A SENSITIZED PHOTOINITIATION SYSTEM ——BIS (7-DIETHYLAMINO COUMARIN ) KETONE-3 AND DIPHENYLIODONIUM SALT COMBINATION

Bis (7-diethylaminocoumarin) ketone- 3(DACK) and diphenyliodonium salt (DPIO)combination as an effective photoinitiation system for radical polymerization has been investigated. The sensitized photolysis of DACK/DPIO leads to bleaching of DACK and decomposition of DPIO to generate initiating radical species. The electron transfer sensitization occurs mainly from the triplet state of DACK. The photobleaching obeyed a second-order kinetics and the rate constant was evaluated to be 31.3mol~(-1)·1·s~(-1) Photopolymerization of MMA initiated by DACK/DPIO was carried out in acetonitrile solution. The polymerization rate was found to be proportional to the concentration of DACK, DPIO and MMA with the exponents of 0.34, 0.40 and 1.0 respectively. The initiated efficiency is comparable to those of small molecular ketones.The sensitized photoinitiation mechanism has been discussed.     

The time-resolved spectra of a crowned indolinospiroben-zopyran

The photochromic process of an indolinospiropyran with a crown ether fragment (BN-BIPS) was studied by nanosecond laser photolysis technique. The results show that quinonic merocyanine B was formed via an excited singlet state from BN-BIPS; in acetonitrile solution, the transient absorption of merocyanine B showed an obvious decay while a new transient absorption at 440nm (from isomer C) was observed simultaneously. The decay of merocyanine B and the formation of isomer C (at 440nm) were accelerated in the presence of alkali metal cation. In contrast, the formation of isomer C was not observed in spiropyran without a crown ether fragment: BIPS.     

Photoinduced intramolecular charge transfer of sodium 4-(N,N-dimethylamino) benzenesulfonate

A new dual fluorescent N,N-dimethylaniline derivative, sodium 4-(N,N-dimethylamino)-benzenesulfonate (SDMAS), is reported. In SDMAS, the electron acceptor is linked to the phenyl ring via a sulfur atom at the para-position of the electron donor. It was found that SDMAS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as formamide, methanol and acetonitrile. In organic solvents only a single-band emission at ca.360 nm was observed in the short wavelength region. The dual fluorescence of SDMAS in water was found at 365 and 475 nm, respectively. Introduction of organic solvent such as ethanol, acetonitrile, and 1,4-dioxane into aqueous solution of SDMAS leads to blue-shift and quenching of the long-wavelength emission. Measurements of steady-state and picosecond time-resolved fluorescence indicate that the long wavelength fluorescence is emitted from a charge transfer (CT) state that is populated from the locally excited (LE) state, with the latter giving off the     

Direct Electrochemical Evidence of the Dissociation and Adsorption Behavior of Acetonitrile at Gold Electrodes by Ultrafast Voltammetry

Ultrafast cyclic voltammetry was used to study the redox behavior of a gold electrode in acetonitrile. The direct electrochemical evidence of the dissociation and adsorption behavior of acetonitrile at gold electrodes was found. It could be stated that two consecutive redox paths are involved, each with a special adsorption state acting as the reaction intermediate. The mean value, obtained of the electron-transfer rate constant of the second path, was 1.3 × 105 s-1 with a standard deviation of 0.24 × 105 s-1.     

