Characterization of Fumed Alumina/Silica/Titania in the Gas Phase and in Aqueous Suspension

Fumed oxide alumina/silica/titania was studied in comparison with fumed alumina, silica, titania, alumina/silica, and titania/silica by means of XRD, ¹H NMR, IR, optical, dielectric relaxation, and photon correlation spectroscopies, electrophoresis, and quantum chemical methods. The explored Al₂O₃/SiO₂/TiO₂ consists of amorphous alumina (22 wt%), amorphous silica (28 wt%), and crystalline titania (50 wt%, with a blend of anatase (88%) and rutile (12%)) and has a wide assortment of Brønsted and Lewis acid sites, which provide a greater acidity than that of individual fumed alumina, silica, or titania and an acidity close to that of fumed alumina/silica or titania/silica. The changes in the Gibbs free energy (ΔG) of interfacial water in an aqueous suspension of Al₂O₃/SiO₂/TiO₂ are close to the ΔG values of the dispersions of pure rutile but markedly lower than those of alumina, anatase, or rutile covered by alumina and silica. The zeta potential of Al₂O₃/SiO₂/TiO₂ (pH of the isoelectric point (IEP) equals ≈3.3) is akin to that of fumed titania (pH(IEP_TiO2) ≈ 6) at pH > 6, but it significantly differs from the ζ of fumed alumina (pH(IEP_Al2O3) ≈ 9.8) at any pH value as well as those of fumed silica, titania/silica, and alumina/silica at pH < 6. The particle size distribution in the diluted aqueous suspensions of Al₂O₃/SiO₂/TiO₂ studied by means of photon correlation spectroscopy depends relatively slightly on pH in contrast to the titania/silica or alumina/silica dispersions. Theoretical calculations of oxide cluster interaction with water show a high probability of hydrolysis of Al–O–Ti and Si–O–Ti bonds strained at the interface of alumina/titania or silica/titania due to structural differences in the lattices of the corresponding individual oxides. Ab initio calculated chemical shift δ_H values of H atoms in different hydroxyl groups at the oxide clusters and in bound water molecules are in agreement with the ¹H NMR data and show a significant impact of charged particles (H₃O⁺ or OH⁻) on the average δ_H values of water droplets with (H₂O)_n at n between 2 and 48.     

Surface structure and properties of mixed fumed oxides

A variety of fumed oxides such as silica, alumina, titania, silica/alumina (SA), silica/titania (ST), and alumina/silica/titania (AST) were characterized. These oxides have different specific surface areas and different primary particle composition in the bulk and at the surface. These materials were studied by FTIR, NMR, Auger electron spectroscopy, one-pass temperature-programmed desorption with mass spectrometry control (OP TPDMS), microcalorimetry, and nitrogen adsorption. Nonlinear changes in the surface content of alumina in SA and AST and titania in ST and AST samples with increasing oxide content along with simultaneous changes in their specific surface area cause complex dependencies of the heat of immersion in water and desorption of water on heating on the structural parameters. Simultaneous analysis of changes in the surface phase composition, in the concentration of hydroxyls, and in the structural characteristics reveals that at a low content of the second phase the structural characteristics (e.g., S(BET)) are predominant; however, at a large content of these oxides the phase composition plays a more important role.     

Influence of morphology and composition of fumed oxides on changes in their structural and adsorptive characteristics on hydrothermal treatment in steam phase at different temperatures

