Synthesis and photoluminescent properties of 1,1'-binaphthyl-based chiral phenylenevinylene dendrimers

New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6'-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1'-binaphthyl derivative (R)-1 and the appropriate dendrons (R)(2n)G(n)-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of the dendrimer on the redox behavior of these systems.     

2020 Roadmap on two-dimensional nanomaterials for environmental catalysis

This roadmap demonstrates a series of two-dimensional nanomaterials, such as graphene, black phosphorus, oxides, layered double hydroxides, chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks, covalent organic frameworks, and others, for environmental catalysis.     

The CuII−CuI−Cu0(Hg) system in the presence of benzotriazole: Part II. A chronocoulometric investigation

Both the oxidation of Cu⁰ at dropping amalgam electrodes immersed in solutions of benzotriazole (BTA) and the reduction of Cu^II at a dropping mercury electrode from BTA solutions have been investigated by the single potential-step chronocoulometric technique. The dependence of the charge Q(t) flowing as a consequence of a given potential jump E_i→E_f upon the initial and final potentials E_i and E_f, as well as upon the time t elapsed from the instant of the potential jump provides direct evidence for the presence of a single adsorbed monolayer of a Cu^I compound on a mercury electrode immersed in a Cu^II solution containing BTA, at applied potentials positive to ≈?0.4 V/SCE. Analogous measurements carried out at dropping amalgam electrodes reveal the presence of a single adsorbed monolayer of a Cu^I compound, or else of an adsorbed multilayer, depending on the potential range investigated. The results of the chronocoulometric measurements are in agreement with those of the polarographic measurements of Part I.     

Studies on decarboxylation reactions. Part 6 . Kinetic study of decarboxylation of 5-amino-1,3,4-oxadiazole-2-carboxylic acid and its N-phenyl derivatives at high hydrochloric acid concentrations

The dissociation constants (K₁) of both acids 4a-c and esters 5a-c and the rate constants of the decarboxylation reaction of acids 4a-c have been measured at various high concentrations of hydrochloric acid (0.5-8.0 M range). The results obtained have enabled us to suggest the probable structure of the zwitterion which undergoes decarboxylation.     

Solid-supported solution-phase synthesis of 4-amino-1,2,4,5-tetrahydro-2-benzazepine-3-ones

Starting from Boc-o-aminomethylphenylalanine, a solution-phase parallel synthesis of 2,4-substituted 4-amino-1,2,4,5-tetrahydro-2-benzazepine-3-ones is described. This heterocycle has two nitrogen functions, which are differentiated and can be selectively substituted. The sources of diversity are aldehydes for the R(1) position and carboxylic acids, sulfonyl chlorides, or isocyanates for the R(2) position. High-throughput synthesis and purification of this multistep synthetic sequence was accomplished using polymer-bound reagents and scavengers and liquid-liquid extraction protocols, and a small library of compounds was prepared. Polymer-bound cyanoborohydride was found to work well for the reductive amination. Scavenging of excess of amine was performed by polymer-bound benzaldehyde, and cyclization was performed in the presence of polymer-bound coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC). After Boc-deprotection, the second nitrogen can be acylated using carboxylic acids, sulfonylated or converted to a urea. The acylation is again performed by polymer-bound EDC. Excellent yields and purities were obtained.     

Synthesis of functionalized polyhedral oligomeric silsesquioxane (POSS) macromers by microwave assisted 1,3-dipolar cycloaddition

In this paper we report the first synthesis of isoxazolidine and isoxazoline-POSS macromers by 1,3-dipolar cycloaddition reactions of vinyl- and styryl-POSS with N-methyl-C-ethoxycarbonylnitrone and ethoxycarbonyl nitrile oxide, promoted by microwave irradiation. The nature of the resulting cycloadducts has been determined by NOE experiments and supported by computational studies at PM3 and DFT B3LYP/6-31G* levels.     

Ion pair charge-transfer complexes between anionic and cationic metal-dithiolenes [M(II) = Pd,Pt

New [M(R(2)pipdt)(2)](BF(4))(2) salts [R(2)pipdt = N,N'-dialkyl-piperazine-2,3-dithione; M = Pd(II), R = Me and M = Pt(II), R = Me, Et, Pr(i)] bearing redox-active cationic dithiolene complexes have been prepared and characterized. These cations react with the redox-active [M(mnt)(2)](2-) [M = Pd(II), Pt(II); mnt = maleonitrile-2,3-dithiolate] anionic dithiolenes to form salts describable as ion pair charge-transfer complexes. X-ray crystallographic studies have shown that [M(Me(2)pipdt)(2)][M(mnt)(2)] complexes, with M = Pd(II) and Pt(II), are isomorphous. Crystal data of the Pt salt (3a): triclinic, Ponemacr; (No. 2); Z = 1; T = 293(2) K; a = 6.784(7) A, b = 8.460(6) A, c = 13.510(5) A, alpha = 100.63(2) degrees, beta = 104.04(2) degrees, gamma = 96.90(2) degrees; R1 = 0.0691 [wR2 = 0.2187 (all data)]. Structural data show that approximately square-planar [Pt(Me(2)pipdt)(2)] dications and regular square-planar [Pt(mnt)(2)] dianions form an infinite anion-cation one-dimensional stack along axis a with a Pt...Pt a/2 distance of 3.392 A and a Pt...Pt...Pt angle of 180 degrees. Anions and cations arrange themselves face-to-face so as to take on a staggered arrangement. These salts exhibit strong absorptions in the visible-near-infrared region assigned to ion pair charge-transfer transitions. A relation between the optical and thermal electron transfer in the solid state is obtained using a "Marcus-Hush model", and a solid-state electrical conductivity in agreement with expectations is observed. Vibrational spectroscopy is in agreement with the existence of charge-transfer interactions between the cationic and anionic components of the salts.     

