Browsing by Subject "Crystallography"
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Item Acid-Catalyzed Condensation of Indole with Cyclic Ketones & Synthesis and Crystallographic Study of 2,6-Dihalobenzonitriles and Isocyanobenzenes(2017-06) Tritch, KennethI. As an extension of ongoing indole-ketone research, one-pot condensation reactions were performed between indole (1) and cyclic ketones with ring sizes n = 4–12 (2d–l) in the presence of boric, phosphoric, acetic, trifluoroacetic, hydrochloric, and toluene-4-sulfonic acids (Scheme 1). From fastest to slowest, the rate of condensation with indole was n = 6, 4, 5, 7, 12, 8, 11, 10, and 9. In addition to oligomerized indole, seven different types of products were isolated and identified. An eighth type of product was obtained from cyclododecanone, but it was not identified. The optimal catalyst for 2:1 condensation varied by ring size. CF3COOH or HCl were the best catalysts for one-pot preparation of all other products. II. Eleven 2,6-dihalobenzonitriles (204) and six corresponding isocyanobenzenes (209) were prepared (Scheme 2). To minimize radical-derived byproducts, it was important to perform cyanation in the presence of excess NaHCO3. Six nitriles and five isocyanides were analyzed by X-ray diffraction to study substituent effects on cyano-halo short contacts and the resulting ribbon or layer structures. All crystals exhibited such contacts. Polytypism of tribromo analogs 204ca and 209ca; and 2:1 anthracene co-crystals of cyano acids 204bc,cc were observed. Numbering. The introduction and discussion material is separated into two parts. Compound numbering begins at 1 and 201, for Part I and Part II, respectively. Main starting materials, intermediates, and products are given the lowest numbers. Entries in Part III and the appendices are given in numerical order, although Part III is also sorted by type of chemical reaction. Thus, several compounds in Part III are given more than one entry because they were prepared by more than one method.Item Crystalline transition metal-based sensors for the optical detection of oxygen(2012-09) Hinkle, Lindsay MarieOxygen is essential to life, motivating the development of optical oxygen sensors. Current sensing methods rely on either electrochemical measurements or an optical response from solutions or polymer based materials. These techniques often suffer from support degradation, oxygen consumption, and response plots that are difficult to interpret. A promising alternative to current optical sensing technologies are porous crystalline solids, as these solids provide a consistent emission site along with the necessary open space to facilitate diffusion of molecular oxygen through the material. This thesis explores neutral, mono-, di-, and tricationic coordination complexes for use as solid-state devices to detect oxygen. This series of transition metal complexes was synthesized, and the packing motifs studied by single crystal X-ray diffraction. After investigating the crystalline packing, photophysical properties, and sensitivity of emission toward oxygen, it was determined that the mono- and dicationic complexes are the most promising materials based on their sensitivity and long term stability. In Chapter 1, a brief introduction to oxygen sensing and the goals of this project are given. In Chapter 2, the synthesis and characterization of a series of neutral zinc(II) compounds are reported. One specific compound, Zn(terpy-*)Br2 (where terpy-* = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine) showed promise for detecting small oxygen concentrations. However, stability testing determined the compound was not stable toward LED illumination and oxygen exposure. In Chapter 3, a monocationic family of compounds based on the [Cu(P^P)(N^N)]+ core (where P^P is a bidentate phosphine and N^N is a bidentate amine) was explored. After the sensing ability of the compounds was determined, their stability was rigorously tested. The studies demonstrate that compounds with tfpb- (where tfpb- = tetrakis[bis-3,5-trifluoromethyl(phenylborate)]) counterions were typically more stable and more sensitive to changes in oxygen than their BF4- and pfpb- (pfpb- = tetrakis-(pentafluorophenyl)borate) counterparts. Additionally, a mechanism for the degradation of these sensors is proposed. In Chapter 4, a zinc(II) dicationic polypyridine complex was tested and compared to a previously reported and analogous ruthenium(II) compound. Based on the knowledge that similarly shaped molecules tend to pack in a similar way, it was hypothesized that crystalline materials of both the Ru(II) and Zn(II) compounds would pack similarly and therefore sense oxygen in a similar manner. Even though the compounds crystallize in a similar manner and the trends in oxygen