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PubMed1990

A new mechanism-based inhibitor of photosynthetic water oxidation: acetone hydrazone. 1. Equilibrium reactions.

The process of photosynthetic water oxidation has been investigated by using a new type of water oxidation inhibitor, the alkyl hydrazones. Acetone hydrazone (AceH), (CH3)2CNNH2, inhibits water oxidation by a mechanism that is analogous to that of NH2OH. This involves binding to the water-oxidizing complex (WOC), followed by photoreversible reduction of manganese (loss of the S1----S2 reaction). At higher AceH concentrations the S1 state is reduced in the dark and Mn is released, albeit to a lesser extent than with NH2OH. Following extraction of Mn, AceH is able to donate electrons rapidly to the reaction center tyrosine radical Z+ (161Tyr-D1 protein), more slowly to a reaction center radical C+, and not at all to the dark-stable tyrosine radical D+ (160Tyr-D2 protein) which must be sequestered in an inaccessible site. Manganese, Z+, and C+ thus appear to be located in a common protein domain, with Mn being the first accessible donor, followed by Z+ and then C+. Photooxidation of Cyt b-559 is suppressed by AceH, indicating either reduction or competition for donation to P680+. Unexpectedly, Cl- was found not to interfere or compete with AceH for binding to the WOC in the S1 state, in contrast to the reported rate of binding of N,N-dimethylhydroxylamine, (CH3)2NOH [Beck, W., & Brudvig, G. (1988) J. Am. Chem. Soc. 110, 1517-1523]. We interpret the latter behavior as due to ionic screening of the thylakoid membrane, rather than a specific Cl- site involved in water oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetone↗
PubMed1990

A new mechanism-based inhibitor of photosynthetic water oxidation: acetone hydrazone. 2. Kinetic probes.

The mechanism of photosynthetic water oxidation in spinach was investigated with a newly developed inhibitor of the water-oxidizing complex, acetone hydrazone (AceH), (CH3)2CNNH2 [Tso, J., Petrouleas, V., & Dismukes, G.C. (1990) Biochemistry (preceding paper in this issue)], by using fluorescence induction and single-turnover flashes to monitor O2 yield and thermoluminescence intensity. AceH binds slowly (1-3 min) in the dark to the S1 (resting) oxidation state of the water-oxidizing complex in thylakoids and PSII membranes. Once bound, it causes a two-flash delay in the pattern of O2 release seen in a train of flashes. This is initiated by reduction of manganese in the S2 oxidation state of the complex in a fast reaction (less than 0.5 s). In thylakoid membranes which have been partially inhibited at low AceH concentrations (less than 2 mM) the inhibition can be reversed by a single flash and a subsequent dark period. This behavior can be explained by two sequential one-electron oxidation steps: S1.AceHhv----S2.AceH in equilibrium S1.AceH+hv----S2.AceH+----S1 + AceH2+ Dissociation of the unobserved radical intermediate, AceH+, from S1 is proposed to account for the recovery from inhibition after one flash. In contrast, recovery from inhibition after a single flash is not observed in detergent-isolated PSII membranes or in intact thylakoid membranes at higher AceH concentrations (greater than 2 mM), where the two-flash delay in O2 release is seen. This suggests either a concerted two-electron process, S2----S0, or tight binding of AceH+ to S1.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetone↗
PubMedDate not supplied

Use of immobilized microbial membrane fragments to remove oxygen and favor the acetone-butanol fermentation.

Oxygen-reducing membrane fragments obtained from Escherichia coli were used with Clostridium acetobutylicum (C. acetobutylicum) to provide an oxygen-free microenvironment for the conversion of glucose to acetone, butanol, and ethanol (ABE). The batch fermentation of suspended C. acetobutylicum NRRL-B-643 and its ability to produce solvents in the presence of membranes as the oxygen-elimination agent are described and compared with the conventional sparging technique used to maintain anaerobiosis. The use of membrane fragments to remove oxygen for fermentation by C. acetobutylicum was successful and gave slightly improved results over the use of sparing with regard to lag, biomass, and solvent production (e.g., final butanol concentration of 3.25 and 2.7 g/L, respectively). Solvent production is also reported for a continuous columnar reactor with coimmobilized cells and membranes in kappa-carrageenan gel beads and air-saturated liquid feed.

Acetone↗
PubMedDate not supplied

Downstream process synthesis for biochemical production of butanol, ethanol, and acetone from grains: generation of optimal and near-optimal flowsheets with conventional operating units.

