Abstract  A photochemical model study of benzophenone triplet ((3)BP) with the MAO-B substrate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine [MPTP (1)] and two of it's derivatives, 1-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (2) and (±)-[trans-2-phenylcyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (3) were performed. Literature precedent and calculations reported herein suggest that the barrier to ring opening for aminyl radical cations derived from N-cyclopropyl derivatives of tertiary amines (such as MPTP) will be low. The LFP results reported herein demonstrate that pathways for the reaction of (3)BP with 1, 2, and 3 are very similar. In each instance, disappearance of (3)BP is accompanied solely by appearance of bands corresponding to the diphenylhydroxylmethyl radical and neutral radical derived from MPTP and it's two derivatives 2 and 3. These results suggest that the reaction between benzophenone triplet and tertiary aliphatic amines proceed via a simple hydrogen atom transfer reaction. Additionally these model examinations provide evidence that oxidations of N-cyclopropyl derivatives of MPTP catalyzed by MAO-B may not be consistent with a pure SET pathway.

Abstract  Standard computational models of cytotoxicity of substituted phenols relate the toxicity to a set of quatitative structure-activity relationship (QSAR) descriptors such as log P, p K a, OH bond dissociation enthalpy (BDE), etc. Implicit in this approach is the idea that the phenoxyl radical is disruptive to the cell and factors increasing its production rate will enhance the toxicity. To improve the QSAR correlations, substituents are usually divided into electron-donating groups (EDG) and electron-withdrawing groups (EWG), which are treated separately and thought to follow different mechanisms of toxicity. In this paper, we focus on one important aspect of toxicity, the rate constant for production of phenoxyl radical. Activation energies are obtained for the reaction of X-phenol with peroxyl radical by using the Evans-Polanyi principle, giving rate constants as a function of DeltaBDE values for both EDG and EWG sets. We show that (i) a plot of log k for phenoxyl formation vs DeltaBDE shows a double set of straight lines with different slopes, justifying the usual EDG and EWG separation but without requiring any change in mechanism; (ii) the same method can be effectively used for different target radicals (e.g., tert-butoxyl) or different sets of parent compounds (e.g., substituted catechols), thus giving a useful general approach to analysis of toxicity data; (iii) regions of constant toxicity in all cases are predicted; and (iv) we argue that competing parallel mechanisms of toxicity are likely to be dominant for EWG-substituted phenols.

Abstract  A time-resolved kinetic study on the reactions of the cumyloxyl radical (CumO(•)) with intramolecularly hydrogen bonded 2-(1-piperidinylmethyl)phenol (1) and 4-methoxy-2-(1-piperidinylmethyl)phenol (2) and with 4-methoxy-3-(1-piperidinylmethyl)phenol (3) has been carried out. In acetonitrile, intramolecular hydrogen bonding protects the phenolic O-H of 1 and 2 from attack by CumO(•) and hydrogen atom transfer (HAT) exclusively occurs from the C-H bonds that are α to the piperidine nitrogen (α-C-H bonds). With 3 HAT from both the phenolic O-H and the α-C-H bonds is observed. In the presence of TFA or Mg(ClO4)2, protonation or Mg(2+) complexation of the piperidine nitrogen removes the intramolecular hydrogen bond in 1 and 2 and strongly deactivates the α-C-H bonds of the three substrates. Under these conditions, HAT to CumO(•) exclusively occurs from the phenolic O-H group of 1-3. These results clearly show that in these systems the interplay between intramolecular hydrogen bonding and Brønsted and Lewis acid-base interactions can drastically influence both the HAT reactivity and selectivity. The possible implications of these findings are discussed in the framework of the important role played by tyrosyl radicals in biological systems.

