Confined Polymerization in Highly Ordered Mesoporous Organosilicas

Hybrid mesoporous organosilica exhibiting crystal‐like order in the walls provided an ideal channel reaction vessel for the confined polymerization of acrylonitrile (PAN). The resulting high‐molecular‐mass PAN fills the channels at high yield and forms an ordered nanostructure of polymer nanobundles enclosed into the hybrid matrix. The in situ thermal transformation of PAN into rigid polyconjugated and, eventually, into condensed polyaromatic carbon nanofibers, retains the periodic architecture. Simultaneously, the matrix evolves showing the fusion of the p‐phenylene rings and the cleavage of carbon?silicon bonds: this gives rise to graphitic‐carbon/silica nanocomposites containing hyper‐oxydrylated silica nanophases. Interestingly, the 3D hexagonal mesostructure survives in the carbonaceous material. The exploitation of porous materials of high capacity and a hybrid nature, for polymerization in the confined state, followed by high temperature treatments, allowed us to achieve unique and precisely fabricated nanostructures, thus paving the way for the construction of fine‐tuned electronic and light‐harvesting materials.     

Clickable Periodic Mesoporous Organosilicas: Synthesis,Click Reactions,and Adsorption of Antibiotics

Pharmaceutical antibiotics are not easily removed from water by conventional water‐treatment technologies and have been recognized as new emerging pollutants. Herein, we report the synthesis of clickable azido periodic mesoporous organosilicas (PMOs) and their use as adsorbents for the adsorption of antibiotics. Ethane‐bridged PMOs, functionalized with azido groups at different densities, were synthesized by the co‐condensation of 1,2‐bis(trimethoxysilyl)ethane (BTME) and 3‐azidopropyltrimethoxysilane (AzPTMS), in the presence of nonionic‐surfactant triblock‐copolymer P123, in an acidic medium. Four different alkynes were conjugated to azide‐terminated PMOs by means of an efficient click reaction. The clicked PMOs showed improved adsorption capacity (241 μg g^?1) for antibiotics (ciprofloxacin hydrochloride) compared with azido‐functionalized PMOs because of the enhanced π–π stacking interactions. These results indicate that click reactions can introduce multifunctional groups onto PMOs, thus demonstrating the great potential of PMOs for environmental applications.     

Synthesis of Large‐Pore Urea‐Bridged Periodic Mesoporous Organosilicas

Bringing order : A new class of periodic mesoporous organosilicas (PMOs) with a urea‐bridged organosilica precursor under acid‐catalyzed and inorganic‐salt‐assisted conditions was obtained. The large‐pore hybrid materials have ordered mesostructure with uniform pore size distributions, which can be seen from the TEM images.

     

Ruthenium‐Immobilized Periodic Mesoporous Organosilica: Synthesis,Characterization, and Catalytic Application for Selective Oxidation of Alkanes

Periodic mesoporous organosilica (PMO) is a unique material that has a crystal‐like wall structure with coordination sites for metal complexes. A Ru complex, [RuCl₂(CO)₃]₂, is successfully immobilized onto 2,2’‐bipyridine (BPy) units of PMO to form a single‐site catalyst, which has been confirmed by various physicochemical analyses. Using NaClO as an oxidant, the Ru‐immobilized PMO oxidizes the tertiary C?H bonds of adamantane to the corresponding alcohols at 57 times faster than the secondary C?H bonds, thereby exhibiting remarkably high regioselectivity. Moreover, the catalyst converts cis‐decalin to cis‐9‐decalol in a 63 % yield with complete retention of the substrate stereochemistry. The Ru catalyst can be separated by simple filtration and reused without loss of the original activity and selectivity for the oxidation reactions.     

Periodic Mesoporous Organosilicas: A Type of Hybrid Support for Water‐Mediated Reactions

Hybrid mesoporous periodic organosilicas (Ph‐PMOs) with phenylene moieties embedded inside the silica matrix were used as a heterogeneous catalyst for the Ullmann coupling reaction in water. XRD, N₂ sorption, TEM, and solid‐state NMR spectroscopy reveal that mesoporous Ph‐PMO supports and Pd/Ph‐PMO catalysts have highly ordered 2D hexagonal mesostructures and covalently bonded organic–inorganic (all Si atoms bonded with carbon) hybrid frameworks. In the Ullmann coupling reaction of iodobenzene in water, the yield of biphenyl was 94 %, 34 %, 74 % and for palladium‐supported Ph‐PMO, pure silica (MCM‐41), and phenyl‐group‐modified Ph‐MCM‐41 catalysts, respectively. The selectivity toward biphenyl reached 91 % for the coupling of boromobenzene on the Pd/Ph‐PMO catalyst. This value is much higher than that for Pd/Ph‐MCM‐41 (19 %) and Pd/MCM‐41 (0 %), although the conversion of bromobenzene for these two catalysts is similar to that for Pd/Ph‐PMO. The large difference in selectivity can be attributed to surface hydrophobicity, which was evaluated by the adsorption isotherms of water and toluene. Ph‐PMO has the most hydrophobic surface, and in turn selectively adsorbs the reactant haloaryls from aqueous solution. Water transfer inside the mesochannels is thus restricted, and the coupling reaction of bromobenzene is improved.     

