Si-O Bond Cleavage Research Articles

Ratiometric fluorescence-based and chromogenic sensors for the detection of fluoride ions and their application in real samples.

This review focuses on the results of synthetic ratiometric fluorescent and colorimetric probes, which have been applied to qualitatively and quantitatively detect fluoride anions in cells, living organisms, and real samples. Primary attention is given to progress made in the working mechanism and applications of these probes to detect fluoride ions in living systems. In addition, design strategies and detection limit for these probes are discussed. This review aims to deliver a comprehensive compilation of the examples reported from 2005 to 2021 on the developments of ratiometric chromogenic and fluorogenic chemosensors for fluoride anions. A total of 20 different ratiometric/colorimetric sensors have been selected for the novelty in their design, sensitivity, detection limit, dynamic range, and speed of detection based on the three fundamental principles of F- ion detection, namely Si-O bond cleavage; excimer emission; and intramolecular charge transfer emission through the B-F monomer, B-F-B bridged dimers, and deprotonation of the amide N-H. Special emphasis has been given to categorize the fluorophores that work in aqueous media, and possible strategies that might be adopted to design green sensors are discussed. Finally, a tabular summary of the comparative studies of all the sensors based on their sensitivity, detection limit, working solvent, and applications is provided. This extensive review may expedite improvements in the development of advanced fluorescent probes for vast and stimulating applications in the future.

Iron(II)-Catalyzed Activation of Si-N and Si-O Bonds Using Hydroboranes.

We report the activation and functionalization of Si-N bonds with pinacol borane catalyzed by a three-coordinate iron(II) β-diketiminate complex. The reactions proceed via the mild activation of silazanes to yield useful hydrosilanes and aminoboranes. The reaction is studied by kinetic analysis, along with a detailed investigation of decomposition pathways using catecholborane as an analogue of the pinacol borane used in catalysis. We have extended the methodology to develop a polycarbosilazane depolymerization strategy, which generates hydrosilane quantitatively along with complete conversion to the Bpin-protected diamine. The analogous Si-O bond cleavage can also be achieved with heating, using silyl ether starting materials to generate hydrosilane and alkoxyborane products. Depolymerization of poly(silyl ether)s using our strategy successfully converts the polymer to 90% Bpin-protected alcohols.

A novel, simple, and quick plate assay to screen silicolytic bacteria and silicase production using different substrates

Silicase helps in dissolving silica by catalyzing the cleavage of SiO and SiC bonds to form silicic acid. It belongs to carbonic anhydrases owing to its highest structural homology. Potential applications of silicase are wide and diverse ranging from e-waste remediation to tailoring nanochips and bio-desilication of rice straw for its utilization as substrate for biofuels production. Herein, a soil bacterium was isolated and screened for its ability to produce silicase. A simple and quick screening method for silicolytic bacteria was established. Different agro-residues including rice straw, wheat straw and bagasse along with silicon dioxide and magnesium trisilicate were investigated for their use as substrate. Silicase activity was found to be the highest for rice straw as a substrate since it has the highest silica content among other agro-residues. FTIR analysis of all production media showed silica dissolution before and after inoculation.

A novel ICT-based chemosensor for F- and its application in real samples and bioimaging

A novel colorimetric and fluorescent chemosensor MQS-Si with intramolecular charge transfer character has been designed and synthesized. The chemosensor shows exclusively “off-on” fluorescence response toward F- at 620 nm in HEPES (pH 7.4): DMSO solution (7:3, v/v), which is attributed to the specific cleavage of Si-O bond. The ultrasensitive detection limit for F- in the fluorescence measurement is down to 30 nM. Application of the chemosensor has been demonstrated by selective detection of F- in drinking water, urine and serum samples and fluorescence imaging of F- in living cells and zebrafish, which proves that MQS-Si has a promising application in vitro and in vivo detection of F- and may be utilized for the diagnosis of fluorosis and esteofluorosis.

Multinuclear Clusters of Manganese and Lithium with Silsesquioxane-Derived Ligands: Synthesis and Ligand Rearrangement by Dioxygen- and Base-Mediated Si-O Bond Cleavage.

