B3LYP/6-311++G** study of alpha- and beta-D-glucopyranose and 1,5-anhydro-D-glucitol: 4C1 and 1C4 chairs, (3,O)B and B(3,O) boats, and skew-boat conformations

Geometry optimization, at the B3LYP/6-311++G** level of theory, was carried out on 4C1 and 1C4 chairs, (3,O)B and B(3,O) boats, and skew-boat conformations of alpha- and beta-D-glucopyranose. Similar calculations on 1,5-anhydro-D-glucitol allowed examination of the effect of removal of the 1-hydroxy group on the energy preference of the hydroxymethyl rotamers. Stable minimum energy boat conformers of glucose were found, as were stable skew boats, all having energies ranging from approximately 4-15 kcal/mol above the global energy 4C1 chair conformation. The 1C4 chair electronic energies were approximately 5-10 kcal/mol higher than the 4C1 chair, with the 1C4 alpha-anomers being lower in energy than the beta-anomers. Zero-point energy, enthalpy, entropy, and relative Gibbs free energies are reported at the harmonic level of theory. The alpha-anomer 4C1 chair conformations were found to be approximately 1 kcal/mol lower in electronic energy than the beta-anomers. The hydroxymethyl gt conformation was of lowest electronic energy for both the alpha- and beta-anomers. The glucose alpha/beta anomer ratio calculated from the relative free energies is 63/37%. From a numerical Hessian calculation, the tg conformations were found to be approximately 0.4-0.7 kcal/mol higher in relative free energy than the gg or gt conformers. Transition-state barriers to rotation about the C-5-C-6 bond were calculated for each glucose anomer with resulting barriers to rotation of approximately 3.7-5.8 kcal/mol. No energy barrier was found for the path between the alpha-gt and alpha-gg B(3,O) boat forms and the equivalent 4C1 chair conformations. The alpha-tg conformation has an energy minimum in the 1S3 twist form. Other boat and skew-boat forms are described. The beta-anomer boats retained their starting conformations, with the exception of the beta-tg-(3,O)B boat that moved to a skew form upon optimization.     

DFT study of alpha- and beta-D-galactopyranose at the B3LYP/6-311++G** level of theory

Forty-one conformations of alpha- and beta-d-galactopyranose were geometry optimized using the B3LYP density functional and 6-311++G** basis set. Full geometry optimization was performed on different ring geometries and different hydroxymethyl rotamers (gg/gt/tg). Analytically derived Hessians were used to calculate zero point energy, enthalpy, and entropy. The lowest energy and free-energy conformation found is the alpha-gg-(4)C(1)-c chair conformation, which is of lower electronic and free energy than the lowest energy alpha-d-glucopyranose conformer because of favorable hydrogen-bonding interactions. The in vacuo calculations showed considerable ( approximately 2.2kcal/mol) energetic preference for the alpha over the beta anomer for galactopyranose in both the (4)C(1) and (1)C(4) chair conformations. Results are compared to glucopyranose and mannopyranose calculations in vacuo. Boat and skew-boat forms were found that remained stable upon gradient optimization, although many starting conformations moved to other boat forms upon optimization. As with glucopyranose and mannopyranose, the orientation and interaction of the hydroxyl groups make the most significant contributions to the conformation-energy relationship in vacuo.     

B3LYP/6-311++G** geometry-optimization study of pentahydrates of alpha- and beta-D-glucopyranose

Five water molecules were placed in 37 different configurations around alpha- and beta-D-glucopyranose in the gt, gg, and tg conformational states, and the glucose-water complexes were geometry optimized using density functionals at the B3LYP/6-311++G** level of theory. The five water molecules were organized in space and energy minimized using an empirical potential, AMB02C, and then further geometry optimized using DFT algorithms to minimum energy positions. Electronic energy, zero point vibrational energy, enthalpy, entropy, stress energy on glucose and the water cluster, hydrogen-bond energy, and relative free energy were obtained for each configuration using thermodynamic procedures and an analytical Hessian program. The lowest energy complex was that of a clustering of water molecules around the 1- and 6-hydroxyl positions of the beta-gt anomer. Configurations in which the water molecules created a favorable network completely around and under glucose were found to have low energy for both alpha and beta anomers. Calculation of the alpha/beta anomeric ratio using the zero point corrected energy gave, approximately 32/68%, highly favoring the beta anomer in agreement with the experimental approximately 36/64% value. This ratio is better than the approximately 50/50% ratio found in our previous monohydrate study. An approximate hydroxymethyl population was obtained by noting average relative energies among the three conformational states, gt, gg, and tg. In the beta anomer complexes the gt conformation was favored over the gg state, while in the alpha anomer complexes the gg state was favored over the gt conformation, with the tg conformations all being of higher energy making little or no contribution to the rotamer population. Some geometry variances, found between glucose in vacuo and glucose after interaction with water molecules, are described and account for some observed C-5-C-6 bond length anomalies reported by us previously for the vacuum glucose structures.     