反相高效液相色谱法同时测定片剂中的加替沙星与盐酸氨溴索

 A reversed-phase high performance liquid chromatography (HPLC) method was developed, validated, and used for the quantitative determination of gatifloxacin (GA) and ambroxol hydrochloride (AM), from its tablet dosage form. Chromatographic separation was performed on a HiQ Sil C18 column (250 mm×4.6 mm, 5 μm), with a mobile phase comprising of a mixture of 0.01 mol/L potassium dihydrogen orthophosphate buffer and acetonitrile (70∶30, v/v), and pH adjusted to 3 with orthophosphoric acid, at a flow rate of 1 mL/min, with detection at 247 nm. Separation was completed in less than 10 min. As per International Conference on Harmonisation (ICH) guidelines the method was validated for linearity, accuracy, precision, limit of quantitation, limit of detection, and robustness. Linearity of GA was found to be in the range of 10-60 μg/mL and that for AM was found to be 5-30 μg/mL. The correlation coefficients were 0.9996 and 0.9993 for GA and AM respectively. The results of the tablet analysis (n=5) were found to be 99.94% with ±0.25% standard deviation (SD) and 99.98% with±0.36% SD for GA and AM respectively. Percent recovery of GA was found to be 99.92%-100.02% and that of AM was 99.86%-100.16%. The assay experiment shows that the method is free from interference of excipients. This demonstrates that the developed HPLC method is simple, linear, precise, and accurate, and can be conveniently adopted for the routine quality control analysis of the tablet.     

PHOTOPOLYMERIZATION INITIATED BY DIMETHYLAMINOCHALCONE/DIPHENYLIODONIUM SALT COMBINATION SYSTEM SENSITIVE TO VISIBLE LIGHT

Several dimethylamino-substituted chalcone (i .e. dimethylaminobenzal acetophenone) (DBA) derivatives with intramolecular charge transfer transition character were used as visible light sensitizers for radical photopolymerization initiated by iodonium salt (DPIO). Initiating radical species is produced from DBA sensitized photolysis of DPIO through the single electron transfer, accompanying the bleaching of DBA, The activity of DBA decreases as a function of substituent attached to phenyl ring in the order: DBA-2 (OCH_3) >DBA-1(H)> DBA-3 (Cl). The kinetic study on photopolymerization of MMA was carried out in CH_3CN solution at 30 ℃by dilatometry. The polymerization rate was determined to be proportional to the concentration with exponents of 0.42, 0.25 and 0.86 for DPIO, DBA-1 and MMA, respectively.     

Visible and near-infrared chiroptical gels containing electrochromic anthraquinone imide groups

A cholesterol-based organogelator bearing an anthraquinone imide(AQI) group was synthesized and characterized.It self-assembled into chiral gels in acetonitrile at low concentrations,which displayed a combination of electrochromic and chiroptical properties.Upon electrochemical reduction at -700 mV,the gel exhibited new absorption bands at around 820 nm corresponding toπ~*-π~*(SOMO→LUMO) transitions of the radical anion of AQI and strong negative Cotton effects in the same spectral region.With further reduction at -1000 mV,a new CD band with a negative Cotton effect in the range from 500 nm to 800 nm appeared concomitant with the variation of absorption spectrum.Thus, with the use of electrochromic AQI chromophore as a switch-responsive unit and the stable gel of compound N-[3β-cholest-5 -en-3-yl N-(2-aminoethyl) carbamate]anthraquinone-2,3-dicarboxylic imide as a chiral scaffold,a redox-triggered chiroptical switch operating in visible and near-infrared region was realized.     

Photochemical properties of a new kind of anti-cancer drug: N-glycoside compound

Due to the nontoxicity and efficient anti-cancer activity, more and more attention has been paid to N-glycoside compounds. Laser photolysis of N-(α-D-glucopyranoside) salicyloyl hydrazine (NGSH) has been performed for the first time. The research results show that NGSH has high photosensitivity and is vulnerable to be photo-ionized via a monophotonic process with a quantum yield of 0.02, generating NGSH · and hydrated electrons. Under the aerobic condition of cells, the hydrated electrons are very easy to combine with oxygen to generate 1O2 and O2-, both of which are powerful oxidants that can kill the cancer cells. In addition, NGSH · can be changed into neutral radicals by deprotonation with a pKa value of 4.02 and its decay constant was determined to be 2.55×109dm3·mol-1·s-1. NGSH also can be oxidized by SO4-. with a rate constant of 1.76×109 dm3·mol-1.s-1, which further confirms the results of photoionization. All of these results suggest that this new N-glycoside compound might be useful for cancer treatment.     

