Electron Pair Of Nitrogen Atom Research Articles

Interaction between dirhodium(II) tetraacetate and PAMAM dendrimer grafted onto magnetite nanoparticles: Effects on magnetic properties

In this study, we report on fabrication and characterization of a novel magnetic nanocarrier based on association of magnetite nanoparticles (NPs) with poly(amidoamine) (PAMAM) dendrimers loading dirhodium(II) tetraacetate complex (DiRh(II)). The pristine magnetite NP was coated with ATPS (3-aminopropyltriethoxysilane). The interaction between PAMAM dendrimer and DiRh(II) and its effects on magnetic properties were investigated. The magnetite spinel phase is confirmed via x-ray diffraction (XRD) and Raman spectroscopy data analysis. A mean crystallite size of 9.5 ± 0.3 nm of magnetite particles is assessed from XRD data, which is close to the values obtained via dynamic light scattering (DLS) and transmission electron microscopy micrographs. Our findings strongly suggest that the Rh(II) ions interact with lone electron pairs of nitrogen atoms in amide-II and primary amines of PAMAM surface-terminated moieties. The onset of an absorption peak at 283 nm in DiRh(II) containing sample, assigned to σRh-L→σ∗Rh-Rh electronic transition, revealed a direct interaction between Rh(II) ions and L moieties of PAMAM dendrimer. Magnetization results indicate that the presence of DiRh(II) attached to PAMAM dendrimer leads to the strong weakening of magnetic dipole–dipole interactions in ATPS- and ATPS + PAMAM coated magnetite nanoparticles.

(Invited) Solar CO2 Conversion into Liquid Fuels By Photoelectrochemical Approaches

Photoelectrochemical (PEC) system for the reduction of CO2 into liquid fuels of formaldehyde/acetaldehyde, methanol and ethanol with trace amount of hydrogen gas bubbling have been described in the aspect of thermodynamics and kinetics of the CO2 reduction reaction to have efficient method by lowering activation energy of CO2 reduction on the electron transfer reaction and to do reduction potential tuning of CO2 reduction reaction for the selective reduction products. Ca/Fe doped TiO2 photoanode oxidizes water and generates the large amount of O2, electrons and protons. On the other side, rGO(reduced graphene oxide)/PVP(poly(4-vinyl)pyridine)/Nafion multi-layers have been coated and fabricated on the surface of Cu foil cathode to reduce CO2 into formaldehyde and acetaldehyde. When solar light was irradiated on the surface of photoanode, electrons get excited to the conduction band of Ca/Fe doped TiO2 and transported to the cathode via external wire with low external bias potential. rGO on Cu foil has been used for the dual functions of reduction potential tuning and multi-electron shuttling process of CO2 reduction reaction. The multi-electron shuttling function was illuminated by larger number and longer life-time of excited electrons and generating electron cloud, which have been confirmed by time-resolved photoluminescence (TR-PL) decay curves and 2D time-resolved photoluminescence (TR-PL) mapping images of Cu/rGO electrode. This allows the sequential multi-electron transport process from Cu/rGOcathode to CO2, which was studied with time-resolved chronoamperometry. N-heterocyclic poly(4-vinyl)pyridine (PVP) helps to capture and do chemical activation of reactant CO2 molecule by complexation as [PVP-CO2*] complex via charge separation and lowering transition state energy level of the electron transfer for the formation of anion radical of carbon dioxide complex with PVP as [e- + PVP-CO2*]≠ complex via electron delocalization, which is basically possible due to high basicity of lone pair electrons of nitrogen atoms of N-heterocyclic PVP compounds. These functions result in the lowered activation energy for the CO2 reduction reaction to have faster kinetics. The decreased amount of activation energy was determined with Tafel plots by measuring the slopes of it and semicircles of the electrochemical impedance spectroscopy (EIS) Nyquist plots at different temperatures. Nafion film coated on the surface of cathode assists the faster transport of H+ ions to CO2 reduction reaction sites for the simultaneous one-pot reaction of proton coupled electron transfer reactions. In the photocataytic system with semi-conducting polymers, CO2 was conversed into liquid solar fuels like formaldehyde and alcohols with solar to fuel efficiency over 2.5% to produce liquid fuel products over mM concentration for 4 hour reaction. Chang Woo Kim, So Jin Yeob, Hui-Ming Cheng, Young Soo Kang*, Selectively Exposed Crystal Facet-Engineered TiO2 Thin Film Photoanode for the Higher Performance of Photoelectrochemical Water Splitting Reaction, Energy and Environmental Sciences. 2015, 8, 3646.Amol U.Pawar, Chang WooKim, Myung Jong Kang, Young Soo Kang*, Crystal facet engineering of ZnO photoanode for the higher water splitting efficiency with proton transferable nafion film, Nano Energy 2015, 20, 156.Chang Woo Kim, Young Seok Son, Myung Jong Kang, Do Yoon Kim, Young Soo Kang*, (040)-Crystal Facet Engineering of BiVO4 Plate Photoanode for Solar Fuel Production, Energy Mater., 2016, 6, 1501754.Jin You Zheng, Amol Uttam Pawar, Chang Woo Kim, Yong Joo Kim, Young Soo Kang*, Highly enhancing photoelectrochemical performance of facilely-fabricated Bi-induced (002)-oriented WO3 film with intermittent short-time negative polarization, Applied Catalysis B 2018, 233, 88.Chang Woo Kim, Myung Jong Kang, Sohyun Ji, and Young Soo Kang*, Artificial Photosynthesis for Formaldehyde Production with 85% of Faradaic Efficiency by Tuning the Reduction Potential, ACS Catalysis 2018, 82, 968-974.Myung Jong Kang, Chang Woo Kim, Amol U. Pawar, Hyun Gil Cha, Sohyun Ji, Wen-Bin Cai, and Young Soo Kang*, Selective Alcohol on Dark Cathode by Photoelectrochemical CO2 Valorization and Their in-situ Characterization, minor revision, ACS Energy Lett. 2019, 4, 1549.Hong Ryeol Park, Amol Uttam Pawar, Umapada Pal, Tierui Zhang, Young Soo Kang, Enhanced solar photoreduction of CO2 to liquid fuel over rGO grafted NiO-CeO2 heterostructure nanocomposite, Nano Energy, 2021, 79, 105483.Amol U. Pawar, Umapada Pal, Jin You Zheng, Chang Woo Kim and Young Soo Kang*, Dynamics controlled CO2 reduction on Cu/rGO/PVP/Nafion multi-layered cathode for selective production of Acetaldehyde and Formaldehyde, Applied Catalysis B: Environmental, 2022, 303, 120921.

