Studies on peroxidized lipids. V. Formation and characterization of 1,4-dihydropyridine-3,5-dicarbaldehydes as model of fluorescent components in lipofuscin

We investigated fluorescence properties of 1,4-dihydropyridine-3,5-dicarbaldehydes and their formation in mild reaction of primary amines and malonaldehyde, in order to clarify the role of malonaldehyde in the formation of fluorescent components of lipofuscin. The compounds exhibited fluorescence with excitation maxima at 375–405 nm and emission maxima at 435–465 nm, which was similar to those of lipofuscin and the fluorescent substances derived from the reaction of oxidized fatty acids with primary amines. Fluorescence of the compounds was greatly affected in acidic medium and little influenced in alkaline medium or by the metal chelator. The compounds lost fluorescence by treatment with sodium borohydride. They were inert to thiobarbituric acid reaction. Some of the fluorescence properties of the compounds were different from those of lipofuscin and the related fluorescent substances. Mild reaction of methylamine with pure malonaldehyde gave a single fluorescent compound, 1,4-dimethyl-1,4-dihydropyridine-3,5-dicarbaldehyde (Ia), and the reaction with the acid hydrolysate of tetramethoxypropane gave Ia and 1-methyl-4-(dimethoxyethyl)-1,4-dihydropyridine-3,5-dicarbaldehyde (IIa), the latter being produced from the impurity in the hydrolysate. These reactions produced a non-fluorescent Schiff base, a 1∶1-adduct of methylamine and malonaldehyde (IIIa), as a major product. It looks unlikely that malonaldehyde is the only product of lipid oxidation that produces fluorescent components in lipofuscin complex.     

Formation of red pigment by a two-step 2-thiobarbituric acid reaction of alka-2,4-dienals. Potential products of lipid oxidation

Reaction of 2,4-hexadienal, 2,4-nonadienal and 2,4-decadienal with 2-thiobarbituric acid (TBA) in aqueous acetic acid produced a 532-nm absorbing red pigment. While the 1∶1 reaction of the aldehyde and TBA produced little pigment, reaction of the aldehyde with an excess amount of TBA produced significant amounts. Instant heating of the reaction mixture did not produce the pigment. However, initial reaction at 5°C and subsequent heating to 100°C produced the pigment efficiently (two-step reaction). Pigment formation required water and dissolved oxygen. The yield of the pigment from the alka-2,4-dienals was 1/10–1/20 of that from malonaldehyde. In the first step of the reaction at 5°C, the 1∶1 adducts of the aldehydes at the5-position of TBA and several other uniden-tified adducts were formed. In the second step, these adducts were converted at 100°C, in the presence of water and oxygen, into the red pigment. The structure of the red pigment from 2,4-hexadienal was elucidated to be the 1∶2 adduct of malonaldehyde and TBA. 2-Hexenal andt-butylhydroperoxide showed marked synergistic effects on the pigment formation from the alka-2,4-dienals. Red pigment formation due to the alka-2,4-dienals may be enhanced by the presence of other aldehydes and hydro-peroxides.     

Formation of fluorescent substances in reaction of aliphatic aldehydes and methylamine

Treatment of monofunctional aliphatic aldehydes (alkanals, 2-alkenals and 2,4-alkadienals) with methylamine at pH 7 produced fluorescence with excitation maxima at 340–360 nm and emission maxima at 410–470 nm. The reaction of 1-butanal and methylamine gave 2-ethyl-2-hexenal (ii), an aldol condensation product of 1-butanal, and 3,5-diethyl-2-propyl-1-methylpyridinium salt (i). The fluorescence was formed by the reaction of 1-butanal and/or ii with methylamine in the presence of molecular oxygen. Fluorescent products I, II and III formed by the reaction were partially purified. Fluorescence characteristics of I, II and III were close to those of the fluorophores derived from the reaction of oxidized fatty acids and primary amines, with respect to maximum wavelengths in excitation and emission, and the resistance to sodium borohydride reduction.     

