Merocyanines based on 1,3‐indanedione: electronic structure and solvatochromism

A series of merocyanines derived from 1,3‐indanedione and heterocycles of various electron‐donating properties was studied in detail. Their solvatochromic properties were explored in a wide range of solvent polarities to reveal the dependences of their chromacity and electronic structure on the key structural parameters – the properties of a donor heterocycle and the polymethine chain length. Also the dyes were studied by NMR spectroscopy and by quantum chemical calculations, both with the semiempirical AM1 and the non‐empirical density functional theory/B3LYP method. The solvatochromic properties of the explored dyes are rather close to those of merocyanines derived from malononitrile as acceptor group. Appreciable distinctions were observed only in protic ethanol; obviously, they are connected with the formation of solvent–solute H‐bonds in the case of 1,3‐indanedione derivatives. The electron‐acceptor properties of 1,3‐indanedione were found to be somewhat stronger in comparison with those of malononitrile even in aprotic solvents, contrary to the known literature data. Analysis of the merocyanines' molecular orbitals and simulation of their electronic spectra were carried out both in vacuum and in the solvent matrix, and the absorption electronic transitions were analyzed. Static nonlinear optical properties were calculated for both the new merocyanines and the corresponding cationic and anionic cyanine dyes. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient synthesis of methyl 4-chloro-6-fluoro-3-formyl-2H-chromene-2-carboxylate and its derivatives

Abstract  

Methyl 4-chloro-6-fluoro-3-formyl-2H-chromene-2-carboxylate was synthesized conveniently using Vilsmeier reagent. A series of new 2H-chromenes was prepared in high yields by introducing a corresponding β-halovinylaldehyde into condensation and cyclization reactions with active methylene compounds.     

Establishing plasmon contribution to chemical reactions: alkoxyamines as a thermal probe

The nature of plasmon interaction with organic molecules is a subject of fierce discussion about thermal and non-thermal effects. Despite the abundance of physical methods for evaluating the plasmonic effects, chemical insight has not been reported yet. In this contribution, we propose a chemical insight into the plasmon effect on reaction kinetics using alkoxyamines as an organic probe through their homolysis, leading to the generation of nitroxide radicals. Alkoxyamines (TEMPO- and SG₁-substituted) with well-studied homolysis behavior are covalently attached to spherical Au nanoparticles. We evaluate the kinetic parameters of homolysis of alkoxyamines attached on a plasmon-active surface under heating and irradiation at a wavelength of plasmon resonance. The estimation of kinetic parameters from experiments with different probes (Au–TEMPO, Au–SG1, Au–SG1–TEMPO) allows revealing the apparent differences associated with the non-thermal contribution of plasmon activation. Moreover, our findings underline the dependency of kinetic parameters on the structure of organic molecules, which highlights the necessity to consider the nature of organic transformations and molecular structure in plasmon catalysis.

Kinetic study of alkoxyamine homolysis revealed the impact of non-thermal effects in plasmon-assisted reactions.     

Synthesis,anticancer and antiviral activities of novel thiopyrano[2,3-d]thiazole-6-carbaldehydes

Novel rel-(6R,7R)-2-oxo-7-phenyl-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-6-carbaldehydes were synthesized via regio- and diastereoselective hetero-Diels-Alder reaction of 5-arylidene-4-thioxo-2-thiazolidinones with acrolein. The synthesized compounds were evaluated for anticancer and antiviral activities by the National Institutes of Health (NIH) following US NCI and AACF protocols. Anticancer activity screening on NCI60 cell lines allowed identification of 7-phenyl-2-oxo-7-phenyl-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-6-carbaldehyde 3a with the highest level of antimitotic activity against leukemia with mean GI₅₀/TGI values 1.26/25.22 μM. The screening of antiviral activity lead to identification of 7-(4-methoxyphenyl)-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-6-carbaldehyde 3b with a promising influence on EBV virus (EC₅₀ = 0.07 μM, SI = 3279) and moderate effect on Herpes simplex virus type 1 and Varicella zoster virus and 7-[4-(benzyloxy)phenyl]-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d][1,3]thiazole-6-carbaldehyde 3e with a promising influence on Hepatitis C virus (EC₅₀ = 12.6 μM, SI = 43.1).     

X-ray study of the anomalous thermal hystereses of the modulation wavevectors in Cs2HgCl4

A rich sequence of structural modulations in Cs₂HgCl₄ as a function of temperature was studied by means of X-ray diffraction. Accurate satellite-position measurements on the cooling and heating paths of the crystal revealed abnormal thermal hystereses for incommensurate phases and coexistences of neighboring commensurate phases. A well-defined X-ray picture of the a-axis modulated phases in the range of 221–184 K were observed on the heating path, while the c-axis modulated phases existing below 184 K were definitely detected on the cooling path. The proper conditions for a precise phase diagram of Cs₂HgCl₄ can be correlated with relatively defect-free transformations of a-axis modulations at heating and of c-axis modulations at cooling. The peculiarity of Cs₂HgCl₄ to switch modulation direction among the a- and c-axes at 184 K allows us deliberately accumulate and thus control a majority of mobile defects on the mutually perpendicular (100) or (001) planes by possessing crystal within temperature domain of a- or c-axes modulations, respectively.     