The synthesis of manganese cluster complexes templated by polyhedral oligomeric silsesquioxane-derived ligands is described. MnII3(Ph7Si7O12)2Pyr4 (1) and MnII4(Ph4Si4O8)2(Bpy)2(Py)2 (3) are prepared by replacement of the amide ligands of Mn(NR2)2 (R = SiMe3) via ligand protolysis by the acidic proton of the respective silsesquioxane-derived silanols. Complex 1 is shown to undergo ligand rearrangement by reaction with O2, which results in oxidation of the cluster to a mixed MnII/III cluster, concomitant with cleavage of the Si-O bonds of the ligand, releasing a [Ph2Si-O]+ unit, opening a new ligating siloxide group, and resulting in the formation of Mn3(Ph6Si6O11)2Pyr4 (2). The ligand framework of 1 can also be perturbed by a base. The addition of LiOH/BuLi delivers a soluble equivalent of Li2O to 1, resulting in cleavage of the Si-O bonds and linkage of the resulting exposed silicon atoms by the new oxide, giving a linked ligand variant that templates a Li2Mn3 cluster, Mn3Li2(Ph7Si7O12OPh7Si7O12)DMF5Pyr (4). These systems are characterized by single-crystal X-ray diffraction, absorption spectroscopy, Fourier transform infrared, cyclic voltammetry, and CHN combustion analysis. Mechanistic implications for the Si-O bond cleavage events are discussed.

Smartphone as a simple device for visual and on-site detection of fluoride in groundwater

Developing a portable device for visual and on-site detection of fluoride in groundwater is highly anticipated. In this paper, 2-(tert-butyl-diphenylsilanyloxy)−5-nitro-1H-benzoimidazole (1) has been rationally designed via a silanization reaction for self-calibration detection of fluoride, and the detection limit was calculated as 0.11 μM. The contact of 1 with fluoride would induce the cleavage of Si-O bond and trigger the emergence of excited state intramolecular proton transfer (ESIPT) process, and then the enol-like emission at 437 nm decreased accompanying with the increase of keto-like tautomerism emission at 550 nm. More importantly, considering the demand of field detection for fluoride in groundwater and combining the function of smartphone to obtain the chroma of photos. The chroma value of the fluorescence color changes from blue to yellow could be conveniently determined through a color recognizer application installed in smartphone. The device can accurately reflect the concentration of fluoride by analyzing the chroma value. The test in actual water samples confirmed that the simple device based on smartphone could be used efficiently for visual, on-site and accurate detection of fluoride in groundwater.

Rationally Designed Self-Immolative Rotaxane Sensor Based on Pillar[5]arene for Fluoride Sensing.

We develop a self-immolative rotaxane sensor for fluoride sensing based on host-guest interactions between pillar[5]arene and fluoride-promoted cleavage of Si-O bond. Because of the selective and fast reaction between silane and fluoride, the rotaxane sensor shows anion selectivity and rapid response. The self-immolative nature of the rotaxane improve its sensitivity. Moreover, a fluoride sensing test paper based on the rotaxane sensor is made, which shows the practicable application of the rotaxane sensor.

On the SN2 reactions modified in vibrational strong coupling experiments: reaction mechanisms and vibrational mode assignments.

Recent experiments have reported modified chemical reactivity under vibrational strong coupling (VSC) in microfluidic Fabry-Pérot cavities. In particular, the reaction rate of nucleophilic substitution reactions at silicon centers (SN2@Si) has been altered when a vibrational mode of the reactant was coupled to a confined light mode in the strong coupling regime. In this situation, hybrid light-matter states known as polaritons are formed and seem to be responsible for the modified chemical kinetics. These results are very encouraging for future applications of polaritonic chemistry to catalyze chemical reactions, with the ability to manipulate chemical phenomena without any external excitation of the system. Still, there is no theory capable of explaining the mechanism behind these results. In this work we address two points that are crucial for the interpretation of these experiments. Firstly, by means of electronic structure calculations we report the reaction mechanism in normal conditions of the two recently modified SN2@Si reactions, obtaining in both cases a triple-well PES where the rate-determining step is due to the Si-C and Si-O bond cleavage. Secondly, we characterize in detail the normal modes of vibration of the reactants. In the VSC experiments, reaction rates were modified only when specific vibrations of the reactants were coupled to a cavity mode. We find that these vibrations are highly mixed among the different fragments of the reactants leading to a completely new assignment of the IR peaks coupled to cavity modes in the original experimental works. Our results are fundamental for the interpretation of the VSC experiments given that in the absence of a theory explaining these results, the current phenomenological understanding relies on the assignment of the character of the vibrational IR peaks.

