A DFT Study on the Reaction Pathways for Carbon?Carbon Bond‐Forming Reactions between Propargylic Alcohols and Alkenes or Ketones Catalyzed by Thiolate‐Bridged Diruthenium Complexes

The reaction pathways of two types of the carbon? carbon bond‐forming reactions catalyzed by thiolate‐bridged diruthenium complexes have been investigated by density‐functional‐theory calculations. It is clarified that both carbon? carbon bond‐forming reactions proceed through a ruthenium–allenylidene complex as a common reactive intermediate. The attack of π electrons on propene or the vinyl alcohol on the ruthenium–allenylidene complex is the first step of the reaction pathways. The reaction pathways are different after the attack of nucleophiles on the ruthenium–alkynyl complex. In the reaction with propene, the carbon? carbon bond‐forming reaction proceeds through a stepwise process, whereas in the reaction with vinyl alcohol, it proceeds through a concerted process. The interactions between the ruthenium–allenylidene complex and propene or vinyl alcohol have been investigated by applying a simple way of looking at orbital interactions.     

Porphyrins-Functionalized Single-Walled Carbon Nanotubes Chemiresistive Sensor Arrays for VOCs

Single-walled carbon nanotubes (SWNTs) have been used extensively for sensor fabrication due to its high surface to volume ratio, nanosized structure and interesting electronic property. Lack of selectivity is a major limitation for SWNTs-based sensors. However, surface modification of SWNTs with a suitable molecular recognition system can enhance the sensitivity. On the other hand, porphyrins have been widely investigated as functional materials for chemical sensor fabrication due to their several unique and interesting physico-chemical properties. Structural differences between free-base and metal substituted porphyrins make them suitable for improving selectivity of sensors. However, their poor conductivity is an impediment in fabrication of prophyrin-based chemiresistor sensors. The present attempt is to resolve these issues by combining freebase- and metallo-porphyrins with SWNTs to fabricate SWNTs-porphyrin hybrid chemiresistor sensor arrays for monitoring volatile organic carbons (VOCs) in air. Differences in sensing performance were noticed for porphyrin with different functional group and with different central metal atom. The mechanistic study for acetone sensing was done using field-effect transistor (FET) measurements and revealed that the sensing mechanism of ruthenium octaethyl porphyrin hybrid device was governed by electrostatic gating effect, whereas iron tetraphenyl porphyrin hybrid device was governed by electrostatic gating and Schottky barrier modulation in combination. Further, the recorded electronic responses for all hybrid sensors were analyzed using a pattern-recognition analysis tool. The pattern-recognition analysis confirmed a definite pattern in response for different hybrid material and could efficiently differentiate analytes from one another. This discriminating capability of the hybrid nanosensor devices open up the possibilities for further development of highly dense nanosensor array with suitable porphyrin for E-nose application.     

Multidentate Europium Chelates as Luminoionophores for Anion Recognition: Impact of Ligand Design on Sensitivity and Selectivity,and Applicability to Enzymatic Assays

The design of photoluminescent molecular probes for the selective recognition of anions is a major challenge for the development of optical chemical sensors. The reversible binding of anions to lanthanide centers is one promising option for the realization of anion sensors, because it leads in some cases to a strong luminescence increase by the replacement of quenching water molecules. Yet, it is an open problem to gain control of the sensitivity and selectivity of the luminescence response. Primarily, the selective detection of (poly)phosphate species such as nucleotides has emerged as a demanding task, because they are involved in many biological processes and enzymatic reactions. We designed a series of pyridyl‐based multidentate europium complexes (seven‐, six‐, and five‐dentate) including sensitizing chromophores and studied their luminescence intensity and lifetime responses to different (poly)phosphates (adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), cyclic adenosine monophosphate (cAMP), pyrophosphate, and phosphate anions), and carboxyanions (citrate, malate, oxalacetate, succinate, α‐ketoglutarate, pyruvate, oxalate, carbonate). The results reveal that the number of free coordination sites has a significant impact on the sensitivity and selectivity of the response. Because of its reversibility, the lanthanide probes can be applied to monitor the activity of ATP‐consuming enzymes such ATPases and apyrases, which is demonstrated by means of the five‐dentate complex.     

Effects of Zr doping on stoichiometric and reduced ceria: a first-principles study

The Zr doping in CeO(2) may change the reduction properties and therefore the redox properties of CeO(2). Using first-principles density functional theory with the inclusion of on-site Coulomb interaction for a 96-atom supercell, these effects are studied by comparing the differences in atomic structures, electronic structures, and reduction energies of the doped CeO(2) and those of the nondoped CeO(2). It is found that (1) Zr doping of the ceria structure results in important modifications involving nonequivalent O atoms; (2) the oxygen anions (still four-coordinated) next to the doping center show considerably lower reduction energies (by 0.6 eV) and larger displacements ("higher mobilities"); (3) an O vacancy is most easily created close to the Zr centers, therefore the Zr-doping centers might serve as nucleation centers for vacancy clustering; and (4) the electrons left by the released oxygen localize on two Ce cations neighboring the vacancy, which results in the reduction of two Ce(4+) ions.     

