Interaction of formic acid with solid water

The interaction of formic acid (HCOOH) with solid water, deposited on tungsten at 80 K, was investigated. We have prepared and annealed formic acid (FA)/water interfaces (FA layers on thin films of solid water and H(2)O adlayers on thin FA films). Metastable impact electron spectroscopy and ultraviolet photoemission spectroscopy (He I and II) were utilized to study the electron emission from the 10a' to 6a' molecular orbitals (MOs) of FA, and the 1b(1), 3a(1), and 1b(2) MOs of H(2)O. These spectra were compared with results of density-functional theory calculations on FA-H(2)O complexes reported in Ref. 14 [A. Allouche, J. Chem. Phys. 122, 234703(2005), (preceding paper)]. Temperature programmed desorption was applied for information on the desorption kinetics. Initially, FA is adsorbed on top of the water film. The FA spectra are distorted with respect to those from FA monomers; it is concluded that a strong interaction exists between the adsorbates. Even though partial solvation of FA species takes place during annealing, FA remains in the top layer up to the desorption of the water film. When H(2)O molecules are offered to FA films at 80 K, no water network is formed during the initial stage of water exposure; H(2)O molecules interact individually via H bonds with the formic acid network. Experiment and theory agree that no water-induced deprotonation of the formic acid molecules takes place.     

Photoionization-induced water migration in the hydrated trans-formanilide cluster cation revealed by gas-phase spectroscopy and ab initio molecular dynamics simulation

Photoionization-induced water migration in the trans-formanilide-water 1:1 cluster, FA-(H(2)O)(1), has been investigated by using IR-dip spectroscopy, quantum chemical calculations, and ab initio molecular dynamics simulations. In the S(0) state, FA-(H(2)O)(1) has two structural isomers, FA(NH)-(H(2)O)(1) and FA(CO)-(H(2)O)(1), where a water molecule is hydrogen-bonded (H-bonded) to the NH group and the CO group, respectively. In addition, the S(1)-S(0) origin transition of FA(CO)-(H(2)O)(2), where a water dimer is H-bonded to the CO group, was observed only in the [FA-(H(2)O)(1)](+) mass channel, indicating that one of the water molecules evaporates completely in the D(0) state. These results are consistent with a previous report [Robertson, E. G. Chem. Phys. Lett., 2000, 325, 299]. In the D(0) state, however, [FA-(H(2)O)(1)](+) produced by photoionization via the S(1)-S(0) origin transitions of FA(NH)-(H(2)O)(1) and FA(CO)-(H(2)O)(1) shows essentially the same IR spectra. Compared with the theoretical calculations, [FA-(H(2)O)(1)](+) can be assigned to [FA(NH)-(H(2)O)(1)](+). This means that the water molecule in [FA-(H(2)O)(1)](+) migrates from the CO group to the NH group when [FA-(H(2)O)(1)](+) is produced by photoionization of FA(CO)-(H(2)O)(1). [FA-(H(2)O)(1)](+) produced by photoionization of FA(CO)-(H(2)O)(2) also shows the IR spectrum corresponding to [FA(NH)-(H(2)O)(1)](+). In this case, the water migration from the CO group to the NH group occurs with the evaporation of a water molecule. Ab initio molecular dynamics simulations revealed the water migration pathway in [FA-(H(2)O)(1)](+). The calculations of classical electrostatic interactions show that charge-dipole interaction between FA(+) and H(2)O induces an initial structural change in [FA-(H(2)O)(1)](+). An exchange repulsion between the lone pairs of the CO group and H(2)O in [FA-(H(2)O)(1)](+) also affects the initial direction of the water migration. These two factors play important roles in determining the initial water migration pathway.     

