Non-isothermal studies of adduct molecules of metallic halides with oxo-compounds in solid state. V

Non-isothermal studies of some adduct molecules of metallic halides with tetrahydropyran as the type MX₂(THP)_y in solid state, were carried out with a Derivatograph, where M  Mn(II), Co(II), Ni(II), Cu(II) or Cd(II), XCl^- or Br^-, THPtetrahydropyran and y0.1–1. These adduct molecules lost tetrahydropyran in single or multiple steps upon heating. Thermally stable intermediate products were isolated and characterised by elemental analysis and IR spectral measurement. The activation energy for each step of decomposition of the adduct was evaluated from the analysis of TG, DTG and DTA curves of the respective derivatogram. The enthalpy change was evaluated from the DTA peak area and the order of reaction was found to be unity, for each step of decomposition. Thermal parameters for the above adducts were compared with the adducts of other oxocompounds like dioxan, tetrahydrofuran, ethylene glycol dimethyl ether and diisopropyl ether.     

Excess volumes and isobaric heat capacities of diisopropyl ether with several alkanols at 298.15 K: Application of the symmetrical extended real associated solution model

Excess molar volumes v^E and isobaric heat capacities C_p^E at 298.15 K were measured for 11 mixtures of diisopropyl ether (DIPE)+alcohol (from methanol to 1-undecanol), DIPE with n-heptane and 2,4-dimethylpentane with 1-octanol. Moreover the excess molar enthalpy h^E of DIPE with n-heptane at the same temperature was also measured in order to obtain the self-association parameters of the symmetrical extended real associated solution (SERAS) model for DIPE. Parameters of the SERAS model corresponding to the interaction of DIPE with each alcohol were obtained by fitting v^E data reported here and h^E data taken from a previous work. The results obtained are compared with those from the literature obtained by using the ERAS model in the traditional way for several of the studied mixtures. C_p^E curves are qualitatively explained in terms of the SERAS model.     

Reactions of OH* and eaq − with uracil and thymine in the presence of Cu(II) ions in dilute aqueous solutions: A pulse radiolysis study

The reactions of OH^* and e_aq ^? adducts of uracil and thymine with Cu(II) ions in aqueous solutions were followed by pulse radiolysis. The transient absorption spectra of the OH^* adducts of uracil when followed in the presence of Cu(II) ions show growth in absorption at wavelengths 420 and 350 nm at 15 μs and 65 μs after the pulse respectively. Similar transient absorption spectra of thymine showed growth in absorption at wavelengths 390 and 320 nm at 38 μs and 65 μs after the pulse respectively. The rates of electron transfer from the OH^* adducts of uracil and thymine to various Cu(II) compounds when monitored at 360 nm lie between 10⁶ and 10⁸ mol^?1 dm³ s^?1 this implies that the electron transfer process is not an efficient process. Low rate constants coupled with the spectral changes suggest formation of a radical copper adduct which decays by water insertion to give cis-glycols as the major product. The electron transfer from the electron adducts of uracil and thymine to various copper(II) compounds takes place more efficiently (rate constants of the order of 10⁸ and 10⁹ mol^?1 dm³ s^?1) compared with that from the OH^* adducts. The t-butanol radicals formed on scavenging the OH^* radicals also produce adducts with Cu(I) ions which are formed on oxidation of the electron adducts by Cu(II) ions. This adduct has absorption around 400 nm both in the case of uracil and thymine.     

Sensitive flotation-spectrophotometric determination of gold based on the gold(III)/bromide/rhodamine 6G system

A very flotation-spectrophotometric method based on the gold(III)/bromide/ tribromide/rhodamine 6G (R6G) system is described. In the presence of bromine, the dibromoderivative (R6G-Br) is formed. The gold compound is floated with di-isopropyl ether, washed with 1 M sulphuric acid and dissolved in methanol, and the absorbance of the solution is measured at 545 nm. The floated compounds is considered to be an adduct of the formula [(R6G-Br⁺)(AuBr^-₄)] · 12[(R6G-Br⁺)[Br^-₃)]. The apparent molar absorptivity is 11.4 × 10⁵] mol^-1 cm^-1. Important interference are Pd, Ag, Hg(II) and Tl(III), belong to the most interfering metals; after a preliminary extraction of gold from acidic bromide medium into di-isopropyl ether, only thallium(III) interferes significantly. The proposed method is applied to determining gold traces in a blister copper samle. Results obtained prove the good precision and accuracy of the method.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. VI

