Studies on the synthesis, characterization, binding with DNA and activities of two cis-planaramineplatinum(II) complexes of the form: cis-PtL(NH3)Cl2 where L = 3-hydroxypyridine and 2,3-diaminopyridine

Background  

Cis-planaramineplatinum(II) complexes like their trans isomers are often found to be active against cancer cell lines. The present study deals with the synthesis, characterization and determination of activity of new cis-planaramineplatinum(II) complexes.     

Theoretical study of the reaction of CF3O radicals with CO

The potential energy surface for the reaction of the CF₃O radicals with CO was investigated. The geometries and vibrational frequencies of the reactants, transition states, intermediates, and products were calculated at the UB3LYP/6-311+G(2d,p), UB3LYP/6-311+G(3df,2p) and UMP2/6-311+G(2d,p) levels of theory. The energies were improved by using the G2M(CC2) and G3B3 methods. The calculation suggests the reaction proceeds via either the fluorine abstraction of CF₃O by CO to produce FCO + CF₂O with a high energy barrier or the barrierless association of the reactants to form the trans-CF₃OCO intermediate. The trans-CF₃OCO is predicted to undergo subsequent isomerization to cis-CF₃OCO or dissociate directly to the products FCO + CF₂O and CF₃ + CO₂. The collisional stabilization of trans-CF₃OCO is dominant at room temperature, while trans-CF₃OCO isomerizing to cis-CF₃OCO followed by dissociating to CF₃ + CO₂ is accessible when temperature rises. The reason for only trans-CF₃OCO without cis-CF₃OCO observable in Ashen’s experiment [S.V. Ahsen, J. Hufen, H. Willner, J.S. Francisco, Chem. Eur. J. 8 (2002) 1189] is cis-CF₃OCO can be produced only via the isomerization of trans-CF₃OCO, and its yield is inappreciable at a low experimental temperature. The enthalpies of formation for the two conformations of CF₃OCO have been deduced: (trans-CF₃OCO) = −196.25 kcal mol⁻¹, (trans-CF₃OCO) = −197.46 kcal mol⁻¹, (cis-CF₃OCO) = −193.64 kcal mol⁻¹, and (cis-CF₃OCO) = −194.90 kcal mol⁻¹.     

Ruthenium complexes of 4,4′-bi-1,2,3-thiadiazole and azoimine ligands: syntheses,crystallography, and electrochemical studies

Abstract  

Five ruthenium complexes of the general type trans-[Ru^II(btd)(Azo)Cl₂] ({Azo = PhN=NC(COMe) = NC₆HY, where Y = H (a), Me (b), OMe (c), Cl (d) or Br (e)} and btd = 4,4′-bi-1,2,3-thiadiazole) have been prepared by the reaction of RuCl₃ with the ligands in the presence of LiCl. These complexes have been characterized by spectroscopic (IR, UV–Vis, and NMR) and electrochemical techniques. In addition, the complex trans-[Ru^II(btd)(L5)Cl₂] (complex 5) has been characterized by X-ray diffraction analysis. The electrochemical parameter for the π-excessive ligand (btd) is reported. The absorption spectrum of complex 5 in acetonitrile has been modeled by time-dependent density functional theory.     

Chemistry of chromium bis-acetylide complexes

Abstract  

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies.     

Synthesis,crystal structures and yeast RNA-binding properties of copper(II) and nickel(II) complexes with a bidentate Schiff base

Abstract  

Trans-CuL₂ and cis-NiL₂ (L = 1-((furan-2-yl)methylene)-4-phenylthiosemicarbazide) were synthesized and characterized by physico-chemical and spectroscopic methods. Their X-ray crystal structures were determined. The complexes contain the same bidentate Schiff base ligand, but with different cis-NiN₂S₂ and trans-CuN₂S₂ square-planar coordination geometries. Three-dimensional supramolecular networks were formed through “face to face” π–π conjugated systems between phenyl and furan rings. The interactions with yeast RNA (yRNA) were investigated by UV spectra and electrochemical methods, which showed that the complexes intercalated into yRNA. The bonding of trans-CuL₂ to yRNA is the stronger of the two, suggesting that the trans geometry is more favorable for interaction with RNA.     

Crystal structures and photoreactivity of trans- and cis-valerophenone diperoxides

Abstract  

The crystal structures of valerophenone diperoxides trans-1 and cis-1 were elucidated by X-ray crystallographic analysis. The 1,2,4,5-tetraoxane rings of both compounds adopt chair conformations. Intermolecular CH···O hydrogen bond, π–π, and CH/π interactions exist in cis-1, whereas only CH/π interactions exist in trans-1. In the asymmetric unit of the crystal, a half molecule exists for trans-1, while one molecule for cis-1 which shows whole-molecule disorder. Solid-state photolysis (at 254 nm) or solution-state thermolysis (at 150 °C) of trans-1 and cis-1 produced valerophenone (2) and butyl benzoate (3). Rationalization of the solid-state photoreactivity of the diperoxides by their crystal structures was attempted.     

