The Charge Transfer Complex between 2, 3-diamino-5-bromopyridine and Chloranilic acid: Preparation,Spectroscopic Characterization,DNA binding,and DFT/PCM analysis

A charge transfer hydrogen bonded complex was prepared and experimentally explored in an acetonitrile (ACN) medium between the proton acceptor (electron donor) 2, 3-Diamino-5-bromopyridine and the proton donor (electron acceptor) chloranilic acid. The stoichiometry of the charge transfer complex is 1:1. The Benesi-Hildebrand equation is used to calculate the molar absorptivity (ε_CT), association constant (K_CT) and other spectroscopic physical characteristics. The solid compound was synthesized and studied using several spectroscopic methods. The presence of charge and proton transfers in the resultant complex was supported by ¹H NMR, FT-IR and SEM-EDX investigations. The complex DNA binding ability was investigated using electron absorption spectroscopy, and the CT complex binding mechanism is intercalative. The intrinsic binding constant (K_b) value is 5.2 × 10⁶M?1. The good binding affinity of the CT complex makes it potentially suitable for usage as a pharmaceutical in the future. Molecular docking calculations have been performed between CT complex and DNA (ID = 1BNA) to study the CT-DNA interaction theoretically. To corroborate the experimental findings, calculations based on DFT were carried out in the gas and PCM analysis where the existence of charge and hydrogen transfers. Finally, good agreement between experimental and theoretical computations was observed confirming that the basis set used is appropriate for the system under examination.     

Metal atom dynamics in a charge transfer complex

Temperature-dependent ⁵⁷Fe Mössbauer spectroscopy over the interval 89 < T < 335 K has been used to study the detailed metal atom dynamics in the charge transfer complex (CT) decamethlferrocene-acenaphthenequinone. The quadrupole splitting, area ratio and recoil-free fraction parameters clearly reflect the phase transition (T_pt) at 257 K. The root-mean-square-amplitude of vibrations of the metal atom in the CT complex have been compared to that determined earlier for decamethyl ferrocene. The vibrational amplitudes are isotropic below T_pt but anisotropic above this temperature.     

2-Ferrocenyl-substituted pyrylium ions from coupling of ethynylferrocene with cyclomanganated chalcones

2-Ferrocenyl-substituted pyrylium salts are produced when orthomanganated chalcones are reacted with ethynylferrocene in CCl₄. When the reaction is carried out in benzene, intermediate ferrocenyl-substituted (η⁵-pyranyl)Mn(CO)₃ species can be isolated which give the pyrylium cations on oxidation. The electrochemistry of the 2-ferrocenyl-pyrylium cations shows both oxidation (of the ferrocenyl) and reduction (of the pyrylium) processes, and the UV-visible spectra show a broad band at ca 680 nm which can be assigned to an intramolecular charge transfer transition.     

Molecular complexes of iodine with metal acetylacetonates

The ability of metal acetylacetonates to act as electron donors and form molecular complexes with I₂ was studied by examining the electronic, vibrational, and NMR spectra of the complexes. The specific compounds used in the study were Al(acac)₃ Sc(acac)₃ Zr(acac)₄, and Th(acac)₄. The electronic spectra of mixtures of the metal acetylacetonates with I₂ in CHCl₃ had, in addition to the absorption peaks characteristic of the free components, two peaks that were due to the charge transfer complexes. For each complex, the highest wavelength peak (near 360 nm) was assigned to the blue shifted I₂ band, while the lower peak (between 270 nm and 305 nm) was attributed to the intermolecular charge transfer. In the i.r. spectra of each complex, the major effect of complexation was to cause the I₂ stretching frequency to appear between 145 cm⁻¹ and 160 cm⁻¹. The positions of the absorption peaks in both the electronic and vibrational spectra led to the conclusion that in these complexes, I₂ had received a large amount of charge from the donors. Complex formation had little effect on the NMR spectra of the donors. Association constants of 1:1 complexes were determined from the concentration dependence of the absorbance of the blue shifted I₂ bands. Values of ΔHdg and ΔS°₂₉₈ for the complex formation were obtained from the temperature variation of the association constants. The data indicate that the complexes are extremely stable species. Both the stability of the complexes and the high degree of charge transfer were rationalized by considering a model for the intermolecular interactions that involved two M(acac) rings simultaneously transferring charge from one donor to an I₂ molecule.     

