Nitrobindin versus myoglobin: A comparative structural and functional study

Most hemoproteins display an all-α-helical fold, showing the classical three on three (3/3) globin structural arrangement characterized by seven or eight α-helical segments that form a sandwich around the heme. Over the last decade, a completely distinct class of heme-proteins called nitrobindins (Nbs), which display an all-β-barrel fold, has been identified and characterized from both structural and functional perspectives. Nbs are ten-stranded anti-parallel all-β-barrel heme-proteins found across the evolutionary ladder, from bacteria to Homo sapiens. Myoglobin (Mb), commonly regarded as the prototype of monomeric all-α-helical globins, is involved along with the oligomeric hemoglobin (Hb) in diatomic gas transport, storage, and sensing, as well as in the detoxification of reactive nitrogen and oxygen species. On the other hand, the function(s) of Nbs is still obscure, even though it has been postulated that they might participate to O2/NO signaling and metabolism. This function might be of the utmost importance in poorly oxygenated tissues, such as the eye's retina, where a delicate balance between oxygenation and blood flow (regulated by NO) is crucial. Dysfunction in this balance is associated with several pathological conditions, such as glaucoma and diabetic retinopathy. Here a detailed comparison of the structural, spectroscopic, and functional properties of Mb and Nbs is reported to shed light on the similarities and differences between all-α-helical and all-β-barrel heme-proteins.

Enhancement of Ni-Zn ferrite nanoparticles parameters via cerium element for optoelectronic and energy applications

This work is concerned with fabricating ferrite nanoparticles of nickel-zinc with the chemical formula: Ni0.55Zn0.45Fe2-xCexO4, 0 ≤ x ≤ 0.011 by co-deposition technique and modifying their electrical, microscopic, spectroscopic, optical, electrical and dielectric properties as advanced engineering materials through doping with the cerium (Ce) element. XRD patterns displayed that the samples have a monophasic Cerium-Nickel-zinc (CNZ) spinel structure without other impurities for cerium concentration (x) ≤ 0.066. Both values of crystallite size and lattice parameters decrease from 33.643 to 23.137 nm and from 8.385 to 8.353 nm, respectively, with the increasing Ce ions substitution content from 0 to 0.066. SEM images indicate that grains of the fabricated compounds are smaller, more perfect, more homogeneous, and less agglomeration than those of the un-doped Ni-Zn nano-ferrites. The maximum intensity of first-order Raman spectral peaks (Eg, F2g(2), A1g(2), and A1g(1)) of CNZ ferrite nanoparticles are observed at about (330, 475, 650, 695) cm-1, respectively, that confirms the CNZ samples have the cubic spinel structure. The direct and indirect optical energy bandgaps of CNZ samples have a wide spectrum of values from semiconductors to insulators according to cerium concentration. The results showed that the values of dielectric constant, dielectric loss factor, and Ac conductivity and the conductivity transition temperature are sensitive to cerium ions content. AC conductivity exhibited by the CNZ samples has the semiconductor materials behavior, where the AC conductivity increases due to temperature or doping concentration. The results indicate that Ni0.55Zn0.45Fe1.944Ce0.066O4 ferrite nanoparticles may be selected for optoelectronic devices, high-frequency circuits, and energy storage applications.

Electronic structures, bonding aspects and spectroscopic parameters of homo/hetero valent bridged dinuclear transition metal complexes

