Chemistry Commons^™

Ab Initio Study Of Intermolecular Potential Of H2o Trimer, G. Chalasinski, M. M. Szczesniak, P. Cieplak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Nonadditive contribution to the interaction energy in water trimer is analyzed in terms of Heitler–London exchange, SCF deformation, induction and dispersion nonadditivities. Nonadditivity originates mainly from the SCF deformation effect which is due to electric polarization. However, polarization does not serve as a universal mechanism for nonadditivity in water. In the double‐donor configuration, for example, the Heitler–London exchange contribution is the most important and polarization yields the wrong sign. Correlation effects do not contribute significantly to the nonadditivity. A detailed analysis of the pair potential is also provided. The present two‐body potential and its components are compared to the existing …

Ab Initio Study Of The Intermolecular Potential Of Ar–H2o, G. Chalasinski, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential‐energy surface of Ar–H₂O. The surface is very isotropic with the lowest barrier for rotation of ∼35 cm⁻¹ above the absolute minimum. The lower bound for D_e is found to be 108 cm⁻¹ and the complex reveals a very floppy structure, with Ar moving freely from the H‐bridged structure to the coplanar and almost perpendicular arrangement of the C₂ –water axis and the Ar–O axis, ‘‘T‐shaped’’ structure. This motion is almost isoenergetic (energy change …

Intermolecular Potential Of The Methane Dimer And Trimer, M. M. Szczesniak, G. Chalansinski, S. M. Cybulski, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The Heitler–London (HL) exchange energy is responsible for the anisotropy of the pair potential in methane. The equilibrium dimer structure is that which minimizes steric repulsion between hydrogens belonging to opposite subsystems. Dispersion energy, which represents a dominating attractive contribution, displays an orientation dependence which is the mirror image of that for HL exchange. The three‐body correction to the pair potential is a superposition of HL and second‐order exchange nonadditivities combined with the Axilrod–Teller dispersion nonadditivity. A great deal of cancellation between these terms results in near additivity of methane interactions in the long and intermediate regions.

A Study Of Denitrosation Of N-Nitroso Compounds By Irradiation With Long-Wavelength Uv Light, Zhenyu J. Wang

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

N-Nitrosamines and N-nitrosamides have been reported to be mutagenic. N-Nitrosamides are direct mutagens that need no activation to be mutagenic, whereas N-nitrosamines need to be enzymatically activated to exert their mutagenicity. Oxidative demethylation of nitrosamines is a commonly accepted activation mechanism. Another pathway of nitroso compounds, denitrosation, has recently been proposed. The mechanism of denitrosation, however, is still unknown.

The purpose of this study was to use a photo -reaction model to explore the possible denitrosation mechanism of N-nitroso compounds. An N-nitrosamine, N-nitrosomorpholi ne (NMOR), and an N-nitrosamide, N-methyl-N'-nitrosoguanidine (MMNG), were irradiated with long-wavelength UV light in the presence of …

Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Nonadditive effects are calculated for (HF)₃ and (HCl)₃ complexes and analyzed via the combination of perturbation theory of intermolecular forces with Møller–Plesset perturbation theory (MPPT). In both systems the nonadditivity is dominated by the self‐consistent field (SCF) deformation effect, i.e., mutual polarization of the monomer wavefunctions. Heitler–London exchange and correlation effects are of secondary importance. Three‐body terms exhibit much lesser basis set dependence than the two‐body effects and even quite moderate basis sets which are not accurate enough for treatment of two‐body forces can yield three‐body effects of quantitative quality. This is due in large measure to the …

Analysis Of The Potential Energy Surface Of Ar–Nh3, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential energy surface of Ar–NH₃. Anisotropy of the self‐consistent field (SCF) potential is determined by the first‐order exchange repulsion. Second‐order dispersion energy, the dominating attractive contribution, is anisotropic in the reciprocal sense to the first‐order exchange, i.e., minima in one nearly coincide with maxima in the other. The estimated second‐order correlation correction to the exchange effect is nearly as large as a half ΔE^SCF in the minimum and has a ‘‘smoothing’’ effect on the anisotropy of …

1-Acyldihydropyridones As Synthetic Intermediates, Michael Andrew Foley

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The most efficient and stereoselective total synthesis of (+/-)- lausbine II to date has been achieved. The key steps in this are the copper-mediated conjugate addition reaction of the Grignard reagent of 1-bromo-4-chlorobutane to a dihydropyridone and a stereoselective reduction of a quinolizidinone.