Backbone extended pyrrolidine PNA (bepPNA): a chiral PNA for selective RNA recognition

Synthesis of cationic, chiral PNA analogues with an extra atom in the backbone (bepPNA) is reported. The (2S,4S) geometry of the pyrrolidine ring, and an additional carbon atom in the backbone of homopyrimidine-bepPNAs resulted in the optimization of the inter-nucleobase distance, such that selective binding to complementary RNA over DNA was observed in the triplex mode. It was evident from circular dichroism studies that oligomers with mixed aminoethylglycyl-bep (aeg-bep) repeating units, and also bepPNA with homogeneous backbone attained structures quite different from those of aegPNA₂:RNA/DNA complexes. The bepPNA, when incorporated in a duplex forming mixed purine-pyrimidine sequence, also showed a preference for binding complementary RNA over DNA.     

New Charge Transfer Complexes of K+-Channel-Blocker Drug (Amifampridine; AMFP) for Sensitive Detection; Solution Investigations and DFT Studies

UV–Vis spectroscopy was used to investigate two new charge transfer (CT) complexes formed between the K⁺-channel-blocker amifampridine (AMFP) drug and the two π-acceptors 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in different solvents. The molecular composition of the new CT complexes was estimated using the continuous variations method and found to be 1:1 for both complexes. The formed CT complexes’ electronic spectra data were further employed for calculating the formation constants (K_CT), molar extinction coefficients (ε_CT), and physical parameters at various temperatures, and the results demonstrated the high stability of both complexes. In addition, sensitive spectrophotometric methods for quantifying AMFP in its pure form were proposed and statistically validated. Furthermore, DFT calculations were used to predict the molecular structures of AMFP–DDQ and AMFP–TCNE complexes in CHCl₃. TD-DFT calculations were also used to predict the electronic spectra of both complexes. A CT-based transition band (exp. 399 and 417 nm) for the AMFP–TCNE complex was calculated at 411.5 nm (f = 0.105, HOMO-1 → LUMO). The two absorption bands at 459 nm (calc. 426.9 nm, f = 0.054) and 584 nm (calc. 628.1 nm, f = 0.111) of the AMFP–DDQ complex were theoretically assigned to HOMO-1 → LUMO and HOMO → LUMO excitations, respectively.     

含噻吩环的吡啶Ru(II)配合物的电子结构和非线性光学性质

采用密度泛函理论(DFT) B3LYP方法对含有噻吩环的吡啶Ru(II)配合物的电子结构和非线性光学(NLO)性质进行理论研究. 结果表明: 配合物[Ru^II(NH₃)₅L]²⁺(L为含噻吩环的有机基团)中, 配位原子与中心金属离子间没有形成稳定的化学键, 但存在较强的供体-受体(D-A)相互作用; NH₃被羰基(CO)取代后, Ru-C间形成了稳定的σ-π配键, 降低了受体的空轨道能级. 噻吩环的增加增大了体系的共轭程度, 有利于分子内电荷转移, 使配合物的极化率α和一阶超极化率β明显增加. 结合配合物的前线分子轨道分析发现, 电荷转移过程中, 对体系二阶NLO系数贡献较大的是配体内电荷转移(ILCT)和配体间电荷转移(LLCT)跃迁, 羰基引入后配体到金属的电荷转移(LMCT)使配合物[Ru^II(CO)₅L]²⁺比对应的配合物[Ru^II(NH₃)₅L]²⁺的β值增大约7倍.     

Cyclopropane PNA: observable triplex melting in a PNA constrained with a 3-membered ring

The first peptide nucleic acid (PNA) with a cyclopropane in the backbone has been synthesized, and the effects of the ring on DNA/RNA binding properties of the PNA have been examined. Well-defined triplex to duplex melting transitions of PNA₂ DNA complexes is clearly observed by variable temperature UV absorbance with the cyclopropane-constrained PNA.     

Spectrophotometric and spectroscopic studies of complexation of 8-hydroxyquinoline with π acceptor metadinitrobenzene in different polar solvents

The complexation of electron donor–acceptor complexes of 8-hydroxyquinoline (8HQ) and metadinitrobenzene (MNB) have been studied spectrophotometrically and thermodynamically in different polar solvent at room temperature. A new absorption band due to charge transfer (CT) transition is observed in the visible region. A new theoretical model has been developed which take into account the interaction between electronic subsystem of 8HQ and MNB. The results indicate the extent of charge transfer complexes (CTCs) formation to be more in less polar solvents. Stoichiometry of the complex was found to be 1:1 by straight line method and ¹H NMR between donor and acceptor at the maximum absorption bands. Ionization potential (I_D) and resonance energy (R_N) were determined from the CT transition energy in different solvents. The formation constants of the complexes were determined in different polar solvents from which ΔG° formation of the complexes was estimated and also extinction coefficient of the charge transfer complex (CTC) was calculated. Oscillator strength, transition dipole strengths and maximum wavelength of the CTC (λ_CT) in various solvents and IR spectra of the CTC have also been discussed. It has been observed that all parameters described above changed with change in polarity and concentration of donor.     

