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PubMed2001

A theoretical study of the reaction of lithium aluminum hydride with formaldehyde and cyclohexanone.

Geometries and energies of the reactants, complexes, and transition states for the reactions of lithium aluminum hydride with formaldehyde and cyclohexanone were obtained using ab initio and density functional (Becke3LYP/6-31G**) molecular orbital calculations. Two pathways for reaction with formaldehyde and four transition states corresponding to axial and equatorial attack at cyclohexanone were located. The transition state structures had reactant-like geometries. Predicted stereoselectivity of the reduction of cyclohexanone strongly favors axial approach of hydrogen, in agreement with experimental data. Analysis of the transition state structures suggests that electronic effects are more important than torsional effects in controlling stereoselectivity.

Journal Article↗
PubMed2005

Micro-Raman investigations of the formaldehyde-ice system.

Rapidly frozen aqueous solutions containing variable amounts of dissolved formaldehyde (0.1, 5, 7, 10, 15, and 20 mol %) have been analyzed by micro-Raman spectroscopy at ambient pressure and low temperature. The importance of the formladehyde-ice system has been repeatedly quoted in various contexts, such as atmospheric and snowpack chemistry and interstellar and cometary ices. Understanding and characterizing the effects of freezing and the interactions of formaldehyde with ice are therefore of relevant interest. In this study, the distinct vibrational signatures of the oligomers present in the solution and in the frozen ice mixtures have been identified in the 120-4000 cm(-1) spectral range. From the subtle changes of the bands assigned to the CO and CH group frequencies, at least two distinct crystalline phases (pI and pII) are found to coexist with ice at different temperatures. Depending on the cooling-rewarming protocol, pI is found to crystallize in the 163-213 K temperature range. Above approximately 213 K, pI gets transformed irreversibly into pII which is stable up to approximately 234 K. pII is found to interact more strongly with ice than pI, as revealed, for example, by the drop in frequency of the bands assigned to the O-H stretching as pI transforms into pII. It is suggested that pII consists of a hydrogen-bonded network of oligomers and water molecules. On the other hand, it is suggested that the oligomers mainly present in pI interact through weak forces with the surrounding water molecules.

Journal Article↗
PubMed2005

Complex behavior in the formaldehyde-sulfite reaction.

The formaldehyde-sulfite reaction is an example of an "acid-to-alkali" clock. It displays an induction period, during which the pH varies only slowly in time, followed by a reaction event, during which the pH increases rapidly by several units. When the reaction is performed in a closed (batch) reactor, the clock time is found to increase with a decrease in initial concentrations of formaldehyde and sulfite and an increase in the total initial concentration of S(IV). At long times, following the clock event, there is a slow decrease in pH. In an open (flow) reactor, bistability between a low-pH steady state (pH approximately 6-8) and a high-pH steady state (pH approximately 11) is observed. Additionally, we report the existence of sustained, small-amplitude oscillations in pH in this system. An extended kinetic mechanism reproduces the batch behavior but fails to account for the complex behavior observed in the flow reactor. Possible additional reaction steps are discussed.

Journal Article↗
PubMed2005

Global mapping of equilibrium and transition structures on potential energy surfaces by the scaled hypersphere search method: applications to ab initio surfaces of formaldehyde and propyne molecules.

Technical details of a new global mapping technique for finding equilibrium (EQ) and transition structures (TS) on potential energy surfaces (PES), the scaled hypersphere search (SHS) method (Ohno, K.; Maeda, S. Chem. Phys. Lett. 2004, 384, 277), are presented. On the basis of a simple principle that reaction pathways are found as anharmonic downward distortions of PES around an EQ point, the reaction pathways can be obtained as energy minima on the scaled hypersphere surface, which would have a constant energy when the potentials are harmonic. Connections of SHS paths between each EQ are very similar to corresponding intrinsic reaction coordinate (IRC) connections. The energy maximum along the SHS path reaches a region in close proximity to the TS of the reaction pathway, and the subsequent geometry optimization from the SHS maximum structure easily converges to the TS. The SHS method, using the one-after-another algorithm connecting EQ and TS, considerably reduces the multidimensional space to be searched to certain limited regions around the pathways connecting each EQ with the neighboring TS. Applications of the SHS method have been made to ab initio surfaces of formaldehyde and propyne molecules to obtain systematically five EQ and nine TS for formaldehyde and seven EQ and 32 TS for propyne.

