Pyridine-acetic Acid Research Articles

Lignin Structure and Solvent Effects on the Selective Removal of Condensed Units and Enrichment of S-Type Lignin.

This study focused on the structural differences of lignin after pyridine–acetic acid–water (PAW) and dioxane–acidic water (DAW) purification processes. These structural differences included the S/G ratio, condensed structure, weight-average (MW) molecular weights, β-O-4 linkages and sugar content. The chemical structure of the isolated crude lignin (CL), PAW purified lignin (PPL) and DAW purified lignin (DPL) was elucidated using quantitative 13C NMR, 2D-HSQC NMR spectra, thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The results showed that the PPL fractions contain fewer condensed structures, higher S/G ratios, more β-O-4 linkages, higher average MW and lower thermal degradation properties compared to the CL and DPL fractions. Furthermore, the PAW process was more selective in removing condensed units and enriching S-type lignin from CL compared to the DAW process. These results provide valuable information for understanding which purification process is more suitable to be applied for lignin.

A combined electronic structure and molecular dynamics approach to computing the OH vibrational feature of strongly hydrogen-bonded carboxylic acids.

Medium and strong hydrogen bonds give rise to vibrational features that can span several hundreds of wavenumbers and have unusual line shapes. For example, dimers consisting of carboxylic acids hydrogen-bonded to nitrogen-containing aromatic bases exhibit a vibrational feature that spans over 900 cm-1 and contains two very broad peaks. In this report, we demonstrate how this feature can be reproduced using a combined molecular dynamics (MD) and electronic structure "spectral map" approach, which has been very successful in modeling the vibrational spectrum of water in different environments. In this approach, spectral maps are created, relating the transition frequencies and probabilities to the electric field along the OH bond, which are obtained from the density functional theory calculations of snapshots taken from a classical MD simulation. This map was used to compute the spectral properties of thousands of geometries of the pyridine-acetic acid dimer sampled by a MD simulation, which were used to compute the overall spectral feature. It was found that this approach reproduced the experimental spectrum better than the previous dimer stretch approaches (which were based on describing the dimer geometries harmonically) through a more accurate sampling of dimer geometries. The broadness of these vibrational features largely originates from the range of geometries present in the condensed phase, while the unusual line shape is caused by strong Fermi resonances.

Association and liquid structure of pyridine-acetic acid mixtures determined from neutron scattering using a 'free proton' EPSR simulation model.

The liquid structure of pyridine-acetic acid mixtures have been investigated using neutron scattering at various mole fractions of acetic acid, χHOAc = 0.33, 0.50, and 0.67 and compared to the structures of neat pyridine and acetic acid. Data has been modelled using empirical potential structure refinement (EPSR) with a 'free proton' reference model, which has no prejudicial weighting towards either the existence of molecular or ionised species. Analysis of the neutron scattering results shows the existence of hydrogen-bonded acetic acid chains with pyridine inclusions, rather than the formation of an ionic liquid by proton transfer.

ChemInform Abstract: Highly Conjugated π-Electron Donors for Organic Metals: Synthesis and Redox Chemistry of New 1,3-Dithiole and 1,3-Selenathiole Derivatives.

The bis(1,3-dithiolium) dication salts 8a–c have been synthesised in three steps (31–51% overall yields) starting from 1,4-bis(bromomethyl)naphthalene, 9,10-bis(chloromethyl)anthracene and 4,4′-bis(chloromethyl)biphenyl, respectively. The bis(halogenomethyl) compounds 5 were converted into the dipiperidiniumbis(dithiocarboxylate) salts 6, which on alkylation with 3-chlorobutane-2-one yielded bis(dithioesters)7; cyclisation of 7 occurred on treatment with concentrated sulphuric acid to give dication salts 8. Dimethyl 1,3-dithiol-2-ylphosphonate 20, dimethyl 4,5-dimethyl-1,3-dithiol-2-ylphosphonate 21 and dimethyl 1,3-selenathiol-2-ylphosphonate 22 were treated with butyllithium in the presence of a range of carbonyl compounds and quinones, e.g., cyclopentanone, cyclohexanone, benzophenone, acetophenone, benzaldehyde, thioxanthen-9-one, anthraquinone, bianthrone and naphthacene-5,12-quinone to yield Wittig–Horner products, e.g., alkenes 26–34 and the anthracenediylidene derivatives 35, 36, 40–43 and 53. Unsymmetrical derivatives 37–39 were prepared in two steps as follows: anthrone reacted with 2-methylthio-1,3-dithiolium iodides 45 and 46 in pyridine-acetic acid to yield ketones 48 and 49 which were then treated with the Wittig–Horner reagents 23–25. Cyclic voltammetric data for the new tetrathiafulvalene, selenatrithiafulvalene and diselenadithiafulvalene derivatives 35–43and 53, show that these systems undergo two-electron redox behaviour which is observed as a single wave. Complexes of these donors with electron acceptors, e.g. 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), have been obtained, some of which are organic semiconductors.

