Naturally occurring iridoids. A review, part 1

A compilation of new naturally occurring iridoid glycosides, iridoid aglycones, iridoid derivatives and bis-iridoids reported during 1994-2005 is provided with available physical and spectral data: mp, [alpha]D, UV, IR, 1H- and 13C-NMR as well as natural source with family and references. 418 compounds with 202 references are cited.     

Suppression of sideband frequency shifts in the modulational instability spectra of wave propagation in optical fiber systems

In standard optical fibers with constant chromatic dispersion, modulational instability (MI) sidebands execute undesirable frequency shifts due to fiber losses. By means of a technique based on average-dispersion-decreasing dispersion-managed fibers, we achieve both complete suppression of the sideband frequency shifts and fine control of the MI frequencies, without any compromise in the MI power gain.     

New iridoid glucoside from Wendlandia tinctoria roots

A new iridoid glucoside,10-O-veratroyleranthemoside(1) was isolated from the roots of Wendlandia tinctoria.The structure was established by spectroscopic(including 2D NMR) and chemical methods.     

Reduction of Sulfur Dioxide to Sulfur Monoxide by Ferrous Porphyrin**

The reduction of SO₂ to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO₂ to H₂S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO₂ to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO₂ by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that Fe^IITPP reduces SO₂ by 2e⁻/2H⁺ to form an intermediate [Fe^III−SO]⁺ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO₂ could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.     

Surface morphology and active sites of TiO<Subscript>2</Subscript> for photoassisted catalysis

The main aim of this work is to discriminate the closely related adsorption and catalytic degradation processes that occur during a photocatalytic reaction. Very high-surface-area TiO₂ and Pd-doped TiO₂ were synthesized by microwave-assisted hydrothermal synthesis and used for degradation of methylene blue as a model pollutant dye. Thorough structural, morphological, and surface analyses of the synthesized catalysts were conducted to investigate key material properties that influence adsorption and catalytic performance. The adsorption capacity of the catalysts was determined by fitting adsorption data using the Langmuir isotherm model, and the photocatalytic activity of the synthesized samples was evaluated by periodically measuring the concentration of methylene blue as it was photocatalytically degraded under ultraviolet (UV) light. The results indicated that noble-metal incorporation compromised adsorption but favored catalytic performance.     

Photon transport in thin disordered slabs

We examine using Monte Carlo simulations, photon transport in optically ‘thin’ slabs whose thickness L is only a few times the transport mean free path l*, with particles of different scattering anisotropies. The confined geometry causes an auto-selection of only photons with looping paths to remain within the slab. The results of the Monte Carlo simulations are borne out by our analytical treatment that incorporates directional persistence by the use of the Ornstein-Uhlenbeck process, which interpolates between the short time ballistic and long time diffusive regimes.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.     

A promising class of luminescent derivatives of Silver(I) and Gold(I)-N-heterocyclic carbene

Starting from proligand 1-methyl-2-(phenyl)imidazo[1,5-a]pyridine-2-iumchloride ( 1 .HCl), 1-methyl-2-(phenyl)imidazo[1,5-a]pyridine silver(I)chloride, ( 2 ) has been prepared. Synthesis, structures and photophysical properties of (2,2^/−bipyridyl)-1-methyl-2-(phenyl)imidazo[1,5-a]pyridinesilver(I)hexaflurophosphate, ( 3 ), 1-methyl-2-(phenyl)imidazo[1,5-a]pyridinesilver(I)carbazolate, ( 4 ) and 1-methyl-2-(phenyl)imidazo[1,5-a]pyridinegold(I)carbazolate, ( 5 ) are focused. Herein we have first reported the NHC-Ag-(bpy/carbazole). All the complexes have been characterized by elemental analysis, various spectroscopic studies and finally screened for luminescent properties. All the complexes are strongly emissive. Solid state structures of 2 , 3 , 4 and 5 have been determined by X-ray diffraction studies. Conventionally, complex 2 adopts linear geometry whereas complex 3 embraces triangular planar geometry around Ag; complex 4 and 5 clinches linear geometry around Ag/Au. All the complexes absorb light within 275–343 nm. Complex 3 is luminous at ~407 mn, whereas complex 4 and 5 luminous at ~360 nm having short life time 1.00–6.97 ns. The quantum yield (Φ_em) of the complexes varies 0.106–0.186. It is expected variation of luminescence arises due to change of metal and the chromophore (bpy/carbazole). Density Functional Theory (DFT) and Temparature Dependent Density Functional Theory (TDDFT) calculations were performed to verify crystallographically derived parameters and to calculate the UV–Vis properties of the ground state as well as of the first excited state of the complexes.