Manufacturing butanol, ethanol, and acetone through grain fermentation has been attracting increasing research interest. In the production of these chemicals from fermentation, the cost of product recovery constitutes the major portion of the total production cost. Developing cost-effective flowsheets for the downstream processing is, therefore, crucial to enhancing the economic viability of this manufacturing method. The present work is concerned with the synthesis of such a process that minimizes the cost of the downstream processing. At the outset, a wide variety of processing equipment and unit operations, i.e., operating units, is selected for possible inclusion in the process. Subsequently, the exactly defined superstructure with minimal complexity, termed maximal structure, is constructed from these operating units with the rigorous and highly efficient graph-theoretic method for process synthesis based on process graphs (P-graphs). Finally, the optimal and near-optimal flowsheets in terms of cost are identified.

Acetone↗
PubMedDate not supplied

Production of acetone butanol ethanol (ABE) by a hyper-producing mutant strain of Clostridium beijerinckii BA101 and recovery by pervaporation.

A silicone membrane was used to study butanol separation from model butanol solutions and fermentation broth. Depending upon the butanol feed concentration in the model solution and pervaporation conditions, butanol selectivities of 20.88-68.32 and flux values of 158.7-215.4 g m(-)(2) h(-)(1) were achieved. Higher flux values (400 g m(-)(2) h(-)(1)) were obtained at higher butanol concentrations using air as sweep gas. In an integrated process of butanol fermentation-recovery, solvent productivities were improved to 200% of the control batch fermentation productivities. In a batch reactor the hyper-butanol-producing mutant strain C. beijerinckii BA101 utilized 57.3 g/L glucose and produced 24.2 g/L total solvents, while in the integrated process it produced 51.5 g/L (culture volume) total solvents. Concentrated glucose medium was also fermented. The C. beijerinckii BA101 mutant strain was not negatively affected by the pervaporative conditions. In the integrated experiment, acids were not produced. With the active fermentation broth, butanol selectivity was reduced by a factor of 2-3. However, the membrane flux was not affected by the active fermentation broth. The butanol permeate concentration ranged from 26.4 to 95.4 g/L, depending upon butanol concentration in the fermentation broth. Since the permeate of most membranes contains acetone, butanol, and ethanol (and small concentrations of acids), it is suggested that distillation be used for further purification.

Acetone↗
PubMed2005

Convenient new chemical actinometer based on aqueous acetone, 2-propanol, and carbon tetrachloride.

A convenient new chemical actinometer was developed to measure the spectral output of laboratory ultraviolet (UV) light sources over the wavelength range of 260-330 nm. It can also be used to measure solar UV irradiance (< or =325 nm). The actinometer is based on the photoreduction of aqueous carbon tetrachloride (CT) to chloroform (CF) in the presence of acetone (the chromophore) and 2-propanol (the reductant). In all cases, CT disappearance (and CF formation) followed zero-order kinetics over 95% of the reaction. The slope of the linear decay curve forms the basis of the new actinometer, which was calibrated using ferrioxalate actinometry. Quantum yields were measured at 10 nm intervals and were found to be uniform throughout the range of 260-300 nm. As expected, quantum yields gradually decreased to zero asthe wavelength was increased from 300 to 340 nm. The high quantum yields (approximately 150), low sensitivityto room light, and the straightforward determination of [CT] and [CF] by gas chromatography offer significant advantages over some other chemical actinometers, which might require the preparation and purification of light-sensitive compounds in a darkened environment and long exposure times.

2-Propanol↗
PubMed2004

Intramolecular chiral relay at stereogenic nitrogen. Synthesis and application of a new chiral auxiliary derived from (1R,2S)-norephedrine and acetone.

(1R,2S)-Norephedrine has been employed in the synthesis of a novel 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one via reductive alkylation with acetone, N-nitrosation, reduction, and cyclization. The oxadiazinone was treated with either propionyl chloride or 3-thiophenylpropionyl chloride to afford the corresponding N(3)-acylated oxadiazinones 9a and 9b, respectively. X-ray crystallographic analysis of the N(3)-thiophenylpropionyl oxadiazinone 9b revealed that the C(2)-urethane carbonyl and the N(3)-carbonyl are arranged in an anti-periplanar conformation. The oxadiazinones were subsequently applied in the titanium-mediated asymmetric aldol addition reaction by treatment with titanium tetrachloride, triethylamine, and a variety of aldehydes at 0 degrees C. The aldol adducts 10a-i and 11a,b were found to have diastereoselectivities ranging from 8:1 to >99:1 favoring the formation of the non-Evans syn configuration. The absolute stereochemistry of the adduct 10a was determined by acid hydrolysis. This process afforded the N(4)-isopropyloxadiazinone 8 and (2S,3S)-3-hydroxy-2-methyl-3-phenylpropanoic acid 14 in >/=95% enantiomeric excess.

