Absorption Spectra Of Aqueous Solutions Research Articles

DETERMINATION OF THE IONIZATION CONSTANT OF FAVIPIRAVIR API

One of the aspects of studying the physical and chemical properties of compounds is the establishment of their ionization constants. These indicators are extremely important from both a theoretical and a practical point of view. Theoretical analysis of proteolytic equilibria and potentiometric titration of an aqueous solution of an oral antiviral drug approved for the treatment of influenza in Japan, AFI favipiravir, were carried out in the paper. The presence of a hydroxy group in the third position of the pyrazine cycle in the molecule determines the ability of favipiravir to exhibit acid-base properties. According to acid-base titration, the ionization constant of Favipiravir API was determined: pKa = 5.05 ± 0.02. On the basis of the found pK value, the degree of formation of protolytic forms was calculated depending on the pH of the solution. It was established that favipiravir API in solutions exists in two protonated (non-ionized), tautomeric forms A1H and A2H and one deprotonated (ionized) form A-. Based on the calculations, the following conclusions can be drawn: - at a pH value of the solution from 0 to 3.5, approximately 100% of the substance will be in two protonated (non-ionized), tautomeric forms A1H and A2H; - at pH = 5, approximately 50% of the substance will be in two protonated (non-ionized), tautomeric forms, A1H and A2H; - at a pH value > 6.5, approximately 100% of the substance will be in one deprotonated (ionized) form of A-. This is confirmed by the nature of the electronic absorption spectra of aqueous solutions of favipiravir. In the spectrum of favipiravir in a 0.1 M hydrochloric acid solution, there are two bands at the wavelengths of 322 nm and 365 nm, which correspond to the two tautomeric forms A1H and A2H. In the spectrum of favipiravir in 0.1 M sodium hydroxide solution, there is one band at a wavelength of 364 nm, which corresponds to one ionized form of A-. At the stage of pharmaceutical development, these data on the acid-base properties of the Favipiravir API can be used in the development of production technology, the creation of quality control methods and their validation, as well as in the study of the solubility of the API and the dissolution profiles of the finished medicinal product.

Effects of the protonation and the polar solvation on the molecular properties of methyl orange: A density functional theory study

AbstractMethyl orange (MO) and its protonated derivatives were investigated at the density functional theory (DFT) level using CAM‐B3LYP functional and 6‐311 + G(d,p) basis sets; their absorption spectra in aqueous solution were simulated, their relative stabilities in both the gas phase and the polar solutions were calculated, and the activation energy barrier for the cis‐to‐trans isomerization in both phases were computed. Except the protonation at the amino group, all the protonated isomers show a bathochromic shift of the most intense absorption peak. In the gas phase, the sulfonate unit turns out to be the most favorable proton acceptor. In the polar solutions, however, azo groups are more effective to accept the proton. The protonation at the azo N atom next to the phenyl‐sulfonate group significantly reduces the energy barrier for the cis‐to‐trans conversion in the aqueous solution, which suggests a swift conversion in the ground state.

Stabilization of Double-Stranded Poly(A)·Poly(U) with ZnTMPyP4 Metalloporphyrin in Aqueous Solution

UV-Vis absorption spectra of aqueous solutions containing both metalloporphyrin Zn(X)TMPyP4 [H2TMPyP4—5,10,15,20-tetrakis(1-methylpyridin-4-yl)-21H,23H-porphyrin] and synthetic polyadenylic-polyuridylic acid Poly(A)·Poly(U) over the temperature range from 20 to 70°C (pH = 7.0, I = 0.15 M.) have been analyzed. Deconvolution of the spectrometric data matrix, without postulating a physicochemical equilibrium model, has allowed estimation of the contribution of the Poly(A)·Poly(U)·(ZnTMPyP4)n complex to the total change in the spectra. Chemometric analysis has shown an increase in the melting temperature of this ternary complex by 9.4°С compared to pure polyribonucleotide, which indicates the stabilization of the bonds between nucleic bases in the Poly(A)·Poly(U) polynucleotide under the influence of bound porphyrin.

