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Substituent Groups (substituent + groups)
Selected AbstractsStudy of the mass spectrometric behaviour of phthalocyanine and azo dyes using electrospray ionisation and matrix-assisted laser desorption/ionisationRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2001A. Conneely The negative ion MALDI-MS and ESI-MS behaviour of sulphonated copper phthalocyanine dyes has shown the presence of both anionic and radical anionic species. Substituent groups such as sulphonates and linker arms, as are present in commercial dyes such as Remazol TB and Everzol TB, are found to be labile and the dyes undergo in-source fragmentation in both MALDI-MS and ESI-MS. Ions corresponding to sodium salts can be formed. It appears that Cu is firmly bound in the phthalocyanine structure, unlike the corresponding Mg and Al chelates that can undergo demetallation. The application of ESI-MSn confirmed that these labile groups can be fragmented from the dye molecules and, in addition, SO2 losses are observed as for EI-MS. Hydrolysed commercial azo dyes such as Remazol Black B (I) and Remazol Red RB (III) showed both singly and doubly charged molecular anion species as well as sodium salts using negative ion ESI-MS, but did not desulphonate like the copper phthalocyanine dyes. The application of ESI-MSn revealed fragmentation of the dye molecules with the loss of entities such as HOCH2CH2SO2C6H4N2 (for both dyes) and SO2 (for Remazol Black B). MALDI-MS, ESI-MS and ESI-MSn can therefore be used for the characterisation of such dyes by exploiting these fragmentation processes, and some structural information can be obtained for the dyes whose structures are not in the public domain. Copyright© 2001 John Wiley & Sons, Ltd. [source] Synthesis of Some New Substituted Photochromic N,N, -Bis(spiro[1-benzopyran-2,2,-indolyl])diazacrown Systems with Substituent Control over Ion ChelationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2006Craig J. Roxburgh Abstract The reversible photochemical ion chelation of the newly synthesised substituted N,N, -bis(spiro[1-benzopyran-2,2,-indolyl])diazacrown systems 15a,c and the subsequent molecular electronic control of this process using appropriately placed substituent groups on the spiro-benzopyran skeleton is reported. The principle of molecular electronic control of ion chelation is demonstrated by comparing the behaviour of the newly synthesised nitro-substituted and pyrido-annulated spiro-benzopyran system 9b with that of the unsubstituted compound 9a. Electronic substituent control over ion chelation is then exemplified for the new N,N, -bis(5,-nitrospiro[1-benzopyran-2,2,-indolyl])diazacrown system 15c and further exemplified for the corresponding 5,-trifluoromethyl derivative 15b, which contains the photochemically more robust trifluoromethyl group. The crown system 15a, unsubstituted in the spiro-indole moiety, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Porphyrin derivatives as photosensitizers for the inactivation of Bacillus cereus endosporesJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2009A. Oliveira Abstract Aims:, In this study, we propose (i) to study the photodynamic inactivation (PDI) efficiency of neutral and cationic porphyrin derivatives, (ii) to characterize the kinetics of the inactivation process using Bacillus cereus as a model endospore-producing bacterium and (iii) to conclude on the applicability of porphyrin derivatives in the inactivation of bacterial endospores. Methods and Results:, The study of PDI of Bacillus cereus endospores, taken as model-endospores, using porphyrin derivatives differing in the number of positive charges and in the meso-substituent groups, showed that neutral, monocationic and dicationic porphyrins are quite ineffective, in contrast with the tri- and tetra-cationic molecules. The most effective porphyrin is a tricationic porphyrin with a meso-pentafluorophenyl group. With this photosensitizer (PS), at 0·5 ,mol l,1, a reduction of 3·5 log units occurs after only 4 min of irradiation. None of the porphyrin derivatives showed toxicity in the absence of light. Conclusions:, Some porphyrin derivatives are efficient PSs for the inactivation of bacterial endospores and should be considered in further studies. Small modifications in the substituent