Synthesis and characterization of luminescent zinc(II) and cadmium(II) complexes with N,S-chelating Schiff base ligands

The reactions of zinc(II) acetate with a variety of 2-substituted benzothiazolines afforded tetrahedral mononuclear complexes with a N 2S 2 donor set, [Zn(RPhC(H) NC 6H 4 S) 2]. The obtained zinc(II) complexes can be divided into three groups based on the characteristics of the absorption spectra; Group 1 (R = 2,4,6-triMe ( 1), 2,6-diCl ( 2)) showing an intense band at 250-300 nm and a weak band at 400-450 nm, Group 2 (R = 4-Cl ( 3), H ( 4), 4-Et ( 5), 4-OMe ( 6)) showing two intense bands at 250-300 nm and a weak band at 400-450 nm, and Group 3 (R = 4-NMe 2 ( 7), 4-NEt 2 ( 8)) showing an intense band at 250-300 nm and two very intense bands at 350-450 nm. The Group 2 and Group 3 complexes exhibited a strong emission on irradiating with ultraviolet light while the Group 1 complexes were not emissive at room temperature. However, all the zinc(II) complexes were luminescent in CH 2Cl 2/toluene glass at 77 K, and their emission peak energies were found to correlate with the Hammett constant of the substituent at para position of a pendent phenyl ring in each complex. Similar reactions of cadmium(II) acetate with 2-substituted benzothiazolines were also carried out to synthesize corresponding cadmium(II) complexes. While [Cd(RPhC(H) NC 6H 4 S) 2] (R = 2,4,6-triMe ( 9)) with bulky substituents at ortho positions of a pendent phenyl ring had a tetrahedral mononuclear structure, other cadmium(II) complexes [Cd 2(RPhC(H) NC 6H 4 S) 4] (R = 4-Et ( 10), 4-OMe ( 11), 4-NMe 2 ( 12)) possessed S-bridged dinuclear structures. These cadmium(II) complexes, which are assumed to have a mononuclear structure in solution, showed photophysical properties similar to those of the corresponding zinc(II) complexes.     

A chromium(III) bis-acetylide complex containing a trans-diethyl-ethylenedithio-substituted tetrathiafulvalene (TTF) derivative: synthesis,crystal structures,and magnetic properties

A new Cr(III) bis-acetylide complex containing redox-active ethynyl-substituted 4-methyl-4′,5′-trans-diethyl-ethylenedithio-tetrathiafulvalene, [Cr(III)cyclam(C≡C-MeEt₂EDT-TTF)₂]ⁿ⁺ ([1]ⁿ⁺) was synthesized. The crystal structures of two salts, [1][Ni(dmit)₂] (dmit?=?2-thioxo-1,3-dithiole-4,5-dithiolate) and [1][Ni(mnt)₂]₃ (mnt?=?maleonitriledithiolate), were determined by single-crystal X-ray diffraction. In the crystal of [1][Ni(dmit)₂], the trans-diethyl group of [1]⁺ is in the axial position and prevents π-stacking of the TTF units, resulting in a negligibly weak spin–spin interaction between Cr³⁺ and [Ni(dmit)₂]^?. In contrast, in [1][Ni(mnt)₂]_3, the trans-diethyl group is in the equatorial position in [1][Ni(mnt)₂]₃ owing to the strong attractive force between the π-stacked TTF⁺ units and the [Ni(mnt)₂]^? anions. This π-stacking has a significant effect on the magnetic property of [1] [Ni(mnt)₂]₃. The π-stacked TTF⁺ units and [Ni(mnt)₂]^? anions behave approximately as a one-dimensional S?=?1/2 antiferromagnetic chain connecting the spins of Cr³⁺ antiferromagnetically.

     

Study of the Complexation of Protactinium(V) with EDTA

Journal of Solution Chemistry - The complex formation of protactinium(V) with ethylenediaminetetraacetic acid (EDTA) was studied at tracer concentration...     

Total synthesis of the hallucinogenic neoclerodane diterpenoid salvinorin A

Total synthesis of salvinorin A (1), a neoclerodane diterpenoid having the most potent hallucinogenic activity and a selective kappa-opioid agonist, was completed in 20 steps starting from enantiomerically pure hydroxy-Wieland-Miescher ketone 5.     