Investigation of Changes in the Absorption Spectrum of Modern Chlorine-Containing Medicines for Photodynamic Therapy and Methylene Blue as a Result of Exposure to LED Emissions with a wavelength of 656 ± 10 nm

Changes in the absorption spectra of aqueous solutions of modern chlorinated photosensitizing drugs for photodynamic therapy “Revixan” (Areal, Russia) and “Chloderm” (Chloderm, Russia) in the range of 600–700 nm depending on the intensity and time of exposure to LED emission with a wavelength of 656 ± 10 nm have been studied. The parameters of the CIE Lab color model of the “Revixan” water solution image before and after LED exposure have been studied. In the range of 400–900 nm, the changes in the absorption spectra of an aqueous solution of methylene blue with different initial concentrations after exposure to LED emission with a wavelength of 656 ± 10 nm and an intensity of 180 ± 20 mW/cm2 have been studied. It has been shown that the effect of LED emission changes the absorption spectra of the studied substances and increases the parameter L (brightness) of the CIE Lab color model for “Revixan”. An increase in the intensity of the LED emission and exposure time causes a decrease in the absorption for “Revixan” and “Chloderm” in the range of 600–700 nm and a shift of the peak of the absorption band lying in this range to the infrared region. The effect of the LED emission on an methylene blue aqueous solution causes a decrease in its absorption in the range of 400–900 nm.

Исследование изменений в спектре поглощения современных хлоринсодержащих препаратов для фотодинамической терапии и метиленового синего в результате воздействия светодиодного излучения с длиной волны 656± 10 nm

The changes in absorption spectra of aqueous solutions of modern chlorine-containing photosensitizing preparations "Revixan" (Areal, Russia) and "Chloderm" (Chloderm, Russia) depending on the intensity of LED radiation with wavelength of 656 ± 10 nm and exposure time were studied in spectral range 600-700 nm. The parameters of the CIE Lab color model of the image of "Revixan" aqueous solution before and after LED exposure were investigated. The changes in absorption spectra of aqueous solutions of methylene blue with different initial concentrations arising after exposure to LED radiation with intensity of 180 ± 20 mW/cm2 were studied in the spectral range 400-900 nm. It was shown that the impact of LED radiation changes the absorption spectra of the studied preparations and increases the parameter L (lightness) of the CIE Lab color model for "Revixan". An increase in the LED radiation intensity and exposure time leads to a decrease in absorption for "Revixan" and "Chloderm" in spectral range 600-700 nm and to a shift of the peaks of absorption bands lying in this range towards a longer wavelength. The impact of LED radiation on aqueous solutions of methylene blue leads to a decrease in their absorption in spectral range 400-900 nm.

Variation in Near-Infrared Spectra of Water Containing Polyhydric Alcohol

Near-infrared absorption spectra of aqueous solutions of eleven polyhydric alcohols (nine dihydric alcohols and two trihydric alcohols) at concentrations up to 20% were obtained at 20, 25, and 30 °C. Variations in the band due to O–H stretching vibration overtones of water and alcohol with changes in concentration and temperature were determined by a multivariate curve resolution-alternating least squares analysis, which identified the components of the band causing the spectral variation. The band consisted of three common components almost independent of the alcohol type. The first and the second components are attributed, respectively, to water molecules weakly hydrogen-bonded (or non hydrogen-bonded) and those strongly hydrogen-bonded with other water molecules, while the third component are due to water interacting with the alcohol and to the alcohol itself. The abundance of the first and third components decreased and increased, respectively, as the alcohol concentration increased. In contrast, the abundance of the second component increased initially and then decreased. The initial increase corresponds to the enhancement of hydrogen bonding by hydrophobic interactions. The subsequent decrease is due to an increase in water–alcohol interactions and a decrease in water concentration. The maximum increase in the abundance of the second component depended on the type of alcohol. The increase in abundance was greater for alcohols with larger alkyl groups. In contrast, the increase in abundance of the second component was smaller for alcohols with more hydric groups.

Density Functional Studies of Coenzyme NADPH and Its Oxidized Form NADP+ : Structures, UV-Vis Spectra, and the Oxidation Mechanism of NADPH.