Formic acid catalyzed hydrolysis of SO3 in the gas phase: a barrierless mechanism for sulfuric acid production of potential atmospheric importance

Computational studies at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(3df,3pd) levels are performed to explore the changes in reaction barrier height for the gas phase hydrolysis of SO(3) to form H(2)SO(4) in the presence of a single formic acid (FA) molecule. For comparison, we have also performed calculations for the reference reaction involving water assisted hydrolysis of SO(3) at the same level. Our results show that the FA assisted hydrolysis of SO(3) to form H(2)SO(4) is effectively a barrierless process. The barrier heights for the isomerization of the SO(3)···H(2)O···FA prereactive collision complex, which is the rate limiting step in the FA assisted hydrolysis, are found to be respectively 0.59 and 0.08 kcal/mol at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(3df,3pd) levels. This is substantially lower than the ~7 kcal/mol barrier for the corresponding step in the hydrolysis of SO(3) by two water molecules--which is currently the accepted mechanism for atmospheric sulfuric acid production. Simple kinetic analysis of the relative rates suggests that the reduction in barrier height facilitated by FA, combined with the greater stability of the prereactive SO(3)···H(2)O···FA collision complex compared to SO(3)···H(2)O···H(2)O and the rather plentiful atmospheric abundance of FA, makes the formic acid mediated hydrolysis reaction a potentially important pathway for atmospheric sulfuric acid production.     

Real structure of formamide entrapped by AOT nonaqueous reverse micelles: FT-IR and 1H NMR studies

Noninvasive techniques such as FT-IR and (1)H NMR spectroscopy have been employed to investigate the solubilization of formamide, FA, and its aqueous solution, FA-water, by sodium 1,4-bis(2-ethylhexyl)sulfosuccinate, AOT, in heptane or isooctane reverse micelles, respectively. Partially deuterated FA (FADH) was used in the FT-IR experiments and nu(OD), n(ND) were analyzed. Also, the nu(C=O) band of FA was investigated. For AOT, the changes of the SO(3)(-) group's symmetric, nu(s), and asymmetric, nu(a), bands were also studied. The results are showing that FA is interacting strongly with the Na+ counterions of the surfactant through electrostatic interactions maintaining their hydrogen bond network present in the FA bulk. Accordingly, partially deuterated FA is "frozen" inside the aggregates and it is possible to detect, by FT-IR technique, the cis and trans isomers. Curve fitting of the nu(OD) (in the FA-water mixture) band requires use of two peaks because the band is asymmetric, not because the solubilizate molecules are present in layers of different structure. The chemical shifts of the (1)H bound to N and C of FA were studied by (1)H NMR. The comparison of the chemical shift of AOT in reverse micelles with FA and the FA-water mixture in the polar core of the aggregate shows that there is a strong preferential solvation of Na+ by FA (through electrostatic interaction) and the AOT's sulfonate group by water (through hydrogen bond interaction).     

Size-selected infrared predissociation spectroscopy of neutral and cationic formamide-water clusters: stepwise growth of hydrated structures and intracluster hydrogen transfer induced by vacuum-ultraviolet photoionization

Vibrational spectroscopy of size-selected formamide-water clusters, FA-(H2O)n , n = 1-4, prepared in a supersonic jet is performed with vacuum-ultraviolet-ionization detected-infrared predissociation spectroscopy (VUV-ID-IRPDS). The cluster structures are determined through comparisons of the observed IR spectra with theoretical calculations at the MP2/6-31++G** level. The FA-(H2O)n , n = 1-3, clusters have ring-type structures, where water molecules act as both single donor and single acceptor in the hydrogen-bond network between the amino and carbonyl groups of FA. For FA-(H2O)4, on the other hand, the absence of the free NH stretching vibration indicates formation of a double ring type structure, where two NH bonds of the amino group and the carbonyl oxygen of FA form hydrogen bonds with water molecules. An infrared spectrum of the formamide-water cluster cation, [FA-H2O](+), is also observed with infrared predissociation spectroscopy of vacuum-ultraviolet-pumped ion (IRPDS-VUV-PI). No band is observed for the free OH stretches of neutral water. This shows [FA-H2O](+) has such a structure that one of the hydrogen atoms of the water moiety is transferred to the carbonyl oxygen of FA(+).     