Methodology has been developed for the convenient synthesis of 1-acyl-2-substituted-1,2,5,6-tetrahydropyridines. This was accomplished by adding novel alkylzinc iodides to the 1-acyliminium ion derived from N-phenoxycarbonyl-4-methoxy-1,2,3,4-tetrahydropyridine.

Synthetic Studies Toward Key Portions Of The Didemnins, Ok-Soon Kim

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Three different synthetic approaches toward N-[(2SR, 4S) - 4-hydroxy-2,5-dimethyl-3-oxohexanoyl]-Lleucine methyl esters were carried out by use of i) aldol condensation and amination ii) Claisen condensation and soft acid coupling reaction iii) methylation of Hia-Leu derivative in relatively high yields. (4S)-3-[(2SR, 4S)-2,5-Dimethyl-1,3-dioxo-4-(methoxyethoxy-methyloxy)hexyl]-4-(1-methyletheyl-2-oxazolidinone was prepared by the reaction of aldol condensation of lithium enolate of Evans' chiral auxilary in 80:20 diastereomeric ratio. A new method for the synthesis of (4S)-4-(t-butoxycarbonyl)amino-5-methyl-3-oxoheptanoic acid ethyl ester (Statone) was developed by the reaction of Boc-leucine with Meldrum's acid, followed by transesterification and decarboxylation in modest yield. Other a-amino acids also were applied to this methodology in …

Interactions Of Vanadium Compounds With Reducing Equivalents: Evidence Of Free Radical Involvement And Possible Mechanisms Of Toxicity, Randal J. Keller

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Vanadium compounds have been reported to cause numerous toxicological effects including NAD(P)H oxidation and lipid peroxidation. The purpose of this thesis is to determine the active form of vanadium in causing these effects, and to determine any possible free radical involvement in these processes. Vanadium-stimulated oxidation of NADH was studied spectrophotometrically and by electron spin resonance spectroscopy. In 25 mM sodium phosphate buffer at pH 7. 4, vanadyl, (V(IV)), is slightly more effective in stimulating NADH oxidation than was vanadate (V(V)). Addition of a superoxide generating system, xanthine/xanthine oxidase, results in a marked increase in NADH oxidation by vanadyl, and …

Structure-Activity Relationships Of Retinoids In Developmental Toxicology, W. Brian Howard

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The teratogenic potency of retinoid analogs was determined in Syrian hamsters and compared to the teratogenic potency of all-trans-retinoic acid (all-trans-RA, ED₅₀ = 10.5 mg/kg). A total of 15 analogs having variations in the cyclohexene ring were evaluated following various amounts of single oral doses on day 8 of gestation. Retinoids containing a five- or six-membered ring were as teratogenic as all-trans-RA, provided they had sufficient lipophilic substituents on the ring. The same pattern emerged for retinoids that had six-membered aromatic ring substitution for the natural cyclohexene ring of vitamin A. Incorporation of a supplementary …

Theoretical Vibrational Study Of The Fx⋅⋅⋅O(Ch3)2 Hydrogen‐Bonded Complex, Y. Bouteiller, C. Mijoule, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

This paper presents the first ab initio attempt to reconstruct the observed band profile of the stretching fundamental v_FX (X=H,D) in the FX⋅⋅⋅O(CH₃)₂ hydrogen‐bonded system. The two‐dimensional potential energy surface V(r_FH,R_F⋅⋅⋅O) is evaluated by means of large basis set SCF calculations. The related force constants up to the fourth order are obtained via the analytical fit to a polynomial expansion. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The side bands of the …