Selective modified SnO2-based materials for gas sensors arrays

An enhancement of selectivity of semiconductor gas sensors, based on nanocrystalline SnO2 is reported. It is shown that modification of the surface of crystallites, forming thick films of conductive sensor materials, with catalytic clusters of gold or oxides of ruthenium, nickel, copper and iron allows selective response of sensors to different gases, such as carbon monoxide, ammonia, hydrogen sulfide, nitrogen dioxide and acetone vapor. These selective sensor responses can be obtained in the ranges of gas concentrations close to or below threshold limit values while the working temperature of sensors can be kept below 300 °C. The described approach for modification of selectivity of sensor materials could be used as perspective route in developingselective gas sensors. These results allow us to propose application of obtained materials in electronic nose sensor systems.     

高选择性比色识别碘离子的氨基硫脲类阴离子受体

设计合成了一系列基于氨基硫脲的阴离子受体（M1～M4）.此类受体以氨基硫脲基团为识别位点,以硝基苯基为信号报告基团,其中受体M1和M3可在乙腈溶液中高选择性的比色识别碘离子.在受体M1或M3的乙腈溶液中加入I^–时,溶液的颜色由浅红色变成无色,而加入其他离子如F^–,Cl^–,Br^–,AcO^–,HSO4^–,H2PO4^–,ClO4^–等阴离子时,受体溶液不会褪色.通过紫外滴定和核磁滴定等方法研究了受体选择性比色识别碘离子的机理.结果表明,受体通过其氨基硫脲基团上的三个NH质子与碘离子形成的三重氢键选择性的结合碘离子.在此过程中,受体构型发生转变,从而导致了颜色变化,产生了比色识别的效果.此类阴离子受体具有合成方法简便,产率高,识别效果好等优点.     

Thiazole-based chemosensor III: synthesis and fluorescence sensing of CH3CO2 based on inhibition of ESIPT

Novel fluorogenic sensors based on urea derivative of 2-(2′-aminophenyl)-4-phenylthiazole (4 and 5) were prepared and used for recognition of anions with similar basicity and surface charge density. Chemosensor 4 was found to be highly selective to acetate ion over other anions. The selectivity was related to the structure matching between the host and the guest. The evaluation of the chemosensors’ interaction with anions was performed by UV-vis and fluorescence titration. This acetate binding affinity was further tuned by varying the acidity of the N-H proton of the urea moiety in chemosensor 5.     

Novel Hydrazone‐Based Tripodal Sensors: Single Selective Colorimetric Chemosensor for Acetate in Aqueous Solution

A series of novel tripodal colorimetric anion sensors based on hydrazone CHN NH groups have been synthesized and their recognition behavior with anionic guests has been studied. In DMSO solutions, sensors 1 and 2 show colorimetric responses for F⁻, H₂PO⁻₄ and AcO⁻, while in DMSO/H₂O (9:1, V/V) solutions, sensor 1 shows single selectivity for AcO⁻. ¹H NMR titration confirms that the tripodal sensors could bind anions through the collaboration of three hydrazone groups and anions residing in the central cavity of the sensors.     

Study on the Anion Recognition Properties of Synthesized Receptors （Ⅲ）： Convenient Synthesis and Anion Recognition Property of Bisthiosemicarbazone Derivative

A new series of bisthiosemicarbazone derivative receptors(1,2 and 3)have been synthesized by simple steps ingood yields.Their anion recognition properties were studied by UV-Vis and ~1H NMR spectroscopy.The resultshowed that the receptors 1,2 and 3 all had a better selectivity to F~-,CH_3COO~- and H_2PO_4~-,but no evidentbinding with Cl~-,Br~-,I~-,NO_3~- and HSO_4~-.Upon addition of the three anions to the receptors in DMSO,thesolution acquired a color change from colorless to dark yellow that can be observed by the naked-eyes,thus the re-ceptors can act as fluoride ion sensors even in the presence of other halide ions.The data showed that it was regularthat the three receptors had different binding ability with the three anions.For the same anion,the association con-stants followed the trend:receptor 1>3>2.The UV-Vis data indicates that a 1:1 stoichiometry complex isformed through hydrogen bonding interactions between compound 1,2 or 3 and anions.     