Resonance scattering spectral detection of ultratrace IgG using immunonanogold-HAuCl_4-NH_2OH catalytic reaction

Nanogold particles of 10 nm were used to label goat anti-human IgG (GIgG) to obtain nanogold-labeled GIgG (AuGIgG). In a citrate-HCl buffer solution of pH 2.27,AuGIgG showed a strong catalytic effect on the reaction between HAuCl4 and NH2OH to form big gold particles that exhibited a resonance scatter-ing (RS) peak at 796 nm. Under the chosen conditions,AuGIgG combined with IgG to form immuno-complex AuGIgG-IgG that can be removed by centrifuging at 16000 r/min. AuGIgG in the centrifuging solution also showed catalytic effect on the reaction. On those grounds,an immunonanogold catalytic RS assay for IgG was designed. With addition of IgG,the amount of AuGIgG in the centrifuging solution decreased; the RS intensity at 796 nm (I796 nm) decreased linearly. The decreased intensity ΔI796 nm was linear with respect to the IgG concentration in the range of 0.08-16.0 ng·mL-1 with a detection limit of 0.02 ng·mL-1. This assay was applied to analysis of IgG in sera with satisfactory sensitivity,selectivity and rapidity.     

Two-dimensional correlation analysis of continuous online in situ ATR-FTIR on the adsorption of butyl xanthate at the surface of α-PbO

The adsorption behavior of butyl xanthate on the surface of lead oxide was investigated using continuous online in situ attenuated total reflectance Fourier transform infrared(ATR-FTIR) spectroscopy technique and two dimensional(2D) correlation analysis.The adsorbed layer studied was prepared by coating α-PbO particles onto the surfaces of the ZnSe crystal.The appearance of spectral peaks at 1203 cm~(-1),1033 cm~(-1) and their red shift indicated the formation and aggregation of xanthate at the surface of α-PbO.According to 1R intensity changes after rinsing with deionized water and a NaOH solution,the adsorption was proved to be a chemisorption type.The competition between xanthate and OH for the surfaces leads to desorption of xanthate at higher pH.The technique of 2D correlation ATR-FTIR spectroscopy was used to evaluate the changing order of spectral intensities in the adsorption process,and the results indicated that xanthate micelles were formed at the surfaces.The adsorption kinetics of butyl xanthate was found to be a pseudo-second-order reaction model and the adsorption capacity of butyl xanthate at α-PbO was as high as 281 mg g~(-1) after 150 min.     

Photophysical and photochemical processes of riboflavin (vitamin B2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B₂) were studied in detail in aqueous solution. The excited triplet state of riboflavin (³RF^*) was produced with 337 nm laser, while under 248 nm irradiation, both³RF^* and hydrated electron (e_aq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of³RF^* including energy transfer, electron transfer and hydrogen abstraction. The RF^·+ was generated by oxidation of SO₄ ^·-radical with the aim of confirming the results of photolysis.     

Photophysical and photochemical processes of riboflavin (vitamin B2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B₂) were studied in detail in aqueous solution. The excited triplet state of riboflavin (³RF^*) was produced with 337 nm laser, while under 248 nm irradiation, both³RF^* and hydrated electron (e_aq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of³RF^* including energy transfer, electron transfer and hydrogen abstraction. The RF^·+ was generated by oxidation of SO₄ ^·-radical with the aim of confirming the results of photolysis.     

Flash photolysis study for reactions of NO3· with sulfur compounds in acetonitrile solution

The rate constants for the reaction of NO₃· with sulfur compounds in acetonitrile have been determined by the flash photolysis method. The rate constant for dimethyl sulfone (2.7 × 10⁴ M^?1s^?1 at ?10°C) is larger than that of the deuterium derivative, indicating that NO₃· abstracts the hydrogen atom from dimethyl sulfone. In the case of dimethyl sulfide, the rate constant was evaluated to be 1.5 × 10⁹ M^?1 s^?1 at ?10°C; the transient absorption band attributable to the cation radical was observed after the decay of NO₃·, suggesting the electron transfer reaction from the sulfide to NO₃·. For diphenyl sulfide and dimethyl disulfide, the electron transfer reactions were also confirmed. For dimethyl sulfoxide, the reaction rate constant of 1.2 × 10⁹ M^?1 s^?1 (at ?10°C) was not practically affected by the deuterium substitution, suggesting that NO₃· adds to sulfur atom forming (CH₃)₂?(O)-ONO₂. On the other hand, for diphenyl sulfoxide, the electron transfer reaction occurs. By the comparison of these rate constants in acetonitrile solution with the reported rate constants in the gas phase, the change of the reaction paths was revealed.     

