Issues in the synthesis of crystalline molecular sieves: towards the crystallization of low framework-density structures.

Fundamental and practical interest in crystalline, microporous, molecular sieves is largely a direct consequence of the fact that their bulk properties can be manipulated through variations in atomic structure. This correspondence between the macroscale and the atomic scale is due to the uniformity of these crystalline materials. Control of the atomic structure therefore is of extreme importance, and is the thesis of this Review. Synthesis mechanisms and the parameters that can direct the crystal assembly pathway and the ultimate product formed are discussed and rationalized.     

Polymeric zinc ferrocenyl sulfonate as a molecular aspirator for the removal of toxic metal ions

A porous bilayered open coordination polymer [Zn(4,4'-bpy)(2)(FcphSO(3))(2)](n) (1; FcphSO(3)Na=m-ferrocenyl benzenesulfonate), has been assembled from Zn(NO(3))(2), m-ferrocenyl benzenesulfonate, and the bridging ligand 4,4'-bipyridine (4,4'-bpy). Ion-exchange induced products [Cd(0.6)Zn(0.4)(4,4'-bpy)(2)(FcphSO(3))(2)](n) (2), [Zn(0.75)Pb(0.25)(4,4'-bpy)(2)(FcphSO(3))(2)](n) (3), and [Cu(0.5)Zn(0.5)(4,4'-bpy)(2)(FcphSO(3))(2)](n) (4) could be obtained directly by suspending a big single crystal of 1 into concentrated solutions of Cd(NO(3))(2), Pb(NO(3))(2), and Cu(NO(3))(2), respectively. Most importantly, the big single crystal of 1 could be partly regenerated after immersion into concentrated aqueous solutions of Zn(NO(3))(2). On the other hand, powdered 1 could also be used as a metal ion adsorbent because of the well-defined pore size and pore shape. Ion exchange takes place along with the process of ion sorption. The big single crystal of 1 removes harmful metal ions by means of ion exchange, whereas powdered 1 removes toxic metal ions mainly through ion sorption. Also, compound 1 could be employed as a multi-ion analysis fluorescent probe to detect dangerous metal ions, such as Pb(2+), Cd(2+), Ag(+), and Cu(2+). The compounds described in this study may have potential applications in the design of new molecular devices.     

Effective polarization energy of the naphthalene molecular crystal: a study on the polarizable force field

polarization energy of the localized charge in organic solids consists of electronic polarization energy, permanent electrostatic interactions, and inter/intra molecular relaxation energies. The effective electronic polarization energies for an electron/hole carrier were successfully estimated by AMOEBA polarizable force field in naphthalene molecular crystals. Both electronic polarization energy and permanent electrostatic interaction were in agreement with the preview experimental values. In addition, the influence of the multipoles from different distributed mutipole analysis (DMA) fitting options on the electrostatic interactions are discussed in this paper. We found that the multipoles obtained from Gauss-Hermite quadrature without diffuse function or grid-based quadrature with 0.325 Å H atomic radius will give reasonable electronic polarization energies and permanent interactions for electron and hole carriers.     

Atomistic in situ investigation of the morphogenesis of grains during pressure-induced phase transitions: molecular dynamics simulations of the B1-B2 transformation of RbCl

The mechanistic details of the pressure-induced B1-B2 phase transition of rubidium chloride are investigated in a series of transition path sampling molecular dynamics simulations. The B2→B1 transformation proceeds by nucleation and growth involving several, initially separated, nucleation centers. We show how independent and partially correlated nucleation events can function within a global mechanism and explore the evolution of phase domains during the transition. From this, the mechanisms of grain boundary formation are elaborated. The atomic structure of the domain-domain interfaces fully support the concept of Bernal polyhedra. Indeed, the manifold of different grain morphologies obtained from our simulations may be rationalized on the basis of essentially only two different kinds of Bernal polyhedra. The latter also play a crucial role for the B1→B2 transformation and specific grain boundary motifs are identified as preferred nucleation centers for this transition.     

