Determination of quinones by a chemiluminescence reaction in solution

Oxidation of p-benzoquinone by hydrogen peroxide in an alkaline medium gives chemiluminescence emission with maximum intensity at 660 and 560 nm. 1,4-Naphthaquinone gives only a single maximum at 660 nm. These emissions can be used for the determination of microg amounts of the quinones. The interference effect of some organic compounds is described.     

Quantitative study of the reaction between quinones and iron(II) in phosphoric acid medium

A simple method is described for the determination of some quinones with ammonium iron(II) sulphate, by titration potentiometrically or with cacotheline, Methylene Blue, Methylene Green, thionine, Toluidine Blue, Azure A, Azure C or Azure-2-eosin as redox indicators. The reverse titrations can be used for estimation of iron(II). Alternatively, excess of iron (II) can be added and the iron(III) produced determined colorimetrically with thiocyanate.     

Determination of total proteins in several tissues of rat: a comparative study among spectrophotometric methods

In the present paper, five spectrophotometric methods — biuret, Lowry modified by Hartree (Lowry/Hartree), p-chloranil, ultraviolet at 280 nm (UV-280 nm), and ultraviolet at 260/280 nm (UV-260/280 nm) — were used for protein determination in several rat tissues and the results were compared. The Lowry/Hartree method showed the highest sensitivity (0.9 μg/ml) and the biuret method the lowest sensitivity (55.7 μg/ml). The results were not statistically different for the following methods and tissues: Lowry/Hartree was compared to biuret for five tissues (adrenal, spleen, whole brain, liver and small intestine), to p-chloranil for two tissues (liver and epididymal fat pad), and to UV-260/280 nm for three tissues (whole brain, liver and pancreas). Since the Lowry/Hartree method needs a larger period of time for a whole assay to be carried out, we recommend for determination of total protein the following methods: UV-260/280 nm for whole brain, liver, and pancreas, p-chloranil for epididymal fat pad, and biuret for other tissues. We do not recommend the UV-280 nm method because there are many interfering substances in the tissues.     

The reaction of diphenyllithioarsine with quinones and aromatic ketones: a convenient synthesis of tetraphenyldiarsine

Diphenyllithioarsine is oxidized by aromatic ketones and quinones to tetraphenyldiarsine. These reactions were studied by means of EPR spectroscopy in order to ascertain the course of the reaction. Tetraphenyldiarsine was charcterized by its mass spectrum, PMR spectrum, and conversion to diphenyldimethylarsonium iodide.     

Cycloaddition reaction of zirconacyclopentadienes to quinones: synthesis of higher para-quinones

Efficient synthetic approaches to higher para-dihydroquinones and -quinones have been developed through zirconium/CuCl-mediated cycloaddition reactions of two alkynes and quinone in a one-pot procedure.     

A study of heterocyclic quinones

A series of Mannich bases has been obtained from 2- and 4-substituted 6-hydroxyquinoline 5,8-quinones, and their structure has been demonstrated by an analysis of their PMR spectra and by oxidation with hydrogen peroxide. A consideration of the ionization constants of the Mannich bases permits the conclusion that they have a zwitterionic structure.     

A study of heterocyclic quinones

By studying their IR spectra it has been shown that in the solid state and in solutions 4-hydroxyquinoline-5, 6-quinones exist in the hydroxy form stabilized by a strong intramolecular hydrogen bond.For Communication IX, see [11].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 8, pp. 1112–1114, August, 1970.     

Uncatalyzed transfer hydrogenation of quinones and related systems: a theoretical mechanistic study