Temporal characteristics of groundwater chemistry affected by the 2016 Kumamoto earthquake using self-organizing maps

Possibilities to perform pre- and post-seismic groundwater chemical comparisons on regional groundwater flow systems are rare due to lack of data and observations. The Kumamoto earthquake provides an unusual opportunity to improve the knowledge on earthquake hydrology and earthquake effects on hydrochemistry of groundwater due to a wealth of pre- and post-quake observations. We analyzed 12 physiochemical parameters (SiO2, (NO3– + NO2–)-N, Fetotal, Mntotal, pH, F−, Cl−, SO42−, Na+, K+, Ca2+, and Mg2+) using self-organizing maps (SOM) combined with hydrological and geological characteristics to improve the understanding of changes in groundwater chemistry after a major earthquake. The results indicate that the earthquake induced hydrological and environmental change via fault forming (Suizenji fault systems), liquefaction, rock fracturing, and ground shaking. These geological processes created rock fresh reactive surfaces, rock loosening, and enhancement of hydraulic conductivity. In turn, this lead to secondary processes in groundwater chemistry by advection, dilution, and chemical reaction. The most obvious indicator of hydrological and environmental change was from the increased dissolved silica content stemming from fracturing and Si-O bond cleavage in silicate rocks. Besides this, decreasing concentration of common ions (Cl−, F−, Na+, K+, Ca2+) was found due to dilution from mountain-side water release. Increase in (NO3– + NO2–)-N, SO42−, and Mg2+ concentration occurred locally due to soil leaching of contaminants or agricultural fertilizers through surface ruptures in recharge areas. Increase of SO42− content also originated from leaching of marine clay in coastal areas and possibly sporadic deep crustal fluid upwelling. Increase in (NO3– + NO2–)-N and Cl− content occurred from sewage water pipe breaks in the Suizenji fault formation in urban areas. Decrease of pH occurred in a few wells due to mixing of river water and different types of aquifer groundwater. Increase of Fetotal and Mntotal concentration possibly originated from leaching of marine clay by liquefaction in coastal areas. However, in most cases the water chemistry changes were subtle, thus not resulting in any groundwater quality deterioration of water supplies.

Rhodol-based fluorescent probes for the detection of fluoride ion and its application in water, tea and live animal imaging.

Herein, we presented two novel turn-on colorimetric and fluorescent probes based on a F- triggered SiO bond cleavage reaction, which displayed several desired properties for the quantitative detection for F-, such as high specificity, rapid response time (within 3 min) and naked-eye visualization. The fluorescence intensity at 574 nm (absorbance at 544 nm) of the solution was found to increase linearly with the concentration of F- (0.00-30.0 μM) with the detection limit was estimated to be 0.47 μM/0.48 μM. Based on these excellent optical properties, the probes were employed to monitor F- in real water samples and tea samples with satisfactory. Furthermore, it was successfully applied for fluorescent imaging of F- in living nude mice, suggesting that it could be used as a powerful tool to predict and explore the biological functions of F- in physiological and pathological processes.