Vibrational Frequencies And Intensities Of H‐Bonded And Li‐Bonded Complexes. H3n⋅⋅Hcl And H3n⋅⋅Licl, M. M. Szczesniak, I. J. Kurnig, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The geometries, energetics, and vibrational spectra are calculated for the two complexes at the SCF and correlated MP2 levels using the 6‐31G∗∗ basis set, augmented by a second set of d functions on Cl. While correlation represents an important factor in the binding of H₃ N⋅⋅HCl, it contributes little to the stronger Li bond. Unlike the HCl stretch ν_s which decreases substantially in frequency and is greatly intensified in H₃ N⋅⋅HCl, the frequency of the LiCl stretch undergoes an increase and little change is noted in its intensity, conforming to prior spectral measurements. The intensities of the …

Synthetic Studies Toward B-Alkylthiolanthionines, Hwa-Ok Kim

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Synthetic routes toward a B-alkylthiolanthionine derivative, as found in the quinomycin depsipeptide antibiotics, have been studied through a sequence involving as the key intermediates and steps (a) (S) - Z-[(benzyloxycarbonyl)amino]-3,3-dimethoxy-l-propanol (2), prepared from N-benzyloxycarbonyl-L-serine in 3 or 4 steps, (b) N-benzyloxycarbonyl- 0 - tetrahydropyranyl-B,B-(ethylsulfinylethylthio)-alaninol (4a), converted from 2, and (c) attempted Lewis acid catalyzed replacement of alkylsulfinyl function by thiol moiety of cysteine, which gave undesired products. Stability of protecting groups used in this study, which are N,0-isopropylidenyl and tetrahydropyranyl functions in N-protected-L-serinol 20 or 26, under acidic conditions was found to play an important role in determining the optical …

Structure, Energetics, And Vibrational Spectrum Of H2o–Hcl, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

H₂O–HCl is studied using a number of basis sets including 6‐31G∗∗ and variants which are augmented by a diffuse sp shell and a second set of d functions on O and Cl. Optimization of the geometry of the complex is carried out including explicitly electron correlation and counterpoise correction of the basis set superposition error (BSSE) at both the SCF and correlated levels. Correlation strengthens and shortens the H bond while BSSE correction leads to an opposite trend; these two effects are of different magnitude and hence cancel one another only partially. ΔH°(298 K) is …

Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hfvibrational Frequencies And Intensities Of H‐Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Frequencies and intensities are calculated by ab initio methods for all vibrational modes of the 1:1 H₃X–HF and 1:2 H₃X–HF–HF complexes (X=N,P). The HF stretching frequencies are subject to red shifts, roughly proportional to the strength of the H bond, and to manyfold increases in intensity. Although the intramolecular frequency shifts within the proton acceptors are relatively modest, the intensities of the NH₃ stretches are magnified by several orders of magnitude as a result of H bonding (in contrast to PH₃ which exhibits little sensitivity in this regard). …

Primary And Secondary Basis Set Superposition Error At The Scf And Mp2 Levels. H3n‐‐Li+ And H2o‐‐Li+, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The primary basis set superposition error (BSSE) results from the artificial lowering of the energy of each subunit of a pair by the presence of ‘‘ghost orbitals’’ of its partner. In addition, these ghost orbitals perturb the one‐electron properties of the molecule, causing a change in the interaction energy, an effect known as secondary BSSE which is not corrected by the counterpoise procedure. The primary and secondary BSSE are calculated for the interactions of NH₃ and H₂O with Li⁺, using a variety of different basis sets. It is found that the 2° BSSE can be …

Data Collection And Presentation Procedures For The U.S. Army's Chemical Hazard Assessment Warning System (Chaws), Michael H. Merry

All U.S. Government Documents (Utah Regional Depository)

This report describes the basic procedures and references more detailed documents for the operation of meteorological and air quality sensing instrumentation, data depiction and analysis systems for an incinerator pilot plant located at the Tooele Army Depot site near Salt Lake City, Utah. It discusses the site topography and climatology, sensor configuration, calibration, quality assurance and data reporting procedures for the monitoring system and demonstrates their compliance with applicable environmental regulations of United States Federal Government and the State of Utah.