sensitivity are the same, the KSV parameters were not as similar as was predicted. The difference in sensing ability is due to a different quenching mechanism in the Ru(II) and Zn(II) complexes. Nonetheless, the Zn(II) family of compounds is a reliable and inexpensive solid-state oxygen sensing material. Finally in Chapter 5, tricationic, 4'-tolyl-2,2':6',2''-terpyridine (tol-terpy) iridium(III) compounds were synthesized and tested for oxygen sensitivity. While none of these materials were sensitive toward changes in oxygen concentration, three new crystal structures of iridium(III) bis-tol-terpy compounds have been reported along with the structure of one neutral mono-tol-terpy complex. These four structures represent a significant contribution to the crystallographic database as only seven structures of this class of compound had been reported before this work.Item Oral history interview with Marvin L. Stein(Charles Babbage Institute, 1984) Stein, Marvin L.In the first session of the interview, Stein discusses his early career and the formation of the University of Minnesota's computing facilities. After learning basic digital and analog operation during World War II, he obtained a doctorate in mathematics from UCLA. While teaching numerical analysis at UCLA, he also worked on missile simulation at Convair, Inc., in San Diego. After becoming familiar with the ERA 1103 computer Convair purchased from Engineering Research Associates, Stein made frequent consultant visits to ERA headquarters in Minnesota. In 1955, the University of Minnesota hired Stein to introduce their first computer courses and administer ERA's gift of free computer time. He describes early computer applications to crystallography and low-energy electron scattering, and the policy he established for the computer center to make users self-sufficient programmers. Stein reviews the growth of the Computer Center: the acquisition of an ERA 1103 computer with National Science Foundation support, the construction and use of a hybrid computer out of the 1103 and a Reeves Electronic Analog Computer (REAC), and the purchase in 1960 of Control Data 1604 and 1700 computers. In the second session, Stein discusses the formation of Minnesota's program in computer science. He explains the rationale for his 1966 proposal for a graduate program in computer science and for the move in 1969 to a department of computer science independent from mathematics and electrical engineering. Stein reviews the curriculum that was intended to introduce students to a wide variety of applications so that they could introduce computer science into other disciplines. Stein discusses the difficulties in hiring enough qualified faculty members, the relations between the computer center and the computer science department, and the state's attempt to bring all educational computing under the control of the Minnesota Educational Computer Consortium.Item Purification, crystallization and structure determination of an azurin variant.(2012-08) Ladd, Melanie AnnX-ray diffraction is a method that allows the three-dimensional structure of a molecule to be determined. To use this technique to study a protein model, high-quality crystals were grown. A biosynthetic approach was taken to model the mammalian protein peptidylglycine α-hydroxylating monooxygenase (PHM), which is a copper-binding protein that hydroxylates the α-carbon of a glycine residue in the production of peptide hormones. In order to understand the mechanism of this reaction, a model of the two copper sites involved in hydroxylation was created using the bacterial protein azurin as a scaffold (Az-PHM). To compare the structural similarity of the model to the native PHM system, Az-PHM crystals were grown for x-ray diffraction using various buffers, salts, polyethylene glycol (PEG) and excess copper. Dozens of the resulting crystals were diffracted, which had lower resolutions (~2.5 Å) and higher mosaicities (0.8 - 1.2° on average). Crystal dehydration and cryoprotection techniques were applied and consistently yielded higher resolution and lower mosaicity crystals. The crystal with the highest resolution and low mosaicity was grown in Tris buffer, lithium nitrate, PEG-2000 and copper chloride. Diffraction images for this crystal were collected on a Rigaku RAPID II X-ray Diffractometer using a copper radiation source with capillary optics and an R-AXIS image plate detector. Data were indexed to yield a P212121 space group, which was then followed by integration, scaling and averaging using CrystalClear 2.1 software. Phases were determined using the Molecular Replacement method in the software CCP4. Finally, structural refinement of the model and electron density map in Coot yielded a 1.3 Å structure with an Rfactor of 17.57% and an Rfree of 20.70%.