X-ray spectral and photoelectron study of the electronic structure of copper phthalocyanine and its fluoro-substituted analog

A complex experimental study of Cu(2p _3/2), Cu(2p _1/2) photoelectron and Kα_1,2 and Lα_1,2 X-ray emission spectra of copper in copper phthalocyanine CuPcH₁₆ and its fluoro-substituted analog CuPcF₁₆ is carried out. A charge transfer model is used to interpret the spectra. It is shown that Kα₁ and Kα₂ lines of the spindoublet of copper have a complex structure due to the processes of metal-to-ligand charge transfer. The role of a satellite in the formation of emission lines is revealed.     

Theoretical study of the geometry and electronic structure of the trinuclear [AunAgm (HNCOH)3] (m + n = 3) complex

The structures and properties of different gold and silver mixed-metal trinuclear complexes, [Au_nAg_m(HNCOH)₃] (m + n = 3), were investigated theoretically. The computed properties were compared with those of the [Au₃(HNCOH)₃] complex. The geometries of all complexes were optimized at the B3LYP level of theory using the GEN basis set. The optimization results revealed that the most stable structures of pure Au and Ag complexes are almost similar. In addition, all complexes are flat and highly symmetric. It was shown that the silver substitution had a significant influence on the electronic properties. The metal–metal distances were in the order of: Au–Au < Au–Ag < Ag–Ag. The ionization potential and hardness were found to be decreased while the electron affinity, HOMO–LUMO gap and chemical potential were found to be increased from the [Au₃(HNCOH)₃] to the [Ag₃(HNCOH)₃] complex. The [Au₃(HNCOH)₃] complex was the least reactive in the studied series with the electronic chemical potential equal to −3.98 eV. On the other hand, the value of the chemical potential characterizing the most reactive complex, [Ag₃(HNCOH)₃], was −3.80 eV.     

Self-assembling formation of a [2] catenane consisting of cyclobis (4,4″-azopyridinium-p-phenylene) and bis-p-phenylene-34-crown-10

A [2]catenane consisting of a π-electron-accepting tetracationic cyclophane of cyclobis(4,4′-azopyridinium-p-phenylene) and a π-electron-donating macrocyclic polyether of bis-p-phenylene-34-crown-10 was synthesized via a template-directed synthesis in 68% yield. The [2]catenane exhibited charge transfer bands with $\text{λ}{}_{\mathrm{<mtext>max</mtext>}}\text{=526}$ nm and 566 nm in CH₃CN. A precursor of the cyclophane, bis[4-(4-pyridylazo)pyridinium], spontaneously formed a charge transfer complex with the macrocyclic polyether. The investigation of the charge transfer complex using UV-visible and ¹H NMR spectroscopy revealed that the complex had a pseudo-rotaxane structure with a stability constant (K_a) of 120 dm³ mol^-1 at 25°C in CH₃CN. The highly efficient catenation of 68% yield was attributable to cooperative self-assembling processes derived from the strongly π-electron deficient 4,4′-azopyridinium and 4-(4-pyridylazo)pyridinium units. These results suggested that there was a new formation mechanism of the catenated structure through preorganization of the charge transfer complex.     

In vitro simulation of the chemical scenario of the action of an anti-thyroid drug: charge transfer interaction of thiazolidine-2-thione with iodine

Thiazolidine-2-thione (T2T) has been studied spectrophotometrically by UV–visible and IR spectra. The spectral studies have indicated that T2T has two tautomeric forms, namely thione and thiole forms, in addition to the dimeric thioamide complex existing as a hydrogen-bonded dimer of two thione forms. Interaction of the T2T as an electron donor with iodine as a typical σ-type acceptor has been studied spectrophotometrically. Electronic absorption spectra of the system T2T–I₂ in several organic solvents of different polarities have performed a clear charge transfer (CT) band in each spectrum. Formation constants (K_CT) and molar absorption coefficients (?_CT) and thermodynamic properties, ΔH, ΔS, and ΔG, of this system in various organic solvents were determined and discussed. The stoichiometric ratio of the T2T–I₂ system in solutions was found to be 1:1 T2T:I₂, whereas the elemental analysis of the prepared solid CT complex has illustrated the same stoichiometry. The obtained K_CT and ?_CT values have indicated that T2T is a donor of moderately strength capable of interacting with the iodine just to form the corresponding CT complex with an iodine molecule without further reducing of the iodine to either of the corresponding poly-iodide ions viz. I₃^?, I₅^?, etc. This action of spongy trapping of iodine simulates in vitro the chemical scenario of the anti-thyroid action of this compound.     

