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1.
The S-R enantiomerization processes of 2,2'-biphenol (biphenol) have been investigated using density functional theory (DFT). Five isomers for biphenol were identified: I0, which is the most stable isomer; I1a and I1b, which are formed by a restricted rotation of one OH group; and I2a and I2b, which are formed by a restricted rotation of the two OH groups where a and b denote cis and trans configurations, respectively. Each isomer has R- and S-enantiomers. The energies relative to the most stable isomer I0 are 1.6, 3.3, 5.3, and 5.5 kcal mol(-1) for I1a, I1b, I2a, and I2b, respectively. The direct enantiomerization of I0, in which the phenol-ring rotation is considered to be the reaction coordinate while the OH rotations are frozen, is forbidden because of the repulsion between the two OH groups. The transition states for isomerizations of I0 to other isomers (I1a, I1b, I2a, or I2b) were calculated as well as those for the other direct enantiomerizations except for that of I0. From the viewpoint of the least number of the transition states and their low energy levels, the probable S-R enantiomerization of I0 is expressed as a sequential process of isomerization: I0,S --> I1a,S, a direct enantiomerization induced by one of the two OH rotations, I1a,S --> I1a,R, and another isomerization, I1a,R --> I0,R, that is, I0,S --> I1a,S --> I1a,R --> I0,R as the whole process. This process is effective in quantum control of the enantiomerization of biphenol and can be carried out by a sequence of a pump-dump IR laser-pulse scheme.  相似文献   

2.
Structural changes during the treatment of films of highly crystalline microfibers of Cladophora cellulose with ethylenediamine (EDA) have been studied by time-resolved X-ray microprobe diffraction methods. As EDA penetrates the sample and converts cellulose I to EDA-cellulose I, the measured profile widths of reflections reveal changes in the shapes and average dimensions of cellulose I and EDA-cellulose I crystals. The (200) direction of cellulose I is most resistant to EDA penetration, with EDA penetrating most effectively at the hydrophilic edges of the hydrogen bonded sheets of cellulose chains. Most of the cellulose chains in the initial crystals of cellulose I are incorporated into crystals of EDA-cellulose I. The size of the emerging EDA-cellulose I crystals is limited to about half of their size in cellulose I, most likely due to strains introduced by the penetration of EDA molecules. There is no evidence of any gradual structural transition from cellulose I to EDA-cellulose I involving a continuously changing intermediate phase. Rather, the results point to a rapid transition to EDA-cellulose I in regions of the microfibrils that have been penetrated by EDA.  相似文献   

3.
A new Cs(I) magnetic ion-imprinted polymer (Cs(I)-MIIP) aimed at the selective adsorption and separation of Cs(I) from salt lake brine was prepared. The Fe3O4@SiO2 was used as supporter, Cs(I) as template ion, and carboxymethyl chitosan as functional monomer. The product was characterized by Fourier transform infrared spectra, XRD, energy-dispersive spectrometry, scanning electron microcopy, thermogravimetric analysis, and vibrating sample magnetometer. The adsorption of the Cs(I)-MIIP in solution was investigated, which indicated the maximum adsorption capacity was 36.15?mg·g?1 under the optimum conditions. The pseudo-first-order kinetic model and the Freundlich isotherm model were applied to predict the adsorption process of Cs(I) onto Cs(I)-MIIP. Selectivity experiments showed that the relative selectivity coefficient (k′) were 24.995, 1.73, 1.43, 4.83, and 1.63 to Cs(I)/Li(I), Cs(I)/Na(I), Cs(I)/K(I), Cs(I)/Rb(I), and Cs(I)/Sr(II) binary solutions, higher than those of NIP, respectively. Furthermore, the Cs(I)-MIIP was successfully applied to the enrichment and separation of Cs(I) from the salt lake brine of Qinghai, with satisfactory Cs(I) recovery rates.  相似文献   