A series of fumed oxides such as silica, titania, alumina, silica/alumina (SA), silica/titania (ST), and alumina/silica/titania (AST), initial and hydrothermally treated (HTT) in the steam phase at T(HTT)=150, 250, and 350 degrees C was studied by adsorption, AFM, XRD, FTIR, and theoretical methods. Diminution of the size of primary particles (corresponding to increasing S(BET)) of initial silica and mixed oxides results in enhancement of their structural changes on HTT with elevating T(HTT) and increasing density of packing of primary particles in the secondary structures. Relative changes in the texture of treated fumed silicas are smaller than those of mesoporous silica gels occurring under similar HTT conditions. On HTT, aggregates of primary particles and their agglomerates become denser but their surface layers become looser because of transfer of silica fragments from one particle to another, and the smaller the initial primary particles, the greater the relative diminution of the specific surface area S(BET) for the same type of primary particle packing in aggregates. Relative changes in the pore volume V(p) (or V(BJHd)) on HTT are more complex than that of S(BET), as for many samples the V(p) value increases especially at T(HTT)=150 degrees C. Alumina and titania partially inhibit structural changes on HTT, which decrease in the series silica > SA > AST approximately ST.     

Solvent effect on distribution ratio of Pd(II) in supercritical carbon dioxide extraction and solvent extraction using 2-methyl-8-quinolinol

The distribution ratio (D_M) of Pd(II) by the extraction with 2-methyl-8-quinolinol (HMQ) was determined using the supercritical carbon dioxide medium (SF-CO₂) and organic solvent media such as perfluoro-methylcyclohexane, heptane, cyclohexane, carbon tetrachloride and benzene. From experimental results of the slopes of log D_M versus pH plot and log D_M versus HMQ concentration plot, the extracted species both in the SF-CO₂ extraction (SFE) and the solvent extraction (SE) were determined to be Pd(MQ)₂. The distribution constant of HMQ (K_D,HMQ) in the SFE and SE systems were determined from the dependence of the distribution ratio of HMQ (D_HMQ) on the pH. A linear relationship was observed between log K_D,HMQ and the solubility parameter (δ) of the extraction medium based on the regular solution theory in both the SFE using SF-CO₂ at the pressure of 8.5–40 MPa and the SE systems. The difference in the slope of the log K_D,HMQ versus δ plot between the SFE and the SE systems is attributable to the extent of the specific interaction of the solute HMQ with the solvent molecules, i.e. CO₂ molecules and the organic solvent molecules. The D_M versus δ plot obtained under a given extraction condition using SF-CO₂ (11–40 MPa) and organic solvents showed clear linearity. The D_M obtained using SF-CO₂ at relatively low pressure range from 8.5 to 11 MPa was independent of the pressure and the δ of SF-CO₂, which coincides with the experimental fact that the solubility of Pd(MQ)₂ in the SF-CO₂ at 8.5–11 MPa was practically constant.     

Structural characteristics of pyrocarbon-fumed silica

Two series of pyrocarbon/fumed silica (CS) samples at different carbon concentrations C_C=0.5–64 wt.% (first series, CSI) and 2.6–53 wt.% (second series, CSII) synthesised by means of pyrolysis of CH₂Cl₂ at fumed silica substrate (S_BET=297 (CSI) and 232 (CSII) m² g⁻¹) under slightly different conditions were studied by using TEM, FTIR-PAS, DTG, and nitrogen adsorption–desorption methods. On methylene chloride carbonisation, disordered carbon deposits can form mainly in the inter-particle volume of secondary particles (aggregates of primary particles and agglomerates of aggregates) covering the surfaces of primary silica particles; therefore, marked reduction of the pore (gaps between primary particles) volume and the specific surface area is observed with increasing C_C. Estimation of distributions of the pore f_SCD(R_p) and particle f(a) sizes using a self-consistent method with binary regularisation with respect to both f_SCD(R_p) and f(a) shows that the average size of particles increases (silica particles are covered by pyrocarbon) and individual pyrocarbon particles (up to 50 nm according to TEM) also appear. Structural parameters of carbosils are characterised by nonlinear changes with increasing carbonisation time. Surface functionalities on CS samples correspond to aromatic and twinned CC bonds with contribution of oxygen-containing groups.     

