Acyl Isomers Research Articles

Calculations and analysis of 55Mn nuclear quadrupole coupling for asymmetric top acyl methyl manganese pentacarbonyl

Revised assignments of the measured transitions for the asymmetric top acyl isomers of methyl manganese pentacarbonyl are presented, along with a corresponding fit to determine rotational and quadrupole coupling constants. New assignments for measured transitions give a better fit to the spectrum and better agreement between experimental and calculated quadrupole coupling strengths. The best agreements were obtained for B3LYP and M11 DFT calculations with triple and quadruple-zeta basis sets. Experimental molecular parameters from the new analysis are: A = 840.0843(52), B = 774.2861(17), C = 625.6528(13). DJ = 0.000212(21). DJK = 0.00488(18), 1.5χaa = −46.96(11), 0.25(χbb - χcc) = -13.44(3) MHz.

Cis-Trans Configuration of Coumaric Acid Acylation Affects the Spectral and Colorimetric Properties of Anthocyanins.

The color expression of anthocyanins can be affected by a variety of environmental factors and structural characteristics. Anthocyanin acylation (type and number of acids) is known to be key, but the influence of acyl isomers (with unique stereochemistries) remains to be explored. The objective of this study was to investigate the effects of cis–trans configuration of the acylating group on the spectral and colorimetric properties of anthocyanins. Petunidin-3-rutinoside-5-glucoside (Pt-3-rut-5-glu) and Delphinidin-3-rutinoside-5-glucoside (Dp-3-rut-5-glu) and their cis and trans coumaroylated derivatives were isolated from black goji and eggplant, diluted in pH 1–9 buffers, and analyzed spectrophotometrically (380–700 nm) and colorimetrically (CIELAB) during 72 h of storage (25 °C, dark). The stereochemistry of the acylating group strongly impacted the spectra, color, and stability of the Dp and Pt anthocyanins. Cis acylated pigments exhibited the greatest λmax in all pH, as much as 66 nm greater than their trans counterparts, showing bluer hues. Cis acylation seemed to reduce hydration across pH, increasing color intensity, while trans acylation generally improved color retention over time. Dp-3-cis-p-cou-rut-5-glu exhibited blue hues even in pH 5 (C*ab = 10, hab = 256°) where anthocyanins are typically colorless. Cis or trans double bond configurations of the acylating group affected anthocyanin spectral and stability properties.

X-ray, FT-IR, NMR and PM5 structural studies and antibacterial activity of unexpectedly stable salinomycin–benzotriazole intermediate ester

The unexpectedly stable benzotriazole ester of salinomycin (SAL-HOBt) – an intermediate product of the amidation reaction of salinomycin has been isolated and structurally characterised (using a single crystal) by X-ray, FT-IR, NMR and semiempirical methods. The results of the X-ray and spectroscopic studies demonstrated that this intermediate ester exist in the solid state and in solution exclusively as the stable O–acyl form. The molecular structure of SAL-HOBt is stabilised by relatively weak intramolecular hydrogen bonds. The PM5 calculation of possible structures of SAL-HOBt has shown that the O–acyl form is more energetically favourable than its N–oxide–N–acyl isomers. The antimicrobial tests show that SAL-HOBt is active against Gram-positive bacteria and clinical isolates methicillin-resistant Staphylococcus aureus (MIC=1–2μg/ml).

A kinetic investigation of the oxidative addition reactions of the dimeric Bu 4N[Ir 2(μ-Dcbp)(CO) 2(PCy 3) 2] complex with iodomethane

