Near infrared photochemistry of pyruvic acid in aqueous solution

Recent experimental and theoretical results have suggested that organic acids such as pyruvic acid, can be photolyzed in the ground electronic state by the excitation of the OH stretch vibrational overtone. These overtones absorb in the near-infrared and visible regions of the spectrum where the solar photons are plentiful and could provide a reaction pathway for the organic acids and alcohols that are abundant in the earth's atmosphere. In this paper the overtone initiated photochemistry of aqueous pyruvic acid is investigated by monitoring the evolution of carbon dioxide. In these experiments CO(2) is being produced by excitation in the near-infrared, between 850 nm and ～1150 nm (11,765-8696 cm(-1)), where the second OH vibrational overtone (Δν = 3) of pyruvic acid is expected to absorb. These findings show not only that the overtone initiated photochemical decarboxylation reaction occurs but also that in the aqueous phase it occurs at a lower energy than was predicted for the overtone initiated reaction of pyruvic acid in the gas phase (13,380 cm(-1)). A quantum yield of (3.5 ± 1.0) × 10(-4) is estimated, suggesting that although this process does occur, it does so with a very low efficiency.     

Photogeneration of distant radical pairs in aqueous pyruvic acid glasses

The lambda > 300 nm photolysis of h4- or d4-pyruvic acid aqueous glasses at 77 K yields identical electron magnetic resonance (EMR) spectra arising from distant (r greater or similar 0.5 nm) triplet radical pairs. Spectra comprise: (1) well-resolved quartets, X, at g approximately ge, that closely match the powder spectra of spin pairs interacting across r approximately 1.0 nm with D approximately 3.0 mT, E approximately 0 mT zero field splittings (ZFS), and (2) broad signals, Y, centered at g approximately 2.07 that display marked g-anisotropy and g-strain, exclude D greater or similar 20.0 mT values (i.e., r less or similar 0.5 spin nm separations), and track the temperature dependence of related g approximately 4 features. These results imply that the n-pi excitation of pyruvic acid, PA, induces long-range electron transfer from the promoted carbonyl chromophore into neighboring carbonyl acceptors, rather than homolysis into contact radical pairs or concerted decarboxylation into a carbene. Since PA is associated into hydrogen-bonded dimers prior to vitrification, X signals arise from radical pairs ensuing intradimer electron transfer to a locked acceptor, while Y signals involve carbonyl groups attached to randomly arranged, disjoint monomers. The ultrafast decarboxylation of primary radical ion pairs, 3[PA+* PA-*], accounts for the release of CO2 under cryogenic conditions, the lack of thermal hysteresis displayed by magnetic signals between 10 and 160 K, and averted charge retrotransfer. All EMR signals disappear irreversibly above the onset of ice diffusivity at approximately 190 K.     

Photoinduced polymerization and oligomerization of 4-vinylbenzophenone

The photopolymerizations of 4-vinylbenzophenone (VBP) in various solvents were investigated to make clear the photoininiation characteristics. It was found that direct photoirradiation produces polymers, oligomers (trimers), and dimers. The dimers were identified as trans- and cis-1,2-bis(4-benzoylphenyl)cyclobutanes. The fraction of trans-form in the cyclobutane dimers produced was about 80%, and was little affected by the reaction conditions. The quantum yields ([VBP] = 0.1M in benzene) was estimated to be 3 × 10^?2 for the dimerization and 2 × 10^?4 for the initiation of polymerization. The photoreactions via π,π^* triplet state of the monomer was suggested from the results.     

Electrosynthesis of lactic acid and 2,3-dimethyltartaric acid from pyruvic acid on lead cathode in aqueous medium

Lactic and 2,3-dimethyltartaric acids have been synthesized from pyruvic acid by changing the nature of the supporting electrolyte and the electrode potential of lead cathode.     

Radiotracer method for the study of the radiolysis of aqueous solutions of pyruvic acid

The purpose of this work is to study the radiolytic behavior of aqueous solutions of¹⁴C-pyruvic acid (oxygen-free). Several parameters were varied such as radiation dose, pH, etc. Gas chromatography, mass spectrometry and high performance liquid chromatography were used extensively for the analysis of radiolytic products. The more abundant product was dimethyltartaric acid. Other products identified were acetic, lactic, succinic, malonic and tricarballylic acids, acetaldehyde, carbon dioxide, and hydrogen. The yields of these products were influenced by the irradiation dose, concentration of the target compound and pH of the solution.     