A potential application for large diameter pellicular supports in the reversed phase study of ultra high molecular mass polystyrenes

Summary Ultra high molecular mass (> 7 million dalton) polystyrenes are prone to degradation in size exclusion chromatography. In gradient elution reversed phase HPLC they do not elute visibly on small particle size porous supports. However, large diameter C18 pellicular particles were successfully employed for reversed phase study of ultra high molecular mass (15 million dalton) polystyrenes without polymer degradation during elution. Although retention for the lower molecular mass polystyrenes was lower than on small diameter porous particles, the medium high molecular mass polystyrenes (0.5–1 million dalton) showed similar retention. The addition of small diameter porous particles in small quantities, to the large diameter pellicular particles, increased the amount of retention of the low molecular mass polystyrenes without affecting the higher molecular mass polystyrenes.     

Phase Transfer Catalysis in Polycondensation Processes: XVIII. Thermal properties and molecular simulation of some polyethers containing oxetane rings in the main chain

A study was made of the influence of the chemical structure of the chains on the thermal stability of a series of copolyethers obtained from 3,3-bis(chloromethyl)oxetane and various bisphenols: 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, 4,4'-thiodiphenol, 1,1-bis(4-hydroxy-phenyl)ethane and 4,4'-dihydroxydiphenylsulfone. For a better correlation between chemical structure and thermal stability, molecular simulations were performed, using the HYPERCHEM (version 4.5) program. The lowest thermal stability was exhibited by the polymers that contain azobenzene units. The best thermal stability was that of the polyethers containing thiodiphenyl and 1,1-bis(phenyl)ethane units.This revised version was published online in November 2005 with corrections to the Cover Date.     

Inductive effect for the phase stability in hydrogen bonded liquid crystals,x-(p/m)BA:9OBAs

A new series of hydrogen bonded liquid crystal (HBLC) complexes, made up with substituted benzoic acids (BAs) and nonyloxy benzoic acid, viz., x-(p/m)BA:9OBAs are reported for x = F, Cl, Br and –CH₃ substituted at para (p) or meta (m) positions of BA moiety. Proton nuclear magnetic resonance (¹H-NMR) spectrum confirms the HBLC complex. Infra red (IR) spectrum confirms linear, double and complementary type of hydrogen bonding (HB) between x-(p/m)BAs and 9OBA. The liquid crystal (LC) phases are characterised by polarisation optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. x-(p/m)BA:9OBA exhibit N, C and G LC phase variance. HB induces tilted phases and enhances LC phase stability. The influence of configuration, size, electronegativity, electron directing capacity and inductive nature of substituent (x) is investigated for the stability of LC phases. An overview of the LC phase data indicates predominant ‘negative inductive effect’ in HBLCs with electron withdrawing substituents. Inductive effect operates effectively for para substitutions. Results are discussed in the wake of reports in other HBLCs.     

High-temperature XRD studies of the phase transformations in a MnOx/Al2O3 catalyst for deep oxidation of hydrocarbons

Omsk Branch of Boreskov Institute of Catalysis     

Influence of the extracted solute on the aggregation of malonamide extractant in organic phases: Consequences for phase stability

Due to their amphiphilic properties, malonamide molecules in alkane are organized in reverse micelle type aggregates, composed of a polar core formed by the malonamide polar heads and the extracted solutes, and surrounded by a hydrophobic shell made up of the extractant alkyl chains. The aggregates interact with one another through an attractive potential, leading to the formation of a third phase. This occurs with the splitting of the organic phase into a light phase composed mostly of diluent, and a heavy third phase containing highly concentrated extractant and solutes. In this article, we show that the aggregation (monomer concentration, domain of stability, and attractive potential between micelles) greatly depends on the nature of the extracted solute, whereas the size of aggregate (aggregation number) is only slightly influenced by this. We describe the extraction of water, nitric acid, neodymium nitrate and uranyl nitrate. Strongly polarizable species induce consistently large attraction potentials and a small stability domain for the dispersion of nanodroplets in the solvent. Highly polarizable ions such as lanthanides or uranyl induce more long-range attractive interactions than do protons.     