Bridged dinuclear metal complexes have fascinated scientists worldwide, and remarkable success has been achieved to unravel the electronic structures, structure-function relationship, coordination environments, and fine mechanistic details of the enzymes owing to the repercussion of biomimetic studies carried out on dinuclear model systems. Molecular level study of these systems integrated with spectroscopic study helps in gaining deep insights about structural and electronic aspects of natural enzymatic systems. Considering the same, here first time we report DFT study on bridged non-heme metal complexes based on N-Et-HPTB ligand system containing homovalent (M^IIM^II); {[(Mn^II)₂(O₂CCH₃)(N-Et-HPTB)]²⁺; Species I), [(Fe^II)₂(O₂CCH₃)(N-Et-HPTB)]²⁺; Species II), [(Co^II)₂(O₂CCH₃)(N-Et-HPTB)]²⁺; Species III)} and heterovalent (M^IIIM^II): {[(Mn^III)(Mn^II)(O₂)(N-Et-HPTB)]²⁺; Species Ia) [(Fe^III)(Fe^II)(O₂)(N-Et-HPTB)]²⁺; Species IIa) and [(Co^III)(Co^II)(O₂)(N-Et-HPTB)]²⁺; Species IIIa)} dinuclear metal centres. Bridging oxygen bears a significant spin density which may prompt important chemical reactions involving activation of bonds like C-H/O-H/N-H etc. TD-DFT calculations for UV-Visible absorption have been carried out to further shed light on structural-functional and electronic structures of these dinuclear species. Studying these dinuclear species may be a good starting point for the study of active sites of the bimetallic centre of dinuclear enzymes and thus may serve as fascinating spectroscopic models. Further, FMO analysis, MEP mapping, and NBO calculations were employed to analyze bonding aspects predict theoretical reactivity behaviour and any kind of stabilizing interactions present in the reported species.

High efficient and broadband ∼3.5 μm emission of Er3+:YAG crystal

The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er³⁺ were successfully grown by the micro-pulling down method and spectroscopic properties of the crystals were investigated. The main interest was focus on the relation between the Er³⁺ concentration and ∼3.5 μm emission of Er³⁺:YAG crystals. Room temperature absorption spectra were analyzed by the Judd-Ofelt theory. The stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. The fluorescence intensities and peak emission cross-sections of the crystals at ∼3.5 μm are slightly decreasing with the increase of Er³⁺ concentration. The trend of the emission properties in NIR and visible region with the Er³⁺ concentration was also discussed and compared. The results indicate that the highly doped Er³⁺ concentration is beneficial to realize the ∼3.5 µm laser output.

Ab initio study of spectroscopic properties and anharmonic force fields of MNH2 (M = Li, Na, K)

The spectroscopic properties and anharmonic force fields of NaNH₂ are studied in present work by DFT (B3P86 and B3PW91) and MP2 methods in combination with 6-311++G(2d, 2p) and 6-311++G(3df, 2pd) basis sets. The calculated equilibrium geometry, ground state rotational constants and centrifugal distortion constants of NaNH₂ at B3P86/6-311++G(3df, 2pd) theoretical level agree very well with the corresponding experimental values. Noteworthy, some spectroscopic constants and anharmonic force fields of NaNH₂, which have not been experimentally measured, are firstly predicted. In addition, the spectroscopic properties of KNH₂ are also predicted at the B3P86/6-311++G(3df, 2pd) level of theory. The influences of metal atoms on the equilibrium geometry, anharmonic constants, rotational constants, centrifugal distortion constants of MNH₂ (M = Li, Na, K) are analyzed intuitively. One can find that the metal atoms affect the rotational constants, part of centrifugal distortion constants (D_K, D_JK, H_K, and H_KJ), M-N bond length and some anharmonic constants of MNH₂.

Superalkali-doped borazine and lithiated borazine complexes: diffuse excess electron and large first-hyperpolarizability

A number of superalkali (M₃O / M₃S; M = Li, Na, K)-doped borazine and hexalithio borazine complexes are considered for the theoretical study of their electronic structure and quadratic polarizability. Electron-rich O/S atom of superalkali species remains very close to one boron atom of the ring through non-covalent interaction. The first-hyperpolarizability increases rather significantly upon superalkali doping. The chosen complexes possess diffuse excess electron which is located on the superpalkali moiety of borazine complexes and at the ring site of lithiated borazines. First-hyperpolarizability of M₃O(S)@B₃N₃Li₆ complexes are significantly larger than that of the corresponding M₃O(S)@B₃N₃H₆ complexes. The magnitude of first-hyperpolarizability of Li₃S@B₃N₃Li₆ is larger than that of Li₃S@B₃N₃H₆ by about three orders of magnitude.

