Investigation of ibuprofen drug using mass spectrometry,thermal analyses,and semi-empirical molecular orbital calculation

Ibuprofen (C₁₅H₁₈O₂) is an anti-inflammatory drug. It is important to investigate its structure to know the active groups and weak bond responsible for its medical activity. Consequently in the present study, ibuprofen was investigated by mass spectrometry (MS) and thermal analyses (TAs) (TG/DTG and DTA), and confirmed by semi-empirical molecular orbital (MO) calculation using PM3 procedure, on the neutral and positively charged forms of the drug. These calculations included bond order, bond length, and bond strain, and charge distribution, heat of formation, and ionization energy. The mass spectra and thermal analysis fragmentation pathways were proposed and compared to each other to select the most suitable scheme representing the correct fragmentation pathway of the drug in both techniques. From the electron ionization (EI) mass spectra, the primary cleavage site of the charged molecule is because of the rupture of COOH group (the lowest bond order) followed by propyl group loss. The TAs of the drug revealed high response of the drug to the temperature variation with very fast rate. It decomposed in several sequential steps in the temperature range 25–360 °C. The initial thermal decomposition is similar to that obtained by MS fragmentation of the first rupture (COOH), then subsequent one of propyl loss, and finally of ethylene loss. These mass losses appear as endothermic peaks required energy values of −214.83, −895.95, and −211.10 J g⁻¹, respectively. The order of these losses is also related to the values of the MO calculation parameters. Therefore, the comparison between MS and TA helps in the selection of the proper pathway representing the decomposition of this drug to give its metabolites in in vivo system. This comparison is also successfully confirmed by MO calculations.     

Mass spectra of gliclazide drug at various ion sources temperature

Gliclazide (GL, C₁₅H₂₁N₃O₃S) drug is used as non-insulin-dependant diabetes mellitus. The drug was investigated using thermal analysis (TA) measurements (TG/DTG) and electron impact mass spectral (EI–MS) fragmentation at 70 eV techniques. The mass spectra of GL at different values of ion source temperatures (400, 416, 425, and 440 K) are recorded and investigated. Semiempirical MO calculation, using PM3 procedure, has been carried out on neutral molecule and positively charged species. These calculations included bond length, bond order, bond strain, partial charge distribution, ionization energy, and heats of formation (ΔH _f). PM3 procedure provides a basis for fine distinction among sites of initial bond cleavage, which is crucial to the rationalization of subsequent fragmentation of the molecule. The primary fragmentation pathway in both TA and MS (at different values of ion source temperature) is initiated by S–N bond rupture. TA and DTG show one main weight loss at 250.38 °C and four peaks at 271.6, 360.99, 427.93 and 479.17 °C in DTA, which may be attributed to various fragments. Also, the rate constant (K′) of thermal degradation has been tested isothermally at 210 and 600 °C. The calculated rate values are 9.6 × 10⁻³ and 0.33 × 10⁻³ s⁻¹, respectively, and discussed. In MS, the effect of ion source temperature on mass spectral fragmentation processes is discussed on the basis of energy considerations using quasi equilibrium theory.     

Mass spectrometric investigation of buspirone drug in comparison with thermal analyses and MO-calculations

The buspirone drug is usually present as hydrochloride form of general formula C(21)H(31)N(5)O(2).HCl, and of molecular weight (MW)=421.96. It is an analgesic anxiolytic drug, which does not cause sedative or depression of central nervous system. In the present work it is investigated using electron impact mass spectral (EI-MS) fragmentation at 70 eV, in comparison with thermal analyses (TA) measurements (TG/DTG and DTA) and molecular orbital calculation (MOC). Semi-empirical MO calculation, PM3 procedure, has been carried out on buspirone both as neutral molecule (in TA) and the corresponding positively charged species (in MS). The calculated MOC parameters include bond length, bond order, particle charge distribution on different atoms and heats of formation. The fragmentation pathways of buspirone in EI-MS lead to the formation of important primary and secondary fragment ions. The mechanism of formation of some important daughter ions can be illuminated from comparing with that obtained using electrospray ESIMS/MS mode mass spectrometer through the accurate mass measurement determination. The losses of the intermediate aliphatic part (CH2)4 due to cleavage of N-C bond from both sides is the primary cleavage in both techniques (MS and TA). The PM3 provides a base for fine distinction among sites of initial bond cleavage and subsequent fragmentation of drug molecule in both TA and MS techniques; consequently the choice of the correct pathway of such fragmentation knowing this structural session of bonds can be used to decide the active sites of this drug responsible for its chemical, biological and medical reactivity.     

