Chemical Center

Lund, Sweden

Chemical Center

Lund, Sweden
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Ponseca C.S.,Chemical Center | Chabera P.,Chemical Center | Uhlig J.,Chemical Center | Persson P.,Lund University | Sundstrom V.,Chemical Center
Chemical Reviews | Year: 2017

Electrons are the workhorses of solar energy conversion. Conversion of the energy of light to electricity in photovoltaics, or to energy-rich molecules (solar fuel) through photocatalytic processes, invariably starts with photoinduced generation of energy-rich electrons. The harvesting of these electrons in practical devices rests on a series of electron transfer processes whose dynamics and efficiencies determine the function of materials and devices. To capture the energy of a photogenerated electron-hole pair in a solar cell material, charges of opposite sign have to be separated against electrostatic attractions, prevented from recombining and being transported through the active material to electrodes where they can be extracted. In photocatalytic solar fuel production, these electron processes are coupled to chemical reactions leading to storage of the energy of light in chemical bonds. With the focus on the ultrafast time scale, we here discuss the light-induced electron processes underlying the function of several molecular and hybrid materials currently under development for solar energy applications in dye or quantum dot-sensitized solar cells, polymer-fullerene polymer solar cells, organometal halide perovskite solar cells, and finally some photocatalytic systems. © 2017 American Chemical Society.

