Triarylborane-Appended Anils and Boranils: Solid-State Emission,Mechanofluorochromism, and Phosphorescence

Herein, the design, synthesis, optical properties, and mechanofluorochromism characteristics of a series of conjugates having covalently linked triarylborane (TAB) and anil/boranil units (TAB-anil: 1 a – 3 a and TAB-boranil: 1 – 3 ) are reported. The electronic interactions between TAB and anil/boranil in 1 a – 3 a and 1 – 3 were fine-tuned by changing the boryl moiety's position on the phenyl spacer connecting the BMes₂ (Mes=mesityl) and anil/boranil units. A boryl moiety at the meta position ( 1 a ) of the phenyl spacer stabilizes the enolic form (E-OH), whereas a boryl moiety at the para position ( 2 a and 3 a ) stabilizes the keto form (Z-NH) in the solid state. However, in solution 1 a , 2 a , and 3 a exhibit keto–enol tautomerism in both ground and excited states. Compounds 1 a – 3 a and 1 – 3 show red-shifted absorption compared with 4 a and 4 , which are devoid of TAB moieties, which indicate effective participation of an empty p orbital on the boron center in 1 a – 3 a and 1 – 3 . Compounds 1 and 2 showed fluorescence variations in response to external stimuli such as mechanical grinding. Long phosphorescence lifetimes of 18–46 ms were observed for compounds 1 – 3 . The observed optical properties of 1 a – 3 a and 1 – 3 are rationalized in the context of quantum mechanical calculations.     

Separation and Identification of Piperine and Chavicine in Black Pepper by TLC and GC–MS

JPC – Journal of Planar Chromatography – Modern TLC -     

Chromatographic Analysis of trans and cis-Citral in Lemongrass Oil and in a Topical Phytonanocosmeceutical Formulation,and Validation of the Method

JPC – Journal of Planar Chromatography – Modern TLC -     

Thin-Layer Chromatographic Separation of Cadaverine and Ornithine,and Spectrophotometric Quantification

JPC – Journal of Planar Chromatography – Modern TLC -     

The chemistry and physics of zinc oxide surfaces

Metal oxides are virtually everywhere – only gold has the property not to form an oxide on its surface when exposed to the ambient. As a result, understanding the physics and chemistry of oxide surfaces is a topic of pronounced general interest and, of course, also a necessary prerequisite for many technical applications. The most important of these is certainly heterogeneous catalysis, but one has to realize that – under ambient conditions – virtually all phenomena occurring at liquid/metal and gas/metal interfaces are determined by the corresponding oxide. This applies in particular to friction phenomena, adhesion and corrosion. A necessary – but not necessarily sufficient – condition for unravelling the fundamentals governing this complex field is to analyze in some detail elementary chemical and physical processes at oxide surfaces. Although the Surface Science of metal surfaces has seen a major progress in the past decades, for oxides detailed experimental investigations for well-defined single crystal surfaces still represent a formidable challenge – mostly because of technical difficulties (charging), but to some extent also due to fundamental problems related to the stabilization of polar surfaces. As a result, the amount of information available for this class of materials is – compared to that at hand for metals – clearly not satisfactory. A particular disturbing lack of information is that about the presence of hydrogen at oxide surfaces – either as hydroxy-species or in form of metal hydrides.In the present review we will summarize recent experimental and theoretical information which has become available from single crystal studies on ZnO surfaces. While the number of papers dealing with another oxide, rutile TiO₂, is significantly larger (although titania does not exhibit a polar surface), also for zinc oxide a basis of experimental and theoretical knowledge as been accumulated, which – at least for the non-polar surfaces – allows to understand physico-chemical processes on an atomic level for an increasing number of cases. In particular with regards to the interaction with hydrogen a number of – often surprising – observations have been reported recently. Some of them carry implications for the behaviour of hydrogen on oxide surfaces in general. We will present the currently available information for both, experiment and theory, and demonstrate the rather large variety of this material’s surface properties.     

