The Reaction of 2,2-Diphenyl-1-picrylhydrazyl with Minerals

Abstract

2,2-Diphenyl-1-picrylhydrazyl (DPPH) is reversibly adsorbed at acidic centers on the surfaces of a variety of common mineral pigments and fillers, and undergoes a subsequent irreversible reaction with adsorbed water or surface hydroxy groups to yield 1,1-diphenyl-2-picrylhydrazine, 1-(4′-nitrophenyl)-1-phenyl-2-picrylhydrazine, and 4,4′-oxybis[N-(4-picryliminocyclohexa-2,5-dienylidene)aniline] as the major products. The rate of the irreversible reaction on kaolinite is second-order with respect to DPPH and probably depends on the disproportionation between a DPPH and a protonated DPPH molecule. The possible use of DPPH as a probe for the activity of mineral fillers in polymer chemistry, and some implications on its use as a diagnostic test for radical species are discussed.     

Control of Axial Chirality by Planar Chirality Based on Optically Active [2.2]Paracyclophane

Optically active X-shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH–π interactions, thereby leading to the expression of the axial chirality, i.e., propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X-shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate Φ_PL and a large g_lum value in the order of 10⁻³ at 25 °C, in solution. In contrast, at −120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality.     

Chirality and Stereogenicity of Square‐Planar Complexes

Square‐planar complexes with achiral and chiral ligands have been enumerated exhaustively under the point‐group D _4h and under the symmetry group S ^[4] of degree 4, where they have been classified in terms of their symmetries and permutabilities. Thereby, their stereochemical properties and relationships have been discussed in detail. In particular, equivalency under point‐group symmetry (e.g., enantiomeric relationships for chiral complexes and prochirality for achiral complexes) and that under permutation‐group symmetry (e.g., proper and improper permutations, stereogenic and astereogenic groups, and enantiostereogenic and diastereogenic groups) have been characterized to give a systematic format for stereochemistry and stereoisomerism.     

Spectrophotometric Determination of Some Pharmaceutical Compounds Using 2,2-Diphenyl-1-picrylhydrazyl

Abstract

A spectrophotometric method for the determination of some pharmaceutical amides, hydrazides and thiols is described. The method is based on the reaction of the studied drugs with 2,2-diphenyl-1-picryl hydrazyl (DPPH). The latter is employed to abstract a hydrogen atom from the drugs thereby promoting a process of radical coupling. This results in a reduction of the violet colour of DPPH with the formation of the yellow coloured 2,2-diphenyl-1-picrylhydrazine (DPPH₂). This fading in colour of DPPH reagent depends on the concentration of the drug being determined. Beer's law is obeyed in the ranges of 1–5 μg/ml (for isocarboxazid and gliclazide), 0.25–2.5 μg/ml (for isoniazid), 0.5–5 μg/ml (for iproniazid), 1–7 μg/ml (for tolazamide), 2–15 μg/ml (for captopril) and 1–6 μg/ml (for sulphathiourea). The validity of the method was tested by analysing the studied drugs in pure form as well as in tablets. Results of analyses were compared statistically with the official or reported methods.     

Chirality control in 2,2'-biphosphole ligand leading to enantiopure Pd complex

Asymmetric alkylation of the 3,4-dimethyl-5-phenyl-2,2'-biphospholyl anion with the (2R,4R)-(-)-pentaneditosylate leads to a new chirally flexible 2,2'-biphosphole ligand as a mixture of three diasteroisomers. By complexation with Pd(II), a chirality control occurs to afford enantiopure Pd complex.     

Structural studies of 2,2-Diphenyl-1-picrylhydrazine: A clathrate forming compound

2,2-Diphenyl-1-picrylhydrazine was crystallized from both tetrahydrofuran and chloroform. The crystal structures of samples from both preparations were determined by X-ray diffraction at low temperatures. Both crystals are clathrates with solvent molecules included as guest species in a host framework formed by the diphenylpicrylhydrazine molecules. The structures are rhombohedral, space groupR3. For the crystal from tetrahydrofuran, at 228 K,a = 25.820(4),c = 15.096(2) Å,Z = 18,R = 0.084 andwR = 0.133. For the crystal from chloroform, at 115 K,a = 25.453(12),c = 15.083(3) Å,Z = 18,R = 0.117 andwR = 0.153. Each unit cell contains three cavities which have approximate cylindrical shape with diameter 7.8 Å and height 6.0 Å, and 3 point symmetry. The integrity of the host framework is maintained only through van der Waals forces rather than through intermolecular hydrogen bonding as is found in many other known organic cathrates. The conformation of the trinitroanilino group of the hydrazine molecule is similar to that in the related trinitroanilinocarbazole molecule. The N-N bond approximates a single bond, and both hydrazine N atoms aresp ² hybridized.     

