Synthesis of ß-Silyl-α-amino Acid Derivatives by Cu-Catalyzed Regio- and Enantioselective Silylamination of α,ß-Unsaturated Esters.

A copper-catalyzed silylamination of α,ß-unsaturated esters with silylboranes and hydroxylamines has been developed to afford the corresponding ß-silyl-α-amino acid derivatives, which are of great interest in medicinal and pharmaceutical chemistry. Additionally, by using a suitable chiral bisphosphine ligand, the asymmetric induction is possible, delivering the optically active ß-silyl-α-amino acids with synthetically acceptable diastereomeric ratios (55:45-82:18 dr) and high enantiomeric ratios (81:19-99:1 er).

Development of Chiral Ligands for the Transition-Metal-Catalyzed Enantioselective Silylation and Borylation of C-H Bonds.

Enantioselective reactions that install functional groups at the positions of unactivated C-H bonds can be envisioned to produce intermediates for the synthesis of the active ingredients in pharmaceuticals and agrochemicals directly from simple feedstocks. Among these C-H bond functionalization reactions, those that form carbon-silicon (C-Si) and carbon-boron (C-B) bonds have been pursued because the products of these reactions can be converted to those containing a wide range of functional groups and because compounds containing silicon and boron possess unique properties that can be valuable for medicinal and materials chemistry. Although the silylation and borylation of C-H bonds have undergone extensive development during the past two decades, enantioselective versions of these reactions were not known until a few years ago. In this Minireview, we present the rapid development of enantioselective silylation and borylation of C-H bonds, with an emphasis on the design and development of the types of chiral ligands needed to achieve these reactions and an intention to inspire an expansion of these types of transformations.

MMP-2-Activatable Photoacoustic Tumor Imaging Probes Based on Al- and Si-Naphthalocyanines.

Enzyme-activatable photoacoustic probes are powerful contrast agents to visualize diseases in which a specific enzyme is overexpressed. In this study, aluminum and silicon naphthalocyanines (AlNc and SiNc, respectively) conjugated with matrix metalloprotease-2 (MMP-2)-responsive PLGLAG peptide sequence and poly(ethylene glycol) (PEG) as an axial ligand were designed and synthesized. AlNc-peptide-PEG conjugates AlNc-pep-PEG formed dimeric species interacting with each other through face-to-face H-aggregation in water, while SiNc-based conjugates SiNc-pep-PEG hardly interacted with each other because of the two bulky hydrophilic axial ligands. Both conjugates formed spherical nanometer-sized self-assemblies in water, generating photoacoustic waves under near-infrared photoirradiation. The treatment of MNc-peptide-PEG conjugates (M = Al, Si) with MMP-2 smoothly induced the cleavage of the PLGLAG sequence to release the hydrophilic PEG moiety, resulting in the aggregation of MNcs. By comparing the PA signal intensity changes at 680 and 760 nm, the photoacoustic signal intensity ratios were shown to be enhanced by 3-5 times after incubation with MMP-2. We demonstrated that MNc-peptide-PEG conjugates (M = Al, Si) could work as activatable photoacoustic probes in the in vitro experiment of MMP-2-overexpressed cell line HT-1080 as well as the in vivo photoacoustic imaging of HT-1080-bearing mice.

Radiosynthesis of [18F]SiFAlin-TATE for clinical neuroendocrine tumor positron emission tomography.

Here, we describe an extension of our silicon fluoride acceptor (SiFA) protocol for 18F-labeling of peptides that addresses challenges associated with preparing a clinical-grade (Tyr3)-octreotate (TATE) tracer for diagnosis of neuroendocrine tumors (NETs). After several iterations of protocol optimization (e.g., finding the optimal pH at which the isotopic exchange (IE) reaction produces high radiochemical yields (RCYs)), the SiFA technology achieved clinical applicability, as showcased by radiosynthesis of [18F]SiFAlin-TATE ([18F]SiTATE), the first SiFA peptide used in the clinical diagnosis of NETs. The TATE peptide binds to somatostatin receptors associated with NETs. Radiolabeled TATE derivatives are routinely applied in clinical oncological PET imaging. The (SiFA) 18F-labeling technology is based on the IE of a 19F atom for a radioactive 18F atom, a highly efficient labeling reaction under mild conditions. The 19F is part of a biomolecule bearing the SiFA building block, composed of a central silicon (Si) atom, a 19F atom connected to the Si atom, and two Si-bound tert-butyl groups. The IE proceeds through a penta-coordinate bipyramidal intermediate, followed by elimination of non-radioactive 19F, yielding the labeled compound in high RCYs at room temperature (22 °C). The simplicity and lack of side-product formation of this approach enable a one-step, kit-like preparation of structurally complex and unprotected radiopharmaceuticals. Compounds such as peptides used for tumor imaging in nuclear medicine can be 18F-labeled without the need for complex purification protocols. [18F]SiTATE can be synthesized within 30 min in preparative RCYs of 42%, radiochemical purity of >97% and high molar activity of 60 GBq/µmol.

