Biobased Polyurethane Composite Foams Reinforced with Plum Stones and Silanized Plum Stones.

In the following study, ground plum stones and silanized ground plum stones were used as natural fillers for novel polyurethane (PUR) composite foams. The impact of 1, 2, and 5 wt.% of fillers on the cellular structure, foaming parameters, and mechanical, thermomechanical, and thermal properties of produced foams were assessed. The results showed that the silanization process leads to acquiring fillers with a smoother surface compared to unmodified filler. The results also showed that the morphology of the obtained materials is affected by the type and content of filler. Moreover, the modified PUR foams showed improved properties. For example, compared with the reference foam (PUR_REF), the foam with the addition of 1 wt.% of unmodified plum filler showed better mechanical properties, such as higher compressive strength (~8% improvement) and better flexural strength (~6% improvement). The addition of silanized plum filler improved the thermal stability and hydrophobic character of PUR foams. This work shows the relationship between the mechanical, thermal, and application properties of the obtained PUR composites depending on the modification of the filler used during synthesis.

Potassium tert-butoxide-mediated regioselective silaboration of aromatic alkenes.

The regio- and diastereoselective silaboration of aromatic alkenes with a silylboron compound proceeds in the presence of a catalytic amount of potassium tert-butoxide, providing a complementary method to the corresponding transition metal-catalyzed reactions.

Chemical reactions in dense monolayers: in situ thermal cleavage of grafted esters for preparation of solid surfaces functionalized with carboxylic acids.

The thermodynamics of a chemical reaction confined at a solid surface was investigated through kinetic measurements of a model unimolecular reaction. The thermal cleavage of ester groups grafted at the surface of solid silica was investigated together with complementary physicochemical characterization of the grafted species. The ester molecules were chemically grafted to the silica surface and subsequently cleaved into the carboxylic acids. A grafting process of a reproducible monolayer was designed using the reaction of monofunctional organosilane from its gas phase. The thermal deprotection step of the ester end-group was investigated. The thermal deprotection reaction behaves in quite a specific manner when it is conducted at a surface in a grafted layer. Different organosilane molecules terminated by methyl, isopropyl and tert-butyl ester groups were grafted to silica surface; such functionalized materials were characterized by elemental analysis, IR and NMR spectroscopy, and thermogravimetric analysis, and the thermodynamic parameters of the thermal elimination reaction at the surface were measured. The limiting factor of such thermal ester cleavage reaction is the thermal stability of grafted ester group according to the temperature order: tert-butyl < i-propyl < methyl. Methyl ester groups were not selectively cleaved by temperature. The thermal deprotection of i-propyl ester groups took place at a temperature close to the thermal degradation of the organofunctional tail of the silane. The low thermolysis temperature of the grafted tert-butyl esters allowed their selective cleavage. There is a definite influence of the surface on the reaction. The enthalpy of activation is lower than in the gas phase because of the polarity of the reaction site. The major contribution is entropic; the negative entropy of activation comes from lateral interactions with the neighbor grafted molecules because of the high grafting density. Such reaction is an original strategy to functionalize the silica surface by carboxylic acid groups by means of a simple, reproducible, and efficient process involving in situ thermolysis of ester groups.

Stereoselective syntheses of trisubstituted olefins via platinum catalysis: alpha-silylenones with geometrical complementarity.

The stereoselective syntheses of alpha-silylenones using catalytic PtCl(2) are reported. Via alkyne activation, alpha-hydroxypropargylsilanes are converted to (Z)-silylenones through a highly selective silicon migration. The complementary (E)-silylenones are accessed by a regioselective hydrosilylation of the ynone precursor. The synthetic utility of these compounds is demonstrated in cross-coupling reactions, highlighting the potential of these protocols for the syntheses of geometrically defined trisubstituted olefins.

Oxo ligand silylation in a uranyl beta-ketoiminate complex.

Addition of Me(3)SiI to UO(2)((Ar)acnac)(2) (ArNC(Ph)CHC(Ph)O, Ar = 3,5-(t)Bu(2)C(6)H(3)) (1) results in the formation of U(OSiMe(3))(2)I(2)((Ar)acnac) (2) in moderate yield. Also formed in the reaction are I(2) and ArNC(Ph)=CHC(Ph)OSiMe(3), the product of [(Ar)acnac](-) abstraction by Me(3)Si(+). In contrast, reaction of 1 with Me(3)SiX (X = Cl, OTf) only results in the formation of UO(2)(OTf)(2)((Ar)acnacH)(2)(Et(2)O) (3) and UO(2)Cl(2)((Ar)acnacH)(2) (4), respectively.

Periodic mesoporous organosilica in confined environments.