DFT study of alpha- and beta-D-allopyranose at the B3LYP/6-311++G ** level of theory

One hundred and two conformations of alpha- and beta-D-allopyranose, the C-3 substituted epimer of glucopyranose, were geometry optimized using the density functional, B3LYP, and the basis set, 6-311++G **. Full geometry optimization was performed on different ring geometries and on the hydroxymethyl rotamers (gg/gt/tg). Analytically derived Hessians were used to calculate zero point energy, enthalpy, and entropy. The lowest energy and free energy conformation found is the alpha-tg(g-)-4C1-c conformation, which is only slightly higher in electronic (approximately 0.2 kcal/mol) and free energy than the lowest energy alpha-D-glucopyranose. The in vacuo calculations showed a small (approximately 0.3 kcal/mol) energetic preference for the alpha- over the beta-anomer for allopyranose in the 4C1 conformation, whereas in the 1C4 conformation a considerable (approximately 1.6 kcal/mol) energetic preference for the beta- over the alpha-anomer for allopyranose was encountered. The results are compared to previous aldohexose calculations in vacuo. Boat and skew forms were found that remained stable upon gradient optimization although many starting boat conformations moved to other skew forms upon optimization. As found for glucose, mannose, and galactose the orientation and interaction of the hydroxyl groups make the most significant contributions to the conformation/energy relationship in vacuo. A comparison of different basis sets and density functionals is made in the Discussion section, confirming the appropriateness of the level of theory used here.     

An investigation of the pyranose ring interconversion path of alpha-L-idose calculated using density functional theory

The interconversion pathways of the pyranose ring conformation of alpha-L-idose from a (4)C1 chair to other conformations were investigated using density functional calculations. From these calculations, four different ring interconversion paths and their transition state structures from the (4)C1 chair to other conformations, such as B(3,O), and (1)S3, were obtained. These four transition-state conformations cover four possible combinations of the network patterns of the hydroxyl group hydrogen bonds (clockwise and counterclockwise) and the conformations of the primary alcohol group (tg and gg). The optimized conformations, transition states, and their intrinsic reaction coordinates (IRC) were all calculated at the B3LYP/6-31G** level. The energy differences among the structures obtained were evaluated at the B3LYP/6-311++G** level. The optimized conformations indicate that the conformers of (4)C1, (2)S(O), and B(3,O) have similar energies, while (1)S3 has a higher energy than the others. The comparison of the four transition states and their ring interconversion paths, which were confirmed using the IRC calculation, suggests that the most plausible ring interconversion of the alpha-L-idopyranose ring occurs between (4)C1 and B(3,O) through the E3 envelope, which involves a 5.21 kcal/mol energy barrier.     

DFT study of alpha- and beta-D-mannopyranose at the B3LYP/6-311++G** level

Thirty-five conformations of alpha- and beta-d-mannopyranose, the C-2 substituted epimer of glucopyranose, were geometry optimized using the density functional (B3LYP), and basis set (6-311++G**). Full geometry optimization was performed on the hydroxymethyl rotamers (gg/gt/tg) and an analytical hessian program was used to calculate the harmonic vibrational frequencies, zero point energy, enthalpy, and entropy. The lowest energy conformation investigated is the beta-tg in the (4)C(1) chair conformation. The in vacuo calculations showed little energetic preference for either the alpha or beta anomer for mannopyranose in the (4)C(1) chair conformation. Results are compared to similar glucopyranose calculations in vacuo where the alpha anomer is approximately 1kcal/mol lower in electronic energy than the beta anomer. In the case of the generally higher energy (1)C(4) chair conformations, one low-energy, low-entropy beta-gg-(1)C(4) chair conformation was identified that is within approximately 1.4kcal/mol of the lowest energy (4)C(1) conformation of mannopyranose. Other (1)C(4) chair conformations in our investigation are approximately 2.9-7.9kcal/mol higher in overall energy. Many of the (3,O)B, B(3,O), (1,4)B, and B(1,4) boat forms passed through transitions without barriers to (1)S(3), (5)S(1), (1)S(5) skew forms with energies between approximately 3.6 and 8.9kcal/mol higher in energy than the lowest energy conformation of mannopyranose. Boat forms were found that remained stable upon gradient optimization. As with glucopyranose, the orientation and interaction of the hydroxy groups make a significant contribution to the conformation/energy relationship in vacuo.     