(Keynote) Solar CO2 Conversion into Liquid Fuels Via Thermodynamic and Kinetic Control

In this report, photoelectrochemical (PEC) system for the reduction of CO2 into liquid fuels of formaldehyde and acetaldehyde with minor hydrogen gas bubbling has been described in the aspect of thermodynamics and kinetics of the CO2 reduction reaction to have efficient method by lowering activation energy of CO2 reduction on the electron transfer reaction and to do reduction potential tuning of CO2 reduction reaction for the selective reduction products. Ca/Fe doped TiO2 photoanode oxidizes water and generates the large amount of O2, electrons and protons. On the other side, rGO(reduced graphene oxide)/PVP(poly(4-vinyl)pyridine)/Nafion multi-layers have been coated and fabricated on the surface of Cu foil cathode to reduce CO2 into acetaldehyde and formaldehyde compounds with different combined functions of each layer in the cathode. When solar light was irradiated on the surface of photoanode, electrons get excited to the conduction band of Ca/Fe doped TiO2 and transported to the cathode via external wire with low external bias potential. rGO on Cu foil has been used for the dual functions of reduction potential tuning and multi-electron shuttling process of CO2 reduction reaction. The multi-electron shuttling function was illuminated by larger number and longer life-time of excited electrons and generating electron cloud, which have been confirmed by time-resolved photoluminescence (TR-PL) decay curves and 2D time-resolved photoluminescence (TR-PL) mapping images of Cu/rGO electrode. This allows the sequential multi-electron transport process from Cu/rGOcathode to CO2, which was studied with time-resolved chronoamperometry and identification of the charge transfer complex formation with UV-vis spectrophotometer. The reduction potential tuning was controlled by the combined function of bias potential given by external wire and reduction degree of rGO to add proper amount of potential energy to transfer multi-electrons to CO2 in the thermodynamic aspect. Those combined functions are given to supply the tuned amount of energy into the open circuit potential of the system for photoanode of Ca/Fe doped TiO2 and Cu/rGO cathode to transport excited electrons to produce CO2 reduction product selectively. N-heterocyclic poly(4-vinyl)pyridine (PVP) helps to capture and do chemical activation of reactant CO2 molecule by complexation as [PVP-CO2*] complex via charge separation and lowering transition state energy level of the electron transfer for the formation of anion radical of carbon dioxide complex with PVP as [e- + PVP-CO2*]≠ complex via electron delocalization, which is basically possible due to high basicity of lone pair electrons of nitrogen atoms of N-heterocyclic PVP compounds. These functions result in the lowered activation energy for the CO2 reduction reaction to have faster kinetics. The decreased amount of activation energy was determined with Tafel plots by measuring the slopes of it and semicircles of the electrochemical impedance spectroscopy (EIS) Nyquist plots at different temperatures. Nafion film coated on the surface of cathode assists the faster transport of H+ ions to CO2 reduction reaction sites for the simultaneous one-pot reaction of proton coupled electron transfer reactions. It was checked with comparing the current density of the I-V curves of cathodes with and without Nafion layer coating of Cu foil cathode. Obtained results of CO2 reduction into liquid fuels via photoelectrochemical process show formaldehyde as major product with 25% current efficiency in Cu/rGO cathode and acetaldehyde as a major product with 35% current efficiency in Cu/rGO/PVP/Nafion as cathode during 4 h of photoelectrochemical reaction at 0.68 V vs RHE as an external bias potential.