Acetone↗
PubMed2004

Highly efficient chemoselective deprotection of O,O-acetals and O,O-ketals catalyzed by molecular iodine in acetone.

An extremely convenient method for deprotection of acetals and ketals catalyzed by molecular iodine (10 mol %) in acetone is reported. The protocol achieved the deprotection of acyclic or cyclic O,O-acetals and O,O-ketals in excellent yields within a few minutes under neutral conditions. The double bond, hydroxyl group, and acetate group remained unchanged, and the highly acid-sensitive furyl, tert-butyl ethers, and ketone-oxime stayed intact under these conditions.

Acetals↗
PubMed2006

New easy approach to the synthesis of 2,5-disubstituted and 2,4,5-trisubstituted 1,3-oxazoles. The reaction of 1-(methylthio)acetone with nitriles.

The reaction of 1-(methylthio)acetone with different nitriles in the presence of triflic anhydride led to the one-pot formation of 2-substituted 5-methyl-4-methylthio-1,3-oxazoles in good yield. 1,2- and 1,4-Bisozaxolyl-substituted benzenes were obtained when the reaction was carried out using aromatic dinitriles. The methylthio group at the C4 position of the oxazole ring was easily removed with Raney nickel to form 2-substituted 5-methyl-1,3-oxazoles in good yields. 4-Methylsulfonyl derivatives were prepared by the oxidation of the MeS group with m-CPBA. The proposed mechanism for the formation of oxazoles involves an unstable 1-(methylthio)-2-oxopropyl triflate, which was detected from the low-temperature NMR spectra.

Acetone↗
PubMed2005

How to model solvation of peptides? Insights from a quantum mechanical and molecular dynamics study of N-methylacetamide. 2. 15N and 17O nuclear shielding in water and in acetone.

This paper represents the second part of a study of solvation of peptides. As in the first part, N-methyl acetamide has been used to model the specific features of solvation of the peptide linkage. In this part of the study, devoted to nuclear magnetic shieldings, acetone and water have been used as examples of polar and/or hydrogen-bond donor/acceptor solvents. Once again, three different solvation models have been tested and compared, namely, a continuum only description, a discrete description in terms of solute-solvent clusters, and a mixed discrete/continuum description in terms of clusters embedded in a continuum. Both QM and classical simulation (e.g., MD) approaches have been used to determine the structure of the clusters. The analysis of the results of the three different models, when combined with those obtained in the first part of the study devoted to IR and UV spectra, has allowed us to identify and characterize different aspects of solvation and to outline a possible computational strategy to describe dynamic and static effects due to bulk and specific peptide-solvent interactions.

Acetamides↗
PubMed2005

Stabilities of the C-H...O bonded complexes of the haloforms HCClnF3-n (n = 0-3) with dimethyl ether, oxirane, and acetone: an experimental and theoretical study.

Complexation enthalpies of the complexes of the haloforms HCCl(n)F(3-)(n) (n = 0-3) with dimethyl ether, oxirane, and acetone have been determined in liquid krypton and/or liquid argon using infrared spectroscopy. The same quantities were derived starting from ab initio complexation energies, calculated at the MP2=FULL/aug-cc-VTZ level, and by correcting these energies for thermodynamic and solvent contributions. The two sets of data are compared and discussed.

Acetone↗
PubMed2005

Toward an understanding of the catalytic role of hydrogen-bond donor solvents in the hetero-Diels-Alder reaction between acetone and butadiene derivative.