The IR and UV/visible kinetic results of the oxidative addition of iodomethane to Bu 4N[Ir 2(μ-Dcbp)(CO) 2(PCy 3) 2] (Dcbp = 3,5-dicarboxylatepyrazolate anion) showed three time separable reactions. The first, very fast reaction corresponds to the a Ir(I)–Ir(III) alkyl species formation within 10 −3 s. The second, relative fast reaction corresponds to Ir(III)–Ir(III) alkyl formation with a rate constant of 3.25(4) × 10 −2 M −1 s −1 while the third and slowest reaction corresponds to Ir(III)–Ir(III) acyl formation with a rate constant of 1.42 × 10 −5 s −1. The IR data clearly show the existence of a number of equilibria with the formation of an Ir(I)–Ir(III) alkyl product which then react to form the Ir(III)–Ir(III) which then slowly react to form the Ir(III)–Ir(III) acyl product. A solvent study indicated increased oxidative addition activity in the presence of polar solvents, which is indicative of a polar transition state. The large negative entropy of activation for the Ir(III)–Ir(III) alkyl formation step ( k 2) of −178(23) JK −1 mol −1 is indicative of an associative process. DFT calculations successfully identified the stereochemistry of the starting complex, [Ir 2(μ-Dcbp)(CO) 2(PCy 3) 2] − as well as that of the Ir-alkyl and acyl isomers. A reaction pathway, using the IR data and DFT calculations, is proposed for the reaction.

Characterisation of acyltransferases from Synechocystis sp. PCC6803

As phylogenetic ancestors of plant chloroplasts cyanobacteria resemble plastids with respect to lipid and fatty acid composition. These membrane lipids show the typical prokaryotic fatty acid pattern in which the sn-2 position is exclusively esterified by C 16 acyl groups. In the course of de novo glycerolipid biosynthesis this prokaryotic fatty acid pattern is established by the sequential acylation of glycerol-3-phosphate with acyl-ACPs by the activity of different acyltransferases. In silico approaches allowed the identification of putative Synechocystis acyltransferases involved in glycerolipid metabolism. Functional expression studies in Escherichia coli showed that sll1848 codes for a lysophosphatidic acid acyltransferase with a high specificity for 16:0-ACP, whereas slr2060 encodes a lysophospholipid acyltransferase, with a broad acyl-ACP specificity but a strong preference for lysophosphatidyglycerol especially its sn-2 acyl isomer as acyl-acceptor. The generation and analysis of the corresponding Synechocystis knockout mutants revealed that lysophosphatidic acid acyltransferase unlike the lysophospholipid acyltransferase is essential for the vital functions of the cells.

Density Functional Study of CO Insertion into the Metal−Alkyl Bond in Bis(cyclopentadienyl)−Zr−(CH3)2

The migratory insertion reaction of CO into the zirconium−alkyl bond in bis(cyclopentadienyl)−Zr−(CH3)2 has been investigated by means of density functional calculations. CO coordination processes prior to insertion have been analyzed considering both the case of “lateral” and “central” coordination, finding lateral coordination, leading to a O-outside arrangement of the ensuming acyl complex, to be thermodynamically and kinetically favored. The relative stability of the O-outside and O-inside η2-bound acyl complexes has been investigated, finding the O-inside isomer to be the most stable by 2.9 kcal/mol, with an energy barrier for the conversion between the two acyl isomers of 12.2 kcal/mol, in excellent agreement with available experimental data. Finally, the insertion of the residual alkyl group into the acyl moiety, leading to a η2-bound ketone, has been investigated.

Analysis of sn‐1(3)‐ and sn‐2‐short‐chain acyl isomers of triacylglycerols in butteroil by gas‐liquid chromatography

AbstractThe aim of the study was to determine major triacylglycerols (TG), and sn‐1(3) and sn‐2 isomers of butyryl and caproyl TG in butteroil (BO) and interesterified butteroil (IBO) by gas‐liquid chromatography (GLC) and silver ion column chromatography. Altogether, 112 molecular species of TG were synthesized by interesterification and their retention indices were determined. Molar empirical correction factors for TG were determined using linear calibration. Retention indices showed that sn‐1(3) and sn‐2 isomers of the TG containing one short‐chain acyl (butyrate, caproate) and two long‐chain acyls (lauroate, myristate, palmitate, stearate, and oleate) were separated on a phenyl (65%) methylsilicone column. The difference between retention indices of 1(3)‐ and 2‐short‐chain acyl isomers ranged from 14 to 19, and from 9 to 16 for butyrates and caproates, respectively. The proportion of sn‐2 isomers of butyrates averaged 1.4%, but only traces of sn‐2 isomers of caproates were detected in butteroil. The ratio of sn‐1(3)‐ to sn‐2‐butyrates and caproates in interesterified butteroil averaged 2.0:1. The most abundant molecular species of mono‐short‐chain TG in butteroil were BPP + BMS (5.6 mol%), BPO + BSPo (4.8 mol%), BMP + BLaS (3.4 mol%), BMO + BPPo (2.7 mol%), BPS (2.5 mol%), and CoPP + CoMS (2.3 mol%).