Ab initio study of spectroscopic properties at anharmonic force fields of LiNH2

This work presents a systematic investigation of the spectroscopic properties at anharmonic force fields of ground electronic state ([Formula: see text]) of LiNH₂, which are calculated using second-order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT) with hybrid GGA and meta-hybrid GGA (M06-2X) exchange-correlation functional. Two high angular momentum basis sets of 6-311+g (2d, p) and 6-311++g (3df, 2pd) are used. The equilibrium geometries, ground-state rotational constants, harmonic frequencies, and quartic and sextic centrifugal distortion constants of LiNH₂ are calculated and compared with corresponding experimental or theoretical data. The predicted accuracy of the calculated constants has been confirmed by analyzing the deviations with respect to experiment. In addition, the anharmonic constants, vibration-rotation interaction constants, force constants, and Coriolis coupling constants of LiNH₂ are firstly obtained. The infrared spectrum is predicted and together with the first prediction on the higher-order anharmonic constants contributes to a better understanding of the vibrational and rotational characteristics of LiNH₂, thus revealing its internal structure. Graphical abstract The IR spectra and the magnified IR spectra at 3500 cm^-1 in harmonic approximations of LiNH₂ using B3P86, M06-2X and MP2 methods combining with 6-311++g(3df,2pd).

Accurate spectroscopic properties by diffusion quantum Monte Carlo calculations

The capability of Diffusion Quantum Monte Carlo (DMC) to produce high quality potential energy curve (PEC) was evaluated. H₂⁺, HeH⁺ and LiH PECs were built by all-electron fixed-node DMC calculations. Trial wave functions were obtained from Hartree-Fock (HF) (H₂⁺), MCSCF and CI (HeH⁺ and LiH) calculations multiplied by Jastrow factor. The quality of these generated PECs was analyzed throughout equilibrium distance, dissociation energy, vibrational energies and rovibrational spectroscopic constants (ω_e, ω_ex_e, ω_ey_e, α_e, γ_e and B_e). The Discrete Variable Representation (DVR) and the Dunham approaches were used to determine the rovibrational spectroscopic constants. The PECs and the aforementioned properties were also obtained by the following methods: MCSCF/aug-cc-pV5Z (LiH), CCSD(T)/aug-cc-pV5Z (HeH⁺ and LiH) and HF (H₂⁺ and HeH⁺) levels. The results of these DMC computations, specially the DMC-DVR procedure, are the most accurate among others DMC calculations available in the literature for these systems. They suggest that DMC can be used to achieve accurate PECs to produce spectroscopic properties with the same level of accuracy of theoretical benchmarks and experimental data of the literature.

Spectroscopic properties analyses and laser characterization simulation of Er3+,Eu3+:YAP single crystal

Er,Eu:YAlO₃ (abbr. as Er,Eu:YAP) crystal was grown by the Czochralski technique for the first time. Its absorption and fluorescence spectra as well as the fluorescence decay curves were measured and investigated. The spectral parameters including absorption cross-section and emission cross-section were calculated. It is found that the crystal has short lifetimes at ⁴I_13/2 and ⁴I_11/2 levels, large absorption cross-section at 974 nm and 790 nm, and large stimulated emission cross-section at 2704 nm. The co-dopant Eu³⁺ decreases the fluorescence lifetime of ⁴I_11/2 level from 400 μs to 59.35 μs, and thus inhibits the self-termination effect of ~2.7 μm in some degree. We develop a theoretical model that simulates the laser characteristics of Er,Eu:YAP crystal numerically. Based on Er³⁺-Eu³⁺ energy level diagrams, the rate equation model was built and discussed. It was found that: when the pump rate increases gradually, the laser quantum efficiency reaches to its upper limit with a fixed value 2-p², and this value is 1.35 for Er,Eu:YAP crystal. The results show that Er,Eu:YAP crystal is an excellent material candidate for ~2.7 μm laser.

Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties

Near-infrared luminescence properties of Nd³⁺ and Ho³⁺ ions in barium gallo-germanate glasses have been reported. Several spectroscopic parameters for Nd³⁺ and Ho³⁺ ions have been determined from the Judd-Ofelt analysis and absorption/luminescence measurements. Quite large luminescence lifetime, quantum efficiency and stimulated emission cross-section have been obtained for the main ⁴F_3/2 → ⁴I_11/2 (Nd³⁺) and ⁵I₇ → ⁵I₈ (Ho³⁺) laser transitions of rare earths in barium gallo-germanate glasses. It suggests that barium gallo-germanate glass is promising for near-infrared laser application at emission wavelengths 1064 nm (Nd³⁺) and 2020 nm (Ho³⁺).

Novel insights into nucleoamino acids: biomolecular recognition and aggregation studies of a thymine-conjugated L-phenyl alanine

This article deals with the synthesis in solid phase and characterization of a nucleoamino amide, based on a phenylalaninamide moiety which was N-conjugated to a thymine nucleobase. In analogy to the natural nucleobase-amino acid conjugates, endowed with a wide range of biological properties, the nucleoamino amide interacts with single-stranded nucleic acids as verified in DNA- and RNA-binding assays conducted by CD and UV spectroscopies. These technologies were used to show also that this conjugate binds serum proteins altering significantly their secondary structure, as evidenced by CD and UV using BSA as a model. The biomolecular recognition seems to rely on the ability of the novel compound to bind aromatic and heteroaromatic moieties in protein and nucleic acids, not hindered by its propensity to self-assemble in aqueous solution, behavior suggested by dynamic light scattering (DLS) and CD spectroscopy in concentration- and temperature-dependent experiments. Finally, the high stability in human serum concurs to define the picture of the nucleoamino amide: this enzymatically stable drug candidate could interfere with protein and single-stranded nucleic acid-driven biological processes, particularly those associated with mRNA poly(A) tail, and its self-assembling nature, in analogy to other L-Phe-based systems, discloses new scenarios in drug delivery technology.

MS-CASPT2 study of the ground and low lying states of CsH. J Mol Model 2017;23:339. [PMID: 29124408 DOI: 10.1007/s00894-017-3503-9]

Correlated ab initio methods [CASPT2 and R-CCSD(T)] in conjunction with the ANO-RCC basis sets in large contraction were used to calculate potential energy curves (PECs) of the ground and excited electronic states of CsH⁺ (doublets and quartets) with the inclusion of the scalar relativistic effects and spin-orbit interaction. The ground X²Σ⁺ state is a rather fragile van der Waals molecular ion. The binding energy of this X²Σ⁺ state provided by both computational methods is estimated to be 0.02-0.04 eV, and is compared with the reported experimental binding energy (0.51-0.77 eV). This large binding energy can be attributed to the A²Σ⁺ state, and can thus explain the apparent disagreement between theory and experiment. The spectroscopic constants of all bound states were calculated from the PECs and compared with previous published data for X²Σ⁺ and A²Σ⁺ states. Graphical abstract Low-lying Ω states of cesium hydride cation.

Hydrological conditions regulate dissolved organic matter quality in an intermittent headwater stream. From drought to storm analysis

Storms and droughts are an essential driver for the dissolved organic matter (DOM) concentration in headwater streams. However, the relationship between DOM quality and discharge (Q) has not been addressed in depth and the impact of other hydro-climatic or biogeochemical drivers has not been explored. In this study DOM quality variability was explored at seasonal and storm event scales during an intensive 2.5-year-long sampling in a Mediterranean stream characterized by a severe summer drought. DOM quality was described in terms of absorbance and fluorescence properties. Most of the DOM properties were strongly related to discharge revealing the input of allochthonous, degraded, aromatic, humic and increased-molecular-size DOM under high flow conditions. However, these relationships disappeared or reversed during drying and rewetting periods. Each DOM response at the storm event scale (DOM-Q hysteresis) was outlined with two descriptors that summarised its trend (dilution/flushing/chemostasis) and shape (linear/nonlinear response). Multiple linear regression and commonality analysis showed that, in addition to the magnitude of storm episodes, antecedent hydrological conditions, namely pre-event basal flow and the magnitude of the previous storm event, played a significant role in regulating the trends and shapes of DOM-Q hysteresis.

