Photochromic fulgides and spirooxazines: mechanism and substituent effect on photoreactions

Molecular design, synthesis and photochromic properties of spirooxazines and fulgides are described. In the case of fulgides, the change of the substituents may lead to different photochromic properties and different photoreactions of the kind of compounds. In photochromic process of pyrryl-substituted fulgides, the excited singlet state is the mam species, but the excited triplet state is also involved. However, no excited triplet state has been observed in cyclization of aryl-substituted fulgides. In the case of spirooxazines, the substituents at 2'-position have great effect on the formation of photoproduct and on the mechanism of photoreaction. The increase of steric hindrance of the 2'-position substituent gives rise to the decrease of the quantum yield for the formation of photochromic merocyanine (PMC) and the increase of the relative quantum yield for the charge separated twist intermediate (CT).     

Combining piracetam and lithium salts: ionic co-crystals and co-drugs?

Mechanochemical reaction of solid piracetam with the inorganic salts LiCl and LiBr yields ionic co-crystals which are also co-drugs, characterized by markedly different thermal properties with respect to pure components, also depending on the method for preparation and/or conditions of measurements; single crystal and powder X-ray diffraction at variable temperatures, DSC, TGA, hot stage microscopy (HSM) and intrinsic dissolution rate have been used to fully characterize the solid products.     

Microtektites and Glassy Microspherules in Loess: Their Discoveries and Implications

It is first in continental sediment-loess that 16 microtektites and 3 ablated glassy Si-Mg microspherules were found. They occur only in the upper layer of L8, a 40—70-cm horizon above the B/M boundary. The age of deposition is about 0.72 Ma. Microtektites in loess are usually sphere, speroid, kidney-form, tear-drop and irregular debris in shape. They are transparent and translucent, and some have the shade of green, amber and yellow in color. Their sizes range from 65 to 220μm. Most of microtektites were badly pitted and corroded, but there remain bubbles, cavities and scorious and flow microstructure in some ones. On the basis of their major oxide compositions, microtektites in loess may be divided into three chemical groups that are described as normal, bottle-green and high-aluminium microtektite. They are similar in chemical composition to microtektites in deep-sea cores. Geochemistry of trace elements show that the origin of microtektite is very complicated and their parent materials are from mu     

Linear and cyclic N-acetyl-α-aryl-glycines: Synthesis and chemiluminescence studies

Summary A series of N-acetyl--arylglycines (IIa,IIb) was prepared by acid-induced electrophilic -amidoalkylation reactions; compounds of typeIIb were transformed into the corresponding 3-acetylaminobenzo[b]furan-2(3H)ones (III) by treatment with acetic anhydride. It was found that most of these new compounds (lactones as well as open chain derivatives) undergo base induced oxidation in the presence of oxygen with the emission of visible light. Preliminary structure-activity relationships for these novel chemiluminescence class are proposed.

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Lineare und cyclische N-Acetyl--aryl-glycine: Synthese und Chemilumineszenz-Untersuchungen

Zusammenfassung Eine Reihe von N-Acetyl--arylglycinen (IIa,IIb) konnte durch sauer induzierte elektrophile -Amidoalkylierung hergestellt werden; die Behandlung von Verbindungen des TypsIIb mit Acetanhydrid führte zu den entsprechenden 3-Acetylaminobenzo[b]furan-2(3H)onen (III). Es zeigt sich, daß die Mehrzahl dieser neuen Verbindungen (sowohl Lactone als auch offenkettige Derivate) bei basisch induzierter Oxidation mit (Luft-)Sauerstoff sichtbares Licht emittieren. Erste Struktur-Aktivitäts-Beziehungen für diese neue chemilumineszenzierende Klasse werden vorgeschlagen.

     

Paradigms and Paradoxes: Electronegativity and Bond Energies—Living Legacies of Linus and Lee

In this paper we will discuss Pauling's classic Eq. (1) that relates bond energies, "D," and electronegativities, "x." Recast to be applicable to enthalpies of formation and reaction, we apply it to the study of hydrogenolysis reactions of dienes, diynes, and alkanes, halogenolysis reactions (with chlorine, bromine, and iodine) and metathetical reactions of organosulfur species (sulfides, sulfoxides, and sulfones). It is with great regret that this equation is found wanting.     

ω-haloalkylphosphoryl compounds: Synthesis and properties

A general method of the synthesis of ω-haloalkylphosphoryl compounds was developed, a series of compounds of phosphonic and phosphine oxide type were synthesized. The ability of some ω-haloalkylphosphonates to undergo intramolecular cyclization into the corresponding 1,2-oxaphospholane and 1,2-oxaphosphorine was investigated depending on the solvent polarity, the presence of halogen ions in the solution, and temperature. Tetrahydrofuran was chosen as one of the most suitable solvents for the alkylation of CH acids with ω-haloalkylphosphoryl compounds.     