Multiclass analysis on repaglinide,flubendazole, robenidine hydrochloride and danofloxacin drugs

The drugs under study; repaglinide (Repag), flubendazole (Flu), robenidine hydrochloride (Roben) and danofloxacin (Dano) are antidiabetic, anthelmintic, anticoccidial, and antibiotic drugs. In the present study, they are investigated using electron impact mass spectral (EI-MS) fragmentation at 70 eV, in comparison with thermal analyses measurements (TGA/DrTGA and DTA) and molecular orbital calculation (MO). Semi-empirical MO calculation, AM1 procedure, has been carried out on Repag, Flu, Roben and Dano both as neutral molecules (in TA) and the corresponding positively charged species (in MS). The calculated MO parameters include bond length, bond order, charge distribution on different atoms and heat of formation. The fragmentation pathways of Repag, Flu, Roben and Dano in EI-MS led to the formation of important primary and secondary fragment ions. The mechanism of formation of some important daughter ions can be illuminated from comparing with that obtained using mass spectrometer through the accurate mass measurement determination. The MO provides a base for fine distinction among sites of initial bond cleavage and subsequent fragmentation of drug molecules in both thermal analysis and MS techniques. The activation thermodynamic parameters, such as, (activation energy E¹), (enthalpy ΔH¹), (entropy ΔS¹) and (Gibbs free energy ΔG¹) are calculated from the DrTGA curves using Coats–Redfern and Horowitz–Mitzger methods.     

Thermal and mass spectral characterization of novel azo dyes of p-acetoamidophenol in comparison with Hammett substituent effects and molecular orbital calculations

Four novel azo compounds were synthesized: o-phenylazo-(C₁₄H₁₃N₃O₂) (I), p-bromo-o-phenylazo-(C₁₄H₁₃BrN₃O₂) (II), p-methoxy-o-phenylazo-(C₁₅H₁₆N₃O₃) (III), and p-nitro-o-phenylazo-p-acetamidophenol (C₁₄H₁₃N₄O₄) (IV). These compounds were carefully investigated using elemental analyses, IR, and thermal analyses (TA) in comparison with electron ionization (EI) mass spectral (MS) fragmentation at 70 eV. Semi-empirical MO calculation, PM3 procedure, has been carried out on the four azo dyes (I–IV), both as neutral molecules and the corresponding positively charged molecular ions. These included molecular geometries (bond length, bond order, and charge distribution, heats of formation, and ionization energies). The mass spectral fragmentation pathways and thermal decomposition mechanisms were reported and interpreted on the basis of molecular orbital (MO) calculations. They are found to be highly correlated to each other. Also, the Hammett’s effects of p-methoxy, p-bromo, and p-nitro-substituents of phenyl azo groups on the thermal stability of these dyes (I–IV) are studied by experimental (TA and MS) in comparison with MO calculations, and the data obtained are discussed. This research aimed chiefly to throw more light on the structures of the four prepared azo derivatives of acetoamidophenol (p-cetamol). The data refering to the thermal stability of these dyes can be used in industry for effective dyeing purposes under different thermal conditions.     

A theoretical charge density study on nitrogen-rich 4,4′,5,5′-tetranitro-2,2′-bi-1H-imidazole (TNBI) energetic molecule

The bond topological and electrostatic properties of nitrogen-rich 4,4′,5,5′-tetranitro-2,2′-bi-1H-imidazole (TNBI) energetic molecule have been calculated from the DFT method with the basis set 6-311G** and the AIM theory. The optimized geometry of this molecule is almost matched with the experimental geometric parameters. The electron density at the bond critical point and the Laplacian of electron density of C–NO₂ bonds are not equal, one of them is much weaker than the other. Similar trend exists in the C–N bonds of the imidazole ring of the molecule. The ratio of the bond dissociation energy (BDE) of the weakest bond to the molecular total energy exhibits nearly a linear correlation with the impact sensitivity; its h ₅₀% value is ~32.01 cm. The electrostatic potential around both the nitro groups are found unequal; the NO₂ group of weakest C–NO₂ bond exhibits an extended electronegative region.     