Abstract  Abstract: A comparison of the tris(trimethylsilyl)silyl I and tris(trimethylsilyl)germyl II radical reactivity is provided. Their formation as well as their reactivity encountered in a large variety of chemical processes (addition to double bond, halogen abstraction, peroxyl radical formation…) is examined by laser flash photolysis, quantum mechanical calculations and electron spin resonance (ESR) experiments. The starting compound (TMS)3GeH is more reactive than (TMS)3SiH toward the t-butoxyl, the t-butylperoxyl and the phosphinoyl radicals. A similar behavior is noted for an aromatic ketone triplet state. II exhibits a lower absolute electronegativity: accordingly, the addition to electron rich alkenes is less efficient than for I. Radical II is also found less reactive for both the peroxylation and the halogen abstraction reactions. The rearrangement of is slower than for ; this is related to the respective exothermicity of the processes. [Copyright 2008 Elsevier] Copyright of Journal of Organometallic Chemistry is the property of Elsevier Science Publishers B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts)

Abstract  Abstract: Principal component analysis (PCA) was performed on experimental rate constant and theoretical barrier height data of radical addition reactions involving various carbon- and sulfur-centered radicals and vinyl-type alkenes. Altogether six data sets were analyzed. In three cases the reactivity data were completed by certain descriptors, i.e., the electron affinity (EA) and negative ionization potential (-IP) of alkenes, as well as the exothermicity (-Delta H(r)) of reactions. It was found that in each case the first two principal components account for more than 93% of the total variance in the data. The scores of the first principal component correlate with EA and (-Delta H(r)), whereas those of the second principal component with (-IP). It is concluded that PCA is able to decompose both experimental and theoretical reactivity data into nucleophilic and electrophilic components, as well as into polar and enthalpy terms. In the plots of component loadings the radicals form significant groups depending on their character. Thus, PCA can classify radicals according to nucleophilicity and electrophilicity. The PCA results were validated by significant correlations of experimental and theoretical reactivity data with Hammett sigma(p) as well as with the descriptors EA, (-Delta H(r)), and (-IP). The hydroxymethyl radical is classified as strongly nucleophilic, the methyl radical as moderately nucleophilic, the tert-butoxycarbonylmethyl and cyanomethyl radicals as weakly nucleophilic, the phenylsulfonyl and tosyl radicals as moderately electrophilic, and the 2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-yl radical as strongly electrophilic. It is concluded that the reactivities of tert-butoxycarbonylmethyl and cyanomethyl radicals are mainly governed by enthalpy effects. This conclusion is in agreement with the findings of Giese et al. [Chem. Ber. 1988, 121, 2063-2066] and Fischer et al. [Helv. Chim. Acta 1995, 78, 194-214]. A symmetry pattern of correlations is proposed: the reactivity correlates with EA for strongly nucleophilic radicals, with EA and (-Delta H(r)) for moderately nucleophilic radicals, with (-Delta H(r)) for weakly nucleophilic or weakly electrophilic radicals, with (-Delta H(r)) and (-IP) for moderately electrophilic radicals, and with (-IP) for strongly electrophilic radicals. On the basis of the symmetry pattern of correlations, it is concluded that the dominant factors influencing radical addition reactions are polar effects alone for strongly nucleophilic or strongly electrophilic radicals, polar and enthalpy effects for moderately nucleophilic or moderately electrophilic radicals, and enthalpy effects alone for weakly nucleophilic or weakly electrophilic radicals. ds: Chemistry cument Delivery No.: 145MV e field[29]: 1,4-Dioxane

Abstract  Bond dissociation enthalpies (BDEs) of a large series of aliphatic amines (21) were measured by means of photoacoustic calorimetry. Despite the different structures studied in the primary, secondary, and tertiary amine series, the alpha(C-H) BDEs were found to be very similar for unconstrained amines with values very close to 91 kcal/mol. alphaC- and N-alkylation or introduction of an hydroxy group only slightly affect the BDEs, a fact in perfect agreement with calculations performed at different CBS levels. This demonstrates the predominance of the two-orbital-three-electron interaction involving the N and alphaC(*) orbitals. On the other hand, the N-H BDE decreases when going from primary to secondary amines. This result is interpreted in term of a hyperconjugation in sigmaC-C bonds, which leads to a stabilization of the aminyl radical. For cyclized amines, the BDEs depend on the relative geometry of the singly occupied alphaC(*) orbital with respect to that of the N atom, disfavoring the two-orbital-three-electron interaction. However, such structures can exhibit through-bond interaction. For a crowded structure such as triisopropylamine, for which the alphaC(*) orbital is not coplanar with the nitrogen one, the relaxation of a strain energy allows the BDE to be comparable to flexible structures.