Tracking ultrasonically structural changes of natural aquatic organic carbon: Chemical fractionation and spectroscopic approaches

In this study, the structural alteration to DOC for a range of ultrasound treatments was investigated with chemical fractionation and UV-vis spectroscopic measurement. Ultrasound treatments were applied in continuous and pulsed modes at power levels of 48 and 84 W for effective treatment times of 5 and 15 min. Overall results show that the ultrasound treatments tended to degrade the hydrophobic aromatic fraction, while increasing the hydrophilic fraction to a lesser extent. The highest recorded reduction of hydrophobic DOC (17.8%) was achieved with pulse treatment of 84 W for15 min, while the highest increase in the hydrophilic DOC (10.5%) was obtained with continuous treatment at 84 W and 5 min. The optimal ultrasound treatment conditions were found to be pulse mode at high power and short treatment time, causing a minimal increase in the hydrophilic fraction of 1.3% with moderate removal of the hydrophobic fraction of 15.52%. The same treatment conditions, with longer treatment time, resulted in the highest removal of SUVA254 and SUVA280 of 17.09% and 16.93, respectively. These results indicate the potential for ultrasound treatments in DOC structural alteration. The hydrophobic fraction showed strong and significant correlations with UV absorbance at 254 and 280 nm. A254/A204 also exhibited strong and significant correlations with the hydrophobic/hydrophilic ratio. The other UV ratios (A250/A365 (E2/E3) and A254/A436) had weak and insignificant correlations with the hydrophobic/hydrophilic ratio. This confirms the applicability of UV indices as a suitable surrogate method for estimating the hydrophobic/hydrophilic structure.

A dithienosilole-based fluorescent chemosensor for multiple logic operations at the molecular level

A chemosensor consisting of two terpyridines covalently linked to a dithienosilole unit (1) has been synthesized, and its optical and metal sensing properties have been investigated. Due to the metal-organic coordination function, 1 can bind with many transition metal ions and display different fluorescence responses that cause it to function as a "turn-off" fluorescent chemosensor. A significant bathochromic shift in the fluorescence spectra is observed in the presence of Zn(2+). Meanwhile, the emission of 1 is weakened upon exposure to Ag(+) and Fe(2+) and completely quenched by Ni(2+), Co(2+), and Cu(2+). Based on the observed results, several logic gates, such as XNOR, INHIBIT, and IMPLICATION, have been achieved by controlling the chemical inputs.

The influence of TeO2 on thermal stability and 1.53 μm spectroscopic properties in Er(3+) doped oxyfluorite glasses

In this work, the thermal and spectroscopic properties of Er(3+)-doped oxyfluorite glass based on AMCSBYT (AlF3-MgF2-CaF2-SrF2-BaF2-YF3-TeO2) system for different TeO2 concentrations from 6 to 21 mol% is reported. After adding a suitable content of TeO2, the thermal ability of glass improves significantly whose ΔT and S can reach to 118 °C and 4.47, respectively. The stimulated emission cross-section reaches to 7.80×10(-21) cm(2) and the fluorescence lifetime is 12.18 ms. At the same time, the bandwidth characteristics reach to 46.41×10(-21) cm(2) nm and the gain performance is 63.73×10(-21) cm(2) ms. These results show that the optical performances of this oxyfluorite glass are very well. Hence, AMCSBYT glass with superior performances might be a useful material for applications in optical amplifier around 1.53 μm.

A Cu²⁺-selective fluorescent chemosensor based on BODIPY with two pyridine ligands and logic gate

A novel near-infrared fluorescent chemosensor based on BODIPY (Py-1) has been synthesized and characterized. Py-1 displays high selectivity and sensitivity for sensing Cu(2+) over other metal ions in acetonitrile. Upon addition of Cu(2+) ions, the maximum absorption band of Py-1 in CH3CN displays a red shift from 603 to 608 nm, which results in a visual color change from pink to blue. When Py-1 is excited at 600 nm in the presence of Cu(2+), the fluorescent emission intensity of Py-1 at 617 nm is quenched over 86%. Notably, the complex of Py-1-Cu(2+) can be restored with the introduction of EDTA or S(2-). Consequently, an IMPLICATION logic gate at molecular level operating in fluorescence mode with Cu(2+) and S(2-) as chemical inputs can be constructed. Finally, based on the reversible and reproducible system, a nanoscale sequential memory unit displaying "Writing-Reading-Erasing-Reading" functions can be integrated.