Effects of different basis sets and donor‐acceptor groups on linear and second‐order nonlinear optical properties and molecular frontier orbital energies

The calculation of molecular hyperpolarizability, molecular frontier orbital energies of some donor‐acceptor oxadiazoles ( 5a – f , 8a – f , and 9a – f ) have been investigated using ab initio methods and different basis sets. Ab initio optimizations were performed at the Hartree–Fock (HF) and density functional (Beckee‐3–Lee–Yang–Parr; B3LYP) levels of theory with 6‐31G basis set. The polarizability (<α>), anisotropy of polarizability (Δα), and ground‐state dipole moment (μ), first hyperpolarizability (β), and molecular frontier orbital (HOMO, highest occupied molecular orbital and LUMO, lowest unoccupied molecular orbital) energies of 5a – f , 8a – f , and 9a – f have been calculated at the HF and B3LYP methods with 6‐31G, 6‐31G(d), 6‐31+G(d), 6‐31++G(d,p), 6‐311G, 6‐311G(d), 6‐311+G(d), and 6‐311++G(d,p) basis sets. Also, the molecular hardness (η) and electronegativity (χ) parameters have been obtained using molecular frontier orbital energies. The <α>, Δα, μ, β, HOMO, LUMO energies, η and χ parameters have been investigated as dependence on the choice of method and basis set. The variation graphics of <α>, Δα, μ, β, η, and χ parameters using HF and B3LYP methods with different basis sets are presented. We have examined the frontier molecular orbital pictures of 5a – f , 8a – f , and 9a – f using B3LYP/6‐31++G(d,p) level. The 5a – f , 8a – f , and 9a – f display significant linear, second‐order molecular nonlinearity, and molecular parameters and provide the basis for future design of efficient nonlinear optical materials having the 1,3,4‐oxadiazole core. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Color and Chemical Reactions of Selected Sesquiterpene Lactones and Ecdysones from Asteraceae on TLC Plates

JPC – Journal of Planar Chromatography – Modern TLC -     

A Simple and Sensitive HPTLC Method for Simultaneous Analysis of Tolperisone Hydrochloride and Etodolac in Combined Fixed-Dose Oral Solid Formulation

JPC – Journal of Planar Chromatography – Modern TLC -     

Mass spectrometry of 3-substituted 4-hydroxyisoquinolines and their derivatives

Under electron impact, 3-aryl-4-hydroxyisoquinolines form [M – H]⁺, [M – CO]⁺ and [M – H – CO]⁺ ions with a subsequent elimination of HCN or CH₃CN. A cyclic structure for the [M – H]⁺ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH₃?, as well as H?; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]⁺, [M – OH]⁺ and [M – CH₅?]⁺ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.     

Preparation of optically active cyclohexenones: Chirons for the lipophilic moiety of flowery- and woody-like odorant ketones

Optically active 2,5,6,6- and 2,4,4,5-tetraalkylcyclohex-2-en-1-ones ((+)- 2a – d and (?)- 5a – d ), important building blocks for flowery- and woody-like odorants, have been prepared. Compounds (+)- 2a – d and (?)- 5a – d were obtained by ozonolysis of the corresponding cyclopentenic precursors, followed by intramolecular aldol condensation. Alternatively, enones (+)- 2a – d were reduced to the corresponding allylic alcohols ad converted to enones (-)- 5a – d via acidic isomerization and oxidation. ¹³C-NMR assignments are presented.     

4‐Substituted 2,3‐Dihydroisoxazoles as Masked Azomethine Ylides: Access to Pyrrole Derivatives by 1,5‐ and 1,7‐Dipolar Electrocyclizations of Enynyl Derivatives

The enynyl‐substituted 2,3‐dihydroisoxazoles (‘isoxazolines') 9 – 14 were prepared by highly (Z)‐selective Peterson olefination reaction from the corresponding carbaldehydes 6 – 8 . On short‐time thermolysis (280 – 406°/10 s) the TMS derivatives 9 – 11 give rise to the annulated pyrrolines 18 – 20 , which, in some cases, suffer CH₄ elimination affording the pyrroles 15 – 17 . In contrast, thermolysis of the terminal alkyne derivatives 12 – 14 leads to the bicyclic compounds 21 – 23 . The reaction pathways are discussed on the basis of the formation of conjugated azomethine ylides as key intermediates, which either undergo a 1,5‐cyclization to 18 – 20 or a 1,7‐ring‐closure affording cycloallene intermediates of type V , which are further transformed into the azepino pyrroles 21 – 23 .     

Methods of Detecting and/or Reducing Systematic Errors in Quantitative Planar Chromatography. Part 3. Evaluation and Calibration Errors

JPC – Journal of Planar Chromatography – Modern TLC -     

Identification and Determination of Gliclazide and its Impurities in Various Medicines by Thin-Layer Chromatography and Densitometry

JPC – Journal of Planar Chromatography – Modern TLC - A thin-layer chromatographic and densitometric method has been developed for the identification and quantitation of gliclazide and...     