News Article | February 15, 2017

PHILADELPHIA (February 14, 2017) - Just before Rare Disease Day 2017, a study from the Monell Center and collaborating institutions provides new insight into the causes of trimethylaminura (TMAU), a genetically-transmitted metabolic disorder that leads to accumulation of a chemical that smells like rotting fish. Although TMAU has been attributed solely to mutations in a single gene called FMO3, the new study combined sensory and genetic approaches to identify additional genes that may contribute to TMAU. The findings indicate that genetic testing to identify mutations in the FMO3 gene may not be sufficient to identify the underlying cause of all cases of TMAU. TMAU is classified as a "rare disease," meaning that it affects less than 200,000 people in the United States. However, its actual incidence remains uncertain, due in part to inconclusive diagnostic techniques. "Our findings may bring some reassurance to people who report fish-like odor symptoms but do not have mutations in the FMO3 gene," said Monell behavioral geneticist Danielle R. Reed, PhD, a senior author on the study. The socially and psychologically distressing symptoms of TMAU result from the buildup of trimethylamine (TMA), a chemical compound produced naturally from many foods rich in the dietary constituent, choline. Such foods include eggs, certain legumes, wheat germ, saltwater fish and organ meats. TMA, which has a foul, fishy odor, normally is metabolized by the liver enzyme flavin-containing monooxygenase 3 (FMO3) into an odorless metabolite. People with TMAU are unable to metabolize TMA, presumably due to defects in the underlying FMO3 gene that result in faulty instructions for making functional FMO3 enzymes. The TMA, along with its associated unpleasant odor, then accumulates and is excreted from the body in urine, sweat, saliva, and breath. However, some people who report having the fish odor symptoms of TMAU do not have severely disruptive mutations in the FMO3 gene. This led the researchers to suspect that other genes may also contribute to the disorder. In the new study, reported in the open access journal BMC Medical Genetics, the research team combined a gene sequencing technique known as exome analysis with sophisticated computer modeling to probe for additional TMAU-related genes. The study compared sensory, metabolic and genetic data from ten individuals randomly selected from 130 subjects previously evaluated for TMAU at the Monell Center. Each subject's body odor was evaluated in the laboratory by a trained sensory panel before and after a metabolic test to measure production of TMA over 24 hours following ingestion of a set amount of choline. Although the choline challenge test confirmed a diagnosis of TMAU by revealing a high level of urinary TMA in all 10 subjects, genetic analyses revealed that the FMO3 gene appeared to be normal in four of the 10. Additional analyses revealed defects in several other genes that could contribute to the inability to metabolize the odorous TMA. "We now know that genes other than FMO3 may contribute to TMAU. These new genes may help us better understand the underlying biology of the disorder and perhaps even identify treatments," said Reed. TMAU's odor symptoms may occur in irregular and seemingly unpredictable intervals. This makes the disease difficult to diagnose, as patients can appear to be odor-free when they consult a health professional. This was evidenced in the current study. Although all of the subjects reported frequent fish-odor symptoms, none was judged by the sensory panel to have a fish-like odor at the time of the choline challenge. Monell analytical organic chemist George Preti, PhD, also a senior author, commented on the diagnostic implications of the combined findings, "Regardless of either the current sensory presentation TMAU or the FMO3 genetics, the choline challenge test will confirm the accumulation of TMA that reveals the presence of the disorder." Moving forward, the researchers would like to repeat the genetic analyses in a larger cohort of TMAU patients without FMO3 mutations to confirm which other genes are involved in the disorder. "Such information may identify additional odorants produced by TMAU-positive patients, and inform the future development of gene-based therapies" said Preti. Also contributing to the research were co-lead author Liang-Dar Hwang, Jason Eades, Chung Wen Yu, Corrine Mansfield, Alexis Burdick-Will, and Fujiko Duke of Monell; co-lead author Yiran Guo, Xiao Chang, Brendan Keating, and Hakon Hakonarson of the Center for Applied Genomics at the Children's Hospital of Philadelphia; co-lead author Jiankang Li, Yulan Chen, and Jianguo Zhang of BGI-Shenzhen (China); Steven Fakharzadeh of the Perelman School of Medicine, University of Pennsylvania; Paul Fennessey of the University of Colorado Health Sciences Center; and Hui Jiang of BGI-Shenzhen, the Shenzhen Key Laboratory of Genomics, and the Guangdong Enterprise Key Laboratory of Human Disease Genomics. Funding for the research was provided by the National Organization of Rare Diseases; Institutional funds from the Monell Chemical Center and the Children's Hospital of Philadelphia Research Institute; National Institute on Deafness and Other Communication of the National Institutes of Health (P30DC011735); Shenzhen Municipal Government of China (CXZZ20130517144604091); Shenzhen Key Laboratory of Genomics (CXB200903110066A); and Guangdong Enterprise Key Laboratory of Human Disease Genomics (2011A060906007). Philanthropic funding was provided by the TMAU Foundation, Volatile Analysis, Inc., the family of Mr. and Mrs. Richard Hasselbusch with matching funds from Merck Easy Match, and the late Ms. Bonnie Hunt. The Monell Chemical Senses Center is an independent nonprofit basic research institute based in Philadelphia, Pennsylvania. Poised to celebrate its 50th anniversary in 2018, Monell advances scientific understanding of the mechanisms and functions of taste and smell to benefit human health and well-being. Using an interdisciplinary approach, scientists collaborate in the programmatic areas of sensation and perception; neuroscience and molecular biology; environmental and occupational health; nutrition and appetite; health and well-being; development, aging and regeneration; and chemical ecology and communication. For more information about Monell, visit http://www. .

Roos B.O.,Chemical Center | Pyykko P.,University of Helsinki
Chemistry - A European Journal | Year: 2010

Quasi-relativistic Douglas-Kroll CASPT2 calculations are reported for the title molecules, mainly to provide primary data for a fit of double-bond covalent radii. Indeed, a well-developed σ2π2 double bond is identified in all cases. For Eu and Yb, however, it is an excited state. The main valence orbitais of all Ln ions are 6s and 5d. In the σ bonds, more 5d than 6s character is found at the Ln. The Ln=C bond lengths show a systematic lanthanide contraction of 13 pm from La to Lu. An agostic symmetry breaking is demonstrated for Ce but its effect on the Ln-C length is small. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Forsman J.,Chemical Center | Woodward C.E.,University of New South Wales | Trulsson M.,Chemical Center
Journal of Physical Chemistry B | Year: 2011

We present a simple, classical density functional approach to the study of simple models of room temperature ionic liquids. Dispersion attractions as well as ion correlation effects and excluded volume packing are taken into account. The oligomeric structure, common to many ionic liquid molecules, is handled by a polymer density functional treatment. The theory is evaluated by comparisons with simulations, with an emphasis on the differential capacitance, an experimentally measurable quantity of significant practical interest. © 2011 American Chemical Society.