Stereoselectivity of the Diels‐Alder Reaction of (E)‐γ‐Oxo‐α,β‐Unsaturated Thioesters with Cyclopentadiene

AbstractThe stereoselectivity of the Diels‐Alder reaction of (E)‐γ‐oxo‐α,β‐unsaturated thioesters 3a‐3d with cyclopentadiene is greatly enhanced in the presence of Lewis acids favoring the endo acyl isomers 4a‐4d. In the absence of Lewis acid, Diels‐Alder reaction of 3a‐3d with cyclopentadiene at 25 °C gave two adducts 4a‐4d and 5a‐5d in a ratio of 1:1 respectively. In the presence of Lewis acids, Diels‐Alder reaction of 3a‐3d with cyclopentadiene gave 4a‐4d and 5a‐5d in ratios of 75‐94:25‐6 respectively. The stereoelectivity was enhanced to ratios of 95‐98:5‐2 with lowering the reaction temperature. The stereochemistry of the cycloadducts 4 and 5 was confirmed by iodocyclization. Reaction of the endo‐thioester 5c with I2 in aqueous THF at 0 °C gave the novel methylthio group rearranged product 6c in 80% yield, the first example of iodo‐lactonization of endo‐thioesters. Reaction of the endo‐acyl isomer 4b with I2 under the same reaction conditions gave an isomeric mixture of 7b and 8b in 1:2 ratio. The stereochemistry of the thioester group in 8b was proved by X‐ray single‐crystal analysis. The solvent effect on the endo selectivity of (Z)‐γ‐oxo‐α,β‐unsaturated thioester 2b was also examined.

Inversion of Lipase Stereospecificity for Fluorogenic Alkyldiacyl Glycerols. Effect of Substrate Solubilization

We synthesized enantiomeric 1-O-alkyl-2,3-diacyl-sn-glycerol and 3-O-alkyl-1,2-diacyl-sn-glycerol containing pyrene as a fluorescent reporter and the trinitrophenylamino residue as a fluorescence quencher; both reporter groups were covalently bound to the omega end of the acyl chains at positions sn-2 and sn-3(1), respectively. The fluorescence of the intact substrate molecules was very low. Chemical or enzymic release of the fatty acyl chains lead to fluorescence dequenching. The rate of lipolysis could be measured from the time-dependent increase in fluorescence intensity. We used the respective substrates for the continuous determination of activity and stereopreference of four different microbial lipases from Chromobacterium viscosum, Candida rugosa, Pseudomonas sp., Rhizopus arrhizus, as well as cutinase from Fusarium solani and lipoprotein lipase from bovine milk. The stereopreference of the lipases depended, in general, on how the substrate was solubilized in the reaction medium. All lipases under investigation preferentially hydrolysed the sn-1 acyl ester bond, if the lipid analog was dispersed in albumin-containing Tris/HCl buffer in the absence of detergent or organic solvent. In mixtures of 1:1 (by vol.) water/ethanol, the enzymes showed higher activity toward the sn-3 acyl ester bond, except for lipoprotein lipase which preferred the sn-1 acyl isomer under all conditions tested. Different stereopreferences were observed with the different lipases if the substrate was solubilized by amphiphiles (micelles of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate). C. rugosa lipase and F. solani cutinase showed high stereopreference for the sn-3 acyl ester, whereas Pseudomonas sp. lipase and C. viscosum lipase hydrolysed both enantiomers at similar rates. From spectroscopic studies, it can be inferred that the conformation of the fluorescent lipids is probably similar in water, mixtures of water and organic solvents, and in micelles. The possible effects of reaction conditions on substrate accessibility and enzyme conformation on stereoselectivity of the respective lipases are discussed.