DFT conformation and energies of amylose fragments at atomic resolution. Part 1: syn forms of α-maltotetraose

DFT optimization studies of 90 syn α-maltotetraose (DP-4) amylose fragments have been carried out at the B3LYP/6-311++G∗∗ level of theory. The DP-4 fragments studied include V-helix, tightly bent conformations, a boat, and a ¹C₄ conformer. The standard hydroxymethyl rotamers (gg, gt, tg) were examined at different locations in the residue sequence, and their influence on the bridge conformations ?/ψ values and conformer energy is described. Hydroxyl groups were considered to be homodromic, that is, they are either in the all clockwise, ‘c’, or all counterclockwise, ‘r’. Energy differences between conformations are examined in order to assess the stability of the different conformations and to identify the sources of energy that dictate amylose polymer formation. A small nearly cyclic compact structure is of low energy as one would expect when these flexible molecules are studied in vacuo. Many conformations in which the only differences are a single hydroxymethyl variation in the residue sequence show similar energies and bridge conformations, with trends being a result of the hydroxymethyl as well as hydroxyl orientation. In general the ‘c’ structures are of lower energy than the ‘r’ structures, although this is only true for the in vacuo state. The solvent dependence on conformational preference of several low-energy DP-4 structures was investigated via the continuum solvation method COSMO. These results suggest that the ‘r’ structures may be favored for fully solvated molecules.     

A comparative proton magnetic resonance conformational study of the tRNA "wobble" nucleosides 5-carboxymethyl-, 5-methoxycarbonylmethyl-, and 5-carbamoylmethyl-uridine

The 270-MHz proton magnetic resonance spectra of 5-carboxymethyluridine, 5-methoxycarbonylmethyluridine, and 5-carbamoylmethyluridine have been obtained, and analyzed iteratively using LAOCOON 3. A standard treatment of the obtained data reveals that in each the 5-substituent produces no significant alteration in the furanose puckers, their equilibrium state, and the relative populations of the gg, tg, and gt exocyclic hydroxymethyl rotamers relative to uridine. The analogous similarity in furanose chemical shifts suggests that these derivatives favor the anti glycosyl state. The 5-substituent may act at the polynucleotide level in modulating the conformation and interaction(s) of the anticodon loop.     

Evaluation of carbohydrate molecular mechanical force fields by quantum mechanical calculations

A quantitative evaluation of 20 second-generation carbohydrate force fields was carried out using ab initio and density functional methods. Geometry-optimized structures (B3LYP/6-31G(d)) and relative energies using augmented correlation consistent basis sets were calculated in gas phase for monosaccharide carbohydrate benchmark systems. Selected results are: (i). The interaction energy of the alpha-d-glucopyranose.H(2)O heterodimer is estimated to be 4.9 kcal/mol, using a composite method including terms at highly correlated (CCSD(T)) level. Most molecular mechanics force fields are in error in this respect; (ii). The (3)E envelope (south) pseudorotational conformer of methyl 5-deoxy-beta-d-xylofuranoside is 0.66 kcal/mol more stable than the (3)E envelope (north) conformer and the alpha-anomer of methyl d-glucopyranoside is 0.82 kcal/mol more stable than the beta-anomer; (iii). The relative energies of the (gg, gt and tg) rotamers of methyl alpha-d-glucopyranoside and methyl alpha-d-galactopyranoside are (0.13, 0.00, 0.15) and (0.64, 0.00, 0.77) kcal/mol, respectively. The results of the quantum mechanical calculations are compared with the results of calculations using the 20 second-generation carbohydrate force fields. No single force field is consistently better than the others for all the test cases. A statistical assessment of the performance of the force fields indicates that CHEAT(95), CFF, certain versions of Amber and of MM3 have the best overall performance, for these gas phase monosaccharide systems.     

