Bor-Stickstoff-Analoga Reaktiver Organischer Moleküle 1,2-Azaborinin, Phenylborylen und das Dewar-Valenzisomer des 1,2-Dihydro-1,2-azaborinins : eine Matrixisolationstudie

Mit Hilfe von Matrixisolationstechniken ist es möglich reaktive Zwischenstufen, die unter normalen Laborbedingungen nicht direkt nachgewiesen werden können, zu generieren und zu isolieren. Diese Arbeit handelt hauptsächlich über Untersuchungen von Borverbindungen mit Hilfe der Matrixisolationstechnik und lässt sich in drei Teilbereiche unterteilen. 1. Matrixisolation von 1,2-Azaborinin: 1,2-Azaborinin, ein BN-Analogon von ortho-Benzin, konnte mit Hilfe von Matrixisolationstechniken in einer Argonmatrix bei 4 K isoliert und mit Hilfe von Infrarotspektroskopie charakterisiert werden. Quantenchemische Rechnungen lassen eine hohe Lewis-Acidität des Bor-Zentrums erwarten und dies konnte durch die Reaktion mit Stickstoff bestätigt werden. Um Nebenprodukte bei der Generierung von 1,2-Azaborinin zu identifizieren bzw. auszuschließen wurden mögliche Isomerisierungs- und Fragmentierungsmechanismen mit Hilfe von quantenmechanischen Rechnungen untersucht. 2. Dewar-Valenzisomer von 1,2-Dihydro-1,2-azaborinin: Die Photochemie von Derivaten des 1,2-Dihydro-1,2-azaborinins wurden sowohl unter Matrixisolationsbedingungen als auch in Lösung bei Zimmertemperatur untersucht. Es zeigte sich ausschließlich die Bildung des Dewar-Valenzisomers als einzigem Reaktionsprodukt. Die Isomerisierung ist thermisch reversibel und Aktivierungsparameter wurden bestimmt. Bei einer Änderung der eingestrahlten Wellenlänge ist eine Cycloreversion der Dewar-Verbindung zum Cyclobutadien und dem entsprechenden Iminoboran zu beobachten. 3. Reaktionen von Phenylborylen: Borylene sind Analoga der Carbene und Nitrene. Doch im Vergleich zu den Carbenen und Nitrenen sind Borylene bisher kaum untersucht worden. In dieser Arbeit konnte die Reaktion zwischen Phenylborylen mit Stickstoff und mit Kohlenstoffmonoxid unter Matrixisolationsbedingungen mit Hilfe mehrerer Spektroskopiemethoden (IR, UV und ESR) gezeigt werden.  Matrix isolation techniques enable generation and isolation of reactive intermediates which usually cannot be detected under conventional laboratory conditions. This thesis is mainly focused on investigation of boron containing compounds using the matrix isolation technique, and is based on three main projects. 1. Matrix isolation of 1,2-azaborinine: 1,2-Azaborinine, the BN analogue of ortho-benzyne, could be generated and isolated by matrix isolation techniques and characterized by IR spectroscopy. A strong Lewis acidic character at the boron center was predicted by computational chemistry and could be supported by the spontaneous reaction with dinitrogen under matrix isolation conditions. To identify the byproducts, which are formed during the generation of 1,2-azaborinine, possible isomerization and fragmentation pathways were investigated by computational chemistry techniques. 2. Dewar valence isomer of 1,2-dihydro-1,2-azaborinine: The photochemistry of 1,2-dihydro-1,2-azaborinine derivatives was investigated in cryogenic matrices and in solution at room temperature. In both media, full conversion exclusively to the Dewar valence isomer was found upon irradiation with UV light. This reaction was observed to be thermally reversible and activation parameters were determined. Changing the wavelength of the UV light results into cycloreversion of the Dewar compound to cyclobutadien and the corresponding iminoborane. 3. Reactions of Phenyl borylene: Borylenes are analogues of carbenes and nitrenes. In contrast to carbenes and nitrenes little is known about borylenes. In this study the reactivity of phenyl borylene was investigated towards dinitrogen and carbon monoxide under matrix isolation conditions using various spectroscopic techniques (IR, UV and ESR)