Density functional theory has been used to study the biologically important coenzyme NADPH and its oxidized form NADP+ . It was found that free NADPH prefers a compact structure in gas phase and exists in more extended geometries in aqueous solution. Ultraviolet-visible absorption spectra in aqueous solution were calculated for NADPH with an explicit treatment of 100 surrounding water molecules in combination with the COSMO solvation model for bulk hydration effects. The obtained spectra using the B3LYP hybrid density functional agree quite well with experimental data. The changes of Gibbs free energies ΔG in reactions of NADPH with O2 observed experimentally in cardiovascular and in chemical systems, that is, NADPH + 2 3 O2 → NADP+ + 2 O2- + H+ and NADPH + 1 O2 + H+ → NADP+ + H2 O2 , respectively, were calculated. The NADPH oxidation reaction in the cardiovascular system cannot proceed without activation since the obtained ΔG is positive. The reaction of NADPH in the chemical system with singlet oxygen was found to proceed in two ways, each consisting of two steps, that is, NADPH firstly reacts with 1 O2 barrierlessly to form NADP+ and HO2- , from which H2 O2 is formed in a spontaneous reaction with H+ , or 1 O2 and H+ initially form 1 HO2+ , which further reacts with NADPH to yield NADP+ and H2 O2 . © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.

Absorption spectra of nanodiamond aqueous dispersions by optical absorption and optoacoustic spectroscopies

The multispectral modality and technique for optically dense samples of optoacoustic spectroscopy were applied to measure spectra and high absorbances of concentrated aqueous dispersions of undoped nanodiamonds. The data from optoacoustic and optical transmission measurements and DSC data of the mean particle size by the Gibbs–Kelvin equation are compared to estimate the difference in composition of various nanodiamond trademarks. Optoacoustic spectra confirm the contribution of surface dimer chains into the absorption of nanodiamonds in the long wavelength range. Optoacoustic and conventional absorption spectra of aqueous solutions of nanodiamond fractions after centrifugation (15300g) and ultracentrifugation (130000g) revealed a separation of a highly absorbing non-diamond sp2 phase. The two-step separation by ultracentrifugation followed by extra centrifugation made it possible to isolate a highly absorbing and soluble nanodiamond phase with the particle size of 3.6 nm, showing a change in spectra compared to the starting nanodiamond material.

Tyrosine absorption spectroscopy: Backbone protonation effects on the side chain electronic properties.

The UV-vis spectrum of Tyrosine and its response to different backbone protonation states have been studied by applying the Perturbed Matrix Method (PMM) in conjunction with molecular dynamics (MD) simulations. Herein, we theoretically reproduce the UV-vis absorption spectrum of aqueous solution of Tyrosine in its zwitterionic, anionic and cationic forms, as well as of aqua-p-Cresol (i.e., the moiety that constitutes the side chain portion of Tyrosine). To achieve a better accuracy in the MD sampling, the Tyrosine Force Field (FF) parameters were derived de novo via quantum mechanical calculations. The UV-vis absorption spectra are computed considering the occurring electronic transitions in the vertical approximation for each of the chromophore configurations sampled by the classical MD simulations, thus including the effects of the chromophore semiclassical structural fluctuations. Finally, the explicit treatment of the perturbing effect of the embedding environment permits to fully model the inhomogeneous bandwidth of the electronic spectra. Comparison between our theoretical-computational results and experimental data shows that the used model captures the essential features of the spectroscopic process, thus allowing to perform further analysis on the strict relationship between the quantum properties of the chromophore and the different embedding environments. © 2018 Wiley Periodicals, Inc.

Unexpected solvent effects on the UV/Vis absorption spectra of o-cresol in toluene and benzene: in contrast with non-aromatic solvents.

Cresol is a prototype molecule in understanding intermolecular interactions in material and biological systems, because it offers different binding sites with various solvents and protonation states under different pH values. It is found that the UV/Vis absorption spectra of o-cresol in aromatic solvents (benzene, toluene) are characterized by a sharp peak, unlike the broad double-peaks in 11 non-aromatic solvents. Both molecular dynamics simulations and electronic structure calculations revealed the formation of intermolecular π-complexation between o-cresol and aromatic solvents. The thermal movements of solvent and solute molecules render the conformations of o-cresol changing between trans and cis isomers. The π-interaction makes the cis configuration a dominant isomer, hence leading to the single keen-edged UV/Vis absorption peak at approximately 283 nm. The free conformation changes between trans and cis in aqueous solution rationalize the broader absorption peaks in the range of 260–280 nm. The pH dependence of the UV/Vis absorption spectra in aqueous solutions is also rationalized by different protonation states of o-cresol. The explicit solvent model with long-ranged interactions is vital to describe the effects of π-complexation and electrostatic interaction on the UV/Vis absorption spectra of o-cresol in toluene and alkaline aqueous (pH > 10.3) solutions, respectively.