Journal Article↗
PubMed2005

Theoretical study of the CH2 + O photodissociation of formaldehyde adsorbed on the Ag(111) surface.

Configuration interaction calculations of the ground and excited states of the H2CO molecule adsorbed on the Ag(111) surface have been carried out to study the photoinduced dissociation process leading to polymerization of formaldehyde. The metal-adsorbate system has been described by the embedded cluster and multireference configuration interaction methods. The pi electron-attachment H2CO- and n-pi* internally excited H2CO* states have been considered as possible intermediates. The calculations have shown that H2CO* is only very weakly bound on Ag(111), and thus that the dissociation of adsorbed formaldehyde due to internal excitation is unlikely. By contrast, the H2CO- anion is strongly bound to Ag(111) and gains additional vibrational energy along the C-O stretch coordinate via Franck-Condon excitation from the neutral molecule. Computed energy variations of adsorbed H2CO and H2CO- at different key geometries along the pathway for C-O bond cleavage make evident, however, that complete dissociation is very difficult to attain on the potential energy surface of either of these states. Instead, reneutralization of the vibrationally excited anion by electron transfer back to the substrate is the most promising means of breaking the C-O bond, with subsequent formation of the coadsorbed O and CH2 fragments. Furthermore, it has been demonstrated that the most stable state for both dissociation fragments on Ag(111) is a closed-shell singlet, with binding energies relative to the gas-phase products of approximately 3.2 and approximately 1.3 eV for O and CH2, respectively. Further details of the reaction mechanism for the photoinduced C-O bond cleavage of H2CO on the Ag(111) surface are also given.

Journal Article↗
PubMed2004

Analytic evaluation of nonadiabatic coupling terms at the MR-CI level. II. Minima on the crossing seam: formaldehyde and the photodimerization of ethylene.

The method for the analytic calculation of the nonadiabatic coupling vector at the multireference configuration-interaction (MR-CI) level and its program implementation into the COLUMBUS program system described in the preceding paper [Lischka et al., J. Chem. Phys. 120, 7322 (2004)] has been combined with automatic searches for minima on the crossing seam (MXS). Based on a perturbative description of the vicinity of a conical intersection, a Lagrange formalism for the determination of MXS has been derived. Geometry optimization by direct inversion in the iterative subspace extrapolation is used to improve the convergence properties of the corresponding Newton-Raphson procedure. Three examples have been investigated: the crossing between the 1(1)B1/2(1)A1 valence states in formaldehyde, the crossing between the 2(1)A1/3(1)A1 pi-pi* valence and ny-3py Rydberg states in formaldehyde, and three crossings in the case of the photodimerization of ethylene. The methods developed allow MXS searches of significantly larger systems at the MR-CI level than have been possible before and significantly more accurate calculations as compared to previous complete-active space self-consistent field approaches.

Journal Article↗
PubMed2005

Hydrothermal reactions of formaldehyde and formic acid: free-energy analysis of equilibrium.

The chemical equilibria concerning formaldehyde and formic acid are computationally investigated in water over a wide range of thermodynamic conditions. The free energy is evaluated in the method of energy representation for the solvent effect on the decomposition processes of these two compounds. The solvation is found to suppress the production of nonpolar species from a polar. In the two competitive decomposition reactions of formic acid, the solvent strongly inhibits the decarboxylation (HCOOH-->CO2+H2) and its effect is relatively weak for the decarbonylation (HCOOH-->CO+H2O). The equilibrium weights for the two decomposition pathways of formic acid are determined by the equilibrium constant of the water-gas-shift reaction (CO+H2O-->CO2+H2), which is an essential and useful process in fuel technology. The reaction control by the solvent is then examined for the water-gas-shift reaction. Through the comparison of the equilibrium constants in the absence and presence of solvent, even the favorable side of the reaction is shown to be tuned by the solvent density and temperature. The reaction equilibrium is further treated for aldehyde disproportionation reactions involving formaldehyde and formic acid. The disproportionation reactions are found to be subject to relatively weak solvent effects and to be dominated by the electronic contribution.