Synthesis, characterization and free radical scavenging activity of modified silica-naringin hybrid system.

This study aimed to develop a procedure for preparing a modified silica-naringin hybrid system. To accomplish, the properties of the obtained material were characterized by FT-IR analysis, UV-Vis spectrophotometry, thermogravimetry, scanning electron microscopy (SEM), and zeta potential. 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to characterize and evaluate the antioxidant activity. The naringin release profile at pH = 1.2 and 7.2 were determined. FT-IR studies confirmed the interaction between the naringin and present carrier. The release study indicated that a release an approximately 20% and 50% of the release occurred in the first 30 min in pH = 1.2 and 7.2, respectively. The thermogravimetry and UV-Vis spectrophotometry analysis allowed us to determine the amount of naringin in the studied hybrid material at the level of several percent. The proposed hybrid material shows good stability, as evidenced by the zeta potential of about +30 and -30 mV in an acidic and alkaline environment, respectively. Antioxidant properties are comparable to those of pure naringin. The results suggest that the obtained hybrid material is a promising product with antioxidant properties.

The physicochemical and biomechanical profile of forsterite and its osteogenic potential of mesenchymal stromal cells.

It has been demonstrated that nanocrystalline forsterite powder synthesised using urea as a fuel in sol-gel combustion method had produced a pure forsterite (FU) and possessed superior bioactive characteristics such as bone apatite formation and antibacterial properties. In the present study, 3D-scaffold was fabricated using nanocrystalline forsterite powder in polymer sponge method. The FU scaffold was used in investigating the physicochemical, biomechanics, cell attachment, in vitro biocompatibility and osteogenic differentiation properties. For physicochemical characterisation, Fourier-transform infrared spectroscopy (FTIR), Energy dispersive X-ray (EDX), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoemission spectrometer (XPS) and Brunauer-Emmett-Teller (BET) were used. FTIR, EDX, XRD peaks and Raman spectroscopy demonstrated correlating to FU. The XPS confirmed the surface chemistry associating to FU. The BET revealed FU scaffold surface area of 12.67 m2/g and total pore size of 0.03 cm3/g. Compressive strength of the FU scaffold was found to be 27.18 ± 13.4 MPa. The human bone marrow derived mesenchymal stromal cells (hBMSCs) characterisation prior to perform seeding on FU scaffold verified the stromal cell phenotypic and lineage commitments. SEM, confocal images and presto blue viability assay suggested good cell attachment and proliferation of hBMSCs on FU scaffold and comparable to a commercial bone substitutes (cBS). Osteogenic proteins and gene expression from day 7 onward indicated FU scaffold had a significant osteogenic potential (p<0.05), when compared with day 1 as well as between FU and cBS. These findings suggest that FU scaffold has a greater potential for use in orthopaedic and/or orthodontic applications.

Ultra-fast, highly efficient and green synthesis of bioactive forsterite nanopowder via microwave irradiation.

Forsterite (Mg2SiO4) has recently attracted considerable attention in different fields because of its wide range of applications. In this paper, pure forsterite nanopowders were synthesized by an ultra-fast, highly efficient and green method for the first time. Microwave irradiation was used to synthesize forsterite nanopowder. The formation of highly crystalline forsterite nanopowder was confirmed by X-ray diffraction (XRD) and energy dispersive X-ray spectrometer (EDS) analyses. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses showed that the agglomerated powder composed of nanocrystalline particles with the mean particle size of ~100 nm. Microwave irradiation significantly accelerated the rate of the reactions and dramatically decreased reaction times from hours to minutes and seconds. In vitro bioactivity evaluation was performed by soaking the forsterite samples in simulated body fluid (SBF). Results indicated that synthesized forsterite nanopowder via microwave irradiation method possessed excellent apatite-forming ability in SBF. Cell viability results showed that synthesized forsterite nanopowder not only showed no cytotoxicity but also improved cell proliferation. Alkaline phosphatase (ALP) activity assay indicated that the fabricated forsterite nanopowder could facilitate the MG63 osteoblast-like cells to proliferate and differentiate. Therefore, microwave-assisted synthesis technique could be considered as a novel, safe and high efficient method in saving time and energy for bioactive forsterite nanopowder production.