MODIFICATION OF EXPANDED PERLITE WITH ORTHOPHENANTHROLINE FOR FORMATION OF ACTIVE SITES FOR ACID DYES: PREPARATION AND CHARACTERIZATION

The expanded perlite (aluminosilicate naturally acid) has been modified with orthophenanthroline (Lewis base). The material was characterized by TG/DTA, XRD and IR. The thermogravimetric curve of the modified expanded perlite presented a lower thermal stability due to the orthophenanthroline and showed 13,6% of mass loss total. However, pure expanded perlite presented only 2,3% of the mass loss. The DTA curve showed endothermic event characteristic of the presence of orthophenanthroline. For XRD analysis is visualized, the presence of reflections in the diffractogram relating to the modified material of orthophenanthroline peaks of crystallinity since no modification perlite is an amorphous material. The band regarding absorption vibration of Si-O group appears at lower wavenumbers than in the unmodified material. So there was an interaction between the OH groups of silanols of perlite groups with unshared electron pairs of nitrogen atoms and C=C bonds (also rich in electrons) in the chemical structure of orthophenanthroline as a result of a hydrogen bond between these groups. thus perlite was modified through the interaction of its acid sites (Si-OH) with Lewis basic sites of orthophenanthroline.

Electronic structure of nickel porphyrin NiP: Study by X-ray photoelectron and absorption spectroscopy

Energy distributions and properties of the occupied and empty electronic states for a planar complex of nickel porphyrin NiP are studied by X-ray photoemission and absorption spectroscopy techniques. As a result of the analysis of the experimental spectra of valence photoemission, the nature and energy positions of the highest occupied electronic states were determined: the highest occupied state is formed mostly by atomic states of the porphine ligand; the following two states are associated with 3d states of the nickel atom. It was found that the lowest empty state is specific and is described by the σ-type b1g MO formed by empty \(Ni3{d_{{x^2} - {y^2}}}\)-states and occupied 2p-states of lone electron pairs of nitrogen atoms. This specific nature of the lowest empty state is a consequence of the donor–acceptor chemical bond in NiP.

