diseases, most notably Alzheimer's disease, but fibril formation can also play a functional role in certain organisms. This review focuses on theoretical studies of the process of fibril formation, with an emphasis on the computational models and methods commonly used to tackle this problem.
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Experimental Implementations of Two-Dimensional Fourier Transform Electronic Spectroscopy
Vol. 66 (2015), pp. 667–690More LessTwo-dimensional electronic spectroscopy (2DES) reveals connections between an optical excitation at a given frequency and the signals it creates over a wide range of frequencies. These connections, manifested as cross-peak locations and their lineshapes, reflect the underlying electronic and vibrational structure of the system under study. How these spectroscopic signatures evolve in time reveals the system dynamics and provides a detailed picture of coherent and incoherent processes. 2DES is rapidly maturing and has already found numerous applications, including studies of photosynthetic energy transfer and photochemical reactions and many-body interactions in nanostructured materials. Many systems of interest contain electronic transitions spanning the ultraviolet to the near infrared and beyond. Most 2DES measurements to date have explored a relatively small frequency range. We discuss the challenges of implementing 2DES and compare and contrast different approaches in terms of their information content, ease of implementation, and potential for broadband measurements.
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Electron Transfer Mechanisms of DNA Repair by Photolyase
Vol. 66 (2015), pp. 691–715More LessPhotolyase is a flavin photoenzyme that repairs two DNA base damage products induced by ultraviolet (UV) light: cyclobutane pyrimidine dimers and 6-4 photoproducts. With femtosecond spectroscopy and site-directed mutagenesis, investigators have recently made significant advances in our understanding of UV-damaged DNA repair, and the entire enzymatic dynamics can now be mapped out in real time. For dimer repair, six elementary steps have been characterized, including three electron transfer reactions and two bond-breaking processes, and their reaction times have been determined. A unique electron-tunneling pathway was identified, and the critical residues in modulating the repair function at the active site were determined. The dynamic synergy between the elementary reactions for maintaining high repair efficiency was elucidated, and the biological nature of the flavin active state was uncovered. For 6-4 photoproduct repair, a proton-coupled electron transfer repair mechanism has been revealed. The elucidation of electron transfer mechanisms and two repair photocycles is significant and provides a molecular basis for future practical applications, such as in rational drug design for curing skin cancer.
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Vibrational Energy Transport in Molecules Studied by Relaxation-Assisted Two-Dimensional Infrared Spectroscopy
Vol. 66 (2015), pp. 717–738More LessThis review presents an overview of the relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy method for measuring structures and energy transport dynamics in molecules. The method strongly enhances the range of accessible distances compared to traditional 2DIR and offers new structural reporters, such as the energy transport time, cross-peak amplification factors, and connectivity patterns. The use of the method for assigning vibrational modes with various levels of delocalization is illustrated. RA 2DIR relies on vibrational energy transport in molecules; as such, the transport mechanism can be conveniently studied by the method. Applications to identify diffusive and ballistic energy transport are demonstrated.
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Previous Volumes
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Volume 75 (2024)
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Volume 74 (2023)
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Volume 73 (2022)
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Volume 72 (2021)
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Volume 71 (2020)
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Volume 70 (2019)
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Volume 69 (2018)
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Volume 68 (2017)
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Volume 67 (2016)
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Volume 66 (2015)
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Volume 65 (2014)
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Volume 64 (2013)
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Volume 63 (2012)
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Volume 62 (2011)
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Volume 61 (2010)
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Volume 60 (2009)
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Volume 59 (2008)
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Volume 58 (2007)
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Volume 57 (2006)
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Volume 56 (2005)
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Volume 55 (2004)
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Volume 54 (2003)
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Volume 53 (2002)
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Volume 52 (2001)
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Volume 51 (2000)
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Volume 50 (1999)
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Volume 49 (1998)
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Volume 48 (1997)
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Volume 47 (1996)
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Volume 46 (1995)
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Volume 45 (1994)
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Volume 44 (1993)
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Volume 43 (1992)
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Volume 42 (1991)
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Volume 41 (1990)
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Volume 40 (1989)
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Volume 39 (1988)
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Volume 38 (1987)
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Volume 37 (1986)
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Volume 36 (1985)
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Volume 35 (1984)
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Volume 34 (1983)
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Volume 33 (1982)
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Volume 32 (1981)
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Volume 31 (1980)
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Volume 30 (1979)
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Volume 29 (1978)
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Volume 28 (1977)
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Volume 27 (1976)
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Volume 26 (1975)
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Volume 25 (1974)
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Volume 24 (1973)
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Volume 23 (1972)
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Volume 22 (1971)
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Volume 21 (1970)
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Volume 20 (1969)
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Volume 19 (1968)
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Volume 18 (1967)
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Volume 17 (1966)
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Volume 16 (1965)
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Volume 15 (1964)
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Volume 14 (1963)
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Volume 13 (1962)
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Volume 12 (1961)
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Volume 11 (1960)
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Volume 10 (1959)
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Volume 9 (1958)
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Volume 8 (1957)
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Volume 7 (1956)
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Volume 6 (1955)
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Volume 5 (1954)
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Volume 4 (1953)
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Volume 3 (1952)
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Volume 2 (1951)
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Volume 1 (1950)
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Volume 0 (1932)