Design, synthesis and photophysical studies of simple fluorescent anion PET sensors using charge neutral thiourea receptors

The synthesis of four fluorescent photoinduced electron transfer (PET) chemosensors 1-4 for anions is described. These are all based on a simple design employing charge neutral aliphatic or aromatic thiourea anion receptors connected to an anthracene fluorophore via a methylene spacer. Here the anion recognition occurred through 1 : 1 hydrogen bonding between the thiourea protons and the anion, as demonstrated by observing the changes in the (1)H NMR in DMSO-d(6) where the two thiourea protons were shifted downfield upon addition of anions. Whereas 1-3 were designed for the detection of anions such as fluoride, acetate or phosphate, 4 was made for the recognition of N-protected amino acids. All the sensors showed 'ideal' behaviour where only the fluorescence emission was quenched upon anion recognition, due to enhanced efficiency of electron transfer quenching from the receptor to the excited state of the fluorophore. By simply varying the nature of the thiourea substituent it was possible to modulate, or tune, the acidity of the thiourea receptor moiety, altering the sensitivity of the anion recognition. For, the anion selectivity and the degree of the fluorescence quenching were in the order of F(-) > AcO(-) > H(2)PO(4)(-), with Cl(-) or Br(-) not being detected.     

A DFT-based analysis of the gold-catalyzed cycloisomerization of 1-siloxy 1,5-enynes to cyclohexadienes

In this work, we present a deep theoretical study on the intriguing and unexpected gold-catalyzed cycloisomerization of siloxy enynes to cyclohexadienes. To this end, we have evaluated the electronic and steric properties for three types of alkynyl substituents along the reaction paths and the implications on the evolution through divergent, competitive pathways. For an alkynyl -OR substituent, the results strongly suggest a polarization of the π electrons along the delocalized C2-C1-O system in the key cyclopropyl-carbene intermediate, which is enhanced by the bulkiness of the R group. The results reproduce the experimental observations in excellent agreement and provide interesting and useful clues for predicting the effects of the alkynyl substituent on the nature of the key intermediate and, hence, on the reactivity mode and selectivity.     

Development of a heterobimetallic Ru(II)-Cu(II) complex for highly selective and sensitive luminescence sensing of sulfide anions

A heterobimetallic ruthenium(II)-copper(II) complex-based luminescent chemosensor, [Ru(bpy)(2)(bpy-DPA)Cu](4+) (bpy: 2,2'-bipyridine; bpy-DAP: 4-methyl-4'-[N,N-bis(2-picolyl)amino-methylene]-2,2'-bipydine), has been designed and synthesized for the highly selective and sensitive recognition and detection of sulfide anions in 100% aqueous solutions. Owing to the high affinity of sulfide to Cu(II), the non-luminescent chemosensor can specifically and rapidly react with sulfide to yield the corresponding ruthenium(II) complex, [Ru(bpy)(2)(bpy-DPA)](2+), accompanied by the remarkable luminescence enhancement. The dose-dependent luminescence enhancement of the sensor shows a good linearity with a detection limit of 20.7 nM for sulfide anions. The novel luminescence sensor has a widely available pH range from 4.5 to 10 and an excellent response selectivity to sulfide only even in the presence of various other anions. Based on this chemosensor, a rapid, selective and sensitive luminescence method for the detection of sulfide anions in wastewater samples was established. The coefficient variations (CVs) of the method are less than 3.1%, and the recoveries are in the range of 90.9-108.5%.     

Record Multiphoton Absorption Cross‐Sections by Dendrimer Organometalation

Large increases in molecular two‐photon absorption, the onset of measurable molecular three‐photon absorption, and record molecular four‐photon absorption in organic π‐delocalizable frameworks are achieved by incorporation of bis(diphosphine)ruthenium units with alkynyl linkages. The resultant ruthenium alkynyl‐containing dendrimers exhibit strong multiphoton absorption activity through the biological and telecommunications windows in the near‐infrared region. The ligated ruthenium units significantly enhance solubility and introduce fully reversible redox switchability to the optical properties. Increasing the ruthenium content leads to substantial increases in multiphoton absorption properties without any loss of optical transparency. This significant improvement in multiphoton absorption performance by incorporation of the organometallic units into the organic π‐framework is maintained when the relevant parameters are scaled by molecular weights or number of delocalizable π‐electrons. The four‐photon absorption cross‐section of the most metal‐rich dendrimer is an order of magnitude greater than the previous record value.     

Flavonol based ruthenium acetylides as fluorescent chemosensors for lead ions

Flavonol based alkynyl ruthenium complexes devoted to the detection of metal traces in solution are described. The sensitivity of both absorption and emission properties of the 3-hydroxyflavone unit as a receptor for the metal cations, and of an alkynyl ruthenium moiety as an extended π-conjugated system, provides an efficient molecular sensor for rapid, sensitive and selective detection of lead(II) cations.     