Adsorption of Acetonitrile on Platinum and its Effects on Oxygen Reduction Reaction in Acidic Aqueous Solutions—Combined Theoretical and Experimental Study

Combined theoretical and experimental study of acetonitrile (AcN) adsorption on platinum was performed and its effects on the kinetics of oxygen reduction reaction in HClO4 and H2SO4 solutions were examined. Using periodic density functional theory calculations, it was shown that AcN molecule can interact with Pt surface either through the unsaturated π electron system or via lone electron pair of nitrogen atom. In both cases, adsorption energy decreases upon increasing coverage, while the modification of electronic structure of Pt surface is localized to the adsorption site. By combining the results of the DFT calculations with the results of blank cyclic voltammetry and rotating disk electrode voltammetry in O2-saturated solutions, it was concluded that the effects of AcN on Pt surface chemistry and ORR kinetics are primarily steric in nature. Resulting measured ORR activities of polycrystalline platinum in the presence of AcN are due to the combination of (i) suppression of (bi)sulfate adsorption (in H2SO4 solution), (ii) suppression of surface oxidation (in both H2SO4 an HClO4 solution), and (iii) site blockage by adsorbed AcN (or products of its electrochemical transformations).

Synthesis, Characterization,in vivoAntimalarial Studies and Geometry Optimization of Lumefantrine/Artemether Mixed Ligand Complexes

Fe(III). Zn(II), Cu(II), Cd(II), Ni(II) and Co(II) complexes of Artemether/Lumefantrine were synthesized. The yield, colour, melting point and solubility of the complexes and antimalarial drug were determined. The complexes were stable, non hygroscopic solids with high melting points. The electronic spectra showed that all the complexes and antimalarial drug absorbed in ultraviolet region because of the presence of C=Cchromophore and ligand to metal charge transfer (LMCT). The infrared spectra of the complexes showed evidence of coordination through the lone pair electrons of nitrogen atom (C-N) stretch in Lumefantrine, lone pair of electrons of oxygen atom (R-O-R) stretch and S=O functional group. In most of he complexes, Artemether behave as a tridentate ligand while Lumefantrine behave as a monodentate ligand. From the in vivo antimalarial studies, it was evident that the addition of the metal to the mixed ligand did not impede/hinder the therapeutic value of the mixed ligand. Thus, it was deduced that Ni-artemether/lumefantrine and Cu-artemether/lumefantrine complexes were more effective than artermether-lumefantrine alone against strains of Plasmodium Berghei. Geometry optimization of artemether/lumefantrine complexes were performed using ArgusLab 4.0.1 software. The minimum potential energy was calculated by geometry convergence function using ArgusLab software. The most feasible position for the complexes to inhibit angiogenesis and modulate host immune function was found to be in the range 591.5027 -727.0168 Kcal/mol.

Urotropine isomer (1,4,6,10-tetraazaadamantane): synthesis, structure, and chemistry.

The first synthesis of 1,4,6,10-tetraazaadamantane, the C3v-symmetrical structural isomer of urotropine (1,3,5,7-tetraazaadamantane), and a series of its derivatives is reported. X-ray and quantum-chemical studies revealed remarkable distinctions in structures of urotropine and "isourotropine" cations, probably arising from different types of hyperconjugation between lone electron pairs of nitrogen atoms and σ*C-N orbitals in these heterocage systems. Since substitution at bridge and bridgehead nitrogen atoms can be easily introduced, 1,4,6,10-tetraazaadamantane may be considered as a new rigid multivalent (3 + 1) scaffold for the design of functional molecules and materials.

Neutral CH bond vs. electron pair of N(sp2): A binding site effect study of macrocycle anion receptor

Abstract To evaluate the effect of neutral C H bond or electron pair of nitrogen atom with sp 2 hybridization (N( sp 2 )) involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2](2,6-bis-(1 H -imidazol-1-yl)pyridine) [2](1,3-dimethylenebenzene) ( 1 4+ ), and cyclo[2](2,6-bis-(1 H -imidazol-1-yl)pyridine)[2](2,6-di methylenepyridine) ( 2 4+ ) were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl − , N 3 − , NO 3 − , and H 2 PO 4 − . The host–guest interactions were characterized via 1 H NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites ( 1 4+ with neutral C H vs. 2 4+ with N ( sp 2 )) vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.

