Kinetic and Stoichiometric Parameters in the Production of Carotenoids by <Emphasis Type="Italic">Sporidiobolus salmonicolor</Emphasis> (CBS 2636) in Synthetic and Agroindustrial Media

With the objective of determining the kinetic behavior (growth, substrate, pH, and carotenoid production) and obtain the stoichiometric parameters of the fermentative process by Sporidiobolus salmonicolor in synthetic and agroindustrial media, fermentations were carried out in shaken flasks at 25°C, 180 rpm, and initial pH of 4.0 for 120 h in the dark, sampling every 6 h. The maximum concentrations of total carotenoids in synthetic (913 μg/L) and agroindustrial (502 μg/L) media were attained approximately 100 h after the start of the fermentative process. Carotenoid bioproduction is associated with cell growth and the ratio between carotenoid production and cell growth (Y _P/X) is 176 and 163 μg/g in the synthetic and agroindustrial media, respectively. The pH of the agroindustrial fermentation medium varied from 4.2 to 8.5 during the fermentation. The specific growth rate (μ _X) for S. salmonicolor in synthetic and agroindustrial media was 0.07 and 0.04 h⁻¹, respectively. The synthetic medium allowed for greater productivity, obtaining maximum cell productivity (P _x) of 0.08 g L⁻¹ h⁻¹ and maximum total carotenoid productivity (P _car) of 14.2 μg L⁻¹ h⁻¹. Knowledge of the kinetics of a fermentative process is of extreme importance when transposing a laboratory experiment to an industrial scale, as well as making a quantitative comparison between different culture conditions.     

The Effect of Different Aqueous Ionic Media on the Acid-Base Properties of Some Open Chain Polyamines

Acid-base properties of some open-chain polyamines (ethylenediamine, diethylenetriamine, triethylenetetramine, spermine, tetraethylenepentamine and pentaethylenehexamine) were studied at different ionic strengths in different aqueous ionic media at 25 °C. Measured were: (i) the protonation constants of triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine from potentiometric measurements [0 ≤I≤2.5 mol⋅L⁻¹ in NaCl and (CH₃)₄NCl)]; and (ii) protonation enthalpies of ethylenediamine, diethylenetriamine, and spermine from calorimetric measurements [NaCl: 0≤I≤1 mol⋅kg⁻¹ for ethylenediamine, diethylenetriamine, 0 ≤I≤2 mol⋅kg⁻¹ for spermine; (C₂H₅)₄NI: 0≤I≤1 mol⋅kg⁻¹; (CH₃)₄NCl: 0 ≤I≤2.5 mol⋅kg⁻¹ only for diethylenetriamine]. Previously published protonation data for these polyamines in aqueous NaCl, (CH₃)₄NCl and (C₂H₅)₄NI, were also examined. The general trends for the Gibbs energy and entropic contributions are, for ΔG: NaCl>(CH₃)₄NCl>(C₂H₅)₄NI, and for TΔS: (C₂H₅)₄NI>(CH₃)₄NCl>NaCl. This trend is more pronounced for the first protonation step. The dependences of these quantities on ionic strength were modeled with the SIT (Specific ion Interaction Theory) equations, and differences found among the different media were interpreted in terms of weak complex formation.     

Investigation of the Electrochemical Reduction of Benzophenone in Aprotic Solvents Using the Method of Cyclic Voltammetry

The reduction of benzophenone (Bzph) in 3-pentanone (PEN), acetone (ACE), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (ACN) and dimethyl sulfoxide (DMSO) with n-tetrabutylammonium hexafluorophosphate (TBAPF₆) as background electrolyte was studied using the technique of cyclic voltammetry at the temperature of 263.15 K. The half-wave potentials (E _1/2) were extracted. The reduction of Bzph occurs in two successive one-electron steps to produce first the free radical anion Bzph⁻ and then the dianion Bzph²⁻. The results indicated that the radical anion Bzph⁻ is reoxidized to Bzph in all investigated solvent media whereas the dianion Bzph²⁻ is reoxidized to Bzph⁻ only in THF. The heterogeneous electron-transfer rate constants (k _s ) were evaluated by employing the electrochemical rate equation proposed by Nicholson. The rate of electron transfer for the Bzph/Bzph⁻ couple was found to be relatively slow in all investigated solvent media. Consequently, the electron-transfer processes can be recognized as quasi-reversible. The diffusion coefficients (D) of Bzph in the investigated solvent media have been calculated using the modified Randles-Sevcik equation. The effect of the physical and chemical properties of the solvent medium on the electrochemical behavior of Bzph has been examined.     