Fulvic acid sorption on muscovite mica as a function of pH and time using in situ X-ray reflectivity

Interfacial structures of the basal surface of muscovite mica in 100 mg kg (-1) Elliott Soil Fulvic Acid II solutions were investigated using in situ X-ray reflectivity. Molecular-scale variations in the thickness and internal structure of the fulvic acid (FA) film were observed and quantified as a function of pH (2-12) and reaction time (3-500 h at pH 3.7). At pH < or =6, the electron-density profile of the FA layer sorbed on the muscovite surface was composed of one near-surface peak followed by a broad peak that diminished in electron density with distance from the surface. The presence of the near-surface peak is attributed to condensation of FA molecules during sorption. The apparent thickness of the FA layer decreased from 12.3 to 7.2 to 6.4 A as pH increased from 2 to 3.7 to 6, respectively. At pH > or =8.5, a distinct interfacial structure was observed, consisting of sharper peaks similar to those previously observed for muscovite in the absence of FA. These peaks are most likely composed of smaller aqueous species, such as H 2O molecules, metal ion impurities from FA, and Na (+) from NaOH. The FA sorbed on the muscovite surface at pH 3.7 maintained a relatively constant thickness after 3 hours. However, the electron density of the near-surface FA peak increased by about 24% from 3 to 12 hours, and remained relatively constant from 12 to 500 hours. The electron density of the more distant part of the sorbed FA layer increased slightly after 12-50 hours of reaction but then decreased, and the broad peak flattened by 500 hours. Internal structural changes are possibly due to the slow sorption rate of FA molecules, or a fractionation effect, i.e., continuous subsitution of smaller FA molecules by larger FA molecules.     

Preferential solvation of Brooker's merocyanine in binary solvent mixtures composed of formamides and hydroxylic solvents

The ET polarity values of 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (Brooker's merocyanine) were collected in mixed-solvent systems comprising a formamide [N,N-dimethylformamide (DMF), N-methylformamide (NMF) or formamide (FA)] and a hydroxylic (water, methanol, ethanol, propan-2-ol or butan-1-ol) solvent. Binary mixtures involving DMF and the other formamides (NMF and FA) as well as NMF and FA were also studied. These data were employed in the investigation of the preferential solvation (PS) of the probe. Each solvent system was analyzed in terms of both solute-solvent and solvent-solvent interactions. These latter interactions were responsible for the synergism observed in many binary mixtures. This synergistic behaviour was observed for DMF-propan-2-ol, DMF-butan-1-ol, FA-methanol, FA-ethanol and for the mixtures of the alcohols with NMF. All data were successfully fitted to a model based on solvent-exchange equilibria, which allowed the separation of the different contributions of the solvent species in the solvation shell of the dye. The results suggest that both hydrogen bonding and solvophobic interactions contribute to the formation of the solvent complexes responsible for the observed synergistic effects in the PS of the dye.     

均相催化剂催化氧气氧化生物质制备甲酸

甲酸是一种重要的化工原料,以可再生生物质为原料,通过催化氧气氧化制备甲酸具有重要意义。对于不溶于水的生物质原料的转化,采用可溶于水的均相催化剂体系证明是有效的。本文总结了均相催化剂体系(包括含钒杂多酸、含钒杂多酸+H₂SO₄、含钒杂多酸基离子液体、NaVO₃+H₂SO₄、VOSO₄、NaVO₃-FeCl₃+H₂SO₄、FeCl₃+H₂SO₄等)在催化氧气氧化生物质(包括生物质模型化合物、纤维素、木材、秸秆和玉米芯等)制备甲酸方面的研究,分析了其转化的过程和机理。最后,指出了目前催化氧化生物质制备甲酸存在的问题和挑战。     

Efficient subnanometric gold-catalyzed hydrogen generation via formic acid decomposition under ambient conditions

Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H(2) from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118,400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H(2) evolution (TOFs up to 252 h(-1) after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO(2) interface.     