Abstract  In our effort to develop selective sphingosine kinase-2 (SphK2) inhibitors as pharmacological tools, a thiazolidine-2,4-dione analogue, 3-(2-amino-ethyl)-5-[3-(4-butoxyl-phenyl)-propylidene]-thiazolidine-2,4-dione (K145), was synthesized and biologically characterized. Biochemical assay results indicate that K145 is a selective SphK2 inhibitor. Molecular modeling studies also support this notion. In vitro studies using human leukemia U937 cells demonstrated that K145 accumulates in U937 cells, suppresses the S1P level, and inhibits SphK2. K145 also exhibited inhibitory effects on the growth of U937 cells as well as apoptotic effects in U937 cells, and that these effects may be through the inhibition of down-stream ERK and Akt signaling pathways. K145 also significantly inhibited the growth of U937 tumors in nude mice by both intraperitoneal and oral administration, thus demonstrating its in vivo efficacy as a potential lead anticancer agent. The antitumor activity of K145 was also confirmed in a syngeneic mouse model by implanting murine breast cancer JC cells in BALB/c mice. Collectively, these results strongly encourage further optimization of K145 as a novel lead compound for development of more potent and selective SphK2 inhibitors.

Abstract  When chick pineal glands were explanted into organ culture at midlight phase of a diurnal cycle of illumination and incubated in the dark, they developed marked increases in serotonin acetyltransferase (acetyl coA:arylamine N-acetyltransferase; EC 2.3.1.5) activity. Either this increase in activity was inhibited or its onset was retarded in glands incubated under constant illumination. Supplements of theophylline, isobutylmethylxanthine, quinidine, and compound Ro 20-1724 (4-(3-butoxyl-4-methoxybenzyl)-2-imidazolidinone) elicited very marked increases in serotonin acetyltransferase activity in glands cultured in the dark. Levels of activity attained after 6 h in culture approached or exceeded the maximum levels attained at middark phase of the diurnal cycle in vivo. Effects of theophylline and compound Ro 20-1724 were additive. Supplements of dibutryl cAMP had little or no effect upon levels of serotonin acetyltransferase activity when tested alone or in combination with theophylline but further enhanced the increase in the level of enzyme activity elicited by Ro 20-1724. Adenosine and cAMP had little or no effect upon levels of serotonin acetyltransferase activity. It is concluded that levels of serotonin acetyltransferase activity in the chick pineal gland are regulated by a repressive, negative-control mechanism, which probably involves a membranous adenosine receptor.