Quantum chemistry calculations have been used to study the uncatalyzed transfer hydrogenation between a range of hydrogen donors and acceptors, in the gas phase and in solution. Our study shows in the first place that in order to obtain reliable condensed-phase transition structures, it is necessary to perform geometry optimization in the presence of a continuum. In addition, the use of a free energy of solvation obtained with the UB3-LYP/6-31+G(d,p)/IEF-PCM/UA0 combination, in conjunction with UMPWB1K/6-311+G(3df,2p)//B3-LYP/6-31+G(d,p) gas-phase energies, gives the best agreement with experimental barriers. In condensed phases, the geometries and energies of the transition structures are found to relate to one another in a manner consistent with the Hammond postulate. There is also a correlation between the barriers and the energies of the radical intermediates in accord with the Bell-Evans-Polanyi principle. We find that in the gas phase, all the transfer-hydrogenation reactions examined proceed via a radical pathway. In condensed phases, some of the reactions follow a radical mechanism regardless of the solvent. However, for some reactions there is a change from a radical mechanism to an ionic mechanism as the solvent becomes more polar. Our calculations indicate that the detection of radical adducts by EPR does not necessarily indicate a predominant radical mechanism, because of the possibility of a concurrent ionic reaction. We also find that the transition structures for these reactions do not necessarily have a strong resemblance to the intermediates, and therefore one should be cautious in utilizing the influence of polar effects on the rate of reaction as a means of determining the mechanism.     

流动注射比浊法测定人体血清总蛋白

基于磺基水杨酸 硫酸钠混合试剂与蛋白质发生浊度反应,设计了具有一个汇合点的FIA单道流路,运用正交实验优化了影响比浊反应的主要因素,并探讨了流动注射分析条件,从而提出了流动注射比浊法测定人血清中总蛋白的新方法。本法实验结果与双缩脲法一致,每小时进样60次,线性范围为0.14～1.40mg mL。     

Hydrogen and electron transfer in the photoreduction reaction of quinones

The primary products of the photoreduction reaction of 3,6-dit-butyl-o-quinone in single crystals of 3,6-di-t-butyl-pyrocatechol are studied by EPR spectroscopy. Ion radical and neutral radical pairs are identified distinctly. In the case of the same o-quinone in single crystals of 2-6-dit-butyl-4-methylphenol the primary product is the radical pair composed of the two hydroxyphenoxyl radicals of phenol. This indicates the possibility of transfer of two hydrogen atoms in a single elementary photochemical event.     

Determination of free,esterified, and total serum cholesterol using a sensitive color reaction

A method is described for the enzymatic determination of free and total cholesterol sequentially in either whole serum or the HDL fraction. Measurement of low levels of free cholesterol is facilitated by the substitution of sodium 2-hydroxy-3,5-dichlorobenzene-sulfonate for phenol in the peroxidase-catalyzed indicator reaction. Both free and total cholesterol may be measured in the same tube or separately. These alternatives may appeal to investigators who for various reasons may prefer to perform these determinations either sequentially or separately. The sequential approach is a means of conserving the relatively expensive enzymatic reagents.     

Ionic liquid-catalyzed Diels-Alder reaction of levopimaric acid with quinones

Diels-Alder reactions of levopimaric acid with quinones are strongly accelerated in the presence of ionic liquids (imidazolium salts) as catalyst.     

The gas-phase chemiionization reaction between samarium and oxygen atoms: a theoretical study

The Sm+O chemiionization reaction has been investigated theoretically using a method that allows for correlation and relativistic effects. Potential energy curves have been calculated for several electronic states of SmO and SmO+. Comparison with available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemiionization reaction Sm+O is proposed. The importance of spin-orbit coupling in the excited states of SmO, in allowing this chemiionization reaction to take place, has been revealed by these calculations. This paper shows the metal-plus-oxidant chemiionization reaction.     

Insights into the reaction mechanism between propadienylidene and ethylene: a DFT study

The reaction mechanism between propadienylidene and ethylene has been systematically investigated employing the B3LYP/6-311++G** and MP2/cc-pVTZ levels of theory to better understand the reactivity of propadienylidene with unsaturated hydrocarbons. Geometry optimization, vibrational analysis, and energy property for the involved stationary points on the potential energy surface have been calculated. Two important initial reaction complexes characterized by three- and four-membered ring structures have been located firstly. After that, three different products possessing three-, four-, and five-membered ring characters have been obtained through three reaction pathways. In the first reaction pathway, a three-membered ring alkyne compound has been obtained. As for the second reaction pathway, it is a diffusion-controlled reaction, resulting in the formation of the four-membered ring conjugated diene compound. A five-membered conjugated diene compound has been obtained in the third reaction pathway, which is the most stable product in the available products thermodynamically. On the other hand, the second reaction pathway is the most favorable reaction to proceed kinetically.     

