Acetate Molecules Research Articles

Densities, excess molar volumes, and refractive indices of ethyl acetate and aromatic hydrocarbon binary mixtures

Densities, excess molar volumes, refractive indices, and changes in refractive index on mixing for (ethyl acetate + benzene, or methylbenzene, or ethylbenzene, or 1-4-dimethylbenzene, or 1-methylethylbenzene, or 1-3-5-trimethylbenzene, or 1-1-dimethylethylbenzene) have been determined atT= 298.15 K. The excess molar volumes and changes in refractive index have been fitted to Redlich–Kister polynomials. The π -electrons interactions of the benzene ring and the peculiar plate shape of the aromatic molecules are noticeably modified by the presence of the ethyl acetate molecules of a different nature. The intermolecular interactions are strongly modified and result in positive excess volumes except for toluene or p -xylene whose values are close to zero. The refractive indices were compared with calculated values using mixing rules proposed by several authors.

A Novel Lead- bis (4-Chloro-2-Methylphenoxy)- Acetate Polymeric Complex

The bis (4-chloro-2-methylphenoxy)acetato lead (II) monohydrate infinite polymer was synthesized and characterized by elemental analysis and infrared spectroscopy. The crystal and molecular structure has been determined and the bond valences were computed. Molecules of the monomer, each occupying an asymmetric unit, are connected by the inversion center and a polymer chain is created by Pb(2O)Pb rings in spiro arrangement. The lead atom is seven coordinate by four oxygen atoms from two chelating carboxyl groups, one water molecule, and two oxygen atoms provided by symmetry generated carboxyl groups. Each carboxyl group acts as a bidentate ligand toward one metal atom and as a monodentate ligand with respect to a second. The lead-oxygen distances are spread over a wide range of values. One molecule of (4-chloro-2-methylphenoxy)acetate in the monomer is close to planarity, and the second is bent. All 4-chloro-2-methylphenoxy groups are almost parallel. The polymer infinite chains are assembled by weak hydrogen bonds to a layered structure.

非接触原子間力顕微鏡 なにがどこまで見えるか？ 吸着有機分子の非接触型原子間力顕微鏡観察 分子像の定量的理解に向けて

Noncontact atomic force microscopy (NC-AFM) images of the mixed monolayers of carboxylates prepared on a TiO2(110)-(1×1) surface are presented. The order of the height of formate, acetate, pivalate, and propiolate molecules is reproduced in the NC-AFM images, while the difference in the height is smaller than that expected from their true heights. The shrinkage of the height difference is ascribed to the contribution of several molecules to the tip-molecule force. On the other hand, trifluoroacetate is imaged as a spot shorter than the acetate though the two ions have an equal true height. This indicates that the image contrast reflects the permanent dipole moment of the molecules. The experimental results show that the organic molecules can be individually identified by the NC-AFM and the experimentally obtained topography is interpreted referring to physical and chemical characteristics of the molecules.

A Comparison of Coulometric Titration and Potentiometric Determination of Chloride Concentration in Rumen Fluid

The concentration of chloride ions in rumen fluid is a useful measure of obstructive gastrointestinal disease in ruminants and camelids. However, rumen fluid is very different from other biological fluids in its bacterial populations, consistency, and concentrations of various anions. Two methods of determining the chloride concentration in biological fluids were compared using centrifuged and filtered rumen fluid containing different amounts of sodium chloride. Although coulometric titration and potentiometric electrode analysis yielded results that had a strong linear relationship, the results of potentiometry were consistently and significantly higher, by about 20 mEq/L. This difference was investigated further by analyzing a series of fluids containing different concentrations of sodium acetate. Acetate was detected as chloride (0.21 chloride molecules per acetate molecule) by potentiometry but not by coulometric titration. Therefore, the acetate concentration of rumen fluid was the most likely cause of the discrepancy between tests in the original trial. In conclusion, the coulometric procedure may be more accurate than the potentiometric procedure for measuring rumen chloride when the concentrations of possible confounding ions are unknown.

Toward the de novo design of a catalytically active helix bundle: a substrate-accessible carboxylate-bridged dinuclear metal center.