Importance of a Fluorine Substituent for the Preparation of meta‐ and para‐Pentafluoro‐λ6‐sulfanyl‐Substituted Pyridines

Although there are ways to synthesize ortho‐pentafluoro‐λ⁶‐sulfanyl (SF₅) pyridines, meta‐ and para‐SF₅‐substituted pyridines are rare. We disclose herein a general route for their synthesis. The fundamental synthetic approach is the same as reported methods for ortho‐SF₅‐substituted pyridines and SF₅‐substituted arenes, that is, oxidative chlorotetrafluorination of the corresponding disulfides to give pyridylsulfur chlorotetrafluorides (SF₄Cl‐pyridines), followed by chloride/fluoride exchange with fluorides. However, the trick in this case is the presence on the pyridine ring of at least one fluorine atom, which is essential for the successful transformation of the disulfides into m‐and p‐SF₅‐pyridines. After enabling the synthesis of an SF₅‐substituted pyridine, ortho‐F groups can be efficiently substituted by C, N, S, and O nucleophiles through an S_NAr pathway. This methodology provides access to a variety of previously unavailable SF₅‐substituted pyridine building blocks.     

Interaction of Polymethine Dyes with Detonation Nanodiamonds

Among cationic, anionic, and merocyanine polymethine dyes, the binding to detonation nanodiamond (DND) colloid particles in hydrosol occurs only for negatively charged dye species. This, in view of the positive ζ-potential of the DND used in this study, suggests the predominance of electrostatic interactions over other intermolecular forces in such systems. Indeed, after decorating the merocyanine and the cationic dye by one and two negatively charged sulfopropyl groups, respectively, so that the net charge of their colored species becomes negative, the compounds also demonstrate affinity to the DND particles. In all cases, the binding of dyes to DND is accompanied by a decrease in fluorescence intensity and a bathochromic shift of their absorption and fluorescence bands. A quantitative study of the dyes adsorption on the DND nanoparticles as performed using the Küster-Freundlich and Langmuir equations reveals some peculiarities of their attaching to the DND aggregates and allows estimating the specific area of the DND particles at a concentration of 0.0212 wt/vol %.     

Stabilization of Pancake Bonding in (TCNQ)2.− Dimers in the Radical-Anionic Salt (N−CH3−2-NH2−5Cl−Py)(TCNQ)(CH3CN) Solvate and Antiferromagnetism Induction

We report a new antiferromagnetic radical-anion salt (RAS) formed from 7,7,8,8-tetracyanquinonedimethane (TCNQ) anion and 2-amino-5-chloro-pyridine cation with the composition of (N−CH₃−2-NH₂−5Cl−Py)(TCNQ)(CH₃CN). The crystallographic data indicates the formation of (TCNQ)₂^.− radical-anion π-dimers in the synthesized RAS. Unrestricted density functional theory calculations show that the formed π-dimers characterize with strong π-stacking “pancake” interactions, resulting in high electronic coupling, enabling efficient charge transfer properties, but π-dimers cannot be stable in the isolated conditions as a result of strong Coulomb repulsions. In a crystal, where (TCNQ)₂^.− π-dimers bound in the endless chainlets via supramolecular bonds with (N−CH₃−2-NH₂−5-Cl−Py)⁺ cations, the repulsion forces are screened, allowing for specific parallel π-stacking interactions and stable radical-anion dimers formation. Measurements of magnetic susceptibility and magnetization confirm antiferromagnetic properties of RAS, what is in line with the higher stability of ground singlet state of the radical-anion pair, calculated by means of the DFT. Therefore, the reported radical-anion (N−CH₃−2-NH₂−5Cl−Py)(TCNQ)(CH₃CN) solvate has promising applications in novel magnetics with supramolecular structures.     

Amination of brominated nanoporous activated carbon beads for the preparation of CO2 adsorbents

Abstract

Nanoporous activated carbon (NAC) beads that prepared by carbonization of microporous polymer 2,6-di-tert-butyl pyridine beads were subjected to bromination followed by amination to synthesize the NAC derivatives carrying amino groups. Grafted bromine groups, 0.41?mmol of Br per 1?g of NAC, are hydrolytic stable at 100 °С and can be successfully substituted by amino groups. SEM, TEM, and texture studies were shown a nanoporosity decrease. However, the aminated NAC beads maintained a narrow nanopore size distribution and high specific surface area, retaining a spherical shape. These beads were evaluated for capturing CO₂ and showed good reversible adsorption capacity. The preparation method can easily be scaled up, and the NAC beads can be used for other adsorption applications where shaped carbon solids with developed nanoporosity are required.