Abstract  The pharmacological properties of YM-16151-1 [(+/-)-dimethyl 4-[2-[4-(2-hydroxy-3-phenoxypropylamino)butoxyl]-5-nitrop hen yl]-2,6- dimethyl-1,4-dihydropyridine-3,5-dicarboxylate hydrochloride] and its optical isomers were evaluated in in vitro studies and radioligand binding assay. In isolated tissues, YM-16151-1 produced a competitive antagonism of CaCl2-induced contraction in the isolated rabbit aorta with a pKca-1 value of 8.17, and also produced a competitive antagonism of isoproterenol-induced positive chronotropic responses in the isolated rat atria with a pA2 value of 8.47. In rat brain membrane preparations, YM-16151-1 produced dose-dependent inhibitions of [3H]nitrendipine and [3H]dihydroalprenolol bindings with pKi values of 7.21 and 8.07, respectively. Calcium entry blocking activity of YM-16151-1 was 7 times weaker and 3 times greater than nifedipine and diltiazem, respectively. Beta-1 adrenoceptor blocking activity of YM-16151-1 was 2 times weaker than that of propranolol. YM-16151-1 showed about 900-fold selectivity for beta-1 adrenoceptor. YM-16151-1 also showed a weak alpha-1 adrenoceptor blocking activity and its potency was about 13 times weaker than that of phentolamine. S-(-)- and R-(+)-isomers of YM-16151-1 showed the same potency of calcium entry blocking activity. However, in beta-1 adrenoceptor blocking activity, the S-(-)-enantiomer was about 13 to 22 times more potent than the R-(+)-enantiomer. Oral administration of YM-16151-1 produced a dose-dependent blood pressure lowering effect without increasing heart rate in conscious spontaneously hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract  Under completely occluded conditions, Celanese Chemical Company - 50-50 Blend in Water of 1,3 Butylene Glycol, was capable of eliciting visible skin changes consistent with the criteria deemed characteristic of a mild fatiguing agent in 2 out of 200 subjects. In the opinion of the investigator, Celanese Chemical Company - 50-50 Blend in Water of 1, 3 Butylene Glycol may be considered safe to use in contact with the skin insofar as primary irritation or sensitization are concerned if the conditions of contact do not exceed those of the test procedure. Insofar as sensitization is concerned, the extrapolation of these results to a general population is limited statistically by the number of test subjects. In this case, since 200 subjects were used, we may predict with 95% certainty that at least 98.17% of a general population will not be sensitized by this material.

Abstract  Rate coefficients and branching ratios for unimolecular reactions of alkoxyl radicals in the temperature range 200 to 1500 K and in the pressure range 10(-2) to 10(4) bar are presented. Special emphasis is given to the change of the relative importance of different reaction channels. This is evident for longer chain alkoxyl radicals which at lower temperatures undergo isomerisation via an energetically favourable six-member ring transition state. At temperatures above >600 K, however, the rates of the alternative decomposition pathways become faster than that of isomerisation.

The theoretical approach to derive unimolecular rate coefficients makes use of extensive (G2/G3) ab initio calculations. These are used as input data for RRKM calculations to which a tunnelling probability of the generalised Eckart type has been included on the microcanonical level. A subsequent multi-channel master equation (ME) treatment yields thermal rate coefficients and complete fall-off curves for arbitrary pressure and temperature conditions.

The kinetics of two linear chain alkoxyl radicals, 1-butoxyl and 2-pentoxyl, have been analysed to show the expected complex temperature and pressure behaviour resulting from the competition of multiple accessible reaction channels, each with its specific p, T-dependence. Additional results are reported for the minimum temperatures where channel switching can occur, the trajectory of these characteristic points on the p, T-surface, and the temperature dependence of the fractional ratios of the unimolecular reaction channels and the bimolecular reaction with oxygen at ambient atmospheric pressure.

Abstract  The study disclosed herein provides for the first time a detailed experimental support for the general mechanism of the cigarette-smoke-derived chemiluminescence, as an example par excellence of the excited-state generation in a chemically complex aerosol medium. The mechanism involves chemiexcitation in a unimolecular transformation of the smoke-borne free radical species. However, the concentration of these radicals, [r∙], obeys a bimolecular (second-order) kinetics and depends on a particulate-phase content (total particulate matter, TPM) of the cigarette smoke. The decrease in [r∙] with increasing the TPM amount manifests radical-scavenging propensity of the smoke particulate phase. Astonishingly, no energy transfer takes place from the primary excited light-emitting species to luminophoric molecules abundant in the smoke. The reported results build up fundamentals of a facile chemiluminescence assay for free radical properties of the smoke. The experimental approaches developed for this study are of general scope and may be used for mechanistic elucidation of the excited-state generation in chemical systems and environments of an arbitrary complexity.

