Estimation of the kinetic characteristics of sorption of an organic ion on a heterogeneous crosslinked polymer sorbent within the framework of a bidisperse model

For the sorption of rubomycin, an antitumor athracycline-type antibiotic, on BDM-12 carboxyl-containing heterogeneous crosslinked polymer sorbent, it was shown that the measured time dependences of the extent of process are determined by two characteristic times: τ₁ (in the range of short times) and τ₂ (at long times). A phenomenological theory of the kinetics of sorption on the heterogeneous sorbent was developed on the basis of a biporous sorbent model. The dependences of the characteristic times τ₁ and τ₂ on the sorbent grain radius were obtained. It was concluded that the theory makes predictions in good agreement with experimental data and allows calculating the most important kinetic parameters of sorption of organic ions on polymer sorbents: the time of diffusion of the sorbate into microgranules, the diffusion coefficient of the sorbate in transport pores, the effective coefficient of the sorbate diffusion into the heterogeneous sorbent, etc.     

Optimization of experimental conditions for the preparative displacement chromatography of antitumor anthracycline antibiotics on carboxylic sorbents

The physico-chemical conditions and the limits of the rates of mobile phases are determined when effective regimes of preparative chromatography in the conditions of sharpening the boundaries of chromatographic zones of anthracycline antibiotics are realized. The influence of pH on the equilibrium, kinetics and dynamics of sorption of anthracycline antibiotics (rubomycin, doxorubicin and carminomycin) on the carboxylic sorbents has been studied.     

Experimental and theoretical studies on the radical-cation-mediated imino-Diels-Alder reaction

The feasibility of an electron transfer imino-Diels-Alder reaction between N-benzylideneaniline and arylalkenes in the presence of a pyrylium salt as a photosensitizer has been demonstrated by a combination of product studies, laser flash photolysis (LFP), and DFT theoretical calculations. A stepwise mechanism involving two intermediates and two transition states is proposed.     

Experimental and theoretical studies on the thermal decomposition of metformin

Journal of Thermal Analysis and Calorimetry - This work is a first attempt to understand the mechanism of metformin thermal decomposition under inert conditions. Thermal gravimetric analysis...     

Experimental and theoretical studies on the identification of p-biphenyloxycarbonylphenyl acrylate

This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate by means of experimental and theoretical evidences. The spectroscopic properties of the compound were experimentally investigated by Fourier transformation-infrared spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). Moreover, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, thermodynamic properties, atomic charges and ultraviolet-visible (UV-vis) spectra were analyzed utilizing ab initio Hartree-Fock (HF) and Density Functional Theory (B3LYP) methods at 6-31G(d,p) calculation level. It was found that the vibrational frequencies and chemical shifts obtained were shown to have a good agreement with available experimental results. We not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also evaluated the transition state and energy band gap clearly.     

Experimental and theoretical studies of the propargyl-allenylindium system

The transient organoindium intermediates formed in the reaction of propargyl bromide with indium in aqueous media and tetrahydrofuran were investigated by NMR spectroscopy and found to be allenylindium(I) and allenylindium(III) dibromide. The influence of solvent and methyl substitution on the propargyl-allenylindium system was also studied. The experimental observations were supported by theoretical calculations using the B3LYP/6-311+G* method.     

Thermal and catalytic isomerization of exomethylenecycloheptadienes. Experimental and theoretical studies

The intermolecular [3+2+2] cycloaddition reaction of ethyl cyclopropylideneacetate with alkynes proceeded in the presence of a Ni(0)/PPh₃ catalyst, and cycloheptadiene derivatives were obtained. However, in the reaction of 1-cyclopropylidene-2-propanone with phenylacetylene, a cycloheptatriene derivative was isolated. It was anticipated that the isomerization of the initially formed cycloheptadiene derivative led to the formation of the cycloheptatriene derivative. In this paper, we report the isomerization of cycloheptadiene derivatives under thermal, acidic and basic conditions. The stability of the products was also studied by theoretical calculations. The effects of substituents and the mechanism of the isomerization were discussed.     

Experimental and theoretical studies on the thermal decomposition of heterocyclic nitrosimines