Synthesis and biological properties of p-azidophenylalanine13-β-melanotropin,a potent photoaffinity label for MSH receptors

p-Azidophenylalanine¹³-α-melantropin ([Pap¹³]-α-MSH) was synthesized in homogeneous solution by the fragment condensation method, and its biological activity was determined in three different assay systems. The pigment-dispersing activity relative to α-MSH was 65%, measured with melanophores of Rana pipiens or of Xenopus laevis tadpoles. The tyrosinase-stimulating activity was 50%, determined with cultured mouse melanoma cells. UV. irradiation of solutions containing ≤10^?4_M[Pap¹³]-α-MSH at 338 nm (intensity: 10^?3 W · cm^?2) led to complete photolysis of the photolabel within <20 min. Under these conditions [Pap¹³]-α-MSH was covalently inserted into MSH-receptors which produced a longlasting pigment dispersion in Xenopus melanphores (see [3]). The extent of this prolonged stimulation depended on the hormone concentration used during photolysis. 1.8·10^?9_M [Pap¹³]-α-MSH which produced a full initial response failed to prolong the effect, whereas 1.2·10^?8_M hormone caused irreversible stimulation. It appears that only about 10% of the initially occupied receptors were covalently labelled because the log dose response curve was shifted to ～ 10x higher concentration after a 200 min wash period: EC₅₀ immediately after photolysis was 6 · 10^?10_M; after 200 min EC₅₀ increased to ～8·10^?9_M.     

Time resolve study on isopropyl-ether porphyrindiol

In the past years extensive studies have been conducted on porphyrin-type photosensitizers because of their photosensitive activity. With regard to their interaction with many important macromolecules such as nucleic acids, proteins and lipids, porphyrin-type photosensitizers are capable of damaging numerous cells. They damage DNA via oxidation of four bases, especially guanine and cytosine pairs[1], damage protein by oxidation of (at least) two amino acids——cysteine and tryptophan residues…     

DAMAGE TO URACIL- AND ADENINE-CONTAINING BASES, NUCLEOSIDES, NUCLEOTIDES AND POLYNUCLEOTIDES: QUANTUM YIELDS ON IRRADIATION AT 193 AND 254 NM

Abstract Photoreactions, such as base release and decomposition of the base moiety, induced by either 20 ns laser pulses at 193 nm or continuous 254 nm irradiation, were studied for a series of uracil and adenine derivatives in neutral aqueous solution. The quantum yield of chromophore loss (φ) depends significantly on the nature of the nucleic acid constituent and the saturating gas (Ar, N₂O or O₂). In the case of polynucleotides the destruction of nucleotides was measured by high-performance liquid chromatography after hydrolysis; the quantum yields (φ) are comparable to those of chromophore loss or larger. The φ_cl and aφ_dn of 0.04–0.1 for poly(U) and poly(dU), obtained for both wavelengths of irradiation, are due to processes originating from the lowest excited singlet state, i.e. formation of photohydrates and photodimers, and a second part from photoionization using λ_irr= 193 nm. Irradiation at 193 nm effectively splits pyrimidine dimers and thus reverts them into monomers. The quantum yield for release of undamaged bases (φ_br) from nucleosides, nucleotides and polynucleotides upon irradiation at 254 nm is typically φ_br= (0.1–1) × 10^?4 Breakage of the N-glycosidic bond is significantly more efficient for λ_irr=193 nm, e.g. φ_br= 1.1 × 10^?3, 0.8 × 10^?3, 4.3 × 10^?3 and 0.5 × 10^?3 for poly(A), poly(dA), poly(U) and poly(dU) in Ar-saturated solution, respectively. Enhanced φ values for λ_irr= 193 nm, essentially for adenine and its derivatives, are caused by photo-processes that are initiated by photoionization.     