Forsman J.,Chemical Center | Woodward C.E.,University of New South Wales
Langmuir | Year: 2010

We investigate the Derjaguin approximation by explicitly determining the interactions between two spherical colloids using density functional theory solved in cylindrical coordinates. The colloids are composed of close-packed Lennard-Jones particles. The solvent particles are also modeled via Lennard-Jones interactions. Cross interactions are assumed to follow the commonly used Lorentz-Berthelot (LB) mixing rule. We demonstrate that this system may display a net repulsive interaction across a substantial separation range. This contradicts the Hamaker-Lifshitz theory, which predicts attractions between identical polarizable particles immersed in a polarizable medium. The source of this repulsion is traced to the LB mixing rule. Surprisingly, we also observe nonmonotonic convergences to the Derjaguin limit. This behavior is best understood by decomposing the total interaction between the colloids into separate contributions. With increasing colloid size, each of these contributions approach the Derjaguin limit in a monotonic manner, but their different rates of convergence mean that their sum may display nonmonotonic behavior. © 2010 American Chemical Society.

Forsman J.,Chemical Center | Woodward C.E.,University of New South Wales
Soft Matter | Year: 2012

We investigate depletion interactions between inert hard colloids in the presence of ideal polymers, with a focus on the case where the polymer radius of gyration (R g) is equal to the radius of the colloids (R c). We first establish structure and fluid-fluid phase equilibria of this model system as accurately as possible. To achieve this, we replace the ideal polymers by "effective spheres", using the approach of Bolhuis and Louis [P. Bolhuis and A. A. Louis, Macromolecules, 2002, 35, 1860.] With this approach, we have been able to simulate (approximate) fluid-fluid phase diagrams in dispersions containing relatively long chains, up to 2401-mers (R g = R c = 20 bond lengths). We devote some effort to illustrate many-body effects, and demonstrate that, at least relatively close to the respective critical point, there is a much stronger tendency to form clusters in the low density phase when many-body interactions are taken into account. This is primarily due to the repulsive contributions from higher-order interactions in the liquid, enforcing a high critical polymer chemical potential. At such a high chemical potential, there is a significant tendency to form small clusters in the gas phase. The results of these "effective sphere" simulations are compared with predictions by a polymer+colloid many-body theory that was recently proposed by us. Our results suggest that this theory, even at the mean-field level is surprisingly accurate. © 2011 The Royal Society of Chemistry.

The pair interaction between two charged colloidal particles, in the presence of a polyelectrolyte as well as simple salt, is analyzed theoretically. Of particular interest is the way in which such a combination of salts can be used to induce a strong, long-range attraction, with at most a minor free energy barrier. We show that the nature of the simple salt is highly relevant, i.e., 2:1, 1:1, and 1:2 salts generate quite different particle interaction free energies at the same overall ionic strength. We adopt several different theoretical levels of description. Defining simulations at the primitive model level with explicit simple salt as our reference, we invoke stepwise coarse-graining with careful evaluations of each approximation. Representing monovalent simple ions by the ionic screening they generate is one such simplification. In order to proceed further, with additional computational savings, we also develop a correlation-corrected classical density functional theory. We analyze the performance of this theory with explicit spherical particles as well as in a flat surface geometry, utilizing Derjaguin's approximation. The calculations are particularly fast in the latter case, facilitating computational savings of many (typically 5-7) orders of magnitude, compared to corresponding simulations with explicit salt. Yet, the predictions are remarkably accurate, and considering the crudeness of the model itself, the density functional theory is a very attractive alternative to simulations. © 2012 American Chemical Society.

