Communication between chromophores is vital for both natural and non‐natural photophysical processes. Spatial confinements offer unique conditions to scrutinize such interactions. Polynorbornene‐ and polycyclobutene‐based ladderphanes are ideal model compounds in which all tetraarylethylene (TAE) linkers are aligned coherently. The spans for each of the monomeric units in these ladderphanes are 4.5–5.5 Å. Monomers do not exhibit emission, because bond rotation in TAE can quench the excited‐state energy. However, polymers emit at 493 nm (Φ=0.015) with large Stokes shift under ambient conditions and exhibit dual emission at 450 and 493 nm at 150 K. When the temperature is lowered, the emission intensity at 450 nm increases, whereas that at 493 nm decreases. At 100 K, both monomers and polymers emit only at 450 nm. This shorter‐wavelength emission arises from the intrinsic emission of TAE chromophore, and the emission at 493 nm could be attributed to the excimer emission in the confined space of ladderphanes. The fast kinetics suggest diffusion‐controlled formation of the excimer. 相似文献
In an attempt to achieve promising cytotoxic agents, a series of new (Z)‐3‐benzyl‐5‐((1‐phenyl‐3‐(3‐((1‐substituted phenyl‐1H‐1,2,3‐triazol‐4‐yl)methoxy)phenyl)‐1H‐pyrazol‐4‐yl)methylene)thiazolidine‐2,4‐diones 10 a‐n were designed, synthesized, and characterized by 1H NMR, 13C NMR, IR, and ESI‐MS techniques. These compounds synthesized from appropriate reaction procedures with better yields. All the novel synthesized compounds 10a‐n were evaluated for their cytotoxic activity against the MCF‐7 cell line (Human breast cancer cell line) at different concentrations of 0.625, 1.25, 2.5, 5, and 10 μM, respectively. The cytotoxic evaluation assay is presented in terms of IC50 values and percentage cell viability reduction compared against standard drug cisplatin. Among all novel synthesized compounds 10a‐n , some of the representative analogues particularly 10g and 10e exhibit remarkable cytotoxic activity with IC50 values 0.454 and 0.586 μM, comparable to that of the standard drug cisplatin, and some analogues 10d , 10f , 10k, and 10m also have shown significant activity. 相似文献
Rate constants for acid-catalyzed dehydration of cis-2-substituted 1,2-dihydro-naphthols are well correlated by the Taft relationship log k = -0.49 - 8.8σ(I), with minor negative deviations for OH and OMe. By contrast the trans substituents show a poor correlation with σ(I) and in most cases react more slowly than their cis isomers. The behavior is consistent with rate-determining formation of a 2-substituted carbocation (naphthalenium ion) intermediate that for cis reactants possesses a 2-C-H bond suitably oriented for hyperconjugation with the charge center. For the trans isomers the 2-substituent itself is oriented for hyperconjugation in the initially formed conformation of the cation. It is argued that k(cis)/k(trans) rate ratios for substituents (Me, 8.4; Bu(t), 12.7; Ph, 3.8; NH(3)(+), 160; OH, 440) reflect their hyperconjugating ability relative to hydrogen. Faster reactions of trans isomers are observed for substitutents known (RS, N(3)) or suspected (EtSO, EtSO(2)) of stabilizing the cation by a π or σ neighboring group effect. The good Taft correlation is taken to indicate that cis substuents are reacting normally, differentiated only by their inductive effects. The slower reactions of the trans isomers are the judged to be "abnormal". This is confirmed by comparing effects of cis and trans β-OH substituents on the reactivities of dihydro phenols, naphthols, and phenanthrols. Whereas k(H)/k(OH) for cis substituents varies by less than 8-fold and is consistent with the influence of an inductive effect of the OH group (k(H)/k(OH) ≈ 2000), k(H)/k(OH) for the trans substituents varies by 3 orders of magnitude, reflecting the additional influence of the lesser hyperconjugating ability of a C-OH bond compared to a C-H bond. The magnitude and variation of this difference is consistent with C-H hyperconjugation conferring aromatic character on the arenium ions. 相似文献