Periodic mesoporous organosilicas with co-existence of diurea and sulfanilamide as an effective drug delivery carrier

In this article we report the synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. The materials possess hexagonal pores with a high degree of uniformity and show long-range order as confirmed by the measurements of small-angle X-ray scattering (SAXS), N₂ adsorption isotherms, and transmission electron microscopy(TEM). FT-IR and solid state ²⁹Si MAS and ¹³C CP MAS NMR spectroscopic analyses proved that the bridging groups in the framework are not cleaved and covalently attached in the walls of the PMOs. It was found that the organic functionality could be introduced in a maximum of 10 mol% with respect to the total silicon content and be thermally stable up to 230 °C. The synthesized materials were shown to be particularly suitable for adsorption and desorption of hydrophilic/hydrophobic drugs from a phosphate buffer solution at pH 7.4.     

Chiral Mesoporous Organosilica Nanospheres: Effect of Pore Structure on the Performance in Asymmetric Catalysis

(R)‐(+)‐1,1′‐Bi‐2‐naphthol ((R)‐(+)‐Binol)‐functionalized (Binol=2,2′‐dihydroxy‐1,1′‐binaphthyl) chiral mesoporous organosilica nanospheres with uniform particle size (100 to 300 nm) have been synthesized by co‐condensation of tetraethoxysilane and (R)‐2,2′‐di(methoxymethyl)oxy‐6,6′‐di(1‐propyl trimethoxysilyl)‐1,1′‐binaphthyl in a basic medium with cetyltrimethylammonium bromide as the template. Nanospheres with a radiative 2D hexagonal channel arrangement exhibit higher enantioselectivity and turnover frequency than those with a penetrating 2D hexagonal channel arrangement (94 versus 88 % and 43 versus 15 h^?1, respectively) in the asymmetric addition of diethylzinc to aldehydes. In addition, under similar conditions, the enantioselectivity of the nanospheres can be greatly improved as the structural order of the framework increases. These results clearly show that the structural order of nanospheres affects enantioselective reactions. The enantioselectivity of the nanospheres synthesized by the co‐condensation method is higher than that of nanospheres prepared by a grafting method and even higher than that of their homogeneous counterpart. These results indicate that the bite angle of (R)‐(+)‐Binol bridging in a more rigid porous network is in a more favorable position for achieving higher enantioselectivity. The efficiency of a co‐condensation method for the synthesis of high‐performance heterogeneous asymmetric catalysts is also reported.     

Water Confined in the Local Field of Ions

Interionic distances are shorter in concentrated ionic solutions, thus instigating the interaction and overlap of hydration shells, as ions become separated by only one or two layers of water molecules. The simultaneous interaction of water with two oppositely charged ions has, so far, only been investigated by computer simulation studies, because the isolated vibrational spectroscopic signature of these molecules remains undetected. Our combined near‐infrared spectroscopic and molecular dynamics simulation studies of alkali halide solutions present a distinct spectral feature, which is highly responsive to depletion of bulk water and merging of hydration shells. The analysis of this spectral feature demonstrates that absorption trends are in good agreement with the law of matching affinities, thus providing the first successful vibrational spectroscopic treatment of this topic. Combined with commonly observed near‐infrared bands, this feature provides a spectral pattern that describes some relevant aspects of ionic hydration.     

Stacking Structure of Confined 1‐Butanol in SBA‐15 Investigated by Solid‐State NMR Spectroscopy

Understanding the complex thermodynamic behavior of confined amphiphilic molecules in biological or mesoporous hosts requires detailed knowledge of the stacking structures. Here, we present detailed solid‐state NMR spectroscopic investigations on 1‐butanol molecules confined in the hydrophilic mesoporous SBA‐15 host. A range of NMR spectroscopic measurements comprising of ¹H spin–lattice (T₁), spin–spin (T₂) relaxation, ¹³C cross‐polarization (CP), and ¹H,¹H two‐dimensional nuclear Overhauser enhancement spectroscopy (¹H,¹H 2D NOESY) with the magic angle spinning (MAS) technique as well as static wide‐line ²H NMR spectra have been used to investigate the dynamics and to observe the stacking structure of confined 1‐butanol in SBA‐15. The results suggest that not only the molecular reorientation but also the exchange motions of confined molecules of 1‐butanol are extremely restricted in the confined space of the SBA‐15 pores. The dynamics of the confined molecules of 1‐butanol imply that the ¹H,¹H 2D NOESY should be an appropriate technique to observe the stacking structure of confined amphiphilc molecules. This study is the first to observe that a significant part of confined 1‐butanol molecules are orientated as tilted bilayered structures on the surface of the host SBA‐15 pores in a time‐average state by solid‐state NMR spectroscopy with the ¹H,¹H 2D NOESY technique.     