Phenomenological model and experimental study of DNA absorption spectra in THz range

The dielectric permittivity tensor is analyzed qualitatively for the DNA nematic liquid crystal in the THz frequency range. The analysis is performed within the self-consistent phonon approximation based on the PBD model. It is found that DNA depolarization and absorption spectra depend on such parameters as molecular length and helix period. Specifically it is shown that a localization of the absorption lines in the frequency range is determined by the DNA helix structure whereas the DNA length is responsible for a separation between the absorption lines. It is also shown that the gyrotropic properties of the considered liquid crystal depend on a relation between the molecular length and its helix period. The molecules with even number of half helix periods demonstrate the strongest gyrotrophy whereas the molecules with odd number of half helix periods have the weakest gyrotrophy. The model is used to suggest the experimental methodology for determining the DNA length and helix structure based on measurements of the depolarization and absorption spectra in aqueous solutions of biopolimers. Methods of applied THz spectroscopy for determination of the conformational state of molecules in solution is announced. Some preliminary experimental results are presented, including details of measuring the absorption spectra of dry DNA sample and aqueous solutions of biopolimers.

Dependence of the electronic absorption spectra of aqueous solutions of iodine monochloride on the conditions of dilution and storage time

The electronic absorption spectra of aqueous solutions of iodine monochloride ICl are studied. The spectra of as-prepared solutions display the absorption band associated with hydrated ICl molecules. An additional band indicating that molecular iodine was formed in the solution emerges in the spectrum as dissolution takes place. Only the band belonging to iodine monochloride remains in the absorption spectra, and no additional bands appear after chloride anions Cl− are added to the solution. The absorption spectrum becomes more complex when ICl is dissolved in an alkaline medium. The band belonging to molecular iodine emerges in the spectra at low alkali concentrations, while being transformed to other shorter-wavelength bands at high alkali concentrations (рН ≥ 12).

Variation of the Near-Infrared Spectrum of Water from Dissolved Salts

In order to investigate the effect of dissolution of salts on the hydrogen-bonded network in liquid water, near-infrared absorption spectra of aqueous solutions of 16 salts, containing Na+ as common cation, were measured in the region where the first overtone of the –OH stretching mode of water is observed. Although the spectral variations of water resulting from dissolution of a salt is dependent on the kind of salt, principal component analysis of the observed spectra revealed that all spectral variations for the 16 salts were almost reproducible with only three components. The first component corresponds to the average of the observed spectra, while the other two components are responsible for the variations. The second component, which almost coincides with the component of the spectral variation of water from changes in temperature, was found to explain mainly the spectral changes by salts that destroy the hydrogen-bonded network. On the other hand, the third component, which includes the spectral changes at a lower wavenumber region than the second component, was found to mainly explain the spectral variation from the salts that expand the hydrogen-bonded network. These results suggest that observed spectral variations are not due to direct interaction between ions and water molecules, but due to the change of the hydrogen-bonded network because all variations produced by these 16 salts can be explained by only two components. The results suggest also that the mechanisms of destruction and expansion of the hydrogen-bonded network by the anions may be different.

Analytical gradients for MP2, double hybrid functionals, and TD-DFT with polarizable embedding described by fluctuating charges.

A polarizable quantum mechanics (QM)/ molecular mechanics (MM) approach recently developed for Hartree–Fock (HF) and Kohn–Sham (KS) methods has been extended to energies and analytical gradients for MP2, double hybrid functionals, and TD‐DFT models, thus allowing the computation of equilibrium structures for excited electronic states together with more accurate results for ground electronic states. After a detailed presentation of the theoretical background and of some implementation details, a number of test cases are analyzed to show that the polarizable embedding model based on fluctuating charges (FQ) is remarkably more accurate than the corresponding electronic embedding based on a fixed charge (FX) description. In particular, a set of electronegativities and hardnesses has been optimized for interactions between QM and FQ regions together with new repulsion–dispersion parameters. After validation of both the numerical implementation and of the new parameters, absorption electronic spectra have been computed for representative model systems including vibronic effects. The results show remarkable agreement with full QM computations and significant improvement with respect to the corresponding FX results. The last part of the article provides some hints about computation of solvatochromic effects on absorption spectra in aqueous solution as a function of the number of FQ water molecules and on the use of FX external shells to improve the convergence of the results. © 2015 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Study on Cupric Lactate Complexes in Electrodeposition of -Oriented Copper(I) Oxide

