Oxygen equilibrium properties of asymmetric nickel(II)-iron(II) hybrid hemoglobin

Asymmetric Ni(II)-Fe(II) hybrid hemoglobin, XL[alpha(Fe)beta(Fe)][alpha(Ni)beta(Ni)], in which the alpha 1 beta 1 dimer containing ferrous protoporphyrin IX and the complementary alpha 2 beta 2 dimer containing Ni(II) protoporphyrin IX were cross-linked between Lys-82 beta 1 and Lys-82 beta 2 by reaction with bis(3,5-dibromosalicyl) fumarate, was synthesized and characterized. We have previously shown that (i) Ni(II) protoporphyrin IX, which binds neither oxygen nor carbon monoxide, mimics a fixed deoxyheme with respect to its effect on the oxygen equilibrium properties of the counterpart iron subunits in both symmetric Ni(II)-Fe(II) hybrid Hbs [Shibayama, N., Morimoto, H., & Miyazaki, G. (1986) J. Mol. Biol. 192, 323-329] and (ii) the cross-linking used in this study little affects the oxygen equilibrium properties of hemoglobin [Shibayama, N., Imai, K., Hirata, H., Hiraiwa, H., Morimoto, H., & Saigo, S. (1991) Biochemistry 30, 8158-8165]. These remarkable features of our model allowed us to measure the oxygen equilibrium curves for the first two steps of oxygen binding to the alpha 1 beta 1 dimer within the hemoglobin tetramer. At all pH values examined, the affinities of this asymmetric hybrid for the first oxygen molecule are as low as those of native hemoglobin. The hybrid did not show cooperative oxygen binding at pH 6.4, while significant cooperativity was observed with rising pH; i.e., the Hill coefficient was increased from 1.41 to 1.53 upon a pH change from 7.4 to 8.4. The electronic absorption spectrum of Ni(II) protoporphyrin IX in the alpha 2 subunit was changed upon carbon monoxide (or oxygen) binding to the alpha 1 beta 1 dimer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of carbochlorination of chromium (III) oxide

Kinetics of the carbochlorination of Cr₂O₃ has been studied with Cl₂+CO gas mixtures between 500 °C to 900 °C using thermogravimetric analysis. The apparent activation energy is about 100 kJ/mol. Mathematical fitting of the experimental data suggests that the shrinking sphere model is the most adequate to describe the carbochlorination mechanism of chromium oxide and that is controlled by the chemical reaction. In the temperature range of 550 °C to 800 °C, the reaction order is about 1.34 and is independent of temperature. Changing the Cl₂+CO content from 15 to 100 pct increases the reaction rate and does not affect the reaction mechanism. Similarly, changing the ratio of Cl₂/(Cl₂+CO) from 0.125 to 0.857 does not modify the carbochlorination mechanism of Cr₂O₃. In these conditions, the reaction rate passes through a maximum when using a chlorinating gas mixture having a Cl₂/(Cl₂+CO) ratio of about 0.5.     

Extraction of chromium (III) from spent tanning baths

Extraction of chromium(III) from a model spent tanning bath of the leather industry has been investigated using ammoniated and non-ammoniated di(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex® 272). Chromium extraction of 95% by 15% (v/v) D2EHPA, 10% (v/v) isodecanol in kerosene and 86.1% by 15% (v/v) Cyanex® 272, 10% (v/v) p-nonylphenol in kerosene was obtained at equilibrium pH values of 4.0 and 5.0, respectively. The separation of small amounts of iron (III) and aluminium (III) present in the solution along with the Cr(III), was also examined and it was found that Cyanex® 272 was a better reagent than D2EHPA. The slow kinetics of extraction and stripping observed in the case of AI(III) was advantageous for its separation from Fe(III) at low pH values. Difficulties faced in the stripping of loaded metals were also studied because only about 80% chromium recovery by 8 M HCl was obtained from both solvents. The incomplete stripping of the metal may be a result of the formation of a stable species in the organic phase and needs further investigation. The Cr(III) can be recovered as chloride from the strip liquor and recycled for retanning purposes.     