Facile Syntheses of Some Thieno[2,3-d] Pyrimidine Derivatives

In one-pot synthesis 2-arylidene-5,6,7,8-tetrahydrothiazolo[3,2-a] cyclopenteno-thieno[2,3-d] pyrimidine-3,5-diones (3) were prepared via the reaction of a ternary mixture of 2-thioxo-1,3,4,5,6,7-hexahydr cyclopentinothieno [2,3-d]-4-one (2), chloroacetic acid and a proper aldehyde. Compound 2 reacted with 3-chloropent-2, 4-dione in ethanolic potassium hydroxide yielding the S-acetyl acetone derivative 5f . The latter compound reacted with hydrazine hydrate and phenyl hydrazine yielded the 2-pyrazolthio derivative 10a, b. Compound 5f also underwent cyclization on heating with acetic acid—pyridine solution to give 11. The 2-methylthio derivative 5a, when treated with hydrogen peroxide gave the corresponding oxidized product 9.

Oxidation of adamantane with hypobromous acid generated in situ from CHnBr4−n and H2O in the presence of molybdenum complexes

Adamantan-1-ol (II) can be synthesized by catalytic oxidation of adamantane (I) with such oxidants as oxygen, hydrogen peroxide, alkyl hydroperoxides, and iodosylbenzene in the presence of Co, Mn, Fe, and Ru complexes [1–12]. Catalytic oxidation of adamantane (I) generally gives mixtures of products. For example, the oxidation of I with atmospheric oxygen in pyridine–acetic acid in presence of an iron catalyst and zinc at 40°C afforded a mixture of adamantan-1-ol and adamantan-2-ol whose ratio ranged, depending on the conditions, from 10 : 1 to 24.8 : 1, the overall yield being 6–16% [8].

Separations of hydrophobic synthetic peptides in counter-current chromatography

Synthetic peptides with many aromatic, aliphatic and especially acidic amino acid residues are not very soluble and require strong solvents for useful partitioning. A chloroform–methanol–acidic solvent system fractionates neutral and basically charged 26-mers to provide high yields. An insoluble 15-mer with 5 Trp residues and 60% overall hydrophobic amino acid content was purified in pyridine–acetic acid and in another basic t-butyl methyl ether– n-butanol–acetonitrile solvent system with high recovery. Two instruments were used, the eccentric-multi-layer hybrid coil planet centrifuge and the new spiral disk planet centrifuge that were able to retain the stationary phase of these solvent systems, some of which have low interfacial tension.

The oxygenation of cyclohexane under Gif IV conditions – The catalytic behaviour of iron complexes

The catalytic oxygenation of cyclohexane to cyclohexanol (-ol) and cyclohexanone (-one) using a series of di- and trivalent iron-picolinate complexes under Gif IV conditions (10:1 v/v pyridine–acetic acid, zinc powder at room temperature under aerobic atmosphere) proceeds with turnover numbers [defined as (moles of oxygenated products)/(moles of catalyst)] of 161–184 and -one:-ol ratios of 4.2–4.7. The corresponding values for the binuclear picolinate complex [Fe 2(μ-OMe) 2(pic) 4] (237 turnovers, -one:-ol ratio 7.2) are significantly higher. Iron complexes bearing functionalised pyridyl ligands exhibit turnover numbers and ketone selectivities of similar magnitude to, and in some cases higher than, the picolinate complexes.

Phosphoralaninate Pronucleotides of Pyrimidine Methylenecyclopropane Analogues of Nucleosides: Synthesis and Antiviral Activity

The Z- and E-thymine and cytosine pronucleotides 3d, 4d, 3e, and 4e of methylenecyclopropane nucleosides analogues were synthesized, evaluated for their antiviral activity against human cytomegalovirus (HCMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human immunodeficiency virus type 1 (HSV-1), and hepatitis B virus (HBV) and their potency was compared with the parent compounds 1d, 2d, 1e, and 2e. Prodrugs 3d and 4d were obtained by phosphorylation of parent analogues 1d or 2d with reagent 8. A similar phosphorylation of N4-benzoylcytosine methylenecyclopropanes 9a and 9b gave intermediates 11a and 11b. Deprotection with hydrazine in pyridine–acetic acid gave pronucleotides 3e and 4e. The Z-cytosine analogue 3e was active against HCMV and EBV. The cytosine E-isomer 4e was moderately effective against EBV.