De novo design of proteins provides an attractive approach to uncover the essential features required for their functions. Previously, we described the design and crystal structure determination of a di-Zn(II) complex of "due-ferri-1" (DF1), a protein patterned after the diiron-dimanganese class of redox-active proteins [Lombardi, A.; Summa, C.; Geremia, S.; Randaccio, L.; Pavone, V.; DeGrado, W. F. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 6298-6305]. The overall structure of DF1, which contains a carboxylate-bridged dinuclear metal site, agrees well with the intended design. However, access to this dimetal site is blocked by a pair of hydrophobic leucine residues (L13 and L13'), which prevent facile entry of metal ions and small molecules. We have now taken the next step in the eventual construction of a catalytically active metalloenzyme by engineering an active site cavity into DF1 through the replacement of these two leucine residues with smaller residues. The crystal structure of the dimanganous form of L13A-DF1 indeed shows a substrate access channel to the dimetal center. In the crystal structure, water molecules and a ligating dimethyl sulfoxide molecule, which forms a monatomic bridge between the metal ions, occupy the cavity. Furthermore, the diferric form of a derivative of L13A-DF1, DF2, is shown to bind azide, acetate, and small aromatic molecules.

NC-AFM topography of HCOO and CH3COO molecules co-adsorbed on TiO2(110)

Organic molecules terminated by a H atom or a CH3 atom-group are identified by using atomic force microscopy operated in non-contact mode (NC-AFM). Formate (HCOO-) and acetate (CH3COO-) molecules co-adsorbed on a TiO2(110) surface are visualized in constant frequency-shift mode. The relation of the experimental image contrast and the atom coordinates of the admolecules is discussed.

Interaction of Acetate Anion with Hydrated Al3+ Cation: A Theoretical Study

Density-functional theory (DFT) methods were used for investigations on the aluminum−hexaaquo complex and on aqueous aluminum−acetate complexes. Solvent effects were computed by means of the polarized continuum model (PCM). Extensive basis set studies and comparison of several functionals lead to efficient and accurate procedures which were applied to the computation of aluminum−acetate complexes. A variety of structural arrangements such as monodentate or bidentate with respect to the bonding of the carboxylate group or cis/trans with respect to the relative position of two acetate molecules were considered. ΔH and ΔG values were calculated for the substitution reaction of water molecules in the aluminum−hexaaquo complex by acetate anions. Characteristic differences in ΔS were found depending on the number of water molecules released per acetate. Overall, we find that monodentate structures are only slightly preferred over bidentate ones and that we expect a relatively complicated system of chemical equi...

STM and FTIR studies of methoxy and acetate on Cu(110) surfaces resulting from reactions with methyl acetate and preadsorbed oxygen

We have used scanning tunneling microscopy (STM) and Fourier transform infrared spectroscopy (FTIR) to examine clean and oxygen-precovered Cu(110) surfaces that have been exposed to methyl acetate (CH 3CO 2CH 3). Both clean and completely saturated (2×1)O surfaces are comparatively inert to methyl acetate exposure. Methyl acetate reacts on surfaces containing (2×1)O islands and areas of the clean surface resulting in the appearance of (5×2) structures. We propose that these (5×2) structures consist of equal numbers of methoxy (CH 3O) and acetate molecules (CH 3CO 2). Over time, these (5×2) structures disappear from the surface due to the decomposition of the methoxy and the resultant formation of a mobile acetate species on this surface. We have performed STM experiments that support these interpretations.

Crystal structure of a (25R)-2α,3α-epoxy-5α-spirostan-6, 23-dione hemi-ethyl acetate solvate

The compound (25R)-2α,3α-epoxy-5α-spirostan-6,23-dione, crystallizes as a hemi-ethyl acetate solvate, having two host molecules of similar conformation per molecule of ethyl acetate, in the asymmetric unit. The O atom of the epoxy group is α-oriented. The presence of the epoxy group disturbs the chair conformation in the ring A of the steroidal nucleus. Ring A has a C5α,C10β half-chair conformation. The six-membered rings B, C, and F have chair conformation as expected. The D ring adopts a C14α-envelope conformation and the E ring is midway between a C22α,O3β half-chair and a C22α-envelope conformations. The A/B, B/C, and C/D ring junctions are trans. Crystal data: C27H38O5·1/2C4H8O2, Monoclinic, space group P21, a = 7.7363(18) b = 28.769(12) c = 12.038(6) A, β = 90.88(5), V = 2679.0(10) A3, Z = 4. The packing of the molecules is assumed to be dictated by van der Waals interactions and by intermolecular C—H ··· O hydrogen bonds.

