Physical Sciences and Mathematics Commons^™

Enhanced Piezoresponse And Nonlinear Optical Properties Of Fluorinated Self-Assembled Peptide Nanotubes, Soma Khanra, Sandra V. Vassiliades, Wendel A. Alves, Kaidi Yang, Rainer Glaser, Kartik Ghosh, Payal Bhattacharya, Ping Yu, Suchismita Guha

Chemistry Faculty Research & Creative Works

Self-assembled L,L-diphenylalanine (FF) nanostructures offer an attractive platform for photonics and nonlinear optics. The nonlinear optical (NLO) coefficients of FF nanotubes depend on the diameter of the tube [S. Khanra et al. Phys. Chem. Chem. Phys. 19(4), 3084-3093 (2017)]. To further enhance the NLO properties of FF, we search for structural modifications. Here, we report on the synthesis of fluorinated FF dipeptides by replacing one ortho-hydrogen atom in each of the phenyl groups of FF by a fluorine atom. Density-functional theoretical calculations yield insights into minimum energy conformers of fluorinated FF (Fl-FF). Fl-FF self-assembles akin to FF into micron-length tubes. …

Experimental And Computational Electrochemistry Of Quinazolinespirohexadienone Molecular Switches – Differential Electrochromic Vs Photochromic Behavior, Eric W. Webb, Jonathan P. Moerdyk, Kyndra B. Sluiter, Benjamin J. Pollock, Amy L. Speelman, Eugene J. Lynch, William F. Polik, Jason G. Gillmore

Faculty Publications

Our undergraduate research group has long focused on the preparation and investigation of electron-deficient analogs of the perimidinespirohexadienone (PSHD) family of photochromic molecular switches for potential application as "photochromic photooxidants" for gating sensitivity to photoinduced charge transfer. We previously reported the photochemistry of two closely related and more reducible quinazolinespirohexadienones (QSHDs), wherein the naphthalene of the PSHD is replaced with a quinoline. In the present work, we report our investigation of the electrochemistry of these asymmetric QSHDs. In addition to the short wavelength and photochromic long-wavelength isomers, we have found that a second, distinct long-wavelength isomer is produced electrochemically. This …

Simulating Hydrogen Bonded Clusters And Zeolite Clusters For Renewable Energy Applications, Qinfang Sun

Doctoral Dissertations

Our research attention is focused on the development of new fuel cell membrane materials and new zeolites which improve biomass conversion rate to meet the increasing demand of renewable and sustainable energy. We have simulated the dynamics of amphiprotic groups (pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, and tetrazole, acetic acid, formic acid, sulfuric acid, and phosphoric acid) as neat liquids and tethered via linkers to aliphatic backbones, to determine how tethering and varying functional groups affect hydrogen bond networks and reorientation dynamics, both factors thought to influence proton conduction. We used the DL_Poly_2 molecular dynamics code with the GAFF force field to …

Nontraditional Hydrogen Bonding In Asymmetric Lewis Acid Catalysis, Brandon Vernier

Electronic Theses and Dissertations

In the field of asymmetric induction, there is a shift from the synthesis of reaction

specific chiral auxiliaries towards a broader mechanistic approach. Our approach is to

develop a theory of asymmetric catalyst design from first principles. The Diels-Alder

reaction of 2-methacrolein and 1,3-cyclopentadiene in the presence of 15 mole % lmenthoxy

aluminum dichloride, reported by Koga, achieved the (S)-exo-Diels-Alder

cycloadduct with 72% ee (0% ee Endo for acrolein). The dramatic change from 72% to 0%

ee is a significant fact that has been overlooked in practical organic synthesis.

In the first phase of this work, the conformational landscape of …

The Lowest-Energy Isomer Of C2si2h4 Is A Bridged Ring: Reinterpretation Of The Spectroscopic Data Based On Dft And Coupled-Cluster Calculations, Jesse J. Lutz, Larry W. Burggraf

Faculty Publications

The lowest-energy isomer of C₂Si₂H₄ is determined by high-accuracy ab initio calculations to be the bridged four-membered ring 1,2-didehydro-1,3-disilabicyclo[1.1.0]butane (1), contrary to prior theoretical and experimental studies favoring the three-member ring silylsilacyclopropenylidene (2). These and eight other low-lying minima on the potential energy surface are characterized and ordered by energy using the CCSD(T) method with complete basis set extrapolation, and the resulting benchmark-quality set of relative isomer energies is used to evaluate the performance of several comparatively inexpensive approaches based on many-body perturbation theory and density functional theory (DFT). Double-hybrid DFT methods are found to …

Micro-Raman Imaging Of Isomeric Segregation In Small-Molecule Organic Semiconductors, Chiung-Wei Huang, Xiao You, Peter J. Diemer, Anthony Joseph Petty Ii, John E. Anthony, Oana D. Jurchescu, Joanna M. Atkin