Structure and stability of a clathrate of bis(dibenzoylmethanato)-dipyridine-nickel(II) with acetone (1:2)

An inclusion compound of constant composition [Ni(DBM)₂Py₂]·2(CH₃COCH₃) is synthesized, Ni = Ni(II), DBM is dibenzoylmethanate-anion (C₆H₅CO)₂CH^?, Py is pyridine. The compound and its dissociation products are examined by structural and thermal analysis, as well as vapor pressure measurements. The crystal structure of the clathrate is solved in the monoclinic space group P2₁/n (temperature 173 K, a = 11.8617(9) Å, b = 10.0096(6) Å, c = 17.2895(9) Å, β = 96.72(1)°, V = 2038.7(2) ų, Z = 2, final R ₁ = 0.032). The host molecule [Ni(DBM)₂Py₂] is an uncharged octahedral complex, the central Ni(II) atom being surrounded by two DBM-anions in the equatorial plane and two terminal pyridines in the axial positions. Pairs of guest molecules are located in the voids of the molecular crystal. Calculated packing coefficients of the clathrate and the stable form of the host complex are 0.685(2) and 0.668(1) at 173 K, respectively. Isochoric melting of the clathrate has incongruent nature and occurs at 58–60°C to yield the solid phase of the host complex, while in air the complex decomposes in gaseous acetone and a metastable form of the host (apohost). The collapse of the metastable form of [Ni(DBM)₂Py₂] to the stable one takes place at 131°C with the release of 11 kJ/mol. The equilibrium vapor pressure of acetone over the clathrate is measured with the spoon gauge technique in a temperature interval from 292 K to 310 K (at 298 K the pressure is 0.48P ₀, P ₀ is the saturated vapor pressure of liquid acetone at this temperature). The experimental dependence logP ? 1/T is used to derive thermodynamic parameters of the process of clathrate dissociation 1/2[Ni(DBM)₂Py₂]· 2(CH₃COCH₃)(s) = 1/2[Ni(DBM)₂Py₂](s) + CH₃COCH₃(gas): ΔH _av ⁰ = 53±3 kJ/mol, ΔS _av ⁰ = 160±10 J/(mol·K), ΔG ₂₉₈ ⁰ = 4.74±0.07 kJ/mol.     

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: with a comment

This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)^1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)^1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm⁻³ and η value from 0.01 to 0.22 g cm⁻¹ s⁻¹, respectively), the slope of the plot of ΔF versus (ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.     

Molecular graph fingerprint: a new molecular structural characterization method for the modelling and prediction of chromatographic retention behaviour of several persistent organic pollutants

How to extract and characterize information on molecular microstructures is deemed to be the key task to accurately simulate and predict molecular properties. In terms of atomic attributes, atoms in a molecule are divided into three levels. Based upon that, inter-atomic correlations are mapped to certain reasonable spatial coordinates in virtue of radial distribution function, generating the novel molecular graph fingerprint (MoGF), which essentially provides insight into molecular inner structures. MoGF, committing itself to transformation of molecular structures into characteristic graph curves, shows valuable advantages such as easy calculation, experimental parameters-free, rich information content, and structural significance and intuitive expressions. QSRR studies were performed for 115 polychlorinated dibenzofurans (PCDFs), 41 polychlorinated dibenzo-p-dioxins (PCDDs), 62 polychlorinated naphthalenes (PCNs), and 210 polychlorinated biphenyls (PCBs including the biphenyl)) tested for their retention behaviours on gas chromatographic column DB-5. The resulting PLS models showed good performances with correlation coefficients for both training and test sets above 0.97.     