DFT conformation and energies of amylose fragments at atomic resolution. Part 2: ‘band-flip’ and ‘kink’ forms of α-maltotetraose

In Part 2 of this series of DFT optimization studies of α-maltotetraose, we present results at the B3LYP/6-311++G∗∗ level of theory for conformations denoted ‘band-flips’ and ‘kinks’. Recent experimental X-ray studies have found examples of amylose fragments with conformations distorted from the usual syn forms, and it was of interest to examine these novel structural motifs by the same high-level DFT methods used in Part 1. As in Part 1, we have examined numerous hydroxymethyl rotamers (gg, gt, and tg) at different locations in the residue sequence, and include the two hydroxyl rotamers, the clockwise ‘c’ and counterclockwise ‘r’ forms. A total of fifty conformations were calculated and energy differences were found to attempt to identify those sources of electronic energy that dictate stressed amylose conformations. Most stressed conformations were found to have relative energies considerably greater (i.e., ∼4 to 12 kcal/mol) than the lowest energy syn forms. Relative energy differences between ‘c’ and ‘r’ forms are somewhat mixed with some stressed conformations being ‘c’ favored and some ‘r’ favored, with the lowest energy ‘kink’ form being an all-gg-r conformation with the ‘kink’ in the bc glycosidic dihedral angles. Comparison of our calculated structures with experimental results shows very close correspondence in dihedral angles.     

Concerning the solvent effect in the tautomerism of uracil, 5-fluorouracil, and thymine by density-functional theory and ab initio calculations

The tautomerism of uracil, 5-fluorouracil, and thymine has been investigated in the gas phase and in solution. Electron correlation effects were included in ab initio computations at the MP2 level, and DFT calculations were performed using the B3LYP level. Full geometry optimizations were conducted at the HF/6-31G**, HF/6-31+G**, and B3LYP/6-31+G** levels. Single-point MP2/6-31+G** calculations were performed on the HF/6-31+G** optimized geometries. The influence of the solvent was examined from self-consistent reaction field calculations performed with )=2.21 (1,4-dioxane) and )=78.54 (water). The calculated relative free energies ((G) indicate that substitution of uracil at the position group does not change the relative free energy order of the uracil tautomers in the gas phase and in 1,4-dioxane (except at the MP2 level) whereas this ordering changes in water. Attachment of a fluorine atom changes the relative free energy order of uracil tautomers in the gas phase and in solution.     

New Karplus equations for 2JHH, 3JHH, 2JCH, 3JCH, 3JCOCH, 3JCSCH, and 3JCCCH in some aldohexopyranoside derivatives as determined using NMR spectroscopy and density functional theory calculations

The (1)H-(13)C coupling constants of methyl alpha- and beta-pyranosides of D-glucose and D-galactose have been measured by one-dimensional and two-dimensional (1)H-(13)C heteronuclear zero and double quantum, phase sensitive J-HMBC spectra to determine a complete set of coupling constants ((1)J(CH), (2)J(CH), (3)J(CH), (2)J(HH), and (3)J(HH)) within the exocyclic hydroxymethyl group (CH(2)OH) for each compound. In parallel with these experimental studies, structure, energy, and potential energy surfaces of the hydroxymethyl group for these compounds were determined employing quantum mechanical calculations at the B3LYP level using the 6-311++G( * *) basis set. Values of the vicinal coupling constants involving (1)H and (13)C in the C5-C6 (omega) and C6-O6 (theta) torsion angles in the aldohexopyranoside model compounds were calculated with water as the solvent using the PCM method. To test the relationship between (3)J(CXCH) (X=C, O, S) and torsion angle C1-X (phi) around the anomeric center, the conformations of 24 derivatives of glucose and galactose, which represent sequences of atoms at the anomeric center of C-glycosides (C-C bond), O-glycosides (C-O bond), thioglycosides (C-S bond), glycosylamines (C-N bond), and glycosyl halides (C-halogen (F/Cl) bond) have been calculated. Nonlinear regression analysis of the coupling constants (1)J(C1,H1), (2)J(C5,H6R), (2)J(C5,H6S), (2)J(C6,H5), (3)J(C4,H6R), (3)J(C4,H6S), (2)J(H6R,H5), and (3)J(H5,H6R) as well as (3)J(CXCH) (X=C, O, S) on the dihedral angles omega, theta, and phi have yielded new Karplus equations. Good agreement between calculated and experimentally measured coupling constants revealed that the DFT method was able to accurately predict J-couplings in aqueous solutions.     