Non-isothermal studies of the dehydration of double salt hydrates of the type K₂AB₄·M(II)SO₄·6H₂O where AB₄BeF^2?₄ or SeO^2?₄ and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D₂O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ～11-～19 kcal mol^?1     

Sensitive spectrophotometric determination of palladium with tin(II) chlorided and rhodamine-6g after flotation

Palladium is determined by reaction with tin(II) chloride and rhordamine-6G in hydrochloric acid medium, flotation of the ion-association complex, [(R6G⁺)₂Pd (SnCl^?₃)₄]·[(R6G⁺) (SnCl^?₃] with di-isopropyl ether, and dissolution in acetone for spectrophotometry. The molar absorptivity is 2.84 x 10⁵ l mol^?1 cm^?1 at 530 nm; Beer's law is obeyed in the range 0.05–0.35 μg Pd ml^?1. Other platinum metals and silver interfere. Traces of palladium in silver metal are determined after extraction of palladium with dimethylglyoxime in chloroform.     

Complexation of selenium to (R)‐Rh2(MTPA)4: thermodynamics and stoichiometry

Variable‐temperature ¹H and ⁷⁷Se NMR data for 3‐phenylselenenyl‐1‐phenyl‐1‐propene (1) in the presence of Rh₂(MTPA)₄ (Rh*) prove that the equilibria are strongly shifted towards the adduct Rh*···1; free selenide molecules cannot be detected as long as uncomplexed rhodium atoms are available. In the case of excess Rh*, both 1 : 2 and 1 : 1 adducts (Rh* vs 1) are formed, and the latter is slightly favoured. With excess selenide, the system strongly favours the complexation of two selenide molecules (1 : 2 adduct), i.e. one at each rhodium atom. In this situation, intermolecular selenide exchange can be monitored by variable‐temperature ¹H NMR spectroscopy and the energy barrier is estimated to be 54–55 kJ mol^?1. Copyright © 2001 John Wiley & Sons, Ltd.     

Lewis acid-base titrations employing megacycle-frequency oscillators : Part III. Preparation,isolation and characterization of some adducts predicted from titration curves

Adducts of stannic chloride with thirteen oxygen bases, isolated as solids from benzene or heptane solution, were characterized by analysis and melting point behavior; several of these are new compounds. Diethyl ether, n-dibutyl ether and tetrahydrofuran form AB₂ adducts; p-dioxane, in conformity with its being a diacid base, forms only a 1 : 1 species. Methyl, ethyl, n-propyl and n-butyl alcohols form simple AB₂ adducts at room temperature which on recrystallization from boiling solvent give SnCl₃(OR)ROH; iso-propyl alcohol gives only the AB₂ adduct; tert.-butyl alcohol only forms SnCl₃. OC₄H₉ (steric hindrance probably prevents formation of the AB2 adduct). Water gives a AB₄ or AB₅ adduct.Adducts of aluminum chloride with three nitrogen bases were similarly prepared from acetonitrile solution. Pyridine forms a 1 : 1 species. Acetonitrile itself forms a AB₂ species. Piperidine forms a AB₃ species. The latter two adducts support the view that AlCI₃ can form other than 1 : 1 adducts with nitrogen bases.     

Mass spectrometric characterization of a series of adenosylated peptides acting as bisubstrate analogs of protein kinases