Novel Photoresponsive Linear,Graft, and Comb‐Like Copolymers with Azobenzene Chromophores in the Main‐Chain and/or Side‐Chain: Facile One‐Pot Synthesis and Photoresponse Properties

Novel photoresponsive linear, graft, and comb‐like copolymers with azobenzene chromophores in the main‐chain and/or side‐chain are prepared via a sequential ring‐opening metathesis polymerization (ROMP) and head‐to‐tail acyclic diene metathesis (ADMET) polymerization in a one‐pot procedure using Grubbs ruthenium‐based catalysts. The diluted solutions of these as‐prepared copolymers containing azobenzene chromophores exhibit photochemical trans–cis isomerization under the irradiation of UV light, followed by their cis–trans back‐isomerization in visible light. The rates of photoisomerization are found to be slower than those of back‐isomerization, and the rate for the comb‐like copolymer is found to be from 3 to 7 times slower than that obtained for the linear or graft copolymer. This is ascribed to the differences in structure of the copolymers and the specific location of azobenzene chromophores in the copolymer, which favor a side‐chain graft structure.

     

A One-Pot Synthesis of trans-N-Alkylaziridine-2-carboxylates from Amino Alcohol Esters

A series of new trans-N-alkylaziridine-2-carboxylates 3 was conveniently synthesized in a one-pot reaction by treatment of 1,2-amino alcohol mono and diesters 1 with methanesulfonyl chloride in the presence of (iPr)₂NEt. The products were obtained in good to excellent yields with high trans-selectivity.

Low-temperature heat capacities and standard molar enthalpy of formation of the solid-state coordination compound trans-Cu(Ala)2(s) (Ala = l-α-alanine)

Low-temperature heat capacities of the solid coordination compound trans-Cu(Ala)₂(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C_p,m) with the reduced temperatures (X), [X = f (T)], by a least square method. The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)₂(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)₂·H₂O(s) + 2Ala (s)} and 2:1 HAc (aq) in 100 ml of 2 mol dm⁻³ HCl, respectively, and trans-Cu(Ala)₂(s) in the solvent [2:1 HAc (aq) + 2 mol dm⁻³ HCl] at T = 298.15 K were determined to be , , and by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess thermochemical cycle.     

High‐precision determination of lithium and magnesium isotopes utilising single column separation and multi‐collector inductively coupled plasma mass spectrometry

Rationale

Li and Mg isotopes are increasingly used as a combined tool within the geosciences. However, established methods require separate sample purification protocols utilising several column separation procedures. This study presents a single‐step cation‐exchange method for quantitative separation of trace levels of Li and Mg from multiple sample matrices.

Methods

The column method utilises the macro‐porous AGMP‐50 resin and a high‐aspect ratio column, allowing quantitative separation of Li and Mg from natural waters, sediments, rocks and carbonate matrices following the same elution protocol. High‐precision isotope determination was conducted by multi‐collector inductively coupled plasma mass spectrometry (MC‐ICPMS) on the Thermo Scientific™ NEPTUNE Plus™ fitted with 10¹³ Ω amplifiers which allow accurate and precise measurements at ion beams ≤0.51 V.

Results

Sub‐nanogram Li samples (0.3–0.5 ng) were regularly separated (yielding Mg masses of 1–70 μg) using the presented column method. The total sample consumption during isotopic analysis is <0.5 ng Li and <115 ng Mg with long‐term external 2σ precisions of ±0.39‰ for δ⁷Li and ±0.07‰ for δ²⁶Mg. The results for geological reference standards and seawater analysed by our method are in excellent agreement with published values despite the order of magnitude lower sample consumption.

Conclusions

The possibility of eluting small sample masses and the low analytical sample consumption make this method ideal for samples of limited mass or low Li concentration, such as foraminifera, mineral separates or dilute river waters.

     

Substituentenabhängigkeit bei der direktentrans →cis-Photoisomerisierung von donator-substituierten 4′-Diphenylphosphinyl-trans-stilbenen

From the fluorescence quantum yield _f , the fluorescence decay time _f ^w and the quantum yield _tc of thetrans cis photoisomerization results the fraction of perpendicular singlet (perp-S₁) decaying to ground statetrans-stilbenes1. The values of the donor substituted 4-diphenylphosphinyl-trans-stilbenes1 in the solvents toluene andn-propanol are dependent on the donor substituent in1 and the solvent. It is concluded for1 that increasing polarity of the first excited singlet state (tr-S₁) promotes thetrans cis photoisomerization.

