Influence of the size of aromatic chelate ligands on the one-dimensional structures of copper(II) 4,4′-oxy-bis(benzoate) coordination polymers

Two one-dimensional coordination polymers, [Cu(Oba)(TATP)] _n · nH₂O (I) and [Cu(Oba)(DPPZ)(H₂O)]n · nH₂O (II) (Oba is 4.4′-oxy-bis(benzoate), TATP is 1,4,8,9-tetranitrogen-tris(phene), DPPZ is dipyrido[3,2-a:2′,3′-c]phenazine), have been synthesized under similar conditions and structurally characterized by elemental analysis, IR spectra, and X-ray crystal structure. Compounds I and II are based on topologically identical chains, where the copper centers chelated by the amine ligands are linked by the Oba bridges, as well as the coordination modes of the Oba ligands. However, the angles between the individual links and the environment of the copper centers are substantially different between the two compounds and were found to be primarily influenced by the sizes of the rigid aromatic chelate ligands. The article is published in the original.     

A systematic capillary electrophoresis study on the effect of the buffer composition on the reactivity of the anticancer drug cisplatin to the DNA model 2′-deoxyguanosine 5′-monophosphate (dGMP)

The development of DNA-targeted next-generation platinum-based anticancer chemotherapeutics is often accompanied by studies on the reactivity to DNA models. However, the incubation conditions used in literature vary widely, and some of the buffer/salts used are known to form complexes with Pt. Such coordination can influence the binding process and also the adducts formed. In a systematic approach, studies on the binding of cisplatin (1 mM) to dGMP (2 mM) in a series of different incubation solutions of relevance to biological systems are reported, employing capillary zone electrophoresis (CZE) with UV/vis and electrospray ionization–mass spectrometric (ESI-MS) detectors. Kinetic experiments performed with CZE–UV showed a high reactivity of dGMP to cisplatin in pure water (τ _1/2?=?4.1?±?0.7 h) but a significantly slowed down in a solution containing a carbonate/phosphate buffer supplemented with NaCl, resulting in a half-life of dGMP of 25?±?3 h. Especially carbonate had a major impact on the binding, though no coordination to the metal center was detectable with the methods used. The only adducts containing buffer components were (phosphate)Pt and tris(ammine)Pt species, as identified by means of CZE–ESI-MS, in addition to the main adduct [Pt(NH₃)₂(dGMP)₂???4H⁺]^2? and other less abundant Pt-containing species.     

Influence of solvent on the photochemistry of 4,4′-diaminostilbene

Studies on the fluorescence and direct trans-cis photoisomerization of 4,4′-diaminostilbene in a variety of solvents, indicate a marked effect of solvent polarity. With increasing solvent polarity there is a decrease in fluorescence yield and lifetime and an increase in the rate of photoisomerization. The results are discussed in terms of a polarity effect on the energy barrier to photoisomerization.     

Effect of some added salts on the kinetics of dissociation of tris-2,2′-bipyridine-Fe(II) complex

Both monovalent cations and anions show a regular gradation, according to their sizes, in their effect on the rate and the activation parameters for the dissociation of tris(2,2′-bipyridine)-Fe(II) complex in acid. ΔS and ΔH of activation in M, 0.1 M and 0.01 M acid decrease in the order Cl⁻ > Br⁻ > I⁻ for anions and Li⁺ > Na⁺ > Cs⁺ for cations. The effect of the bulky tetra-alkyl ammonium ions is anomalous and does not depend on their sizes. The effect of the anions can be rationalized in terms of their involvement with the vacant coordination site of the partially bonded intermediate. The effect of cations is probably due to their altering the water structure at high concentration. The anomalous of the tetra-alkyl ammonium ions supports this view.     

The influence of ms-substitution on the properties of 3,3′-bis(dipyrrolylmethenes) and their coordination compounds

We have compared the coordination properties of decamethyl-substituted 3,3′-bis-(dipyrrolylmethenes) (H₂L) with different ms-spacers separating the dipyrrolylmethene domains: methylene -CH₂-, methoxyphenylmethylene -CH(p-C₆H₄OMe)-, and trifluoromethylmethylene -CH(CF₃)-. The stable binuclear homoligand complexes [M₂L₂] are formed in reactions of the ligands with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates. In the cases of all H₂L ligands the thermodynamic constants of the complex formation reactions increase in the following series: Cu(II) < Cd(II) < Hg(II) < Ni(II) < Co(II) < Zn(II). The change in -CH₂- ms-spacer to -CH(p-C₆H₄OMe)- or -CH(CF₃)- results in a decrease in the constant of H₂L complex formation by 1–4 orders of magnitude, the cation being the same. The influence of ms-substitution on the stability and luminescence properties of [M₂L₂] has been discussed.     

The influence of the nature of the solvent on the crystal structure and the character of formation of hydrogen bonds inN′-(5-nitrofurfurylidene)isonicotinehydrazide

N(5-Nitrofurfurylidene)isonicotinehydrazide (1) was synthesized in the reaction of nicotinic acid hydrazide with 5-nitrofurfurol in anhydrous or aqueous ethanol. Crystals of different shape and color were obtained depending on the conditions of synthesis and the nature of the solvent. As was established by IR spectroscopy, compound1 in the crystalline state forms solvates of various types. An X-ray study of two different crystals, one obtained by recrystallization from methanol (1a), and the other obtained from aqueous acetic acid (1b), was performed. In the crystal structure of1a intermolecular hydrogen bonds (IMHB) of the NH...N(Py) type occur; the crystals1b are built of solvates with one molecule of acetic acid in which the components are bonded by the IMHB (Ac)O-H..N(Py). The solvates are linked in an infinite chain by the amidohydrate IMHB C=O...W...H-N.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2263–2268, September, 1996.     

Theoretical study on the hydrolysis mechanism of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine

The hydrolysis mechanisms of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine (FA-3TC) in the gas phase and in aqueous solution were studied by use of the density functional theory B3LYP/6-31 G(d, p) method. Two possible reaction pathways in the title reaction were considered. In one pathway water attacks the C=N double bond first (path A) while in the other water attacks the C—N single bond first (path B). The calculated results indicate that the first step in both pathways is the rate-limiting process and path A is more favorable than path B in the gas phase. The effect of solvent water on the title reaction was assessed at the B3LYP/6-31 G(d, p) level of theory based on the po-larizable continuum model (CPCM). In water the first mechanism (path A) is also favored.     

Effects of Processing Temperature on the Oxygen Quenching Behavior of Tris(4,7′-diphenyl-1,10′-phenanthroline) Ruthenium (II) Sequestered Within Sol-Gel-Derived Xerogel Films

Sol-gel processing methods offer novel pathways for tailoring glasses. Amongst the issues that have received the least attention are the effects of the curing temperature on the behavior and photophysics of a dopant molecule sequestered within a sol-gel-derived xerogel. Of particular interest to our group are the effects of processing variables on the ability of a dopant molecule, that is sequestered within a xerogel glass, to be accessed by an analyte and the distribution of the dopant sites within the xerogel. The thermal stability of the luminophore tris(4,7-diphenyl-1,10-phenanthroline) ruthenium (II) ([Ru(dpp)₃]²⁺) provides a convenient way to address these issues and develop an understanding of how one might best exploit curing temperature to construct improved chemical sensors. This paper focuses on quantifying how the film curing temperature affects the spectroscopy and O₂ quenching of ([Ru(dpp)₃]²⁺) sequestered within sol-gel-derived xerogel thin films. Our quenching data on films once they have been cured demonstrate that there is a dramatic increase in the sensitivity of the ([Ru(dpp)₃]²⁺) molecules to O₂ quenching when the films have been cured at elevated temperatures. This arises primarily because there are two main types of ([Ru(dpp)₃]²⁺) microenvironments within the glass and higher temperature curing leads to an increase in the bimolecular quenching rate between O₂ and ([Ru(dpp)₃]²⁺). This is accomplished as follows. Below a curing temperature of 100–150°C, 15% of the xerogel-doped ([Ru(dpp)₃]²⁺) molecules are not accessed to any detectable degree by the O₂ molecules during the ([Ru(dpp)₃]²⁺) excited-state luminescence lifetime. However, as the xerogel is cured at or above 150°C, residual silanol-bound waters (or other impurities) dissociate from the xerogel and those ([Ru(dpp)₃]²⁺) molecules that were initially inaccessible become accessible to O₂. The dissociation of these water molecules, plus other events, also causes the originally inaccessible ([Ru(dpp)₃]²⁺) population to ultimately exhibit a quenching rate that is greater than the fraction of initially accessible ([Ru(dpp)₃]²⁺) molecules that were formed under ambient curing conditions.     

Stereochemistry of the asymmetric reduction of (1′s)-1,3-dimethyl-4(1′-phenylethylimino)piperidine

The stereochemistry of the asymmetric reduction of the imine obtained from 1,3-dimethylpiperidin-4-one and (S)--phenylethylamine has been studied. It is shown that hydride reduction of imine 1 by sodium borohydride in methanol is asymmetric and gives the cis and trans diastereomeric pair 1,3-dimethyl-4-(-phenyl-ethylamino) piperidine in the ratio 3:1. Using sodium in isopropanol gives only one trans diastereomeric pair.¹H NMR has been used to identify the stereochemical structure and diastereomer excess of the cis and trans isomers of 1,3-dimethyl-4-(-phenylethylamino)piperidine which had been separated by column chromatography.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 219–221, February, 1996.     

Aromatic Polybenzimidazoles on the Basis of 4,4′-Diphenylmethane Diisocyanate and Bis(arylene)hydroxamic Acids

Aromatic polybenzimidazoles are synthesized via cyclopolycondensation of bis(arylene)hydroxamic acids with 4,4′-diphenylmethane diisocyanate and the structure of polymers is confirmed by the data of elemental analysis, IR and PMR spectroscopy. The properties of the obtained polymers are comparable to the characteristics of aromatic polybenzimidazoles prepared via the conventional scheme on the basis of о-phenylenediamines and dicarboxylic acids.     

Solvent effect in the preparation of iron(III) azomethine complexes based on 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-N′-ethyl-N-ethylenediamine

Mono- and bis-chelate iron(III)-containing complexes with a tridentate azomethine ligand based on n-dodecyloxybenzoic acid ester derivatives with oxybenzoyl-4-salidene-N??-ethyl-N-ethylenediamine with NO ₃ ^? counterions are obtained. The structure of the compounds is determined by IR spectroscopy, elemental analysis, and mass spectrometry (MALDI-ToF MS). It is found that the complexation of iron salts with tridentate ligands in a mixture of solvents (alcohol:benzene) results in the formation of bischelate compounds of the composition 1:2 with octahedral packing of iron in the complex, while in pure alcohol solutions, asymmetric mono-chelate complexes are obtained.     

Spectroscopy of the excited-state complex of zinc(II) with 3,3′-bis(dipyrrolylmethene)

Spectra of nonstationary transient absorption of metal bis(dipyrrolylmethene) complexes in cyclohexane and ethanol, which exhibit different photophysical and photochemical properties in these solvents, have been measured and the yields of excited triplet states have been evaluated. It has been shown that the yield of triplets is determined by the intramolecular structure and the difference in fluorescence and phototransformation yields is due to intermolecular interaction of the excited molecules with the solvation shell.     

Synthesis of 5′-C- and 2′-O-(Bromoalkyl)-Substituted Ribonucleoside Phosphoramidites for the Post-synthetic Functionalization of Oligonucleotides on Solid Support

The preparation of building blocks for the incorporation of 6′-O-(5-bromopentyl)-substituted β-D -allofuranosylnucleosides and 2′-O-[(3-bromopropoxy)methyl]-substituted ribonucleosides into oligonucleotide sequences is presented (Schemes 1 and 2). These reactive building blocks can be modified with a variety of soft nucleophiles while the (fully protected) sequence is still attached to the solid support. As an example of this strategy, we carried out some preliminary solid-phase substitution and conjugation reactions with DNA sequences containing a 2′-O-[(3-bromopropoxy)methyl]-substituted ribonucleoside (Scheme 3) and determined the pairing properties of duplexes obtained therefrom.     

The Effect of the Oxygen Preadsorption on the Adsorption of Nitric Oxide on Mo (111)

The adsorption of nitric oxide adsorption on clean Mod(111), Mo(111)/O2-(4×4), Mo(111)/O2-(1×3), Mo(111)/O2-(112) facets and Mo(111) oxide surfaces was studied. Mass 28 (N2) desorption spectra show two high temperature peaks at approximate 1030 (β1) and 1200K (β2). For NO exposures less than 0. 1 L only the ft peak was observed. At higher exposures, the ft peak appeared and small amounts of N2O as well as NO desorbed. The preadsorption of oxygen blocked the β2 desorption partially on the (4×4) and (1×3) surfaces and fully on the (112) facet and oxide surfaces. In addition, the β1 desorption peak shifted to higher temperatures with increasing oxygen preexposure.     

Effects of Thermal Activation on the Electrocatalysis of the Ru(0001) Surface

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Crystallographic and computational study of the structure of copper(II) 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl

The reaction of M(OAc)₂ with 2,2′-bis(2-hydroxybenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl (H₂L1) allows the synthesis of 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl complexes of Cu(II) (CuL1), Co(II) (CoL1) and Ni(II) (NiL1) that were characterized by elemental analysis, FTIR spectroscopy and for CuL1 also by X-ray crystallography verifying a tetradentate binding mode of L1 via an (ONNO) motif of the two phenolic oxygen atoms and two azomethine nitrogen atoms. Recrystallization from a solvent mixture of dichloromethane and methanol promotes the formation of methanol adducts. Different binding modes of the methanol–complex were investigated using density functional theory calculations and binding energies, and thermodynamic data of the interaction are reported. The results show that the favored interaction occurs when the methanol molecule acts as a Lewis acid weakly binding via an O–H···O hydrogen bridge to a phenoxide moiety leading to an elongation of the respective M–O bond.

     

Effect of Co-solvent and Pressure on the Thermal Decomposition of 2,2′Azobis-(isobutyronitrile) in Supercritical CO_2

Recently, researchers pay much attention to the polymerization in supercritical (SC) CO2. 2, 2(-Azobis (isobutyronitrile) (AIBN) is a commonly used initiator in free radical polymerization in supercritical CO21. It is well known that the decomposition rate of the initiator AIBN plays an important role for a polymerization process2. Guan et al. have studied the effect of pressure on the decomposition rate of AIBN in SC CO22. A small amount of polar cosolvent can influence the propertie…     

Role of anions in the kinetics of the acid catalyzed dissociation of tris-(2,2′bipyridine) Fe(II) complex

Excess of Cl⁻ and NO₃⁻ ions bring about a significant increase in the rate of dissociation of the tris-(2,2′bipyridine) Fe(II) complex in HCl, HClO₄ and H₂SO₄ in a very narrow range of H⁺ concentration (∼0·1−0·3 M). Above and below this concentration range, these anions do not lead to significant variation in the rate of dissociation. This points to the involvement of these ions in a kinetic step which is only important in the rate expression in this narrow range. It is suggested that the anions occupy the coordination site left vacant by the partial dissociation of the complex leading to the half bonded intermediate. This would significantly lower the free energy of activation for the subsequent protonation step leading to complete dissociation and thus lead to acceleration. The lowering of the free energy of activation will be mainly due to an increase in entropy of this intermediate on account of charge reduction and lower rigidity due to lack of hydrogen bonding. The retarding effect of SO₄²⁻ concentrations and the unambiguously interpreted as its addition leads to simultaneous changes in H⁺ and HSO₄⁻ concentrations and the possibility of ion pair formation with the complex cannot be ruled out.