Inversion of Lipase Stereospecificity for Fluorogenic Alkyldiacyl Glycerols. Effect of Substrate Solubilization

We synthesized enantiomeric 1-O-alkyl-2,3-diacyl-sn-glycerol and 3-O-alkyl-1,2-diacyl-sn-glycerol containing pyrene as a fluorescent reporter and the trinitrophenylamino residue as a fluorescence quencher; both reporter groups were covalently bound to the ω end of the acyl chains at positions sn-2 and sn-3(1), respectively. The fluorescence of the intact substrate molecules was very low. Chemical or enzymic release of the fatty acyl chains lead to fluorescence dequenching. The rate of lipolysis could be measured from the time-dependent increase in fluorescence intensity. We used the respective substrates for the continuous determination of activity and stereopreference of four different microbial lipases from Chromobacterium viscosum, Candida rugosa, Pseudomonas sp., Rhizopus arrhizus, as well as cutinase from Fusarium solani and lipoprotein lipase from bovine milk. The stereopreference of the lipases depended, in general, on how the substrate was solubilized in the reaction medium. All lipases under investigation preferentially hydrolysed the sn-1 acyl ester bond, if the lipid analog was dispersed in albumin-containing Tris/HCl buffer in the absence of detergent or organic solvent. In mixtures of 1:1 (by vol.) water/ethanol, the enzymes showed higher activity toward the sn-3 acyl ester bond, except for lipoprotein lipase which preferred the sn-1 acyl isomer under all conditions tested. Different stereopreferences were observed with the different lipases if the substrate was solubilized by amphiphiles (micelles of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate). C. rugosa lipase and F. solani cutinase showed high stereopreference for the sn-3 acyl ester, whereas Pseudomonas sp. lipase and C. viscosum lipase hydrolysed both enantiomers at similar rates. From spectroscopic studies, it can be inferred that the conformation of the fluorescent lipids is probably similar in water, mixtures of water and organic solvents, and in micelles. The possible effects of reaction conditions on substrate accessibility and enzyme conformation on stereoselectivity of the respective lipases are discussed.

Reaction of silylcobalt tetracarbonyls with oxiranes. Kinetics and mechanism

It has been shown that (β-silyloxyacyl)cobalt tetracarbonyls are formed in the reaction between silylcobalt tetracarbonyl, terminal oxirane, and carbon monoxide. The linear acyl isomer is obtained with a regioselectivity of about 80%, which is practically independent of the nature of the substituents in the silyl group. Kinetic studies have revealed a first order dependence on Ph 3SiCo(CO) 4, an increasing order with respect to ethyloxirane, and zero order with respect to [Co(CO) 4] − and CO. A mechanism involving a rapid formation of a tight ion pair, rate-determining internal S N2 type substitution, and fast insertion of CO is suggested.

Photoreactions of the triruthenium cluster HRu3(CO)10 (.mu.-COCH3). Isomerization of the bridging alkylidyne ligand and competing ligand substitutions

Irradiation of the title compound HRu{sub 3}(CO){sub 10}({mu}-COCH{sub 3}) (A) in hydrocarbon solution under CO leads to the formation of the bridging {mu},{eta}{sup 2} acyl isomer HRu{sub 3}(CO){sub 10}({mu}{eta}{sup 2}-C(O)CH{sub 3}) (B). Quantum yields for isomerization {phi}{sub i} were wavelength dependent ranging from < 10{sup {minus}5} at 405-nm excitation to about 0.05 at 313-nm excitation under P{sub CO} 1.0 atm. In addition, over the range 0-1.0 atm, the {phi}{sub i} values proved to be linearly dependent on P{sub CO} despite the absence of a stoichiometric requirement for CO in the isomerization. A key observation was that photoisomerization of A {sup 13}C labeled specifically at the bridging alkylidyne carbon, i.e., HRu{sub 3}(CO){sub 10}({mu}-{sup 13}COCH{sub 3}), gives B specifically labeled at the bridging acyl carbon, i.e., HRu{sub 3}(CO){sub 10}({mu}{eta}{sup 2}-{sup 13}C(O)CH{sub 3}), with no evidence of scrambling of the label with other carbons in the complex. Photolysis in the presence of {sup 13}CO or other added ligands demonstrated the lability of the cluster coordinated carbonyls to photosubstitution reactions. The quantum yield for photosubstitution {phi}{sub s} follows the same wavelength dependence as does {phi}{sub i}, and it is proposed that the two processes result from competitive decay pathways of common intermediates. Limiting quantummore » yields for photosubstitution are about 0.25. A mechanism for these reactions related to that proposed previously for the photofragmentation of the parent triruthenium cluster Ru{sub 3} (CO){sub 12} is discussed. Prolonged 313-nm irradiation of HRu{sub 3}(CO){sub 10}({mu},{nu}{sup 2}-C(O)CH{sub 3}) under CO leads to cluster fragmentation and the formation of Ru(CO){sub 5} plus acetaldehyde. 29 refs., 6 figs., 5 tabs.« less