Characteristics of the thiobarbituric acid reactivity of human urine as a possible consequence of lipid peroxidation

A 532 nm red pigment formed in the thiobarbituric acid (TBA) assay of human urine was characterized after separation of the pigment by high-performance liquid chromatography. The yield of the red pigment was some-what higher at pH 2 than at pH 5; its development was not inhibited by ethylenediaminetetraacetic acid. The characteristics of the pigment were similar to those of the pigment derived from standard malonaldehyde. The amount of the pigment formed was roughly equal to the content of malonaldehyde derivatives estimated as 1-(2,4-dinitrophenyl)pyrazole. Pigment formation was significantly enhanced byt-butyl hydroperoxide (t-BuOOH) and ferric ions, which may be due to pigment formed from aldehydes other than malonaldehyde; the presence of these aldehydes was confirmed by the formation of the corresponding 2,4-dinitrophenylhydrazones. The amount of pigment produced from 24-h urine samples of 12 healthy subjects was estimated to be 26–95 nmol/kg, and 65–182 nmol/kg in the presence oft-BuOOH. These values are lower than those for urine of rabbit or rat. The TBA reactivity in the absence and presence oft-BuOOH of human urine was not related to age or sex. The TBA reactivity of human urine collected in the afternoon and in the evening was higher than that of urine collected in the morning.     

Thiobarbituric acid reaction of aldehydes and oxidized lipids in glacial acetic acid

Thiobarbituric acid (TBA) reaction of several aldehydes and oxidized lipids in glacial acetic acid was performed. All the samples were freely soluble in the solvent used. Saturated aldehydes produced a stable yellow pigment with an absorption maximum at 455 nm, a red pigment derived from malonaldehyde at 532 nm, and an orange pigment due to dienals at 495 nm. The absorbance maximum was 7–9 per μmol for saturated aldehydes, 27.5 per μmol for malonaldehyde and about 2 per μmol for dienals. Autoxidation of unoxidized lipids increased progressively in glacial acetic acid. When the TBA test was performed under nitrogen, autoxidation of unoxidized lipids was inhibited completely. While saturated aldehydes produced no yellow pigment under nitrogen, oxidized lipids produced a considerable amount of stable yellow pigment. The value for absorbance at 455 nm as a function of autoxidation time paralleled those of peroxide values. The absorbance of most oxidized lipids at 455 nm was higher than at 532 nm. Yellow pigment formation in the TBA test under nitrogen could not be ascribed to free saturated aldehydes but rather to unspecified closely related substances. The stable yellow pigment was found to be an excellent indicator of lipid oxidation.     

Pseudohalogenation of methyl 9-hydroxy-cis-12-and 12-hydroxy-cis-9-octadecenoate

Pseudohalogenation of methyl 9-hydroxy-cis-12-octadecenoate (I) and methyl 12-hydroxy-cis-9-octadecenoate (II) has been carried out with N,N-dibromobenzenesulfonamide (NNDBS). Compounds I and II, on reaction with NNDBS, formed four and three products, respectively. The interesting feature of these reactions was the formation of 1,4-epoxy compounds. The structures of individual compounds were established with the help of elemental and spectral analysis.     

Thiobarbituric acid-reactive substances from peroxidized lipids

The thiobarbituric acid (TBA) reaction was performed on linoleic acid 13-monohydroperoxide, autoxidized fatty esters, edible fats and oils, rat liver microsomal lipids, and on human erythrocyte ghost lipids in order to determine which substances from peroxidized lipids are TBA-reactive. The reaction was carried out in 2% acetic acid containing butylated hydroxytoluene using two different reaction modes: a one-step mode which involves heating at 100°C, and a two-step mode which involves first treatment at 5°C and subsequent heating at 100°C. Yields of the red 1∶2 malonaldehyde/TBA adduct, as estimated by absorbance, fluorescence intensity and high-performance liquid chromatography, were much higher than the malonaldehyde content as determined by direct chemical analysis. Yields of red pigment obtained by the two-step mode were slightly higher than those obtained by the one-step mode. Pigment yields were dramatically increased by addition oft-butyl hydroperoxide. Red pigment formation from alkenals and alkadienals was similarly enhanced by the two-step mode or by addition oft-butyl hydroperoxide, whereas pigment formation from malonaldehyde was not. It appears likely that a component of the total red pigment formed from the peroxidized lipids was due to aldehyde species other than malonaldehyde.     