Metal-amyloid-β peptide interactions: a preliminary investigation of molecular mechanisms for Alzheimer''''s disease

Although humans have spent exactly 100 years combating Alzheimer's disease (AD), the molecular mechanisms of AD remain unclear. Owing to the rapid growth of the oldest age groups of the population and the continuous increase of the incidence of AD, it has become one of the crucial problems to modern sciences. It would be impossible to prevent or reverse AD at the root without elucidating its molecular mechanisms. From the point of view of metal-amyloid-β peptide (Aβ) interactions, we review the molecular mechanisms of AD, mainly including Cu2 and Zn2 inducing the aggregation of Aβ, catalysing the production of active oxygen species from Aβ, as well as interacting with the ion-channel-like structures of Aβ. Moreover, the development of therapeutic drugs on the basis of metal-Aβ interactions is also briefly introduced. With the increasingly rapid progress of the molecular mechanisms of AD, we are now entering a new dawn that promises the delivery of revolutionary developments for the control of dementias.     

Chiral diaminopyrrolic receptors for selective recognition of mannosides, part 2: a 3D view of the recognition modes by X-ray, NMR spectroscopy, and molecular modeling

The structural features of a representative set of five complexes of octyl α- and β-mannosides with some members of a new generation of chiral tripodal diaminopyrrolic receptors, namely, (R)-5 and (S)- and (R)-7, have been investigated in solution and in the solid state by a combined X-ray, NMR spectroscopy, and molecular modeling approach. In the solid state, the binding arms of the free receptors 7 delimit a cleft in which two solvent molecules are hydrogen bonded to the pyrrolic groups and to the benzenic scaffold. In a polar solvent (CD(3)CN), chemical shift and intermolecular NOE data, assisted by molecular modeling calculations, ascertained the binding modes of the interaction between the receptor and the glycoside for these complexes. Although a single binding mode was found to adequately describe the complex of the acyclic receptor 5 with the α-mannoside, for the complexes of the cyclic receptors 7 two different binding modes were required to simultaneously fit all the experimental data. In all cases, extensive binding through hydrogen bonding and CH-π interactions is responsible for the affinities measured in the same solvent. Furthermore, the binding modes closely account for the recognition preferences observed toward the anomeric glycosides and for the peculiar enantiodiscrimination properties exhibited by the chiral receptors.     

Derivatization of 2-chlorophenol with 4-amino-anti-pyrine: a novel method for improving the selectivity of molecularly imprinted solid phase extraction of 2-chlorophenol from water

Molecularly imprinted polymer (MIP) may not selectively recognize small template of limited number of functional groups, such as 2-chlorophenol (2-CP). In this work, a novel method was proposed to improve the recognition ability of the molecularly imprinted solid phase extraction (MISPE) of 2-CP from environmental waters. This was achieved by derivatization of 2-CP with 4-amino-anti-pyrine (4-AAP) to enlarge its molecular size and add more binding sites. For that purpose, two MISPE methods of 2-CP were developed. In method 1, a polymer imprinted with 2-CP was used as the extracting sorbent but it suffered from low selectivity and high detection limit of 2-CP (7.10 ng L⁻¹). In method 2, a polymer imprinted with 4-AAP derivatized 2-CP (2-CP-4-AAP) was used as the extracting sorbent. Prior to loading the water sample it was subjected to a simple derivatization procedure with 4-AAP. Method 2 showed high recognition ability/selectivity towards 2-CP-4-AAP with lower detection limit of 0.05 ng L⁻¹ for 2-CP-4-AAP. Method 2 was able to detect the presence of 2-CP-4-AAP in unspiked real water samples and almost full spike recovery was achieved.     

The F NMR spectrum of bis-trifluoromethylmercury Hg(CF3)2 in the nematic phase: DAISY — a novel program system for the analysis and simulation of NMR spectra

The ¹⁹F NMR spectrum of bis-trifluoromethylmercury in the nematic phase has been analysed using the DAISY program system. The scalar and the dipolar coupling constants have been obtained.