Electron transfer from α-aminoalkyl radicals to methyl viologen

The reactions of tert-butoxyl radicals with amines, leading to the formation of α-aminoalkyl radicals, and the reactions of these with the electron acceptor methyl viologen have been examined using laser flash photolysis techniques. For example, the radicals CH₃?HNEt₂ and HOCH₂?H N(CH₂CH₂OH)₂ react with methyl viologen with rate constants equal to (1.3 ± 0.1) × 10⁹ and (2.1 ± 0.4) × 10⁹M^?1 · s^?1, respectively, in wet acetonitrile at 300 K.     

Molecular Structure,Theoretical Calculation and Thermal Behavior of DAG(NTO)

A new compound, [DAG(NTO)], was prepared by mixing the NaNTO•H2O aqueous solution and diaminogaunidine hydrochloride aqueous solution. Single crystals suitable for X-ray measurement were obtained by recrystallization from water at room temperature. The crystal belongs to triclinic, space group P-1 with crystal parameters of a＝0.6732(3) nm, b＝0.6745(3) nm, c＝0.9840(4) nm, α＝88.309(7)°, β＝77.255(6)°, γ＝86.520(7)°, V＝4.349(3) nm3, Z＝2, μ＝0.144 mm－1, F(000)＝228, and Dc＝1.674 g/cm3. The theoretical investigation on DAG(NTO) as a structural unit was carried out by B3LYP, MP2 and HF methods with 6-31＋G(d) basis set. The apparent activation energy and pre-exponential constant of the exothermic decomposition reaction of DAG(NTO) are 112.15 kJ•mol－1 and 109.603 s－1, respectively. The critical temperature of thermal explosion is 208.6 ℃.     

Kinetics of the reaction HO2 + NO2(+M) = HO2NO2 using molecular modulation spectrometry

Rate constants for the reaction HO₂ + NO₂(+ M) = HO₂NO₂(+ M) have been obtained from direct observations of the HO₂ radical using the technique of molecular modulation ultraviolet spectrometry. HO₂ was generated by periodic photolysis of Cl₂ in the presence of excess H₂ and O₂, and k₁ was determined from the measured concentrations and lifetime of HO₂ with NO₂ present. k₁ increased with pressure in the range of 40–600 Torr, and a simple energy transfer model gave the following limiting second- and third-order rate constants at 283 K: k₁^∞ = 1.5 ± 0.5 × 10^?12 cm³/molec·sec and k₁^III = 2.5 ± 0.5 × 10^?31 cm⁶/molec·sec. The ultraviolet absorption spectrum of peroxynitric acid was also recorded in the range of 195–265 nm; it showed a broad feature with a maximum at 200 nm, σ_max = 4.4 × 10^?18 cm².     

Kinetics of the 1,5-dipolar cyclization of 2-Vinylpyridinium ylides to Indolizines. Determination of rate parameters by laser flash photolysis

Nanosecond laser flash photolysis (λ = 355 nm) of an aqueous solution of 3-chloro-3-p-chlorophenyldiazirine in isooctane produces a transient absorption at 310 nm due to the formation of the carbene. In the presence of 2-vinylpyridine, a second transient with a broad absorption band peaking at 520 nm grows in. This absorption is attributed to 2-vinylpyridinium ylide. The ylide decays with a lifetime equal to 33 µs at 25°C independent of the concentration of 2-vinylpyridine. As the ylide decays, there is a concomitant growth of an absorption at 330 nm, attributed to the formation of inodolizine. The activation parameters for the 1,5-dipolar cyclization of the ylide to indolizine were determined; E_a = 12.1 kcal mol^?1 and log A = 13.4. © 1994 John Wiley & Sons, Inc.