Photo and thermal polymerizations sensitized by donor–acceptor interaction. II. Photopolymerization and electronic spectroscopy of the isobutyl vinyl ether–acrylonitrile system

Photopolymerization of acrylonitrile (AN), an acceptor monomer, was found to be accelerated in the presence of isobutyl vinyl ether (IBVE), a donor monomer. The propagation is completed by a radical mechanism as judged by copolymer compositions; in contrast to the N-vinylcarbazole–AN system studied previously. This photopolymerization system is entirely stable if kept in the dark. The comparison of the relation between R_p and [IBVE]/[AN] ratio in the monomer feed found for the spontaneous photopolymerization with that for radical polymerization initiated by azobisisobutylonitrile in the dark leads to the conclusion that the rate of photoinitiation is enhanced by the interaction between AN and IBVE, whereas the propagation step by a radical mechanism is retarded by increasing concentration of IBVE. The contact charge-transfer complex between IBVE and AN was confirmed by electronic spectroscopy of the polymerization system, which showed photosensitization by charge-transfer interaction. The spectroscopic study of other weak donor–weak acceptor systems is also discussed.     

Naringenin Schiff base: antioxidant activity,acid–base profile,and interactions with DNA

A Schiff base derived from naringenin (NTSC) and its complex with Cu(II) ([Cu(H₃L)(OAc)]·H₂O, Cu(II)–NTSC) have been synthesized and characterized by physicochemical and spectroscopic methods. EPR studies confirmed that nitrogen, oxygen, and sulfur are the donor atoms bound to Cu(II) in the complex. The geometry of the complex has been modelled using DFT methods. Furthermore, naringenin and NTSC were used for the formation of Cu(II) complexes in solution, for comparison of biological activities. Antioxidant studies confirmed better radical scavenging activity of both NTSC and its Cu(II) complex compared to naringenin. The interaction of these compounds with calf thymus DNA was monitored by UV–Vis spectroscopy.     

Heteroleptic Tetrapyrrole‐Fused Dimeric and Trimeric Skeletons with Unusual Non‐Frustrated Fluorescence

Phthalocyanine (Pc) and porphyrin (Por) chromophores have been fused through the benzo[α]pyrazine moiety, resulting in unprecedented heteroleptic tetrapyrrole‐fused dimers and trimers. The heteroleptic tetrapyrrole nature has been clearly revealed based on single‐crystal X‐ray diffraction analysis of the zinc dimer. Electrochemical analysis, theoretical calculations, and time‐resolved spectroscopic results disclose that the two/three‐tetrapyrrole‐fused skeletons behave as one totally π‐conjugated system as a result of the strong conjugative interaction between/among the tetrapyrrole chromophores. In particular, the effectively extended π‐electron system through the fused‐bridge induced strong electronic communication between the Pc and Por moieties and large transition dipole moments in the Pc–Por‐fused systems, providing high fluorescence quantum yields (>0.13) and relatively long excited state lifetimes (>1.3 ns) in comparison with their homo‐tetrapyrrole‐fused analogues.     

Homolytic Decomposition of Sulfonyl Chlorides

The products, kinetic parameters, and activation entropy of thermal decomposition of sulfonyl chloride groups in chlorosulfonated polyethylene (CSPE) have been studied for the first time, and it has been demonstrated that the decomposition mechanism involves simultaneous cleavage of two bonds (carbon–sulfur and sulfur–chlorine) to give an SO₂ molecule and two free radicals, which can be useful in the process of polymer structuring. The radical mechanism has been confirmed by the formation of 2,3-diphenyl-2,3- dimethylbutane on heating CSPE in isopropylbenzene. The simultaneous cleavage of two bonds is supported by the low activation energy and pre-exponential factor in the Arrhenius equation, as well as by negative activation entropy values.     

中国典型超高硫煤有机相中分子氯存在的实验证据

运用,主性能静态二次离子质谱从中国贵州六枝超高硫无烟煤有机相中观测到分子氯（Cl2）的团簇负离子,从而首次获得分子氯在原煤中存在的实验证据。结合不久前从相同原煤有机相观测到元素硫（S8）的研究结果,表明易挥发性元素能够以其化学单质状态在原煤有机相中稳定存在;其来源可能与地球排气作用与原煤的富含纳米孔隙性质和化学还原微环境密切相关。     

Magnetic field effect corroborated with docking study to explore photoinduced electron transfer in drug-protein interaction