19F NMR Spectroscopy as a Highly Sensitive Method for the Direct Monitoring of Confined Crystallization within Nanoporous Materials

The introduction of fluorine into the structure of pharmaceuticals has been an effective strategy for tuning their pharmacodynamic properties, with more than 40 new drugs entering the market in the last 15 years. In this context, ¹⁹F NMR spectroscopy can be viewed as a useful method for investigating the host–guest chemistry of pharmaceuticals in nanosized drug‐delivery systems. Although the interest in confined crystallization, nanosized devices, and porous catalysts is gradually increasing, understanding of the complex phase behavior of organic molecules confined within nanochambers or nanoreactors is still lacking. Using ¹⁹F magic‐angle‐spinning NMR spectroscopy, we obtained detailed mechanistic insight into the crystallization of flufenamic acid (FFA) in a confined environment of mesoporous silica materials with different pore diameters (3.2–29 nm), providing direct experimental evidence for the formation of a molecular‐liquid‐like layer besides crystalline confined FFA form I.     

乙烷桥键介孔材料的制备及其在反相液相色谱中的应用

以1,2-二(三甲氧基硅基)-乙烷为硅源、聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物(EO20PO70EO20,P123)为模板剂、十六烷基三甲基溴化铵(CTAB)为共模板剂、乙醇为共溶剂,在酸性条件下合成了一种乙烷桥键有序介孔材料(PME)。研究表明,该PME具有高的比表面积(1152 m2/g)、高度有序的孔结构(二维六方相)、窄的孔径分布及表面光滑的球形形貌。将该PME不经化学改性直接用作反相高效液相色谱固定相,能够有效分离5种多环芳香族化合物(苯、萘、联苯、菲和芘)。     

Stable Tetrahedral Aluminum Sites in Hexagonal Mesoporous Aluminosilicates

A unique templating approach for the synthesis of hexagonal mesoporous aluminosilicates via self-assembly of pre-formed aluminosilcate nacoclusters with the templating micella formed by cetyltrimethylammonium bromide (CTAB) is described ,The obtained materials of MAS-5 are hydrothermally stable,which is shown by X-ray diffraction (XRD) analysis,Further-more,as charaacterized by NMR technique ,MAS-5 has taable tetrahedral aluminum sites that is the major contributions to the acidity of aluminosilicate molecular sieve ,and on non-frame-work aluminium species in the saples was observed.     

High-resolution solid-state 19F-NMR spectroscopy of the sorption and diffusion of fluorine-containing aromatic molecules in polymeric media

High-resolution ¹⁹F solid-state NMR spectroscopy was employed to study the sorption properties of hexafluorobenzene (HFB) and 3,5-bis (trifluoromethyl) aniline (TFMA) in polystyrene (PS) and butyl rubber (BR). The NMR spectra indicate that the penetrants undergo dual-mode sorption in the glassy polymer (PS), but are highly mobile in the rubbery polymer (BR). In addition, the NMR method was utilized in the experimental determination of diffusion coefficients for the HFB/PS, TFMA/PS, and HFB/BR systems through desorption studies. The diffusion results for the TFMA/PS case agree very well with those previously obtained via resonance nuclear reaction analysis. © 1993 John Wiley & Sons, Inc.     

Peculiarities of the Porous Structure of Aluminosilicate Mesoporous Substances Obtained in The Presence of Biotemplates

Supramolecular structures of lecithin occurred to be the template in the synthesis of mesoporous aluminosilicates; using of various combinations of lecithin and cetyltrimethyl-ammonium bromide or octadecylamine as templating agents allowed to obtain mesoporous substances with pores up to 100 Å, as well as biporous materials in aluminosilicate system. In the presence of glucose oxidase and cetyltrimethyl-ammonium bromide combinations aluminosilicate substances with complex porous structure were shown to be formed (pore size distributions exhibited 3 peaks, corresponding 3 effective size of mesopores in the 30–100 Å range). The investigation of sorption of glucose oxidase on obtained aluminosilicate mesoporous substances was carried out, the results obtained allowus to consider such materials as prospect for creation high capable and selective sorbents for biomolecules sorption, as well as active elements of chemical and biosensors.     