Photochemistry of the iron(III) complex with pyruvic acid in aqueous solutions

Photochemistry of the 1: 1 Fe^pIII complex with pyruvic acid (PyrH) in aqueous solutions was studied by stationary photolysis and nanosecond laser flash photolysis with the excitation by the 3rd harmonics of an Nd:YAG laser. The quantum yield of [FeIIIPyr]2+ under the excitation at 355 nm is 1.0±0.1 and 0.46±0.05 in the absence and in the presence of dissolved oxygen, respectively. In experiments on laser flash photolysis, a weak intermediate absorption in the region 580–720 nm was found. The absorption was ascribed to the [FeII…MeC(O)COO•]^p2+ radical complex. Laser flash photolysis of [FePyr]^p2+ in the presence of methyl viologen dications (MV^p2+) resulted in the formation of the MV•+ radical cations. The proposed reaction mechanism includes the inner-sphere electron transfer in the light-excited complex accompanied by the formation of the [Fe^pII…MeC(O)COO•]^p2+ radical complex followed by its transformation into the reaction products.     

Thermodynamics and kinetics of indole oligomerization: Preliminary results in aqueous sulfuric acid

Reaction rates and equilibrium constants of indole dimerization and trimerization in aqueous sulfuric acid at 298 K are reported. The equilibrium of oligomerization is attained in about 4–5 h, and formation of oligomers with more than three monomeric unit is not observed. The equilibrium of formation of the indole dimer is influenced by the protonation equilibrium of indole, which means the pK_IH values of indole strongly influences equilibria and kinetics of the whole process. In the evaluation of the kinetic constants, the pK_IH values of indole have been taken into account; in this way, the kinetic constant of formation of the dimer (k_D) results almost four order of magnitude larger than that of the trimer (k_T), suggesting a higher electrophilicity of the 3H‐indolium cations with respect to the protonated dimer (which is an aliphatic ammonium salt). Further indole addition to the trimer, which is a protonated 2‐alkyl‐aniline, does not occur, since the anilinium ion is ineffective as an electrophile. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 107–112, 2009     

Photoinduced reversible pH change in aqueous solution of azoaromatic poly(carboxylic acid)

To regulate the pH value of an aqueous solution containing polyelectrolyte by photoirradiation, an azoaromatic poly(carboxylic acid), acrylic acid(AA)-p-phenylazoacrylanilide (PAAn) copolymer was synthesized and the photoresponse of the polymer solution was investigated. AA-PAAn copolymer, which takes a compact form in the ordinary state owing to the presence of azoaromatic side chains, is transformed into an extended form when azoaromatic moieties are isomerized by photoirradiation. Thus, the pH value of the solution can be reversible regulated by irradiation and interruption of light through a change in polymer conformation. The range of the pH change was about 0.15. These phenomena can be explained on the basis of polarity change induced by the photoisomerization of azoaromatic side chains.     

Oxidation of propylene glycol and lactic acid to pyruvic acid in aqueous phase catalyzed by lead-modified palladium-on-carbon and related systems

Oxidation of propylene glycol and related compounds to pyruvic acid was carried out in aqueous phase at 90 °C with a controlled pH of 8 in the presence of Pd/C modified by Pb, Bi and/or Te as additives. Oxidation of propylene glycol was observed on Pd/C at both the primary and secondary hydroxyl groups to yield lactic acid, hydroxyacetone and pyruvic acid with low selectivities. Pd/C, which alone was inactive in the oxidation of lactic acid, bound Pb on the metallic Pd with a strong interaction. The resultant Pb/Pd/C revealed activity for the selective conversion of lactic acid into pyruvic acid. A trace amount of the additive Pb as low as the atomic ratio Pb/Pd = 0.05, was enough to afford pyruvic acid, and the initial rate of the oxidation showed a maximum at Pb/Pd=0.3. Similar catalysts gave results as follows: Pb/Pt/C, highly active, but less selective; Te/Pd/C, highly selective to pyruvic acid with mild activity; Bi/Pd/C, moderate in both activity and selectivity. Commercially available Pb/Pd/CaCO₃ (Lindlar catalyst) and Pb/Pd/Al₂O₃ were also active, giving 60% yield of pyruvic acid.     