Adsorption of linear and cyclic siloxanes on activated carbons for biogas purification: Sorbents regenerability

Two commercial activated carbons, namely STIX and AP4, were selected to investigate their ability for siloxane adsorption and further thermal regeneration in relation with their different physico-chemical properties. In the frame of biogas purification, the studied siloxanes were L2, L3, L4 (linear molecules) and D4, D5 (cyclic molecules). The maximum capacity of adsorption was estimated by gas chromatography and gravimetric methods. AP4 presents better adsorptive properties comparing with STIX irrespective of the type of siloxane. Thermal regeneration after siloxanes adsorption was followed up to 400 °C by both gas chromatography and in situ DRIFTS. Except L2, the siloxane polymerization proceeds on the AC containing alkali metals (K, Na) as revealed by the observed release of their decomposition products during the thermodesorption treatment. The same sites are responsible for the cleavage of SiO bonds in linear molecules and formation of L2 as primary product above 100 °C. The presence of such sites, possibly strong basic sites, is detrimental to the regenerability of the spent adsorbent and to the adsorption which could be limited by partial blockage of the AC porosity. Interestingly the regenerability of the alkali-free AC depends only on the volatility of the siloxane.

A rationally designed flavone-based ESIPT fluorescent chemodosimeter for highly selective recognition towards fluoride and its application in live-cell imaging

Fluoride recognition and sensing via artificial receptors have attracted a great deal of attention since it plays an important and indispensable role in biological and environmental processes. Herein, a novel colorimetric and fluorescent chemodosimeter (3-triisopropylsilylflavone 1) based on 3-hydroxyflavone framework has been rationally designed and synthesized for selective recognition towards fluoride. As confirmed by UV–vis and fluorescence techniques, the fluorescent probe 1 exhibited a highly sensitive and selective as well as rapidly responsive (20 s) recognition towards fluoride with a large Stokes shift of 180 nm. The detection limit was deduced to be 0.68 μM, which is much lower than the limit concentration level in drinking water specified by USEPA. The distinctive sensing mechanism is attributed to fluoride-triggered desilylation reaction on the cleavage of SiO bonds, leading to the strong excited-state intramolecular proton transfer emission of 3-hydroxyflavone. In addition, test strips experiment based on the sensor demonstrated the excellently practical feasibility of 1 to sense fluoride even in ppm level. Moreover, the probe is cell permeable and can be capable of reliably detecting fluoride in living cells.

Interaction of Poly(dimethylsiloxane) and octamethylcyclotetrasiloxane with aluminum oxides comprising different acid-base properties

Interactions between polymer matrices and inorganic mineral surfaces are especially relevant in polymer-filler composites and in adhesion science. Knowledge about underlying mechanisms at the interphase is a prerequisite for understanding functionality and aging. Therefore, interactions of poly(dimethylsiloxanes) (PDMS) and octamethylcyclotetrasiloxane (D4) with aluminum oxides comprising different acid-base properties were studied. For this purpose, thin layers of siloxanes were applied on aluminum oxides and analyzed by Raman spectroscopy and thermogravimetric analysis. It was observed that aluminum oxides are able to react with PDMS and D4 by heterolytic bond cleavage of SiO bonds, either by reactions with physisorbed water under catalysis of aluminum oxide or by direct reaction of the surface with siloxanes. Both reaction paths can yield SiOAl bonds and thus chemisorption which lead to strong interactions between siloxanes and aluminum oxides. However, the shown reaction paths concomitantly act as aging mechanisms leading to degradation of polymer.

Ratiometric sensing of fluoride anion through selective cleavage of Si[sbnd]O bond

A new imidazole-based ratiometric fluorescent probe for fluoride anion was designed and synthesized. The sensing abilities of the probe towards various anions were studied by absorption and emission spectroscopies in dimethylsulfoxide (DMSO) as well as in DMSO/H2O. The spectroscopic studies reveal that the signalling mechanism involves the release of excited state intramolecular proton transfer (ESIPT) activated imidazole via Si-O bond cleavage.