Study of Electron Donor–Acceptor Complex Formation of o-Chloranil With a Series of Phosphine Oxides and Tri- n-butyl Phosphate by the Absorption Spectrometric Method

Electron donor–acceptor (EDA) complex formation of o-chloranil with six different phosphine oxides and tri-n-butyl phosphate (TBP) has been studied in CCl ₄ solution by the UV-VIS absorption spectrophotometric technique. An absorption band due to a charge–transfer (CT) transition is observed in the visible region. Utilizing the CT transition energy, the electron affinity of o-chloranil in solution has been calculated. Degrees of charge transfer, and oscillator and transition dipole strengths have also been calculated for all of the investigated EDA complexes. Except for TBP, other phosphine oxides, viz., tri-n-octyl phosphine oxide, tri-n-butyl phosphine oxide, triphenyl phosphine, octyl(phenyl)-N,N-diisobutylcarbamoylphosphine oxide, octyl(phenyl)-N,N-dicyclohexylcarbamoylmethylphosphine oxide and octyl(phenyl)-N,N-diisopropylcarbamoylmethylphosphine oxide have been shown to form stable 1:1 EDA complexes with o-chloranil. The complex of TBP with o-chloranil decays slowly into a secondary product. Formation constants of the EDA complexes have been determined.     

VUV spectroscopic properties of rare-earth (RE3+ = Sm3+, Eu3+, Tb3+, Dy3+) -activated layered borate Ba6Gd9B79O138

Vacuum ultraviolet (VUV) spectroscopic properties of rare-earth RE³⁺- activated (RE³⁺ = Sm³⁺, Eu³⁺, Tb³⁺ and Dy³⁺) Ba₆Gd₉B₇₉O₁₃₈ borates (BGBO) are investigated. The strong absorption bands in the VUV range of un-doped and RE³⁺-activated BGBO were observed. The band range from 140 to 200 nm with a peak at about 173 nm results from the host lattice absorption. For Sm³⁺-activated BGBO, the charge transfer transition from O^2- to Sm³⁺ was observed at 202 nm. In addition, it exhibits bright red emission originating from the Sm³⁺ f-f transitions of ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2 and 9/2). The O^2--Eu³⁺ charge transfer (CT) at 249 nm is observed in the excitation spectrum for Eu³⁺-doped BGBO. For Tb³⁺-activated BGBO, the broad bands around 208 and 230 nm are due to the spin-allowed and spin-forbidden f-d transitions of Tb³⁺, respectively. In addition, the absence of the f-d transitions of Sm³⁺ and Dy³⁺ in the excitation spectra probably due to the photo-ionization effect. It is demonstrated that there are energy transfers from the BGBO host lattice to the luminescent activators depending on the activators.     

Electronic structure of lanthanum transition-metal oxyarsenides LaMAsO (M = Fe,Co, Ni) and LaFe1−xM′xAsO (M′ = Co,Ni) by X-ray photoelectron and absorption spectroscopy

The electronic structures of the quaternary oxyarsenides LaMAsO (M = Fe, Co, Ni) were examined with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Interpretation of the metal 2p_3/2 and arsenic 3d_5/2 binding energies, as well as a satellite feature in the Co 2p XPS spectrum, suggests charges that are much less extreme than expected (i.e., not M²⁺ and As^3?) because of the strong covalent character within the M–As bonds. As M is varied, the differing degrees of charge transfer from M to As atoms within these bonds are manifested by shifts in the As 3d_5/2 binding energies and changes in the As K-edge intensities. This charge transfer is isolated within the [MAs] layer and does not influence the O 1s and La 3d XPS spectra. Fitting the experimental valence band spectra of these oxyarsenides LaMAsO yielded electron populations of states that support the formal charge assignment [La³⁺O^2?][M²⁺As^3?]. The mixed-metal series LaFe_1?xM′_xAsO (M′ = Co, Ni) was examined by XANES; analysis of the metal K- and L-edges, as well as of the Co 2p XPS satellite feature, revealed that no metal–metal charge transfer takes place.     