Mechanistic Studies on the Oxidation of Hydroquinone by an Oxo-bridged Diiron(III,III) Complex in Weakly Acidic Aqueous Media

The kinetics of oxidation of hydroquinone (H₂Q) by a μ-oxo-bridged diiron(III,III) complex, Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) has been investigated in aqueous media at 25.0 °C in presence of an excess of 1,10-phenanthroline (phen). The overall redox rate increases with increase in [H⁺]. The title complex (1) and its conjugate bases, [Fe₂(μ-O)(phen)₄(OH)₂]³⁺(2) and [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3), participate in the reaction with H₂Q as the only kinetically reactive reducing species. Rate constants (in dm³ mol⁻¹ s⁻¹) for the parallel reactions (1) + H₂Q → Products, (2) + H₂Q → Products and that for (3) + H₂Q → Products are, respectively, 500 ± 40, 100 ± 6 and 30 ± 2. Substantial rate retardation in D₂O media in comparison to that in H₂O media suggests that electron transfer is coupled with proton movements in the rate-determining step.     

Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

 The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄.     

Critical Evaluation of Protonation Constants. Literature Analysis and Experimental Potentiometric and Calorimetric Data for the Thermodynamics of Phthalate Protonation in Different Ionic Media

The protonation constants of phthalate were determined in aqueous NaCl (0.1 ≤ I ≤ 5,mol⋅L⁻¹) and in aqueous Me₄NCl (0.1 mol⋅L⁻¹ ≤ I ≤ 3,mol⋅L⁻¹) at t = 25,^∘C. Experimental data were employed in conjunction with literature data from studies in different ionic media (Et₄NI: 0 ≤ I ≤ 1,mol⋅L⁻¹; NaClO₄: 0.05 mol⋅L⁻¹ ≤ I ≤ 2,mol⋅L⁻¹)to study the dependence on ionic strength using different models, such as the SIT and Pitzer equations, and an Extended Debye-Hückel type equation. Experimental calorimetric data in NaCl and protonation constants at different temperatures in Et₄NI (5 ≤ t ≤ 45^∘C) and in NaClO₄ (15 ≤ t ≤ 35 ^∘C) were also used to study their dependence on temperature. Recommended equilibrium data are reported together with a short discussion of a prospective protocol for drawing these data.     

Investigation on the thermal decomposition some heterodinuclear NiII-MII complexes prepared from ONNO type reduced Schiff base compounds ( M II=ZnII, CdII)

N,N′-bis(salicylidene)-1,3-propanediamine (LH₂), N,N′-bis(salicylidene)-2,2′-dimethyl-1,3-propanediamine (LDMH₂), N,N′-bis(salicylidene)-2-hydroxy-1,3-propanediamine (LOH₃), N,N′-bis(2-hydroxyacetophenylidene)-1,3-propanediamine (LACH₂) and N,N′-bis(2-hydroxyacetophenone)-2,2′-dimethyl-1,3-propanediamine (LACDMH₂) were synthesized and reduced to their phenol-amine form in alcoholic media using NaBH₄ (L^HH₂, LDM^HH₂, LOH^HH₂, LAC^HH₂ and LACDM^HH₂). Heterodinuclear complexes were synthesized using Ni(II), Zn(II) and Cd(II) salts, according to the template method in DMF media. The complex structures were analyzed using elemental analysis, IR spectroscopy, and thermogravimetry. Suitable crystals of only one complex were obtained and its structure determined using X-ray diffraction, NiLAC^H·CdBr₂·DMF₂, space group orthorhombic, Pbca, a=20.249, b=14.881, c=20.565 ? and Z=8. The heterodinuclear complexes were seen to be of [Ni·ligand·MX₂·DMF₂] structure (ligand=L^H2−, LDM^H2−, LOH^H2−, LAC^H2−, LACDM^H2−, M=Zn^II, Cd^II, X=Br⁻, I⁻). Thermogravimetric analysis showed irreversible bond breakage of the coordinatively bonded DMF molecules followed by decomposition at this temperature.     

