A spectrophotometric study on the interaction of hemoglobin in a diazo coupling reaction of neonatal bilirubin: II. Interaction of bilirubin and hemoglobin in the Jendrassik-Grof diazo coupling reagents

The foregoing experiments have shown some of the difficulties in establishing a mechanism of action for hemoglobin in diazo coupling reactions for bilirubin. All attempts to understand the reaction are complicated by a variety of factors, including the diversity of the reactions generally referred to as Jendrassik-Grof, the heterogeneity of the reaction matrix, and the potential multiple interactions of any generated intermediate or product with other constituents present in the diazo reagents. Probing of the reaction mechanism with an enzyme such as catalase seems to be of questionable value at this point. Because of the unusually high concentrations of enzyme required to inhibit azobilirubin fading, there is a greater possibility for side reactions in the diazo media. The possibility of the occurrence of a Fenton reaction with the spontaneous generation of a superoxide ion or OH radical by a chelated ferrous species cannot be conclusively defined from the several experiments described. However, a hint involving peroxide formation is suggested by the catalase and SOD experiments.     

A study on electrochemistry of histidine and its metabolites based on the diazo coupling reaction

The diazo coupling reaction of diazotized p-aminoacetophenone (DPAAP) with histidine and its metabolites form the basis of the differential pulse adsorption stripping voltammetry (DPASV) method for determination of histidine and its metabolites. The adsorption and electrochemical reaction mechanism of the coupling products were studied in detail by structure analysis, cyclic voltammetry, chronocoulometry, control potential electrolysis, electrocapillary curves, UV spectroscopy and the effect of temperature and surfactants. The adsorption of azo-histidine was found to obey Frumkin adsorption isotherm. The calculation results of the maximum surface excess (Gamma(m)=3.08x10(-11) mol cm(2)), diffusion coefficient (D=2.27x10(-6) cm(2) s(-1)), adsorption coefficient (beta=1.06x10(7)) and interactive factor (gamma=0.9900) showed that the azo-histidine conjugation molecules adsorbed on the mercury electrode surface were attracted each other and the electrode process was adsorption controlled.     

The Rôle of Solvent Participation in Electrophilic Aromatic Substitution: Rates of a diazo coupling reaction in water and in aprotic polar solvents. 24th Communication on diazo coupling reactions

The rates of the diazo coupling reaction of 4-toluenediazonium salts with N, N-dimethylaniline in tetramethylene sulfone, acetonitrile, water, and nitromethane at 30°C are the same within a factor of 5. No significant influence of ‘gegenions’ (HSO or BF) was found. The results are explained by postulating little solvent reorganisation in the transition state. They are discussed comparatively with solvent effects in other electrophilic aromatic substitutions, particularly with regard to the reactions of nitronium salts.     

Kinetic study of Berthelot reaction steps in the absence and presence of coupling reagents

Several reaction steps in the Berthelot reaction for the determination of ammonia have been separately studied. A reaction order of two has been confirmed for the reaction between HOCl and NH(3). The rate constant for this reaction has been determined to be 3.2 x 10(6)l.mole(-1).sec(-1). The first evidence for the formation of benzoquinonechlorimine is presented. Pentacyanoferrate coupling reagents which accelerate the production of indophenol have been found to operate on the reaction between NH(2)Cl and phenol. The rate constant for the final step of the reaction sequence has been determined to be 5.3 x 10(-3)l.mole(-1).sec(-1). A reaction between chlorimine and pentacyanoferrate compounds has been found to be responsible for the formation of a green product in the presence of excess of coupling reagent.     

A spectrophotometric study of the colour reaction between chloranil and aromatic amines

The colour reaction between aromatic amines and chloranil was studied spectrophotometrically. A 1 : 1 adduct formed in solution, with some dissociation. The effects of solvents, acid and alkali were examined. The adducts exhibited intense, and characteristic, broad absorption bands, which could be used for the detection and estimation of an aromatic amine, in the absence of substances of similar light absorption characteristics. A correlation between the basicities of an amine and the ight absorption of the adduct was established.     