4.
The formation of neutral I2 by the photodissociation of the methyl iodide dimer, (CH3I)2, excited within the A band at 249.5 nm is evaluated using velocity map imaging. In previous work [J. Chem. Phys. 122, 204301 (2005)], we showed that the formation of I2+ from photodissociation of the methyl iodide dimer takes place via ionic channels (through the formation of (CH3I)2+). It is thus not possible to detect neutral I2 by monitoring I2+. Neutral I2 is detected in this study by monitoring I atoms arising from the photodissociation of I2. Iodine atoms from I2 photodissociation have a characteristic kinetic energy and angular anisotropy, which is registered using velocity map imaging. We use a two-color probe scheme involving the photodissociation of nascent I2 at 499 nm, which gives rise to I atoms that are ionized by (2+1) resonance enhanced multiphoton ionization at 304.67 nm. Our estimate of the yield of nascent I2 is based on the comparison with the signal from I2 at a known concentration. Using molecular beams with a small fraction of CH3I (1% in the expanded mixture) where smaller clusters should prevail, the production of I2 was found to be negligible. An upper estimate for the quantum yield of I2 from (CH3I)2 dimers was found to be less than 0.4%. Experiments with a higher fraction of CH3I (4% in the expanded mixture), which favor the formation of larger clusters, revealed an observable formation of I2, with an estimated translational temperature of about 820 K. We suggest that this observed I2 signal arises from the photodissociation of several CH3I molecules in the larger cluster by the same UV pulse, followed by recombination of two nascent iodine atoms is responsible for neutral I2 production.  相似文献   

5.
The electronic spectra of the title compounds I (n), n = 1 to 5, were recorded under standard conditions for quantitative comparison. Spectra of I(1) to I(4) in the gas phase and of I(2) to I(5) in nonpolar solutions are presented in a computer plotted form, and wave length maxima and intensities are listed. Tentative assignments of the medium-intensity, first transition ( A band) and the ultrahigh-intensity, second transition ( B band) are given. Finally, spectra of I(2) to I(5) recorded at ? 150° are presented and discussed ( A band). The syntheses of I(3) to I(5) are given in detail.  相似文献   

6.
Acridine and 9-chloroacridine form charge-transfer complexes with iodine in which the nitrogen-bound I2 molecule is amphoteric; one end serves as a Lewis acid to the heterocyclic donor, while the other end acts as a Lewis base to a second I2 molecule that bridges two acridine.I2 units. In the acridine derivative [(acridine.I2)2.I2, 1], the dimer has a "zigzag" conformation, while in the 9-chloroacridine derivative [(9-Cl-acridine.I2)2.I2, 2], the dimer is "C-shaped". The thermal decomposition of the two complexes is very different. Compound 1 loses one molecule of I2 to form an acridine.I2 intermediate, which has not been isolated. Further decomposition gives acridine as the form II polymorph, exclusively. Decomposition of 2 involves the loss of two molecules of I2 to form a relatively stable intermediate [(9-Cl-acridine)2.I2, 3]. Compound 3 consists of two 9-Cl-acridine molecules bridged through N...I charge-transfer interactions by a single I2 molecule. This compound represents the first known example, in which both ends of an I2 molecule form interactions in a complex that is not stabilized by the extended interactions of an infinite chain structure. The ability of the terminal iodine of an N-bound I2 to act either as an electron donor (complexes 1 and 2) or as an electron acceptor (complex 3) can be understood through a quantum mechanical analysis of the systems. Both electrostatic interactions and the overlap of frontier molecular orbitals contribute to the observed behavior.  相似文献   

7.
Let me say first of all that I am much less fortunate than Professor Kennedy who was properly coached and told what he has to say. Not only that nobody coached me and told me what I should say in my final remarks, but nobody told me even that I have to make these remarks. So, in desperation, I tried to make a few notes during the meeting. I know that my secretary can read them, but I don't know if I can do it.  相似文献   