Photophysical Properties of Safranine T in Aqueous Glycol Oligomer Mixtures

The photophyscial behavior of the dye Safranine T in the ground and excited states in aqueous mixtures of glycol oligomers was investigated by absorption and fluorescence spectroscopic techniques. The formation of a 1:1 complex in the excited state was inferred from fluorescence studies. The calculated equilibrium constants of the complex are directly proportional to the molar mass of the glycol. Microviscosity values of the aqueous glycol mixtures were determined by employing Auromine O as a fluorescence probe. Stokes shift values were correlated with the bulk dielectric constant and the microviscosity of the media. Also employing Stokes shifts, solvent parameters such as the Kowoser Z values and the intramolecular charge transfer energy, E _T (30), were evaluated. The fluorescence quenching of Safranine T by the inorganic ions [Fe(CN)₆]³⁻, [Fe(CN)₆]⁴⁻, and [I]⁻ in aqueous oligomer mixtures at a fixed concentration was investigated. The ions influenced the quenching process to different extents, and the efficiency of quenching of the dye in the glycol media for [Fe(CN)₆]⁴⁻ and [I]⁻ ions follows the order EG > DEG > TEG > TTEG. In the case of ferricyanide ion the reverse order was observed. The microviscosity and bulk dielectric constant of the media played a major role in the collisional quenching process.     

Effect of dielectric medium on angiotensin converting enzyme inhibitors binding to Zn<Superscript>2+</Superscript>

The Becke3LYP density functional was used to study structural and thermodynamic parameters of bivalent zinc cation complexes with selected substrates and ACE inhibitors (H₂O/OH⁻, neutral forms of captopril, zofenoprilat, omapatrilat, CH₃CONHCH₃, and N-terminal anions of captopril, zofenoprilat, omapatrilat, enalaprilat, perindoprilat, trandolaprilat, and fosinoprilat). The combination of DFT and the conductor-like polarizable continuum model (CPCM) were employed to compute the Gibbs interaction energies (ΔG) between Zn²⁺ and the selected ACE inhibitors for dielectric media with ɛ = 5 (to simulate the protein environment) and for water media (ɛ = 78.39) for comparison purposes. The results show that ΔG is sensitive to the dielectric constant of the environment and that lower dielectric medium favors the binding of inhibitors to the zinc cation.     

Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

Summary.  The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄. Corresponding author. E-mail: grampp@ptc.tu-graz.ac.at Received January 30, 2002; accepted (revised) June 5, 2002     

Studies on the electrochemical and thermodynamic behaviour of Hg-HgS electrode in the presence of sulphide ions

Mercury-mercury (II) sulphide electrode has been prepared and its electrochemical and thermodynamic behaviour has been studied in different media. The electrode is found to show Nernstian response to pS (− log [S²⁻]) over the range 5.19–10.38. In the pH range 7.96–11.98, at constant [S²⁻]_v, its response is also Nernstian. The values of thermodynamic functions, viz., ΔG⁰. ΔH⁰, and ΔS⁰ for the electrode reaction: Hg₍₃)+S²⁻ _aμ ⇌HgS_(s)+2e, have been determined. Further, the standard free energy of formation (ΔG _f ⁰ ) and solubility product constant (K _vp ) of HgS in aqueous medium at 25±0.1°C have also been determined.     

含氟体系中高性能T型分子筛膜的合成

含氟体系中,在负载晶种的大孔莫来石支撑体表面快速合成了高性能且取向生长的T型分子筛膜。采用XRD、SEM和MAS NMR等手段对分子筛膜层和粉末进行表征。讨论了添加物、氟硅比、合成温度和合成时间等条件对膜生长与分离性能的影响,并阐述了含氟体系中T型分子筛膜快速晶化的机理。碱金属氟盐的加入促进了T型分子筛晶体层的晶化速率,并对晶体层形貌产生了一定的影响。膜应用于75℃、水/异丙醇(10∶90,w/w)体系的平均渗透通量和分离因子分别为(4.91±0.18)kg·m-2·h-1和7 060±1 130。     