groups, in addition to charge, significantly improve the effectiveness of the molecule as a PS for endospore inactivation. Significance and Impact of the Study:, Tetrapyrrolic macrocycles should be regarded as worthy to explore for the PDI of spore-producing gram-positive bacteria. The development of molecules, more selective and effective, emerges as a new objective. [source] Theoretical studies on four-membered ring compounds with NF2, ONO2, N3, and NO2 groupsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2008Xiao-Wei Fan Abstract Density functional theory (DFT) method has been employed to study the geometric and electronic structures of a series of four-membered ring compounds at the B3LYP/6-311G** and the B3P86/6-311G** levels. In the isodesmic reactions designed for the computation of heats of formation (HOFs), 3,3-dimethyl-oxetane, azetidine, and cyclobutane were chosen as reference compounds. The HOFs for N3 substituted derivations are larger than those of oxetane compounds with ONO2 and/or NF2 substituent groups. The HOFs for oxetane with ONO2 and/or NF2 substituent groups are negative, while the HOFs for N3 substituted derivations are positive. For azetidine compounds, the substituent groups within the azetidine ring affect the HOFs, which increase as the difluoroamino group being replaced by the nitro group. The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. The strain energy (SE) for the title compounds has been calculated using homodesmotic reactions. For azetidine compounds, the NF2 group connecting N atom in the ring decrease the SE of title compounds. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. For the oxetane compounds, the ONO2 bond is easier to break than that of the ring CC bond. For the azetidine and cyclobutane compounds, the homolysises of CNX2 and/or NNX2 (X = O, F) bonds are primary step for bond dissociation. Detonation properties of the title compounds were evaluated by using the Kamlet,Jacobs equation based on the calculated densities and HOFs. It is found that 1,1-dinitro-3,3-bis(difluoroamino)-cyclobutane, with predicted density of ca. 1.9 g/cm3, detonation velocity (D) over 9 km/s, and detonation pressure (P) of 41 GPa that are lager than those of TNAZ, is expected to be a novel candidate of high energy density materials (HEDMs). The detonation data of nitro-BDFAA and TNCB are also close to the requirements for HEDMs. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] The polarisability potential as a steric index,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Cristopher Camacho Abstract The acid-catalysed hydrolysis of carboxylic esters is the reference chemical reaction used for the empirical evaluation of steric effects. In this work, the polarisability potential (Hehre, et al., J. Am. Chem. Soc. 1986, 108, 1711,1712) is identified as quantum-mechanical size of substituent groups. Correlation is found between this quantity and reactivity features of the reference reaction. Copyright © 2010 John Wiley & Sons, Ltd. [source] Alkyl side chain driven tunable red,yellow,green emission: Investigation on the new ,-conjugated polymers comprising of 2,7-carbazole unit and 2,1,3-benzo-thiadiazole units with different side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Junping Du Abstract Four new soluble polymers containing a 2,7-carbazole unit and a 2,1,3-benzothiadiazole unit in the main chain were synthesized by Suzuki polycondensation. Variation of the substituent groups (R) at 5-position of 2,1,3-benzothiadiazole unit resulted in different color emission of the copolymers. Thus, when R was CH3 (or H), the polymer showed yellow,green (or red) emission; whereas the polymers showed the emission from green to yellow,green, when R was CH2(CH2)5CH3 or CH2OCH(CH3)2. To investigate the nature of the color change, a Gaussian 03 program was used for estimation of the dihedral angles between a 5-R-2,1,3-benzothiadiazole unit and a 2,7-carbazole unit. The results showed that the different substituents at 5-position of 2,1,3-benzothiadiazole brought about different the dihedral angles, which gave the different conjugation levels to the polymers. Hence, the tunablity of emission color may be attributed to the different conjugation levels between 2,7-carbazole units and 5-R-2,1,3-benzothiadiazole units induced by simply changing substituent