Poster Session

Posters presented by: P01: Adam S. Abbott, University of Georgia P02: Yasmeen Abdo, University of Mississippi P03: Vibin Abraham, Virginia Tech P04: Asim Alenaizan, Georgia Institute of Technology P05: Isuru R. Ariyanthna, Auburn University P06: Brandon W. Bakr, Georgia Institute of Technology P07: [Matthew Bassett, Georgia Southern University] P08: Alexandre P. Bazanté, University of Florida P09: Andrea N. Becker, University of Tennessee P10: Randi Beil, University of Tennessee P11: Andrea N. Bootsma, University of Georgia/Texas A&M University P12: Adam Bruner, Louisiana State University P13: Lori A. Burns, Georgia Institute of Technology P14: Chanxi Cai, Emory University P15: Katherine A. Charbonnet, University of Memphis P16: Marjory C. Clement, Virginia Tech P17: Wallace D. Derricotte, Emory University P18: Harkiran Dhah, University of Tennessee P19: Manuel Díaz-Tinoco, Auburn University P20: Vivek Dixit: Mississippi State University P21: Eric Van Dornshuld, Mississippi State University P22: Katelyn M. Dreux, University of Mississippi P23: Narendra Nath Dutta, Auburn University P24: William Earwood, University of Mississippi P25: Thomas L. Ellington, University of Mississippi P26: Marissa L. Estep, University of Georgia P27: Yanfei Guan, Texas A&M University P28: Andrew M. James, Virginia Tech P29: Yifan Jin, University of Florida P30: Dwayne John, Middle Tennessee State University P31: Sarah N. Johnson, University of Mississippi P32: Noor Md Shahriar Khan, Auburn University P33: Monika Kodrycka, Auburn University P34: Ashutosh Kumar, Virginia Tech P35: Elliot Lakner, University of Alabama P36: Robert W. Lamb, Mississippi State University P37: S. Paul Lee, University of Mississippi P38: Zachary Lee, University of Alabama P39: Conrad D. Lewis, Middle Tennessee State University P40: Guangchao Liang, Mississippi State University P41: Chenyang Li, Emory University P42: Hannah C. Lozano, University of Memphis P43: SharathChandra Mallojjala, University of Georgia/Texas A&M University P44: Zheng Ma, Duke University P45: Elvis Maradzike, Florida State University P46: Ashley S. McNeill, University of Alabama P47: Stephen R. Miller, University of Georgia P48: W. J. Morgan, University of Georgia P49: Apurba Nandi, Emory University P50: Daniel R. Nascimento, Florida State University P51: Brooke N. Nash, Mississippi College P52: Carlie M. Novak, Georgia Southern University P53: Young Choon Park, University of Florida P54: Kirk C. Pearce, Virginia Tech P55: Rudradatt (Randy) Persaud, University of Alabama P56: Karl Pierce, Virginia Tech P57: Kimberley N. Poland, University of Mississippi P58: Chen Qu, Emory University P59: Duminda S. Ranasinghe, University of Florida P60: Hailey B. Reed, University of Mississippi P61: Matthew Schieber, Georgia Institute of Technology P62: Jeffrey B. Schriber, Emory University P63: Thomas Sexton, University of Mississippi P64: Holden T. Smith, Louisiana State University P65: Aubrey Smyly, Mississippi College P66: B. T. Soto, University of Georgia P67: Trent H. Stein, University of Alabama P68: Cody J. Stephan, Georgia Southern University P69: Thomas Summers, University of Memphis P70: Zhi Sun, University of Georgia P71: Monica Vasiliu, University of Alabama P72: Jonathan M. Waldrop, Auburn University P73: Tommy Walls, Southern Louisiana University P74: Qingfeng (Kee) Wang, Emory University P75: Constance E. Warden, Georgia Institute of Technology P76: Jared D. Weidman, University of Georgia P77: Melody Williams, University of Memphis P78: Donna Xia, University of Alabama P79: Qi Yu, Emory University P80: Boyi Zhang, University of Georgia P81: Tianyuan Zhang, Emory University P82: Michael Zott, Georgia Institute of Technolog

Developing novel 1,2-azaborine building blocks & the basic science of 1,2-azaborine as hydrogen-bond donors:

Thesis advisor: Shih-yuan LiuThesis advisor: Xiao-Xiang ZhangThe overarching theme of this dissertation is developing 1,2-azaborine motif as a novel arene pharmacophore. The first chapter of this dissertation is about exploring the synthesis and character of a new α-boryl diazo family-diazomethyl-1,2-azaborine and its diverse reaction chemistry. As a remarkable 1,2-azaborine building block, it can undergo a variety of classical diazo reactions including C–H activation, O–H activation, [3+2] cycloaddition, halogenation, and Ru-catalyzed carbonyl olefination. In the second chapter, we take a closer look at the hydrogen bond donor ability of 1,2-azaborines. A congeneric series of 1,2-azaborine ligands were used to probe the strength of hydrogen bonding as a function of the ligand’s steric effects. The results of this study provide fundamental reference data for establishing 1,2-azaborines as potential pharmacophores. Lastly, 1,2-azborine as a new ligand for T4 lysozyme double mutant L99A/M102 was investigated, and a new mode of ligand-protein interaction was discovered and evaluated by X-ray crystallography and ITC.Thesis (PhD) — Boston College, 2022.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Chemistry