Highly Dispersed X/SiO(2) and C/X/SiO(2) (X=Alumina, Titania, Alumina/Titania) in the Gas and Liquid Media

Fumed oxides, such as silica, alumina, titania, and mixed X/silicas (X=Al₂O₃ (AS), TiO₂ (TS), CVD-TiO₂, Al₂O₃/TiO₂ (AST)), pristine or covered by carbon deposits formed due to pyrolysis of cyclohexene, were studied using nitrogen adsorption–desorption, photon correlation spectroscopy particle sizing, and electrophoresis. A significant influence of the nature of surface-active sites and structural features of oxides (individual silica, mixed fumed, or prepared using chemical vapor deposition (CVD)) on the pyrolysis of cyclohexene is observed with respect to the pore size distributions due to differences between primary particles in aggregates and on their outer surfaces in the filling of channels by pyrocarbon, resulting also in a decrease in fractal dimension. Structural characteristics and dependences of the particle size distribution and electrokinetic potential of X/SiO₂ and C/X/SiO₂ on the pH of aqueous suspensions suggest that the carbon deposit covers mainly acidic sites at the X/SiO₂ interfaces and X phase patches possessing catalytic activity in pyrolysis, as the negative charge of particles is reduced by pyrocarbon grafting.     

Effect of salts on the electrical conductance of a fluorine-containing poly(carboxylic acid), PPFNA

Electrical conductance and other solution properties of aqueous solutions of a fluorine-containing poly(carboxylic acid), (poly(9H,9H-perfluoro-2,5-dimethyl-3,6-dioxa-8-nonenoic acid), PPFNA) were studied with special attention to the salt effect. This polymer dissociated strongly resulting in a low pH value in unneutralized state (β = 0, β: degree of neutralization). The specific conductance was the highest at β = 0 and decreased as β increased. A considerable increase in conductance was observed by titrating NaCl at low β, because large amounts of bound protons were released by addition of NaCl. The amounts of released protons exceeded those originally dissociated at β = 0. Such an anomalous proton liberation suggests that this polymer is a fairly strong polyacid but not a typical one such as poly(styrene sulfonic acid). Under fully neutralized state (β = 1), however, the solution conductance was lower than the sum of the polymer and NaCl added, due to polyion–salt ion interaction.     

Dynamics of 4,4'-di-n-heptylazoxybenzene (HAB) studied using dielectric and 2H NMR relaxation measurements

Results of studies of 4,4'-di-n-heptylazoxybenzene (HAB) in the isotropic, nematic and smectic A phases are presented. Two experimental methods were employed: broad band dielectric spectroscopy and nuclear magnetic resonance spectroscopy. The complex dielectric permittivity, ε*(ω)=ε'(ω)-iε'(ω), was measured in the frequency range 1 kHz-4 GHz. This allowed two main relaxation processes to be separated in all the phases studied: the low frequency (l. f.) process connected with molecular reorientations around the short axes, and the high frequency (h. f.) process connected with the rotations around the long axes. The corresponding relaxation times and activation enthalpies were obtained. The l. f. relaxation time changes step-wise at the phase transitions, whereas the h. f. relaxation time passes smoothly through all the phases. The measurement of ²H spin-lattice relaxation times was carried out throughout the mesophase range at 61.38 MHz. These data were analysed together with the relaxation times measured at 10.00 and 46.04 MHz, available from previous studies. Using suitable theoretical models the principal components of the diffusional tensor, D_‖ and D_⊥, as well as the diffusion coefficients D_R relative to the internal rotation of the phenyl rings, were determined. The results of both studies are compared and discussed.     