8.
2-取代苯亚胺基噻唑烷类化合物的晶体结构研究   总被引:2,自引:0,他引:2  
A series of 2-phenyliminothiazolidines has been successfully synthesized; and 2-(2-methylphenyl) iminothiazolidine (I a) and 2-(4-methylphenyl) iminothiazolidine (I b) have been selected to determine their crystal structures by X-ray diffraction technique,from their molecular graph of it is shown that double bond at 2-carbon atom of the heterocycle is all extro-cychc at the crystal state,and there are two main plaines in I a and I b.But in I a ,the angle between the planes is 61.4° and in I b the angle is about 41.4°.And so there is a strong conjugative effect in I b than in I a.So it is thought that the difference in fungicidal activities between 2-substitutedphenyl compounds (I a) and 4-substitutedphenyl compounds(I b) is due to their space factors.  相似文献   

9.
Using first-principles pseudo-potential plane wave method, the energetics, geometrical and electronic structures of three Al13I cluster isomers were calculated. The calculation results of the binding energy indicate Al13I cluster is more stable than Al13 cluster although its electrons are not a magic number as in Al13 cluster, and among Al13I cluster isomers the "Bridge" structure is the most stable, the second is the "Ontop" structure, and the worst is the "Hollow" structure. By analyzing the geometrical structures of Al13I cluster isomers, it is found that after I atom and Al13 cluster combine the geometrical structures of Al13 moieties are changed besides Al13IHollow cluster, in which the Al13 moiety is still a regular icosahedron. For Al13IOntop cluster, the Al13 moiety has a shrinking trend to I, whereas in Al13IBridge cluster it is distorted. Mulliken population analysis shows for the interaction of electrons between Al(I atoms in Al13I cluster not only there exists an ionic bonding but there is a covalent bonding. Part of electrons in the Al13 cluster transfer to I as Al13 cluster and I atom combine. The order of the strength of covalent bonding between Al13 moiety and I in Al13I cluster isomers is Al13IBridge>Al13IHollow>Al13IOntop. Further analysis of electric structures of Al13 and Al13I clusters indicates a higher stability of Al13I cluster than Al13 cluster can be attributed to the s-p hybridization of 3s and 3p electrons of Al in Al13 moiety induced by I doped, which leads to fewer electrons N(EF) at EF in Al13I and a larger energy gap ΔEH-L between HOMO and LUMO levels in Al13I cluster. The distinguish of structural stability of Al13I cluster isomers mainly originates from their different magnitudes in decrease of N(EF) and increase of ΔEH-L relative to Al13 cluster. The fewest N(EF) and the largest ΔEH-L are responsible for the high stability of Al13IBridge cluster .  相似文献   

10.
Photoelectron spectra and angular distributions in 267 nm detachment of the I(-)Ar, I(-)H(2)O, I(-)CH(3)I, and I(-)CH(3)CN cluster anions are examined in comparison with bare I(-) using velocity-map photoelectron imaging. In all cases, features are observed that correlate to two channels producing either I((2)P(3/2)) or I((2)P(1/2)). In the photodetachment of I(-) and I(-)Ar, the branching ratios of the (2)P(1/2) and (2)P(3/2) channels are observed to be approximately 0.4, in both cases falling short of the statistical ratio of 0.5. For I(-)H(2)O and I(-)CH(3)I, the (2)P(1/2) to (2)P(3/2) branching ratios are greater by a factor of 1.6 compared to the bare iodide case. The relative enhancement of the (2)P(1/2) channel is attributed to dipole effects on the final-state continuum wave function in the presence of polar solvents. For I(-)CH(3)CN the (2)P(1/2) to (2)P(3/2) ratio falls again, most likely due to the proximity of the detachment threshold in the excited spin-orbit channel. The photoelectron angular distributions in the photodetachment of I(-), I(-)Ar, I(-)H(2)O, and I(-)CH(3)CN are understood within the framework of direct detachment from I(-). Hence, the corresponding anisotropy parameters are modeled using variants of the Cooper-Zare central-potential model for atomic-anion photodetachment. In contrast, I(-)CH(3)I yields nearly isotropic photoelectron angular distributions in both detachment channels. The implications of this anomalous behavior are discussed with reference to alternative mechanisms, affording the solvent molecule an active role in the electron ejection process.  相似文献   