A spectroscopic study on the interaction between ferric oxide nanoparticles and human hemoglobin

Magnetic nanoparticles can promote many attractive functions in biomedicine, which may contribute to the prevention of human disease but also may be potentially harmful. In the present study, the interaction of Fe₂O₃ nanoparticles with human hemoglobin (Hb) was studied by fluorescence, circular dichroism and UV/vis spectroscopies. Fluorescence data revealed that the fluorescence quenching of Hb by Fe₂O₃ nanoparticles was the result of the formed complex of Fe₂O₃ nanoparticles-Hb. Binding constants and other thermodynamic parameters were determined at three different temperatures. The hydrophobic interactions are the predominant intermolecular forces to stabilize the complex. Circular dichroism studies did not show any changes in the content of secondary structure of hemoglobin after Fe₂O₃ nanoparticles treatment. This study provides important insight into the interaction of Fe₂O₃ nanoparticles with hemoglobin, which may be a useful guideline for further using of these nanoparticles in biomedical applications.     

Mechanistic study on gold(I)‐catalyzed crosscoupling of diazo compounds: A DFT study

The reaction mechanisms of the gold(I)‐catalyzed cross‐coupling reaction of aryldiazoacetate R1 with vinyldiazoacetate R2 leading to N‐substituted pyrazoles have been theoretically investigated using density functional theory calculations. Two possible reaction mechanisms were examined and discussed. The preferred reaction mechanism (mechanism A) can be characterized by five steps: the formation of the gold carbenoid A2 via the attack of catalyst to R1 (step I), nucleophilic addition of another reactant R2 to generate intermediate A3 (step II), intramolecular cyclization of A3 to form intermediate A4 (step III), hydrogen migration to give intermediate A5 (step IV), and catalyst elimination affording the final product P1 (step V). Step IV is found to be the rate‐determining step with an overall free energy barrier of 28.3 kcal/mol. Our calculated results are in good agreement with the experimental observations. The present study may provide a useful guide for understanding these kinds of gold(I)‐catalyzed cross‐coupling reactions of diazo compounds.     

A spectrophotometric study on the interaction of neutral red with double-stranded DNA in large excess

With the measurement of molecular absorption, the interaction of neutral red (NR) with double-stranded DNA in large excess was investigated. It was found that the interaction of NR, existing in the acidic state (HNR) at pH 4.56, with double-stranded structure DNA displays different spectral features depending on the molar ratio of HNR/DNA, R. If R>1.33, the binding process is characterized by a binding constant at the 10(6) level with each nucleotide residue of double-stranded DNA binding one HNR molecule. If R<0.67, the binding constant is reduced to the 10(4) level, and the binding number for each nucleotide residue of double-stranded DNA to HNR is less than one.     

Catalytic spectrophotometric determination of vanadium in seawaters based on the bromate oxidative coupling reaction of metol and 2,3,4-trihydroxybenzoic acid.

A new, simple, sensitive and selective catalytic method is developed for the determination of vanadium in natural and sea waters. The method is based on the catalytic effect of V(V) and/or V(IV) on the bromate oxidative-coupling reaction of metol with 2,3,4-trihydroxybenzoic acid (THBA). The reaction is followed spectrophotometrically by tracing the oxidation product at 380 and/or 570 nm after 5 min of mixing the reagents. The optimum reaction conditions are 6.4 x 10(-3) mol l-1 of metol, 2.0 x 10(-3) mol l-1 of THBA and 0.16 mol l-1 of bromate at 35 degrees C and in the presence of an activator-buffer solution of 1 x 10(-2) mol l-1 of tartrate (pH = 3.10). Following the recommended procedure, V(V) and/or V(IV) can be determined with linear calibration graphs up to 0.75 ng ml-1 and detection limits, based on the 3Sb criterion, of 0.008 and 0.018 ng ml-1 at 380 and 570 nm, respectively. The developed method was successfully applied, without any separation or preconcentration processes, to the determination of vanadium in natural and seawaters following the direct calibration and standard addition techniques, respectively.     