Structural characterisation of [Pt(NH3)4]2[W(CN)8][NO3]·2H2O donor–acceptor complex

The bimetallic [Pt(NH₃)₄]₂[W(CN)₈][NO₃]·2H₂O is characterised by single-crystal X-ray diffraction [S.G.P2₁/m(11), a=8.0418(7), b=19.122(2), c=9.0812(6) Å, Z=2]. All platinum centres have the square-plane D_4h geometry with average dimensions Pt(1)–N 2.042(2) and Pt(2)–N 2.037(10) Å. The octacyanotungstate anion has the square-antiprismatic D_4d configuration with average dimensions W(1)–C 2.164(13), C–N 1.140(12), W(1)–N 3.303(5) Å. The structure exhibits two different mutual orientations of Pt versus W units resulting in Pt(2)–W(1), W(1)^* separations of 4.77(2), 4.55(2)^* and Pt(1)–W(1) of 6.331(8) Å. A centrosymmetric structure reveals groups of two distinct columns: the first is formed by intercalated NO₃⁻ between parallel [Pt(1)(NH₃)₄]²⁺ planes and the second consists of [W(CN)₈]³⁻ interlayered by, parallel to square faces of W-antiprisms, [Pt(2)(NH₃)₄]²⁺. The structure is stabilised through a three-dimensional hydrogen bond network via nitrogen atoms of cyanide ligands, hydrogen atoms of NH₃ ligands, water molecules and oxygen atoms of NO₃⁻ counteranions. The vibrational pattern and the range of ν(CN) frequencies attributable to the electronic environment of W(V) and W(IV) are consistent with the ground state Pt(II)↔W(V) charge transfer.     

Synthesis of a novel copper(II) complex and its crystal structure

One novel chiral copper(II) complex was successfully synthesized from the reaction of chiral 1,3-thiazolidine-2-thione ligand with CuCl₂ in dichloromethane in the presence of Et₃N and DMAP at room temperature. Its unique crystal structure was unambiguously disclosed by X-ray analysis. The crystal is tetragonal, space group I4(1), space group a=15.0875(11), b=15.0875(11), c=19.362(3) Å, =90, β=90, γ=90°, V=4407.4(8) ų, Z=8, ρ_calc=1.639 mg cm⁻³.     

低相对分子质量有机酸对α-FeO(OH)吸附As(Ⅲ)的影响

制备并表征了α-FeO(OH),探究了4种低相对分子质量有机酸(LMW)对α-FeO(OH)吸附As(Ⅲ)的影响,并阐明了机理。 单一和混合LMW对α-FeO(OH)吸附As(Ⅲ)均有抑制作用,4种LMW的影响大小顺序为:草酸(OA)>柠檬酸(CA)>乳酸(LA)、水杨酸(SA)。 混合LMW的影响为:OA会加剧CA对α-FeO(OH)吸附As(Ⅲ)的影响,而SA几乎不起作用。 当ρ(As(Ⅲ))较低,LMW通过与α-FeO(OH)的静电引力、与α-FeO(OH)表面的铁离子形成配合物、生成沉淀从而影响α-FeO(OH)对As(Ⅲ)的吸附;当ρ(As(Ⅲ))较高,LMW还通过阻碍As(Ⅲ)在α-FeO(OH)上的扩散和沉淀作用产生影响。 实验结果为土壤中As(Ⅲ)的迁移转化、污染治理提供技术支撑。     

Predicted radiolysis yield in a Fricke solution irradiated with various heavy ions

Experimental data on the spatial distribution of the energy deposited around an energetic heavy ion, from 1 MeV proton to 5.9 MeV/n uranium ion, which have been reported in the literature were documented to obtain a scaled radial dose distribution; (β/Z*)² D(Z*, β,t)=200 (for t=0–1), 200/t² (for t=1t_c), and 200 t_c/t³ (for t>t_c) where Z* and β are the effective charge and velocity relative to c, the velocity of light, of the incident ion, respectively, D the dose in unit of Gy, t the radial distance in unit of nm, t_c the critical distance empirically determined.

