Metal-ion induced FRET in macrocyclic dynamic tweezers

We report here about effective FRET process (73–99%) in mono-Mg²⁺ complexes of symmetrical crown ether bis(styryl) dyes. The FRET process has not been observed in the free state and in binuclear complexes. The formation of mononuclear complex provides two styrylic fragments with appropriate positions of absorption and emission bands for FRET. The other important parameter for FRET is the proper geometric orientation of both chromophores, which attain sandwich conformation with close positioning of complexed and free styryl fragments induced by ion-modulated geometry reorganization of the bis-dye.     

Mass Discrimination in High-Mass MALDI-MS

In high-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), the accessible m/z range is limited by the detector used. Therefore, special high-mass detectors based on ion conversion dynodes (ICDs) have been developed. Recently, we have found that mass bias may exist when such ICD detectors are used [Weidmann et al., Anal. Chem. 85(6), 3425–3432 (2013)]. In this contribution, the mass-dependent response of an ICD detector was systematically studied, the response factors for proteins with molecular weights from 35.9 to 129.9 kDa were determined, and the reasons for mass bias were identified. Compared with commonly employed microchannel plate detectors, we found that the mass discrimination is less pronounced, although ions with higher masses are weakly favored when using an ICD detector. The relative response was found to depend on the laser power used for MALDI; low-mass ions are discriminated against with higher laser power. The effect of mutual ion suppression in dependence of the proteins used and their molar ratio is shown. Mixtures consisting of protein oligomers that only differ in mass show less mass discrimination than mixtures consisting of different proteins with similar masses. Furthermore, mass discrimination increases for molar ratios far from 1. Finally, we present clear guidelines that help to choose the experimental parameters such that the response measured matches the actual molar fraction as closely as possible.

Characterization of hemicyanine Langmuir-Blodgett films by picosecond time-resolved fluorescence

Hemicyanine Langmuir-Blodgett films have been elaborated and characterized using stationary and time-resolved spectroscopic techniques. Depending on the experimental conditions, especially the pH of the water subphase, the absorption spectra of the films indicate the presence of non-fluorescent H-aggregates in the monolayer. Time-resolved fluorescence measurements revealed three mono-exponential decay times: a very short one (20-23 ps) attributed to an excited intramolecular charge transfer state and two longer ones (100-120 ps and 400-590 ps) attributed to the photoisomerization of the chromophores.     

Surface‐enhanced Raman scattering sensing on black silicon

Reactive ion etching was used to fabricate black‐Si over the entire surface area of 4‐inch Si wafers. After 20 min of the plasma treatment, surface reflection well below 2% was achieved over the 300–1000 nm spectral range. The spikes of the black‐Si substrates were coated by gold, resulting in an island film for surface‐enhanced Raman scattering (SERS) sensing. A detection limit of 1 × 10^?6 M (at count rate > 10² s^?1 . mW^?1) was achieved for rhodamine 6G in aqueous solution when drop cast onto a ～ 100‐nm‐thick Au coating. The sensitivity increases for thicker coatings. A mixed mobile‐on‐immobile platform for SERS sensing is introduced by using dog‐bone Au nanoparticles on the Au/black‐Si substrate. The SERS intensity shows a non‐linear dependence on the solid angle (numerical aperture of excitation/collection optics) for a thick gold coating that exhibits a 10 times higher enhancement. This shows promise for augmented sensitivity in SERS applications.     

Discrete uniform distribution for a sum of additive functions

We consider the limit distribution of values of a sum of sets of strongly additive arithmetic functions with shifted argument. We obtain sufficient and necessary conditions for a weak convergence of distributions of that sum to the discrete uniform law. The case where those functions take values 0 or 1 on primes is studied.     

C3-triiodocyclotriveratrylene as a key intermediate to fluorescent probes: application to selective choline recognition

A new strategy to obtain fluorescent cyclotriveratrylene (CTV) probes is proposed. The key intermediate, a triiodo CTV, is prepared in 3 steps with 47% overall yield. The whole synthesis requires only one purification step. The potential of this triiodo CTV as an intermediate is illustrated through the synthesis of a fluorescent phosphorylated probe that is able to bind choline and acetylcholine in pseudo-physiological conditions, with selectivity towards choline. As a consequence, this intermediate should allow us to rapidly form a library of probes in order to highlight the most promising ones.     

Modification of the amorphous carbon films by the ns-laser irradiation

The effect of a nanosecond laser irradiation of thin (60 and 145 nm) amorphous, diamond-like carbon films deposited on Si substrate by an ion beam deposition (IBD) from pure acetylene and acetylene/hydrogen (1:2) gas mixture was analyzed in this work. The films were irradiated with the infrared (IR) and ultraviolet (UV) radiation of the nanosecond Nd:YAG lasers working at the first (1.16 eV) and the third (3.48 eV) harmonics, using a multi-shot regime. The IR laser irradiation stimulated a minor increase in the fraction of sp² bonds, causing a slight decrease in the hardness of the films and initiated SiC formation. Irradiation with the UV laser caused the formation of carbides and increased hydrogenization of the Si substrate and the fraction of sp² sites. Spalliation and ablation were observed at a higher energy density and with a large number of laser pulses per spot.     

Investigation of the electronic structure of the SbSeBr cluster

The energy levels of valence bands (VB) in SbSeBr crystals were calculated for investigation of the photoelectron emission spectra of A⁵B⁶C⁷ — type crystals. The molecular model of this crystal was used for calculation of VB by the Density Functional Theory (DFT) and Unrestricted Hartree — Fock (UHF) methods. The molecular cluster consisting of 20 molecules of SbSeBr was used for calculations of averaged total density of states including atom vibrations. The spectra of averaged total density of states from VB in the SbSeBr cluster were compared with experimental photoelectron emission spectra from VB of A⁵B⁶C⁷ — type crystals. The results of comparison clarify that the atomic vibrations are one of possible reasons for the smoother appearance of the experimental X-ray photoelectron spectrum (XPS).      

The alkali metal cation effect on the surface-enhanced Raman spectra of phosphate anions adsorbed at silver electrodes

The interaction of adsorbed phosphate anions with alkali metal cations at the Ag|aqueous solution interface has been investigated by surface-enhanced Raman spectroscopy (SERS). Formation of ion pairs at the interface was evident from the cation-induced perturbations in the SER spectra of anions. The frequency of the external vibration, silver–oxygen (Ag---O′), was not sensitive to the nature of cation, while the relative intensity of this mode was cation-dependent and was explored as a sensitive probe for the monitoring of coadsorption of ions at the interface. From the internal phosphate vibrations, both asymmetric modes, δ_as(PO) and ν_as(PO), were found to be the most sensitive to the nature of the cation. At a relatively positive potential (0.00 V vs. Ag | AgCl) the spectral parameters for the Cs⁺ and K⁺ cations were very similar indicating the same bonding type with anions. A more inhomogeneous chemical environment for the phosphate oxygen atoms was detected in the case of Na⁺ and Li⁺ cations. An increase in ν_as(PO) frequency by ca. 10 cm⁻¹ was the characteristic spectral signature for the interaction of phosphates with Li⁺. The formation of water-shared ion pairs at the interface was suggested based on the absence of splitting in the ν_as(PO) mode and the previously observed frequency sensitivity of this band to solvent H₂O substitution by D₂O. At negative potential (−0.80 V), a stabilization effect of Cs⁺ on the phosphate adlayer was detected based on the twofold increase in intensity of the ν(Ag---O′) mode compared with Li⁺. Splitting of the ν_as(PO) mode suggested the contact interaction of anions with specifically adsorbed Cs⁺ cations.