Kinetics of chlorination and oxychlorination of chromium (III) oxide

Thermogravimetric analysis (TGA) is used to study the kinetics of chlorination of Cr₂O₃ with Cl₂+N₂ and Cl₂+O₂ gas mixtures in the temperature range of 550 °C to 1000 °C. The reactivity of Cr₂O₃ toward the chlorine-oxygen gas mixture is higher than that toward the chlorine-nitrogen one. Chlorination of Cr₂O₃ proceeds with an apparent activation energy of about 86 kJ/mol between 550 °C and 1000 °C. The apparent reaction order with respect to chlorine is about 1.23 at 800 °C. At temperatures lower than 650 °C, the shrinking sphere model is the most appropriate for describing the reaction kinetics. Oxychlorination of Cr₂O₃ is characterized by an apparent activation energy of about 87 and 46 kJ/mol for temperatures lower than 650 °C and higher than 700 °C, respectively. At 800 °C and using a Cl₂+O₂ gas mixture, the maximum reaction rate is obtained when the Cl₂/O₂ molar ratio is equal to 4, confirming the formation of chromium oxychloride. At this temperature, the reaction orders with respect to chlorine, oxygen, and Cl₂+O₂ are about 1.08, 0.23, and 1.29, respectively. Mathematical fitting of the experimental data is discussed.     

Electroreduction of chromium(III) chloride in a thermal battery

The discharge characteristics and the reduction products of the CrCl₃ cathodic material in a thermal battery are studied. The maximum discharge capacity of the cathodic material is found to be 0.45 A h g^–1 (550°C). A mechanism for the reduction of CrCl₃ to metallic chromium via an intermediate formation of the melt of Li₃CrCl_6x(Br_6(1–x)) complexes is proposed.     

High-temperature oxidation of chromium (II) sulfide in air

Translated from Poroshkovaya Metallurgiya, No. 11 (347), pp. 51–55, November, 1991.     

Factors affecting the precipitation of chromium(III) in jarosite-type compounds

Jarosite precipitation is a useful means of stabilizing toxic species, and accordingly, the factors affecting the precipitation of chromium(III) in jarosite-type compounds was systematically investigated in a series of laboratory experiments. Although end-member Cr(III) analogues of jarosite-type compounds could not be precipitated at temperatures <100 °C, several percent Cr(III) substitution for Fe(III) in potassium jarosite and sodium jarosite was observed. However, at temperatures >200 °C, the Cr(III) analogue of potassium jarosite (KCr₃(SO₄)₂(OH)₆) is readily precipitated. The Cr(III) analogue has the R $\bar 3$ m structure characteristic of jarosite-type compounds, with a=7.23±0.02Å and c=17.02±0.02 Å. The well-crystallized material typically contains (wt pct): ～7K, ～25Cr, and ～41SO₄. The composition suggests the partial substitution of hydronium ion for potassium and some chromium vacancies in the structure. The formation of the Cr(III) analogue is promoted by increasing temperatures, retention times, and Cr(III) concentrations. Increasing acid concentrations reduce the amount of product formed but suppress the undesirable precipitation of amorphous phases. Although increasing K₂SO₄ concentrations result in a greater mass of precipitate, the products formed from concentrated K₂SO₄ solutions are contaminated with an amorphous phase. In fact, the overall results suggest that an amorphous phase precipitates initially and that the Cr(III) analogue of potassium jarosite forms by the recrystallization, or the dissolution-reprecipitation, of the amorphous phase.     

The coprecipitation behavior of Co(II) and Ni(II) with Fe(III), Cr(III) and Al(III) from aqueous ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with iron(III), chromium(III) and aluminum(III) from ammoniacal solutions has been investigated. The coprecipitation behavior was found to be very sensitive to the solution pH and total ammonia concentration. Co(II) and Ni(II) can be precipitated from low ammonia concentration solutions but are readily redissolved at higher ammonia concentrations. The coprecipitate of divalent and trivalent species was found to contain very large amounts of the divalent metals (up to a mole ratio M M(II)/M(III) of 2.5) when aluminum was the trivalent species, whereas with iron(III) or chromium(III), the ratio was only 0.5.     

Stability of chromium (III) sulfate in atmospheres containing oxygen and sulfur

The stability of chromium (III) sulfate in the temperature range from 880 to 1040 K was determined by employing a dynamic gas-solid equilibration technique. The solid chromium sulfate was equilibrated in a gas stream of controlled SO₃ potential. Thermogravimetric and differential thermal analyses were used to follow the decomposition of chromium sulfate. Over the temperature range studied, the change in the Gibbs’ free energy of formation of chromium sulfate Cr₂O₃(s) + 3SO₃(g) → Cr₂(SO₄)₃(s) can be expressed as ΔG⁰ = •143,078 + 129.6T (±300) cal mole^•1 ΔG⁰ = •598,350 + 542T (±1250) J mole^•1. X-ray diffraction analysis indicated that the decomposition product was crystalline Cr₂O₃ and that the mutual solubility between Cr₂(SO₄)₃ and Cr₂O₃ was negligible. Over the temperature range investigated, the decomposition pressures were significantly high so that chromium sulfate is not expected to form on commercial alloys containing chromium when exposed to gaseous environments containing oxygen and sulfur (such as those encountered in coal gasification).     