Hydrogen Bonding Governs the Elastic Properties of Poly(vinyl alcohol) in Water: Single-Molecule Force Spectroscopic Studies of PVA by AFM

The mechanical properties of single poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) molecules under different solvent conditions were investigated using a new atomic force microscope (AFM) based techniquesingle-molecule force spectroscopy. The single-molecule force spectrum of PVA shows a kink at around 200 pN, deviating from the entropic elasticity of a random coil predicted from the WLC model. Since the single-molecule force spectra of PVAc and PVA in 8 M urea indicate that both behave like ideal entropic springs, the hydrogen bonding of hydroxyl groups in PVA must govern the elastic behaviors of PVA in water. Because of hydrogen bonding, PVA assumes a multiple stranded suprastructure in water. Upon stretching, the suprastructure undergoes a conformational transition to an overstretched state. This conformational change is fully reversible and is thus in thermodynamic equilibrium. This study demonstrates the unique utility of AFM in exploiting of suprastructures and conformational changes of synthetic polymers.

FTIR investigations of solid precursor materials for sol-gel deposition of WO3 based electrochromic films

Peroxypolytungstic acid derivative (APTA) and peroxypolytungstic acid derivative coupled with a dicarboxylic acid additive i.e., oxalic acid dihydrate (APTA + OAD) in xerogel form, synthesized by a wet chemistry route were the solid sol-gel precursors for casting WO3 films. These bulk materials have a complex structure owing to the presence of several groups such as acetate, peroxy anions and water molecules in their basic matrix. Additionally, oxalate ions constitute an integral part of the structure in the APTA + OAD xerogel. Detailed FTIR analysis of these coordination compounds has thrown light on the modes of association of the various anions or groups with tungsten metal ion. The mode of coordination of the acetate ion as a bidentate as well as a monodentate ligand enabling chelate formation and the several other chemical linkages prevalent in APTA have been established. Upon the incorporation of OAD in APTA, the net ramifications are drastic changes in the structure inclusive of changes in the nature and strength of metal - ligand bonding, which is exemplified by FTIR studies of (APTA + OAD) xerogel.

Monolayer dispersion of MoO 3, NiO and their precursors on γ-Al 2O 3

The dispersion capacities of MoO 3, NiO and their precursors on the surface of γ-Al 2O 3 are studied by XPS and XRD techniques. As a relatively low melting point oxide, MoO 3 gives a dispersion capacity higher than its precursor molybdate based on mole of MoO 3 on γ-Al 2O 3. Dispersion capacities of molybdate on γ-Al 2O 3 depend on the pH of molybdate solution used for impregnation while the dispersion capacity of MoO 3 on γ-Al 2O 3 is independent of its precursors. As a high-melting point oxide, the dispersion capacity of NiO based on mole of NiO is the same as that of its precursor. By one-step impregnation, dispersion capacity of nickel nitrate and its derived NiO on γ-Al 2O 3is larger than that of nickel acetate and its derived NiO. This difference can be attributed to the larger size of nickel acetate molecule. The utmost dispersion capacity of NiO on γ-Al 2O 3 is achieved through one-step impregnation when nickel nitrate is used as the precursor, while the same capacity can only be achieved through multiple impregnation when nickel acetate is used as the precursor.