We are currently developing strategies to synthesize bisubstrate analogs as potential inhibitors of serine and tyrosine protein kinases; several such analogs have been synthesized. The initial target proteins were the cAMP dependent protein kinase (cAPK) and the Ca⁺²/calmodulin dependent protein kinase (CaM kiiase II). These bisubstrate analogs were based on either known peptide substrates such as kemptide, a seven amino acid peptide substrate of cAPK, or on inhibitory peptides such as a seventeen amino acid peptide encompassing the autoinhibitory domain of CaM kinase II. Peptides containing a single phosphoserine group were first synthesized and then adenosine 5′-monophosphate (AMP), adenosine 5′-diphosphate (ADP), or adenosine 5′-triphosphate (ATP) was coupled through the serine phosphate with prior activation by 1,1-carbonyldiimidazole using either a solution or solid phase reaction scheme. In this current study, we report the characterization of the bisubstrate analogs by liquid secondary ionization mass spectrometry (LSIMS), matrix-assisted laser desorption mass spectrometry (MALDI), and tandem mass spectrometry (MS/MS). In the positive-ion mode, the LSIMS spectra of the bisubstrate analogs yielded a series of molecular ions containing mono-, di-, and trivalent cation adducts. Cation adducts were absent in the negative-ion mode where the dominant species were deprotonated molecular ions, [M ? H]^?, making this latter technique more useful for confirming product identity and assessing purity. Analysis of these compounds by MALDI in both the positive- and negative-ion modes yielded molecular ions which also contained metal ion adducts, although they were limited primarily to Fe⁺² adducts. Unlike LSIMS, the MALDI spectra showed no evidence for the elimination of the phosphoadenosine or other structural moieties. When these compounds were subjected to high energy collision-induced dissociation (CID), the dominant fragmentation pathways under positive-ion MS/MS conditions resulted from cleavage of the phosphate linkages to the adenosine moiety with charge retention on the peptide, although a major peak for 5′-deoxyadenosine was also seen at m/z 250. Charge retention in the negative-ion mode was most pronounced for ion fragments containing the highly acidic phosphate moieties and yielded phosphoadenosine related ions, for example, (AMP-H)^?, (AMP-H-H₂O)^?, (ADP-H)^?, etc., as well as ions originating from the phosphate linker such as PO₃ ^?, H₂PO₄ ^?, HP₂O₆ ^?, H₃P₂O₇ ^?, and H₂P₃O₉ ^?. The largest phosphoadenosine ion in the negative-ion CID spectra for each bisubstrate analog, for example, m/z 426 (ADP-H)^?, m/z 506 (ATP-H)^?, or m/z 586 (AP₄-H)^?, indicated that the desired covalent modification had been formed between the phosphoserine and AP_n moieties.     

High resolution mass spectrometry based profiling of diet-related deoxyribonucleic acid adducts

Exposure of DNA to endo- and exogenous DNA binding chemicals can result in the formation of DNA adducts and is believed to be the first step in chemically induced carcinogenesis. DNA adductomics is a relatively new field of research which studies the formation of known and unknown DNA adducts in DNA due to exposure to genotoxic chemicals. In this study, a new UHPLC-HRMS(/MS)-based DNA adduct detection method was developed and validated. Four targeted DNA adducts, which all have been linked to dietary genotoxicity, were included in the described method; O⁶-methylguanine (O⁶-MeG), O⁶-carboxymethylguanine (O⁶-CMG), pyrimidopurinone (M1G) and methylhydroxypropanoguanine (CroG). As a supplementary tool for DNA adductomics, a DNA adduct database, which currently contains 123 different diet-related DNA adducts, was constructed. By means of the newly developed method and database, all 4 targeted DNA adducts and 32 untargeted DNA adducts could be detected in different DNA samples. The obtained results clearly demonstrate the merit of the described method for both targeted and untargeted DNA adduct detection in vitro and in vivo, whilst the diet-related DNA adduct database can distinctly facilitate data interpretation.     

Carbonyl derivatives of phthalocyaninatoiron(II), especially those containing group VI axial donor atoms. Crystal and molecular structure of carbonyl(N,N-dimethylformamide)phthalocyaninatoiron(II) and mössbauer studies of some of the products

The carbonyl adduct of phthalocyaninatoiron(II), FePc, with N,N-dimethylformamide (DMF) as axial ligand, FePc(CO)DMF, was prepared by the reaction of iron carbonyls, Fe(CO)₅ or Fe₂(CO)₉, with o-phthaalonitrile in DMF as solvent. Several carbonyl adducts of FePc of general formula FePc (CO)L are reported, with L being a ligand with oxygen, sulphur and nitrogen donor atoms (L = tetrahydrofuran, H₂O, CH₃OH, dimethylsulphoxide, tetrahydrothiophene, ammonia, n-propylamine, diethylamine, triethylamine). The crystal and molecular structure of FePc(CO)DMF·DMF was investigaed by X-ray diffraction methods. The compound has a monoclinic unit cell and space group P2₁/n, a 9.86(1), b 17.35(3), c 19.79(4) », β 87.9(2)°, Z = 4, U 3383 »³, D₃ 1.458 g cm^?3. The iron atom is hexacoordinated to the four inner nitrogen atoms of the macrocyle, to carbon monoxide (Fe—C distance 1.72(2) ») and to DMF (Fe—O distance 2.07(1) »). The extra DMF occupies lattice sites. All of the compounds reported in this paper are substantially diamagnetic. Mössbauer spectra show typical isomer shift parameters for the bis-adducts and for the carbonyl adduct, substantially independent of the nature of the axial ligand. The quadrupole splitting parameter of the carbonyl adducts is strongly affected by the nature of the axial ligand.     