A detailed theoretical investigation of the catalytic role of hydrogen-bond- (HB-) donor molecules (water, methanol, chloroform, dichloromethane, and chloromethane) in the hetero-Diels-Alder reaction between acetone and N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene is presented. This work extends a previous study (Domingo, L. R.; Andres, J. J. Org. Chem. 2003, 68, 8662) in which the importance of weak HB-donor solvents to catalyze more effectively than solvents with a higher dielectric constant but no HB-donor capability was analyzed. Now, based on density functional theory (DFT) at B3LYP/6-31+G(d) level calculations, different techniques for analyzing the nature of HB interaction, namely, natural bond orbital (NBO) theory, topological analysis of the electron density (atoms in molecules, AIM, theory), and the electron localization function (ELF) and decomposition of the interaction energy between monomers (energy decomposition analysis, EDA), have been applied to understand why only some HB-donor solvents are able to catalyze the reaction. The catalytic effect of the solvent arises from the improved HB-acceptor capability of the oxygen atom at the transition structure (TS) due to the strong polarization of the carbonyl group. The HB acceptor presents three lone pairs (NBO analysis), and the ELF shows an increment of the electronic charge of the lone pairs of 0.50e with respect to the reactant. All solvent molecules form stronger HB interactions at the TS, but only those presenting larger charge-transfer interactions (water, methanol, chloroform) benefit more from the polarization of the carbonyl group than other solvents (dichloromethane, chloromethane) with less "covalent" character.

Acetone↗
PubMed2006

IR spectroscopy of M+(Acetone) complexes (M = Mg, Al, Ca): cation-carbonyl binding interactions.

M(+)(acetone) ion-molecule complexes (M = Mg, Al, Ca) are produced in a pulsed molecular beam by laser vaporization and studied with infrared photodissociation spectroscopy in the carbonyl stretch region. All of the spectra exhibit carbonyl stretches that are shifted significantly to lower frequencies than the free-molecule value, consistent with metal cation binding on the oxygen of the carbonyl. Density functional theory is employed to elucidate the shifts and patterns in these spectra. Doublet features are measured for the carbonyl region of Mg(+) and Ca(+) complexes, and these are assigned to Fermi resonances between the symmetric carbonyl stretch and the overtone of the symmetric carbon stretch. The carbonyl stretch red shift is greater for Al(+) than it is for the Mg(+) and Ca(+) complexes. This is attributed to the smaller size of the closed-shell Al(+), which enhances its ability to polarize the carbonyl electrons. Density functional theory correctly predicts the direction of the carbonyl stretch shift and the relative trend for the three metals.

Acetone↗
PubMed2006

Molecular dynamics simulation of the cybotactic region in gas-expanded methanol-carbon dioxide and acetone-carbon dioxide mixtures.

Local solvation and transport effects in gas-expanded liquids (GXLs) are reported based on molecular simulation. GXLs were found to exhibit local density enhancements similar to those seen in supercritical fluids, although less dramatic. This approach was used as an alternative to a multiphase atomistic model for these mixtures by utilizing experimental results to describe the necessary fixed conditions for a locally (quasi-) stable molecular dynamics model of the (single) GXL phase. The local anisotropic pair correlation function, orientational correlation functions, and diffusion rates are reported for two systems: CO2-expanded methanol and CO2-expanded acetone at 298 K and pressures up to 6 MPa.

Acetone↗
PubMed1998

Relationship between 2,5-hexanedione concentrations in nerve, serum, and urine alone or under co-treatment with different doses of methyl ethyl ketone, acetone, and toluene.

To ascertain the relationship among 2,5-hexanedione (2,5-HD) concentrations in nerve, serum and urine, rats were injected subcutaneously with 2.6 mmol/kg 2,5-HD alone, or together with 2.6 or 13.0 mmol/kg of methyl ethyl ketone, acetone and toluene. 2,5-HD concentrations in sciatic nerve (NC), serum (SC) and urine (UC) were determined, and the linear regression between each two of NC, SC, and UC were calculated. There was good correlation between NC and SC, SC and UC in the 2,5-HD alone group, and good correlation between NC and SC in the co-treated groups. Co-treatment solvent had little effect on the relationship between SC and NC. 13.0 mmol/kg co-treated solvent tended to decrease the regression coefficients compared with 2.6 mmol/kg co-treated solvent. These results show that SC can be used in estimating NC in the 2,5-HD alone or co-treated groups, and UC can be used in estimating SC in the 2,5-HD alone group.

Acetone↗
PubMed2004

Controllable regioselective enzymatic synthesis of polymerizable 5'-O-vinyl- and 3'-O-vinyl-nucleoside analogues in acetone.

An efficient synthesis of polymerizable 3'- and 5'-O-acyl-nucleoside derivatives has been developed from inosine and 2'-deoxyuridine by enzyme-catalyzed regioselective acylation with divinyl dicarboxylates. In acetone, Lipozyme (immobilized lipase from Mucor miehei) gave 5'-O-acyl-nucleoside products, and PPL (lipase from porcine pancreas) provided 3'-O-acyl-nucleoside products.

Acetone↗