Electron paramagnetic resonance of Gd 3+ in praseodymium triacetate monohydrate

X-band (∼9.6 GHz) electron paramagnetic resonance measurements were carried out on a Gd 3+-doped praseodymium triacetate monohydrate, Pr(CH 3COO) 3·H 2O, single crystal in the temperature range 4.2–295 K. The spin-Hamiltonian parameters were estimated at room, liquid-nitrogen and liquid-helium temperatures by the use of a rigorous least-squares fitting technique. The absolute sign of the zero-field splitting parameter, b 0 2, was determined to be negative by comparison of the intensities of the high- and low-field EPR lines at room and liquid-helium temperatures. The behaviour of EPR spectrum was studied as a function of temperature; the variation of the linewidth and line positions indicated a significant reordering of acetate and water molecules at about 240 K. The present Gd 3+ EPR results in praseodymium triacetate monohydrate are compared with those in the rare-earth triacetate tetrahydrate hosts with Sm, Nd, Er, Y, Yb and Dy ions.

Oxygen Exchange between Acetate and the Catalytic Glutamate Residue in Glutaconate CoA-transferase from Acidaminococcus fermentans: IMPLICATIONS FOR THE MECHANISM OF CoA-ESTER HYDROLYSIS

The exchange of oxygen atoms between acetate, glutaryl-CoA, and the catalytic glutamate residue in glutaconate CoA-transferase from Acidaminococcus fermentans was analyzed using [(18)O(2)]acetate together with matrix-assisted laser desorption/ionization time of flight mass spectrometry of an appropriate undecapeptide. The exchange reaction was shown to be site-specific, reversible, and required both glutaryl-CoA and [(18)O(2)]acetate. The observed exchange is in agreement with the formation of a mixed anhydride intermediate between the enzyme and acetate. In contrast, with a mutant enzyme, which was converted to a thiol ester hydrolyase by replacement of the catalytic glutamate residue by aspartate, no (18)O uptake from H(2)(18)O into the carboxylate was detectable. This result is in accord with a mechanism in which the carboxylate of aspartate acts as a general base in activating a water molecule for hydrolysis of the thiol ester intermediate. This mechanism is further supported by the finding of a significant hydrolyase activity of the wild-type enzyme using acetyl-CoA as substrate, whereas glutaryl-CoA is not hydrolyzed. The small acetate molecule in the substrate binding pocket may activate a water molecule for hydrolysis of the nearby enzyme-CoA thiol ester.

Thioploca spp.: filamentous sulfur bacteria with nitrate vacuoles

Thioploca spp. are multicellular, filamentous, colorless sulfur bacteria inhabiting freshwater and marine sediments. They have elemental sulfur inclusions similar to the phylogenetically closely related Beggiatoa, but in contrast to these they live in bundles surrounded by a common sheath. Vast communities of large Thioploca species live along the Pacific coast of South America and in other upwelling areas of high organic matter sedimentation with bottom waters poor in oxygen and rich in nitrate. Each cell of these thioplocas harbors a large liquid vacuole which is used as a storage for nitrate with a concentration of up to 500 mM. The nitrate is used as an electron acceptor for sulfide oxidation and the bacteria may grow autotrophically or mixotrophically using acetate or other organic molecules as carbon source. The filaments stretch up into the overlying seawater, from which they take up nitrate, and then glide down 5–15 cm deep into the sediment through their sheaths to oxidize sulfide formed by intensive sulfate reduction. New major occurrences have been found in recent years, both in lakes and in the ocean, and have stimulated the interest in these fascinating bacteria.

The first gene in the biosynthesis of the polyketide antibiotic TA Of Myxococcus xanthus codes for a unique PKS module coupled to a peptide synthetase

The polyketide antibiotic TA is synthesized by the Gram negative bacterium Myxococcus xanthus in a multi-step process in which a unique glycine-derived molecule is used as a starter unit and elongated through the condensation of 11 acetate molecules by polyketide synthases (PKSs). Analysis of a 7.2 kb DNA fragment, encoding the protein that carries out the first condensation step, revealed that the fragment constitutes a single open reading frame, referred to as Ta1, which lacks the 5′ and 3′ ends and displays two regions of similarity to other proteins. The first 1020 amino acid residues at the N terminus of the polypeptide are similar to sequences of the large family of enzymes encoding peptide synthetases. They are followed by a second region displaying a high degree of similarity to type I PKS genes. The genetic analysis of this open reading frame is compatible with the proposed chemical structure of TA. The data indicate that the genes encoding TA have a modular gene organization, typical of a type I PKS system. The unusual feature of Ta1 is that the first PKS module of TA resides on the same polypeptide as the peptide synthetase functional unit.