Inhibitory effect of fumaric acid on 3'-methyl-4-(dimethylamino)azobenzene-induced hepatocarcinogenesis in rats

Fumaric acid (FA) suppressed the carcinogenesis in the liver of rats fed 3'-methyl-4-(dimethylamino)azobenzene (3'-Me-DAB), and a study was performed to examine the effect of FA on deoxyribonucleic acid (DNA) synthesis and subcellular structures of hepatocytes under the anticarcinogenic regimens. Male Donryu strain rats were given 3'-Me-DAB by being fed a diet containing 0.06% 3'-Me-DAB for 50 d. They were then given a diet containing 1% FA and drinking water containing 0.025% FA for 53 to 69 weeks. Hepatocytes were isolated from the liver by the collagenase perfusion method and placed in culture, and their activity for DNA synthesis was measured in terms of the incorporation of [3H]dThd into DNA. An enhanced DNA synthesis of hepatocytes was noted in the rats given FA, indicating that FA enhanced the proliferation of hepatocytes to counteract the carcinogenic effect of 3'-Me-DAB. An electron microscopic examination indicated that the distribution of subcellular organella was almost normal in the FA-treated hepatocytes.     

Conformation resolved induced infrared activity: trans- and cis-formic acid isolated in solid molecular hydrogen

We report combined experimental and theoretical studies of infrared absorptions induced in solid molecular hydrogen by different conformers of formic acid (HCOOH, FA). FTIR spectra recorded in the H(2) fundamental region (4120-4160 cm(-1)) reveal a number of relatively strong trans-FA induced Q-branch absorptions that are assigned by studying both FA-doped parahydrogen (pH(2)) and normal hydrogen (nH(2)) samples. The induced H(2) absorptions are also studied for HCOOD doped nH(2) crystals for both the trans and cis conformers that show resolvable differences. Samples containing >90% of the higher energy cis-HCOOD conformer are produced by in situ IR pumping of the OD stretching overtone of trans-HCOOD using narrow-band IR light. Minimum energy structures for 1:1 complexes of H(2) and FA are determined using ab initio methods. The measured differences in the cis- versus trans-HCOOD induced spectra are in qualitative agreement with the frequencies and intensities calculated for the identified cluster structures as discussed in terms of the model of specific interactions.     

MODIFICATION OF MEMBRANE COMPOSITION, EICOSANOID METABOLISM, AND IMMUNORESPONSIVENESS BY DIETARY OMEGA-3 AND OMEGA-6 FATTY ACID SOURCES, MODULATORS OF ULTRAVIOLET-CARCINOGENESIS

Dietary sources of lipids containing predominantly n-3 or n-6 fatty acids (FA) have been examined for effect upon several potential pathophysiologic parameters. Epidermal, plasma, and red blood cell (RBC) membrane FA composition exhibited marked differences between animals fed the respective dietary lipid sources. Reduced levels of 18:1, 20:3 and 20:4 occurred in the n-3 FA fed animals which exhibited significantly higher levels of 20:5 and 22:6. Approximately equal levels of 18:2 were present in animals fed either diet. Despite marked differences in RBC membrane FA composition, only marginal effect upon osmotic fragility occurred. Lower levels of 20:3 and 20:4 found in n-3 fed animals could result from a deficit of elongase and/or delta 5-desaturase activity. Whether lower 20:4 levels in n-3 fed animals could rate-limit eicosanoid metabolism is unknown, but epidermal capacity to metabolise arachidonic acid in these animals was found to be closely related to n-6 FA intake. Animals fed n-3 FA exhibited markedly lower levels of plasma PGE2, even when the diet was supplemented with n-6 FA. In addition, UV-radiated animals receiving the n-3 FA source demonstrated a reduced (approximately 30%) response to inflammatory stimulus and a greater (4.5-fold) delayed hypersensitivity (DH) to dinitrochlorobenzene than animals fed the n-6 FA source. These data demonstrate that dietary lipid strongly influences tissue FA composition, eicosanoid metabolism, and, in the case of DH, at least one type of T-cell mediated immune response in UV-irradiated animals.     