Prediction of conditions for use of spectrophotometric reagents: p-dimethylaminobenzilidenerhodanine as a spectrophotometric reagent for silver and palladium

A method for theoretical estimation of the detection limits of spectrophotometric reagents is reported. The concentration limits of Beer's law when p-dimethylaminobenzilidenerhodanine is used for determination of silver and palladium are defined on the basis of the stability constants. Conditions for determination of 2-10mug, of Ag per 25ml and 1-5mug of Pd per 25ml with standard deviation 0.03mug per 25 ml are proposed.     

Spectrophotometric study of bilirubin and hemoglobin interactions in several hydrogen peroxide generating procedures

The interference effects of bilirubin and hemoglobin have been described for the peroxidase-hydrogen peroxide oxidation of a hydrogen donor and the catalase-hydrogen peroxide oxidation of methanol to formaldehyde. A competition between bilirubin and the intended hydrogen donor is shown for the substitute analyte, hydrogen peroxide, with a resultant diminution of color due to the loss of intended reaction. No inhibition of peroxidase action appears to take place; its action when complexed with hydrogen peroxide is directed toward the competing hydrogen donor, bilirubin. The final color measured appeared to be partially compensatory, that is the sum of intended color plus the color of residual bilirubin. The subtraction of a serum blank representing a static system will result in a lowered value and a larger error. Hemoglobin, with its strong Soret band can, if its concentration is excessive, cause a major interference in reactions such as the Hantzsch reaction which result in overlapping bands at the reaction wavelength. Samples which are both hemolyzed and jaundiced would present as formidable blanking problems. Further studies on bilirubin and its glucuronide and their individual effect on the peroxidase-peroxide reaction are presently in progress.     

Derivatives of rhodanine as spectrophotometric analytical reagents : I. Condensation at C-5 with aromatic pyridine and nonpyridine aldehydes

The synthesis, characteristics, properties, and reactions with metallic ions of five aromatic (three nonpyridine and two pyridine) derivatives of rhodanine have been studied. Nonpyridine derivatives exhibit one pK value in aqueous solution and two pyridine reagents, and with Pd(II), Au(III), Hg(II), and Cu(I) and (II) form stable complexes which show an absorption band, at the visible zone of the spectrum, with molar absorptivities adequate for spectrophotometric measurements. Finally, suggestions have been made about the group responsibile for the reactionability.     

Cu(I)-catalyzed reaction of diazo compounds with terminal alkynes: a direct synthesis of trisubstituted furans

A method for the synthesis of tri-substituted furans has been developed based on Cu(I)-catalyzed reaction of terminal alkynes with β-keto α-diazoesters. This method for the synthesis of 2,3,5-trisubstituted furans is operationally simple and applicable to wide substrate scope. Moreover, this synthesis employs cheap Cu(MeCN)₄PF₆ as the catalyst and no additional ligand is needed. Similar reaction has also been applied to ethyl (E)-2-diazo-3-(methoxyimino)butanoate for the synthesis of 2,3,5-trisubstituted N-methoxypyrroles with limited success.     

荧光猝灭法研究胆红素与牛血清白蛋白的相互作用

在模拟生理条件下,利用荧光猝灭法研究了胆红素(BR)和牛血清白蛋白(BSA) 的相互作用.结果表明胆红素对BSA有较强的荧光猝灭作用,两者形成了新的复合物,属于静态荧光猝灭,发生了分子内的非辐射能量转移.计算了不同温度下的结合位点数n,结合常数KA,以及对应的热力学参数ΔG,ΔH和ΔS.根据Foster非辐射能量转移理论确定了胆红素和BSA间的结合距离r.此外,利用同步荧光光谱,分析了胆红素对牛血清白蛋白构象的影响.     

CH自由基和NO~2反应研究: I. 反应的热力学计算

探讨了CH自由基与NO~2反应的可能路径,通过计算确定了反应物,产物和稳定中间体的电子状态和平衡构型,并运用Gaussian-3方法和MRCISD方法对可能的反应路径进行了热力学计算。在多数情况下与实验值符合较好。对于个别与理论计算差别较大的实验值进行了评述。