Water sorption in poly(zwitterions) of the ammonioalkoxydicyanoethenolate type

Water sorption by amorphous (meth)acrylic poly(zwitterions)-bearing quaternary ammonioalkoxydicyanoethenolate side groups , dipole moment μ(D) = 25.9 and 30.8 for p = 2 and 3, respectively was studied at 23°C over a broad range of water activity a (0.14–0.98). Water diffusion is nearly Fickian (D_s = 5.9 10^?7 cm².s^?1 for a = 0.63) and the sorption isotherms may be quantitatively analyzed according to the Guggenheim-Anderson-De Boer equation for a multilayer process characterized by a number of site-bound water molecules per monomeric unit, n_m ? 0.7. The Flory χ interaction parameter is a strongly increasing function of the water content in the glassy hydrated systems and it always remains higher than 0.75. Clustering of water molecules (Zimm-Lundberg theory) is never observed. Differential scanning calorimetry allows to quantify nonfreezable bound water (type I) of strong plasticization efficiency, n(I) = 2.8 mol. of water per monomeric unit, and it points out the quasisimultaneous emergence of low amounts of freezable bound water (type II) crystallizing at ?40°C and melting at ?1°C and of bulkfree water (type III, n(II)/n(III) ? 0.1). All these typical features distinguish these rather hydrophobic poly(zwitterions) from their hydrophilic homologues of the quaternary ammoniopropanesulfonate type . © 1995 John Wiley & Sons, Inc.     

ACD/Structure Elucidator: 20 Years in the History of Development

The first methods associated with the Computer-Assisted Structure Elucidation (CASE) of small molecules were published over fifty years ago when spectroscopy and computer science were both in their infancy. The incredible leaps in both areas of technology could not have been envisaged at that time, but both have enabled CASE expert systems to achieve performance levels that in their present state can outperform many scientists in terms of speed to solution. The computer-assisted analysis of enormous matrices of data exemplified 1D and 2D high-resolution NMR spectroscopy datasets can easily solve what just a few years ago would have been deemed to be complex structures. While not a panacea, the application of such tools can provide support to even the most skilled spectroscopist. By this point the structures of a great number of molecular skeletons, including hundreds of complex natural products, have been elucidated using such programs. At this juncture, the expert system ACD/Structure Elucidator is likely the most advanced CASE system available and, being a commercial software product, is installed and used in many organizations. This article will provide an overview of the research and development required to pursue the lofty goals set almost two decades ago to facilitate highly automated approaches to solving complex structures from analytical spectroscopy data, using NMR as the primary data-type.     

Interfacial Structure of Water as a New Descriptor of the Hydrogen Evolution Reaction

Driven by the persisting poor understanding of the sluggish kinetics of the hydrogen evolution reaction (HER) on Pt in alkaline media, a direct correlation of the interfacial water structure and activity is still yet to be established. Herein, using Pt and Pt–Ni nanoparticles we first demonstrate a strong dependence of the proton donor structure on the HER activity and pH. The structure of the first layer changes from the proton acceptors to the donors with increasing pH. In the base, the reactivity of the interfacial water varied its structure, and the activation energies of water dissociation increased in the sequence: the dangling O−H bonds < the trihedrally coordinated water < the tetrahedrally coordinated water. Moreover, optimizing the adsorption of H and OH intermediates can re-orientate the interfacial water molecules with their H atoms pointing towards the electrode surface, thereby enhancing the kinetics of HER. Our results clarified the dynamic role of the water structure at the electrode–electrolyte interface during HER and the design of highly efficient HER catalysts.     

Influence of Pore Structure on Catalytic Properties of Mesoporous Silica-supported Co-B Amorphous Alloys in Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol

Co‐B amorphous alloy catalysts supported on three kinds of mesoporous silica (common SiO₂, MCM‐41 and SBA‐15) have been systematically studied focusing on the effect of pore structure on the catalytic properties in liquid‐phase hydrogenation of cinnamaldehyde to cinnamyl alcohol (CMO). Structural characterization of a series of different catalysts was performed by means of N₂ adsorption, X‐ray diffraction, transmission electron microscopy, hydrogen chemisorption, and X‐ray photoelectron spectroscopy. Various characterizations revealed that the pore structure of supports profoundly influenced the particle size, location and dispersion degree of Co‐B amorphous alloys. Co‐B/SBA‐15 was found more active and selective to CMO than either Co‐B/SiO₂ or Co‐B/MCM‐41. The superior catalytic activity could be attributed to the higher active surface area, because most of Co‐B nanoparticles in Co‐B/SBA‐15 were located in the ordered pore channels of SBA‐15 rather than on the external surface as found in Co‐B/SiO₂ and Co‐B/MCM‐41. Meanwhile, the geometrical confinement effect of the ordered mesoporous structure of SBA‐15 was considered to be responsible for the enhanced selectivity to CMO on Co‐B/SBA‐15, inhibiting the further hydrogenation of CMO to hydrocinnamyl alcohol.