含氟体系中高性能T型分子筛膜的合成

含氟体系中,在负载晶种的大孔莫来石支撑体表面快速合成了高性能且取向生长的T型分子筛膜。采用XRD、SEM和MASNMR等手段对分子筛膜层和粉末进行表征。讨论了添加物、氟硅比、合成温度和合成时间等条件对膜生长与分离性能的影响,并阐述了含氟体系中T型分子筛膜快速晶化的机理。碱金属氟盐的加入促进了T型分子筛晶体层的晶化速率,并对晶体层形貌产生了一定的影响。膜应用于75℃、水/异丙醇（10：90,w/w）体系的平均渗透通量和分离因子分别为（4.91±0.18）kg·m^-2·h^-1和7060±1130。     

Solvent Effect on Protonation Constants of 5, 10, 15, 20-Tetrakis(4-sulfonatophenyl)porphyrin in Different Aqueous Solutions of Methanol and Ethanol

The protonation constants of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin, H₂tpps⁴⁻, were determined in water–ethanol and water–methanol mixed solvents, using a combination of spectrophotometric and potentiometric methods at 20 °C and 0.1 mol⋅dm⁻³ sodium perchlorate as supporting electrolyte. Two protonation constants, K ₁ and K ₂, were characterized and were analyzed in various media in terms of the Kamlet, Abboud and Taft (KAT) parameters. Single-parameter correlations of the protonation constant K ₁ versus α (hydrogen-bond donor acidity) and π ^* (dipolarity/polarizability) are poor in all solutions, but dual-parameter (α and π ^*) correlation represents a significant improvement with regard to the single- and multi-parameter models. However, the single-parameter correlation of log ₁₀ K ₂ in terms of β (hydrogen-bond acceptor basicity) shows a better result than dual- and multi-parameter correlations. Linear correlation is observed when the experimental log ₁₀ K ₁ and log ₁₀ K ₂ values are plotted versus the calculated ones when the KAT parameters are considered. To evaluate the protonation constants of H₂tpps⁴⁻, the Yasuda-Shedlovsky extrapolation is used to obtain the log ₁₀ K ₁ and log ₁₀ K ₂ values at zero percent organic solvent. Finally, the results are discussed in terms of the effect of the solvent on protonation.     

Electrooxidation of Chlorpromazine in Aqueous and Micellar Media and Spectroscopic Studies of the Derived Cationic Free Radical and Dication Species

Summary.  The electrochemical behaviour of chlorpromazine has been examined in phosphate buffers in aqueous as well as micellar media at a pyrolytic graphite electrode surface. Two oxidation peaks were obtained in linear sweep voltammetry of chlorpromazine. The first peak corresponds to the formation of the cationic free radical, which on further 1e⁻-oxidation gives a dication. The spectroscopic changes and kinetics of the cationic free radical and dication species generated during electrooxidation of chlorpromazine were investigated in both media. The decay of the dication was studied chronoamperometrically and was found to follow first-order kinetics with a half-life of ∼25 ms. Surfactants affect both E _p and i _p values. The anionic surfactant SDS has been found to catalyze the reaction of the free radical cation and the dication.     

Chromium(III) complexes with lutidinic acid: kinetic studies in HClO<Subscript>4</Subscript> and NaOH solutions

Chromium(III)-lutidinato complexes of general formula [Cr(lutH) _n (H₂O)_6−2n ]³⁻ⁿ (where lutH⁻ is N,O-bonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH)₃]⁰ leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1–1.0 M HClO₄ and 0.4–1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were characterized. The dependencies of pseudo-first-order rate constants on [H⁺] are as follows: k _obs1 = k ₁ + k ₋₁/K ₁[H⁺] and k _obs2 = k ₂ K ₂[H⁺]/(1 + K ₂[H⁺]), where k ₁ and k ₂ are the rate constants for the chelate-ring opening and the ligand dissociation, respectively, k ₋₁ is the rate constant for the chelate-ring closure, and K ₁ and K ₂ are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate, respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH⁻]: k _obs1 = k _OH(1) + k _O[OH⁻], where k _OH(1) and k _O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and K ₂ is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH)₄]³⁻ were also studied and the values of the pseudo-first-order rate constants are [OH⁻] independent.     

Kinetics of oxidation of nickel(II) aza macrocycles by peroxydisulphate in aqueous media

The kinetics of the oxidation of nickel (II) hexaaza and nickel (II) pentaaza macrocycles by the peroxydisulphate anion, S₂O₈ ²⁻, were studied in aqueous media. Effect of pH on reaction rate was also studied. The rate increases with increase of S₂O₈ ²⁻ concentration. Rates are almost independent of acid betweenpH 4 and 2, giving overall a relatively simple second-order rate law followed by oxidation within the ion pair solvent shell. Using rate =+1/2 d[Ni(L)³⁺]/dt =k[Ni(L)²⁺][S₂O₈ ²⁻], oxidation rate constants were determined.     