Cooperative hydration of pyruvic acid in ice

About 3.5 +/- 0.3 water molecules are still involved in the exothermic hydration of 2-oxopropanoic acid (PA) into its monohydrate (2,2-dihydroxypropanoic acid, PAH) in ice at 230 K. This is borne out by thermodynamic analysis of the fact that QH(T) = [PAH]/[PA] becomes temperature independent below approximately 250 K (in chemically and thermally equilibrated frozen 0.1 < or = [PA]/M < or = 4.6 solutions in D2O), which requires that the enthalpy of PA hydration (DeltaHH approximately -22 kJ mol(-1)) be balanced by a multiple of the enthalpy of ice melting (DeltaHM = 6.3 kJ mol(-1)). Considering that: (1) thermograms of frozen PA solutions display a single endotherm, at the onset of ice melting, (2) the sum of the integral intensities of the 1deltaPAH and 1deltaPA methyl proton NMR resonances is nearly constant while, (3) line widths increase exponentially with decreasing temperature before diverging below approximately 230 K, we infer that PA in ice remains cooperatively hydrated within interstitial microfluids until they vitrify.     

An ab initio study of pyruvic acid

The geometries and vibrational frequencies of two conformers of pyruvic acid have been obtained at the ab initio second order Möller-Plesset level of theory using the 6-311++G^** basis set. While the calculated geometries have been compared to the experimental microwave data, the vibrational frequencies have been assigned, using the experimental gas phase IR spectra of 13 isotopes of pyruvic acid by a recently developed scaling procedure (IRPROG). An attempt has been made to explain the stability of the eclipsed conformation over the staggered conformation of pyruvic acid by taking account of the molecular orbitals.     

Synthesis and crystal structure of diorganotin(IV) complexes with pyruvic acid benzoylhydrazone and pyruvic acid salicylhydrazone

Six diorganotin esters of Schiff-base ligands formulated as [R₂SnLY]₂, where L₁ is C₆H₅CON₂C(CH₃)CO₂ with Y?=?CH₃CH₂OH, R?=?mClC₆H₄CH₂ (1), oFC₆H₄CH₂ (2), pFC₆H₄CH₂ (3) and L₂ is 2-HOC₆H₄CON₂C(CH₃)CO₂ with Y?=?CH₃OH, R?=?oFC₆H₄CH₂ (4), pFC₆H₄CH₂ (5), mClC₆H₄CH₂ (6) have been prepared and characterized by elemental analysis, IR, ¹H and ¹¹⁹Sn NMR spectra. The crystal structures of complexes 1 and 4 have been determined by X-ray single crystal diffraction. The structure analyses reveal that the Sn atom in both 1 and 4 is seven-coordinate in distorted pentagonal bipyramid geometries with a planar SnO₄N unit and two apical aryl carbon atoms, thus forming a dimeric molecule, which sits on a crystallographic center of symmetry. Intramolecular or intradimeric hydrogen bonds contribute to the stability and compactness of the crystal structures.     

Base-catalysed reduction of pyruvic acid in near-critical water

The reduction of pyruvic acid in near-critical water has successfully been conducted under conditions of various temperatures, pressures, reaction time and the presence of formic acid as the reducing agent. In this work, additives (K₂CO₃, KHCO₃, and sodium acetate) used in the reduction of pyruvic acid were also investigated. The results showed that by adding K₂CO₃ (25 mole %) a markedly higher lactic acid yield (70.7 %) was obtained than without additives (31.3 %) at 573.15 K, pressure of 8.59 MPa, 60 min, and in the presence of 2 mol L^?1 formic acid. As a base catalyst, K₂CO₃ definitely accelerated the reduction of pyruvic acid. The reaction rate constants, average apparent activation energy and pre-exponential factor were evaluated in accordance with the Arrhenius equation. The reaction mechanism of the reduction was proposed on the basis of the experimental results.     

Photoinduced electron transfer on aqueous carbon nanohorn-pyrene-tetrathiafulvalene architectures

Water-soluble carbon-nanohorn-tetrathiafulvalene (CNH-TTF) nanoensembles were prepared by utilizing positively charged pyrene as an assembly medium and characterized by spectroscopy and electron microscopy. Electronic interactions within the nanoensemble were probed by optical spectroscopy, indicating electron transfer between the TTF units and CNHs after light illumination.     