Periodic mesoporous organosilica (PMO) mesophases based on bis(triethoxysilyl)ethane (BTSE) were synthesized within the confined tubular environment of anodic alumina membrane (AAM) channels. The resulting mesophases were investigated by transmission small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), nitrogen sorption, and transmission electron microscopy (TEM). Two different surfactants--nonionic Brij 56 and ionic cetyltrimethylammonium bromide (CTAB)--were used in an acid-catalyzed evaporation-induced self-assembly (EISA) process. Brij 56 as the structure-directing agent (SDA) resulted in the formation of either the hexagonal circular or the cubic mesophase. While the hexagonal circular mesophase is common for such kinds of composites, the cubic mesophase has never been reported before. The template could be removed from the mesophases by template extraction and calcination after annealing the samples. When using CTAB as the SDA during EISA, the only mesophase observed was the hexagonal circular structure. This is in contrast to previous experiments and reports on pure silica mesophases, where the only mesophase formed with CTAB is hexagonal columnar.

Palladium-catalysed cis- and trans-silaboration of terminal alkynes: complementary access to stereo-defined trisubstituted alkenes.

Palladium-catalysed cis- and trans-silaboration of terminal alkynes has been developed via the addition of (chlorodimethylsilyl)pinacolborane, followed by a one-pot conversion of the chloro group on the silicon atom to an isopropoxy group.

Synthesis and antimicrobial applications of 5,5'-ethylenebis[5-methyl-3-(3-triethoxysilylpropyl)hydantoin].

A novel, durable, long lasting, N-halamine siloxane monomer precursor, 5,5'-ethylenebis[5-methyl-3-(3-triethoxysilylpropyl)hydantoin] has been prepared and characterized by (1)H-NMR and FTIR for the purpose of functionalizing the surfaces of various materials. In this work, the precursor N-halamine moiety was attached by siloxane covalent bonding to surfaces of cotton fibers. Simulated laundering tests indicated that the chlorinated N-halamine structure could survive many repeated home launderings. The materials were rendered biocidal after exposure to oxidative halogen solutions, i.e. dilute household bleach. Once chlorinated, these materials were biocidal against Staphylococcus aureus and Escherichia coli. Upon loss of the halogen from either long-term use or consumption by the microbes on the surfaces, they could be simply recharged by further exposure to dilute bleach to regain biocidal activity.

Regioselective silylation of sugars through palladium nanoparticle-catalyzed silane alcoholysis.

Palladium(0)-catalyzed silane alcoholysis was applied to sugars for the first time using tert-butyldimethylsilane (TBDMS-H) and Ph(3)SiH as the silanes. The catalyst is a colloidal solution of Pd(0) generated in situ from PdX(2) (X = Cl(-), OAc(-)) and TBDMS-H in N,N-dimethylacetamide. The colloid has been characterized by dynamic light scattering and transmission electron microscopy and consists of catalytically highly active nanoparticles of approximately 2 nm diameter. The silane alcoholysis reaction is an effective method for the regioselective silylation of methyl and phenyl glycosides and generates hydrogen gas as the only side product. For many of the sugar substrates investigated, the distribution of regioisomers obtained is complementary to that of the traditional R(3)SiCl/base (base = pyridine, imidazole) methodology and gives convenient access to the 3,6- rather than the 2,6-silylated pyranosides, obtained as the main product by the silyl chloride method. The method also allows a selective axial silylation of levoglucosan and 1,3,5-O-methylidene-myo-inositol. In an attempt to rationalize the observed regioselectivities, ab initio predictions (HF/3-21G) have been made on the relative energies of some of the silylated products. They suggest that the observed regioselectivities do not reflect a kinetic vs thermodynamic product distribution but are induced by the silylation agent employed. Models for the possible origin of the observed regioselectivity in both silylation methods (silane- and silyl chloride-based) are discussed.

Synthesis and anti-HIV activity of thymidine analogues bearing a 4'-cyanovinyl group and some derivatives thereof.

Treatment of 3'-O-tert-butyldimethylsilyl-2',5'-dideoxy-5'-oxothymidine (4) with potassium or magnesium nitromethanide afforded in good yield the resolvable epimeric mixture of the expected blocked nitronucleosides 5 which upon dehydration led to the corresponding E-nitroenofuranosylthymidine 6. Nucleophilic attack of cyanide onto the nitrovinyl group led to a nucleoside analogue bearing a terminal 1-cyanovinyl group (7), a soft electrophilic group which, upon reaction with benzeneselenol, underwent a conjugate addition to the phenylselenonucleoside derivative 9. All these compounds, eventually de-O-silylated, were subject of in vitro biological testing, some exhibiting interesting cytotoxic or antiviral properties.