Synthesis and anti‐HIV Activity of L‐β‐3′‐C‐Cyano‐2′,3′‐unsaturated Nucleosides and L‐3′‐C‐Cyano‐3′‐deoxyribonucleosides.

Abstract An efficient synthetic method was developed for l -β-3′- C -cyano-2′,3′-unsaturated nucleosides and l -3′- C -cyano-3′-deoxyribonucleosides. The key intermediate 11 was obtained from l -xylose, from which a series of pyrimidine and purine nucleosides were prepared in high yield by the coupling of 11 and various silyl-protected bases in the presence of TMSOTf. These nucleosides were eliminated, followed by deprotecting to give l -β-3′- C -cyano-2′,3′-unsaturated nucleosides. When selectively deprotected by hydrazine hydrate in buffered acetic acid–pyridine followed by treatment with potassium carbonate in methanol, l -3′- C -cyano-3′-deoxyribonucleosides were obtained. The synthesized nucleosides were tested for anti-HIV activity.

Synthesis and intramolecular reactions of Tyr-Gly and Tyr-Gly-Gly related 6- O-glucopyranose esters

6- O-( l-Tyrosylglycyl)- and 6- O-( l-tyrosylglycylglycyl)- d-glucopyranose were synthesized by condensation of the pentachlorophenyl esters of the respective di- and tripeptide with fully unprotected d-glucose. The intramolecular reactivity of the sugar conjugates was studied in pyridine–acetic acid and in dry methanol, at various temperatures and for various incubation times. The composition of the incubation mixtures was monitored by a reversed-phase HPLC method that permits simultaneous analysis of the disappearance of the starting material and the appearance of rearrangement and degradation products. To determine the influence of esterification of the peptide carboxy group on its amino group reactivity, parallel experiments were done in which free peptides were, under identical reaction conditions, incubated with d-glucose (molar ratios 1:1 and 1:5). Depending on the starting compound, different types of Amadori products (cyclic and bicyclic form), methyl ester of peptides, and Tyr-Gly-diketopiperazine were obtained.

Synthesis and anti-HIV activity of l-β-3′- C-cyano-2′,3′-unsaturated nucleosides and l-3′- C-cyano-3′-deoxyribonucleosides

An efficient synthetic method was developed for l-β-3′- C-cyano-2′,3′-unsaturated nucleosides and l-3′- C-cyano-3′-deoxyribonucleosides. The key intermediate 11 was obtained from l-xylose, from which a series of pyrimidine and purine nucleosides were prepared in high yield by the coupling of 11 and various silyl-protected bases in the presence of TMSOTf. These nucleosides were eliminated, followed by deprotecting to give l-β-3′- C-cyano-2′,3′-unsaturated nucleosides. When selectively deprotected by hydrazine hydrate in buffered acetic acid–pyridine followed by treatment with potassium carbonate in methanol, l-3′- C-cyano-3′-deoxyribonucleosides were obtained. The synthesized nucleosides were tested for anti-HIV activity.

Hydrogen-Bonding Interactions between Formic Acid and Pyridine

The structure, energetics, vibrations, and barrier to internal rotation around the N···H−O hydrogen bond of the binary pyridine−formic acid complex are calculated using one properly selected hybrid density functional theory procedure. The calculations demonstrate that the most stable isomer of the complex has a strong N···H−O hydrogen-bonding interaction, whose strength is enhanced by the presence of an agostic interaction between the carbonylic oxygen and the α hydrogen of the pyridine. Rotation around N···H−O, which prevents such an agostic interaction to occur, results in a decrease of the bonding energy of the complex from 11.1 kcal/mol to 6.43 kcal/mol. Additionally, a normal-mode analysis of the vibrations of the two most stable complexes characterized has been carried out and compared with the experimental vibrational frequencies of the pyridine-acetic acid complex. Furthermore, the effect of the specific solvation by one more formic acid molecule and one methanol molecule has also been considered....

Structural studies of the glycopeptides of B-chain of cinnamomin--a type II ribosome-inactivating protein by nuclear magnetic resonance.