Ionic liquid-type surfactant modified attapulgite as a novel and efficient dispersive solid phase material for fast determination of pyrethroids in tea drinks.

In this study, a novel ionic liquid-type surfactant modified attapulgite named as 1-dodecyl-3-methylimidazolium bromide-attapulgite (C12MIM-ATP) is successfully prepared and applied in dispersive solid phase extraction (dSPE) for the fast determination of pyrethroid residues in tea drinks. The primary factors that influenced the extraction efficiency, including sorbent type, amount of sorbent, extraction time, desorption conditions, pH and ionic strength, are investigated. The optimized results reveal that the extraction and desorption equilibria are rapidly obtained within 1 min. Under the optimized conditions, good linearity (2-500 µg/L) is observed for four pyrethroids in tea drinks with determination coefficients (r2) ranged from 0.9992 to 1.0000. The limits of detection (LODs) are 0.6 µg/L for all pesticides. Acceptable extraction recoveries of target analytes are found from 90.28 to 107.56% with relative standard deviations (RSDs) less than 8.30% in real tea drink samples. The batch-to-bath repeatability is evaluated by recovery test on five independent synthesized C12MIM-ATP sorbents. Satisfactory batch-to-batch repeatability is obtained with the recovery factors varied in 15%. A small matrix effect is observed using C12MIM-ATP as the sorbent for detection pyrethroids in tea drinks.

A neutral auxiliary ligand enhanced dysprosium(iii) single molecule magnet.

An approximately equatorial three-coordinated dysprosium(iii) complex DyL2[N(SiMe3)2] (L = bis(2-(2,5-dimethyl-1H-pyrrol-1-yl)ethyl)amine) with an additional neutral auxiliary pyrrole ligand was synthesised and structurally characterized. The magnetic property measurement shows that it is an equatorial charge distributed field-induced single-molecule magnet. Ab initio calculations reveal that the neutral pyrrole ligand plays an important role in stabilizing the ground doublet and thus enhancing the magnetic anisotropy.

Synthesis and characterization of nanocrystalline forsterite coated poly(L-lactide-co-ß-malic acid) scaffolds for bone tissue engineering applications.

In this research, after synthesizing poly(L-lactide-co-ß-malic acid) (PLMA) copolymer, hybrid particles of ice and nanocrystalline forsterite (NF) as coating carriers were used to prepare NF-coated PLMA scaffolds. The porous NF-coated scaffolds were directly fabricated by a combined technique using porogen leaching and freeze-drying methods. The obtained results indicate that the scaffolds were structurally porous with NF particles on their surfaces. When compared to the uncoated scaffolds, the NF coating improved both mechanical properties as well as enhanced bioactivity of the scaffolds. In addition, in vitro biological response of the rat bone marrow stromal cells indicated that NF significantly increased the biocompatibility of NF-coated scaffolds compared with PLMA.

Synthesis of boronic-acid-functionalized magnetic attapulgite for selective enrichment of nucleosides.

2,4-Difluoro-3-formyl-phenylboronic acid (DFFPBA)-modified magnetic attapulgite (ATP-Fe3O4-NH2-DFFPBA) was synthesized and employed to capture and enrich cis-diol-containing biomolecules. The resulting material exhibited a high saturation magnetization value of 20.71 emu/g, allowing the absorbent to be conveniently magnetically separated. Combining the Fe3O4 nanoparticles with the high specific surface area of attapulgite yielded a material with a high capture capacity (13.78 mg/g) for adenosine. Furthermore, ATP-Fe3O4-NH2-DFFPBA was found to possess remarkable selectivity for adenosine at a low molar ratio of adenosine/2-deoxyadenosine (1:500). The potential applications of this material were explored by using it to extract five nucleosides from urine samples, and the results demonstrate that it can decrease matrix interference and selectively enrich analytes.

Synthesis and luminescence characterization of Pr(3+) doped Sr1.5Ca0.5SiO4 phosphor.