Structural characterization of polymethoxymethylsiloxanes by electrospray ionization tandem mass spectrometry

Poly(methoxymethylsiloxane)s (PMMS) are silicon-based polymers usually prepared according to a poorly controlled synthesis route, yielding samples of high structural dispersity. Collision induced dissociation of PMMS was hence studied in detail in order to propose MS/MS rules to be usefully employed for end-group characterization. Lithium adduction did not provide meaningful insights through charge remote dissociation while ammonium adduction allowed PMMS to readily dissociate according to two main information-rich charge driven routes. On one hand, after precursor ions have eliminated methanol together with ammonia, a series of 46Da (CH2O+CH4) losses was observed, the number of which could be used to decipher the polymerization degree of the dissociating precursor. On the other hand, cleavage of SiO bonds in the polymer backbone generated two series of product ions of low m/z values, each containing one or the other end-group found to be methoxy and tetramethyltetramethoxycyclotetrasiloxy terminations. Proposed mechanisms were all supported by accurate mass measurements and MS3 experiments. Based on these two highly complementary routes, the three main species of a PMMS sample were thoroughly characterized, allowing unique insights on the synthesis mechanism.

DFT study of the hydrolysis reaction in atranes and ocanes: the influence of transannular bonding.

Thermochemical kinetics of hydrolysis reactions of compounds with transannular intramolecular M…N bonds, i.e., atranes RM(OCH2CH2)3N and ocanes R2M(OCH2CH2)2NH (M = Si, Ge; R = F, Cl, Me), is studied at the B3LYP/aug-cc-pVDZ theoretical level. Several DFT methods are assessed for the reproduction of the experimental activation barrier for the Si-O bond cleavage of 1-methylsilatrane. Activation barriers for atranes and ocanes show the tendency for their growth with the decrease of the electronegativity of a substituent R on going from F to Me and their decrease from Si to Ge. Hydrolysis activation barriers of atranes and ocanes are compared with those of their acyclic analogs RM(OCH3)3 and R2M(OCH2)2NH in order to study the role of transannular M…N bonds in the stability of these molecules to hydrolysis. Substantially larger barriers for atranes support the opinion that stability of atranes may be explained by the formation of intramolecular bonds; however, the strengthening of transannular M…N bonds results in lower M-O cleavage barriers. It was proposed that the M-O cleavage barrier height is determined not by a weak M…N bonding itself, but rather by the contribution of a nitrogen lone pair to the antibonding orbitals of M-O bonds. The NBO analysis show that this interaction increases with the decrease of the electronegativity of a substituent R and decreases on going from atranes to ocanes. In ocanes, the presence of M…N bonds does not kinetically hinder the hydrolytic process; M-O cleavage activation barriers for acyclic analogs are higher. M-Hal cleavage barriers are substantially higher than those for M-O cleavage for R = F, but lower for R = Cl. Graphical Abstract The experimental barrier height of the Si-O bond cleavage in 1-methylsilatrane is well reproduced when three explicit water molecules are included in the B3LYP/aug-cc-pVDZ theoretical model.

A selective chromofluorogenic chemodosimeter for fluoride ions based on distyrylbenzenes derivatives containing dual Si–O groups

A new chemodosimeter for fluoride ions based on F(-) triggered dual Si-O bond cleavage of distyrylbenzenes derivatives was developed for the first time. Upon the addition of F(-) ions, the chemodosimeter (7) displayed apparent color changes from colorless to faint yellow, with a dramatic red-shift in the emission wavelength (~100 nm), and higher selectivity for fluoride over other common anions. With the aid of fluorescence measurements, the limit of detection could be as low as 89.8 nm. Using a 'dipstick' approach, chemodosimeter (7) might serve as a prototype device for fluorescent detecting F(-) without the need for any additional equipment. Copyright © 2015 John Wiley & Sons, Ltd.