Then, if we know the yield of any chemical reaction as a function of dose from the results of experiments using γ-radiations or fast electrons or theoretical calculations, we can calculate the probability for the yield of the chemical reaction in the system bombarded with a heavy ion of the effective charge Z* and velocity β. The results of the present calculation of the LET-values and of G(Fe³⁺) in the ferrous sulfate acidic solution are presented and compared with reported experimental results.     

Relation of lattice ion solution composition to octacalcium phosphate dissolution kinetics

The kinetics of dissolution of octacalcium phosphate (OCP) has been investigated under conditions of constant relative undersaturation with respect to OCP, σ_OCP=−0.57, at pH 4.500, and ionic strength (I), 0.15 mol l⁻¹. The molar calcium/phosphate ratio (R) in the solutions was varied from 0.1 to 10. The dissolution rate decreased by 160% as R increased from 0.1 to 10. The ζ-potential of the OCP surfaces was measured in solutions equilibrated with respect to OCP at pH values ranging from 5.0 to 11. Under stoichiometric conditions (R=1.33), OCP was positively charged at pH values from 5.0 to 10. As the solution calcium concentration was increased, ζ became more positive over the entire pH range studied. At R=0.1, two isoelectric points were apparent at pH values of about 6.3 and pH 9.5. This behavior may be related to the solubility product (K_sp) of OCP. The relationship between surface characteristics and dissolution rate are discussed in terms of kink density and the kinetic ionic ratio model developed previously (J. Zhang, G.H. Nancollas, J. Colloid Interf. Sci., 200 (1998) 131.     

金属串配合物[MM′M″(dpa)4(Cl)2](M=Co,Ni;M′,M″=Co,Rh)电子输运的理论研究

采用密度泛函理论DFT/BP86方法研究金属串配合物[MM'M″(dpa)₄(Cl)₂] [MM'M″=CoCoCo(1), CoCoRh(2), CoRhRh(3), NiCoRh(4)] 的结构和电子输运性质. 结果表明, 配合物1, 2和4的最稳定自旋态均存在1个(MM'M″)⁶⁺的离域$\sigma_{3}^{3}$键($\sigma^{2}\sigma_{nb}^{1}\sigma^{*0}$); 但配合物3具有1个(MM'M″)⁶⁺的离域$\sigma_{3}^{4}$键($\sigma^{2}\sigma_{nb}^{2}\sigma^{*0}$)和2个$\pi_{3}^{5}$键($\pi^{4}\pi_{nb}^{4}\pi^{*2}$), 故Rh—Rh键和Co—Rh键较强; Rh的引入使M—M键增强, Ni的引入则使M—M键减弱, 键强次序为Rh—Rh>Co—Rh>Co—Co>Ni—Co. 配合物14的传输通道均含有π和σ型轨道. 正偏压下, 配合物2和3的电流大于配合物1和4的. 负偏压下, 配合物4中出现负微分电阻效应. 配合物3中形成传输通道的σ_nbα/β和π^*α/β轨道能级分裂明显, (MM'M″)⁶⁺对β自旋的π^*轨道的贡献(88%)比α自旋(74%)的大, 使β自旋的电子更易传输, 具有较好的自旋过滤效应(70%80%).     

Coordination geometry of chromium(VI) species. The first example of cis-bridging chromate ions in helically structured catena(μ-CrO4-O,O′)[Ni(HIm)3H2O]