Conventional spectroscopic tools such as absorption, fluorescence, and circular dichroism spectroscopy used in the study of photoinduced drug-protein interactions can yield useful information about ground-state and excited-state phenomena. However, photoinduced electron transfer (PET) may be a possible phenomenon in the drug-protein interaction, which may go unnoticed if only conventional spectroscopic observations are taken into account. Laser flash photolysis coupled with an external magnetic field can be utilized to confirm the occurrence of PET and authenticate the spin states of the radicals/radical ions formed. In the study of interaction of the model protein human serum albumin (HSA) with acridine derivatives, acridine yellow (AY) and proflavin (PF(+)), conventional spectroscopic tools along with docking study have been used to decipher the binding mechanism, and laser flash photolysis technique with an associated magnetic field (MF) has been used to explore PET. The results of fluorescence study indicate that fluorescence resonance energy transfer takes place from the protein to the acridine-based drugs. Docking study unveils the crucial role of Ser 232 residue of HSA in explaining the differential behavior of the two drugs towards the model protein. Laser flash photolysis experiments help to identify the radicals/radical ions formed in the due course of PET (PF(?), AY(?-), TrpH(?+), Trp(?)), and the application of an external MF has been used to characterize their initial spin-state. Owing to its distance dependence, MF effect gives an idea about the proximity of the radicals/radical ions during interaction in the system and also helps to elucidate the reaction mechanisms. A prominent MF effect is observed in homogeneous buffer medium owing to the pseudoconfinement of the radicals/radical ions provided by the complex structure of the protein.     

Quantum Chemical Spin Densities for Radical Cations of Photosynthetic Pigment Models

The spin densities of radical cations of magnesium porphyrin, magnesium chlorine and a truncated chlorophyll a model are calculated with density‐functional theory and multiconfigurational quantum chemical methods. The latter serve as a reference for approximate density‐functional theory which yields spin densities that may suffer from the self‐interaction error. We carried out complete active space self‐consistent field calculations with increasing active orbital spaces to systematically converge qualitatively correct spin densities. In particular, for the magnesium chlorine and chlorophyll a model radical cations, this is not easy to achieve because of the lower symmetry compared to magnesium porphyrin. Strategies had to be employed which allowed us to consider very large active orbital spaces. We explored restricted active space self‐consistent field and density‐matrix renormalization group calculations. Based on these reference data, we assessed the accuracy of different density‐functional approximations. We show that in particular, exchange–correlation model potentials with correct asymptotic behavior yield good spin densities, and we find, in agreement with previous studies on different classes of compounds, that hybrid functionals systematically increase spin‐polarization effects with increasing amounts of exact exchange. Our results provide a starting point for investigations of spin densities of more complex systems such as the hinge model for the primary electron donor in photosystem II.     

Host–guest Complex of a Water-soluble Cucurbit[6]uril Derivative with the Hydrochloride Salt of 3-amino-5-phenylpyrazole

Interaction between tetramethylcucurbit[6]uril and 3-amino-5-phenylpyrazole hydrochloride in aqueous solution has been investigated by using ¹H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by a single crystal X-ray diffraction determination. The ¹H NMR spectra analysis established a basic interaction model in which an inclusion complex with a host:guest ratio of 1:1 forms, in which the host selectively binds the phenyl moiety of the guest. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes quantitatively as 6.8 × 10⁵ mol^? 1 L at pH 2.6; the interaction is pH dependent, decreasing as pH rises. The single crystal X-ray structure of the isolated inclusion complex shows the phenyl moiety of the guest inserted into the host cavity, which supports particularly the ¹H NMR spectroscopic study in solution. In the crystal structure of the inclusion complex, the host–guest interaction involves both inter- and intra-complex hydrogen bonding, forming 2:2 dimers that stack in one dimension as supramolecular tubes.     

Near-infrared diode laser spectroscopy of free radicals

Spectroscopic results on the radicals HCSi, CCO, and FeC obtained by studying in detail energy level structures using 0.8 microm diode laser system are reported. Of these radicals, the CCO radical was investigated mainly using Fabry-Perot type diode lasers with inconvenient mode gaps in the early stage of our near-infrared diode laser spectroscopic study of free radicals, and on the other hand, the FeC and HCSi radicals were studied using an external cavity diode laser. For the FeC radical, which is an interesting radical composed of an iron atom having 3d electrons, information on spin-orbit interaction between the triplet electronic ground state and a low-lying singlet electronic excited state is reported somewhat in detail. For the HCSi and CCO radicals, spectral particularities produced by a Renner-Teller interaction and a spin-orbit interaction are described for their high-resolution spectroscopic interest.     