Synthesis, spectroscopic, thermal and antimicrobial studies of neodymium(III) and samarium(III) complexes derived from tetradentate ligands containing N and S donor atoms

Trivalent lanthanide complexes of the type [Ln(L)Cl(H2O)2] (where Ln=Nd(III) or Sm(III) and LH2=Schiff bases derived by the condensation of 3-(phenyl/substitutedphenyl)-4-amino-5-mercapto-1,2,4-triazole with diacetyl/benzil) have been synthesized by the reactions of anhydrous lanthanide(III) chloride with Schiff bases in methanol. The structures of the complexes have been proposed on the basis of elemental analysis, electrical conductance, magnetic moment, spectroscopic measurements (IR, 1H, 13C NMR and UV-vis spectra) and X-ray diffraction studies. The spectral data reveal that the Schiff base ligands behave as dibasic tetradentate chelating agents having coordination sites at two thiol sulfur atoms and two azomethine nitrogen atoms. The presence of coordinated water in metal complexes was confirmed by thermal and IR data of the complexes. All the Schiff bases and their metal complexes have also been screened for their antibacterial activity against Bacillus subtilis, Staphylococcus aureus and antifungal activities against Aspergillus niger, Curvularia pallescens and Colletotrichum capsici.

An unexpected Schiff base-type Ni(II) complex: synthesis, crystal structures, fluorescence, electrochemical property and SOD-like activities

An unexpected Schiff base-type Ni(II) complex, [Ni(L(2))2]⋅CH3OH (HL(2) = 1-(2-{[(E)-3, 5-dibromo-2-hydroxybenzylidene]amino}phenyl)ethanone oxime), has been synthesized via complexation of Ni(II) acetate tetrahydrate with HL(1) (2-(3,5-dibromo-2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazoline 3-oxide) originally. HL(1) and its corresponding Ni(II) complex were characterized by IR, (1)H NMR spectra, as well as by elemental analysis, UV-Vis and emission spectroscopy, respectively. Crystal structures of the ligand and complex have been determined by single-crystal X-ray diffraction. Each complex links two other molecules into an infinite 1-D chain via intermolecular hydrogen bonding interactions. Moreover, the electrochemical property of the nickle complex was studied by cyclic voltammetry. In addition, SOD-like activities of HL(1) and Ni(II) complex were also investigated.

A detailed experimental and theoretical study of two novel substituted trifluoromethylchromones. The influence of the bulky bromine atom on the crystal packing

The new 3-methyl-2-trifluoromethylchromone (1) and 3-bromomethyl-2-trifluoromethylchromone (2) compounds were synthesized and characterized by vibrational (IR, Raman), UV-Vis and NMR ((1)H, (13)C and (19)F) spectroscopy and MS spectrometry. The crystal structures of 1 and 2 were determined by X-ray diffraction methods. Both compounds crystallize in the monoclinic P21/c space group with Z=4 molecules per unit cell. The structures were solved from 1423 (1) and 1856 (2) reflections with I>2σ (I) and refined by full-matrix least-squares to agreement R1-values of 0.0403 (1) and 0.0554 (2). Because of π-bonding delocalization, the organic molecular skeletons are planar and the molecular bonding structures can be described by formally single, double and resonant bonds. In 2, the CF3 group revealed a strong rotational disorder around the CCF3 bond, which could be explained in terms of four split positions with about uniform angular distribution. The vibrational, electronic and NMR, spectra were discussed and assigned with the assistance of DFT calculations.

