Perturbations produced by electrospray ionization mass spectrometry in the speciation of aluminium(III)/1,6‐dimethyl‐4‐hydroxy‐3‐pyridinecarboxylate aqueous solutions

Electrospray ionization mass spectrometry (ESI‐MS) is very often employed to study metal/ligand equilibria in aqueous solution. However, the ionization process can introduce perturbations which affect the speciation results in an unpredictable way. It is necessary to identify these perturbations in order to correctly interpret the ESI‐MS speciation results. Aluminium(III)/1,6‐dimethyl‐4‐hydroxy‐3‐pyridinecarboxylate (DQ716) aqueous solutions at various pH were analysed by ESI‐MS, and speciation results were compared with those obtained by equilibrium techniques. Differences observed were both qualitative and quantitative. The ESI‐MS spectral changes due to different settings of the following instrumental parameters were analyzed: the solution flow rate (F_S), the nebulizer gas flow rate (F_G), the potential applied at the entrance capillary (E_C), and the temperature of the drying gas (T_G). The effects produced by F_S and E_C on the spectra strongly suggest the key role of surface activity in determining the relative fraction of the ions reaching the detector. The experimental effects of F_S and T_G were interpreted considering the presence of at least two reactions in the gas phase and a dimerization occurring in the droplets. These perturbations cannot be generalized because they appear to be chemical system‐related and instrument‐dependent. Therefore, the identification of perturbations is a required task for any metal‐ligand equilibrium study performed by ESI‐MS. Our results indicate that perturbations can be identified by evaluating the effects produced in the spectra by a change of instrumental parameters. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterisation of hydrogen bond perturbations in aqueous systems using aquaphotomics and multivariate curve resolution-alternating least squares

Aquaphotomics is a new discipline that provides a framework for understanding changes in the structure of water caused by various perturbations, such as variations in temperature or the addition of solutes, using near infrared spectroscopy (NIRS). One of the main purposes of aquaphotomics is to identify water bands as main coordinates of future absorbance patterns to be used as biomarkers. These bands appear as consequence of perturbations in the NIR spectra. Curve resolution techniques may help to resolve and find new water bands or confirm already known bands. The aim of this study is to investigate the application of multivariate curve resolution-alternating least squares (MCR-ALS) to characterise the effects of various perturbations on the NIR spectra of water in terms of hydrogen bonding. For this purpose, the perturbations created by temperature change and the addition of four solutions of different ionic strength and Lewis acidity were studied (NaCl, KCl, MgCl₂ and AlCl₃, with concentrations ranging from 0.2 to 1 mol L⁻¹ in steps of 0.2 mol L⁻¹). Transmission spectra of all salt solutions and pure water were obtained at temperatures ranging from 28 to 45 °C. We have found that three distinct components with varying temperature dependence are present in water perturbed by temperature. The salt solutions studied exhibited similar trends with respect to the temperature perturbation, while the peak locations of their MCR-ALS pure components varied according to the ionic strength of the salt used.     

New equation for calculating total interaction energy in one noncyclic ABC triad and new insights into cooperativity of noncovalent bonds

In this work, a new equation consist of A???B, B???C, A???BC, and AB???C interactions is proposed for calculating the total interaction energy of noncyclic ABC triads. New equations are also proposed for calculating the changes in values of A???B and B???C interactions on the formation of triad from the corresponding dyads. The advantages of equations proposed here in comparison with many‐body interaction energy approach are discussed. All proposed equations were tested in F₃MLi???NCH???HLH and F₃MLi???HLH???HCN (M = C, Si; L = Be, Mg) as well as H₃N???XY???HF (X, Y = F, Cl, Br) noncyclic A???B???C triads. The data show that the total cooperativity of triad correlates well with the sum of the changes in values of A???B and B???C interactions calculated through new equations proposed here. © 2016 Wiley Periodicals, Inc.     

Photochemistry of semiconductor colloids: Properties of extremely small particles of Cd3P2 and Zn3P2

Extremely small particles of Zn₃P₂ and Cd₃P₂ were prepared as colloids in aqueous solution and in the solid state. The onset of absorption and the fluorescence band, which lie in the infrared for the macrocrystalline materials, can be shifted through the whole range of the visible by changing the particle size. Fluorescence quantum yields of 15% were obtained. The optical effects are due to the strong perturbations in the electronic energy levels as a consequence of carrier confinement (Q-type materials). The solid particles, which fluoresce strongly, can be redissolved without changes in size. Methylviologen quenches the fluorescence and promotes the photoanodic dissolution.     