Radical terpolymerization of sulfur dioxide,styrene, and methyl methacrylate

The radical terpolymerization of sulfur dioxide, styrene, and methyl methacrylate in o-dichlorobenzene with 2,2′-azobisisobutyronitrile was carried out in order to clarify the propagation mechanism of the radical copolymerization of sulfur dioxide and styrene, especially as a function of total concentration of sulfur dioxide and styrene. From the analysis of the trigonal composition diagrams it has been definitely shown that the radical copolymerization of sulfur dioxide and styrene proceeds by the propagation of two monomers, but the usual type of copolymerization mechanism, explicable in terms of the Lewis-Mayo equation, is not applicable to this copolymerization. The participation in the propagation of a monomer charge-transfer complex consisting of sulfur dioxide and styrene was also ruled out.     

Photochemistry and Reactivity of the Phenyl Radical–Water System: A Matrix Isolation and Computational Study

The reaction of the phenyl radical 1 with water has been investigated by using matrix isolation spectroscopy and quantum chemical calculations. The primary thermal product of the reaction between 1 and water is a weakly bound complex stabilized by an OH???π interaction. This complex is photolabile, and visible‐light irradiation (λ>420 nm) results in hydrogen atom transfer from water to radical 1 and the formation of a highly labile complex between benzene and the OH radical. This complex is stable under the conditions of matrix isolation, however, continuous irradiation with λ>420 nm light results in the complete destruction of the aromatic system and formation of an acylic unsaturated ketene. The mechanisms of all reaction steps are discussed in the light of ab initio and DFT calculations.     

Polymerization products of p-benzoquinone as thermal stabilizers for rigid poly(vinyl chloride): Part I—Preparation of the stabilizer

The solid phase cationic polymerization of p-benzoquinone using tin (II) chloride as catalyst has been investigated by isolation and identification of the reaction products. The polymerization reaction leads to formation of polymeric chains of hydroquinone nuclei linked together by SnOSn bonds and free from combined chlorine. The tin content of the polymer is increased by increasing the molar ratio of the catalyst and ranges from 4·7 to 55·6% tin. It is probable that the tin atoms are involved in the reaction products as a result of the interaction between polymeric chains having terminal catalyst residues. The resulting polymeric products are characterized by high thermal stability with a decomposition temperature in the region of 400°C. A mechanism which can account for the polymerization products has been developed. In view of the expected high potency of these products, together with their high thermal stability, they will be investigated as radical scavengers in the stabilization of polymeric material against radical degradation processes.     

钯配合物[Pd(phen)(L-asp)]·3H2O的结构，DNA键合和细胞活性研究

本文用常温方法合成了钯配合物,化学式[Pd(phen)(L-asp)]•3H2O,并用元素分析和红外图谱的方法进行分析,经单晶X射线衍射对其结构表征。以顺铂为参照,研究了该配合物对三种不同癌细胞（人宫颈癌细胞,肝癌细胞,口腔癌细胞）的细胞毒素作用,结果证明该钯配合物对人宫颈癌细胞有较强的抑制作用。通过多种光谱手段同时研究了该配合物与鱼精DNA作用模式,结果说明通过插入方式阻断鱼精DNA的复制。同时,测定配合物与pBR322质粒DNA作用的凝胶电泳。     

聚-γ-巯丙基硅氧烷羰基铑催化剂结构的XPS研究

<正> 本文报道聚-γ-巯丙基硅氧烷羰基铑催化剂结构上的研究结果。与以往作者报道的不同。这里的X-射线光电子能谱(XPS)实验结果证实这一新合成的催化剂是属于置换反应所导致的化合物型结构。同时定域在本文所研究的化合物分子中Rh离子和S离子上的Pauling计算电荷进一步支持作者的XPS试验结果。     

Synthesis,structure, DNA binding studies and nuclease activities of two luminescent neodymium complexes

Two neodymium(III) complexes, [Nd(Phen)(NO₃)₃(DMF)₂] (1) and [Nd(Phen)₂(NO₃)₃] (2) (phen = 1,10-phenanthroline; DMF = dimethylformamide), have been synthesized with a view to design artificial luminescent nucleases and nuclease mimics. The complexes were characterized by spectroscopic, powder, and single crystal XRD studies. The complexes, as expected, have luminescent properties. The DNA binding studies of both complexes have been carried out by spectroscopic studies e.g. electronic absorption (UV–Vis), fluorescence emission as well as viscosity measurements. The nuclease activity of the complexes has been established by gel electrophoresis using pUC19 circular plasmid DNA. The results of DNA binding as well as DNA cleavage activity and the model studies of interaction with pNPP indicate that both neodymium complexes demonstrate nuclease activity through phosphoester bond cleavage.     