Voltammetric, Potentiometric and Spectrophotometric Studies of Some Hydrazones and Their Metal Complexes in Ethanolic-Aqueous Buffered Solutions

Summary. The electrochemical behavior of some hydrazones derived from 6-chloro-2-hydrazinopyridine in the Britton-Robinson universal buffer of pH 2–11 containing 35% ethanol was investigated at the mercury electrode using dc-polarography, controlled-potential coulometry, and cyclic voltammetry techniques. The examined hydrazones were reduced in solutions of pH < 9 in a single 4-electron diffusion-controlled irreversible step corresponding to both the saturation of –N=C< double bond and cleavage of the –HN–NH– single bond of the hydrazone molecule via the consumption of two electrons for each center. Whereas the starting compound, 6-chloro-2-hydrazinopyridine, was reduced in a single 2-electron diffusion-controlled irreversible step corresponding to cleavage of its –NH–NH₂ single bond. The mechanistic pathway of the electrode reaction of the studied compounds was elucidated and discussed. The pK_a values of the examined hydrazones and the stoichiometry of their complexes in solution with some transition metal ions were determined spectrophotometrically. The dissociation constants and the thermodynamic parameters of the investigated hydrazones, and the stability constants of their metal complexes in solution were determined potentiometrically.     

Electron Transfer Dissociation (ETD) of Peptides Containing Intrachain Disulfide Bonds

The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z + 33 Da, c + 32 Da, and z–32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N–Cα backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N–Cα bond was cleaved first, and radical-driven reactions caused cleavage at either an S–S bond or an S–C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%–100% of possible backbone fragmentation.     

Novel C<Subscript>β</Subscript>–C<Subscript>γ</Subscript> Bond Cleavages of Tryptophan-Containing Peptide Radical Cations

In this study, we observed unprecedented cleavages of the C_β–C_γ bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M^•+) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M – 116]⁺ ions. The formation of an α-carbon radical intermediate at the tryptophan residue for the subsequent C_β–C_γ bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH – 43]⁺ and [WGGGH – 116]⁺, obtained from the CID of [LGGGH]^•+ and [WGGGH]^•+, respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind]^•-2), in agreement with the CID data for [WGGGH]^•+ and [W_1-CH3GGGH]^•+; replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C_β–C_γ bond cleavage. Hydrogen atom transfer or proton transfer to the γ-carbon atom of the tryptophan residue weakens the C_β–C_γ bond and, therefore, decreases the dissociation energy barrier dramatically.     

A Density Functional Investigation on C2Aun+ (n?=?1, 3, 5) and C2Aun (n?=?2, 4, 6): from Gold Terminals, Gold Bridges, to Gold Triangles

A systematic density functional theory investigation on C₂Au _n ⁺ (n = 1,3,5) and C₂Au _n (n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like C_s C₂Au⁺ (C=C–Au⁺) and D_∞h C₂Au₂ (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C_2v C₂Au₃ ⁺ ([Au–C≡C–Au]Au⁺) and C_s C₂HAu₂ ⁺([H–C≡C–Au]Au⁺). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au₃) in the head-on coordinated C_2v C₂Au₄ (Au–C≡C–Au₃) and the side-on coordinated C_2v C₂Au₅ ⁺ ([Au–C≡C–Au]Au₃ ⁺). Similar –Au₃ triangular units exist in the head-on coordinated C_2v C₂HAu₃ (H–C≡C–Au₃) and D_2d C₂Au₆ (Au₃–C≡C–Au₃). The existence of stable –Au₃ triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au₃ triangles originates from the fact that an equilateral D_3h Au₃ ⁺ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature. The extension from H/Au analogy to H/Au₃ analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials.     

Carbon–carbon bond activation by B(OMe)3/B2pin2-mediated fragmentation borylation

Selective carbon–carbon bond activation is important in chemical industry and fundamental organic synthesis, but remains challenging. In this study, non-polar unstrained Csp²–Csp³ and Csp²–Csp² bond activation was achieved by B(OMe)₃/B₂pin₂-mediated fragmentation borylation. Various indole derivatives underwent C2-regioselective C–C bond activation to afford two C–B bonds under transition-metal-free conditions. Preliminary mechanistic investigations suggested that C–B bond formation and C–C bond cleavage probably occurred in a concerted process. This new reaction mode will stimulate the development of reactions based on inert C–C bond activation.

Non-polar unstrained Csp²–Csp³ and Csp²–Csp² bond activation was achieved via B(OMe)₃/B₂pin₂-mediated fragmentation borylation, in which C–C bond activation occurred regioselectively at the C2-position in various substituted indoles.     

