Thermal and photochemical cycloaddition reactions of thiocarbonyls: a qualitative molecular orbital analysis

A comprehensive analysis of thermal and photochemical reactions of thiocarbonyls has been undertaken within the PMO framework employing MINDO/3 orbital energies and wavefunctions. The model is generally successful in rationalizing the observed regiochemistry of such reactions. In particular, the indicated regiochemistry for [4 + 2] thermal cycloadditions of saturated thiones to 2-substituted dienes, for the dimerization of α,β-unsaturated thiones, and for the photochemical cycloadditions of thioketones and thioenones are all in agreement with experimental observations. Interesting predictions are also made concerning cycloadditions of saturated, conjugated, and arylalkyl thiones which have not yet been studied experimentally. The analysis reveals the decisive role played by secondary orbital interactions in determining the observed product selectivity in the photochemical reactions between thioenone and olefins.

Polarization Caging in Diffusion-Controlled Electron Transfer Reactions in Solution

In some bimolecular diffusion-controlled electron transfer (ET) reactions such as ion recombination (IR), both solvent polarization relaxation and the mutual diffusion of the reacting ion pair may determine the rate and even the yield of the reaction. However, a full treatment with these two reaction coordinates is a challenging task and has been left mostly unsolved. In this work, we address this problem by developing a dynamic theory by combining the ideas from ET reaction literature and barrierless chemical reactions. Two-dimensional coupled Smoluchowski equations are employed to compute the time evolution of joint probability distribution for the reactant (P-(1)(X,R,t)) and the product (p((2))(X,R,t)), where X, as is usual in ET reactions, describes the solvent polarization coordinate and R is the distance between the reacting ion pair. The reaction is described by a reaction line (sink) which is a function of X and R obtained by imposing a condition of equal energy on the initial and final states of a reacting ion pair. The resulting two-dimensional coupled equations of motion have been solved numerically using an alternate direction implicit (ADI) scheme (Peaceman and Rachford, J. Soc. Ind. Appl. Math. 1955, 3, 28). The results reveal interesting interplay between polarization relaxation and translational dynamics. The following new results have been obtained. (i) For solvents with slow longitudinal polarization relaxation, the escape probability decreases drastically as the polarization relaxation time increases. We attribute this to caging by polarization of the surrounding solvent, As expected, for the solvents having fast polarization relaxation, the escape probability is independent of the polarization relaxation time. (ii) In the slow relaxation limit, there is a significant dependence of escape probability and average rate on the initial solvent polarization, again displaying the effects of polarization caging. Escape probability increases, and the average rate decreases on increasing the initial polarization. Again, in the fast polarization relaxation limit, there is no effect of initial polarization on the escape probability and the average rate of IR. (iii) For normal and barrierless regions the dependence of escape probability and the rate of IR on initial polarization is stronger than in the inverted region. (iv) Because of the involvement of dynamics along R coordinate, the asymmetrical parabolic (that is, non-Marcus) energy gap dependence of the rate is observed.

Isolation and characterization of heat-stable allergens from shrimp (Penaeus indicus)

Shrimp are among the more common causes of immediate hypersensitivity reactions to food. To characterize better the allergenic substances within shrimp, extracts from heated shrimp were systematically examined with solid-phase radioimmunoassay and sera from patients clinically sensitive to shrimp. Two heat-stable protein allergens, designated as Sa-I and Sa-II, were identified from boiled shrimp (Penaeus indicus) extracts. Sa-I was isolated by ultrafiltration, Sephadex G-25, and diethylaminoethyl-Sephacel chromatography, whereas Sa-II, the major allergen, was purified by successive chromatography on diethylaminoethyl-Sephacel, Bio-Gel P-200, and Sepharose 4B columns. Sa-I, which was homogeneous by polyacrylamide gel electrophoresis (PAGE), elicited a single band on sodium dodecyl sulfate-PAGE corresponding to a molecular weight of 8.2 kd. Sa-II was also found to be homogeneous by PAGE, crossed immunoelectrophoresis, and immunoblotting. On sodium dodecyl sulfate-PAGE, it elicited a single band with a molecular weight of 34 kd. Sa-II was found to contain 301 amino acid residues and was particularly rich in glutamate/glutamine and aspartate/asparagine. Solid-phase radioimmunoassay-inhibition studies revealed that Sa-I and Sa-II share 54% of the allergenic epitopes, suggesting that Sa-I may be a fragment of Sa-II.SDS-PAGE, Sodium dodecyl sulfate-polyacrylamide gel electrophoresis; MW, Molecular weight; BSA, Bovine serum albumin; DEAE, Diethylaminoethyl; SPRIA, Solid-phase radioimmunoassay; CIE, Crossed immunoelectrophoresis .