Modeling of overloaded gradient elution of nociceptin/orphanin FQ in reversed-phase liquid chromatography

The Reversed-phase (RP) gradient elution chromatography of nociceptin/orphanin FQ (N/OFQ), a neuropeptide with many biological effects, has been modeled under linear and non-linear conditions. In order to do this, the chromatographic behavior has been studied under both linear and nonliner conditions under isocratic mode at different mobile phase compositions--ranging from 16 to 19% (v/v) acetonitrile (ACN) in aqueous trifluoracetic acid (TFA) 0.1% (v/v)-on a C-8 column. Although the range of mobile phase compositions investigated was quite narrow, the retention factor of this relatively small polypeptide (N/OFQ is a heptadecapeptide) has been found to change by more than 400%. In these conditions, gradient operation resulted thus to be the optimum approach for non-linear elution. As the available amount of N/OFQ was extremely reduced (only a few milligrams), the adsorption isotherms of the peptide, at the different mobile phase compositions examined, have been measured through the so-called inverse method (IM) on a 5 cm long column. The adsorption data at different mobile phase compositions have been fitted to several models of adsorption. The dependence of the isotherm parameters on the mobile phase composition was modeled by using the linear solvent strength (LSS) model and a generalized Langmuir isotherm that includes the mobile phase composition dependence. The overloaded gradient separation of N/OFQ has been modeled by numerically solving the equilibrium-dispersive (ED) model of chromatography under a selected gradient elution mode, on the basis of the previously determined generalized Langmuir isotherm. The agreement between theoretical calculations and experimental overloaded band profiles appeared reasonably accurate.     

Substitutional carbon defects in silicon: A quantum mechanical characterization through the infrared and Raman spectra

The infrared (IR) and Raman spectra of eight substitutional carbon defects in silicon are computed at the quantum mechanical level by using a periodic supercell approach based on hybrid functionals, an all electron Gaussian type basis set and the CRYSTAL code. The single substitutional C _s case and its combination with a vacancy (C _sV and C _sSiV) are considered first. The progressive saturation of the four bonds of a Si atom with C is then examined. The last set of defects consists of a chain of adjacent carbon atoms C, with i = 1–3. The simple substitutional case, C _s, is the common first member of the three sets. All these defects show important, very characteristic features in their IR spectrum. One or two C related peaks dominate the spectra: at 596 cm⁻¹ for C _s (and C _sSiV, the second neighbor vacancy is not shifting the C _s peak), at 705 and 716 cm⁻¹ for C _sV, at 537 cm⁻¹ for C and C (with additional peaks at 522, 655 and 689 for the latter only), at 607 and 624 cm⁻¹, 601 and 643 cm⁻¹, and 629 cm⁻¹ for SiC, SiC, and SiC, respectively. Comparison with experiment allows to attribute many observed peaks to one of the C substitutional defects. Observed peaks above 720 cm⁻¹ must be attributed to interstitial C or more complicated defects.     

3-nitrocoumarins as dienophiles in the Diels-Alder reaction in water. An approach to the synthesis of nitrotetrahydrobenzo[c]chromenones and dihydrodibenzo[b,d]furans

The [4 + 2] cycloadditions of 3-nitrocoumarin (1a), 6-chloro-3-nitrocoumarin (1b), and 6-, 7-, and 8-hydroxy-3-nitrocoumarins (1c, 5, and 6) with (E)-piperylene (7), isoprene (8), 2,3-dimethyl-1,3-butadiene (9), 2-methoxy-1,3-butadiene (10), 2,3-dimethoxy-1,3-butadiene (11), and cyclopentadiene (12) were investigated in aqueous medium, in organic solvent and under solventless conditions. The reactions performed in water occurred in heterogeneous phase but were faster than those executed in toluene or dichloroethane (DCE). 1a-c, 5, and 6 behaved as 2pi components in the Diels-Alder cycloadditions with 7-10 and 12, and exo adducts were preferentially or exclusively produced. Surprisingly 1a, behaved as a 4pi component in the cycloaddition in water with 11 and 4-substituted 3-nitrochromanones 20 and 21 were isolated. The cycloadditions of hydroxy-3-nitrocoumarins 1c, 5, and 6 with 1,3-diene 9 did not work in water or in organic solvent, but did work under solventless conditions. Nitrotetrahydrobenzo[c]chromenones 13-16, 24, and 25, originating from the normal electron-demand Diels-Alder reactions, were converted into dihydrodibenzo[b,d]furans 27-31 in water, via one-pot Nef-cyclodehydration reactions.