Rare earths in lead-free oxyfluoride germanate glasses

Spectroscopic properties of rare earths in lead-free oxyfluoride germanate glasses were studied. The absorption and luminescence spectra of Eu(3+), Pr(3+) and Er(3+) ions were examined as a function of BaF₂ concentration and several spectroscopic parameters for rare earths were determined. The ratio of integrated luminescence intensity of the (5)D₀→(7)F₂ transition to that of the (5)D₀→(7)F₁ transition of Eu(3+) decrease significantly with increasing BaF₂ content. The absorption (Er(3+)) and emission (Pr(3+)) 'hypersensitive transitions' of rare earths are shifted in direction to shorter wavelengths with increasing BaF₂ content in glass composition. Emission spectra and their decays corresponding to the main (4)I₁₃/₂→(4)I₁₅/₂ laser transition of Er(3+) were also analyzed. Quite long-lived NIR luminescence of Er(3+) is observed for lead-free glass samples with low BaF₂ concentration.

Synthesis and spectroscopic properties of some new difluoroboron bis-β-diketonate derivatives

Six new bis-β-diketones (RCOCH2CO-C7H7N-COCH2COR) were synthesized from 3,5-diacetyl-2,6-dimethylpyridine via Claisen condensation with the corresponding esters, and then reacted with boron trifluoride etherate to afford difluoroboron bis-β-diketonate derivatives. Their spectroscopic properties were investigated by UV-vis, FTIR, (1)H NMR and fluorescence spectroscopic techniques. It was found that these boron complexes exhibited violet or blue fluorescence emission at 422-445nm and possessed high extinction coefficients. The results indicate that the extending π-conjugation can increase the fluorescence intensity and quantum yield for these boron complexes. Especially, the compound 2b displayed the stronger fluorescence intensity and the highest fluorescence quantum yield (Φu=0.94) in these boron compounds. However, compounds 2c and 2d had the lower fluorescence intensity and quantum yield as a result of the heavy atom effect of the chlorine atom in the molecules.

Synthesis of quinoline derivatives containing pyrazole group and investigation of their crystal structure and spectroscopic properties in relation to acidity and alkalinity of mediums

Two series of quinoline derivatives containing pyrazole group were synthesized and characterized by means of (1)H NMR, FT-IR, MS, elemental analysis and X-ray single crystal diffraction, and their UV-vis absorption behavior and fluorescence properties were also measured. Moreover, the effects of acetic acid and triethylamine on the spectroscopic properties of synthesized products were examined with compounds 3a and 5a as examples. It has been found that all synthesized quinoline derivatives show maximum absorption peak at 303 nm and emission peaks around 445 nm. Besides, both acetic acid and triethylamine can change the acidity of the medium, thereby influencing the UV-vis absorption spectra and fluorescence spectra of synthesized products. Moreover, theoretical investigations indicate that the integration of H(+) and N atom of quinoline ring favors the formation of a new product in the presence of acetic acid, and the product obtained in this case shows a new UV-vis absorption peak at 400 nm.

Distribution and spectral characteristics of chromophoric dissolved organic matter in a coastal bay in northern China

The absorption spectra of chromophoric dissolved organic matter (CDOM), along with general physical, chemical and biological variables, were determined in the Bohai Bay, China, in the springs of 2011 and 2012. The absorption coefficient of CDOM at 350 nm (a350) in surface water ranged from 1.00 to 1.83 m⁻¹ (mean: 1.35 m⁻¹) in May 2011 and from 0.78 to 1.92 m⁻¹ (mean: 1.19 m⁻¹) in April 2012. Little surface-bottom difference was observed due to strong vertical mixing. The a350 was weakly anti-correlated to salinity but positively correlated to chlorophyll a (Chl-a) concentration. A shoulder over 260-290 nm, suggestive of biogenic molecules, superimposed the overall pattern of exponentially decreasing CDOM absorption with wavelength. The wavelength distribution of the absorption spectral slope manifested a pronounced peak at ca. 300 nm characteristic of algal-derived CDOM. All a250/a365 ratios exceeded 6, corresponding to CDOM molecular weights (Mw) of less than 1 kDa. Spectroscopically, CDOM in the Bohai Bay differed substantively from that in the Haihe River, the bay's dominant source of land runoff; photobleaching of the riverine CDOM enlarged the difference. Results point to marine biological production being the principal source of CDOM in the Bohai Bay during the sampling seasons. Relatively low runoff, fast dilution, and selective photodegradation are postulated to be among the overarching elements responsible for the lack of terrigenous CDOM signature in the bay water.