Determination of total basicity and available lysine in proteins by nonaqueous titrimetry

A simple method is presented for the determination of the available lysine residues of proteins. The sample is titrated directly with 0.05 or 0.1 M perchloric acid in anhydrous acetic or propionic acid to a potentiometric end-point. The titration is repeated after acylation of the sample. The difference between the two basicity values gives the available lysine content of the proteins. Results are provided for the available lysine contents of bovine serum albumin, human γ-globulin, β-casein, soya bean meals meat meal and milk protein; in most cases, they agree closely with literature data obtained by other methods. The standard error for the procedure is <3.9%.     

Association reaction between SiH3 and H2O2: a computational study of the reaction mechanism and kinetics

The association reaction between silyl radical (SiH₃) and H₂O₂ has been studied in detail using high-level composite ab initio CBS-QB3 and G4MP2 methods. The global hybrid meta-GGA M06 and M06-2X density functionals in conjunction with 6-311++G(d,p) basis set have also been applied. To understand the kinetics, variational transition-state theory calculation is performed on the first association step, and successive unimolecular reactions are subjected to Rice–Ramsperger–Kassel–Marcus calculations to predict the reaction rate constants and product branching ratios. The bimolecular rate constant for SiH₃–H₂O₂ association in the temperature range 250–600 K, k(T) = 6.89 × 10^?13 T ^?0.163exp(?0.22/RT) cm³ molecule^?1 s^?1 agrees well with the current literature. The OH production channel, which was experimentally found to be a minor one, is confirmed by the rate constants and branching ratios. Also, the correlation between our theoretical work and experimental literature is established. The production of SiO via secondary reactions is calculated to be one of the major reaction channels from highly stabilized adducts. The H-loss pathway, i.e., SiH₂(OH)₂ + H, is the major decomposition channel followed by secondary dissociation leading to SiO.     

The gas-phase reaction between O3 and HO radical: a theoretical study.

We report a theoretical study on the reaction of ozone with hydroxyl radical, which is important in the chemistry of the atmosphere and in particular participates in stratospheric ozone destruction. The reaction is a complex process that involves, in the first stage, a pre-reactive hydrogen-bonded complex (C1), which is formed previous to two transition states (TS1 and TS2) involving the addition of the hydroxyl radical to ozone, and leads to the formation of HO4 polyoxide radical before the release of the products HO2 and O2. The reaction is computed to be exothermic by 42.72 kcal mol(-1), which compares quite well with the experimental estimate, and the energy barriers of TS1 and TS2 with respect to C1 are computed to be 1.80 and 2.26 kcal mol(-1) at 0 K. A kinetic study based on the variational transition state theory (VTST) predicts a rate constant, at 298 K, of 7.37 x 10(-14) cm3 molecule(-1) s(-1), compared to the experimentally recommended value of 7.25 x 10(-14) cm3 molecule(-1) s(-1).     

Interaction strength between proteins and polyelectrolyte brushes: a small angle X-ray scattering study

We present an investigation of β-lactoglobulin adsorption onto spherical polyelectrolyte brushes (SPBs) by small angle X-ray scattering (SAXS). The SPB consists of a polystyrene core onto which long chains of poly(styrene sulfonate) are grafted. The amount and the distribution of proteins adsorbed in the brush layer at low ionic strength can be derived from SAXS. The analysis of the SAXS data reveals additionally that some of the protein molecules form aggregates of about six monomers in the adsorbed state. Furthermore, the position and the amount of slightly bound protein can be detected by the combination of the SAXS results and the SPB loading after extensive ultrafiltration. The total amount of adsorbed protein is compared to data derived from isothermal titration calorimetry. The comparison of both sets of data demonstrates that the protein molecules in the inner layers of the spherical polyelectrolyte brush are firmly bound. Proteins located in the outer layers are only weakly bound and can be washed out by prolonged ultrafiltration.