Copper(I) oxide (Cu2O) with cubic cuprite structure is known as an intrinsic p-type semiconductor, and it has 2.1 eV band gap and high optical-absorption coefficient (~104 cm−1). Hence, Cu2O is often used in connection with n-type ZnO to fabricate p-n junction solar cells. The Cu2O-ZnO device consisting of ubiquitous elements has attracted increasing attention because of its low fabrication cost. Additionally, <111>-oriented Cu2O is favorable considering the lattice match with {0001} plane of wurtzite ZnO, giving high permeability of light. Electrodeposition of Cu2O from aqueous solutions containing lactic acid and hydrated copper(II) salt has been reported in previous works[1-3]. It was revealed that Cu2O electrodeposited from pH 9.5 and 10.0 solution oriented <100> and those from pH 10.5, 11.5 and 12.5 solution oriented <111>, and <111>-oriented Cu2O could be electrodeposited even from pH 9.5 and 10.0 solution by lowering the cathode potential (see Fig. 1(b)). However, according to the E-pH diagram (see Fig. 1(a)) based on given thermodynamic data[4], above pH~8, it is expected that Cu2+ ion hydrolyzes and Cu(OH)2 precipitates. However, in our experiment, Cu2O was electrodeposited without any precipitation, implying that the stability regions for cupric lactate complexes are larger. In this study, we performed titration and UV-vis absorption spectroscopy of solutions containing lactic acid and hydrated copper(II) salt. It is discussed what kinds of complexes exist in the solution and the orientation of Cu2O. Aqueous solution containing lactic acid and hydrated copper(II) nitrate was examined by titration with potassium hydroxide aqueous solution. Above pH~4, deviation was observed from the calculated curve using given thermodynamic data[4]; moreover, a theoretical plateau centered at pH~7.2 was not seen. As a result, formation of Cu(OH)2 seems not to be realistic. Figure 2(b) demonstrates UV-vis absorption spectra of aqueous solutions containing lactic acid and hydrated copper(II) acetate at 2.0 < pH < 13.5. As pH increased from 6.0 to 9.0, blue shift was observed between 500 nm and 1000 nm, while red shift was seen between 300 nm and 400 nm. In addition, as pH increased from 9.0 to 10.5, the absorption edge shifted from about 420 nm to 380 nm. These results strongly suggest some kinds of cupric lactate complexes in the region of 6.0 < pH < 13.5. Here, we assumed three complexes (Cu(OH)L2−, Cu(OH)2L−, CuL4 2− ) at 9.5 < pH < 12.5 and three Nernst equations with a corresponding number of protons and electrons (see Table I). Figure 1(b) shows relationship between the orientation of Cu2O[3] and three assumed equations. For many cases, Cu2O electrodeposited from pH 9.5 and 10.0 solution oriented <100> and those from pH > 10.5 solution oriented <111>. Exceptionally, in the case of Eq.3, even at pH 9.5 and 10.0, we obtained <111>-oriented Cu2O when lowering the cathode potential because of increased current density proportional to v (CuOH) = k[Cu][OH] [2,3]. Suppose Eq.3 agrees with the experimental fact, since current density cannot be increased so large when lowering cathode poential considering deposition overpotential of Cu2O, Cu2O obtained from pH 9.5 and 10.0 solution should orient <100>. In consequence, Eq.3 may be inconsistent with the experimental fact and the unidentified cupric lactate complexes should be assumed as Cu(OH)L2− and/or Cu(OH)2L−.[1] K. Mizuno et al., J. Electrochem. Soc., 152, C179 (2005).[2] T. Shinagawa et al., Cryst. Growth Des., 13(1), 52 (2013).[3] Y. Seki et al., 58, The ECS Meet ing s, Vol. 2013-02, CA, USA, Oct 29, 2013.[4] R. M. Smith et al., Critical Stability Constants, Vol. 5, First Supplement, (Plenum Press, NewYork, 1982), p.291.