Viscoelastic properties of (cellulose oligo‐oxymethylene ether) acylates with bulky side chain

AbstractA series of (cellulose oligo‐oxymethylene ether) acylates (COAs) are characterized by the presence of the micro‐Brownian motion of the side chain (β process) which appears separately from that of the main chain (α process). Both the alpha; and β processes are largely affected by the kind of acyl groups introduced in the side chain. To clarify the effect of the acyl group on these processes, we investigated the dynamic mechanical properties of newly prepared COAs with acyl side chain, bulky in chemical structure (iso‐butyrate, privalate, and benzoate) in relation to those for COAs with linear acyl side chain (acetate, butyrate, and valerate). By substituting bulky acyl isomer for linear acyl group in COAs, we observed that the temperature region of both the α and β processes moved to higher temperature. Furthermore, with an increase in molecular size of bulky acyl group, the β region shifts were much larger than the α region, indicating that the mobility of the side chain became comparable to that of the main chain. Finally, when such a large bulky group, for example, benzoate was introduced, the micro‐Brownian motion of the side chain prior to that of the main chain ceased. The apparent activation energy for a third process (γ) due to the motion of the oligo‐oxymethylene parts in the side chain was estimated to be 10.3 kcal/mol.

Immunological characterization of sn-1,2-diacylglycerol and sn-2-monoacylglycerol kinase from pig brain.

Rabbit antisera were raised against diacylglycerol kinase purified from pig brain cytosol. Upon immunoblot analysis, the antibody was specifically reactive with the kinase (Mr = 79,000-80,000). Pig brain cytosol, microsomal, and synaptosomal fractions all contained the immunoreactive Mr = 80,000 polypeptide, thus showing that the same enzyme is present in the soluble as well as membrane fractions of the brain. The antibody could precipitate only 60% of the kinase activity present in the crude cytosol. Further, the antibody exhibited very little or no cross-reactivity toward liver cytosolic enzymes obtained from different animals including pigs. Immunostaining of brain tissues demonstrated that neurons, in particular, their nuclei, were positively stained, whereas glial cells were not stained. It is likely that there exists a tissue-and/or cell-dependent immunological multiplicity of diacylglycerol kinase. The enzyme activities phosphorylating sn-1 and sn-2 monoacylglycerols were co-precipitated by the antibody, indicating their identity with diacylglycerol kinase. The enzyme activity toward sn-1 monoolein was much lower than that obtained with sn-2 monoolein. Enzymic as well as chemical analyses of acyl isomers of the reaction products showed that even tested with pure (greater than 95%) sn-1 monoolein, about 70% of the formed lysophosphatidate was of the sn-2 acyl type. The results show that diacylglycerol kinase phosphorylates almost exclusively the sn-2 acyl type of monoacyl-glycerol.

Acylation of lysophosphatidylserine by rat brain microsomes.