11.
A reversed-phase liquid chromatographic method was developed to determine parts-per-million and higher levels of Sudan 1, 1-(phenylazo)-2-naphthalenol, in the disulfo monoazo color additive FD&C Yellow No. 6 and in a related monosulfo monoazo color additive, D&C Orange No. 4. Sudan I, the corresponding unsulfonated monoazo dye, is a known impurity in these color additives. The color additives are dissolved in water and methanol, and the filtered solutions are directly chromatographed, without extraction or concentration, by using gradient elution at 0.25 mL/min. Calibrations from peak areas at 485 nm were linear. At a 99% confidence level, the limits of determination were 0.008 microg Sudan I/mL (0.4 ppm) in FD&C Yellow No. 6 and 0.011 microg Sudan I/mL (0.00011%) in D&C Orange No. 4. The confidence intervals were 0.202 +/- 0.002 microg Sudan I/mL (10.1 +/- 0.1 ppm) near the specification level for Sudan I in FD&C Yellow No. 6 and 20.0 +/- 0.2 microg Sudan I/mL (0.200 +/- 0.002%) near the highest concentration of Sudan I found in D&C Orange No. 4. A survey was conducted to determine Sudan I in 28 samples of FD&C Yellow No. 6 from 17 international manufacturers over 3 years, and in a pharmacology-tested sample. These samples were found to contain undetected levels (16 samples), 0.5-9.7 ppm Sudan I (0.01-0.194 microg Sudan I/mL in analyzed solutions; 11 samples including the pharmacology sample), and > or =10 ppm Sudan I (> or = 0.2 microg Sudan I/mL; 2 samples). Analyses of 21 samples of D&C Orange No. 4 from 8 international manufacturers over 4 years found Sudan I at undetected levels (8 samples), 0.0005 to < 0.005% Sudan I (0.05 to < 0.5 microg Sudan I/mL in analyzed solutions; 3 samples, including a pharmacology batch), 0.005 to <0.05% Sudan I (0.5 to <5 microg Sudan I/mL; 9 samples), and 0.18% Sudan I (18 microg Sudan I/mL; 1 sample).  相似文献   

12.
Cytochrome P450 3A4 is involved in the metabolism of 50% of all swallowed drugs. The enzyme functions by means of a high-valent iron-oxo species, called compound I (Cpd I), which is formed after entrance of the substrate to the active site. We explored the features of Cpd I using hybrid quantum mechanical/molecular mechanical calculations on various models that are either substrate-free or containing one and two molecules of diazepam as a substrate. M?ssbauer parameters of Cpd I were computed. Our major finding shows that without the substrate, Cpd I tends to elongate its Fe-S bond, localize the radical on the sulfur, and form hydrogen bonds with A305 and T309, which may hypothetically lead to Cpd I consumption by H-abstraction. However, the positioning of diazepam close to Cpd I, as enforced by the effector molecule, was found to strengthen the NH...S interactions of the conserved I443 and G444 residues with the proximal cysteinate ligand. These interactions are known to stabilize the Fe-S bond, and as such, the presence of the substrate leads to a shorter Fe-S bond and it prevents the localization of the radical on the sulfur. This diazepam-Cpd I stabilization was manifested in the 1W0E conformer. The effector substrate did not influence Cpd I directly but rather by positioning the active substrate close to Cpd I, thus displacing the hydrogen bonds with A305 and T309, and thereby giving preference to substrate oxidation. It is hypothesized that these effects on Cpd I, promoted by the restrained substrate, may be behind the special metabolic behavior observed in cases of multiple substrate binding (also called cooperative binding). This restraint constitutes a mechanism whereby substrates stabilize Cpd I sufficiently long to affect monooxygenation by P450s at the expense of Cpd I destruction by the protein residues.  相似文献   