Journal Article↗
PubMed2006

Two-photon absorption cross sections: an investigation of solvent effects. Theoretical studies on formaldehyde and water.

The effects of a solvent on the two-photon absorption of microsolvated formaldehyde and liquid water have been studied using hybrid coupled-cluster/molecular mechanics (CC/MM) response theory. Both water and formaldehyde were considered solvated in water, where the solvent water molecules were described within the framework of molecular mechanics. Prior to the CC/MM calculations, molecular dynamics simulations were performed on the water/formaldehyde and water/water aggregates and many configurations were generated. By carrying out CC/MM response calculations on the individual configurations, it was possible to obtain statistically averaged results for both the excitation energies and two-photon absorption cross sections. For liquid water, the comparison between one- and two-photon absorption spectra is in good agreement with the experimental data available in the literature. In particular, the lowest energy transition occurring in the one-photon absorption spectrum of water only occurs with a relatively small strength in the two-photon absorption spectrum. This result is important for the interpretation of two-photon absorption data as these results show that in the absence of selection rules that determine which transitions are forbidden, the spectral profile of the two-photon absorption spectrum can be significantly different from the spectral profile of the one-photon absorption spectrum.

Journal Article↗
PubMed1984

Formaldehyde activation factor, tetrahydromethanopterin, a coenzyme of methanogenesis.

An oxygen-labile formaldehyde activation factor (FAF) was isolated in highly purified form by use of anoxic fractionation procedures. The molecular weight of FAF was determined to be 776 and that of methanopterin (MPT) 772 by fast-atom-bombardment mass spectrometry (FABMS). High-resolution FABMS measurements on MPT and FAF indicated molecular formulas of C(30)H(41)N(6)O(16)P and C(30)H(45)N(6)O(16)P, respectively. The presence of phosphorus was confirmed by 100-MHz (31)P NMR. The 360-MHz (1)H NMR spectrum of FAF in deuterium oxide was similar to that of MPT. A functional relationship between MPT and FAF was documented; both compounds stimulated the reductive demethylation of 2-(methylthio)ethanesulfonic acid (CH(3)-S-CoM) to CH(4) when formaldehyde oxidation provided a source of electrons, and FAF replaced MPT in the CH(3)-S-CoM-stimulated conversion of CO(2) to CH(4) under H(2) (the RPG effect). MPT was enzymically converted to FAF during the reduction of CH(3)-S-CoM, and HCHO to CH(4) under H(2). Evidence indicates that FAF is tetrahydromethanopterin.

Journal Article↗
PubMed2001

Characterization of formaldehyde by gas chromatography using multiple pulsed-discharge photoionization detectors and a flame ionization detector.

Formaldehyde, water, methanol, butanal, and butanone are characterized by gas chromatography using three pulsed-discharge photoionization detectors (PDPIDs) and a flame ionization detector (FID). One of the PDPIDs is operated in helium mode, and the other two are operated in argon and krypton modes. The FID is included for comparison. The PDPIDs are used to efficiently differentiate between and quantitatively identify formaldehyde and the other three compounds in a sample mixture. This is accomplished by using butanone as the internal standard and correlating the relative responses of the four organic compounds in the helium-, argon-, and krypton-mode PDPIDs with their relative retention times.

Journal Article↗
PubMed1984

Formaldehyde dehydrogenase from Pseudomonas putida: a zinc metalloenzyme.

The NAD+-dependent formaldehyde dehydrogenase from Pseudomonas putida C-83 was found to contain 4 gram atoms of zinc per mol, corresponding to 2 gram atoms of zinc per subunit monomer. Treatment of the enzyme with o-phenanthroline resulted in removal of 1 gram atom of zinc per subunit and caused a complete inactivation of the enzyme. The activity lost was restored by the addition of zinc ions, by which the zinc content was also reversed to almost the same level as that of the native enzyme. Another zinc atom that was resistant to metal chelator-treatment was liberated from the enzyme only after the irreversible denaturation of the enzyme. These results indicate that the formaldehyde dehydrogenase of P. putida is a zinc metalloenzyme and one of two zinc atoms per subunit participates in the catalytic activity of the enzyme, another zinc being presumably involved in maintaining the native conformation of the enzyme. Treatment of the enzyme with bipyridine also caused a reversible inactivation of the enzyme, but the zinc content remained unchanged. The spectrophotometric analysis indicated that the formation of a enzyme-Zn-bipyridine complex took place. Incubation of the enzyme with p-chloromercuribenzoate also resulted in a complete loss of the activity. These results suggest that an intrinsic zinc and sulfhydryl group together with NAD+ participate in the dehydrogenation reaction of substrate by the enzyme.