     

Module structure of interphotoreceptor retinoid-binding protein (IRBP) may provide bases for its complex role in the visual cycle – <Emphasis Type="Italic">structure/function study of Xenopus IRBP</Emphasis>

Background  

Interphotoreceptor retinoid-binding protein's (IRBP) remarkable module structure may be critical to its role in mediating the transport of all-trans and 11-cis retinol, and 11-cis retinal between rods, cones, RPE and Müller cells during the visual cycle. We isolated cDNAs for Xenopus IRBP, and expressed and purified its individual modules, module combinations, and the full-length polypeptide. Binding of all-trans retinol, 11-cis retinal and 9-(9-anthroyloxy) stearic acid were characterized by fluorescence spectroscopy monitoring ligand-fluorescence enhancement, quenching of endogenous protein fluorescence, and energy transfer. Finally, the X-ray crystal structure of module-2 was used to predict the location of the ligand-binding sites, and compare their structures among modules using homology modeling.     

trans–cis and trans–cis–trans Microstructure Evolution of Azobenzene Liquid‐Crystal Polymer Networks

The photomechanics of azobenzene LCNs is modeled using a nonlinear continuum mechanics approach that couples photoisomerization of liquid crystal domain structures with light absorption and deformation of a glassy polymer network. The effects during UV‐stimulated trans–cis photomechanical deformation versus blue‐green light (trans–cis–trans) photomechanical deformation are simulated. Different bending deformation is predicted by assuming liquid‐crystal order/disorder behavior during trans–cis photoisomerization in comparison to light‐polarization‐driven reorientation of the trans phase during potential trans‐cis‐trans photoisomerization. Light‐controlled deformation mechanisms offer support for improved control of photo‐responsive morphing structures with a single blue‐green polarized light source.

     

A new aspect of Heck catalyst formation

Abstract  

The mechanism of the formation of the active Pd(0) complex from trans-dichlorobis(diethanolamine-N)palladium(II) complex in the presence of strong base was investigated by using density functional theory (M06 method). Our investigation shows that in the basic environment trans-dichlorobis(diethanolamine-N)palladium(II) complex undergoes abstraction of the alcoholic proton, and coordination of alkoxide oxygen to palladium. The intermediate complex, in which hydrogen is coordinated to Pd, undergoes reductive elimination of HCl, yielding the catalytically active low ligated Pd(0) complex.     

cis–trans Isomerisation of Substituted Aromatic Imines: A Comparative Experimental and Theoretical Study

The cis–trans isomerisation of N‐benzylideneaniline (NBA) and derivatives containing a central C?N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans${{\mathop \rightarrow \limits ^{h\nu }_{}}}$ cis isomerisation and the kinetics of the thermal backreaction cis${{\mathop \rightarrow \limits ^{\Delta }_{}}}$ trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition‐state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time‐dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify “optimal switches” with good photochromicity and reasonable thermal stability.     

The Regio‐ and Stereoselective Synthesis of trans‐2,3‐Dihydropyridine N‐oxides and Piperidines

Reactivity N? Own : Pyridine N‐oxides can be used for the complete regio‐ and stereoselective synthesis of trans‐substituted piperidines. The sequential addition of Grignard reagents and aldehydes or ketones to pyridine N‐oxides yields a complete regio‐ and stereoselective trans 2,3‐addition reaction in high yields, and the substituted 2,3‐dihydropyridine N‐oxide can be reduced to form 2,3‐trans‐substituted piperidines (see scheme).

     

Ruthenium(II) 2,2′-bipyridine complexes incorporating substituted phenylazo-(2-(phenylthio))phenylmethine ancillary ligands. Synthesis,crystal structure,spectroscopic and redox properties

Abstract  

Five ruthenium complexes bearing phenylazo-(2-(phenylthio))phenylmethine ligands of the general type trans-[Ru^II(bpy)(L)(Cl)₂] (C1–C5) {L = YC₆H₄N=NC(COCH₃)=NC₆H₄(2-SC₆H₅), H (L1), Cl (L2), OCH₃ (L3), Br (L4), or NO₂ (L5)} have been synthesized. The crystal structure of trans-[Ru(bpy)(L1)(Cl)₂] (C1) is reported and shows no direct metal–S interaction. The complexes have been characterized through spectroscopic (IR, UV/vis and NMR) and electrochemical (CV) techniques. The electrochemical parameters (E _L(L)) of the azoimine ligands are reported.     

Synthesis and Thermal Properties of Regio‐ and Stereoregular Poly(silylene‐1,4‐phenylenevinylene)s

Polymerization of p‐(dimethylsilyl)phenylacetylene in toluene at 25 and 80°C using RhI(PPh₃)₃ as the catalyst afforded highly regio‐ and stereoregular poly(dimethylsilylene‐1,4‐phenylenevinylene)s (cis‐ 3 a and trans‐ 3 a ) containing 98% cis‐ and 99% trans‐vinylene moieties, respectively. Similarly, poly(butylmethylsilylene‐1,4‐phenylenevinylene)s ( 3 b with 91% cis‐ and 95% trans‐structures) and poly(diisopropylsilylene‐1,4‐phenylenevinylene) with 95% trans‐structure were synthesized. All polymers were soluble in common organic solvents. The trans‐type polymers showed red shifts and hyperchromic effects in the UV‐visible spectrum. The onset temperature of weight loss (T₀) of cis‐ 3 a was much higher than that of trans‐ 3 a .