A series of substituted 2-nitrosiminobenzothiazolines (2) were synthesized by the nitrosation of the corresponding 2-iminobenzothiazolines (6). Thermal decomposition of 2a--f and of the seleno analogue 7 in methanol and of 3-methyl-2-nitrosobenzothiazoline (2a) in acetonitrile, 1,4-dioxane, and cyclohexane followed first-order kinetics. The activation parameters for thermal deazetization of 2a were measured in cyclohexane (Delta H(++) = 25.3 +/- 0.5 kcal/mol, Delta S(++) = 1.3 +/- 1.5 eu) and in methanol (Delta H(++) = 22.5 +/- 0.7 kcal/mol, Delta S(++) = -12.9 +/- 2.1 eu). These results indicate a unimolecular decomposition and are consistent with a proposed stepwise mechanism involving cyclization of the nitrosimine followed by loss of N(2). The ground-state conformations of the parent nitrosiminothiazoline (9a) and transition states for rotation around the exocyclic C==N bond, electrocyclic ring closure, and loss of N(2) were calculated using ab initio molecular orbital theory at the MP2/6-31G* level. The calculated gas-phase barrier height for the loss of N(2) from 9a (25.2 kcal/mol, MP4(SDQ, FC)/6-31G*//MP2/6-31G* + ZPE) compares favorably with the experimental barrier for 2a of 25.3 kcal/mol in cyclohexane. The potential energy surface is unusual; the rotational transition state 9a-rot-ts connects directly to the orthogonal transition state for ring-closure 9aTS. The decoupling of rotational and pseudopericyclic bond-forming transition states is contrasted with the single pericyclic transition state (15TS) for the electrocyclic ring-opening of oxetene (15) to acrolein (16). For comparison, the calculated homolytic strength of the N--NO bond is 40.0 kcal/mol (MP4(SDQ, FC)/6-31G*//MP2/6-31G* + ZPE).     

Experimental and theoretical studies of the dimerizations of imidoylketenes

Reaction conditions are presented that, for the first time, allow the generation and dimerization of N-alkylimidoylketenes, e.g.,1d, while avoiding the intramolecular rearrangements observed under conventional conditions. The dimer of 1d (22a) is the result of [4 + 2] cycloaddition across the C=C bond of one ketene. In contrast, the N-H imidoylketene 1c dimerizes across the C=O bond to form 24b. Furthermore, N-methylbenzoimidoylketene (5b), in equilibrium with the more stable benzoazetidinone 14b, gives the formal [4 + 4] dimer 8b. B3LYP/6-31G(d) transition structure calculations on these three modes of dimerization reproduce and offer explanations for these divergent regiochemistries. Both [4 + 2] dimerizations have planar, pseudopericyclic transition structures (25a and 29b). Five transition structures were found for the formation of 8b. A unique pseudopericyclic dimerization of 5b with an orthogonal [4 + 4] geometry (31) has a barrier of only 0.7 kcal/mol. However, the overall lowest energy pathway involves concerted addition of 5b across a sigma bond in 14b via 35.     

Studies on arugomycin,a new anthracycline antibiotic part II. structural elucidation of arugomycin

The total structure of arugomycin has been determined as shown in Fig. 1 based on spectroscopic data and chemical degradation.     

Synthetic studies of the antitumor antibiotic streptonigrin. I. Synthesis of the A-B ring portion of streptonigrin

Bromination of 6-methoxy-5,8-quinolinedione gave the 7-bromo derivative in quantitative yield. Treatment of the bromo compound with sodium azide followed by hydrogenation yielded 7-amino-6-methoxy-5,8-quinolinedione, the A-B ring portion of the antitumor antibiotic strep tonigrin. The corresponding 2-methyl homolog was prepared in a similar manner from 6-methoxy-2-methyl-8-nitroquinoline, which in turn, was obtained by a Skraup synthesis from 2-nitro-anisidine and crotonaldehyde.     

Synthetic studies of the antitumor antibiotic streptonigrin. II. Synthesis of the C-D ring portion of streptonigrin

Partial mclhylalion of gallopropiophenonc ( 4 ) followed by benzylation and base-catalyzed condensation with ethyl acetate yielded 3-(2-benzyloxy-3,4-din]etlK>xy)benzoyl-2-butanonc ( 6 ). Animation of the latter and subsequent base-catalyzed cyclization with ethyl cyanoacetate gave 4-(2-benzyloxy-3,4-dimethoxy)phenyl-5,6-dimethyl-2-oxo-1,2-dihydropyridine ( 8 ). Removal of the 2-oxo group of 8 through chlorination and dechlorination and stepwise conversion of the 5-cyano and 2-methyl groups into the 5-amino and 2-carboxylic acid groups, respectively, with introduction and removal of protecting groups at proper stages, yielded the C-D ring moiety of the antitumor antibiotic streptonigrin.     

杂氮硼三环类化合物的UPS及化学键的理论研究

报道了六种杂氮硼三环类化合物的紫外光电子能谱(UPS).采用RHF/3-21G优化了各分子的优势构型,根据化合物UPS的谱带特征结合RHF/6-31G^*的计算结果对化合物的UPS进行了解析和指认,精确给出了各化合物中σN-B配键电子的电离峰位置.利用电子密度拓扑分析方法对各化合物的成键情况的研究显示:在该类化合物中B原子具有较为明显的阳离子的特征,N,B原子间均存在键鞍点.从实验和理论上证实了该类体系中σN-B的存在.各化合物的UPS,SCFMO计算和电子密度拓扑分析都表明,在该类体系中环上CH~3,CH~2的引入削弱了B,N间的成键作用;环上羰基的引入增强了B,N间的成键作用。     

Experimental and theoretical studies on the conjugation of the phosphorus-carbon double bond with a cyclopropyl group

X-ray structural analysis for (Z)-2-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaethene (2) was performed to confirm that the cyclopropyl group largely interacts with the P[double bond]C group compared with its carbon analogue, vinylcyclopropane (1). Absorption spectrum and redox properties of 2 were also studied to prove the conjugation. Theoretical investigation for nonsubstituted derivatives (4) indicated conjugative interaction between the P[double bond]C and cyclopropyl groups and revealed the physicochemical similarities between the P=C and C[double bond]C.     