Nickel(II) chromate complex with imidazole (HIm) was isolated from the [Ni²⁺–HIm–CrO₄²⁻] system in various experimental conditions, i.e. reagent molar ratios and nickel(II) salts. The catena(μ-CrO₄-O,O′)[Ni(HIm)₃H₂O] (1) crystallizes in monoclinic crystal system—space group P2₁/n with cell parameters: a=11.784(2), b=8.899(2), c=13.934(3) (Å), β=95.19(3) (°). The unit cell contains two independent helixes, left- and right-handed, stabilized by intrahelical and interhelical hydrogen bonds (HB) and π–π interactions. The cis coordination of the CrO₄²⁻ anions and the HB systems appeared to be the main determinants of the helical architecture. To the best of our knowledge the cis-chromate coordination was observed for the first time. The cis coordination causes the distortion of the nickel octahedron, which was analysed by 4 K single crystal electronic spectra with D_4h symmetry approximation (gaussian resolution and crystal field parameters). This symmetry was also confirmed with the polarised electronic spectra. The magnetic properties of the complex suggest the occurrence of weak intrachain antiferromagnetic interactions between the magnetic Ni^II center. The computational DFT studies of complex 1 assuming three possible isomers mer[(HIm)₃]–cis[(CrO₄²⁻)₂], mer–trans and fac–cis suggested that the main contribution to the stability of 1 might have interhelical and intrahelical hydrogen bonds.     

Syntheses and structural determination of nine-coordinate K3[Nd(nta)2(H2O)]·6H2O and K3[Er(nta)2(H2O)]·5H2O

The syntheses and structural determination of Nd^III and Er^III complexes with nitrilotriacetic acid (nta) were reported in this paper. Their crystal and molecular structures and compositions were determined by single-crystal X-ray structure analyses and elemental analyses, respectively. The crystal of K₃[Nd^III(nta)₂(H₂O)]·6H₂O complex belongs to monoclinic crystal system and C2/c space group. The crystal data are as follows: a=1.5490(11) nm, b=1.3028(9) nm, c=2.6237(18) nm, β=96.803(10)°, V=5.257(6) nm³, Z=8, M=763.89, D_c=1.930 g cm⁻³, μ=2.535 mm⁻¹ and F(000)=3048. The final R₁ and wR₁ are 0.0390 and 0.0703 for 4501 (I>2σ(I)) unique reflections, R₂ and wR₂ are 0.0758 and 0.0783 for all 10474 reflections, respectively. The Nd^IIIN₂O₇ part in the [Nd^III(nta)₂(H₂O)]³⁻ complex anion has a pseudo-monocapped square antiprismatic nine-coordinate structure in which the eight coordinate atoms (two N and six O) are from the two nta ligands and a water molecule coordinate to the central Nd^III ion directly. The crystal of the K₃[Er^III(nta)₂(H₂O)]·5H₂O complex also belongs to monoclinic crystal system and C2/c space group. The crystal data are as follows: a=1.5343(5) nm, b=1.2880(4) nm, c=2.6154(8) nm, b=96.033(5)°, V=5.140(3) nm³, Z=8, M=768.89, D_c=1.987 g cm⁻³, μ=3.833 mm⁻¹ and F(000)=3032. The final R₁ and wR₁ are 0.0321 and 0.0671 for 4445 (I>2σ(I)) unique reflections, R₂ and wR₂ are 0.0432 and 0.0699 for all 10207 reflections, respectively. The Er^IIIN₂O₇ part in the [Er^III(nta)₂(H₂O)]³⁻ complex anion has the same structure as Nd^IIIN₂O₇ part in which the eight coordinate atoms (two N and six O) are from the two nta ligands and a water molecule coordinate to the central Nd^III ion directly.     