Reaction of a bis(bimetallic)-supported butadiyndiyl ligand with terminal acetylenes

The bis(bimetallic) diyndiyl complex [{Fe₂(CO)₆(μ-PPh₂)}₂(μ-C≡CC≡C)] reacts readily with terminal alkynes to give a number of products. One of these has been crystallographically and spectroscopically characterised, revealing facile insertion of a terminal alkyne into one metal-C σ-bond of the precursor to give a novel tetrametallic compound which features an extended “carbon-rich” ligand. The product is derived from a Fe–C bond cleavage reaction, coupled with C–C and C–P bond formation, and further illustrates the remarkable, and as yet poorly mapped, reactivity of C₄ fragments on polymetallic frameworks. Dedicated to Professor Dieter Fenske, an inspirational pioneer of organometallic chemistry.     

Photofragmentation of a benzophenone derivative having benzylic C–O bond studied by laser flash photolysis in solution

Photochemical profiles of p-(4-phenylphenoxy)methylbenzophenone (PPMeBP) in solution were investigated by means of emission and transient absorption measurements. PPMeBP showed that fluorescence originating from the corresponding p-phenylphenoxy (PP) moiety at 295 K, and dual phosphorescence originating from the corresponding p-benzoylbenzyl (BB) and PP moieties at 77 K was observed. These observations indicated that the BB and PP moieties of PPMeBP have very little electronic conjugation. 266- and 308-nm laser flash photolyses of PPMeBP showed the formation of the p-phenylphenoxy radical, indicating that photoexcited PPMeBP undergoes C–O bond cleavage. Upon 355-nm laser photolysis of PPMeBP, the C–O bond did not dissociate, and formation of the triplet state of the PP moiety was observed. The apparent quantum yields of fragmentation of PPMeBP were found to depend on the excitation wavelength. Triplet sensitization of PPMeBP using benzophenone revealed that the C–O bond does not cleave in the triplet state of the PP moiety. Based on the schematic energy diagram for excited PPMeBP, the mechanism of the C–O bond was discussed.     

Structure of N-chloromethyllactams and features of the interaction of atoms in them as a result of ab initio calculations

Quantum-chemical calculations have been carried out by the RHF/6-31G(d) and MP2/6-31+G(d) methods of molecules of N-chloromethylpyrrolidone, N-chloromethylcaprolactam, N-chloromethyl-succinimide, and N-chloromethylphthalimide with full optimization of their geometry, and also N-chloromethylpyrrolidone molecule by the RHF/6-31G(d) method at various angles of rotation of the CH₂Cl group around the C―N bond. It was shown that the lower frequencies of the ³⁵Cl NQR of the first two molecules in comparison with the later are mainly determined by the high populations of the p _σ -orbitals of their Cl atoms. The population of the orbitals of the unshared electron pair of the N atom is practically unchanged on rotating the CH₂Cl group, but the N atom polarizes the C―Cl bond in the indicated molecule. This does not confirm the supposed p,σ*-conjugation in the Cl―C―N grouping. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1537–1544, October, 2008.     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

Thermal degradation behavior of a carboxylic acid-terminated amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)

The thermal degradation of an amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)-carboxylic acid terminated (PE-b-80%PEO–CH₂COOH) and its salt obtained as intermediary product from chemical oxidation of the end group of poly(ethylene)-b-poly(ethylene oxide) (PE-b-80%PEO) has been studied using a thermogravimetric mass spectrometry (TG/MS) coupled system. The isothermal fragmentation of PE-b-80%PEO–CH₂COOH showed a more complex fragmentation pattern than PE-b-80%PEO owing to the simultaneous occurrence of the polyether block and the carboxylic end group fragmentations. This led to the appearance of four overlapping ion current peaks of fragments with m/z 44 and two peaks relative to m/z 18 at different times by acid-terminated copolymer. For the PE-b-80%PEO copolymer, two ion current peaks associated to m/z 44 and one large peak relative to m/z 18 fragments were detected. The intermediary product (PE-b-80%PEO–CH₂COO⁻ K⁺) showed differences related to the fragmentation behavior. It has more defined ion current signals and presented characteristic peaks attributed to m/z 43 fragment at the very beginning of the thermal degradation process, which it not detected in the acid copolymer.     

A new photoproduct of 5-methylcytosine and adenine: a theoretical study

Both the cycloaddition mechanism of 5-methylcytosine with adenine and the deamination mechanism of the cycloaddition product have been studied using density functional theory method. The results suggest that the cycloaddition reaction could occur more easily through photochemical reaction pathway than through thermal reaction pathway. The obtained four-member ring structure could be easily transformed to an eight-member ring structure through bond cleavage of C₅–C₆ (the energy barrier is <2 kcal/mol). Then hydrolytic deamination reaction takes place with water assistance. The hydroxyl group of one water molecule attacks the C₄^′ atom and the hydrogen atom of another water molecule attacks N₃^′ atom to form a tetrahedral intermediate. Subsequently, the hydrogen atom of hydroxyl group transfers to N₈^′ to produce ammonia, and the amino group of the former 5-methylcytosine changes to carboxyl oxygen. Our calculations explain the phenomena that 5-methylcytosine and adenine could obtain the same photoproduct as thymine and adenine from theoretical aspects.     