Experimental and theoretical study on the kinetics and mechanism of thermal decomposition of 1,2-dichloroethane

The kinetics and mechanism for the thermal decomposition of 1,2-dichloroethane (EDC) was studied in a flow system over the temperature range of 849–1064 K and pressure range of 10–300 Torr under homogeneous conditions in a tubular quartz reactor. Gas chromatography was used to measure the concentration of products. Four-center HCl elimination was found to be the most important channel in this system. Minor products such as methane, ethylene, acetylene, chloroethane, and chloroprene were identified. Ab initio calculations at the DFT, CASMP2, and QCISD(T) levels of theory were carried out to investigate the mechanism of this system and to calculate necessary parameters to compute the rate constants of different steps. Dependence of formation of vinyl chloride on the total pressure is measured, experimentally.     

Microthermogravimetric studies of the kinetics and thermodynamics of heterogeneous reactions in sulfur-containing atmospheres

A thermobalance for studies of the high-temperature sulfidation of metals and alloys is described. This apparatus permits the determination of mass changes in the sulfidized sample as functions of temperature and sulfur vapour pressure with an accuracy of 10^–6 g. Besides heterogeneous kinetics measurements, it has been shown that the chemical diffusion coefficients and deviations from stoichiometry of metal sulfides can also be studied as functions of temperature and sulfur pressure by means of equilibration measurements.

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Zusammenfassung Es wird eine Thermowaage zur Untersuchung der Hochtemperatur-Sulfidierung von Metallen und Legierungen beschrieben. Diese Apparatur ermöglicht die Bestimmung von MassenverÄnderungen der sulfidierten Proben in AbhÄngigkeit von der Temperatur und dem Schwefeldampfdruck mit einer Genauigkeit von 10^–6 g. Es wird gezeigt, da\ damit, sofern Gleichgewichtsmessungen ausgeführt werden, auch die chemischen Diffusionskoeffizienten und Abweichungen der Metallsulfide von der Stöchiometrie in AbhÄngigkeit von der Temperatur und dem Schwefeldampfdruck untersucht werden können.

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Experimental and theoretical studies of a silver complex of O-functionalized N-heterocyclic carbene

Experimental and theoretical studies of a silver complex namely, [1-i-propyl-3-(2-oxo-2-t-butyl ethyl)imidazol-2-ylidene]AgCl (1b), supported over an O-functionalized N-heterocyclic carbene ligand are reported. Specifically, [1-i-propyl-3-(2-oxo-2-t-butyl ethyl)imidazol-2-ylidene]AgCl (1b) was synthesized by reaction of 1-i-propyl-3-(2-oxo-2-t-butyl ethyl)imidazolium chloride 1a with Ag₂O in 42% yield. The 1-i-propyl-3-(2-oxo-2-t-butyl ethyl)imidazolium chloride 1a was synthesized by the alkylation reaction of 1-i-propylimidazole with α-chloropinacolone in 70% yield. The molecular structures of 1a and 1b have been determined by X-ray diffraction. Detailed theoretical investigation has been performed using the density functional theory method with the B3LYP functional. Bonding in 1b has been probed with the help of charge decomposition analysis (CDA), atoms in molecule (AIM) approach as well as natural bond orbital (NBO) methods. The Ag-NHC bond has a dominantly covalent character with NHC acting as an effective σ-donor. The π-back-bonding from the metal to the ligand was found to be negligible.     

Experimental and theoretical studies on the Nazarov cyclization/Wagner-Meerwein rearrangement sequence

Highly functionalized cyclopentenones can be generated by a chemoselective copper(II)-mediated Nazarov/Wagner-Meerwein rearrangement sequence of divinyl ketones. A detailed investigation of this sequence is described including a study of substrate scope and limitations. After the initial 4π electrocyclization, this reaction proceeds via two different sequential [1,2]-shifts, with selectivity that depends upon either migratory ability or the steric bulkiness of the substituents at C1 and C5. This methodology allows the creation of vicinal stereogenic centers, including adjacent quaternary centers. This sequence can also be achieved by using a catalytic amount of copper(II) in combination with NaBAr(4)(f), a weak Lewis acid. During the study of the scope of the reaction, a partial or complete E/Z isomerization of the enone moiety was observed in some cases prior to the cyclization, which resulted in a mixture of diastereomeric products. Use of a Cu(II)-bisoxazoline complex prevented the isomerization, allowing high diastereoselectivity to be obtained in all substrate types. In addition, the reaction sequence was studied by DFT computations at the UB3LYP/6-31G(d,p) level, which are consistent with the proposed sequences observed, including E/Z isomerizations and chemoselective Wagner-Meerwein shifts.