Luminescence properties of Pr(3+) activated Sr1.5Ca0.5SiO4 phosphors synthesized by solid state reaction method are reported in this work. Blue, orange red and red emissions were observed in the Pr(3+) doped sample under 444nm excitation and these emissions are assigned as (3)P0→(3)H4, (3)P0→(3)H6 and (3)P0→(3)F4 transitions. The emission intensity shows a maximum corresponding to the 0.5wt% Pr(3+) ion. The decay analysis was done for 0.05 and 0.5wt% Pr(3+) doped samples for the transition (3)P0→(3)H6. The life times of 0.05 and 0.5wt% Pr(3+) doped samples were calculated by fitting to exponential and non-exponential curve respectively, and are found to be 156 and 105µs respectively. The non-exponential behaviour arises due to the statistical distribution of the distances between the ground state Pr(3+) ions and excited state Pr(3+) ions, which cause the inhomogeneous energy transfer rate. The XRD spectrum confirmed the triclinic phase of the prepared phosphors. The compositions of the samples were determined by the energy dispersive X-ray spectra. From the SEM images it is observed that the particles are agglomerated and are irregularly shaped. IR absorption bands were assigned to different vibrational modes. The well resolved peaks shown in the absorption spectra are identical to the excitation spectra of the phosphor samples. Pr(3+) activated Sr1.5Ca0.5SiO4 phosphors can be efficiently excited with 444nm irradiation and emit multicolour visible emissions. From the CIE diagram it can be seen that the prepared phosphor samples give yellowish-green emission.

Non-precious metals catalyze formal [4 + 2] cycloaddition reactions of 1,2-diazines and siloxyalkynes under ambient conditions.

Copper(I) and nickel(0) complexes catalyze the formal [4 + 2] cycloaddition reactions of 1,2-diazines and siloxyalkynes, a reaction hitherto best catalyzed by silver salts. These catalysts based on earth abundant metals are not only competent, but the copper catalyst, in particular, promotes cycloadditions of pyrido[2,3-d]pyridazine and pyrido[3,4-d]pyridazine, enabling a new synthesis of quinoline and isoquinoline derivatives, as well as the formal [2 + 2] cycloaddition reaction of cyclohexenone with a siloxyalkyne.

Synthesis, structural and luminescence properties of Mn doped ZnO/Zn2SiO4 composite microphosphor.

Manganese doped ZnO/Zn2SiO4 (MZS) composite phosphors were successfully prepared by conventional solid state reaction method. The structural and optical properties of as-prepared samples were analysed by means of XRD, SEM, PLE and PL. The result shows that the samples consist of both ZnO and ZnSiO4 phases which confirms the composite phosphor. The strain acting on the phosphor is found to be in the range of 0.0040-0.0058 for different concentration of Mn(2+) doping. The doping of Mn(2+) significantly influences the optical properties of phosphor. Under 266 nm laser excitation samples show green emission (∼530 nm) and with 355 nm laser excitation blue emission (∼441 nm) is shown. The enhancement of luminescence intensity is achieved with Mn(2+) doping up to an optimum concentration (10 at.%) and then decreases. On 266 nm excitation, blue emission intensity decreases with Mn(2+) doping. This composite phosphor shows both blue and green emission under different excitations.

Nanocrystalline forsterite for biomedical applications: synthesis, microstructure and mechanical properties.

Forsterite (Mg2SiO4) because of its exceptionally high fracture toughness which is close to that of cortical bones has been nominated as a possible successor to calcium phosphate bioceramics. Recent in vitro studies also suggest that forsterite possesses good bioactivity and promotes osteoblast proliferation as well as adhesion. However studies on preparation and sinterability of nanocrystalline forsterite remain scarce. In this work, we use a solid-state reaction with magnesium oxide (MgO) and talc (Mg3Si4(OH)2) as the starting precursors to synthesize forsterite. A systematic investigation was carried out to elucidate the effect of preparatory procedures including heat treatment, mixing methods and sintering temperature on development of microstructures as well as the mechanical properties of the sintered forsterite body.

Chemical tricks to stabilize silanones and their heavier homologues with E=O bonds (E=Si-Pb): from elusive species to isolable building blocks.

In contrast to the well-established chemistry of ketones (R2C=O), the reactivity of the elusive heavier congeners R2E=O (E=Si, Ge, Sn, Pb) is far less explored because of the high polarity of the E=O bonds and hence their tendency to oligomerize with no activation barrier. Very recently, great advances have been achieved in the synthesis of isolable compounds with E=O bonds, including the investigation of donor-stabilized isolable silanones and the first stable "genuine" germanone. These compounds show drastically different reactivities compared to ketones and represent versatile building blocks in silicon-oxygen and germanium-oxygen chemistry. This and other exciting achievements are described in this Minireview.

Easy access to silicon(0) and silicon(II) compounds.