Complexation of rhodium(II) tetracarboxylates with aliphatic diamines in solution: 1H and 13C NMR and DFT investigations

The complexation of rhodium(II) tetraacetate, tetrakistrifluoroaceate and tetrakisoctanoate with a set of diamines (ethane‐1,diamine, propane‐1,3‐diamine and nonane‐1,9‐diamine) and their N,N′‐dimethyl and N,N,N′,N′‐tetramethyl derivatives in chloroform solution has been investigated by ¹H and ¹³C NMR spectroscopy and density functional theory (DFT) modelling. A combination of two bifunctional reagents, diamines and rhodium(II) tetracarboxylates, yielded insoluble coordination polymers as main products of complexation and various adducts in the solution, being in equilibrium with insoluble material. All diamines initially formed the 2 : 1 (blue), (1 : 1)_n oligomeric (red) and 1 : 2 (red) axial adducts in solution, depending on the reagents' molar ratio. Adducts of primary and secondary diamines decomposed in the presence of ligand excess, the former via unstable equatorial complexes. The complexation of secondary diamines slowed down the inversion at nitrogen atoms in NH(CH₃) functional groups and resulted in the formation of nitrogenous stereogenic centres, detectable by NMR. Axial adducts of tertiary diamines appeared to be relatively stable. The presence of long aliphatic chains in molecules (adducts of nonane‐1,9‐diamines or rhodium(II) tetrakisoctanoate) increased adduct solubility. Hypothetical structures of the equatorial adduct of rhodium(II) tetraacetate with ethane‐1,2‐diamine and their NMR parameters were explored by means of DFT calculations. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal decomposition reactions of metal carboxylato complexes in the solid state. I.: Thermographic and differential thermal studies of metal oxalato,malonato and succinato complexes

Thermal investigation of metal carboxylato complexes of the first transition metals, Mn(II), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) and non-transition metals like Zn(II) and Cd(II) in the solid state has been carried out under non-isothermal conditions in nitrogen atmosphere by simultaneous TG and DTA. TG and DTA curves inferred that the thermal stability of the complex decreased approximately with the increase of the standard potential of the central metal ion. The thermal parameters like activation energy, E_a, enthalpy change, ΔH, and entropy change, ΔS, corresponding to the dehydration and decomposition of the complexes are determined from TG and DTA curves by standard methods. A linear correlation is found between ΔH and ΔS and E_a and ΔS in dehydration and decomposition processes. DTA curves show an irreversible phase transition for Na₂Mn(mal)₂], Na₂[Cu(mal)₂] and Na₂,[Co(suc)₂] complexes. The residual products in these decomposition processes being a mixture of two oxides, of oxide and carbonate or a mixture of two carbonates.     

Influence of sodium addition on taurine adduct formation generated in acetic acid/acetate salt buffer applied in LC–MS/MS analysis

To investigate the influence of sodium ion addition on analyte adduct formation generated in acetic acid/acetate salt buffer appropriate infusion experiments of a 1 and 10 μg/mL taurine solution prepared both in methanol with a 1 mmol L^?1/10 mmol L^?1 CH₃COONH₄/CH₃COOH buffer and with a 1 mmol L^?1/10 mmol L^?1 CH₃COONa/CH₃COOH buffer were performed. The results achieved revealed that sodium ion concentration has a relevant influence on taurine adduct formation in the negative electrospray ionisation mode since depending on conditions applied different analyte adducts are favored. Sodium ions which originate from the glassware/chemicals make an effective detection of taurine dimer adducts possible, but taurine adducts with sodium acetate are not formed effectively. On the other side sodium ion addition enables an effective taurine adduct formation with sodium acetate, but taurine dimer based adducts can be observed only at higher analyte concentrations.     