13.
荧光探针法测定甜菜碱cmc的研究   总被引:3,自引:0,他引:3  
荧光探针法测定甜菜碱cmc的研究任学贞,李干佐,王弘立,翟立民,隋卫平,徐欣艳(山东大学化学系,济南,250100)关键词甜菜碱,芘,临界胶束浓度Ekwall等[1]发现,表面活性剂的溶液能够增溶多环芳烃并发射较强的荧光.在常用的测定表面活性剂临界胶...  相似文献   

14.
Crystal and molecular structure of μ-oxo-bis[trifluoroacetato(p-tolyl)iodine] (I) synthesized by a new procedure was determined by X-ray diffraction analysis. Crystals I are orthorhombic, unstable, space group Pbcn, a=17.684(3), b=8.453(3), c=30.560(4) Å, Z=8. The structure of I was solved by direct and Fourier methods and refined by the full-matrix least-squares procedure in an anisotropic-isotropic approximation to R=0.098 (CAD-4 automatic diffractometer, λCuKα, 1200 observed reflections with I≥2σ). In molecule I, two iodine atoms have T-configuration of valence bonds with the average bond angles O?I?O 169(1) and O?I?C 86(2)°, average bond lengths I?Oμ 2.009(9), I?Oacet 2.269(9), and I?Caryl 2.11(1) Å, and the bond angle I?O?I 118.1(5)°. In molecule I, two p-Tol substituents are directed to approximately the same side of the medium plane of the central O?I?O?I?O fragment. Crystal structure I has I...O type intra-and intermolecular nonvalent interactions (secondary bonds).  相似文献   

15.
X-ray photoelectron spectroscopy (XPS) along with inductively coupled plasma analysis (ICP-AE) and Raman spectroscopy have been used to define the location and to quantify the amount of iodine in HiPco SWNT samples loaded with molecular I(2) via sublimation (I(2)-SWNTs). The exterior-adsorbed I(2) can be removed (as I(-)) by reducing the sample of filled nanotubes with Na(0)/THF or by heating the I(2)-SWNTs to 300 degrees C (without reduction), leaving I(2) contained only within the interior of the SWNTs (I(2)@SWNTs) as proven by XPS. These I(2)@SWNTs contain approximately 25 wt % of I(2) and are stable without the loss of I(2) even after exposure to additional reduction with Na(0)/THF or upon heating to ca. 500 degrees C.  相似文献   

16.
The β-cyclodextrin (β-CD) polyiodide inclusion complex (β-CD)(2)·Co(0.5)·I(7)·21H(2)O has been synthesized, characterized and further investigated via FT-Raman spectroscopy in the temperature range of 30-120°C. The experimental results point to the coexistence of I(-)(7) units (I(2)·I(-)(3)·I(2)) that seem not to interact with the Co(2+) ions and I(-)(7) units that display such interactions. The former units exhibit a disorder-order transition of both their I(2) molecules above 60°C due to a symmetric charge-transfer interaction with the central I(-)(3) [I(2)←I(-)(3)→I(2)], whereas in the latter units only one of the two I(2) molecules becomes well-ordered above 30°C. The other I(2) molecule remains disordered presenting no charge-transfer phenomena. The Co(2+) ion induces a considerable asymmetry on the geometry of the I(-)(3) anion and a significant modification of its Lewis base character. Complementary dielectric measurements suggest no important involvement of H···I contacts in the observed modification of the I(-)(3) electron-transfer properties.  相似文献   

17.
This review highlights some structural features and luminescent properties of homo- and hetero-multinuclear silver(I)–pyridinyl complexes. It focuses on the coordination and geometry of the silver(I) ions to the pyridinyl-nitrogen. For this reason, we have considered only pyridinyl-N–Ag(I) complexes whose crystal data are available. In addition, this review does not consider mononuclear silver(I)–pyridinyl complexes as these have been reviewed elsewhere. This is motivated by the fact that multinuclear silver(I)–pyridinyl complexes have been shown to be more stable in solution, possess enhanced properties, and have fascinating structures compared to their mononuclear counterparts. The introduction highlights pyridinyl ligands used in complexation of silver(I) ions. The main body highlights complexation of silver(I) through pyridinyl nitrogen and the interactions found in the multinuclear silver(I)–pyridinyl complexes as well as the coordination number and geometry of silver(I) centers. Though silver(I) has been flaunted to prefer linear twofold coordination geometry, from this review, it is clear that higher coordination numbers in varied geometries are possible. These include distorted trigonal planar, T-shaped, distorted tetrahedral, trigonal bipyramidal, and octahedral geometries. Coordination of silver(I) to pyridinyl ligands and their metalloligands has been observed to impart or enhance luminescent properties in the ensuing complexes.  相似文献   