Two different synthetic methodologies of silicon dihalide bridged biradicals of the general formula (L(n)•)2SiX2 (n = 1, 2) have been developed. First, the metathesis reaction between NHC:SiX2 and L(n): (L(n): = cyclic akyl(amino) carbene in a 1:3 molar ratio leads to the products 2 (n = 1, X = Cl), 4 (n = 2, X = Cl), 6 (n = 1, X = Br), and 7 (n = 2, X = Br). These reactions also produce coupled NHCs (3, 5) under C-C bond formation. The formation of the coupled NHCs (L(m) = cyclic alkyl(amino) carbene substituted N-heterocyclic carbene; m = 3, n = 1 (3) and m = 4, n =2 (5)) is faster during the metathesis reaction between NHC:SiBr2 and L(n): when compared with that of NHC:SiCl2. Second, the reaction of L(1):SiCl4 (8) (L(1): =:C(CH2)(CMe2)2N-2,6-iPr2C6H3) with a non-nucleophilic base LiN(iPr)2 in a 1:1 molar ratio shows an unprecedented methodology for the synthesis of the biradical (L(1)•)2SiCl2 (2). The blue blocks of silicon dichloride bridged biradicals (2, 4) are stable for more than six months under an inert atmosphere and in air for one week. Compounds 2 and 4 melt in the temperature range of 185 to 195 °C. The dibromide (6, 7) analogue is more prone to decomposition in the solution but comparatively more stable in the solid state than in the solution. Decomposition of the products has been observed in the UV-vis spectra. Moreover, compounds 2 and 4 were further converted to stable singlet biradicaloid dicarbene-coordinated (L(n):)2Si(0) (n = 1 (9), 2 (10)) under KC8 reduction. Compounds 2 and 4 were also reduced to dehalogenated products 9 and 10, respectively when treated with RLi (R = Ph, Me, tBu). Cyclic voltametry measurements show that 10 can irreversibly undergo both one electron oxidation and reduction.

Diol-linked microporous networks of cubic siloxane cages.

A new class of inorganic-organic hybrid porous materials has been synthesized by a reaction between octa(hydridosilsesquioxane) (H(8)Si(8)O(12)), which has a double-four-ring (D4R) structure, and various diols, such as 1,3-propanediol (PD), 1,4-cyclohexanediol (CHD), and 1,3-adamantanediol (AD). Solid-state (29) Si magic-angle-spinning NMR spectroscopic analysis confirmed that most of the corner Si-H groups reacted with diols to form Si-O-C bonds with retention of the D4R cage. Nitrogen adsorption-desorption studies showed that the products are microporous solids with high BET surface areas (up to ≈580 m(2) g(-1) for CHD- and AD-linked products). If n-alkanediols are used as linkers, the surface area becomes smaller as the number of carbon atoms is increased. The thermal and hydrolytic stability of the products strongly depend on the type of diol linkers. The highest stabilities are found for the AD-linked products, which are thermally stable up to around 400 °C and remain intact even after being soaked in water for 1 day. In contrast, the PD-linked product is easily hydrolyzed in water to give microporous silica. These results offer a new route toward a series of silica-based porous materials with unique structures and properties.

Raman study of the formation of beta silicomolybdic acid supported on silica, prepared by impregnation method.

Beta silicomolibdic acid/silica (ß-SMA, a metastable form of silicomolybdic acid - H(4)SiMo(12)O(40)) forms by the impregnation of fumed silica into molybdenum solution obtained by hydrolyzation of MoO(2)Cl(2.) ß-SMA/silica is found to be stable up to 300 °C after calcination for 1h due to the existence of an interlayer MoO(3) between silica surface and ß-SMA. Structures of molybdenum species in the preparation process (including precursor solution) were analyzed by Raman spectroscopy and XRD.

CdSiO3:Pr³âº nanophosphor: synthesis, characterization and thermoluminescence studies.

A series of Pr(3+) (1-9 mol%) doped CdSiO(3) nanophosphors have been prepared for the first time by a low temperature solution combustion method using oxalyldihydrizide (ODH) as a fuel. The final product was characterized by Powder X-ray diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The average crystallite size was calculated using Debye-Scherrer's formula and Williamson-Hall (W-H) plots and found to be in the range 31-37 nm. The optical energy band gap (E(g)) of undoped for Pr(3+) doped samples were estimated from Tauc relation which varies from 5.15-5.36 eV. Thermoluminescence (TL) properties of Pr(3+) doped CdSiO(3) nanophosphor has been investigated using γ-irradiation in the dose range 1-6 kGy at a heating rate of 5 °C s(-1). The phosphor shows a well resolved glow peak at ∼171 °C along with shouldered peak at 223 °C in the higher temperature side. It is observed that TL intensity increase with increase of Pr(3+) concentration. Further, the TL intensity at 171 °C is found to be increase linearly with increase in γ-dose which is highly useful in radiation dosimetry. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics was estimated by Luschiks method and the results are discussed.