差示光度法测定硅铝(钡)铁中硅

硅铝 (钡 )铁中硅的分析早已有报导。开始曾采用ＮａＯＨ -Ｎａ2 Ｏ2 熔样 ,高氯酸脱水重量法测定。后来改进为ＮａＯＨ溶样 ,硅钼兰光度法或氟硅酸钾容量法测定。前者分析周期长 ,操作烦琐 ,试剂消耗量大 ,成本高。后者由于吸光度过高 ,超出正常比色范围 ,误差较大 ;而氟硅酸钾容量法 ,铝严重干扰硅的测定。随着硅铝 (钡 )铁冶炼方式的改变 ,硅铝 (钡 )铁中常含有 1 %～ 3%钛、0 1 %～ 2 %锰、0 1 %～ 2 %铜 ,以及少量的镍、铬、钙、镁等 ,用ＮａＯＨ溶样 ,常有部分样品溶解不完全 ,影响分析结果。本文采用ＮａＯＨ高温熔样 ,稀硝酸酸化 …     

Structural features of Glycera dibranchiata monomer hemoglobins. Primary sequences of monomer hemoglobin components II and III

Glucocorticoids promote the development of many organs including intestine. At the cellular level, the activity of glucocorticoids is regulated by 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) which converts active glucocorticoids to inactive metabolites. As 11 beta HSD is also expressed in the intestine, this enzyme may be an important regulator of intestinal maturation. To investigate this, we have performed the systematic study of the development of intestinal 11 beta HSD activity and its cofactor preference as well as of the effect of 11 beta HSD inhibition by carbenoxolone on postnatal development of sucrase, alkaline phosphatase and Na,K-ATPase in the intestine. The activity of 11 beta HSD was low in ileum of suckling rats and significantly increased during the weaning period. In colon, the activity was already high in suckling rats and gradually rose during the postnatal development. 11 beta HSD activity was undetectable in jejunum both in young and adult rats. At 14.5 nM corticosterone, colonic 11 beta HSD utilized predominantly NAD as a cofactor, but displayed significant sensitivity also to NADP. Ileal 11 beta HSD had similar sensitivity to both cofactors. With NAD as a cofactor, ileal 11 beta HSD had a Km (59 +/- 10 nM) compatible with the colonic enzyme (81 +/- 14 nM). Carbenoxolone administration to suckling and weanling rats in vivo did not result in any changes of sucrase activity in jejunum and ileum, alkaline phosphatase activity in ileum and distal colon or Na,K-ATPase activity in ileum. However, carbenoxolone significantly increased Na,K-ATPase activity in distal colon. Our results indicate that the high-affinity type of 11 beta HSD is expressed not only in colon but also in ileum and that 11 beta HSD is an important factor in the regulation of tissue levels of active glucocorticoids in developing colon but not in the small intestine.     

Extraction of chromium(III) from sodium chloride solutions by means of carboxylic acids

Studies of Cr(III) extraction with carboxylic acids showed that the extraction process takes place at a pH of the aqueous phase ranging from 4 to 5. It was shown that sodium chloride is active with respect to chromium(III) as a salting-out agent. For extraction of Cr(III) with hexanoic acid it was shown that in the organic phase trinuclear complexes of the [Cr(OH)R₂·HR]₃ formula are formed.     

Resonance Raman spectra of iron(III)-, copper(II)-, cobalt(III)-, and manganese(III)-transferrins and of bis(2,4,6-trichlorophenolato)diimidazolecopper(II) monohydrate, a possible model for copper(II) binding to transferrins