Delhorme M.,Laboratory Interdisciplinaire Carnot de Bourgogne | Labbez C.,Laboratory Interdisciplinaire Carnot de Bourgogne | Jonsson B.,Chemical Center
Journal of Physical Chemistry Letters | Year: 2012

Anisotropic interactions in colloidal suspensions have recently emerged as a route for the design of new soft materials. Nonisotropic particles can form nematic, smectic, hexatic, and columnar liquid crystals. Although the formation of these phases is well rationalized when excluded volume is solely at play, the role of electrostatic interactions still remains unclear and even less so when particles present a charge heterogeneity, for example, clays. Here, we use Monte Carlo simulations of concentrated suspensions of charged disk-like particles to reveal the role of Coulomb interactions and charge anisotropy underlying liquid crystal formation and structures. We observe a vast zoo of exotic structures, going from hexatic to columnar phases, which are shown to be controlled by the charge anisotropy. The particle volume fraction at which these phases start to form is found to decrease with increasing Coulomb interactions and charge anisotropy, which suggests a route to tune the structure of aqueous liquid crystals. © 2012 American Chemical Society.

Segad M.,Chemical Center | Jonsson B.,Chemical Center | Akesson T.,Chemical Center | Cabane B.,University of Paris Descartes
Langmuir | Year: 2010

Ca/Na montmorillonite and natural Wyoming bentonite (MX-80) have been studied experimentally and theoretically. For a clay system in equilibrium with pure water, Monte Carlo simulations predict a large swelling when the clay counterions are monovalent, while in presence of divalent counterions a limited swelling is obtained with an aqueous layer between the clay platelets of about 10 Å. This latter result is in excellent agreement with X-ray scattering data, while dialysis experiments give a significantly larger swelling for Ca montmorillonite in pure water. Obviously, there is one "intra- lamellar" and a second "extra-lamellar" swelling. Montmorillonite in contact with a salt reservoir containing both Na+ and Ca 2+ counterions will only show a modest swelling unless the Na + concentration in the bulk is several orders of magnitude larger than the Ca2+ concentration. The limited swelling of clay in presence of divalent counterions is a consequence of ion?ion correlations, which reduce the entropic repulsion as well as give rise to an attractive component in the total osmotic pressure. Ion?ion correlations also favor divalent counterions in a situation with a competition with monovalent ones. A more fundamental result of ion?ion correlations is that the osmotic pressure as a function of clay sheet separation becomes nonmonotonic, which indicates the possibility of a phase separation into a concentrated and a dilute clay phase, which would correspond to the "extra-lamellar" swelling found in dialysis experiments. This idea also finds support in the X-ray scattering spectra, where sometimes two peaks corresponding to different lamellar spacings appear. © 2010 American Chemical Society.

The crystal structures of the binary cadmium-rich complex metal alloys NiCd6+δ (-0.32 ≤ δ ≤ 0.35) and NiCd 1+δ (0 ≤ δ ≤ 0.05) were studied by means of single crystal X-ray diffraction. The partitioning of the NiCd6+δ structure into clusters grouped around all 16 high symmetry points of the face centered cubic cell leads to the identification of two partial structures forming replicas of two disjointed, interpenetrating, zinc blende-type nets. In one partial structure the nodes are NiTi2-type Ni4Cd 18 and bcc-type NiCd26 clusters. This substructure is ordered and compositionally more or less invariant in the whole homogeneity range with the fixed composition Ni5Cd44. The complementary substructure varies in composition and exhibits vacancy, substitutional and positional disorders. The structure of NiCd 1+δ (0 ≤ δ ≤ 0.05) can be described by a 34-atom Ti2Ni-type cluster. © 2013 The Royal Society of Chemistry.

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