水＋甲酰胺＋环己烷＋二乙二醇丁醚拟三元系的三临界现象

用改进的体积法研究了拟三元体系水＋甲酰胺＋环己烷＋二乙二醇丁醚的三临界现象. 以水+甲酰胺作为拟“纯组分”，通过控制甲酰胺在拟“纯组分”中的质量分数w，逐渐向三临界点逼近，当w从0增加到0.206时，三相区范围ΔT从1.500 ℃减小到0.228 ℃. 由实验数据得到体系的临界质量分数w=0.286±0.003，临界温度为（54.8±0.7） ℃. 实验发现平均温度下三相区三角形的水-油边与三角坐标中的水-油边几乎平行，而且三相区三角形水-油边的边长及其对应的高与ΔT的指数关系符合三临界的经典理论.     

Presence of β-Turn Structure in Recombinant Spider Silk Dissolved in Formic Acid Revealed with NMR

Spider dragline silk is a biopolymer with excellent mechanical properties. The development of recombinant spider silk protein (RSP)-based materials with these properties is desirable. Formic acid (FA) is a spinning solvent for regenerated Bombyx mori silk fiber with excellent mechanical properties. To use FA as a spinning solvent for RSP with the sequence of major ampullate spider silk protein from Araneus diadematus, we determined the conformation of RSP in FA using solution NMR to determine the role of FA as a spinning solvent. We assigned ¹H, ¹³C, and ¹⁵N chemical shifts to 32-residue repetitive sequences, including polyAla and Gly-rich regions of RSP. Chemical shift evaluation revealed that RSP is in mainly random coil conformation with partially type II β-turn structure in the Gly-Pro-Gly-X motifs of the Gly-rich region in FA, which was confirmed by the ¹⁵N NOE data. In addition, formylation at the Ser OH groups occurred in FA. Furthermore, we evaluated the conformation of the as-cast film of RSP dissolved in FA using solid-state NMR and found that β-sheet structure was predominantly formed.     

叶酸修饰星型端氨基PEG-PLGA纳米胶束的制备及肿瘤细胞靶向作用

合成了星型多臂端氨基聚乙二醇(PEG)/聚乳酸-羟基乙酸(PLGA)两亲性嵌段共聚物(4s-PLGA-PEG-NH₂), 并通过核磁共振和凝胶渗滤色谱法对其结构进行表征; 采用溶剂挥发法制备阿霉素载药纳米胶束, 利用EDC缩合法与叶酸偶联, 得到叶酸修饰的星型端氨基PEG-PLGA纳米胶束; 采用动态光散射、 紫外光谱及透射电镜等手段对纳米胶束进行了表征; 对载药纳米胶束在HeLa细胞中的摄取及细胞毒性进行了初步评价. 结果表明, 经叶酸修饰的星型多臂端氨基PEG-PLGA载药纳米胶束可有效提高HeLa细胞的摄取率以及对HeLa细胞的杀伤率, 表明其可作为一类新型的靶向抗肿瘤药物递送载体.     

Structures,vibrational frequencies,topologies, and energies of hydrogen bonds in cysteine‐formaldehyde complexes

The hydrogen bonding interactions between cysteine (Cys) and formaldehyde (FA) were studied with density functional theory regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules and natural bond orbital analyses were employed to elucidate the interaction characteristics in the Cys‐FA complexes. The intramolecular hydrogen bonds (H‐bonds) formed between the hydroxyl and the N atom of cysteine moiety in some Cys‐FA complexes were strengthened because of the cooperativity. Most of intermolecular H‐bonds involve the O atom of cysteine/FA moiety as proton acceptors, while the strongest H‐bond involves the O atom of FA moiety as proton acceptor, which indicates that FA would rather accept proton than providing one. The H‐bonds formed between the CH group of FA and the S atom of cysteine in some complexes are so weak that no hydrogen bonding interactions exist among them. In most of complexes, the orbital interaction of H‐bond is predominant during the formation of complex. The electron density (ρ_b) and its Laplace (?²ρ_b) at the bond critical point significantly correlate with the H‐bond parameter δR, while a linearly relationship between the second‐perturbation energy E(2) and ρ_b has been found as well. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Structural characterization of electron-induced proton transfer in the formic acid dimer anion, (HCOOH)2-, with vibrational and photoelectron spectroscopies