Cinnamomin is a plant type II ribosome-inactivating protein (RIP) isolated from the seeds of Cinnamomum camphora. It consists of two nonidentical polypeptide chains (A- and B-chain) held together through one disulfide linkage. Its A- and B-chain contain 0.3% and 3.9% sugars respectively. The B-chain of cinnamomin was digested by pronase E and then the liberated glycopeptides were separated from non-glycopeptides by gel filtration chromatography on a Bio-Gel P-4 column. Three crude glycopeptides were obtained by continuing chromatography over anion-exchange resin (AG1-X2) in the buffer of 2% pyridine-acetic acid (pH 8.3) with a polygradient elution system. Through further purification by the gel filtration chromatography and HPLC, three major glycopeptides, GP1, GP2 and GP3 were obtained. Mainly by two-dimensional Nuclear Magnetic Resonance (NMR) including TOCSY, DQF-COSY, NOESY, HMQC and HMBC, their primary structures were analyzed as: Man\balpha1,3Man\balpha1,6(Man\balpha1,3)(Xyl\bbeta1,2)Man\bbeta1,4GlcNAc\bbeta1,4GlcNAc\bbeta1-(Gly-)Asn-Asn-Thr(GP1), Man\balpha1,6(Man\balpha1,3)(Xyl\bbeta1,2)Man\bbeta1,4GlcNAc\bbeta1,4(Fuc\balpha1,3)GlcNAc\bbeta1-Asn-Ala-Thr(GP2),Man\balpha1,6(Man\balpha1,3)Man\balpha1,6(Man\balpha 1,2 Man\balpha1,3)Man\bbeta1,4GlcNAc\bbeta1,4GlcNAc\bbeta1-(Ala-)Asn-Gly-Thr(GP3).

Medium and temperature effects on the infrared spectra and structure of carboxylic acid–pyridine complexes: acetic acid

Transformations of the infrared spectrum of strongly hydrogen bonded (H-bonded) complex pyridine–acetic acid, caused by transition from the gas phase to solution, by increase of solvent polarity and by temperature decrease in solutions have been investigated. For comparison, spectrum of acetic acid dimer has been studied under similar conditions. It has been found that in contrast to the dimer, transition of the complex from the gas to condensed phase, as well as an increase of polarity of the complex solution, leads to significant low frequency shift, broadening and intensity increase of νOH band, high frequency shift of ν σ band and low frequency shift of νCO band. All these changes can be treated as spectral manifestation of essential strengthening of the H-bond in the complex, accompanied by shifting of the bridging proton toward the nitrogen atom. Temperature behaviour of νOH band in polar solvents, such as butyl chloride or methylene chloride, is determined mainly by two factors: (a) changing of population of the low frequency levels of hydrogen bond vibrations; (b) ordering and polarization of the solvent in complex vicinity, which provides H-bond strengthening. In the inert unpolar solvents, like hexane, temperature decrease in some cases leads to an increase of contribution of the complexes with more complicated composition than 1:1. The data obtained are analysed using the earlier developed theory of the solvent effects on vibrational spectra of H-bonded complexes.

Solvent effect on acid–base clustering between acetic acid and pyridine

The solvent effect on the acid–base interaction between acetic acid and pyridine has been studied by the mass spectrometric analysis of clusters isolated from liquid droplets. The clusters resulting from the acetic acid–pyridine, acid–base, interaction in water are quite different from those in acetonitrile solvent. In water (acetic acid∶pyridine∶water = 1∶1∶10) the acid–base interaction occurs through the intercluster interaction between acetic acid and pyridine clusters. On the other hand, in acetonitrile (acetic acid∶pyridine∶acetonitrile = 1∶1∶10), the acid–base interaction proceeds through an intermonomer interaction between an acetic acid molecule and pyridine molecule, and the clusters are produced through the aggregation of a polar (acetic acid)δ–(pyridine)δ+ complex. This solvent effect is mainly attributed to the cluster structure of acetic acid and pyridine in water and acetonitrile solvent.

The conversion of saturated hydrocarbons into carboxylic acids using Fe(CO) 5H 2O 2 oxidation

Saturated hydrocarbons are transformed into their corresponding homologous carboxylic acids by treatment with iron pentacarbonyl and hydrogen peroxide in pyridine-acetic acid. A mechanism for this reaction is proposed. A tteention is also directed to a new and convenient procedure for the determination of carbon monoxide.

The carboxylation of saturated hydrocarbons by Gif systems. (Fe III trispicolinate/P(OMe) 3/CO/H 2O 2 in pyridine-acetic acid).

Saturated hydrocarbons are transformed into the corresponding homologous carboxylic acids by treatment with Fe(Pa) 3/P(OMe) 3/CO/H 2O 2 in pyridine-acetic acid. Optimisation of the reaction conditions and mechanistics studies are reported.

The effect of triphenylphosphine in the GoAgg II system.

The usual formation of ketone and alcohol under GoAgg II conditions [FeCl 3·6H 2O (cat.), H 2O 2 in pyridine-acetic acid] can be totally replaced by the formation of the corresponding mono-alkyl substituted derivatives by addition of PPh 3 and alkali metal salts.

ChemInform Abstract: The Carboxylation of Saturated Hydrocarbons by Gif Systems (Fe0/CO/O2 and Cu0/CO/O2 in Pyridine‐Acetic Acid).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.