Mass spectral fragmentation pathways of N-acetylnitramines: 1-acetylhexahydro-3,5-dinitro-1,3,5-triazine and 1-acetyloctahydro-3,5,7-trinitro-1,3,5,7-tetrazocine

Mass spectra of the N-acetylnitramines l-acetylhexahydro-3,5-dinitro-l,3,5-triazine (TAX) and 1-acetyloctahydro-3,5,7-trinitro-l,3,5,7-tetrazocine (SEX) were recorded in electron impact (EI) and positive and negative chemical ionization (PCI and NCI) modes, and the fragmentation pathways were compared with those of other nitramines which have been well documented and characterized. Unexpectedly, for both acetylnitramines in the EI mode (and in the PCI mode) proton adducts were the only molecular ion species observed; in neither mode was there evidence for higher adducts. In contrast, for TAX in the NCI mode the [M + NO₂]^? adduct was the second most abundant ion (70%); relatively small amounts of the [M + NO]^? adduct (2%) and the hydrogen adduct [MH]^? (3%) were observed. Under identical NCI conditions no molecular ion species or adduct ions were detected for SEX; the ion of highest m/z corresponded to loss of NO₂ or HNO₂ from a molecular ion species. The findings of collision-induced dissociation experiments are also discussed.     

DSC-TG studies on kinetics of curing and thermal decomposition of epoxy–ether amine systems

The cure behavior of diglycidyl ether of bisphenol A with a simple ether amine (4,7,10, trioxa -1,13, tridecane diamine), system I and a polyether amine (polypropylene glycol block polyethylene glycol block polypropylene glycol bis 2 amino propyl ether), system II was compared by Differential Scanning Calorimetry. The exothermicity of the curing reaction of system I is higher than that of system II (316 ± 15 J g^?1 for System I and 230 ± 15 J g^?1 for system II). Kinetic parameters viz., activation energy, pre-exponential factor, and rate constant for curing were evaluated by Kissinger method and Kissinger–Akahira–Sunose isoconversion method. Both systems showed low glass transition temperatures and System II shows a much lower T _g (?38 °C) than system I (26 °C). The thermogravimetric analysis of the two cured epoxy amine systems showed comparable thermal stability.     

Thermal decomposition reactions of metal carboxylato complexes in the solid state: II. Thermographic and differential thermal studies of metal oxalato,malonato and succinato complexes

The thermal investigations of metal carboxylato complexes of the first transition metals, Mn(II), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) and non transition metals like Zn(II) and Cd(II) in solid state were carried out under non-isothermal condition in nitrogen atmopshere by thermogravimetric (TG) and differential thermal analyses (DTA) methods. The results of DTA curves inferred that the thermal stability of the complex decreased approximately with the increase of standard potential of the central metal ion. The thermal parameters like activation energy (E_a¹), enthalpy change (ΔH) and entropy change (ΔS) corresponding to deaquation, deammoniation and decomposition processes occurred simultaneously or separately were determined from TG and DTA curves by the standard methods. A linear correlation has been found in the plots of ΔH vs. ΔS and E_a¹ vs. ΔS in deaquation, deammoniation and decomposition processes. An irreversible phase transition was noticed for H₂[Mn(suc)₂] and H₂[Co(suc)₂] complexes in DTA curves. The residual pyrolysed products were metal carbonates.     

Ion cyclotron resonance studies of ambident nucleophiles. The reactions of the trimethylsilyl cation with alkenyl ethers and alkoxy ketones

Alkenyl ethers react through oxygen with Me₃Si⁺ to yield intermediates which undergo characteristic fragmentations. In the particular case of allyl ethers, the decomposing adduct undergoes several fragmentations through the allyl substituent via 6-membered transition states. The reaction between Me₃Si⁺ and alkoxy carbonyl derivatives yields both ‘ether’ and ‘keto’ adducts, characterized by their fragmentation patterns. The ‘ether’ adducts formed from Me₃Si⁺ and alkoxy acetones undergo the same basic eliminations as those observed for the allyl ether/Me₃Si⁺ systems.     

Effect of copper(II) ions on the stability of spin adducts formed by the reaction of 5,5-dimethylpyrroline-N-oxide with hydroxyl and hydroxylalkyl radicals

The reactions of copper(II) species with spin adducts formed by reaction of OH·, CH₃CHOH or (CH₃)₂COH with DMPO (5,5-dimethylpyrroline-N-oxide) have been investigated. The spin adducts prepared by -irradiation of appropriate solutions were detected using esr. Copper(II) in the form of aqua, phen, or 1-alanine complexes reacted rapidly with the OH· adduct to give products that gave no esr signal, but with the hydroxylalkyl adducts, reacted to give a new 9-line esr signal, identified as due to the H· adduct, (DMPO-H·). Measurement of the yield of Cu(phen) ₂ ⁺ formed by reaction of the copper(II) complex with the spin adduct showed that approximately 25% of the radiation-produced radicals formed esr detectable spin adducts. The implications of these findings for the use of spin trapping to detect radical intermediates in biological systems is discussed.