Abstract— The acylation of lysophosphatidylserine, prepared by snake venom digestion of phosphatidylserine, by rat brain microsomes is described. Acylation was monitored by spectrophotometric assay and by measuring the incorporation of radioactively labelled acyl CoA thioesters. Acylation was time dependent, showed an approximately linear response to enzyme concentration and had a pH optimum of 9.0. Maximum acylation was attained at a concentration of about 100 μM for lysophosphatidylserine and about 40μM for acyl CoA thioesters. Positional distribution studies with [14C]oleoyl CoA and [14C]arachidonoyl CoA showed incorporation was predominantly at position ‐2, but with significant labelling at position–1, particularly with oleoyl CoA, possibly as a result of isomerization of the 1–acyl isomer of lysophosphatidylserine. Both saturated and unsaturated thioesters could serve as acyl group donors. Myristoyl CoA was considerably superior to palmitoyl CoA and stearoyl CoA, which were poor acyl group donors. Some selectivity was shown among the long chain unsaturated thioesters, linoleoyl, linolenoyl and arachidonoyl CoA being the most effective acylating agents. Although docosahexaenoic acid is a major unsaturated fatty acid in brain phosphatidylserine, its CoA ester was a relatively poor acyl group donor. Relative acylation rates remained essentially constant over a wide range of lysophosphatidylserine concentrations. It is concluded that acyl transfer mechanisms are active in brain for the regulation of the fatty acid profile of phosphatidylserine.

Mixed ligand carbonyl complexes of rhodium(I) and rhodium(III)

Evidence is presented which suggests that the compounds trans-[RhX(CO)2PPh3](Ia)(X = Cl, Br, I), made from [RhCl(CO)2]2 and triphenylphosphine (1 : 2 molar ratio), should be reformulated as the dimeric complexes trans-[RhXCOPPh3]2(Ib). Similar compounds with X = SCN,OCOMe are also described. Detailed i.r. solution studies of the preparative reaction for X = Cl are interpreted in terms of the initial formation of a labile intermediate cis-[RhCl(CO)2PPh3]n(III)(n probably 2), followed by partial decarbonylation and isolation of (Ib) and a small amount of cis-[RhCl(CO)PPh3]2(Ic). The compounds (Ib) undergo bridge cleavage reactions with various Lewis bases, giving [RhX(CO)(PPh3)L](L = PPh3,PMePh2, P(C6H11)3, AsPh3, SbPh3, C5H5N, Me2S, etc.). With SbPh3, the five-co-ordinate complex [RhCl(CO)PPh3(SbPh3)2] is also formed. The 1H n.m.r. of [RhCl(CO)(PPh3)(PMePh2)] shows only a singlet for the methyl resonance, indicative of easy phosphine exchange in a strongly coupled PP′ complex. As expected, [RhCl(CO)(PPh3)(AsPh3)] readily undergoes oxidative addition reactions, giving [RhClYZCO(PPh3)(AsPh3)](YZ = Cl2, I2, CH3l). The latter product is in equilibrium with its acyl isomer [RhClI(COCH3)(PPh3)(AsPh3)]0·5CH3l. However, pure [RhClI(CH3)(CO)(PPh3)(AsPh3)] can be synthesised by reaction of the acyl–alkyl mixture [RhClI(CH3)(CO)PPh3]2(IV) and [RhClI(COCH3)PPh3]2(V)(previously formulated as the single compound [RhClI(CO)(COCH3)PPh3]) with AsPh3. Similarly, [RhClI(CH3)(CO)PPh3L](L = PPh3 or SbPh3) can be obtained. These compounds readily undergo isomerisation to the more stable acyl isomer. Finally, [RhCl3(CO)PPh3(AsPh3)] can also be prepared by reaction of trans-[RhCl3(CO)PPh3]2(originally formulated as trans-[RhCl3(CO)2PPh3]) with AsPh3.

AMINOACYL POSITION IN AMINOACYL SRNA.

Chromatographic systems capable of resolving the 2'- and 3'-isomers of valyladenosine and N-acetylvalyladenosine are used to show that valyladenosine isolated from valyl-sRNA is the equilibrium mixture of 2'- and 3'-acyl isomers by the time of chromatography. Acyl migration in N-acetylvalyladenosine is shown to be a rapid, base-catalyzed reaction with a rate 40,000 times the rate of hydrolysis under equivalent conditions. Calculations indicate that the pool of free aminoacyl sRNA exists in vivo as the equilibrium mixture of the 2'- and 3'-aminoacyl isomers