Kinetic Studies of Reactions of Hydroxyporphyrins on Silicate Surface

Construction of the monolayer film of semiconductive and redox-active porphyrins on the metal oxides such as silicate or titanates attracts interests for possible applications of the process in fabricating organic electronic devices, organic catalysts, and organic-inorganic hybrid materials. Porphyrins bearing linker functional groups such as hydroxy or bromo groups in the peripheral meso-phenyl groups were reacted with the surface silanol groups of silicate glass at 80 to 240 oC in a solid-solid reaction to obtain the monolayer film of porphyrin on the silicate glass. The rates of the reaction were determined by visible spectroscopic studies and they decreased in the order: primary alcohol > primary bromide ~ tertiary alcohol. In addition to the structures of the linker groups, melting points of porphyrins also affect the reactivity of the porphyrin. Porphyrins with long alkyl chains reacted faster than those without long alkyl chains, because the long alkyl groups would facilitate molecular motion to reach the transition state of the reaction. Hydrolysis of the porphyrin monolayer prepared from primary alcohol in 1 M aq. HCl at 50 oC proceeded in a similar rate to that prepared from tertiary alcohol. Base catalyzed hydrolysis in 1 M aq. NH3 at 30 oC of the porphyrin monolayer prepared from tertiary alcohol proceeded 20 times slower than that prepared from the primary alcohol. In the literature, it is well established that the hydrolysis of the silicate ester bond proceeds via the Si-O bond cleavage, since the silicon atom can form a penta-coodinated structure, and much more reactive than carbon atom toward a substitution reaction. Hydrolysis of the porphyrin monolayer prepared from the tertiary alcohol in H2 18O afforded 18O-labelled tertiary alcohol, indicating that there was a covalent bond between the porphyrin and silicate glass, and the C-O bond was cleaved in the acid catalyzed hydrolysis reaction of the tertiary alkyl silicate ester on the silicate glass.

Fluorescent sensing of fluoride in cellular system.

Fluoride ions have the important roles in a lot of physiological activities related with biological and medical system, such as water fluoridation, caries treatment, and bone disease treatment. Great efforts have been made to develop new methods and strategies for F- detection in the past decades. Traditional methods for the detection of F- including ion chromatography, ion-selective electrodes, and spectroscopic techniques have the limitations in the biomedicine research. The fluorescent probes for F- are very promising that overcome some drawbacks of traditional fluoride detection methods. These probes exhibit high selectivity, high sensitivity as well as quick response to the detection of fluoride anions. The review commences with a brief description of photophysical mechanisms for fluorescent probes for fluoride, including photo induced electron transfer (PET), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), and excited-state intramolecular proton transfer (ESIPT). Followed by a discussion about common dyes for fluorescent fluoride probes, such as anthracene, naphalimide, pyrene, BODIPY, fluorescein, rhodamine, resorufin, coumarin, cyanine, and near-infrared (NIR) dyes. We divide the fluorescent probes for fluoride in cellular application systems into nine groups, for example, type of hydrogen bonds, type of cleavage of Si-O bonds, type of Si-O bond cleavage and cylization reactions, etc. We also review the recent reported carriers in the delivery of fluorescent fluoride probes. Seventy-four typical fluorescent fluoride probes are listed and compared in detail, including quantum yield, reaction medium, excitation and emission wavelengths, linear detection range, selectivity for F-, mechanism, and analytical applications. Finally, we discuss the future challenges of the application of fluorescent fluoride probes in cellular system and in vivo. We wish that more and more excellent fluorescent fluoride probes will be developed and applied in the biomedicine field in the future.

Highly sensitive and selective fluoride ion sensors based on microcantilevers modified with hydrogels.

We have developed two microcantilever sensors, one modified with chitosan/gelatin hydrogels doped with CH3(OCH2CH2)3OTBDPS and another modified with chitosan-OTBDPS/gelatin hydrogels, for the sensitive and selective detection of fluoride ions (F-) in aqueous solution. Upon exposure to F-, the microcantilevers underwent bending deflection due to the cleavage of Si-O bond on reacting with F- in the hydrogel. The results show that the maximum bending deflections are proportional to the concentrations of F-, and the limits of detection are 10(-8) M and 10(-9) M for the two microcantilevers, respectively. Other ions, such as Cl-, Br-, NO3-, H2PO4-, HSO4-, and AcO- have little effect on the deflection of the microcantilevers. The results show that the microcantilever may be used for in situ quantitative detection of F- in an aqueous solution and the mechanism of the bending are discussed.