18.
A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the simultaneous determination of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone, the active components of Salvia miltiorrhiza in rat plasma, was developed. After liquid-liquid extraction with tariquidar as an internal standard, tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone were eluted from an Atlantis dC18 column within 5 min with a mixture of methanol and ammonium formate (10 mm, pH 6.5; 85:15, v/v). The analytes were detected by an electrospray ionization tandem mass spectrometry in the selected reaction monitoring (SRM) mode. The standard curves were linear (r=0.999) over the concentration range of 0.25-80 ng/mL for tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone in rat plasma. The coefficients of variation and the relative errors of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone for intra- and inter-assay at four quality control (QC) concentrations were 1.1-5.1% and -4.0-6.0%, respectively. The lower limit of quantification for tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone was 0.25 ng/mL from 100 microL of plasma. This method was successfully applied to the pharmacokinetic study of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone after oral administration of PF2401-SF, the standardized fraction of Salvia miltiorrhiza enriched with tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone to male Sprague-Dawley rats.  相似文献   

19.
A combination of neutron activation and gamma-ray coincidence counting technique is used to determine the concentration of both long-lived fission produced129I and natural127I in environmental samples. The neutron reactions used for the activation of the iodine isotopes are129I(n, )130I and127I(n, 2n)126I. Nuclear interferences in the activation analysis of129I and127I can be caused by production of130I or126I from other constituents of the materials to be irradiated, i.e. Te, Cs and U impurities and from the125I tracer used for chemical yield determination. Chemical interferences can be caused by129I and127I impurities in the reagents used in the pre-irradiation separation of iodine. The activated charcoals used as iodine absorbers were carefully cleaned. Different chemical forms of added125I tracer and129I and127I constituents of the samples can cause different behaviour of125I tracer and sample iodine isotopes during pre-irradiation separation of iodine. The magnitude of the nuclear and chemical interferences has been determined. Procedures have been developed to prevent or control possible interferences in low-level129I and127I activation analysis. For quality control a number of biological and environmental standard samples were analyzed for127I and129I concentrations.  相似文献   

20.
We present results from atomic force microscopy (AFM) images indicating various experimental conditions, which alter the morphological characteristics of self-assembled cyanobacterial PS I on hydroxyl-terminated self-assembled alkanethiolate monolayers (SAM/Au) substrates. AFM topographical images of SAM/Au substrates incubated in solutions containing different PS I concentrations solubilized with Triton X-100 as the detergent reveal large columnar aggregates (~100 nm and hence, much taller than a single PS I trimer) at high PS I concentrations. Depositions from dilute PS I suspensions reveal fewer aggregates and relatively uniform surface topography (~10 nm). Confocal fluorescence microscopy analysis of fluorescently tagged PS I deposited on to SAM/Au substrates using electric field and gravity driven techniques reveal preliminary indications of directionally aligned PS I attachments, besides corroborating a uniform monolayer formation, for the former deposition method. The complex attachment dynamics of PS I onto SAM substrates are further investigated from the AFM images of PS I/SAM/Au substrates prepared under different experimental conditions using: 1) PS I isolated as monomers and trimers 2) adsorption at elevated temperatures, and 3) different detergents with varying pH values. In each of the cases, the surface topology indicated distinct yet complex morphological and phase characteristics. These observations provide useful insight into the use of experimental parameters to alter the morphological assembly of PS I on to SAM substrates en route to successful fabrication of PS I based biohybrid photoelectrochemical devices.  相似文献   

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