Dendritic β-diketiminato titanium and zirconium complexes: synthesis and ethylene polymerisation

The cyclopentadienyl(β-diketiminato)titanium and zirconium chlorides (η⁵-C₅H₅)MCl₂(CH(C(NC₆H₄-4-OR)CH₃)₂) (M = Ti (4-dend), Zr (5-dend)), where R corresponds to the first generation carbosilane dendron (dendritic wedge) Si(CH₂CH₂SiMePh₂)₃, have been synthesised. After activation with methylaluminoxane, the activity of 4-dend and 5-dend as catalysts for ethylene polymerisation has been determined and compared with that of the non-dedritic counterpart (η⁵-C₅H₅)MCl₂(CH(C(NC₆H₅)CH₃)₂) (M = Ti (4), Zr (5)).     

Imploded bilirubins: synthesis and properties of 10-nor-mesobilirubin-XIIIα and analogs

Abstract  Six 10-nor-bilirubin analogs have been synthesized and investigated. Lacking the C(10) CH₂ group, these linear tetrapyrroles have a bipyrrole core rather than a dipyrrylmethane core and thus a different shape. Whereas the propionic acid groups of bilirubin are well engaged in intramolecular hydrogen bonding to the dipyrrinones, molecular modeling studies of the 10-nor-rubins predict that propionic acid chains are too short to engage the CO₂H hydrogen fully in intramolecular hydrogen bonding with the dipyrrinones. Butyric acid chains, however, can and do lead to a stabilized conformation with a bipyrrole dihedral angle of approximately 115°. Spectroscopic studies verify the predictions and vapor pressure osmometry indicates that the 10-nor-rubins with butyric acids are monomeric in CHCl₃. Graphical abstract  

Carotenoids and β-cyclodextrin inclusion complexes: Raman spectroscopy and theoretical investigation

In the present study, the inclusion processes of β-carotene, astaxanthin, lycopene, and norbixin (NOR) into the β-cyclodextrin (β-CD) cavity were investigated by means of Raman spectroscopy and quantum mechanics calculations. The Raman ν(1) band assigned to C═C stretching was sensitive to the host-guest interaction and in general undergoes a blue shift (3-13 cm(-1)) after inclusion takes place, which is the consequence of the localization of single and double bonds. This is supported by the molecular modeling prediction, which inclusion complexes show the ν(1) band blue shifted by 1-8 cm(-1). The calculated complexation energies was small for most of derivatives and was found to be -11.1 kcal mol(-1) for inclusion of AST and +0.27 kcal mol(-1) for NOR. The stability order was qualitatively correlated to topological parameters accounting for the opening angle of the chain. This means that after inclusion the guest molecules assume a slightly more extended conformation, which enhances the host-guest contact, improving the interaction energy. The results discussed here clearly demonstrate the matrix effect on the carotenes' spectroscopic profile and should contribute to fully characterize the raw samples.     

New 1,2,4‐ and 1,3,4‐oxadiazole materials: synthesis,and mesomorphic and luminescence properties

The synthesis and liquid crystalline properties of new series of 1,2,4‐ and 1,3,4‐oxadiazole derivatives (2a–f and 5a–f respectively) are reported. These compounds contain only one terminal flexible alkoxy chain, the other terminal substituent is a protecting benzyl group. All compounds of series 2 exhibit an enantiotropic nematic phase. The homologue with the longest chain (2f) displays an enantiotropic dimorphism smectic A– nematic. None of the compounds of series 5 shows mesomorphism and only crystal–isotropic transitions were observed. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X‐ray measurements. Luminescence properties, in chloroform solution, of 2f and the series 5 compounds were evaluated. Good photoluminescence quantum yields for compounds of series 5 were observed. Compound 2f, incorporating the 1,2,4‐oxadiazole ring shows a very strong reduction in emissive properties.     

Dicyano and pyridine derivatives of β-carotene: synthesis and vibronic, electronic, and photophysical properties

Density functional theory and time-dependent density functional theory calculations provide pictures of the molecular orbitals involved in the ground and excited states of two cyano derivatives of 8'-apo-β-caroten-8'-al synthesized via an acid-base-catalyzed Knoevenagel condensation reaction. Population analysis shows that the symmetry-allowed transition, S(0) ((1)A(g)) → S(2) ((1)B(u)) based on the C(2h) symmetry is a HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) π → π* transition with electron densities located mostly on the polyene chain. Calculated and actual steady-state absorption spectra show similar features with low-energy peak maxima between 550 and 600 nm.     