Probing O-dealkylation and deamination aging processes in tabun-conjugated AChE: a computational study

The mechanisms of the aging process of tabun-conjugated acetylcholinesterase were explored using density functional theory calculations. The free energy surfaces were calculated for O-dealkylation (C–O bond breaking) and deamination (P–N bond breaking) pathways for the aging process of tabun-conjugated acetylcholinesterase as suggested by mass and crystallographic studies. Initially, the calculations were performed using tabun-conjugated serine (SUN) molecule. O-dealkylation mechanism proceeds via one-step S_N2 type process, whereas the deamination process proceeds via two steps addition–elimination reaction at the phosphorus center of SUN molecule. The recent proposal of another deamination mechanism using human butyrylcholinesterase (hBChE) conjugated with N-mono methyl analogue of tabun (TA4) has also been explored (Nachon et al. in Chem Biol Interact 187:44–48, 2010). The rate-determining activation barrier calculated for this deamination mechanism (26.3 kcal/mol) was comparable with O-dealkylation process (26.9 kcal/mol) with B3LYP/6-31+G* level of theory. To examine the influence of catalytic residue His447, additional calculations were performed with imidazole group of His447 residue. The incorporation of imidazole group of catalytic residue His447 showed marked decrease in the free energies of activation for all the studied aging processes of tabun-inhibited serine. The aging mechanisms have been explored with TA4-inhibited serine, and calculated results showed that the deamination with the rearrangement process is markedly preferred in this case, which supports the Nachon et al. proposal based on the crystallographic studies.     

Molecular structure and conformation of triphenylsilane from gas-phase electron diffraction and theoretical calculations, and structural variations in H4?nSiPhn molecules (n?=?1–4)

The molecular structure of triphenylsilane has been investigated by gas-phase electron diffraction and theoretical calculations. The electron diffraction intensities from a previous study (Rozsondai B, Hargittai I, J Organomet Chem 334:269, 1987) have been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from calculations. The free molecule has a chiral, propeller-like equilibrium conformation of C ₃ symmetry, with a twist angle of the phenyl groups τ = 39° ± 3°; the two enantiomeric conformers easily interconvert via three possible pathways. The low-frequency vibrational modes indicate that the three phenyl groups undergo large-amplitude torsional and out-of-plane bending vibrations about their respective Si–C bonds. Least-squares refinement of a model accounting for the bending vibrations gives the following bond distances and angles with estimated total errors: r _g(Si–C) = 1.874 ± 0.004 ?, 〈r _g(C–C)〉 = 1.402 ± 0.003 ?, 〈r _g(C–H)〉 = 1.102 ± 0.003 ?, and ∠_aC–Si–H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si–C bonds in H_4−n SiPh _n molecules (n = 1–4) increase gradually with n, due to π → σ*(Si–C) delocalization. They also show that the mean lengths of the ring C–C bonds are about 0.003 ? larger than in unsubstituted benzene, due to a one hundredth angstrom lengthening of the C_ipso–C_ortho bonds caused by silicon substitution. A small increase of r(Si–H) and decrease of the ipso angle with increasing number of phenyl groups is also revealed by the calculations.     

Thermal, spectral and AFM studies of calcium silicate hydrate-polymer nanocomposite material

A non-ionic polymer (poly(vinyl alcohol) (PVA)) has been incorporated into the inorganic layers of calcium silicate hydrate (C–S–H) during precipitation of quasicrystalline C–S–H from aqueous solution. C–S–H and a C–S–H-polymer nanocomposite (C–S–HPN) material were synthesized and characterized by X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR) and ¹³C cross-polarization nuclear magnetic resonance (¹³C CP NMR) spectroscopy, atomic force microscopy (AFM), thermal conductivity, thermogravimetric analysis (TG) and differential thermal analysis (DTA). Thermal conductivity of PVA, C–S–H and C–S–HPN material was studied in the temperature range 25–50°C. C–S–HPN materials exhibited the highest thermal conductivity at 25 and 50°C. The thermal conductivity increases from 25 to 50°C are 7.03, 17.46 and 14.85% for PVA, C–S–H and C–S–HPN material, respectively. Three significant decomposition temperature ranges were observed on the TG curve of C–S–HPN material.