Theoretical study on the ground state intramolecular proton transfer (IPT) and solvation effect in two Schiff bases formed by 2-aminopyridine with 2-hydroxy-1- naphthaldehyde and 2-hydroxy salicylaldehyde

The tautomerization mechanism the isolated and monohydrated forms of two Schiff bases 1 and 2, and the effect of solvation on the proton transfer from enol-imine form to the keto-enamine form have been investigated using the B3LYP hybrid density functional method at the 6-31G** basis set level. The barrier heights for H₂O-assisted reactions are significantly lower than that of unassisted tautomerization reaction in the gas phase. Nonspecific solvent effects have also been taken into account by using the continuum model (IPCM) of four different solvent. The tautomerization energies and the potential energy barriers are decreased by increasing solvent polarity. Figure The tautomerization mechanism the isolated and monohydrated forms of two Schiff bases 1 and 2, and the effect of solvation on the proton transfer from enol-imine form to the keto-enamine form have been investigated using the B3LYP hybrid density functional method at the 6-31G** basis set level     

Crystal and molecular structure of methyl 4-O-methyl-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside

The cellulose model compound methyl 4-O-methyl-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside (6) was synthesised in high overall yield from methyl beta-D-cellobioside. The compound was crystallised from methanol to give colourless prisms, and the crystal structure was determined. The monoclinic space group is P2(1) with Z=2 and unit cell parameters a=6.6060 (13), b=14.074 (3), c=9.3180 (19) A, beta=108.95(3) degrees. The structure was solved by direct methods and refined to R=0.0286 for 2528 reflections. Both glucopyranoses occur in the 4C(1) chair conformation with endocyclic bond angles in the range of standard values. The relative orientation of both units described by the interglycosidic torsional angles [phi (O-5' [bond] C-1' [bond] O-4 [bond] C-4) -89.1 degrees, Phi (C-1' [bond] O-4 [bond] C-4 [bond] C-5) -152.0 degrees] is responsible for the very flat shape of the molecule and is similar to those found in other cellodextrins. Different rotamers at the exocyclic hydroxymethyl group for both units are present. The hydroxymethyl group of the terminal glucose moiety displays a gauche-trans orientation, whereas the side chain of the reducing unit occurs in a gauche-gauche conformation. The solid state (13)C NMR spectrum of compound 6 exhibits all 14 carbon resonances. By using different cross polarisation times, the resonances of the two methyl groups and C-6 carbons can easily be distinguished. Distinct differences of the C-1 and C-4 chemical shifts in the solid and liquid states are found.     

Study of the hydrogen bond in different orientations of adenine-thymine base pairs: An <Emphasis Type="Italic">ab initio</Emphasis> study

In order to gain deeper insight into structure, charge distribution, and energies of A-T base pairs, we have performed quantum chemical ab initio and density functional calculations at the HF (Hartree-Fock) and B3LYP levels with 3-21G*, 6-31G*, 6-31G**, and 6-31++G** basis sets. The calculated donor-acceptor atom distances in the Watson-Crick A-T base pair are in good agreement with the experimental mean values obtained from an analysis of 21 high resolution DNA structures. In addition, for further correction of interaction energies between adenine and thymine, the basis set superposition error (BSSE) associated with the hydrogen bond energy has been computed via the counterpoise method using the individual bases as fragments. In the Watson-Crick A-T base pair there is a good agreement between theory and experimental results. The distances for (N2...H23-N19), (N8-H13...O24), and (C1...O18) are 2.84, 2.94, and 3.63 A, respectively, at B3LYP/6-31G** level, which is in good agreement with experimental results (2.82, 2.98, and 3.52 A). Interaction energy of the Watson-Crick A-T base pair is -13.90 and -10.24 kcal/mol at B3LYP/6-31G** and HF/6-31G** levels, respectively. The interaction energy of model (9) A-T base pair is larger than others, -18.28 and -17.26 kcal/mol, and for model (2) is the smallest value, -13.53 and -13.03 kcal/mol, at B3LYP/6-31G** and B3LYP/6-31++G** levels, respectively. The computed B3LYP/6-31G** bond enthalpies for Watson-Crick A-T pairs of -14.4 kcal/mol agree well with the experimental results of -12.1 kcal/mol deviating by as little as -2.3 kcal/mol. The BSSE of some cases is large (9.85 kcal/mol) and some is quite small (0.6 kcal/mol).     