X-ray structure and spectroscopy of novel trans-[Ni(L)(NO(3))(2)] and [Ni(L)](ClO(4))(2)·2H(2)O complexes

Ni(L)(NO(3))(2) (complex 1) and [Ni(L)](ClO(4))(2)·2H(2)O (complex 2) [L=3,14-diethyl-2,6,13,17-tetraazatricyclo(16.4.0.0(7,12))docosane] have been prepared and structurally characterized by single-crystal X-ray diffraction at 200K. For these constrained macrocycle complexes, nickel(II) exists in a distorted octahedral environment with the four nitrogen atoms of the macrocyclic ligands and two oxygen atoms from nitrate in axial positions in complex 1. The macrocyclic ligand in complex 1 adopts the most stable trans-III conformation. The Ni-N distances in both the complex 1 (2.094(4)-2.051(4)Å) and complex 2 (2.042(8)-1.996(7)Å), are typical but the axial ligands are coordinating, with NiO bond length, 2.198(3)Å for complex 1. The complex 2 adopts square planner geometry around the Ni(II) with four nitrogen atoms from macrocyclic ligand. The crystals are stabilized in a 3-D network by intra and intermolecular hydrogen bonds that are formed among the secondary nitrogen hydrogen atoms and nitrate in 1, and intermolecular hydrogen bonds are formed by perchlorate and NH groups in 2. The electronic absorption, IR and PL spectral properties are also discussed.

Ground and excited states of the diatomic dianion Cl2(2-)

The QCISD(T)/aug-cc-pVQZ and CIS/aug-cc-pVQZ calculations have been carried out to obtain potential energy curves (PECs) of the Cl2(2-) diatomic dianion in order to address possibility of its formation in the merged beam fragmentation of Cl2(-) questioned based on the observation of the Cl(-)+Cl+e(-) channel. Results show that two of the excited states, namely A(1)Σg and a(3)Σg are metastable with PECs having wells deep enough to suite several bound states, with minima located at Re=2.8280 Å and Re=2.5972 Å, and Coulomb barriers of 1648.288 and 1403.835 cm(-1) heights located at 4.0320 and 3.6130 Å, respectively. Transition probabilities and tunneling predissociation lifetimes corresponding to these metastable states are also calculated and analyzed. Ground state X(1)Σg and excited states B(1)Σu, C(1)Πg and D(1)Πu calculated for this dianion are all repulsive. Calculated Franck-Condon factors suggest that Cl2(2-) can be produced in its excited states via an electron impact process initiating from the ground states of Cl2 and Cl2(-) .

Computational studies of the electronic, conductivities, and spectroscopic properties of hydrolysed Ru(II) anticancer complexes

The mechanism of activation of metal-based anticancer agents was reported to be through hydrolysis. In this study, computational method was used to gain insight to the correlation between the chemistry of the hydrolysis and the anticancer activities of selected Ru(II)-based complexes. Interestingly, we observed that the mechanism of activation by hydrolysis and their consequential anticancer activities is associated with favourable thermodynamic changes, higher hyperpolarizability (β), lower band-gap and higher first-order net current. The Fermi contact (FC) and spin dipole (SD) are found to be the two most significant Ramsey terms that determine the spin-spin couplings (J(HZ)) of most of the existing bonds in the complexes. Many of the computed properties give insights into the change in the chemistry of the complexes due to hydrolysis. Besides strong correlations of the computed properties to the anticancer activities of the complexes, using the quantum theory of atoms in a molecule (QTAIM) to analyse the spectroscopic properties shows a stronger correlation between the spectroscopic properties of Ru atom to the reported anticancer activities than the sum over of the spectroscopic properties of all atoms in the complexes.