Kinetics and equilibria of the axial ligation of alkyl(aquo)cobaloximes by imidazole and cyanide have been measured spectrophotometrically
in aqueous solutions of ionic strength 1.0 M at 25°C as a function of pH. Comparison of KIMD and KCN- of CH3, C2H5 and BrCH2cobaloximes indicates that their stability is in the order BrCH2>CH3>C2H2. As the electron-withdrawing capacity of the alkyl grouptrans to water increases, the electron density of the cobalt(III) decreases and thus it becomes a stronger Lewis acid and binds
more strongly to imidazole and cyanide. The association and dissociation rate constants are better correlated to the relative
softness of the ligand showing that cyanide binds 30 times faster than imidazole. These complexes are isolated and are characterized
by IR and1H NMR spectra. 相似文献
The first enantiospecific total synthesis of the tricyclic sesquiterpene (+)-seychellene, starting from (R)-carvone via (S)-3-methylcarvone, has been accomplished employing a combination of an intermolecular Michael addition-intramolecular Michael addition sequence and an intramolecular alkylation reaction for the generation of the two vicinal quaternary carbon atoms. 相似文献
Summary 0.02 g/0.2 ml of potassium ferricyanide can be detected on a spot plate by utilising its catalytic effect on the reaction of cerium (III) with sulphosalicylic acid. A probable mechanism is discussed.
Zusammenfassung Die katalytische Wirkung von Hexacyanoferrat(III) auf die Reaktion zwischen Cer(III) und Sulfosalicylsäure wird zur einem empfindlichen Tüpfelnachweis für [Fe(CN)6]3– benutzt. Noch 0,02 g/0,2 ml können nachgewiesen werden. Der Reaktionsmechanismus wird diskutiert.
Summary Three new bifunctional phosphinoamide ligands of the type Ph2PCH2C(O)NHR (R = H, HDPA; Me, MDPA; Ph, PDPA) were prepared and characterized. Their ruthenium(II) complexes prepared from two different precursors, RuCl2-(DMSO)4 and RuCl2(PPh3)3, are of similar composition and correspond to the formula, [RuCl(L)2(P-O)2]Cl (L = DMSO/PPh3; phosphinoamide). However, RuCl3-(AsPh3)2(MeOH) reacts with the phosphinoamide to yield a reduced product of the cis-RuCl2(P-O)2 type. The ligands and complexes were characterized by mass, i.r. and n.m.r. spectroscopy. Possible stereochemistries for the complexes are proposed. 相似文献
A novel, sensitive, stability indicating RP-LC method has been developed for the quantitative determination of mitotane, its impurity in both bulk drugs and pharmaceutical dosage forms. Efficient chromatographic separation was achieved using a C18 stationary phase with simple mobile phase combination delivered in an isocratic mode and quantitation was by ultraviolet detection at a wavelength of 230 nm. The mobile phase consisted of buffer and acetonitrile (25:75, v/v) delivered at a flow rate of 1.0 mL min−1. Buffer consisted of 10 mM potassium dihydrogen orthophosphate monohydrate, pH adjusted to 2.5 by orthophosphoric acid. In the developed LC method the resolution (Rs) between mitotane and its impurity namely Imp-1 was found to be greater than 2.5. Regression analysis shows an r value (correlation coefficient) greater than 0.999 for mitotane and its impurity. This method was capable to detect the impurity of mitotane at a level of 0.003% with respect to test a concentration of 0.2 mg mL−1 for a 10 μL injection volume. The inter- and intra-day precision values for mitotane and its impurity was found to be within 2.0% RSD. The method has shown good and consistent recoveries for mitotane in bulk drugs (99.2–101.5%), pharmaceutical dosage forms (98.2–103.1%) and for its impurity (99.7–102.1%). The test solution was found to be stable in diluent for 48 h. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in basic stress hydrolysis. The stress samples were assayed against a qualified reference standard and the mass balance was found close to 99.97%. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness.