Curing and thermal behaviour of a flame retardant cycloaliphatic epoxy resin based on phosphorus containing poly(amide–imide)s

The curing behaviour of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate was investigated by the dynamic differential scanning calorimetry (DSC) using phosphorus-containing poly(amide–imide)s (PAIs) having free amine groups, 4,4′-diaminodiphenylmethane (PM) and p-phenylenediamine (PA), in the ratio of 1:1. The PAIs were prepared by co-polymerization of diimide–diacid (DIDA) and phosphorus-containing triamines having phenylene moiety. l-Tryptophan and pyromellitic anhydride were used to synthesize DIDA. Triamines used in the synthesis PAIs were tris(3-aminophenyl) phosphine (TAP), tris(3-aminophenyl) phosphine oxide (TAPO) and bis(3-aminophenyl) aminotolyl phosphine (BAP). TAP-, TAPO- and BAP-containing PAIs were designated as PTAP, PTAPO and PBAP, respectively. These PAIs with free amine groups were characterized by FTIR, ¹H NMR, ¹³C NMR spectroscopic techniques and elemental analysis. The mixture of PAIs and PM or/and PA in the ratios of 0:1, 1:0 and 0.5:0.5 was used for investigation. DSC was used to study the curing of epoxy by recording the DSC scans at heating rates of 10 °C min^?1. Thermal stability of epoxy resin cured isothermally was evaluated by recording thermo gravimetric traces in nitrogen atmosphere at the heating rate of 20 °C min^?1. All samples are highly stable, and the 10 % mass loss found was in the range of 335–520 °C. The percent char yield was highest in case of resin sample E/PM/PTAPO. The flame-retardant properties of cured epoxy resins were investigated by the limiting oxygen index test (LOI) and UL94 test. When phosphorus was incorporated in epoxy resin, the epoxy resin system met the UL94 V-0 classification and the LOI reached at 37.8, because of nitrogen–phosphorus synergistic effect.     

Cytotoxic properties of platinum(IV) and dinuclear platinum(II) complexes and their ligand substitution reactions with guanosine-5′-monophosphate

The substitution reaction of the Pt(IV) complex [PtCl₄(bipy)] with guanosine-5??-monophosphate (5??-GMP) was studied by UV?CVis spectrophotometry. This reaction was investigated under pseudo-first-order conditions at 37?°C in 25?mM Hepes buffer (pH?=?7.2) in the presence of 10?mM NaCl to prevent the hydrolysis of the complex. The substitution of chlorides in [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complex by 5??-GMP was followed by ¹H NMR spectroscopy under second-order conditions. Very similar values for the rate constants of both substitution steps were obtained. The Pt(IV) complexes, [PtCl₄(bipy)] and [PtCl₄(dach)], as well as dinuclaer Pt(II) [{trans-Pt(NH₃)₂Cl}₂(??-pyrazine)](ClO₄)₂ (Pt1), [{trans-Pt(NH₃)₂Cl}₂(??-4,4??-bipyridyl)](ClO₄)₂?·?DMF (Pt2) and [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complexes, displayed potent cytotoxic activity against human ovarium carcinoma cell line TOV21G and lower activity toward human colon carcinoma HCT116 cell line at the same concentrations. Our data indicate that these platinum complexes could be explored further, as potential therapeutic agents for ovarian cancer.     

Virtual and experimental high-throughput screening (HTS) in search of novel inosine 5′-monophosphate dehydrogenase II (IMPDH II) inhibitors

IMPDH (Inosine 5??-monophosphate dehydrogenase) catalyzes a rate-limiting step in the de novo biosynthesis of guanine nucleotides. IMPDH inhibition in sensitive cell types (e.g., lymphocytes) blocks proliferation (by blocking RNA and DNA synthesis as a result of decreased cellular levels of guanine nucleotides). This makes it an interesting target for cancer and autoimmune disorders. Currently available IMPDH inhibitors such as mycophenolic acid (MPA, uncompetitive inhibitor) and nucleoside analogs (e.g., ribavirin, competitive inhibitor after intracellular activation by phosphorylation) have unfavorable tolerability profiles which limit their use. Hence, the quest for novel IMPDH inhibitors continues. In the present study, a ligand-based virtual screening using IMPDH inhibitor pharmacophore models was performed on in-house compound collection. A total of 50,000 virtual hits were selected for primary screen using in vitro IMPDH II inhibition up to 10???M. The list of 2,500 hits (with >70?% inhibition) was further subjected to hit confirmation for the determination of IC₅₀ values. The hits obtained were further clustered using maximum common substructure based formalism resulting in 90 classes and 7 singletons. A thorough inspection of these yielded 7 interesting classes in terms of mini-SAR with IC₅₀ values ranging from 0.163???M to little over 25???M. The average ligand efficiency was found to be 0.3 for the best class. The classes thus discovered represent structurally novel chemotypes which can be taken up for further development.     

Greener and practical synthesis of 4,4′-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s through a conventional heating and a mechanochemical procedure

A new catalytic application of 4,4′-trimethylenedipiperidine for the efficient synthesis of 4,4′-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s is developed. According to the principles of green chemistry, the reaction was performed by conventional and non-conventional processes: (a) in the refluxing ethanol using a catalytic amount of organocatalyst; (b) at room temperature in the presence of organocatalyst in a planetary ball mill under solvent-free conditions. The organocatalyst could be reused up to 10 runs, and a negligible reduction of catalytic activity was detected. A variety of substituted 4,4′-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s were obtained in good–to-excellent yields under eco-friendly conditions. 4,4′-Trimethylenedipiperidine is commercially available and easy to handle and storage, less toxic, non-flammable, as well as it shows high thermal stability and good solubility in water. The current methodology has merits including (a) wide substrate-scope and high yields of the desired products in the short reaction times, (b) avoiding the use of hazardous solvents and acidic and metal-containing catalysts, (c) minimize the generation of hazardous waste, and (d) simple workup process. Based on great potential as a promising organocatalyst, we hope it can be used as a greener alternative to piperidine for other organic transformations.     

Complexes of cadmium(II) and mercury(II) ions with cytidine or cytidine-5′-monophosphate in ternary systems including tetramines

Interactions between Hg(II) and Cd(II) ions in binary systems with 3,3,3-tet (1,11-diamino-4,8-diazaundecane) and in ternary systems with Cyd (cytidine) or CMP (cytidine-5′-monophosphate) and 3,3,3-tet or Spm (1,12-diamino-4,9-diazadodecane, spermine) have been studied. The presence of the following species has been detected: MH _x (3,3,3-tet), M(3,3,3-tet), M(3,3,3-tet)(OH) _x and M(Cyd or CMP)(PA), M(Cyd or CMP)(H _x PA) (M?=?Cd or Hg, PA?=?3,3,3-tet or Spm). Overall stability constants (log β) have been determined and equilibrium constants for complex formation (log?K _e) calculated. The mode of coordination in these species has been proposed on the basis of the equilibrium and ¹³C NMR, ³¹P NMR and IR studies. Unlike the biogenic amine Spm, its homologue 3,3,3-tet coordinates with Cd(II) and Hg(II) ions with the involvement of all available donor nitrogen atoms. In Cd(Cyd)(3,3,3-tet) the {N5} chromophore is formed, while in Cd(Cyd)(Spm) the {N4} chromophore is involved (only three nitrogen atoms from Spm are involved in metallation). Introduction of the polyamine into the system Cd(II)/CMP (at pH below 7) leads to changes in coordination mode in the anchoring Cd(CMP) complex and the phosphate group of CMP is involved in bonding. In ternary systems, Hg(II)/Cyd(or CMP)/tetramine, the nitrogen atom N(3) and the phosphate group of the nucleotide take part in coordination. The presence of PA in the inner coordination sphere does not change the mode of metal–CMP coordination with respect to that in the binary system.     

1,1-Bis-(4-methoxyphenyl)-1′-pyrenyl methyl (bmpm): a new fluorescent 5′ protecting group for the purification of unmodified and modified oligonucleotides

By replacing the phenyl by a pyrenyl in the dimethoxytrityl (DMTr) group commonly used for 5′-protection in oligonucleotide synthesis, we have obtained a fluorescent acid-labile protecting group which exhibits similar chemical properties to those of DMTr. Here we demonstrate the usefulness of the new protecting group in the purification of both charged and neutral DNA fragments.     

The influence of (5′R) and (5′S)-5′,8-cyclo-2′-deoxyadenosine for the electronic properties of nucleosides pairs. The theoretical quantum mechanics studies

Oxidatively generated damage to DNA frequently appears in the human genome as the effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents such as ionization radiation. In this paper, for the first time, the electronic properties of nucleoside pairs containing 5′,8-cyclo-2′-deoxyadenosine (cdA) in their 5′R and 5′S diastereomeric forms (cdA(R)::T and cdA(S)::T) as the simplest model of ds-DNA have been discussed. The following values of the selected electronic parameters, measured in eV, were found for cdA(R)::T, cdA(S)::T, and dA::T, respectively, adiabatic/vertical electron affinity: 0.39/0.24, 0.35/0.18, 0.33/0.21; and adiabatic/vertical ionization potential: 7.27/7.50, 7.7.25/7.49, 7.03/7.27. Moreover, based on the results of the relaxation energy, the presence of cdA(S)::T should provide the highest barrier for electron transfer in ds-DNA. Analyses of hydrogen bond length deviations reveal that the formation of cationic forms results in higher elongation than that of anionic forms. Moreover, during the electron attachment or detachment for the investigated cdA(R)::T, cdA(S)::T, and dA::T nucleoside pairs, the same scheme of changes in hydrogen bond length was noted.      

Understanding the role of flexible 4′-functionalized polyethylene glycoxy chains on the behavior of platinum(II) (4′-(ethylene glycoxy)-2,2′:6′,2′′-terpyridine: a kinetic and a mechanistic study

The ligand substitution kinetics of 4′-functionalized mononuclear Pt(II) (4′-(ethylene glycoxy)-2,2′:6′,2′′-terpyridine complexes, [Pt(nY-tpy)Cl)Cl] (where Y = ethylene glycoxy, n = number of ethylene, glycoxy units = 1, 2, 3, and 4, and tpy = 2,2′:6′,2′′-terpyridine), with thiourea, 1,3-dimethyl-2-thiourea, 1,1,3,3-tetramethyl-2-thiourea, and iodide were investigated under pseudo-first-order conditions as a function of concentration and temperature by conventional stopped-flow technique. The observed first-order rate constants followed the simple rate law k_obs = k₂[Nu]. The data obtained show that the ethylene glycoxy pendant, trans to the leaving group, acts as a σ-donor into the terpyridine ligand and is effective only up to n = 1, beyond which the substitution reactivity of the complexes are controlled by the steric influence of the appended ethylene glycoxy pendant units, which decreases with increase in the number of ethylene glycoxy units. The activation parameters obtained support an associative mechanism, where bond formation in the transition state is favored. The observed reactivity trends were supported by density functional theory calculations.     

Characterization and spectroscopic study of new complexes of Cd(II), Hg(II) and Pb(II) with the sodium salt of morin-5′-sulfonic acid

Solid compounds of Cd(II), Hg(II) and Pb(II) with the sodium salt of morin-5′-sulfonic acid (NaMSA) were obtained. The molecular formula of the complexes are: Cd(C₁₅H₈O₁₀SNa)₂?·?6H₂O, CdOH(C₁₅H₈O₁₀SNa)?·?4H₂O, Hg(C₁₅H₈O₁₀S)?·?4H₂O and Pb(C₁₅H₈O₁₀S)?·?3H₂O. Some of their physicochemical properties such as UV-Vis, infrared, ¹³C NMR and mass spectra, thermogravimetric analysis, and solubility were studied. On the basis of spectroscopic data NaMSA was bound to Cd²⁺ via 4C=O and 3C?–?oxygen and the Hg²⁺ and Pb²⁺ ions by 5C–OH, 4C=O and 3C–OH.     

Interactions of cadmium(II) ions with adenosine as well as adenosine-5′-monophosphate and diamine or triamines in the ternary systems

The mode of coordination in complexes formed in the systems Cd(II)/Ado/di- or triamine and Cd(II)/AMP/di- or triamine has been established on the basis of the equilibrium and spectral investigation. The overall stability constants (log?β) and equilibrium constants of formation (log?K _e) of the complexes formed in the above systems have been determined. In the species, the main interaction centres are the nitrogen atoms N(1) or N(7) of the purine ring of Ado and AMP, while in the nucleotide also the oxygen atoms of the phosphate group and donor nitrogen atoms of the polyamine (PA) molecule. The effect of polyamine on the coordination dichotomy has been ascertained. For example, the presence of polyamine in the ternary system is responsible for involvement of only N(7) of the nucleoside in the metallation in Cd(Ado)H(Put), while in the binary system Cd(II)/Ado, the N(1)/N(7) dichotomy occurs in the whole pH range studied. Polyamine can also affect the character of the phosphate group of the nucleotide. The phosphate group, inactive in the binary system Cd(II)/AMP, after introduction of the polyamine becomes engaged in the interactions, e.g. in the complex Cd(AMP)H(dien). In Cd(AMP)H(en) and Cd(AMP)H(Put) no participation of the oxygen atom of the phosphate group has been found. This group is involved in weak interactions with a protonated amine group PA located in the outer coordination sphere. On the other hand, in the Cd(AMP)H(3,3-tri) complex the phosphate group is the only site of Cd(II) bonding. In this species the donor nitrogen atoms N(1) and N(7) of the nucleotide are outside the inner coordination sphere and involved in noncovalent interactions with protonated amine group from 3,3-tri.     

Efficient synthesis of terminal 4-methylumbelliferyl labeled 5-fluoro-2′-deoxyuridine-5′-O-tetraphosphate (Um-PPPP-FdU): a potential probe for homogenous fluorescent assay

Efficient synthesis of 5-fluoro-2′-deoxyuridine-5′-O-tetraphosphate bearing 4-methylumbelliferyl label on the terminal phosphate is reported. This compound has the potential as a promising probe molecule for homogenous fluorescent polymerase assay. This class of compounds will aid in quantification of cellular internalization and DNA incorporation of nucleotide based chemotherapeutic agents to offer mechanistic insights.     

Synthesis and characterization of a 2, 5-Bis(trimethylsilyl)-substituted Bis(1, 1′-silolide) dianion

A novel silyl-substituted bis(1, 1′-silolide) dianion has been isolated and characterized by single-crystal X-ray analysis for the first time. The ¹H, ²⁹Si, and ¹³C NMR spectra show significant delocalization of the negative charges to the silole ring. X-ray crystallography revealed equalized C?C distances and DFT calculation also indicates for significant aromaticity. Reaction with trimethylchlorosilane gave the expected bis(1, 2, 5-tris(trimethylsilyl)-3, 4-diphenyl-silacyclopentadienyl).     

Facile Grafting of Silver Nanoparticles into Copper and Guanosine 5′-Monophosphate Metal Organic Frameworks (AgNPs@Cu/GMP): Characterization and Antimicrobial Activity

Journal of Cluster Science - Silver nanoparticles (AgNPs) are effective antibacterial agent but lack of stability and rapid aggregation limits their antibacterial efficiency in biomedical...     

N-(n-Alkyl)-N′-diphenylphosphorylureas as a new type of extractants for preconcentration of actinides and lanthanides

N-(n-Alkyl)-N′-diphenylphosphorylureas Ph₂P(O)NHC(O)NHC _n H_2n+1 (n = 6–10) were synthesized by the reaction of diphenylphosphoryl isocyanate with primary n-alkylamines C _n H_2n+1NH₂. The products (especially N-diphenylphosphoryl-N′-n-octylurea) are efficient extractants capable of extracting actinides and lanthanides from nitric acid solutions with high distribution coefficients. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 374–379, February, 2008.     

5-(2′-Carboxyphnyl) Azo-8-quinolinol as a Sensitive Reagent for Extractive Spectrophotometric Determination of Nickel

Abstract

A new sensitive extractive spectrophotometric method for the determination of nickel in sub-microgram level is discussed. 5-(2′-carboxyphenyl) azo-8-quinolinol reats with nickel at pH 5.2 to 6.1 to produce a wine red complex extractable in isomayl alcohol. The complex is stable for 24 hrs. Beer's law is obeyed in the range 0.04 to 0.60 ug of nickel per ml. The molar absorptivity and Sandell's sensitivity of the method are 5.5 × 10⁴1. mol^?1 cm^?1 and 0.001 μg cm^?2, respectively, at wavelength of maximum absorption (λ max 540 nm). Effects of diverse ions and variables have been studied in detail. The method has been applied to the determination of nickel in alloys like manganin, constantan, german silver, bronze, steel and in geological samples. Features of the method include high sensitivity, excelllent reproducibility and reliability.     

Synthesis, spectroscopic studies of new water-soluble Co(II) and Cu(II) macrocyclic complexes of 4,15-bis(2-hydroxyethyl)-2,4,6,13,15,17-hexaazatricyclodocosane: their interaction studies with calf thymus DNA and guanosine 5′ monophosphate

New water soluble Co(II) 1, Ni(II) 2 and Cu(II) 3 complexes of 4,15-bis(2-hydroxyethyl)-2,4,6,13,15,17-hexaazatricyclodocosane Co(II) were synthesized and characterized by various techniques, viz. elemental analysis, conductivity measurements, infrared, electronic, ESI-MS, ¹H and ¹³C NMR spectroscopy. Molar conductance measurements in aqueous solution showed that complexes 1, 2 and 3 are ionic in nature. On the basis of spectroscopic data, a square planar geometry was assigned to the complexes involving four N-atoms of the two cyclohexane moieties. Interaction studies of 1 and 3 with CT-DNA were carried using UV/Visible absorption spectroscopy, fluorescence spectrophotometry, cyclic voltammetry and viscosity measurements. Absorption spectral traces reveal 27.7 and 23.3% hyperchromism for complexes 1 and 3, respectively indicative of strong binding to CT-DNA. These results were authenticated by fluorescence quenching experiments and viscosity measurements. The intrinsic binding constants K _b of 1 and 3 are 2.94 × 10⁴ and 2.71 × 10⁴ M^?1, respectively. Early transition metals show preference for O6 position while later ones copper and cobalt prefer N7 position of DNA base guanine. To validate this hypothesis, interaction studies of copper (II) and cobalt (II) complexes were carried out with 5′GMP, which revealed electrostatic interactions are more favored along with hydrogen bonding than coordinate covalent interaction to N7 position of guanine.     

Synthesis and applications of (5-substituted benzimidazolo)-benzo-15-crown-5 and 4,4′-bis-benzimidazolo-dibenzo-15-crown-5 for the colorimetric detection of Au3+

In the present work, we have reported the synthesis of benzimidazoles functionalized crown ether derivatives of 4-formyl benzo-15-crown-5/4,4′-diformyl dibenzo-15-crown-5 and substituted diamine pyridine using sulfamic acid as a catalyst in DMSO. These molecules are used for the colorimetric determination of Au³⁺ selectively among other metal cations such as Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Au³⁺ and Ag⁺ ions_.