Asymmetric Synthesis of Novel Ferrocenyl Ligands with Planar and Central Chirality

A stereogenic center at the position β to the metallocene backbone is present in ferrocenyl ligands 2 , which are interesting for asymmetric catalysis. These planar-chiral compounds are accessible for the first time by a highly diastereoselective and enantioselective synthesis (de=93–97 %; ee≥96 %) from the ferrocenyl ketones 1 . A variety of donor groups (E¹=Ph₂P⋅BH₃, SMe, SiPr; E²=SMe, STol, SePh, Ph₂P⋅BH₃, iPr₂P⋅BH₃) can be introduced as electrophiles. Tol=tolyl=CH₃C₆H₄.     

Alignment and Dynamic Inversion of Planar Chirality in Pillar[n]arenes

Pillar[n]arenes are symmetrical macrocyclic compounds composed of benzene panels with para-methylene linkages. Each panel usually exhibits planar chirality and prefers chirality-aligned states. Because of this feature, pillar[n]arenes are attractive scaffolds for chiroptical materials that are easy to prepare and optically resolve and show intense circular dichroism (CD) signals. In addition, rotation of the panels endows the chirality of pillar[n]arenes with a dynamic nature. The chirality in tubular oligomers and supramolecular assemblies sometimes show time- and procedure-dependent alignment phenomena. Furthermore, the CD signals of some pillar[n]arenes respond to the addition of chiral guests when their dynamic chirality is coupled with host–guest properties. By using diastereomeric pillar[n]arenes with additional chiral structures, the response can also be caused by achiral guests and changes of the environment, providing molecular sensors.     

几种天然黄酮类化合物对二苯代苦味肼自由基的清除作用

采用循环伏安法、示差脉冲伏安法对四种天然黄酮类化合物清除二苯代苦味肼自由基（DPPH）的能力进行了探讨.研究表明：此法可直接观测样品对DPPH的清除作用,而且灵敏度高、准确可靠,是一种检测自由基及物质对其清除作用的有效方法.     

1-Chloroisatin and 2,2-Diphenyl-2,3-dihydro-3-one-1,5,7-trichloroindole: New Oxidants

In 1969 1-chlorobenzotriazole was proposed as a new oxidant, espe cially in view of its ease of preparation, it stability, its mild and rapid action, and the ease of remuval of side products.“¹ In this communication we describe 1-chloroisatin (1) and 2,2-diphenyl -2,3-dihydro-3-one-1,5,7-trichloroindole (2) as new convinient oxi dants.     

Synthesis and Catalytic Activity of Ferrocenyl Phosphinosulfoxide Ligand with Planar and Central Chirality

通过二茂铁侧链上具有手性中心的杂原子的邻位导向作用合成了具有平面手性和中心手性的二茂铁亚砜膦配体(3),其结构经1H NMR,13C NMR,IR,MS和元素分析表征.将络合物Pd-3用于催化1,3-二苯基-2-丙烯基乙酸酯与丙二酸二甲酯/氢化钠的模板反应,收率92％,20％ee.     

Planar Chiral Dialkoxysilane: Introduction of Inherent Chirality and High Reactivity in Conventional Achiral Alkene

A simple eight‐membered dialkoxysilane (E)‐ 1 prepared from 2‐pentene‐1,5‐diol, showed remarkably stable planar chirality along with high reactivity toward epoxidation, Diels–Alder reaction, and cycloaddition reaction with azide.     

Synthesis of Ferrocenylamides with Planar Chirality by ( - )-Sparteine Mediated Directed Ortho-Lithiation

So far, the method for preparing enantiopure planar chiral ferrocene derivatives relies mainly upon the use of stereogenic ortho-directed auxiliaries[1] to a diastereoselective ortho-lithiation and subsequent reaction with an ap propriate electrophile.     