Catalytic mechanism of the inverting N-acetylglucosaminyltransferase I: DFT quantum mechanical model of the reaction pathway and determination of the transition state structure

The complex N-glycan structures on glycoproteins play important roles in cell adhesion and recognition events in metazoan organisms. A critical step in the biosynthetic pathway leading from high mannose to these complex structures includes the transfer of N-acetylglucosamine (GlcNAc) to a mannose residue by the inverting N-acetylglucosaminyltransferase I (GnT-I). The catalytic mechanism of this enzymatic reaction is explored herein using DFT quantum chemical methods. The computational model used to follow the reaction is based on the X-ray crystallographic structure of GnT-I and contains 127 atoms that represent fragments of residues critical for the substrate binding and catalysis. The mechanism of the catalytic reaction was monitored by means of a 2D potential energy map calculated as a function of predefined reaction coordinates at the B3LYP/6-31G** level. This potential energy surface revealed one transition state associated with a reaction pathway following a concerted mechanism. The reaction barrier was estimated, and the structure of the transition state was characterized at the B3LYP/6-311++G**// B3LYP/6-31G** level.     

Theoretical potential functions and vibrational analysis for halocarbonyl azides CXO-NNN (X=F,Cl and Br)

The structural stability of halocarbonyl azides CXO-NNN (X=F, Cl and Br) was investigated by DFT and MP2 calculations using the 6-311++G** basis set. From the calculations, the molecules were found to have an s-cis<--> s-trans conformational equilibrium with cis being the lower -energy form. Full energy optimizations were carried out for the transition states and the minima at the B3LYP/6 -311++G** and MP2/6 -311++G** levels, from which the rotational barriers were calculated to be of the order 8-10 kcal x mol(-1). The vibrational frequencies were computed at the DFT -B3LYP level and the vibrational assignments for the normal modes of the stable conformers were made on the basis of normal coordinate calculations.     

DFT studies of the conversion of four mesylate esters during reaction with ammonia

The energetics of the Menshutkin-like reaction between four mesylate derivatives and ammonia have been computed using B3LYP functional with the 6-31+G** basis set. Additionally, MPW1K/6-31+G** level calculations were carried out to estimate activation barrier heights in the gas phase. Solvent effect corrections were computed using PCM/B3LYP/6-31+G** level. The conversion of the reactant complexes into ion pairs is accompanied by a strong energy decrease in the gas phase and in all solvents. The ion pairs are stabilized with two strong hydrogen bonds in the gas phase. The bifurcation at C2 causes a significant activation barrier increase. Also, bifurcation at C5 leads to noticeable barrier height differentiation. Both B3LYP/6-31+G** and MPW1K/6-31+G** activation barriers suggest the reaction 2 (2a?+?NH₃) to be the fastest in the gas phase. The reaction 4 is the slowest one in all environments.

Specificity or affinity of cytotoxic T cells for self H-2K determinants apparently does not change between primary and secondary responses to ectromelia virus infection.

Lysis of virus-infected target cells by virus-specific cytotoxic T cells occurs where donors of T cells and targets share either H-2K or H-2D genes. The effect of four H-2K mutations on virus-induced antigens recognized by cytotoxic T cells from in vitro secondary response to infection was studied. B10.A(5R) cytotoxic T cells (which share the K end of H-2 with the mutant strains, except for the mutated gene(s)) efficiently killed virus-infected macrophage targets from mutant strains B6-H-2bg1 and B6-H-2bg2, were less effective against B6-H-2bh and did not appear to be cytotoxic for B6.C-H-2ba target cells. Conversely, B6-H-Ibg1 and B6-H-2bg2 cytotoxic T cells were more effective in killing virus-infected B10.A(5R) macrophages than B6-H-2bh and B6.C-H-2ba cytotoxic cells respectively. In addition, B6-H-2bg1 and B6-H-2bg2 cells appeared to be only slightly different from wild-type with respect to the interaction between virus-infected cells and T cells. The data obtained suggested that virus-induced antigenic patterns on infected B6.C-H-2ba (mutant) cells are more different antigenically from those on wild-type cells than are those on infected cells from the other mutants, B6-H-2bh, B6-H-2bg1 and B6-H-2bh2. This agrees with previous data using primary cytotoxic T cells and thus suggests that no detectable change in the affinity or specificity of cytotoxic T cell receptors occurs between primary and secondary responses to infection. These findings are also discussed in relation to the exclusion of T cells with receptors for H-2K determinants that are common to the mutants and wild-type, from the response to virus-infected self cells.     

Structural, IR, and EPR studies of the bis(methoxyacetato)diaquo-copper(II) complex

The structure, stability, and the IR, and EPR spectroscopic properties of bis(methoxyacetato)diaquo-copper(II) were studied both experimentally using FT-IR and theoretically using B3LYP/6-31G**, B3LYP/6-311G, BWP91/6-31G** methods. The same approaches were used to calculate the harmonic frequencies and to compare them to the experimental solid state values. The g-tensors are calculated using the NMR/GIAO computational method.