Synthesis and structural characterization of diorganotin(IV) esters with pyruvic acid isonicotinyl hydrazone and pyruvic acid salicylhydrazone Schiff bases

Eight diorganotin esters of Schiff base ligands formulated as [R₂SnLY]₂, where L₁ is 4-NC₅H₄CON₂C(CH₃) CO₂ with Y = H₂O, R = Ph (1), PhCH₂ (2), m-ClC₆H₄CH₂ (3), and L₂ is 2-HOC₆H₄CON₂C(CH₃) CO₂ with Y = CH₃OH, R = PhCH₂ (4), o-ClC₆H₄CH₂ (5), m-ClC₆H₄CH₂ (6), o-FC₆H₄CH₂ (7), p-FC₆H₄CH₂ (8) have been prepared and characterized by elemental analysis, IR, ¹H and ¹¹⁹Sn NMR spectra. The crystal structures of compounds 1, 2 and 4 have been determined by X-ray single crystal diffraction. Their structures show that the tin atoms of three compounds are all rendered seven-coordinated in distorted pentagonal bipyramid geometries with a planar SnO₄N unit and two apical aryl carbon atoms. A comparison of the IR spectra of the ligands with those of the corresponding compounds, reveals that the disappearance of the bands assigned to carbonyl unambiguously conforms that the ligands coordinate with tin in the enol form.     

Kinetics of oxidation of pyruvic acid by [ethylenebis(biguanide)]silver(III) in aqueous acidic media

The oxidation of pyruvic acid by the title silver(III) complex in aqueous acidic (pH, 1.1–4.5) media is described. The reaction products are MeCO₂H and CO₂, together with a colourless solution of the Ag⁺ ion. The free ligand, ethylenebis(biguanide) is released in near-quantitative yield upon completion of the reduction. The parent complex, [Ag(H₂L)]³⁺ and one of its conjugate bases, [Ag(HL)]²⁺, participate in the reaction with both pyruvic acid (HPy) and the pyruvate anion (Py^–) as the reactive reducing species. Ag⁺ was found to be catalytically inactive. At 25.0°C, I=1.0moldm^–3, rate constants for the reactions [Ag(H₂L)]³⁺+HPy (k ₁), [Ag(H₂L)]³⁺+Py^– (k ₂), [Ag(HL)]²⁺+HPy (k ₃) and [Ag(HL)]²⁺+Py^– (k ₄) arek ₁=(94±6)×10^–5dm³mol^–1s^–1, (k ₂ K _a+k ₃ K _a1)= (1.3±0.1)×10^–5s^–1 and k ₄=(58±4)×10^–5dm³mol^–1s^–1, respectively, where K _a1is the first acid dissociation constant of the [Ag(H₂L)]³⁺ and K _a is for pyruvic acid. A comparison between the k ₁ and k ₄ values is indicative of the judgement that k ₂k ₃. A one-electron inner-sphere redox mechanism seems more justified than an outer-sphere electron-transfer between the redox partners.     

丙酮酸及其衍生物的某些特异反应研究

合成了3个丙酮酸的衍生物.结果发现,2'-(N-苄氧羰基甘氨酰脯氨酰胺基)丙酮酸乙酯不稳定,该化合物可以通过自催化水解;与其他脂肪酸不同,丙酮酸与N,N-二异丙基碳二亚胺(DIC)反应形成稳定的加合物,该加合物对醇以及二级胺不敏感;在酰肼的作用下,1-氯-N,N,2-三甲基丙烯胺不能将丙酮酸转化为丙酮酰氯,而是得到2-羟基丙烯酸异丁基酯.     

Effect of ultrasound stimulation on metabolic modulation of pyruvic acid

Pyruvic acid lay on the center position of Eremothecium ashbyii metabolic fluxes, during fermentation, a high performance liquid chromatography (HPLC) method is presented for the simultaneous determination of pyruvic acid in the Eremothecium ashbyii cell culture of both with ultrasound stimulation and the control. Dry weight and riboflavin are also mentored. The results of this study show that the ultrasound stimulation can give rise to pyruvic acid change, at the same time; change of pyruvic acid concentration is correlative to that of dry weight of mycelium and content of riboflavin.     

Enzymatic synthesis of pyruvic acid from acetaldehyde and carbon dioxide

A new enzymatic synthesis of pyruvic acid from acetaldehyde and carbon dioxide has been developed.