Aldehyde Oxidoreductases↗
PubMed2002

Physiological role of the glutathione-dependent formaldehyde dehydrogenase in the methylotrophic yeast Candida boidinii.

The methylotrophic yeast Candida boidinii exhibits formaldehyde dehydrogenase activity (FLD, EC 1.2.1.1) during growth on methanol as a sole carbon source. The structural gene, FLD1, was cloned from a genomic library of C. boidinii. The 1263 bp FLD1 gene contained a 123 bp intron and its exon encoded a gene product of 380 amino acids, whose predicted amino acid sequence showed high similarity to the sequences of FLDs from other organisms. The FLD1 gene was disrupted in the C. boidinii genome by one-step gene disruption. The fld1Delta strain could not grow on methanol as a carbon source under methanol-limited chemostat culture conditions, even with low dilution rates (D<0.05 x h(-1)), whereas a strain with a disruption in the gene for formate dehydrogenase (FDH; another NADH-generating dehydrogenase involved in the formaldehyde oxidation pathway) could survive. These results indicated that FLD, but not FDH, is essential for growth of C. boidinii on methanol.

Amino Acid Sequence↗
PubMed2006

Modification of intracellular levels of glutathione-dependent formaldehyde dehydrogenase alters glutathione homeostasis and root development.

Glutathione (GSH)-dependent formaldehyde dehydrogenase (FALDH) is a highly conserved medium-chain dehydrogenase reductase and the main enzyme that metabolizes intracellular formaldehyde in eukaryotes. It has been recently shown that it exhibits a strong S-nitrosoglutathione (GSNO) reductase activity and could be a candidate to regulate NO-signalling functions. However, there is a lack of knowledge about the tissue distribution of this enzyme in plants. Here, we have studied the localization and developmental expression of the enzyme using immunolocalization and histochemical activity assay methods. We conclude that FALDH is differentially expressed in the organs of Arabidopsis thaliana mature plants, with higher levels in roots and leaves from the first stages of development. Spatial distribution of FALDH in these two organs includes the main cell types [epidermis (Ep) and cortex (Cx) in roots, and mesophyll in leaves] and the vascular system. Arabidopsis thaliana mutants with modified levels of FALDH (both by over- and under-expression of the FALDH-encoding gene) show a significant reduction of root length, and this phenotype correlates with an overall decrease of intracellular GSH levels and alteration of spatial distribution of GSH in the root meristem. Tansgenic roots are partially insensitive to exogenous GSH, suggesting an inability to detect reduction-oxidation (redox) changes of the GSH pool and/or maintain GSH homeostasis.

Aldehyde Oxidoreductases↗
PubMed1994

Structure of the Drosophila melanogaster glutathione-dependent formaldehyde dehydrogenase/octanol dehydrogenase gene (class III alcohol dehydrogenase). Evolutionary pathway of the alcohol dehydrogenase genes.

The glutathione-dependent formaldehyde dehydrogenase gene (gfd) of Drosophila melanogaster encodes an enzyme that is active toward S-hydroxymethylglutathione, an adduct of formaldehyde with glutathione, and also with long-chain primary alcohols, both properties typical of class III alcohol dehydrogenases, gfd hybridizes at the 86D division of the third chromosome, in agreement with the known location of the Drosophila octanol dehydrogenase gene (odh), gfd/odh was isolated from a lambda EMBL-4 genomic library and consists of three exons (with coding segments of 21, 90 and 1029 bp) and two introns (69 bp and 70 bp, respectively). The introns are small in size like the Drosophila interrupting sequences and are located at the 5' end of the coding region. Comparisons with the homologous genes of Saccharomyces, Candida and humans provide information on the evolution of the class III alcohol dehydrogenases. Moreover, results from analysis of exon/intron distributions in eleven dehydrogenases are compatible with the hypothesis of intron loss accounting for aspects of the present structure of these genes.