The ab initio calculation of molecular electric, magnetic and geometric properties

We give an account of some recent advances in the development of ab initio methods for the calculation of molecular response properties, involving electric, magnetic, and geometric perturbations. Particular attention is given to properties in which the basis functions depend explicitly both on time and on the applied perturbations such as perturbations involving nuclear displacements or external magnetic fields when London atomic orbitals are used. We summarize a general framework based on the quasienergy for the calculation of arbitrary-order molecular properties using the elements of the density matrix in the atomic-orbital basis as the basic variables. We demonstrate that the necessary perturbed density matrices of arbitrary order can be determined from a set of linear equations that have the same formal structure as the set of linear equations encountered when determining the linear response equations (or time-dependent self-consistent-field equations). Additional components needed to calculate properties involving perturbation-dependent basis sets are flexible one- and two-electron integral techniques for geometric or magnetic-field differentiated integrals; in Kohn-Sham density-functional theory (KS-DFT), we also need to calculate derivatives of the exchange-correlation functional. We describe a recent proposal for evaluating these contributions based on automatic differentiation. Within this framework, it is now possible to calculate any molecular property for an arbitrary self-consistent-field reference state, including two- and four-component relativistic self-consistent-field wave functions. Examples of calculations that can be performed with this formulation are presented.     

Proline-40 is Essential to Maintaining Cytochrome b_5''''s Stability and Its Electron Transfer with Cytochrome c

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Depolarization dispersion curves of resonance Raman fundamentals of metalloporphyrins and metallophthalocyanines subject to asymmetric perturbations

A model is presented that allows the investigation of depolarization dispersion curves of a_1g,a_2g,b_1g and b_2g resonance Raman fundamentals in the region of the Q state of metalloporphyrins and metallophthalocyanines. This dispersion results from electronic and/or vibronic perturbations of A_2g,B_1g and B_2g symmetry due to asymmetric substituents and/or metal ion-ring interaction acting on the porphyrin (phthalocyanine) ring. The electronic perturbations affect the electronic configuration interaction pattern between the four orbital components of the Q and B states, yielding thereby similar depolarization dispersion curves for all modes of a given symmetry, whereas the vibronic perturbations affect selectively the vibronic coupling matrix of a particular mode. Depolarization dispersion curves resulting from A_2g and B_1g perturbations are treated separately, and many helpful perturbational formulas are given for use in analyzing experimental data. Examples of depolarization dispersion curves and excitation profiles of fundamentals of a_1g, a_2g, b_1g and b_2g symmetry are presented. It is shown that strong depolarization dispersion observed in copper chelate of mesoporphyrin IX dimethyl ester for a_1g and a_2g fundamentals can be explained in terms of an A_2g electronic perturbation and a vibronic a_2g perturbation suffered by the a_1g(1131 cm^?1) fundamental. Similarly, the depolarization dispersion curves observed for fundamentals in cytochrome c and Pt-phthalocyanine are explained in terms of an electronic B_1g perturbation, together with selective b_1g vibronic perturbations acting on the 1310 cm^?1 a_2g fundamental in cytochrome c and the 482 cm^?1 b_2g fundamental in Pt-phthalocyanine. The agreement between the depolarization dispersion curves predicted by our model and experimental data is shown to be satisfactory.     

Rate equations for multi-photon excitation in strong fields

The excitation of an N-level quantum oscillator by a strong oscillating electric field in the presence of external perturbations can in general be described by a Boltzmann equation for the density matrix. In this paper it is shown that under certain circumstances this may be reduced to a set of rate equations for the level populations. In contrast to the weak field situation, these rate equations explicitly contain multi-photon transition rates.     

Dynamics of a climbing surfactant-laden film II: stability

The linear and nonlinear stability of a spreading film of constant flux and a drop of constant volume, discussed in [1], are examined here. A linear stability analysis (LSA) is carried out to investigate the stability to spanwise perturbations, by linearisation of the two-dimensional (2-D) evolution equations derived in [1] for the film thickness and surfactant concentration fields. The latter correspond to convective-diffusion equations for the surfactant, existing in the form of monomers (present at the free surface and in the bulk) and micelles (present in the bulk). The results of the LSA indicate that the thinning region, present upstream of the leading front in the constant flux case, and the leading ridge in the constant volume case, are unstable to spanwise perturbations. Numerical simulations of the 2-D system of equations demonstrate that the above-mentioned regions exhibit finger formation; the effect of selected system parameters on the fingering patterns is discussed.