Glycine Surfactants Derived from Dodecenyl Succinic Anhydride

We report the synthesis and properties of two surfactants with a novel head group based on glycine. A monocarboxylic surfactant N-glycine methyl ester (2-dodecen-1-yl succinamic acid) (I) was prepared by ring opening of an n-alkyl succinic anhydride. Hydrolysis of the ester functionality yields a dicarboxylic acid II. The sodium salts of I and II were effective surfactants at neutral pH giving a low minimum surface tension (<30 mN m⁻¹ at 20 °C). At high pH (~12) the surface activity of both surfactants is reduced compared to neutral pH, indicating that at neutral pH an ‘acid soap’ is formed. The pK _a of the acid form of the surfactants was determined. Addition of calcium ions reduced the CMC of II but did not reduce the surface tension above the CMC. The resistance of II to calcium ion precipitation was measured at pH 7.     

A comparative study of fatty acid profiles of <Emphasis Type="Italic">Passiflora</Emphasis> seed oils from Uganda

A comparative study is presented of the FA composition (FAC) of the seed oils from the yellow passion fruit Passiflora edulis Sims var. flavicarpa (I), the purple fruit Passiflora edulis Sims var. edulis (II), the purple Kawanda hybrid, which is a cross between I and II (III), and the light-yellow apple passion fruit Passiflora maliformis L. (IV) grown in Uganda. Oil yields from the four varieties were between 18.5 and 28.3%. A GC analysis of the oils showed the most dominant FA to be linoleic (67.8–74.3%), oleic (13.6–16.9%), palmitic (8.8–11.0%), stearic (2.2–3.1%), and α-linolenic (0.3–0.4%) acids. The unsaturated FA content in the oils was high (85.4–88.6%). Iodine values of the seed oils of I, II, III, and IV calculated from the FAC were 133, 141, 133, and 138, respectively. The FAC and the iodine value of the seed oil in III are distinctly closer to the rootstock (I) than the scion (II). This indicates that the rootstock influence on the FAC of passion fruit seeds is graft-transmissible. The study further confirms that passion fruit seed oils represent a good source of essential unsaturated FA.     

Synthesis and characterization of polyimides based on isopropylidene-containing bis(ether anhydride)s

Two bis(ether anhydride)s, 4,4′-[1,4-phenylenebis(isopropylidene-1,4-phenyleneoxy)]-diphthalic anhydride (IV _a) and 4,4′-[isopropylidenebis(1,4-phenylene)dioxy]diphthalic anhydride (IV _b), were prepared in three steps starting from the nucleophilic nitrodisplacement reaction of 4-nitrophthalonitrile with α,α ′-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene (I _a) and 4,4′-isopropylidenediphenol (I _b) in N,N-dimethylformamide (DMF) in the presence of potassium carbonate. The bis(ether anhydride)s IV _a and IV _b were polymerized with various aromatic diamines to obtain two series of poly(ether amic acid)s VI _a–g and VII _a–g with inherent viscosities in the range of 0.30∼0.74 and 0.29∼1.01 dL/g, respectively. The poly(ether amic acid)s were converted to poly(ether imide)s VIII _a–g and IX _a–g by thermal cyclodehydration. Most of the poly(ether imide)s could afford flexible and tough films, and they showed high solubility in polar solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, and m-cresol. The obtained poly(ether imide) films had tensile strengths of 45∼83 MPa, elongations-to-break of 6∼27%, and initial modulus of 0.6∼1.7 GPa. The T_gs of poly(ether imide)s VIII _a–g and IX _a–g were in the range of 194∼210 and 204∼243 °C, respectively. Thermogravimetric analysis (TG) showed that 10% weight loss temperatures of all the polymers were above 500 °C in both air and nitrogen atomspheres.     