Planar Chirality: Synthesis and Transannular Reactions of Unsaturated Optically Active Azoninones Bearing E-Olefins

The zwitterionic aza-Claisen rearrangement of optically active trans 4-silyloxy-2-vinylpyrrolidines and carboxylic acid fluoride generated nine-membered ring lactams with high yields. The reaction proceeded with an almost complete 1,4-chirality transfer and the exclusive generation of the E-double bond in the medium sized rings to cause additional planar chiral information. The initially formed azoninones were characterized by a pS-arrangement of the olefin with respect to the ring. The rather kinetically stable conformation underwent a flipping of the double bond to give the pR-azoninones as the thermodynamically stable products. The planar diastereomers were subjected to regio- and diastereoselective transannular ring contractions to give indolizidinones. The stereochemical outcome was strongly dependent from the planar chiral information of the double bond and the lactam unit. The so-formed optically active bicycles bearing a defined substitution pattern should serve as versatile building blocks in alkaloid synthesis.     

Temperature-Driven Planar Chirality Switching of a Pillar[5]arene-Based Molecular Universal Joint

The study of an enantiopure bicyclic pillar[5]arene-based molecular universal joint (MUJ) by single-crystal X-ray diffraction allowed for the first time the unequivocal assignment of the absolute configuration of a planar chiral pillar[5]arene by circular dichroism spectroscopy. Crucially, the absolute configuration of the MUJ was switched reversibly by temperature, with an accompanying sign inversion of the anisotropy factor that varied by as much as 0.03, which is the largest value ever reported. Mechanistically, the reversible chirality switching of the MUJ is driven by the threading/dethreading motion of the fused ring and hence is dependent on both the size and nature of the ring and the solvent employed, reflecting the critical balance between the self-complexation of the ring by pillar[5]arene, the solvation to the excluded ring, and the inclusion of solvent molecules in the cavity.     

Evaluation of the Stereochemical Lability of Benzo-Cycloheptene-Based Drugs Endowed with Potentially Modulable Planar Chirality

An experimental and theoretical study was carried out to analyze the configurational lability possessed by some of the most common drugs endowed with a central non-planar seven-membered cycloheptadiene ring, which confers chirality to these compounds. In fact, the absence of planarity allows the existence of two enantiomeric species that can interconvert thanks to a ring overturning mechanism. The energy barrier that opposes the inversion of the chiral tricyclic scaffold characterizing such species, which is strongly dependent on the presence of appropriate substituents on the two external cycles, has been investigated through Dynamic-HPLC and off-column racemization techniques, as well as through assessments based on molecular modelling approaches. Interesting indications were obtained by making targeted structural changes to allow accurate control of the stereolability characterizing the tricyclic framework.     

Spin Trapping of the Phosphorus-centered Radicals Generated from Hydrogen Abstraction Reaction by 2,2-Diphenyl-1-picrylhydrazyl

IntroductionSPin trapping technique has been widely used for the detection and identification of unstable radicals. As traps, nitrones and nitroso compounds are most widely usedll--4]. However,the identification of spin adducts by EPR spectroscopy is rather difficult because the variationof the hyperfine coupling constants(hfccs) of spin adducts caused by the structural changes oftrapped radicals is not very large. Recently, the ph osp horns- con t al m ng m t rox id e h a s att ra ctedmuch …     

The Interaction of Maleic Anhydride,N -Vinylpyrrolidone,and Their Mixture with 2,2-Diphenyl-1-picrylhydrazyl

Spectrophotometry studies have shown that N-vinylpyrrolidone and/or maleic anhydride interact with 2,2-diphenyl-1-picrylhydrazyl radical in a solution. Thermochemical parameters of the most probable reactions involving these compounds have been estimated by means of the PM6 and B3LYP/6-31+G(d) (gas phase) density functional theory methods. It has been suggested that the stable radical is attached to the monomer molecule, the resulting radical being involved in the chain growth reactions. Termination via the oligomeric radicals recombination is the most probable.     

Determination of Free Phenolic Acids in Plant-Derived Foods by High-Performance Thin-Layer Chromatography with Direct 2,2-Diphenyl-1-Picrylhydrazyl Assay

JPC – Journal of Planar Chromatography – Modern TLC - The healthy properties of functional food are associated with the presence of a wide range of phenolic antioxidants. Thus, the aim...