The (HCOOH)(2) anion, formed by electron attachment to the formic acid dimer (FA(2)), is an archetypal system for exploring the mechanics of the electron-induced proton transfer motif that is purported to occur when neutral nucleic acid base-pairs accommodate an excess electron [K. Aflatooni, G. A. Gallup, and P. D. Burrow, J. Phys. Chem. A 102, 6205 (1998); J. H. Hendricks, S. A. Lyapustina, H. L. de Clercq, J. T. Snodgrass, and K. H. Bowen, J. Chem Phys. 104, 7788 (1996); C. Desfrancois, H. Abdoul-Carime, and J. P. Schermann, ibid. 104, 7792 (1996)]. The FA(2) anion and several of its H∕D isotopologues were isolated in the gas phase and characterized using Ar-tagged vibrational predissociation and electron autodetachment spectroscopies. The photoelectron spectrum of the FA(2) anion was also recorded using velocity-map imaging. The resulting spectroscopic information verifies the equilibrium FA(2)(-) geometry predicted by theory which features a symmetrical, double H-bonded bridge effectively linking together constituents that most closely resemble the formate ion and a dihydroxymethyl radical. The spectroscopic signatures of this ion were analyzed with the aid of calculated anharmonic vibrational band patterns.     

Quantitative determination of folic acid in multivitamin/multielement tablets using liquid chromatography/tandem mass spectrometry

Two different isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods for the quantitative determination of folic acid (FA) in multivitamin/multielement tablets are reported. These methods represent distinct improvements in terms of speed and specificity over most existing microbiological and chromatographic methods for the determination of FA in dietary supplements. The first method utilizes an aqueous/organic-based extraction solvent combined with positive-ion mode LC/MS/MS detection of protonated [M + H]+ FA molecules and the second method utilizes a pure aqueous-based extraction solvent combined with negative-ion mode LC/MS/MS detection of deprotonated [M - H]- FA molecules. The LC/MS/MS methods exhibit comparable linear dynamic ranges (> or =3 orders of magnitude), limits of detection (0.02 ng on-column) and limits of quantification (0.06 ng on-column) for FA. Two methods employing different extraction and different MS detection modes were developed to allow method cross-validation. Successful validation of each measurement procedure supports the use of either method for the certification of FA levels in dietary supplements. The accuracy and precision of each measurement procedure were evaluated by applying each method to the quantitative determination of FA in a NIST standard reference material (NIST SRM 3280 multivitamin/multielement tablets). The FA measurement accuracy for both methods was > or =95% (based on the manufacturer's assessment of the FA level in SRM 3280) with corresponding measurement precision values (% RSD) of approximately 1%.     

Ordered structures of poly(1H,1H,2H,2H-perfluorodecyl α-substituted acrylate)S

Ordered structures of poly(1H,1H,2H,2H-perfluorodecyl α-fluoroacrylate) (P17FF), poly(α-chloroacrylate) (P17FC), poly(methacrylate) (P17FM) and poly(acrylate) (P17FA) were investigated by X-ray diffraction, DSC and polarizing microscopic observations. At room temperature, both P17FF and P17FC prefer the layered structure of single-layer packing of the fluoroalkyl side chains, while P17FM contains both single-layer and double-layer packing, and P17FA forms double-layer packing. As temperature increases, particularly in P17FF and P17FC, there was observed a structural rearrangement of the single-layer packing to double-layer one accompanied by melting of the side chain crystallites, which may come from an intermolecular interaction between the main chains caused by polar effect of the α-substituents.