Synthesis of methoxypoly(oxyethylene)propionic acid

Summary We have investigated the reaction chemistry of methoxypoly(oxyethylene)propionitrile, I, to synthesize methoxypoly(oxyethylene)propionic acid, II. We have found that II can be prepared by converting I first to the corresponding amide. Subsequent hydrolysis of the amide then yields II. Received: 4 March 1999/Revised version: 17 June 1999/Accepted: 17 June 1999     

Facile and rapid synthesis of piperidinium-6-amino-4-aryl-3, 5-dicyano-1,4-dihydropyridine-2-thiolate

A fast and convenient protocol for the synthesis of a new class of piperidin-1-ium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-thiolate (piperidinium salt) derivatives is developed by the one-pot, three-component reactions of cyanothioacetamide, aromatic aldehydes and piperidine in dichloromethane at room temperature. The features such as operational simplicity, mild conditions, absence of catalyst, high yields in short reaction times, simple purification process with no chromatographic technique make the protocol highly attractive.     

Living tandem free radical polymerization of a liquid crystalline monomer

Treatment of 1-β-(4′-acetylphenyl)vinyl-3-vinyl-1,1,3,3-tetramethyldisiloxane (I) (an AB₂ monomer) with dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) leads to a hyperbranched material, poly[1-β-(4′-acetylphenyl)vinyl-3-vinyl-1,1,3,3-tetramethyldisiloxane] (II). I has been prepared by a Pd catalyzed Heck reaction between 4-bromo-acetophenone and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The structure of the soluble hyperbranched material (II) has been determined by ¹H, ¹³C and ²⁹Si NMR, as well as by IR and UV spectroscopy. It has also been characterized by GPC, TGA, DSC and elemental analysis. Polymerization occurs by Ru catalyzed addition of the aromatic C−H bonds which are ortho to the activating acetyl group of I across the C−C double bond of the terminal Si-vinyl group in an anti-Markovnikov manner. Received: 8 September 1997/Revised version: 19 October 1997/Accepted: 20 November 1997     

Synthesis and characterization of new poly(ether–ester–imide)s as a generation of soluble and thermally stable polymers

A new-type of dicarboxylic acid 6 was synthesized from the reaction of 1,4-bis[4-aminophenoxy]butane 4 with trimellitic anhydride 5 in a solution of glacial acetic acid/pyridine (Py) at refluxing temperature. 1,4-Bis[4-nitrophenoxy]butane 3 was prepared by reaction of 4-nitrophenol 1 with 1,4-dibromo butane 2 in N,N-dimethylformamide (DMF) solution. Then dinitro 3 was reduced to 1,4-bis[4-aminophenoxy]butane 4 by using 10% Pd–C, ethanol, and hydrazine monohydrate. So six new thermally stable and organosoluble poly(ether–ester–imide)s (PEEIs) 8a–f with good inherent viscosities were synthesized by the direct polycondensation reaction of new 1,4-bis[4-(trimellitimido)phenoxy]butane 6 with several aromatic diols 7a–f through direct polycondensation using tosyl chloride (TsCl)/pyridine (Py)/DMF system as condensing agent. The resulted polymers were fully characterized by means of FTIR and ¹H NMR spectroscopy, elemental analyses, inherent viscosity, solubility tests, differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), and derivative of thermogravimetric (DTG).     

Synthesis and surface properties of chemodegradable anionic surfactants: Diastereomeric (2-n-alkyl-1,3-dioxan-5-yl) sulfates with monovalent counter-ions

Sodium, potassium and ammonium cis- and trans-(2-n-alkyl-1,3-dioxan-5-yl) sulfates 6–8 (alkyl: n-C₉H₁₉, 6a–8a, and n-C₁₁H₂₃, 6b–8b) were synthesized in a reaction of aliphatic aldehydes 1a,b with glycerol 2 followed by separation in high yields of individual geometric isomers of cis-and trans-2-n-alkyl-5-hydroxy-1,3-dioxanes, cis-3a,b and trans-3a,b, followed by sulfation with sulfur trioxide-pyridine complex, and finally neutralization with NaOH, KOH, and NH₄OH, respectively. Physical data of the compounds and some surface properties of 2-n-nonyl derivatives, such as critical micelle concentration (CMC), effectiveness of aqueous surface tension reduction (Π_CMC), surface excess concentration Γ_CMC, and the surface area demand per molecule (A_CMC), were determined. It was shown that the surface activity of these compounds is influenced both by their geometric structure and by the monovalent counter-ion.     