Near-Infrared Studies of Glucose and Sucrose in Aqueous Solutions: Water Displacement Effect and Red Shift in Water Absorption from Water-Solute Interaction

We used near infrared spectroscopy to obtain concentration dependent glucose absorption spectra in aqueous solutions in the near-infrared range (3800-7500 cm(-1)). Here we introduce a new method to obtain reliable glucose absorption bands from aqueous glucose solutions without measuring the water displacement coefficients of glucose separately. Additionally, we were able to extract the water displacement coefficients of glucose, and this may offer a new general method using spectroscopy techniques applicable to other water-soluble materials. We also observed red shifts in the absorption bands of water in the hydration shell around solute molecules, which comes from the contribution of the interacting water molecules around the glucose molecules in solutions. The intensity of the red shift gets larger as the concentration increases, which indicates that as the concentration increases more water molecules are involved in the interaction. However, the red shift in frequency does not seem to depend significantly on the concentration. We also performed the same measurements and analysis with sucrose instead of glucose as solute and compared.

Photophysical Properties of Self-assembled Cyanine-dye Dimmer Formation Assisted by Cyclodextrin Inclusion Complexation

We investigated a series of carbocyanine dye dimers formed in a cyclodextrin (CD) nanocavity by analyzing their steady-state absorption spectra in aqueous solution. As increasing CD concentrations, a blue-shifted additional peak was enhanced in several dye/CD combinations. This blue-shifted peak indicates that a ‘sandwich-type’ dimer is formed in CD. In order to obtain dimer-formation constants, we fitted dimer/monomer absorbance ratio to a theoretical equilibrium equation and the dimer structure was estimated on the basis of observed energy splittings in the absorption spectra. These values are significantly influenced by steric factors (poly-methine chain length, bulkiness of the end-group, CD cavity-size, etc.).

Selectivity of the Highly Preorganized Tetradentate Ligand 2,9-Di(pyrid-2-yl)-1,10-phenanthroline for Metal Ions in Aqueous Solution, Including Lanthanide(III) Ions and the Uranyl(VI) Cation

Some metal ion complexing properties of DPP (2,9-Di(pyrid-2-yl)-1,10-phenanthroline) are reported with a variety of Ln(III) (Lanthanide(III)) ions and alkali earth metal ions, as well as the uranyl(VI) cation. The intense π-π* transitions in the absorption spectra of aqueous solutions of 10(-5) M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln(III) (Ln = lanthanide) ions. It was found that log K(1)(DPP) for the Ln(III) ions has a peak at Ln(III) = Sm(III) in a plot of log K(1) versus 1/r(+) (r(+) = ionic radius for 8-coordination). For Ln(III) ions larger than Sm(III), there is a steady rise in log K(1) from La(III) to Sm(III), while for Ln(III) ions smaller than Sm(III), log K(1) decreases slightly to the smallest Ln(III) ion, Lu(III). This pattern of variation of log K(1) with varying size of Ln(III) ion was analyzed using MM (molecular mechanics) and DFT (density functional theory) calculations. Values of strain energy (∑U) were calculated for the [Ln(DPP)(H(2)O)(5)](3+) and [Ln(qpy)(H(2)O)(5)](3+) (qpy = quaterpyrdine) complexes of all the Ln(III) ions. The ideal M-N bond lengths used for the Ln(III) ions were the average of those found in the CSD (Cambridge Structural Database) for the complexes of each of the Ln(III) ions with polypyridyl ligands. Similarly, the ideal M-O bond lengths were those for complexes of the Ln(III) ions with coordinated aqua ligands in the CSD. The MM calculations suggested that in a plot of ∑U versus ideal M-N length, a minimum in ∑U occurred at Pm(III), adjacent in the series to Sm(III). The significance of this result is that (1) MM calculations suggest that a similar metal ion size preference will occur for all polypyridyl-type ligands, including those containing triazine groups, that are being developed as solvent extractants in the separation of Am(III) and Ln(III) ions in the treatment of nuclear waste, and (2) Am(III) is very close in M-N bond lengths to Pm(III), so that an important aspect of the selectivity of polypyridyl type ligands for Am(III) will depend on the above metal ion size-based selectivity. The selectivity patterns of DPP with the alkali-earth metal ions shows a similar preference for Ca(II), which has the most appropriate M-N lengths. The structures of DPP complexes of Zn(II) and Bi(III), as representative of a small and of a large metal ion respectively, are reported. [Zn(DPP)(2)](ClO(4))(2) (triclinic, P1, R = 0.0507) has a six-coordinate Zn(II), with each of the two DPP ligands having one noncoordinated pyridyl group appearing to be π-stacked on the central aromatic ring of the other DPP ligand. [Bi(DPP)(H(2)O)(2)(ClO(4))(2)](ClO(4)) (triclinic, P1, R = 0.0709) has an eight-coordinate Bi, with the coordination sphere composed of the four N donors of the DPP ligand, two coordinated water molecules, and the O donors of two unidentate perchlorates. As is usually the case with Bi(III), there is a gap in the coordination sphere that appears to be the position of a lone pair of electrons on the other side of the Bi from the DPP ligand. The Bi-L bonds become relatively longer as one moves from the side of the Bi containg the DPP to the side where the lone pair is thought to be situated. A DFT analysis of [Ln(tpy)(H(2)O)(n)](3+) and [Ln(DPP)(H(2)O)(5)](3+) complexes is reported. The structures predicted by DFT are shown to match very well with the literature crystal structures for the [Ln(tpy)(H(2)O)(n)](3+) with Ln = La and n = 6, and Ln = Lu with n = 5. This then gives one confidence that the structures for the DPP complexes generated by DFT are accurate. The structures generated by DFT for the [Ln(DPP)(H(2)O)(5)](3+) complexes are shown to agree very well with those generated by MM, giving one confidence in the accuracy of the latter. An analysis of the DFT and MM structures shows the decreasing O--O nonbonded distances as one progresses from La to Lu, with these distances being much less than the sum of the van der Waals radii for the smaller Ln(III) ions. The effect that such short O--O nonbonded distances has on thermodynamic complex stability and coordination number is then discussed.

