Carotenoid-chlorophyll complexes: Ready-to-harvest

2005 ◽  
Vol 77 (6) ◽  
pp. 925-945 ◽  
Author(s):  
Harsha M. Vaswani ◽  
Nancy E. Holt ◽  
Graham R. Fleming
Keyword(s):  
Density Functional ◽  
High Efficiency ◽  
Light Harvesting ◽  
Photosynthetic Apparatus ◽  
Functional Theory ◽  
Naturally Occurring ◽  
Harvesting Systems ◽  
Harvesting Efficiency ◽  
Pigment Protein Complex

The fundamental interactions between naturally occurring pigments in light-harvesting systems are responsible for the high efficiency of the photosynthetic apparatus. We describe the role of carotenoids (Cars) in light-harvesting systems, including our work elucidating the mechanism of energy transfer from the optically dark Car singlet excited state (S1) to chlorophyll (Chl) and calculations on the electronic structure of Cars by means of time-dependent density functional theory (TDDFT). We highlight new studies on the charge-transfer state of the Car, peridinin (Per), which enhances the light-harvesting efficiency of the Car by increasing the electronic coupling to Chl. The role of another Car, zeaxanthin (Zea), is discussed with respect to its role in the mechanism of the feedback deexcitation quenching in green plants, a vital regulation process under light conditions which exceed photosynthetic capacity. Lastly, we provide insight on how the 96 Chls in Photosystem I are optimized to generate a pigment-protein complex which utilizes solar energy with near unit efficiency.

scholarly journals Cooperative Activation of Cellulose with Natural Calcium

2020 ◽  
Author(s):  
Gregory G. Facas ◽  
Vineet Maliekkal ◽  
Cheng Zhu ◽  
Matthew Neurock ◽  
Paul Dauenhauer
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Activation Barrier ◽  
Functional Theory ◽  
Glycosidic Bonds ◽  
Naturally Occurring ◽  
Catalyzed Reactions ◽  
Kinetics Of ◽  
Cooperative Activation

Naturally occurring metals such as calcium catalytically activate the inter-monomer β-glycosidic bonds in long chains of cellulose initiating reactions to volatile oxygenates for renewable applications. In this work, the millisecond kinetics of calcium catalyzed reactions were measured via the method of pulse-heated analysis of solid/surface reactions (PHASR) at high temperature (370-430 °C) to reveal accelerated glycosidic ether scission with a second order rate dependence on Ca<sup>2+</sup> ions. First principles density functional theory (DFT) calculations were used to identify stable binding configurations for two Ca<sup>2+</sup> ions that demonstrated accelerated transglycosylation kinetics with an apparent activation barrier of 50 kcal mol<sup>-1</sup> for a cooperative calcium catalyzed cycle. The agreement of mechanism with calcium cooperativity to the experimental barrier (48.7 ± 2.8 kcal mol<sup>-1</sup>) suggests that calcium enhances reactivity through a dual role of disrupting native H-bonding and stabilizing charged transition states.

scholarly journals Cooperative Activation of Cellulose with Natural Calcium

2020 ◽  
Author(s):  
Gregory G. Facas ◽  
Vineet Maliekkal ◽  
Cheng Zhu ◽  
Matthew Neurock ◽  
Paul Dauenhauer
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Activation Barrier ◽  
Functional Theory ◽  
Glycosidic Bonds ◽  
Naturally Occurring ◽  
Catalyzed Reactions ◽  
Kinetics Of ◽  
Cooperative Activation

Naturally occurring metals such as calcium catalytically activate the inter-monomer β-glycosidic bonds in long chains of cellulose initiating reactions to volatile oxygenates for renewable applications. In this work, the millisecond kinetics of calcium catalyzed reactions were measured via the method of pulse-heated analysis of solid/surface reactions (PHASR) at high temperature (370-430 °C) to reveal accelerated glycosidic ether scission with a second order rate dependence on Ca<sup>2+</sup> ions. First principles density functional theory (DFT) calculations were used to identify stable binding configurations for two Ca<sup>2+</sup> ions that demonstrated accelerated transglycosylation kinetics with an apparent activation barrier of 50 kcal mol<sup>-1</sup> for a cooperative calcium catalyzed cycle. The agreement of mechanism with calcium cooperativity to the experimental barrier (48.7 ± 2.8 kcal mol<sup>-1</sup>) suggests that calcium enhances reactivity through a dual role of disrupting native H-bonding and stabilizing charged transition states.

The Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge XAS

2020 ◽  
Author(s):  
Tulin Okbinoglu ◽  
Pierre Kennepohl
Keyword(s):  
Density Functional ◽  
Chemical Properties ◽  
Functional Theory ◽  
Rotational Barriers ◽  
Td Dft ◽  
Nitrogen Bonds ◽  
X Ray Absorption ◽  
Related Compounds ◽  
And Chemical Properties

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest due to their many uses and chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet their continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge x-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to explore the role of S<sub>3p</sub> contributions to π-bonding in sulfonamides, sulfinamides and sulfenamides. We explore the nature of electron distribution of the sulfur atom and its nearest neighbors and extend the scope to explore the effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with TD-DFT calculations confirm that sulfonamides, and the other sulfinated amides in this series, have essentially no S-N π bonding involving S<sub>3p</sub> contributions and that electron repulsion and is the dominant force that affect rotational barriers.

γ-Valerolactone-Introduced Controlled-Isomerization of Glucose for Lactic Acid Production over Sn-Beta Catalyst

2021 ◽  
Author(s):  
Xinpeng Zhao ◽  
Zhimin Zhou ◽  
hu luo ◽  
Yanfei Zhang ◽  
Wang Liu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Lactic Acid ◽  
Dft Calculations ◽  
Acid Production ◽  
Density Functional ◽  
Lactic Acid Production ◽  
Hydrothermal Conversion ◽  
Functional Theory ◽  
Environment Friendly

Combined experiments and density functional theory (DFT) calculations provided insights into the role of the environment-friendly γ-valerolactone (GVL) as a solvent in the hydrothermal conversion of glucose into lactic acid...

scholarly journals Role of Chemistry and Crystal Structure on the Electronic Defect States in Cs-Based Halide Perovskites

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1032
Author(s):  
Anirban Naskar ◽  
Rabi Khanal ◽  
Samrat Choudhury
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Covalent Bond ◽  
Density Functional Theory Calculations ◽  
Antisite Defect ◽  
Defect States ◽  
Functional Theory ◽  
Electronic Defect ◽  
Constituent Elements

The electronic structure of a series perovskites ABX3 (A = Cs; B = Ca, Sr, and Ba; X = F, Cl, Br, and I) in the presence and absence of antisite defect XB were systematically investigated based on density-functional-theory calculations. Both cubic and orthorhombic perovskites were considered. It was observed that for certain perovskite compositions and crystal structure, presence of antisite point defect leads to the formation of electronic defect state(s) within the band gap. We showed that both the type of electronic defect states and their individual energy level location within the bandgap can be predicted based on easily available intrinsic properties of the constituent elements, such as the bond-dissociation energy of the B–X and X–X bond, the X–X covalent bond length, and the atomic size of halide (X) as well as structural characteristic such as B–X–B bond angle. Overall, this work provides a science-based generic principle to design the electronic states within the band structure in Cs-based perovskites in presence of point defects such as antisite defect.

scholarly journals First-Principles Study of a MoS2-PbS van der Waals Heterostructure Inspired by Naturally Occurring Merelaniite

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1649
Author(s):  
Gemechis D. Degaga ◽  
Sumandeep Kaur ◽  
Ravindra Pandey ◽  
John A. Jaszczak
Keyword(s):  
Density Functional ◽  
Van Der Waals ◽  
Hole Mobility ◽  
Functional Theory ◽  
Mos2 Monolayer ◽  
Naturally Occurring ◽  
Weak Interlayer ◽  
Bulk Structure ◽  
P Type ◽  
Interlayer Bonding

Vertically stacked, layered van der Waals (vdW) heterostructures offer the possibility to design materials, within a range of chemistries and structures, to possess tailored properties. Inspired by the naturally occurring mineral merelaniite, this paper studies a vdW heterostructure composed of a MoS2 monolayer and a PbS bilayer, using density functional theory. A commensurate 2D heterostructure film and the corresponding 3D periodic bulk structure are compared. The results find such a heterostructure to be stable and possess p-type semiconducting characteristics. Due to the heterostructure’s weak interlayer bonding, its carrier mobility is essentially governed by the constituent layers; the hole mobility is governed by the PbS bilayer, whereas the electron mobility is governed by the MoS2 monolayer. Furthermore, we estimate the hole mobility to be relatively high (~106 cm2V−1s−1), which can be useful for ultra-fast devices at the nanoscale.

On the role of steric and exchange–correlation effects in halogenated complexes

2021 ◽  
Author(s):  
Mojtaba Alipour ◽  
Parisa Fallahzadeh
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Partitioning ◽  
Correlation Effects ◽  
Functional Theory ◽  
Exchange Correlation

Density functional theory formalisms of energy partitioning schemes are utilized to find out what energetic components govern interactions in halogenated complexes.

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