Polymerization by phase transfer catalysis

Summary Poly(amido-carbonate)s and poly(amido-thiocarbonate)s derived from 1,6-bis(4-hydroxyphenyl-carbamoyl)-hexamethylene I and 1,4-bis(4-hydroxyphenyl-carbamoyl)-phenylene II, and phosgene or thiophosgene, have been synthesized by a phase transfer catalysis process, which was ineffective for polymers derived from monomer I because the best results were obtained without catalyst, but was effective for those derived from monomer II obtaining higher yields when the catalysts were used. The ineffectivity was attributed to a hydrolytic process of the polymeric chains in the reaction media.     

Interesting Copper(I) and Mercury(II) 1D Coordination Polymers Based on 3,6-Bis(2-pyridylthio)pyridazine Ligand: Syntheses,Structures and Properties

Two interesting d¹⁰ metal complexes of 3,6-bis(2-pyridylthio)pyridazine ligand (PTP), [Cu₃I₃(PTP)] _n (1) and [HgI₂(PTP)] _n (2), have been synthesized and characterized by IR, elemental analysis, UV–Vis–NIR spectra, thermal analysis and single crystal X-ray diffraction analysis. Single-crystal X-ray analyses show that two complexes are both 1D chain coordination polymer. Complex 1 is a linear chain structure which is constructed from trinuclear Cu₃I₃ butterfly-shaped units by means of Cu–I bonds. Complex 2 is one-dimensional helical chain structure. In complex 2, two helical single chains form a double helix structure, and these double helix structures are further assembled to form a quasi 2D network by C–H⋯I hydrogen bonds. Optical diffuse-reflection spectra results suggest complex 1 has the property of the semiconductor.     

Synthesis,Crystal Structures and Fluorescent Properties of Two Bimetallic Coordination Polymers

Two novel 2D and 3D bimetallic Cd^IINi^II coordination polymers, Cd(2Mpz)(H₂O)Ni(CN)₄ (I) (2Mpz: 2-methylpyrazine) and Cd(2Epz)(H₂O)Ni(CN)₄ (II) (2Epz: 2-ethylpyrazine), have been synthesized and characterized by elemental analysis, powder X-ray diffraction, IR spectra, fluorescent spectra, single crystal X-ray diffraction and thermogravimetric analysis. Based on the analysis of structures, it can be found that the Cd(II) ions in the two complexes have the similar octahedral coordination geometry of CdN₅O, which are linked by [Ni(CN)₄]²⁻ units at the equatorial plane to form 2D sheet layers [CdNi(CN)₄] _n . However, it’s noted that the coordination environment of Ni(II) ions and action of ligands are different. All the Ni(II) ions in I are the five-coordinated pentahedron configuration and 2-methylpyrazine acts as a bridging ligand linking the Cd(II) and Ni(II) ions of the adjacent layers, leading to the 3D metal–organic framework. The structure of II indicates all the Ni(II) ions are the four-coordinated square plane and 2-ethylpyrazine is a terminal ligand coordinated to Cd(II) ions, forming the 2D layer structure. Moreover, the two complexes display significant thermal stability and fluorescent properties.     

Syntheses, Structures and Properties of Two Metal–Iodide Polymers Based on a Flexile N-Donor Ligand

Two novel metal–organic frameworks based on 1,3-bis(imidazol-1-ylmethyl)-benzene (m-bix), namely [(Cu₄I₄)(bix)₂] _n (1) and [HgI₂(bix)] _n (2) have been synthesized and characterized by IR, elemental analysis, thermogravimetry, luminescent properties and X-ray crystallography. The structure of compound 1 exhibits a 1D metal–organic chain composed of Cu₄I₄ clusters and m-bix ligands, and such chains are further united together to generate a 3D supramolecular structure through inter-chain π···π interactions. In compound 2, the HgI₂-bix chains interact each other to form a layer structure through π···π interactions, then the layers are extended to 3D supramolecular architecture through intermolecular C–H···π interactions.