Theoretical 14N and 17O nuclear quadrupole resonance parameters for tirapazamine and related metabolites

Density functional theory (DFT) calculations were performed to realize the effects of the N–O group on the reactivity and electronic properties of 3-amino-1,2,4-benzotriazines. The electric field gradient, EFG, tensors of 14N and 17O nuclei and natural bond orbital (NBO) analysis in the tirapazamine (TPZ) and its four derivatives were calculated at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) method in the gas phase. The NBO analysis reveal that the bond strength, proton affinity and position of N–O group in the heterocyclic ring have major influence on the reactivity of considered molecules. Accordingly, we suggest that the TPZ and 4-oxide (d) structures due to having a weaker N–O bond with larger negative charge on the oxygen atom at the 4-position are more active than the other ones. Calculated 14N and 17O EFG tensors were used to evaluate nuclear quadrupole coupling tensors, χ, and asymmetry parameters, η Q . Results showed that oxidation of a nitrogen atom at any position have significant influence on its 14N nuclear quadrupole resonance (NQR) parameters. Also, the occupancy of nitrogen lone pair plays an important role in determination of the q zz and χ values of mentioned nuclei. It is found that the η Q and χ are appropriate parameters to study the contribution of lone pair electrons of nitrogen atom in the formation of chemical bond or conjugation with the aromatic system. Finally, a linear correlation is observed between the χ(14N) and χ(17O) values in the N–O bond which may be associated with the reactivity of these compounds.

Novel molecular complexation between meso-tetraarylporphyrinato magnesium(II) and phosphorus(III) chloride

Abstract The interaction between meso-tetraarylporphyrinato magnesium(ІІ) [MgT(4-X)PP] (X = H, CH3, and CH(CH3)2) and PCl3, as an electron acceptor, produced new molecular complexation [MgT(4-X)PP(PCl3)2]. The synthesized molecular complexes were characterized by (1H, 31P) NMR, UV–Vis, FT-IR spectroscopies and electric conductivity. In these molecular complexes, the central core of porphyrin, corrugates and two lone electron pairs of nitrogen atoms in the metalloporphyrin act as σ-electron donors to a phosphorous atom in PCl3 and the second PCl3 molecule acts as a ligand to magnesium(II) ion. The molar ratio of metalloporphyrin to PCl3 in the molecular complexes was 1:2. The synthesized molecular complexes in acetone solvent showed no electric conductivity.

New diketopyrrolopyrrole (DPP) derivative as fluorescent probe for Zn2+

New turn-on fluorescent probe DPPL2, was rationally designed and synthesized based on the skeleton of diketopyrrolopyrrole (DPP), which presented sensitivity, selectivity for Zn2+ over other metal ions except some disturbance with Cd2+. Particularly, results demonstrated fluorescence enhancement and blue shift of DPPL2 upon Zn2+ binding. This phenomenon was a typical photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) process which was attributed to diminishing the electron of the nitrogen lone pair delocalization on the DPP core upon Zn2+ binding. For comparison, DPPL3 (acylation of nitrogen atom of DPPL2) was synthesized and no fluorescence enhancement was observed, which further indicated that lone pair electrons of nitrogen atoms attached to DPP core were ascribed to PET process. 1H NMR titrations and DFT calculations also proved that PET and ICT process of system.

Trimethylaluminum and Borane Complexes of Primary Amines

Trimethylaluminum (TMA) complexes of methyl-, n-propyl-, cyclopropyl-, allyl-, and propargylamine were synthesized and their experimental properties and theoretical characteristics were compared with the respective amine-borane analogues. The amine ligand of an amine-TMA Lewis acid-base complex can be easily changed by another amine through a 2:1 amine-TMA intermediate in pentane at room temperature. The exchange of the same ligands in the case of amine-boranes requires remarkably more time in line with the calculated relative energy of the respective transition state. The (1)H and (13)C NMR experiments examining the addition of one or more equivalent of amine to the respective Lewis acid-base complex conclude in the fast exchange of the amine ligand in the NMR time scale only in the cases of amine-TMA complexes, which could also be caused by similar 2:1 complexes. However, in gas phase, only 1:1 amine-TMA complexes are present as evidenced by ultraviolet photoelectron spectroscopy (UPS). The observed UP spectra, which are the first recorded photoelectron spectra of primary amine-TMA compounds, indicate that the stabilization effect of the lone electron pair of nitrogen atom in amines during the borane complexation is stronger than that of the TMA complexation. In line with this observation, the destabilization of the σ(Al-C) orbitals is lower than that of σ(B-H) orbitals during the formation of amine-TMA and amine-borane complexes, respectively. As showed by theoretical calculations, the CH(4) elimination of the studied amine-TMA complexes is exothermic, indicating the possibility of using these compounds in metal organic chemical vapor deposition techniques (MOCVD). On the other hand, our experimental conditions avoid this methane elimination and constitutes the first procedure employing distillation to isolate primary amine-TMA complexes.