Abstract  Solvent effects on the kinetics for hydrogen abstraction from a lactone antioxidant were determined for alkoxyl and nitroxyl radicals; their reactivity differ by about 7 orders of magnitude. A decrease by approximately 12 and approximately 35 were determined for H-abstraction by tert-butoxyl and nitroxyl radicals, respectively, upon changing the solvent from hexane to acetonitrile. Results of solvent and isotope studies indicate that the antioxidant properties of lactone antioxidants should be attributed to the enol, not the lactone. [reaction: see text]

Abstract  The kinetics of the title reactions have been studied by relative-rate methods as a function of temperature. Relative-rate coefficients for the two decomposition channels of 2-methyl-2-butoxyl have been measured at five different temperatures between 283 and 345 K and the observed temperature dependence is consistent with the results of some previous experimental studies. The kinetics of the two decomposition channels of 2-methyl-2-pentoxyl have also been investigated, as a function of temperature, relative to the estimated rate of isomerisation of this radical. Room-temperature rate coefficient data for the two decomposition channels of both 2-methyl-2-pentoxyl and 2-methyl-2-butxoyl (after combining the relative rate coefficient for this latter with a value for the rate coefficient of the major channel, extrapolated from the data presented by Batt et al., Int. J. Chem. Kinet., 1978, 10, 931) are shown to be consistent with a non-linear kinetic correlation, for alkoxyl radical decomposition rate data, previously presented by this laboratory (Johnson et al., Atmos. Environ., 2004, 38, 1755-1765).

Abstract  Photoacoustic Calorimetry is used to determine the a-C-H bond dissociation Energy (BDE) in 1,2,3,4-tetrahydronaphthalene (tetralin) in the neat liquid as well as in competition with hydrogen abstraction from tetrahydrofuran (THF). Also, the a-C-H BDE in THF was determined in the neat liquid. The experiments found to be 82.9 +/- 1.2 and BDE(gas) (THF) to be 92.1 +/- 1.6 kcal mol(-1). The revised global rate constant of hydrogen abstraction from THF is found to be 4.6 x 10(6) M(-1) s(-1) at 297 K.

Abstract  The consumption rates of three monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) and eight analogues using horseradish peroxidase (HRP)-H2O2 as an oxidant were measured and compared with the anodic peak potentials thereof measured with cyclic voltammetry. 3-Monosubstituted p-coumaryl alcohols, i.e., 3-methoxy-, 3-ethoxy-, 3-n-propoxy-, and 3-n-butoxy-p-coumaryl alcohols, had faster reaction rates than p-coumaryl alcohol. This is most probably due to the electron-donating effect of alkoxyl groups. However, the reaction rates gradually decreased with an increase in the molecular weight of the alkoxyl groups. Furthermore, t-butoxyl group, which is a very bulky substituent, caused an extreme reduction in the reaction rate, even though its electron-donating effect was almost the same as that of other alkoxyl groups. The reaction rates of 3,5-disubstituted p-coumaryl alcohols, especially 3,5-dimethyl-p-coumaryl alcohol, were very low compared with 3-monosubstituted p-coumaryl alcohols. These results suggest that there are three main factors of hindrance during the approach of monolignols to the active site of HRP. First, from the results of 3-monoalkoxy-p-coumaryl alcohols, it was suggested that the volume of substituents could decrease their oxidation rates. Second, from the results of 3,5-disubstituted p-coumaryl alcohols, it was suggested that local steric hindrance by the amino residues quite near the heme decreased the oxidation rates. Third, from the results of the substrates with hydrophobic substituents at their 3,5-positions, we suggested that hydrophilicity near heme would decrease their oxidation rates.

Abstract  3-(3-t-Butoxyl)succinimidyl acetyl chloride was obtained by a series of reactions starting from malic acid. 3-(3-t-Butoxyl)succinimidyl acetyl chloride reacted with Schiff bases 1a similar to 1h to yield 8 new 3-(3-t-butoxyl)succinimidyl monocyclic P-lactam derivatives 2a similar to 2h. The structures of the new compounds were confirmed by IR, H-1 NMR, MS spectra and elemental analysis.