Au-Catalyzed Energy Release in a Molecular Solar Thermal (MOST) System: A Combined Liquid-Phase and Surface Science Study

Molecular solar thermal systems (MOSTs) are molecular systems based on couples of photoisomers (photoswitches), which combine solar energy conversion, storage, and release. In this work, we address the catalytically triggered energy release in the promising MOST couple phenylethylesternorbornadiene/quadricyclane (PENBD/PEQC) on a Au(111) surface in a combined liquid-phase and surface science study. We investigated the system by photoelectrochemical infrared reflection absorption spectroscopy (PEC-IRRAS) in the liquid phase, conventional IRRAS and synchrotron radiation photoelectron spectroscopy (SRPES) in ultra-high vacuum (UHV). Au(111) is highly active towards catalytically triggered energy release. In the liquid phase, we did not observe any decomposition of the photoswitch, no deactivation of the catalyst within 100 conversion cycles and we could tune the energy release rate of the heterogeneously catalyzed process by applying an external potential. In UHV, submonolayers of PEQC on Au(111) are back-converted to PENBD instantaneously, even at 110 K. Multilayers of PEQC are stable up to ~220 K. Above this temperature, the intrinsic mobility of the film is high enough that PEQC molecules come into direct contact with the Au(111) surface, which catalyzes the back-conversion. We suggest that this process occurs via a singlet–triplet mechanism induced by electronic coupling between the PEQC molecules and the Au(111) surface

Stable Aromatic Organoborane Materials

The work included herein describes the synthesis and study of stable aromatic organoborane materials. The materials synthesized are based upon the architecture of 1,2-azaborines, aromatic hydrocarbons with a single CC for BN bond substitution. The aromaticity and electronics of both molecular and macromolecular materials are investigated. A large portion of this work is focused on the development of the monomer BN 2-vinylnaphthalene (BN2VN) and homo- and copolymers of BN2VN resulting from radical polymerization. BN2VN functionalized polymers can be converted to novel materials owning to the implicit reactivity of organoboranes

Structural Effects on Nonadiabatic Photocyclization in ortho-Arenes

Nonadiabatic photocyclization is the chemical dynamic relevant to the function of many photoswitchable materials as well as photochemical synthesis of polyaromatic hydrocarbons by cyclodehydrogenation. ortho-arenes are an under-studied class of molecular photoswitch owing to their low cyclized product stabilities that otherwise provide a unique opportunity for the experimentalist to study photocyclization mechanisms in detail. Through the use of time-resolved absorption spectroscopy on femtosecond to microsecond timescales the entire photocyclization process can be monitored from “birth” to “death,” i.e. ring-fusion to ring-fission. Following ultraviolet photoexcitation OTP undergoes cyclization to form DHT. Although global spectral analysis with simple kinetic models adequately fits spectral dynamics, signatures of DHT formation are obscured by spectral overlap with the excited-state that has a lifetime of ~3 picoseconds. Thermal ring-reopening of DHT to regenerate OTP occurs with a 38 nanosecond lifetime and an activation energy of 0.27 eV. Following the study of OTP a variety of other ortho-arenes were examined by systematic substitution, including phenyl substituted analogs, 1,2,3-triphenylbenzene, ortho-quaterphenyl and hexaphenylbenzene, as well as boron-nitrogen substituted analogs, including hexaphenylborazine and 1,2:3,4:5,6 tris(o,o’-biphenylylene) borazine. Generally these substitutions increased the excited-state lifetime relative to OTP due to an increase in either electronic delocalization or structural hindrance within excited-state geometries while the stability of the corresponding photoproducts decreased relative to DHT due to entropic effects. A notable exception is hexaphenylbenzene, which exhibits a 2 microsecond lifetime for ring-reopening of the photoproduct tetraphenyl-DHT that is a consequence of entropic stabilization due to increased phenyl-phenyl steric interactions that constrain thermally activated relaxation to the transition state. Furthermore, excited hexaphenylborazine decays within 3 picoseconds due to the localized electronic character of the borazine ring. No direct spectroscopic observation of cyclization was observed for any boron-nitrogen substituted system due to the increase in charge localization that reduces the stability of the conjugated DHT photoproduct. More recent experiments utilizing pump-repump-probe spectroscopy have determined that the observed excited-state decay is kinetically decoupled from photocyclization, which occurs in less than 200 femtoseconds. The results presented in this thesis provide insight for the improvement of photoswitch and photosynthetic efficiency through the generalization of these structure-dynamics relationships