groups at 5-position of benzothiadiazole unit. Electrochemically, the copolymers exhibited a higher oxidation potential as well as the reversible reduction behavior bearing from 2,1,3-benzothiadiazole unit. To investigate the electroluminescent properties of the polymers, the nonoptimized devices were fabricated and the results showed that the electroluminescent emission wavelength was basically similar to that of the photoluminescent. All polymers showed good thermal stability with 5 wt % loss temperature of more than 296 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1376,1387, 2008 [source] Unusual cationic copolymerization behavior of a six-membered ring spiro-orthocarbonate bearing adamantane backbones with a monofunctional epoxideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005Tetsuo Hino Abstract Copolymerizations of a six-membered ring spiro-orthocarbonate bearing adamantane backbones (AD - SOC, 1) and a monofunctional epoxide, PGE, in the presence of cationic initiators such as Sc(OTf)3 were carried out under various reaction conditions. As a result, instead of the anticipated poly(ether-ether-carbonate) 11, two types of copolyethers (12 and 18) consisting of two or three types of ether components having different substituent groups were unusually formed along with the evolution of carbon dioxide gas, in which AD - SOC efficiently acted as the corresponding oxetane equivalent monomers 3 and 4. Furthermore, the copolymerization behavior, including the formation of copolyethers 12 and 18, unexpectedly and significantly depended on the reaction conditions, such as the concentration of the initiator. For example, the copolymerizations with 5 mol % of Sc(OTf)3 mainly afforded copolyether 18, while those with 1 mol % mainly gave copolyether 12. In addition, treatments with 5 mol % of Sc(OTf)3 also yielded CH2Cl2, THF, and DMF-insoluble networked products, indicating relatively higher thermal stability compared with a common polyether. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1729,1740, 2005 [source] Surface-enhanced resonance Raman spectroscopy of rifamycins on silver nanoparticles: insight into their adsorption mechanismsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2006Barry D. Howes Abstract Three widely used antibiotics from the rifamycin family, rifamycin SV sodium salt, rifampicin and rifaximin, have been characterized by resonance Raman (RR) and surface-enhanced resonance Raman spectroscopy (SERRS). SERRS spectra were recorded using aqueous silver colloidal dispersions prepared with two reducing agents, sodium borohydride and hydroxylamine hydrochloride, for a range of pH values to identify the SERRS-active substrate surface most suitable for each of the three antibiotics. Rifampicin was found to give intense SERRS signals only for the borohydride-reduced colloid and only at pH < 7.7, whereas the hydroxylamine HCl-reduced colloid was the best substrate for rifaximin, giving considerably more intense SERRS spectra than the borohydride colloid. SERRS spectra of rifaximin were observed only at pH < 7.0. It is proposed that the marked pH dependence of the SERRS enhancement results from a transition from an anionic to a neutral zwitterionic state. SERRS spectra of rifamycin SV were not observed for any experimental conditions. The antibiotics display remarkably contrasting SERRS behaviour, reflecting differences in the nature of the substituent groups on the chromophore ring. A vibrational assignment of the RR spectra and detailed comparison between the RR and SERRS data have given insight into the mechanism of adsorption of the antibiotics onto the Ag surface. Rifampicin and rifaximin adsorb adopting an approximately similar vertical orientation of the chromophore ring with respect to the surface; however, rifampicin adsorbs by direct chemical interaction with the Ag whereas rifaximin does not form a direct bond with the Ag surface. Copyright © 2006 John Wiley & Sons, Ltd. [source] Electrochemical Polymerisation of N -Arylated and N -Alkylated EDOT-Substituted Pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) Derivatives: Influence of Substitution Pattern on Optical and Electronic PropertiesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 21 2009Kai Zhang Abstract New pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) derivatives