Abstract  A simple method for the preparation of 5-epi-nojirymycin (5-epi-DNJ) by a reductive amination of sugar derived alkoxyamines is presented. The latter were prepared in situ from the respective alkylated sugar oximes, which were obtained from the readily available methyl alpha-D-glucoside in a few well defined steps. The stereoselectivity of the reductive amination/cyclisation step depended on the size of the alkyl group in the oxime moiety and was best for the derivative decorated with a bulky tert-butoxyl group (5-epi-DNJ:DNJ = 82:18). The stereochemical outcome of this reaction was rather surprising since the analogous process performed for sugar alkylamines usually provides predominantly derivatives of DNJ. (C) 2016 Elsevier Ltd. All rights reserved.

Abstract  A kinetic study on the effect of acetic (AcOH) and trifluoroacetic acid (TFA) on hydrogen abstractions from the C-H bonds of basic substrates by the cumyloxyl radical (CumO(center dot)) was carried out in acetonitrile. With tetrahydropyran no significant effect on k(H) was observed after acid addition. With the more basic tertiary amines acid addition led to greater than 4-orders of magnitude decreases in k(H). Protonation at nitrogen decreases the degree of overlap between the alpha-C-H sigma* orbital and the lone-pair leading to an increase in the strength of the C-H bond and a destabilization of the radical formed after abstraction. Evidence that C-H deactivation extends up to the gamma-C-H bonds and for the reversibility of this approach was also provided. With TFA no reaction was observed up to [amine] = [TFA], pointing towards stoichiometric protonation. At [amine] > [TFA], k(H) values that are very similar to those measured in the absence of added acid were obtained. With the weaker acid, AcOH, no reaction was observed up to [AcOH]/[amine] similar to 4, and a curved plot was observed with increasing [amine], as a result of the acid-base equilibrium between AcOH and the amine. With 1,4-dimethylpiperazine, a quantitative evaluation of the C-H deactivation determined by sequential protonation of one or both nitrogen centers was obtained. These observations show that protonation provides an extremely efficient, precise and tunable method for the deactivation of the C-H bonds of basic substrates allowing moreover for careful control over the hydrogen abstraction selectivity. The implications of this approach are discussed.

Abstract  Surface binding between the carboxylic group and the TiO2 nanoparticle is important in the potentially applicable dye-sensitized mesoporous TiO2 crystalline solar cell. However, the nature of the surface binding is still not clear enough. We propose a new method to study the surface binding between the carboxylic group and the TiO2 surface atoms by using an interface-sensitive molecular probe. The principle underlying this method is based on the triplet-triplet absorption of the probe molecule all-trans-retinoic acid (ATRA) formed by the photoinduced charge recombination between the TiO2 nanoparticle and the probe molecule. By characterizing the individual triplet absorption spectra of ATRA in different forms, including the synthesized ester-like linkage model compound tri-butoxyl titanium (IV) all-trans-retinoate (Ti(IV)(OBu)(3)RCOO; RCOO = retinoate), the composition of different surface binding forms of carboxylic groups on TiO2 nanoparticle surfaces in hexanol has been determined. The result shows that the simple adsorption form (anion, hydrogen bonding) comprises about 3% of the total adsorbed form, the ester-like form accounts for 63%, and chelating together with bridging form accounts for 34%.

Abstract  Non-conventional techniques, such as power ultrasound (US) has been used to promote one-pot synthesis of second generation ionic liquids (ILs), reducing reaction times and improving yields. Because of the emerging importance of the ILs as green materials with wide ranging applications and our general interests in green processes such as sonication, 1-butoxyl-3-butyl imidazolium bromide (alkoxyl-functionalized) and their derivatives were synthesized using a facile and green US assisted procedure. Their structures were characterized by FT-IR, H-1-NMR, C-13-NMR and mass spectroscopy.