Synthesis, X-ray and spectroscopic analysis of 2-hydrazino-6-methyl-4-(methoxymethyl)-5-nitropyridine-3-carbonitrile

Pyridine derivative 2-hydrazino-6-methyl-4-(methoxymethyl)-5-nitropyridine-3-carbonitrile ( 2) has been obtained from 2-chloro-4-(methoxymethyl)-6-methyl-5-nitropyridine-3-carbonitrile ( 1) by novel protocol and its structure was determined by X-ray diffraction method. An analysis revealed some structural differences in 2 compared to corresponding 3-cyano-5-nitro-pyridines and 2-hydrazinopyridines. Supramolecular structure contains one N H⋯N and two N H⋯O hydrogen bonds, as well as one C H⋯O hydrogen bond. Structural features have been also studied by FT-IR, FT-R and NMR spectroscopy. FT-IR dilution experiments showed that the character of intermolecular NH⋯O and NH⋯N interactions in solution depends on concentration. The spectral properties were investigated by UV–vis absorption and fluorescence spectroscopy techniques. Absorption spectra of compounds have been recorded in protic and aprotic solvents in the range 200–550 nm and solvent effects on the absorption spectra of this compound are interpreted. Absorption spectra of aqueous solution of compound 2 were also recorded at different temperatures and pH values and protonation constant was calculated. Unlike previously studied structurally similar compound 1, the title compound 2 does not emit fluorescence.

Solvent effect on the UV/Vis absorption spectra in aqueous solution: The nonequilibrium polarization with an explicit representation of the solvent environment

An explicit solvation model was presented in this work to estimate the solvent effect on the UV/Vis absorption spectra in aqueous solution. Different from others’ concern, we concentrate on the establishment of proper electrostatic solvation energy formula for nonequilibrium polarization in explicit solvent model with adopting the constrained equilibrium approach, which was originally proposed by Leontovich and firstly introduced by us to cope with the nonequilibrium solvation problem. The formulation of this model was deduced entirely based on the explicit representation of the solvent surrounding with discrete dipoles and polarizability for each solvent molecule. The external field, applied to construct the virtual constrained equilibrium state, can be expressed by the physical quantities before and after the Franck–Condon transition. The newly established solvation energy formulation for nonequilibrium was implemented under the popular QM/MM strategy with modifying the nonequilibrium module in the averaged solvent electrostatic potential/molecular dynamics program to carry out numerical calculations. The new codes were further utilized to study the solvatochromic shift of the n → π ∗ transition in formaldehyde in aqueous solution. Different contributions to the total solvent shift were analyzed and the main component comes from the electrostatic interaction between the solute and solvent and the solvent polarization also has a significant influence. The solute molecule properties and the microscopic solvent structure were also discussed to uncover more details.