Synthesis of New Functionalized Citric Acid-based Dendrimers as Nanocarrier Agents for Drug Delivery.

Citric acid-polyethylene glycol-citric acid (CPEGC) triblock dendrimers can serve as potential delivery systems. In this investigation, CPEGC triblock dendrimers were synthesized and then imidazole groups were conjugated onto the surface of the G1, G2 and G3 of the obtained dendrimers. In order to study the type of the interactions between the functionalized dendrimers and a drug molecule, Naproxen which contains acidic groups, was examined as a hydrophobic drug in which the interactions would be of the electrostatic kind between its acidic groups and the lone pair electrons of nitrogen atom in imidazole groups. The quantity of the trapped drug and also the amount of its release were measured with UV spectrometric method in pH 1, 7.4 and 10. The average diameter of the nanocarriers was measured by Dynamic Light Scattering (DLS) technique. The size range of particles was determined to be 16-50 nm for different generations. The rate of the release increased in pH=10 in all generations due to the increases in Naproxen solubility and the hydrolysis of the esteric bonds in the mentioned pH. The results showed that the amount of the trapped drug increased with the increase in the generation of the dendrimer and pH. Based on our findings, we suggest CPEGC triblock dendrimers possess great potential to be used as drug/gene delivery system.

Application of Cryptand to Diazo/PVA Resists

Photo- and thermal reaction of p-substituted benzene diazo compounds (SBD) with [2.2.2]-cryptand (CRP) was studied by UV spectrum and degradation temperature (D.T.). Diazo cation of p-chloro benzene diazo compound (ClBD) was reacted with lone pair electrons of nitrogen atom of CRP by UV spectrum data. When CRP was added, photo-decomposition rate of SBD with electron withdrawing-substituent (WSBD) and of SBD with electron donating-substituent (DSBD) were accelerated two and ten times larger than that without CRP, respectively. D.T. of WSBD with CRP in solid were lower than that without CRP, but D.T. of DSBD with CRP was similar to that without CRP. Photodecomposition rate of a diphenylamine-4-diazonium sulfate salt/formaldehyde condensate (DSR) / Polyvinyl alcohol (PVA) resist with CRP was 3 times higher than that without CRP. Diazo/PVA resist with CRP will be improved in sensitivity without decreasing thermal stability.

Cation complexation behavior of pyrene- and anthracene-appended new crown ether derivatives

Pyrene- and anthracene-appended new crown ether derivatives have been synthesized by Schiff's base reaction, and cation complexation behavior was investigated by fluorescence spectroscopy measurements. Based on photo-induced electron transfer and intramolecular charge transfer mechanism, the host molecules emit stronger fluorescence in the presence of various cations Na +, K +, Rb +, Cs + and NH 4 + since the complexation between guest cations and crown ether compounds inhibit partial electron transfer from the nitrogen atom to the chromophores and subsequently fluorescence is enhanced. The binding constants were estimated from the plots of the fraction of binding sites filled for crown ether compound as a function of free-ion concentration. Results show that 15-crown-5 derivatives exhibit higher binding ability with sodium cations while 18-crown-6 derivatives had higher affinity for potassium cations, which is consistent with the hole-size relationship of the crown ethers. Ammonium ion complexation caused largest fluorescence enhancement. It is understood that ammonium ion cannot only complex with crown ether, but also interact directly with the lone pair electrons of nitrogen atom in C N bond so that electron transfer from the nitrogen atom to chromophores is further inhibited.

SERS of quinoxaline adsorbed at silver surfaces: Evidence for the two types of orientations

Surface-enhanced Raman spectra of quinoxaline adsorbed on silver colloid particles were observed by altering the concentration of quinoxaline and the degrees of colloid aggregation. The time evolution of the intensities of five Raman lines of adsorbed quinoxaline was also studied in an electrode system. The SER spectral feature of combination band region is characteristic of adsorbed quinoxaline. The results indicate that the adsorbed quinoxaline anchores through the lone pair electrons of nitrogen atom and assumes two types of orientations, flat and sticking-up form, under the respective conditions.