Microfoundations of HRM effects: Individual and Collective Attitudes and Performance

Previous research on Human Resource Management (HRM) has focused extensively on the potential relationships between the use of HRM practices and organizational performance. Extant research in HRM has been based on the underlying assumption that HRM practices can enhance organizational performance through their impact on positive employee attitudes and performance, that is, employee reactions to HRM. At the current state of research however, it remains unclear how employees come to perceive and react to HRM practices and to what extent employees in organizations, units and teams react to such practices in similar or widely different ways. In fact, recent HRM studies indicate that employee reactions to HRM may be far less homogeneous than assumed. This raises the question of whether or not the linkage between HRM and organizational outcomes can be explained by employee reactions in terms of attitudes and performance, if these reactions are largely idiosyncratic. Accordingly, this thesis aims to shed light on the processes that shape individuals’ reactions to HRM practices and how these processes may influence the variance or sharedness in such reactions among employees in organizations, units and teams. By theoretically developing and empirically examining the effects of employee perceptions of HRM practices from the perspective of ‘HRM as signaling’ and psychological contract theory, the main contributions of this thesis focus on the following research questions: i) How employee perceptions of the HRM practices relate to individual and collective employee attitudes and performance. ii) How employee perceptions of HRM practices relates to variance in employee attitudes and performance. iii) How collective employee performance mediates the relationship between employee perceptions of HRM practices and organizational performance. Regarding the first research questions the findings indicate that individuals do respond positively to HRM practices by adjusting their felt obligations towards the employer. This finding is in line with the idea of HRM as a signaling device where each HRM practice, implicitly or explicitly, sends signals to employees about promised rewards (inducements) and behaviors (obligations) expected in return. The relationship was also confirmed at the group level of analysis. What is more, variance was found to play an important role in that employee groups with more similar perceptions about the HRM system displayed a stronger relationship between HRM and employee obligations. Concerning the second question the findings were somewhat contradictory in that a strong HRM system was found negatively related to variance in employee performance but not employee obligations. Regarding the third question, the findings confirmed linkages between the HRM system and organizational performance at the group level and the HRM system and employee performance at the individual level. Also, the entire chain of links from the HRM system through variance in employee performance, and further through the level of employee performance to organizational performance was significant.

Reactions of tetrahalogeno-o-benzoquinones—Part VII. Reaction of alkyl-2-naphthols with tetrachloro-o-benzoquinone

Reaction of 8-methyl-2-naphthol (4a) with the quinone3 gave a mixture of 8-methyl-2,2-(tetrachlorohenylenedioxy)naphthalen-1(2H)-one (1b) and 8-methyl-1,1-(tetrachloro-o-phenylenedioxy)naphthalen-2(1H)-one (2b) in almost equal amounts. Similarly, reaction of the naphthols (4b), (4d) and (4e) with3 gave the corresponding dienones (1c &2c), (1e &2e) and (1f &2f) in almost equal amounts. Reaction of 8-t-butyl-2-naphthol (4c) with3 gave exclusively 8-t-butyl-2,2-(tetrachloro--henylenedioxy)-naphthalen-1(2H)-one (1d). Oxidation of 3-t-butyl-2-naphthol (4f) with3 gave a mixture of 3-t-butyl-2,2-(tetrachloro-o-phenylendioxy) nephthalene-1(2H)-one(1g) and 3-t-butyl-1,1-(tetrachloro--phenylenedioxy)naphthelen-2 (1H)-one (2g) in the ratio 1∶6. Thus, onlyt-butyl group exherts pronounced steric influence on the rearrangement observed in the reaction of β-naphthol with the quinone3. Structures of all the compounds have been established by spectral data.

Electrophilic Substitution Reactions of Copper(II) Acetylacetoneimine Complexes with Arene Diazonium Ions

Copper(II) complexes of ethylene/propylene-bis(acetylacetoneimine), Cu(baen) or Cu(bapn), react quickly and quantitatively in aqueous methanol at the methine position with arene diazonium ions in a stepwise manner to yield mono- and di-substituted copper(II) complexes. All the complexes are paramagnetic with μeff∼1.88 B.M. In all the complexes the diazo substituted part of the ligand coordinates to the metal through the agr-nitrogen of the azo group and the imine nitrogen, forming glyoxaliminearylhydrazone type of ligand system. The complexes have been characterized by elemental analysis, electronic, esr, ir and mass spectroscopic methods.