The kinetics of the chlorine isotopic exchange between chloride ion at O,O-diarylphosphorochloridates or O,O-diarylphosphorochloridothionates

The kinetics of the chlorine isotopic exchange reaction between tetraethylammonium chloride-³⁶Cl and O,O-diarylphosphorochloridates (p-RC₆H₄O)₂POCl or O,O-diarylphosphorochloridothionates (p-RC₆H₄O)₂PSCl has been studied in acetonitrile solution. Good Hammett's correlations of the rate constants with Taft's σ⁰ constants were obtained. The values of the reaction constants ρ were found identical for phosphoryl and thiophosphoryl compounds. In comparison with oxygen in the phosphoryl group, the sulfur atom exhibits an electron-donating effect (Δσ⁰ ～ 0.80). No correlation has been found for the enthalpy and entropy of activation. The effect of the substituents aryloxy groups, oxygen, or sulfur atoms in the phosphoryl group on the kinetics of the S_N2-P reaction is discussed. The reactivity of the investigated compounds is determined by the extent of the positive charge localized on the phosphorus atom. The positive charge is formed by the direct interactions of the substituents with the reaction center and the indirect–intramolecular interactions revealed in the structure of the compound.     

Substituted Tetraaza‐ and Hexaazahexacenes and their N,N′‐Dihydro Derivatives: Syntheses,Properties, and Structures

The palladium‐catalyzed coupling of a substituted o‐diaminoanthracene and a substituted o‐diaminophenazine to substituted 2,3‐dichloroquinoxalines furnishes 10 differently substituted N,N′‐dihydrotetraaza‐ or ‐hexaazahexacenes with the quinoxaline group of the azaacenes carrying fluorine, chlorine, or nitro groups. The N,N′‐dihydrotetraazahexacenes with hydrogen, chlorine, and fluorine subtituents are oxidized to azaacenes, whereas only the parent N,N′‐dihydrohexaazahexacenes, with hydrogen substituents, are oxidized by MnO₂. The resultant azaacenes are characterized by their optical and spectroscopic data. In addition, single‐crystal X‐ray structures have been obtained for the parent tetraazahexacenes and their difluoro‐substituted derivatives. The di‐ and tetrachloro derivatives of the N,N′‐dihydrohexaazahexacene have also been structurally characterized.     

Spectroscopic characterization of the conversion of poly(p-phenylene-vinylene) precursor by ion irradiation

Different spectroscopic techniques show that poly(p-phenylene vinylene) films can be derived from a sulphonium precursor by irradiation with ion beams at energies of the order of 100 keV. The comparison with the pyrolysis conversion shows less chlorine and sulfur residues in the irradiated thickness, whereas some ketone structures are evidenced. The formation of nanometric scale carbon clusters induced by the irradiation degradation of PPV is however indicated by UV spectrophotometry, leading to bandgap narrowing and increase of the conductivity. The irradiation with doping species allows the conversion and doping of PPV films in a single stage. The induced conductivity is limited by the formation of complexes with chlorine residues through a gettering process.     

Amelioration in the Detection of Chlorine Using Electric Field Assisted LIBS

The detection of chlorine and improvement in its detection has remained a challenge despite the use of a single pulse and a dual pulse laser induced breakdown spectroscopic technique (LIBS). In this article, we presented an alternate technique for improving the detection of chlorine (Cl) using LIBS in conjunction with an external electric filed. A comparison of the emission intensity enhancement and plasma parameters in the absence and presence of an external field has been also presented. The implication of the presented technique for the detection of Cl is much easier and inexpensive as compared with the dual pulse LIBS.

     

主链型热致性液晶高分子芳香共聚酯的红外光谱研究

本文用傅里叶红外光谱法结合变温方法和偏振技术研究了主链型芳香共聚酯热致性高分子液晶。测定了光谱的变温性质以及液晶的有序度参数。结果表明分子链中液晶基元上苯环之间的相互作用在液晶相形成过程中起重要作用。液晶有序度参数与Roca和Yoon的理论值相一致。