Structural and optical absorption studies of barium substituted strontium ferrite powder

Attempt has been made to synthesize Ba_xSr_1−xFeO_3−ξ (x = 0–1.0) ferrite powder by decomposition of sol–gel derived oxalate at 800–1000 °C for 5–10 h to study the effect of barium insertion with regard to phase(s), stability, optical behavior, oxidation states of iron, and oxygen deficiency. It is shown that these ferrites possess a perovskite-type cubic phase (a = 3.877–4.020Å, Z = 1, space group Pm3m) for 0.1 ≤ x ≤ 0.94, a mixture of 82% rhombohedral (a_R = 5.666Å and α_R = 59.761°, Z = 2, space group R3c) and 18% hexagonal phases for x = 0.96 and a pure hexagonal (a = 5.689Å, c = 13.944Å, Z = 6, space group P6₃/mmc) phase for x = 1. Barium substitution in SrFeO_3−ξ system leads to lattice expansion, weakening of the metal-oxygen bond, reduction of tetravalent iron ions (as evident from Mossbauer analysis), and decrease of oxygen content. The optical absorption peaks observed in the range 3.17–4.11 eV are attributed to charge transfer transitions from O²⁻ (2p) to Fe (3d) band. The values of optical energy band gap of Ba_xSr_1−xFeO_3−ξ are found to be ∼5.48 and ∼4.04 for x = 0.1 and 1.0, respectively. A stable perovskite-type cubic phase in Ba_xSr_1−xFeO_3−ξ system with significant anion deficiency (ξ = 0.26–0.32) may possibly act as an oxygen permeable membrane.     

无机晶体中Zr4+电荷迁移能与基质平均能隙关系

电荷迁移跃迁是指电子在配体的低能轨道受激往金属离子的高能轨道发生的跃迁[1].其光谱位置较高,一般位于真空紫外(VUV)区域,可以有效地吸收200 nm左右的激发能量,因此,对真空紫外发光材料起着非常重要的作用翻[2].     

Vibrational spectra of 2-methylpropanal: Assignments,self-associations and solvent effects

Raman and infrared spectra of 2-methylpropanal (CH₃)₂CHCHO, (CH₃)₂CDCHO and (CH₃)₂CHCDO in different physical states (liquid, solid and solution) have been investigated between 4000 and 40 cm⁻¹. A complete assignment is carried out on the basis of one predominant conformer (anticlinal) in equilibrium with another less stable one (synperiplanar). Some vibrational modes of the synperiplanar form are identified. The CO stretching region is carefully examined. The complex structure of this band as a function of the physical state of the pure aldehyde and the polarity of the solvent for solutions is discussed. The structure can be explained by Fermi resonances between combinations and the fundamental νCO mode. In the pure liquid, as well as in solution, the broadness of the band can be due to random dipolar interactions. In polar basic solvents (CH₃CN and DMSO), these interactions implicate both aldehyde and solvent. When the solvent is slightly acidic (HCCl₃), weak hydrogen bonds between the aldehydic group and the solvent may occur. Moving from the liquid to the solid state, in addition to the fact that the less stable conformer disappears, molecular association between the CO groups by charge transfer may account for the observed changes.     

TD-DFT Calculation on UV-Vis Spectra of the Complex 8-((Trimethoxysilyl)methylthio)quinoline⋅ZnCl<Subscript>2</Subscript>

The electronic structure and absorption spectra properties of the complex 8-((trimethoxysilyl)methylthio)quinoline⋅ZnCl₂ in the gas phase and in acetonitrile (MeCN) have been investigated by means of DFT/TD-DFT calculations. Calculation results indicate that the broad and weak experimentally observed absorption bands of the complex in MeCN at 335.6 nm originates from spin-forbidden singlet-triplet transitions, but the other experimentally observed absorption bands at 318.5 nm, 310.6 nm and 237.5 nm arise from spin-allowed singlet-singlet transitions. Inclusion of MeCN as solvent leads to dramatic changes in the electronic structures and energy levels of the frontier molecular orbitals of the complex, and hence transition mechanisms of the absorption bands are also changed. For the complex, whether in the gas phase or in MeCN, the metal Zn does not participate in the transitions involved, in the gas phase the calculated lowest-energy absorption band of the complex comes from π→π ^∗ mixed with n→π ^∗ transitions with LLCT (ligand-to-ligand charge transfer) character, while in MeCN, the calculated lowest-energy absorption band is of LLCT/ILCT (intra-ligand charge transfer) character.