The Potential Energy Surface Of (Nh3)2, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio calculations at the SCF and correlated levels are carried out to characterize the potential energy surface of the NH₃ dimer. The two basis sets used are 4‐31G∗ and a larger one containing two sets of d‐functions on N centers, 6‐31G∗∗ (1p, 2d). The only minimum occurring on the surface is a cyclic C_2h structure in which the two H‐bonding protons are displaced 42° from the N‐‐N axis. The surface contains a very shallow valley along the direction leading from this geometry to a single linear H bond although …

Correction Of The Basis Set Superposition Error In Scf And Mp2 Interaction Energies. The Water Dimer, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

There has been some discussion concerning whether basis set superposition error is more correctly evaluated using the full set of ghost orbitals of the partner molecule or some subset thereof. A formal treatment is presented, arguing that the full set is required at the Møller–Plesset level. Numerical support for this position is provided by calculation of the interaction energy between a pair of water molecules, using a series of moderate sized basis sets ranging from 6‐31G∗∗ to the [432/21] contraction suggested by Clementi and Habitz. These energies, at both the SCF and MP2 levels, behave erratically with respect to changes …

Comparison Of Proton Transfers In (S2h5)+ And (O2h5)+, L. Bigham, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The energetics and electronic rearrangements associated with proton transfer between S atoms in (H₂S–H–SH₂)⁺ are calculated using ab initio molecular orbital methods and compared with similar data in the first‐row analog (H₂O–H–OH₂)⁺. The full potential energy surface of (S₂H₅)⁺, calculated as a function of the H‐bond length as well as the position of the proton, contains two equivalent minima separated by a small energy barrier, whereas the surface of (O₂H₅)⁺ contains a single minimum corresponding to a symmetric …

Contribution Of Dispersion To The Properties Of H2s‐‐Hf And H2s‐‐Hcl, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio calculations are carried out using a doubly polarized basis set. Dispersion, evaluated by second‐order Møller–Plesset perturbation theory (MP2), is found to have a profound influence on the stabilities and structures of the H‐bonded complexes. The contribution of dispersion to the H‐bond energies of H₂S‐‐HF and H₂S‐‐HCl is 44% and 69%, respectively, placing this attractive term second in magnitude only to electrostatics. Reductions of the intermolecular distance of 0.17 and 0.34 Å result from inclusion of correlation effects. Nevertheless, the influence of dispersion upon the angular characteristics of the …

Influence Of Basis Set On The Calculated Properties Of (H3n–Hcl), Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The structure of (H₃N–HCl) is investigated by ab initio calculations using a number of different basis sets ranging from minimal to split valence. The effects of including a diffuse sp shell and d orbitals on Cl are considered as well. The geometries of the complex and the isolated subunits are fully optimized. Minimal basis sets (STO‐3G, STO‐6G, and MINI‐1) lead to an overestimate of the interaction between the subunits. Addition of d functions produces only a marginal improvement. The 3‐21G, 3‐21+G, MIDI‐1, and LP‐31G split‐valence sets erroneously predict an ion pair …

Photoaffinity Labeling Of The Antimycin Binding Site In Rhodopseudomonas Sphaeroides, Emily Wilson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The purpose of this study was to identify the site of interaction of antimycin with the ubiquinone-cytochrome b-c1 oxidoreductase in the photosynthetic bacteria, Rhodopseudomonas sphaeroides. To accomplish this goal, three areas of research were undertaken: the synthesis of a radiolabeled, photoaffinity analog of antimycin, identification of the inhibitory characteristics of this analog, and the photoaffinity labeling of the antimycin binding site. All three areas were accomplished.

The major finding of this study was the identification of an 11,000 dalton polypeptide as the predominantly labeled protein. Although this polypeptide was not exclusively labeled, it was consistently labeled and showed competition …

Effects Of Basis Set And Electron Correlation On The Calculated Properties Of The Ammonia Dimer, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio calculations are carried out for (NH₃)₂ with a 6‐31G∗∗(1p,2d) basis set containing diffuse polarization functions. Electron correlation is included via second‐order Møller–Plesset perturbation theory (MP2). At the SCF level, the equilibrium R(NN) distance is 3.54 Å and the interaction energy is −2.35 kcal/mol. Inclusion of correlation enhances the attraction substantially, increasing the energy to −4.05 kcal/mol and reducing the intermolecular separation by 0.20 Å. Comparison with previous results at the SCF level demonstrates a variety of errors including exaggerated dipole moments, underestimation of polarization …