carrying 3,4-ethylenedioxy-thiophenylphenyl (EDOT-phenyl) substituent groups in the 3- and 6-position, or in the 2- and 5-position of the DPP chromophore were synthesised and electrochemically polymerised. The properties of the polymers were investigated using cyclic voltammetry and UV/Vis absorption spectroscopy. It was found that the optical and electronic properties differ greatly between the two polymers. Materials with EDOT-phenyl groups in the 3- and 6-positions represent conjugated polymers with a low oxidation potential and reversible electrochromic properties, whereas the polymer with EDOT-phenyl groups in the 2- and 5-positions is non-conjugated and possesses a high oxidation potential and irreversible redox behaviour. [source] 15N NMR chemical shifts of ring substituted benzonitrilesMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2006Abstract 15N chemical shifts in an extensive series of para (15) and meta (15) as well as ortho (8) substituted benzonitriles, XC6H4CN, were measured in deuteriochloroform solutions, using three different methods of referencing. The standard error of the average chemical shift was less than 0.03 ppm in most cases. The results are discussed for both empirical correlations with substituent parameters and quantum chemical calculations. The 15N chemical shifts calculated at the GIAO/B3LYP/6,31 + G*//B3LYP/6,31 + G* level reproduce the experimental values well, and include nitrogen atoms in the substituent groups (range of 300 ppm with slope 0.98 and R = 0.998, n = 43). The 15N shifts in hydroxybenzonitriles are affected by interaction with the OH group. Therefore, these derivatives are excluded from the correlation analysis. The resultant 15N chemical shift correlates well with substituent constants, both in the simple Hammett or DSP relationships and the 13C substituent-induced chemical shifts of the CN carbon. Copyright © 2006 John Wiley & Sons, Ltd. [source] Influence of substituent groups at the 3-position on the mass spectral fragmentation pathways of cephalosporinsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2010Jin Li The structural fragment ions of nine cephalosporins were studied by electrospray ionization quadrapole trap mass spectrometry (Q-Trap MSn) in positive mode. The influence of substituent groups in the 3-position on fragmentation pathway B, an ,-cleavage between the C7C8 single bond, coupled with a [2,4]-trans-Diels-Alder cleavage simultaneously within the six-membered heterocyclic ring, was also investigated. It was found that when the substituent groups were methyl, chloride, vinyl, or propenyl, fragmentations belonging to pathway B were detected; however, when the substituents were heteroatoms such as O, N, or S, pathway B fragmentation was not detected. This suggested that the [M,R3]+ ion, which was produced by the bond cleavage within the substituent group at the 3-position, had a key influence on fragmentation pathway B. This could be attributed to the strong electronegativity of the heteroatoms (O, N, S) that favors the production of the [M,R3]+ ion. Moreover, having the positive charge of the [M,R3]+ ion localized on the nitrogen atom in the 1-position changed the electron density distribution of the heterocyclic structure, which prohibits a [2,4]-reverse-Diels-Alder fragmentation and as a result fragmentation pathway B could not occur. The influence of the substituent group in the 3-position was determined by the intensity ratio (e/d) of ions produced by fragmentation pathway A, a [2,2]-trans-Diels-Alder cleavage within the quaternary lactam ring, including the breaking of the amide bond and the C6C7 single bond (ion d), and fragmentation pathway B (ion e). The results indicate that the electronegativity of the substituent group was a key influencing factor of pathway B fragmentation intensity, because the intensity ratio (e/d) is higher for a chlorine atom, a vinyl, or a propenyl group than that of a methyl group. This study provided some theoretical basis for the identification of cephalosporin antibiotics and structural analysis of related substances in drugs. Copyright © 2010 John Wiley & Sons, Ltd. [source] Heteropolynuclear Palladium Complexes with Pyrazolate and Its 3- tert -Butyl Derivatives: The Effect of Heterometal Ions on the Rate of IsomerizationCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2006Keisuke Umakoshi Prof. Dr. Abstract The heteropolynuclear complexes [Pd2M,2(,-pz)6] (M,=Ag (1), Au (2); pzH=pyrazole), HT -[Pd2M,2(,-3- tBupz)6] (M,=Ag (3,a), Au (4,a); 3- tBupzH=3- tert -butylpyrazole), and HH -[Pd2Au2(,-3- tBupz)6] (4,b) have been prepared and some of them were structurally characterized. When 3- tert -butylpyrazolate was employed as a bridging ligand, two linkage isomers (head-to-tail (HT) and head-to-head (HH)) arise from the difference in orientation of the substituent groups on the pyrazolate bridges between the two Pd atoms. 