Fe(III), Cu(II), Co(III), and Mn(III) complexes of ovo- and human serum transferrins show resonance enhanced Raman bands near 1600, 1500, 1270, and 1170 cm-1 upon excitation with laser frequencies which fall within the visible absorption bands of those metalloproteins. Comparison of the visible absorption and resonance Raman spectra of the Cu(II)-transferrin complexes with those for the Cu(II) model compound, bis(2,4,6-trichlorophenolato)diimidazolecopper(II) monohydrate, indicates that the resonance Raman bands are due to enhancement of phenolic vibrational modes. For the model (Cu(II) compound, a normal coordinate analysis was used to aid our assignment of the observed resonance bands at 1562, 1463, 1311, and 1122 cm-1 to A1 vibrational modes of the 2,4,6-trichlorophenolato moiety. These assignments are consistent with those made for Cu(II)-transferrins. The latter assignments were based upon calculated A1 frequencies for p-methylphenol (Cummings, D.L., and Wood, J.L. (1974), J. Mol. Struct. 20, 1). The wavelength shifts in the resonance bands for the model compound from those for Cu(II)-transferrins are due to the influence of the chloro substituents on the planar vibrations of phenol. These results clearly identify tyrosine as a ligand in copper binding to transferrins.     

Mutational spectrum induced by chromium(III) in shuttle vectors replicated in human cells: relationship to Cr(III)-DNA interactions

Trivalent chromium (Cr(III)), the ultimate species of chromium (VI) intracellular reduction, can associate with DNA forming Cr(III) monoadducts and DNA-DNA cross-links. However, the mutational specificity of Cr(III) has not been determined partly because Cr(III) has difficulty entering cells. In this study, we have characterized the types of Cr(III)-induced DNA lesions in two buffer systems and the mutational spectrum of Cr(III)-treated shuttle vectors replicated in human 293 cells. Plasmids were treated with Cr(III) in buffers consisting of either 10 mM potassium phosphate, pH 7.5 (designated as KP), or 0.2 mM Tris-HCl and 20 microM EDTA, pH 7.4 (designated as TE/50). The amounts of Cr(III) bound to DNA increased as Cr(III) concentration increased in both buffers; these Cr(III)-DNA associations were stable in both buffers during a 24-h dialysis. The electrophoretic mobility of supercoiled DNA was markedly retarded in samples treated with Cr(III) in TE/50 but not KP buffer, suggesting that Cr(III)-mediated DNA-DNA cross-links were generated in TE/50 but did not form in KP. Polymerase-stop assay showed that DNA polymerases were mostly blocked at the 3' adjacent bases of guanines on templates treated with Cr(III) in TE/50 but were not observed on those treated in KP. The signals of Cr(III)-mediated cross-links generated in TE/50 buffers were reduced when they were dialyzed against KP buffers. Similarly, Cr(III)-DNA monoadducts formed in KP were converted to primer-template cross-links by dialysis against TE/50. The mutation frequency of Cr(III) in the supF gene of pSP189 or pZ189 shuttle vectors replicated in human cells increased as Cr(III) concentration increased in both buffers. DNA sequencing analysis showed that single-base substitutions (61-68%), two-base substitutions (3-5%), and deletions (21-34%) were induced in similar frequencies in plasmids treated with Cr(III) in either TE/ 50 or KP. The Cr(III)-induced base-substitution hot spots are different from those occurring spontaneously. Cr(III) enhances G.C base substitutions, particularly G.C-->C.G transversions, at 5'GA, 5'CG, and 5'AG sites. Base-substitution hot spots did not correlate with strong polymerase-stop sites, suggesting that base substitutions are derived from Cr(III) monoadducts, not from DNA-DNA cross-links.     

苯浮选Cr(Ⅲ)-二苯偶氮碳酰络合物光度法测定痕量Cr(Ⅵ)和Cr(Ⅲ)

在酸性条件下,Cr(能将二苯碳酰二肼(DPC)氧化成紫红色二苯偶氮碳酰,自身被还原为Cr(Ⅲ),Cr(Ⅲ)可与二苯偶氮碳酰生成深紫红色Cr(Ⅲ)-二苯偶氮碳酰络合物,该络合物在水相中不易溶解且不稳定,而在有机溶剂苯中稳定且极易溶解,用N2将Cr(Ⅲ)-二苯偶氮碳酰络合物浮选于苯中,形成真溶液,通过测定有机相吸光度测定溶液中Cr(含量。通过用过硫酸铵将溶液中Cr(Ⅲ)氧化成Cr(可测定Cr(和Cr(Ⅲ)合量(∑Cr),差减法计算出Cr(Ⅲ)含量。由于采用了大剂量富集倍数,使灵敏度大大提高,ε540=4.2×105,比水相光度法提高10倍。50 mL溶液中,Cr(质量线性范围0~12μg,测定5.0μg Cr(,RSD=1.8%(n=6),方法检出限7.1×10-9mol/L。由于络合和浮选的选择性,使本法选择性大大提高,实测了天然水中Cr(和Cr(Ⅲ),结果令人满意。