Chemistry Faculty Publications

Charge transport in organic semiconductors is highly sensitive to film heterogeneity and intermolecular interactions, but probing these properties on the length scales of disorder is often difficult. Here we use micro-Raman spectroscopy to assign vibrational modes of isomerically pure syn and anti 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT) by comparing to density functional theory calculations. With polarization-dependent measurements, we determine the orientation of crystallites in pure isomers. In mixed-isomer samples, we observe narrow linewidths and superposition spectra, indicating coexistence of isomerically pure sub-domains on length scales smaller than the probe area. Using the ring breathing modes close to 1300 cm⁻¹ as indicators …

Molecular Insights Into Cage Occupancy Of Hydrogen Hydrate: A Computational Study, Rui Ma, Hong Zhong, Jinxiang Liu, Jie Zhong, Youguo Yan, Jun Zhang, Jiafang Xu

Chemistry Department: Faculty Publications

Density functional theory calculations and molecular dynamics simulations were performed to investigate the hydrogen storage capacity in the sII hydrate. Calculation results show that the optimum hydrogen storage capacity is ~5.6 wt%, with the double occupancy in the small cage and quintuple occupancy in the large cage. Molecular dynamics simulations indicate that these multiple occupied hydrogen hydrates can occur at mild conditions, and their stability will be further enhanced by increasing the pressure or decreasing the temperature. Our work highlights that the hydrate is a promising material for storing hydrogen.

Full Correlation In A Multiconfigurational Study Of Bimetallic Clusters : Restricted Active Space Pair-Density Functional Theory Study Of [2fe-2s] Systems, Samuel J. Stoneburner, Davide Presti, Donald G. Truhlar, Laura Gagliardi

Educator Scholarship

Iron-sulfur clusters play a variety of important roles in protein chemistry, and understanding the energetics of their spin ladders is an important part of understanding these roles. Computational modeling can offer considerable insight into such problems; however, calculations performed thus far on systems with multiple transition metals have typically either been restricted to a single-configuration representation of the density, as in Kohn-Sham theory, or been limited to correlating excitations only within an active space, as in active-space self-consistent field methods. For greater reliability, a calculation should include full correlation, i.e., not only correlation internal to the active space but also …

Beyond Density Functional Theory: The Multiconfigurational Approach To Model Heterogeneous Catalysis, Samuel J. Stoneburner, Carlo Alberto Gaggioli, Christopher J. Cramer, Laura Gagliardi

Educator Scholarship

Catalytic processes are crucially important for many practical chemical applications. Heterogeneous catalysts are especially appealing because of their high stability and the relative ease with which they may be recovered and reused. Computational modeling can play an important role in the design of more catalytically active materials through the identification of reaction mechanisms and the opportunity to assess hypothetical catalysts in silico prior to experimental verification. Kohn-Sham density functional theory (KS-DFT) is the most used method in computational catalysis because it is affordable and it gives results of reasonable accuracy in many instances. Furthermore, it can be employed in a …

Density Functional Theory-Supported Studies Of Structural And Electronic Properties Of Substituted-Phenol Derivatives Synthesized By Efficient O- Or C-Arylation Via Chan--Lam Or Suzuki Cross-Coupling Reactions, Hafiz Mansoor Ikram, Nasir Rasool, Muhammad Ali Hashmi, Muhammad Arfan Anjum, Kulsoom Ghulam Ali, Muhammad Zubair, Gulraiz Ahmad, Tariq Mahmood

Turkish Journal of Chemistry

The present study reports the efficient synthesis and computational studies of the structural and electronic properties of some interesting substituted phenol derivatives. Efficient and versatile procedures to synthesize a series of diaryl ether derivatives (2a-2c, 4a-4h) and bis-arylated products (5a-5c) are described. In this manuscript, using the commercially available starting material 1 and 3, a 1-step approach was developed by means of Cu(II)-mediated Chan-Lam and Pd-catalyzed Suzuki cross-coupling reactions to synthesize diaryl ether and bis-arylated products with moderate to good yields. The starting substrates, 2-bromo-4-methylphenol 1 or 2,4-dibromophenol 3, were both treated with several arylboronic acids, which led to the …

The Importance Of Properly Modeling The Hydrogen Bond In Histidine, Falonne M. Tchodimo, Guoquan Zhou, Hua-Jun Fan

Pursue: Undergraduate Research Journal

The hydrogen bond plays a vital role in many reactions. This study is to investigate the effect of different hydrogen bonding modes, such as single and double hydrogen bonds, via the quantum mechanic (QM) methods. Four histidine models (A, B, C, and D) with different numbers of intra-molecular hydrogen bonds were studied. The QM model results indicate that the double hydrogen bond is plausible and has a more stable geometry. However, this study suggests that the data from QM methods require further evaluation with solvation models to produce an even better energy profile.