How DNA Packaging and Processing Proteins Affect Dynamic DNA Alkylation

DNA alkylating agents are commonly considered toxic due to the irreversible nature of the lesions that they form and the failure of DNA repair enzymes to remove their lesions. However, compounds that alkylate DNA in a reversible manner may not share the same toxicity as irreversible alkylating agents. Quinone methides (QMs) are a class of transient electrophiles that reversibly alkylate DNA. A bifunctional QM conjugated to the DNA intercalator acridine (bisQMAcr) has previously been synthesized in order to examine the dynamics of reaction with DNA. BisQMAcr’s reversible chemistry facilitates its stepwise migration from one end of a duplex DNA to the other in a bipedal manner. However, bisQMAcr requires 7 days to traverse 10 base pairs, which may be too slow to be effective in vivo to evade DNA repair. Two monofunctional QMs were linked together using a flexible polyammonium alkyl chain (diQMs) to potentially facilitate faster QM migration. Additionally, BisQMs conjugated to weakly intercalative quinoxalines were synthesized to avoid the strength of acridine’s intercalation that may have suppressed QM migration. However, neither of the new QMs alkylated DNA reversibly. Thus, bisQMAcr remains the most dynamic QM synthesized to date. The environment within cells likely influences the potency of QMs’ reversible DNA alkylation, since cellular DNA is packaged around histone proteins to form nucleosomes. The assembly of DNA into nucleosomes weakens QMs’ potency as DNA alkylating agents by 90% relative to DNA free in solution. Nucleosomes possess an additional protective function against bisQMAcr’s DNA alkylation, as the histone proteins serve as terminal acceptors of bisQMAcr’s DNA adducts. BisQMAcr can release from its adducts on DNA and alkylate the histones, leaving the DNA unmodified. However, QM alkylation of the histones does not interfere with their assembly into nucleosomes, as adducts formed in the core regions of the protein that may not disrupt with the necessary DNA-protein contacts for nucleosome formation. The ability of DNA polymerases and helicases to modulate the dynamics of bisQMAcr’s DNA alkylation and of bisQMAcr’s crosslinks to inhibit replication was also investigated to determine whether biological machines may hasten QM migration. The Klenow Exo- and φ29 DNA polymerases were unable to cause bisQMAcr’s crosslinks to break apart and failed to extend DNA primers in the presence of the crosslinks. However, the T7 bacteriophage gene 4 protein (T7GP4) DNA helicase was able to unwind DNA containing reversible QM crosslinks. The helicase induced dissociation of only 40% of bisQMAcr’s crosslinks, while the remaining 60% remained intact. Irreversible DNA crosslinks formed by mechlorethamine completely resisted unwinding by the T7GP4 helicase, suggesting that only reversible crosslinks separate during DNA unwinding. Reversible QM crosslinks may not pose an absolute block to replication like many irreversible crosslinking agents do. The ability of a helicase to remove QM adducts from DNA essentially affords DNA repair without relying on specific DNA repair proteins. This work describes the potency of reversible QM alkylation in a biological setting. Transfer of reversible adducts to the histone proteins and loss of DNA adducts by helicases’ translocation may afford their repair by means of their intrinsic reversible chemistry

Technological Innovations in Photochemistry for Organic Synthesis: Flow Chemistry, High-Throughput Experimentation, Scale-up, and Photoelectrochemistry

[Image: see text] Photoinduced chemical transformations have received in recent years a tremendous amount of attention, providing a plethora of opportunities to synthetic organic chemists. However, performing a photochemical transformation can be quite a challenge because of various issues related to the delivery of photons. These challenges have barred the widespread adoption of photochemical steps in the chemical industry. However, in the past decade, several technological innovations have led to more reproducible, selective, and scalable photoinduced reactions. Herein, we provide a comprehensive overview of these exciting technological advances, including flow chemistry, high-throughput experimentation, reactor design and scale-up, and the combination of photo- and electro-chemistry

DESIGN, SYNTHESIS AND CHARACTERIZATION OF MOLECULAR AND POLYMERIC CYCLOSILANES

The structural complexity of crystalline silicon has inspired synthetic chemists to design cyclosilane building blocks for well-defined novel silicon materials with tunable optical properties. This dissertation describes synthetic strategies of constructing novel molecular and polymeric cyclosilane materials and their structure-property-relationships. Polycyclosilanes exhibit microstructure-dependent thermal properties and connectivity-dependent UV-vis absorption features. Novel hybrid sigma,pi-conjugated cyclosilane building blocks with pre-defined stereochemistry allow access to stereoregular polysilanes. Constitutional isomers of sulfur-incorporated π,n,σ-conjugated cyclosilanes can exhibit distinct conformations and delocalization patterns. Theoretical investigations through density functional theory calculations contribute to understanding the optical and electronic properties of these molecular and polymeric cyclosilane materials

2009 Annual Progress Report: DOE Hydrogen Program

This report summarizes the hydrogen and fuel cell R&D activities and accomplishments of the DOE Hydrogen Program for FY2009. It covers the program areas of hydrogen production and delivery; fuel cells; manufacturing; technology validation; safety, codes and standards; education; and systems analysis