The effects of the solvent and the ligand chirality on the regioselectivity of alkene oxidative esterification by PdII carboxylates

The effects of the solvent and the ligand chirality on the regioselectivity of oxidative esterification of propylene and cyclohexene by Pd^II carboxylates were studied using achiral (MeCO₂ ⁻, Me₂CHCH₂CO₂ ⁻), racemic ((±)-CF₃CF₂CF₂OC^*F(CF₃)CO₂ ⁻), and chiral ((S)−(+)−MeC^*H(Et)CO₂ ⁻, (+)−CF₃CF₂CF₂OC^*F(CF₃)CO₂ ⁻) carboxylate ligands. The oxidation of alkenes in aprotic media (CHCl₃, CH₂Cl₂, CO₂, THF) affords mainly allylic esters (in the case of cyclohexene also homoallylic esters) and the oxidative esterification at the vinylic position is absent. In weakly solvating media (CHCl₃, CH₂Cl₂) the regioselectivity of cyclohexene oxidation (the allyl to homoallyl ratio) increases substantially on going from achiral or racemic acido ligands to chiral acido ligands. In a more donor medium (THF) the ligand chirality effect almost vanishes. The effects of the ligand chirality and the nature of the solvent on the mechanism of alkene oxidation by Pd^II complexes are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1695–1703, September, 1999.     

Thermodynamic Protonation Parameters of some Sulfur-Containing Anions in NaCl<Subscript>aq</Subscript> and (CH<Subscript>3</Subscript>)<Subscript>4</Subscript>NCl<Subscript>aq</Subscript> at <Emphasis Type="Italic">t</Emphasis>=25 °C

Protonation constants of one thiocarboxylate (thioacetate) and four sulfur-containing carboxylates (2-methylthioacetate, thiolactate, thiomalate, 3-mercaptopropionate) were determined by potentiometric measurements in a wide ionic strength range [0≤I≤5 mol⋅L⁻¹ in NaCl and 0 ≤I≤3 mol⋅L⁻¹ in (CH₃)₄NCl] at t=25 °C. For two of these ligands (2-methylthioacetate and thiolactate), the protonation enthalpies were also determined by calorimetric measurements in NaCl ionic medium [0 ≤I≤5 mol⋅L⁻¹] at t=25 °C. Individual UV spectra of the protonated and unprotonated 3-mercaptopropionate species, together with values of the protonation constants, were obtained by spectrophotometric titrations. Results were analyzed in terms of their dependence on the ionic medium by using different thermodynamic models [Debye-Hückel type, SIT (Specific ion Interaction Theory) and Pitzer’s equations]. Differences among protonation constants obtained in different media were also interpreted in terms of weak complex formation.     

Kinetic studies on H<Superscript>+</Superscript>-catalysed aquation of chromium(III)-oxalato-asparaginato and chromium(III)-oxalato-histidinato complexes

Three chromium(III) complexes with asparagine (Asn) and histidine (His) of the [Cr(ox)₂(Aa)]²⁻ type, where Aa = N,O–Asn, N,O–His or N,N′–His, were obtained and characterized in solution. The complexes with N,O–Aa undergo acid-catalysed aquation to give a free amino acid and cis-[Cr(ox)₂(H₂O)₂]⁻, whereas the complex with N,N′–His undergoes parallel reaction paths: (1) isomerization to the N,O–His complex and (2) liberation of an oxalate ligand. Kinetics of the N,O–Aa complexes in HClO₄ media were studied spectrophotometrically under pseudo-first-order conditions. The absorbance changes were attributed to the chelate ring opening at the Cr–N bond. The linear dependence of rate constants on [H⁺] was established, and a mechanism for the chelate ring cleavage was postulated. The existence of a metastable intermediate with O-monodentate Aa ligand was proved experimentally. Effect of [Cr(ox)₂(Aa)]²⁻ on 3T3 fibroblasts proliferation was studied. The tests revealed low cytotoxicity of the complexes. Complexes with Ala, His and Cys are good candidates for biochromium sources.