Archaeolithoporella and Tubiphytes : Affinties and Paleoecology in Permian Reefs of South China

Archaeolithoporella is one of the most important Permian reef-building organisms, but itsaffinity has long been controversial. It was first reported in Japan and was considered as a coralline red alga. Since then it has been recognized in Permian reefs in other parts of the world. Many researchers have studied the materials they had found and the Japanese holotype specimen. Most have concluded that it is a problematic alga. or just a problematica because of weak criteria for definition. Some have even considered it inorganic. However, relict cellular structures and microtubular laminae found in well-preserved specimens from Permian reefs in South China strongly support a coralline red algal affinity for the genus.In situ preserved Archaeolithoporella is restricted within the typical framework facies and it occurs most abundantly in syndepositionally cemented framestones. This suggests that Archaeolithoporella required a firm substrate and clear but agitated sea water. Archaeolithoporella is often found     

Ph₂N-susbtituted ethylene-bridged p-phenylene oligomers: synthesis and photophysical and redox properties

For a series of p-phenylene-based oligomers terminated with two triphenylamines, their absorption, photoluminescence, and band gaps show a pattern of extensive π-conjugation with increasing array size. Oligomers with large central arrays have greater quantum yields than their small analogues. Cyclic voltammetric (CV) measurements indicated two-step oxidations of the two diphenylamino groups for compounds 1-5 and one-step oxidations for the two amines of large oligomers 6 and 7.     

Enhanced π-conjugation and emission via icosahedral carboranes: synthetic and spectroscopic investigation

The ability of ortho-, meta- and para-carboranes to enhance the emission intensity has been compared. For this purpose a series of carborane-appended 1,3,5-triphenylbenzene (TB) and 1,3,5- tris(biphenyl-4-yl)benzene (TBB) containing three ortho-, meta- and para-carborane clusters directly attached to the conjugated cores have been synthesized employing Suzuki, Heck, and trimerization reactions. The incorporation of the icosahedral carboranes was associated with a red shift in the UV absorption spectrum of up to 13 nm as well as enhancements of the emission intensities of up to 154%. The presence of ortho-carboranes showed the maximum red shift in the UV spectrum whereas the maximum enhancement of the emission intensity was observed in the presence of meta-carborane clusters. The order of π-conjugation extension is found to be ortho > meta ≈ para. A comparative thermal analysis indicated o-carborane-appended trimers to be the most thermally stable in the series. Proton NMR spectra of reported carborane-appended trimers indicated that ortho- and meta-carborane cages have benzenelike characteristics.     

New nucleoside analogues and their 5′-triphosphates: Synthesis and biological properties

Bicyclic furano-and pyrrolo[2,3-d]pyrimidine nucleosides and purine nucleosides modified at the N¹ atom and/or the 6-position have been synthesized. Among the tested nontoxic bicyclic nucleosides and N⁶-carboxyalkyladenosines, only furo[2,3-d]pyrimidine with the C₁₀H₂₁ substituent and N⁶-carboxymethyladenosine exhibit moderate anti-HCV activity in the virus replicon system and N¹-hydroxyinosine exhibits high anti-HCV activity and significant cytotoxicity. The corresponding 5′-triphosphates have been synthesized and studied as substrates/inhibitors of HCV enzymes: NS5B protein (RNA-dependent RNA polymerase) and NS3 protein (NTP-dependent RNA helicase).     

Fe- and Cr-substituted mullites: Mössbauer spectroscopy and rietveld structure refinement

Fe-substituted mullite samples Al_4.5-yFe_ySi_1.5O_9.75 (y = 0.25 and 0.50) have been prepared using a sol-gel route involving Si and Al alkoxides and iron nitrate as precursors. Mössbauer spectroscopy reveals the presence of three different Fe(III) sites but does not allow to conclude concerning the ion environments, tetrahedral or octahedral. Rietveld refinements reveal that Fe ions are distributed between octahedral and tetrahedral positions, the proportion of octahedral iron increasing from y = 0.25 to y = 0.50. On the other hand, for Cr-substituted mullite, Cr ions arc mainly located on octahedral positions. This difference between Fe and Cr has been attributed to the fact that Cr shows a clear trend to occupy octahedral sites compared to Fc and that it is incorporated inside the mullite structure only at high temperature.     

Iridium oxide fabrication and application: A review

Despite the scarcity and cost of iridium oxide,it is still the material of choice in numerous fields of science and applications,including capacitors,electrochromism,sensors,and various oxidation electrocatalysis(e.g.,chlorine evolution reaction,detoxification,and oxygen evolution reaction).Such versatility is attributed to the distinct features of iridium oxides,such as their activity,biocompatibility,conductivity,and durability.The features and properties of iridium oxides are strongly dependent on the fabrication method.In this review,methodologies relating to the synthesis and fabrication of solid-state iridium oxides have been thoroughly collected and discussed.Structuring and crystallization techniques for iridium oxides are also noted.At the end of the review,the effects of utilizing a certain fabrication method on the characteristics of the iridium oxide product are recapitulated,together with the recommended application of the product in various fields.     

Chiral α-Aminophosphonates: Synthesis and Transport Properties

Abstract

Synthesis of chiral α-aminophosphonates and their transport properties (rates, enantioselectivity) as membrane carriers for oxy and amino acids are discussed.