1H NMR spectroscopy has been used to identify and to follow the reversible stereochemical rearrangement of the HH isomer of [Pd2Ag2(,-3- tBupz)6] (3,b) to form the HT isomer 3,a in CDCl3 and the HT isomer of [Pd2Au2(,-3- tBupz)6] (4,a) to form the HH isomer 4,b in C6D6. Kinetic studies of the reaction have established the rate law to be ,d(HH)/dt=d(HT)/dt=k2[HH],k1[HT] for 3,b and ,d(HT)/dt=d(HH)/dt=k1[HT],k2[HH] for 4,a, where k1 and k2 denote the rate of isomerization from the HT to the HH isomer and that from the HH to the HT isomer, respectively. For typical runs at 50,°C in C6D6, k1=13.8×10,5 s,1, k2=18.6×10,5 s,1, and Keq=k2/k1=1.24 for 3,b, and k1=1.26×10,5 s,1, k2=3.52×10,5 s,1, and Keq=k1/k2=0.36 for 4,a. Temperature-dependent rate measurements reveal ,H, and ,S, to be 100(1) kJ,mol,1 and 0(3) J,mol,1,K,1 for 3,b and 112(5) kJ,mol,1 and 20(17) J,mol,1,K,1 for 4,a, respectively. The rate of isomerization is essentially unaffected by the concentration of the complex or by the presence of neutral bridging ligands. These data and observations imply that the isomerization involves an intramolecular exchange process. [source] Photoinduced Excited State Intramolecular Proton Transfer of New Schiff Base Derivatives with Extended Conjugated Chromophores: A Comprehensive Theoretical SurveyCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Qi Wang Abstract This paper presented comprehensive theoretical investigation of excited state intramolecular proton transfer (ESIPT) of four new large Schiff base derivatives with extended conjugated chromophores. The properties of the ground state and the excited state of phototautomers of C1 to C4 [C1: 2-(4,-nitro-stilbene-4-ylimino)methylphenol; C2: 2-(4,-cyano-stilbene-4-ylimino)methylphenol; C3: 2-(4,-methoxyl-stilbene-4-ylimino)methylphenol; C4: 2-(4,- N,N -diethylamino-stilbene-4-ylimino)methylphenol], which included geometrical parameter, energy, rate constant, frontier orbit, Mulliken charge, dipole moment change, were studied by DFT (density functional theory), CIS (configuration interaction singles-excitation), TDDFT (time-dependent DFT) methods to analyze the effects of chromophore part on the occurrence of ESIPT and the role of substituent groups. The structural parameter calculation showed that the shorter RHN and larger ROH from enol to enol* form, and less twisted configuration in the excited state implied that these molecules could undergo ESIPT as excitation. Stable transition states and a low energy barrier were observed for C1 to C4. This suggested that chromophore part increased some difficulty to undergo ESIPT for these molecules, while the possibility of occurrence of ESIPT was quite high. The negative ,E* (,9.808 and ,9.163 kJ/mol) of C1 and C2 and positive ,E* (0.599 and 1.029 kJ/mol) of C3 and C4 indicated that withdrawing substituent groups were favorable for the occurrence of ESIPT. The reaction rate constants of proton transfer of these compounds were calculated in the S0 and S1 states respectively, and the high rate constants of these compounds were observed at S1 state. C1 even reached at 1.45×1015 s,1 in the excited state, which is much closed to 2.05×1015 s,1 of the parent moiety (salicylidene methylamine). Electron-donating and electron-withdrawing substituent groups had different effects on the electron density distribution of frontier orbits and Mulliken charges of the atoms, resulting in different dipole moment changes in enol*,keto* process. These differences in turn suggested that C1 and C2 had more ability to undergo ESIPT than C3 and C4. The ultraviolet/visible absorption spectra, normal fluorescence emission spectra and ESIPT fluorescence emission spectra of these compounds were predicted in theory. [source] | ||||||||||||||||||||||