Energetic Study of the Disordered Solvent in the Crystal Structure of an Isoxazole Derivative

In the crystal structure of ethyl (Z)-3-{[3-(3,5-dichloro-2,4,6-trimethylphenyl)isoxazol-4-yl]-2-butenylidene}carbazate–ethyl acetate solvate, C19H21Cl2N3O3.0.34-C4H8O2 (R 1 = 0.072, wR 2 = 0.228), the host molecules are linked by intermolecular N—H...N hydrogen bonds, giving rise to infinite channels which contain molecules of ethyl acetate. Packing potential energy calculations carried out for host–guest model crystals account for the disorder of the solvent molecules in the crystal state.

Enzymatic acylation of cellulose acetate in organic media

Cellulose fatty esters were prepared by acylation of cellulose acetate with various fatty acids catalyzed by immobilized lipase from Candida antarctica (Novozyme) in acetonitrile. The reaction parameters affecting the biocatalytic process such as the role of the nature of the substrates, the concentration of the enzyme and the reactants as well as the agitation speed of the reaction mixture have been investigated. At optimum reaction conditions about 35% of the initial amount of fatty acid were incorporated on the modified cellulose acetate molecule, while an increase of 2% of the ester bonds was observed on the final product.

Pathway for the biosynthesis of 4-methyl-1-hexanol volatilized from petal tissue of Nicotiana sylvestris

Compounds volatilized from plant tissues play important roles in plant-insect and plant-herbivore interactions and are important to food quality/preference, and to the perfume and flavorant industries. While the chemistry of plant volatiles is well understood, less is known about the biosynthesis of this diverse group of compounds. This is particularly the case for non-terpenoid components such as volatile acyclic alcohols and their esters. Here we have studied metabolic pathways leading to formation of the anteiso-branched alcohol 4-methyl-1-hexanol volatilized by petal tissue of Nicotiana sylvestris. Evidence presented supports the involvement of steps in the pathways of both biosynthesis and degradation of isoleucine to form 2-oxo-3-methylvaleric acid then 2-methylbutyryl CoA. Results indicate that 2-methylbutyryl CoA is then elongated by addition of one acetate molecule via fatty acid synthase, followed by reduction to yield 4-methyl-1-hexanol. This pathway is in contrast to elongation of 2-oxo-3-methylvaleric acid via α-keto acid elongation leading to the formation of 4-methylhexanoyl acyl groups of tobacco leaf-trichome-secreted sugar esters.

Theoretical and Experimental Study on the Time−Dipole Correlation Function of 2-(Acetyloxy)ethyl-2-(2-naphthyl) Acetate (ANA)

The complex dielectric permittivity * of the 2-(acetyloxy)ethyl-2-(2-naphthyl) acetate molecule, ANA, was measured as function of both temperature (in the range -130 to 0 °C) and frequency (from 10 -4 to 10 2 kHz). Isochrone values of the loss component ′′ present a prominent peak with the maximum for 1 Hz located at -43 °C, close to the calorimetric value of Tg. Analysis of the temperature dependence of these absorptions allows the evaluation of the relative free volume of the sample at Tg as …g/B ) 0.026. Molecular dynamics simulations seeking the evaluation of the time-dipole correlation function (t) including both auto- and cross-correlation terms were performed for a canonical ensemble of 15 molecules of ANA (i.e., 540 atoms) contained within a cubic box with periodic boundary conditions at constant temperature. Simulations were performed at T ) 300, 500, 750, and 1000 K, and the results at 300 K indicate that the molecule does not statistically sample the whole conformational space during the time allowed to the simulation (i.e., 0.5 fs), so (t) was not computed at this temperature. The values of (t) obtained at the other three temperatures proved that the cross-correlation terms are negligible. Fitting of (t) to the KWW equation (t) ) exp[-(t/U) ‚ ]i s very good, giving values of U ) 5.6, 1.8, and 1.0 ps, respectively, for T ) 500, 750, and 1000 K, while ‚ h) 0.65 ( 0.02 is temperature independent. Values of ′ (real) and ′′ (loss) components of * computed with these values of (t) are in good agreement with experimental results.