Alcohol Oxidoreductases↗
PubMed1999

Purification and molecular characterization of the tungsten-containing formaldehyde ferredoxin oxidoreductase from the hyperthermophilic archaeon Pyrococcus furiosus: the third of a putative five-member tungstoenzyme family.

Pyrococcus furiosus is a hyperthermophilic archaeon which grows optimally near 100 degreesC by fermenting peptides and sugars to produce organic acids, CO2, and H2. Its growth requires tungsten, and two different tungsten-containing enzymes, aldehyde ferredoxin oxidoreductase (AOR) and glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR), have been previously purified from P. furiosus. These two enzymes are thought to function in the metabolism of peptides and carbohydrates, respectively. A third type of tungsten-containing enzyme, formaldehyde ferredoxin oxidoreductase (FOR), has now been characterized. FOR is a homotetramer with a mass of 280 kDa and contains approximately 1 W atom, 4 Fe atoms, and 1 Ca atom per subunit, together with a pterin cofactor. The low recovery of FOR activity during purification was attributed to loss of sulfide, since the purified enzyme was activated up to fivefold by treatment with sulfide (HS-) under reducing conditions. FOR uses P. furiosus ferredoxin as an electron acceptor (Km = 100 microM) and oxidizes a range of aldehydes. Formaldehyde (Km = 15 mM for the sulfide-activated enzyme) was used in routine assays, but the physiological substrate is thought to be an aliphatic C5 semi- or dialdehyde, e.g., glutaric dialdehyde (Km = 1 mM). Based on its amino-terminal sequence, the gene encoding FOR (for) was identified in the genomic database, together with those encoding AOR and GAPOR. The amino acid sequence of FOR corresponded to a mass of 68.7 kDa and is highly similar to those of the subunits of AOR (61% similarity and 40% identity) and GAPOR (50% similarity and 23% identity). The three genes are not linked on the P. furiosus chromosome. Two additional (and nonlinked) genes (termed wor4 and wor5) that encode putative tungstoenzymes with 57% (WOR4) and 56% (WOR5) sequence similarity to FOR were also identified. Based on sequence motif similarities with FOR, both WOR4 and WOR5 are also proposed to contain a tungstobispterin site and one [4Fe-4S] cluster per subunit.

Aldehyde Oxidoreductases↗
PubMed2000

Assessment of genotoxicity of dental antiseptics: ability of phenol, guaiacol, p-phenolsulfonic acid, sodium hypochlorite, p-chlorophenol, m-cresol or formaldehyde to induce unscheduled DNA synthesis in cultured Syrian hamster embryo cells.

To assess the genotoxicity of seven dental antiseptics, the ability of these agents to induce unscheduled DNA synthesis (UDS) was examined using Syrian hamster embryo (SHE) cells. Treatment of SHE cells with phenol or formaldehyde induced UDS in a concentration-dependent manner as determined by direct scintillation counting of [3H]thymidine incorporated into DNA during repair synthesis. Guaiacol or m-cresol induced UDS only in the presence of exogenous metabolic activation. p-Phenolsulfonic acid, sodium hypochlorite and p-chlorophenol failed to induce UDS in the presence or absence of exogenous metabolic activation. Our results suggest that phenol, guaiacol, m-cresol and formaldehyde are genotoxic to mammalian cells.

Animals↗
PubMed2002

Effects of GroESL coexpression on the folding of nicotinoprotein formaldehyde dismutase from Pseudomonas putida F61.

The overexpression of fdm, which encodes the formaldehyde dismutase from Pseudomonas putida F61, resulted in the formation of inclusion bodies made up of aggregated enzyme, leaving little activity in the soluble fraction of the transformant cells. On the other hand, coexpression of groESL along with fdm facilitated in vivo solubilization of the enzyme protein in its active form. When coexpressed with groESL, formaldehyde dismutase purified from E. coli had the same crystalline form (i.e., a regular octahedron) as the native enzyme, and like the native enzyme, it bound 1 mol of NAD(H) and 2 mol of zinc in each subunit.

Alcohol Oxidoreductases↗