硅胶基质固定相离子对反相液相色谱法测定强离解化合物的正辛醇/水分配系数

反相液相色谱(RPLC)是测定正辛醇/水分配系数(log P)的有效方法,但由于缺少同类型模型化合物,RPLC在测定强离解化合物的log P时遇到挑战。该文在硅胶基质C18色谱柱上,采用离子抑制反相液相色谱(IS-RPLC)和离子对反相液相色谱(IP-RPLC)分别对中性化合物、酚酸、羧酸、磺酸及部分两性化合物的保留行为进行了系统研究。在IS-RPLC模式下,利用中性化合物、弱离解的酚酸和苯羧酸作为模型化合物,建立了表观正辛醇/水分配系数(log D)与纯水相保留因子对数值(log k_w)的定量结构-保留行为关系(QSRR)模型,测定了19种离解化合物的log D值,作为后续IP-RPLC的模型化合物及验证化合物。在IP-RPLC模式下,将中性、弱离解和强离解化合物作为混合模型组,以溶质静电荷n_e、氢键酸碱性参数A和B为桥梁,建立了线性良好的log D-log k_w-IP模型,采用3种不同类型的离解化合物进行了外部验证实验,预测值误差低于10%,证实了模型的可靠性。在此基础上,预测了8种强离解化合物的log D_7.0值(pH 7.0条件下的log D值)。研究表明,利用结构相关参数沟通不同类型的模型化合物,是实现IP-RPLC测定强离解化合物log D值的一种行之有效的方法。与聚乙烯醇基质色谱柱相比,通用型的硅胶基质色谱柱上尽管存在着更多的次级作用,但可以为强离解化合物log D的测定提供更灵活的选择。     

A triple helical calcium-based coordination polymer with strong blue fluorescent emission

A hydrothermal reaction of 1,3-dicyanobenzene and Ca(OH)₂ yielded a triple helical calcium-based coordination polymer of the formula, C₂₀H₂₅Ca_2.50O_18.50 (1). The 1,3-benzenecarboxylate anion, found in the final product was generated in situ during the synthesis by the hydrolysis of 1,3-dicyanobenzene. X-ray diffraction study shows that the complex 1 crystallizes in the monoclinic system, C2/c space group, a=15.5701(5), b=21.4445(7), c=17.1601(6) Å, β=111.7400(7)°, V=5322.1(3) Å³, Z=8, D_c=1.651 Mg/m³. The calcium atoms show differences in the coordination environments. Complex 1 emits strong blue fluorescent light (λ_em(max)=419 nm) when it is excited by UV light (λ_ex(max)=316 nm) in the solid state at room temperature.     

Preparation, characterization and biodegradation of biopolymer nanocomposites based on fumed silica

PLA and PCL based nanocomposites prepared by adding three different types of fumed silica were obtained by melt blending. Materials were characterized by means of Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic–Mechanical Thermal Analysis (DMTA).A good distribution of the fumed silica into both polymer matrices was observed. The highest thermo-mechanical improvements were reached by addition of the fumed silica with higher surface area. PLA and its nanocomposites were degraded in compost at 58 °C; at this temperature all samples presented a significant level of polymer degradation, but a certain protection action of silica towards PLA degradation was observed, whereas the addition of fumed silica did not show considerable influence on the degradation trend of PCL. These dissimilarities were attributed to the different degradation mechanism of the two polymers.     

Tautomeric properties, conformations and structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine

The crystal structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine (C₁₃H₁₀NO₂Cl) was determined by X-ray analysis. It crystallizes orthorhombic space group P2₁2₁2₁ with a=12.967(2) Å, b=14.438(3) Å, c=6.231(3) Å, V=1166.5(6) Å³, Z=4, D_c=1.41 g cm⁻³ and μ(MoK)=0.315 mm⁻¹. The title compound is thermochromic and the molecule is nearly planar. Both tautomeric forms (keto and enol forms in 68(3) and 32(3)%, respectively) are present in the solid state. The molecules contain strong intramolecular hydrogen bonds, N1–H1O1/O2 (2.515(1) and 2.581(2) Å) for the keto form and O1–H01N1 for the enol one. There is also strong intermolecular O2–HO1 hydrogen bonding (2.599(2) Å) between neighbouring molecules. Minimum energy conformations AM1 were calculated as a function of the three torsion angles, θ₁(N1–C7–C6–C5), θ₂(C8–N1–C7–C6) and θ₃(C9–C8–N1–C7), varied every 10°. Although the molecule is nearly planar, the AM1 optimized geometry of the title compound is not planar. The non-planar conformation of the title compound corresponding to the optimized X-ray structure is the most stable conformation in all calculations.