香豆素类荧光传感器*

荧光传感器能够将分子识别的信息转换成荧光信号,荧光法在灵敏度、选择性和实时原位检测等方面优势突出。实时检测被分析物的水平已引起包括化学家、生物学家、临床生物化学家和环境学家的极大兴趣。以香豆素为基础的荧光传感器近年来已成为一个新兴的研究热点。本文综述了香豆素类荧光传感器在阳离子、阴离子、中性分子识别检测中的分子设计、作用机理和应用效果,展望了该领域的发展方向。     

Phenyl-calix[4]arene-based fluorescent sensors: cooperative binding for carboxylates

Tetrakis-(4-carbamoylphenyl)-substituted and tetrakis-(4-amidophenyl)-substituted calix[4]arenes as well as the monomeric biphenylcarbamate have been synthesized as fluorescent receptors for anion sensing. Their binding properties with various anions including F-, CH3COO-, Ph-COO-, and H2PO4- were investigated by fluorescence titrations, Job plot experiments, 1H NMR spectroscopies, and ESI-MS measurements. Importantly, we have found that calix[4]arene-based sensors exhibit greatly enhanced binding affinity and selectivity toward carboxylates. The binding associations of tetrakis-(4-carbamoylphenyl)-substituted calix[4]arene for carboxylates are 1-2 orders of magnitude greater than those of the monomeric biphenylcarbamate sensor. Such an enhancement in the binding affinity and selectivity is attributed to the cooperative binding of the multiple ligating groups as revealed from the ab inito DFT calculations. Although tetrakis-(4-amidophenyl)-substituted calix[4]arene exhibited relatively weaker binding affinity toward anions, its superior binding selectivity for acetate ion over fluoride ion is evident. Our results also suggest that carbamate functionality is a useful H-bond donor for hydrogen-bonding interactions in molecular recognition and supramolecular chemistry.     

Chemical Sensors for Electronic Nose Systems

Chemical sensors have been widely used for the analysis of volatile organic compounds. Employing chemical sensors in an array format with pattern recognition provides a higher degree of selectivity and reversibility leading to an extensive range of applications. When such systems are used for odour analysis they are termed electronic noses. Application of electronic noses ranges from the food industry, medical industry to environmental monitoring and process control. Many types of different gas sensors have been employed in the array. These include conducting polymers, metal oxide semiconductors, piezoelectric, optical fluorescence and amperometric gas sensors The transducer principle of these sensors is varied and is discussed in detail within this review. Examples of the current trends in sensor array technology as well as the applications to which the sensor-based noses have been applied are also discussed.     

Electrotelluration: a new approach to tri- and tetrasubstituted alkenes

A novel electrotelluration process is described in which a Michael addition of an alkyl or aryl tellurolate anion occurs onto an activated alkyne with subsequent trapping of a vinyl anion with electrophiles (aldehydes and ketones) other than a proton. This process provides an efficient regio- and stereospecific route to tri- and tetrasubstituted alkenes. Methodologically significant examples of this chemistry were studied in which aryl and alkyl tellurolate anions were added to omega-keto alkynyl esters in a Michael reaction, and the incipient vinyl anions were trapped intramolecularly by the internal aldehydes. The reactive centers were tethered by different lengths of alkyl chains to form highly functionalized five-, six-, seven-, and eight-membered rings in modest to good yields.     

A new sulfate-selective electrode and its use in analysis

The improvement of the steric accessibility of exchange centers of higher quaternary ammonium salts (QAS) by replacing several long-chain alkyl substituents at the nitrogen atom with methyl groups enhanced the selectivity of ion-selective electrodes (ISEs) based on the specified ion exchangers for the SO ₄ ^2? ion up to six orders of magnitude in the presence of singly charged anions. This can be qualitatively explained by the specific features of ion pair formation between quaternary ammonium cations and singly and doubly charged anions. The effect of the steric accessibility of the QAS exchange center on the selectivity of ISEs is partially retained in the presence of a neutral anion carrier, hexyl p-trifluoroacetylbenzoate (HTFAB), which is used for enhancing the selectivity for the sulfate ion in the presence of singly charged anions. A sulfate-selective electrode with a reasonable selectivity for practical purposes was proposed. It is based on the HTFAB-higher QAS ion pair bearing three methyl substituents at the nitrogen atom. The ISE was used in the analysis of natural water.     

Ruthenium-vinylhelicenes: remote metal-based enhancement and redox switching of the chiroptical properties of a helicene core

Introducing metal-vinyl ruthenium moieties onto [6]helicene results in a significant enhancement of the chiroptical properties due to strong metal-ligand electronic interactions. The electro-active Ru centers allow the achievement of the first purely helicene-based redox-triggered chiroptical switches. A combination of electrochemical, spectroscopic, and theoretical techniques reveals that the helicene moiety is a noninnocent ligand bearing a significant spin density.