Ab Initio Comparison Of H Bonds And Li Bonds. Complexes Of Lif, Licl, Hf, And Hcl With Nh3, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio calculations are carried out on the complexes H₃N–LiF, H₃N–LiCl and their analogs H₃N–HF and H₃N–HCl as well as the isolated subunits. Double‐zeta basis sets, augmented by two sets of polarization functions, are used in conjunction with second‐order Moller–Plesset perturbation theory (MP2) for evaluation of electron correlation effects. The Li bonds are found to be substantially stronger than their H‐bonding counterparts, due in large measure to the greater dipole moments of the LiX subunits. Correlation has a large effect on the geometry and energetics of …

Studies Of Dispersion Energy In Hydrogen‐Bonded Systems. H2o–Hoh, H2o–Hf, H3n–Hf, Hf–Hf, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Dispersion energy is calculated in the systems H₂O–HOH, H₂O–HF, H₃N–HF, and HF–HF as a function of the intermolecular separation using a variety of methods. M≂ller–Plesset perturbation theory to second and third orders is applied in conjunction with polarized basis sets of 6‐311G∗∗ type and with an extended basis set including a second set of polarization functions (DZ+2P). These results are compared to a multipole expansion of the dispersion energy, based on the Unsöld approximation, carried out to the inverse tenth power of the intermolecular distance. Pairwise evaluation is also carried out using both atom–atom …

Proton Transfers Between First‐ And Second‐Row Atoms: (H2ohsh2)+ And (H3nhsh2)+, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio molecular orbital methods are used to study the transfer of the central proton along the hydrogen bonds in (H₂OHSH₂)⁺ and (H₃NHSH₂)⁺. Proton transfer potentials are generated using the 4‐31G∗ basis set at the Hartree–Fock level for various values for the hydrogen bond length R(XS). Full geometry optimizations are carried out at each stage of proton transfer. The barrier to proton transfer increases as the hydrogen bond is lengthened. For a given bond length, the highest barriers are observed for transfer from …

Ab Initio Study Of Fh–Ph3 And Clh–Ph3 Including The Effects Of Electron Correlation, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio calculations are carried out for FH–PH₃ and ClH–PH₃ using a basis set including two sets of polarization functions. Electron correlation is incorporated via Møller–Plesset perturbation theory to second and (in part) to third orders. The basis set is tested and found to produce satisfactory treatments of subsystem properties including geometries and dipole moments as well as the proton affinity and inversion barrier of PH₃. Electron correlation is observed to markedly enhance the interaction between PH₃ and the hydrogen halides. Its contribution to the complexation energy is 30% …

Theoretical Study Of H2o–Hf And H2o–Hcl: Comparison With Experiment, M. M. Szczesniak, Steve Scheiner, Y. Bouteiller

Chemistry and Biochemistry Faculty Publications

The H bonds in H₂O–HF and H₂O–HCl are studied and compared using ab initio molecular orbital methods and the results compared to experimental data. Basis sets used are: (i) triple valence 6‐311G∗∗ and (ii) double ζ with two sets of polarization functions. Electron correlation, included via second‐ and third‐order Møller–Plesset perturbation theory, is found to have profound effects on both systems, particularly H₂O–HCl. Both H bonds are strengthened substantially with a concomitant reduction in length. H‐bond energies and geometries calculated at correlated levels are in excellent accord with …

Photochemical Energy Storage (Photosensitized Isomerization Of Norbornadiene To Quadricyclane By Copper(I) Complexes), Dennis J. Fife

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This research has focused on the sensitized photoisomerization step of a solar energy storage system based on the interconversion of norbornadiene (NBD) and quadricyclane (Q). Sensitizers studied in the photoisomerization were arylphosphine complexes of copper(I) halides [(Ph₃P)₃CuX, (MePh₂P)₃CuX, (DIPHOS)CuCl; X = Cl, Br, I and DIPHOS = Ph₂P(CH₂)₂PPh₂]. The lowest electronic excited state of the complexes can be an effective triplet energy sensitizer as evidenced by a maximum quantum yield of 1.0 with (MePh₂P)₃CuX. The sensitization mechanism of the L …