Sequential C-H activation and dinuclear insertion of ethylene promoted by a diiridium complex

Two ethylene molecules, bonded to different metal atoms of a diiridium(I) complex, can be converted into a bridging 3-butenyl-1-yl ligand and a terminal hydride. Such transformation is initiated by an ethylene C-H activation step and followed by an insertion of the second ethylene into a bridging vinyl ligand. This result illustrates the potentiality of diiridium(I) complexes to promote and support reaction sequences of alkene functionalization through C-H activation.     

Macroscopic and microscopic ionization constants of the thiol and amine groups in 1-methyl-4-mercaptopiperidine

The acid dissociation constants of 1-methyl-4-mercaptopiperidine (pK(1) = 9.51, pK(2) = 11.33), the 1,1-dimethyl-4-mercaptopiperidinium ion (pK(A) = 9.59) and 1-methyl-4-(methylthio)piperidine (pK(B) = 10.18) have been determined potentiometrically in 3M sodium perchlorate (10% methanol) medium. The ultraviolet absorption of the mercaptide ion has been used to determine the relative proton affinity of the sulphur and nitrogen functions in 1-methyl-4-mercaptopiperidine under the same conditions, and its four microscopic constants (pK(a) = 9.49, pK(b) = 10.23, pK(c) = 11.34, pK(d) = 10.60) have been calculated; pK(A) has also been determined spectrophotometrically. From the results obtained, it can be concluded that the thiol group is more acidic than the amine group and that the Adams relation, K(a) + K(b) = K(1), holds very well when it is assumed that the spectrophotometric values for K(a), and K(b), can be replaced by K(A) and K(B) respectively.     

Addition of water across Si-Ir bonds in iridium complexes with κ-P,P,Si (biPSi) pincer ligands

Electrophiles such as Me(+), Ag(+), or protons react with the five-coordinate Ir(III) complex [IrClH(biPSi)] (biPSi = κ-P,P,Si-Si(Me){(CH(2))(3)PPh(2)}(2)) by abstracting its chloride ligand. The resulting species can be stabilized by a variety of L ligands to give the cationic complexes [IrH(biPSi)L(2)](+). The derivative [IrH(biPSi)(NCMe)(2)](+) has been subjected to a kinetic study regarding the facile dissociations of its acetonitrile ligands. The presence of water changes the course of the reaction producing dihydride complexes that contain the silanol ligand κ-O,P,P-HOSi(Me){(CH(2))(3)PPh(2)}(2) (biPSiOH). The water activation product [IrH(2)(biPSiOH)(NCMe)](CF(3)SO(3)) undergoes insertion reactions with ethylene and phenylacetylene. The use of hydrolyzable fluorinated counterions such as PF(6)(-) or BF(4)(-) further modifies the reaction by provoking the incorporation of fluoride at the silicon atom of the former biPSi ligand. The dihydride resulting after such a process, [IrH(2)(biPSiF)(NCMe)(2)]BF(4) (biPSiF = κ-P(2)-FSi(Me){(CH(2))(3)PPh(2)}(2)), displays a trans-chelating diphosphine ligand. When dehydrogenating the Ir center, spontaneously or using ethylene as hydrogen acceptor, the diphosphine backbone undergoes a Si-C bond cleavage leading to a new Ir(III) species with κ-P,Si and κ-C,P chelate ligands.     

How to Turn an Electron Transfer Protein into a Redox Enzyme for Biosensing

Cytochrome c is a small globular protein whose main physiological role is to shuttle electrons within the mitochondrial electron transport chain. This protein has been widely investigated, especially as a paradigmatic system for understanding the fundamental aspects of biological electron transfer and protein folding. Nevertheless, cytochrome c can also be endowed with a non-native catalytic activity and be immobilized on an electrode surface for the development of third generation biosensors. Here, an overview is offered of the most significant examples of such a functional transformation, carried out by either point mutation(s) or controlled unfolding. The latter can be induced chemically or upon protein immobilization on hydrophobic self-assembled monolayers. We critically discuss the potential held by these systems as core constituents of amperometric biosensors, along with the issues that need to be addressed to optimize their applicability and response.     

Energy scaling-up of stable single filament

The influence of the input pulse chirp and energy on the filamentation process is studied. Output beam profiles, spectra and energies were systematically measured by changing the pulse chirp for different input energies. A map of the different energy-chirp regions was compiled. It shows that high-energy stable single filament can be obtained by using chirped input pulses, allowing the scaling-up of the energy throughput in the filament. Moreover, under high-energy regimes nonlinear effects induced by chirped pulses could produce pulse post-compression.     

Formation of a Nonlinear Optical Host–Guest Hybrid Material by Tight Confinement of LDS 722 into Aluminophosphate 1D Nanochannels

In this work, hemicyanine dye LDS 722 is encapsulated into the 1D elliptical nanochannels of MgAPO‐11 aluminophosphate by a crystallization inclusion method. The synthesis of the hybrid material has been optimized through a systematic variation of the crystallization conditions in order to obtain pure and large crystals (around 20 μm×30 μm) suitable for optical applications. The tight fitting between the molecular size of the guest dye and the pore dimensions of the host has favored a rigid planar conformation of the dye, restricting its inherent flexibility, which is confirmed by molecular simulations. Consequently, the encapsulation of LDS 722 into MgAPO‐11 has led to an astonishing enhancement of the fluorescence with respect to the dye into MgAPO‐5, with slightly larger cylindrical channels, and with respect to the dye in solution. Moreover, the perfect alignment of LDS 722 (dye with intrinsic nonlinear‐optical properties) along the channels of MgAPO‐11 has revealed attractive second‐order nonlinear properties, such as second harmonic generation, proven through microscopy measurements in single crystals.     

Characterization of sub-two-cycle pulses from a hollow-core fiber compressor in the spatiotemporal and spatiospectral domains

We have post-compressed 25 fs (Fourier limit) amplified pulses in an argon-filled hollow-core fiber. The output pulses were compressed using a pair of wedges and chirped mirrors down to 4.5 fs (Fourier limit of 4.1 fs), which corresponds to less than two optical cycles. We then performed the characterization of the pulses by combining the d-scan and the STARFISH techniques. The temporal (and spectral) measurement of the pulses is done with d-scan, which is used as the reference to extend the characterization to the spatiotemporal (and spatiospectral) amplitude and phase of the pulses by means of STARFISH. The post-compressed pulses at the output of the hollow-fiber had an energy of 150 μJ. The analysis of the pulses revealed larger spectral broadening and blue-shift, and shorter duration at the center of the beam. For the first time, we demonstrate the complete characterization of intense ultra-broadband pulses in the sub-two-cycle regime, which provides an improved insight into the properties (space–time and space–frequency) of the pulses and is highly relevant for their applications.     

Analytical treatment for the study of an erbium-doped fiber ring laser fed by a sinusoidally modulated pump power

An analytical procedure is employed to account for the response of an erbium-doped fiber ring laser whose pump power is sinusoidally modulated. The approximations considered, only strictly valid for very low modulation indexes (of the order of some hundredths), reveal the origin of some relationships between resonances of the main harmonics present in the laser response. However, both experimental and numerical results show how qualitative conclusions concerning relationships between harmonics are also valid for modulation indexes much higher than the ones corresponding to the approximation validity range.     

Generalized contractions on partial metric spaces

In the present paper, we give some fixed point theorems for generalized contractive type mappings on partial metric space. Also, a homotopy result is given.