A Sensitive and Specific High-Performance Thin-Layer Chromatography—Densitometry Method for Determination of Rebamipide in the Bulk Material and in Pharmaceutical Formulation

JPC – Journal of Planar Chromatography – Modern TLC -     

Synthesis of Thiazole and Fused Thiazolo Derivatives

The syntheses of thiazole and fused thiazolo derivatives 2 – 4 , 6 – 8 , 10a – 11b , 13 – 16 from heterocylic isothiocyanates 1 , 5 , 9 , and 12 bearing an ortho ester group and bifunctional reagents, such as substituted propargylamines, is described. Different regioselectivity of intramolecular nucleophilic attack of the thiourea S-atom on the C ? C bond, resulting in the formation of both thiazolo and thiazino derivatives, as well as NMR structure elucidation are discussed.     

Use of Reversed-Phase and Normal-Phase Preparative Thin-Layer Chromatography for Isolation and Purification of Coumarins from Peucedanum tauricum Bieb. Leaves

JPC – Journal of Planar Chromatography – Modern TLC -     

Synthesis and Application of Some Azo and Azomethine Dyes Containing Pyrazolone Moiety

3-Amino-1-phenyl-4,5-dihydro-1H-pyrazol-5-one (1) was used as starting material for the synthesis of a number of azo compounds 3a—3c and azomethine derivative 4. The deblocking of 3a—3c and 4 gave rise to 5a—5c and 6 in which a free amino was revealed. The diazonium salts of 5a—5c and 6 were coupled with several phenols to produce a number of bis azo compounds 7a—7c and 8a—8c with azomethine in position 4 and azoic group in position 3. The prepared dyes were structurally confirmed by elemental analysis, spectral methods and applied to different fibers (wool, polyester and blend of wool/polyester) as disperse dyes and their fastness properties were measured.     

Densitometric HPTLC Method for Qualitative and Quantitative Analysis of Piperitone

JPC – Journal of Planar Chromatography – Modern TLC -     

Development and Validation of High-Performance Thin-Layer Chromatographic Method for the Simultaneous Determination of Rifampicin,Isoniazid, and Pyrazinamide in a Fixed Dosage Combination Tablet

JPC – Journal of Planar Chromatography – Modern TLC -     

Synthesis of Monosaccharide‐Derived Spirocyclic Cyclopropylamines and Their Evaluation as Glycosidase Inhibitors

The glucose‐, mannose‐, and galactose‐derived spirocyclic cyclopropylammonium chlorides 1a – 1d, 2a – 2d and 3a – 3d were prepared as potential glycosidase inhibitors. Cyclopropanation of the diazirine 5 with ethyl acrylate led in 71% yield to a 4 : 5 : 1 : 20 mixture of the ethyl cyclopropanecarboxylates 7a – 7d , while the Cu‐catalysed cycloaddition of ethyl diazoacetate to the exo‐glycal 6 afforded 7a – 7d (6 : 2 : 5 : 3) in 93–98% yield (Scheme 1). Saponification, Curtius degradation, and subsequent addition of BnOH or t‐BuOH led in 60–80% overall yield to the Z‐ or Boc‐carbamates 11a – 11d and 12a – 12d , respectively. Hydrogenolysis of 11a – 11d afforded 1a – 1d , while 12a – 12d was debenzylated to 13a – 13d prior to acidic cleavage of the N‐Boc group. The manno‐ and galacto‐isomers 2a – 2d and 3a – 3d , respectively, were similarly obtained in comparable yields (Schemes 2 and 4). Also prepared were the differentially protected manno‐configured esters 24a – 24d ; they are intermediates for the synthesis of analogous N‐acetylglucosamine‐derived cyclopropanes (Scheme 3). The cyclopropylammonium chlorides 1a – 1d, 2a – 2d and 3a – 3d are very weak inhibitors of several glycosidases (Tables 1 and 2). Traces of Pd compounds, however, generated upon catalytic debenzylation, proved to be strong inhibitors. PdCl is, indeed, a reversible, micromolar inhibitor for the β‐glucosidases from C. saccharolyticum and sweet almonds (non‐competitive), the β‐galactosidases from bovine liver and from E. coli (both non‐competitive), the α‐galactosidase from Aspergillus niger (competitive), and an irreversible inhibitor of the α‐glucosidase from yeast and the α‐galactosidase from coffee beans. The cyclopropylamines derived from 1a – 1d or 3a – 3d significantly enhance the inhibition of the β‐glucosidase from C. saccharolyticum by PdCl , lowering the K_i value from 40 μM (PdCl ) to 0.5 μM for a 1 : 1 mixture of PdCl and 1d . A similar effect is shown by cyclopropylamine, but not by several other amines.