Induction of Optical Activity in an Oligothiophene Synchronized with pH‐Sensitive Folding of Amylose

Control of the helical sense in α‐sexithiophene (6T) through pH‐responsive wrapping with left‐handed‐helical amylose is demonstrated. A change in pH of the medium caused a significant conformational change in amylose as the host polymer, which resulted in either supramolecular complexation with 6T as the guest molecule to induce optical activity or decomplexation leading to loss of optical activity. Furthermore, we observed that chirality reversal in 6T does not require hosts of opposite helical chirality, but can be made possible simply by taking advantage of the pH sensitivity of the amylose folding, which is dependent on the pH history of the aqueous medium. In helical amylose, 6T assumes a clockwise‐twisted conformation when the pH is changed from acidic to neutral, but assumes an anticlockwise‐twisted conformation when the aqueous solution is acidified from very basic conditions.     

Calorimetric study of correlated disordering in [Hdamel]2[Cu(II)(tdpd)2] x 2 THF crystal

The heat capacity of [Hdamel]2[Cu(II)(tdpd)2] x 2 THF was measured from 6 to 250 K by adiabatic calorimetry. There are four heat anomalies around 150 K associated with disordering in the orientation of the uncoordinated THF molecules and in the conformation of the out-of-plane allyl groups of [Hdamel](+) units. The total entropy of transition was determined to be 19.8 J K(-1) mol(-1), less than the 4R ln 2 (R = gas constant) expected from the crystal structure at room temperature. The smallness of the total entropy change on phase transitions proves the presence of the strong motional correlation between the adjacent allyl groups. The calorimetric conclusion agreed with the crystal structure at 200 K re-examined in this study.     

Photo-responsive gel droplet as a nano- or pico-litre container comprising a supramolecular hydrogel

Photo-responsive gel droplets having nano- or pico-L volume that showed photo-induced gel-sol transition were successfully developed, for which the inter-droplet mass transport and the subsequent enzymatic reactions in the interior of the gel droplets were photo-triggered.     

Metal ion induced allosteric transition in the catalytic activity of an artificial phosphodiesterase

An artificial phosphodiesterase () bearing two types of metal binding sites, a catalytic site and a regulatory bipyridine site showed a unique allosteric transition in the catalytic activity against the metal concentration. The rate constants for the hydrolysis reaction of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) and RNA dimer (ApA) with and without an effector metal ion were evaluated; the k(obs) value of HPNP hydrolysis for .(Zn(2+))(3) (2.0 x 10(-4) s(-1)) is 3.3 times larger than that for .(Zn(2+))(2). In the case of and Cu(2+), a 19.4 times larger k(obs) value was obtained for .(Cu(2+))(3) (1.2 x 10(-3) s(-1)) against .(Cu(2+))(2). The increase in the catalytic activity is ascribed to the allosteric conformational transition of induced by the coordination of effector metal ion to the Bpy moiety. A detailed investigation revealed that a conformational change of induced by the third M(2+) complexation enhances the rate of hydrolysis rather than a change in the substrate affinity.     

Development of low cost pulmonary surfactants composed of a mixture of lipids or lipids-peptides using higher aliphatic alcohol or soy lecithin

The artificial pulmonary surfactant composition in the present study is characterized by a lipid mixture system composed of higher aliphatic alcohol, egg yolk phosphatidylcholine (egg PC), soy lecithin and higher aliphatic acid as the major components or a peptide-lipid mixture system composed of a combination of the lipid mixture system to which a peptide is added. Three peptides with amphiphilic surface-staying, membrane spanning, and both properties were designed and synthesized. The evaluation of pulmonary surfactant assay was performed by a hysteresis curve drawn upon the measurement for the surface tension-area curve with the Wilhelmy surface tensometer in vitro and the recovery of lung compliance for the pulmonary surfactant-deficient rat models in vivo. Lipid-mixture systems composed of octadecanol or soy lecithins containing no peptide were favorable hysteresis curves as compared with commercially available Surfacten((R)), but were not prominent. The peptide-lipid mixture systems composed of a combination of the lipid mixture of alkyl alcohol or soy lecithin to which peptides designed were added were desirable hysteresis curves similar to Surfacten((R)) and amphiphilic Hel 13-5 peptide-lipids mixture systems were much more effective than the lipid mixture system. Particularly, the recovery of lung compliance treated with hydrogenated soy lecithin-fractionated soy lecithin PC70-palmitic acid-peptide Hel 13-5 (40:40:17.5:2.5, w/w) was comparable to that with Surfacten((R)). Because the artificial pulmonary surfactant compositions of this study can be prepared at lower costs, they are useful for the treatment of respiratory distress syndrome and acute respiratory distress syndrome as well as for inflammatory pulmonary diseases, dyspnea caused by asthma, etc.