A theoretical investigation of the excited states of OCLO radical, cation, and anion using the CASSCF/CASPT2 method

Using the complete active space self-consistent field method with a large atomic natural orbital basis set, 10, 13, and 9 electronic states of the OClO radical, OClO(+) cation, and OClO(-) anion were calculated, respectively. Taking the further correlation effects into account, the second-order perturbation (CASPT2) calculations were carried out for the energetic calibration. The photoelectron spectroscopy of the OClO radical and OClO(-) anion were extensively studied in the both case of the adiabatic and vertical ionization energies. The calculated results presented the relatively complete assignment of the photoelectron bands of the experiments for OClO and its anion. Furthermore, the Rydberg states of the OClO radical were investigated by using multiconfigurational CASPT2 (MS-CASPT2) theory under the basis set of large atomic natural orbital functions augmented with an adapted 1s1p1d Rydberg functions that have specially been built for this study. Sixteen Rydberg states were obtained and the results were consistent with the experimental results.     

A CASSCF/CASPT2 study on the low‐lying electronic states of the CH3SS and its cation

Complete active space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) calculations with contracted ANO‐RCC basis set were performed for low‐lying electronic states of CH₃SS and its cation in C_s symmetry. For the ground state X²A″ of CH₃SS, the calculated S‐S stretching mode is in good agreement with experimental reports. The electron transitions of CH₃SS⁺, X¹A′ → 1¹A″, X¹A′ → 2¹A′, and X¹A′ → 2¹A″, are predicted at 1.055, 3.247, and 3.841 eV. Moreover, the calculated adiabatic and vertical ionization potential and adiabatic affinity are in reasonable agreement with the experimental data. The CASSCF/CASPT2 potential energy curves (PECs) were calculated for S₂‐loss dissociation from the X²A″, 1²A′, and 2²A″ states. The electronic states of the CH₃ radical and S₂ molecule as the dissociation products were carefully determined by checking energies and geometries of the asymptote products. The S₂‐loss PEC for CH₃SS indicate that S₂‐loss dissociation occurs from the X²A″ state leading to CH₃ (1²A″) + S₂ (X³Σ), the 1²A′ and 2²A″ leading to CH₃ (1²A″) + S₂ (¹Δ_g). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012.     

Theoretical treatment of first-order reversible reactions occurring in a chromatographic reactor, on the basis of consecutive reactions

Summary Analytical peak-shape equations were derived for first-order reversible reactions occurring in a chromatographic reactor by treating the reversible reactions as consecutive reactions with alternating products. The results of the analytical peak-shape equations were compared with those from a numerical solution of the partial differential equation system modeling the chromatographic reactor. For small to medium conversions the correspondence was found to be sufficiently close to enable substitution of the numerical solution in fitting procedures for the determination of rate constants. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

A CASSCF study on the lowest π→π* excitation of urocanic acid

The photochemical cis/trans isomerization of urocanic acid (UCA, (E)‐3‐(1′H‐imidazol‐4′‐yl)propenoic acid) was investigated using complete active space SCF (CASSCF) ab initio calculations. The singlet ground state and the triplet and the singlet manifolds of the lowest‐lying π→π* (HOMO→LUMO) excitation of the neutral and the anionic UCA were calculated using the 6‐31G* and the 6‐31+G* basis sets, respectively. The torsional barrier of the double bond of the propenoic acid moiety in UCA is observed to be considerably lower in the T₁ and S₁ excited states of the neutral UCA and in the T₁ but not in the S₁ excited state of the anionic UCA, as compared to the S₀ state of the respective protonation form. The cis‐isomer of both the neutral and the anionic UCA is lower in energy than the trans‐isomer in the S₀, T₁, and S₁ states. This energy difference is larger in the excited states than in the ground state, probably due to strengthening of the intramolecular hydrogen bond of cis‐UCA as the molecule is excited. The results of the calculations, interpreted in terms of the idea that UCA is deprotonated upon electronic excitation, led to construction of a new model for the photoisomerization mechanisms of UCA. According to this model, the trans‐to‐cis isomerization proceeds via both the triplet and the singlet manifolds in the deprotonated form of UCA. This isomerization may occur in the S₀ state of the neutral UCA as well. The cis‐to‐trans isomerization is suggested to proceed only in the S₀ state of the neutral UCA. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 25–37, 1999     

An efficient method for recovery of target ssDNA based on amino-modified silica-coated magnetic nanoparticles

In this paper, an improved recovery method for target ssDNA using amino-modified silica-coated magnetic nanoparticles (ASMNPs) is reported. This method takes advantages of the amino-modified silica-coated magnetic nanoparticles prepared using water-in-oil microemulsion technique, which employs amino-modified silica as the shell and iron oxide as the core of the magnetic nanoparticles. The nanoparticles have a silica surface with amino groups and can be conjugated with any desired bio-molecules through many existing amino group chemistry. In this research, a linear DNA probe was immobilized onto nanoparticles through streptavidin conjugation using covalent bonds. A target ssDNA(I) (5′-TMR-CGCATAGGGCCTCGTGATAC-3′) has been successfully recovered from a crude sample under a magnet field through their special recognition and hybridization. A designed ssDNA fragment of severe acute respiratory syndrome (SARS) virus at a much lower concentration than the target ssDNA(I) was also recovered with high efficiency and good selectivity.     

Validation of an analytical method to determine sulfamides in kidney by HPLC-DAD and PARAFAC2 with first-order derivative chromatograms

Six sulfamides were extracted from kidney and analysed by high-performance liquid chromatography with diode array detection (HPLC-DAD): sulfadiazine, sulfamethazine, sulfamethoxypyridazine, sulfamethoxazole, sulfadimethoxine and sulfaquinoxaline.Two main difficulties arose in identifying and quantifying the analytes. Firstly, the chromatographic peaks of the matrix interferences overlapped with those of the analytes. The uniqueness property of PARAFAC2 solved this problem. Secondly, the gradient elution caused a baseline drift. The first-order derivative of the chromatograms minimized its effect.The analytical method was validated. As the performance criteria detailed in the European Decision 2002/657/EC are based on specific signals, this paper generalizes those criteria for higher-order and non-specific signals. In this sense the proposed methodology is general and can be applied to any chromatographic method (HPLC or GC) with a detector that provide a multivariate signal (MS, DAD, EC, etc.).     

An efficient method for the synthesis of lignans

An efficient approach for the synthesis of several types of lignans (dibenzylbutanediols, dibenzylbutanes, substituted tetrahydrofurans, aryldihydronaphthalenes, arylnaphthalenes, and aryltetralins) was developed. The regioselective oxidative coupling of ethyl ferulate was used as the key step.     

An efficient method for the synthesis of gem-difluoroolefins

A series of gem-difluoroolefin derivatives were synthesized in moderate to good yields by the reaction of α,α-difluoro-β-carbonyl benzothiazol-2-yl sulfones (DFBTs) with various carbon nucleophiles. Using dl-proline as organocatalyst, the reaction of DFBT with acetone gave a tertiary alcohol, which could be further converted to the corresponding difluoroolefin by LDA.     

An efficient synthesis of chalcones based on the Suzuki reaction

A general method for the synthesis of chalcones based on the Suzuki reaction either between cinnamoyl chlorides and phenylboronic acids or between benzoyl chlorides and phenylvinylboronic acids is described.     

Use of a highly efficient and recyclable solid-phase catalyst based on nanocrystalline titania for the Pechmann condensation

Nanocrystalline titania-based sulfonic acid was used as an efficient and reusable catalyst for the synthesis of coumarins. The clean, mild acidity condition, the quantitative yields of products, the short reaction time, and the low reaction temperature are attractive features of this method, making it suitable for heat- or acid-sensitive substrates, particularly in drug synthesis. In practice, this method affords an advantageous combination of satisfactory yields, easy product isolation and purification.     

An efficient method for the synthesis of 1-chlorophenazines based on the selective cathodic reduction of 3,3,6,6-tetrachloro-1,2-cyclohexanedione

An efficient method for the synthesis of 1-chlorophenazines has been established. It is based on the use of 3,6,6-trichloro-2-hydroxy-2-cyclohexen-1-one 4 as a synthetic equivalent of 3-chloro-1,2-benzoquinone 3. The intermediate 4 was prepared in near quantitative yield by electroreductive monodechlorination of 3,3,6,6-tetrachloro-1,2-cyclohexanedione 1, which is an inexpensive and easily available starting material. Efficient reactions of 4 with primary 1,2-phenylenediamines provided the corresponding 1,1,4-trichloro-1,2,3,4-tetrahydrophenazines 6, which were directly aromatized by treatment with 2,6-lutidine to give the title compounds in high yields. X-ray crystallographic structures for 1,1,4-trichloro-1,2,3,4-tetrahydro-6-methylphenazine 6f, 8-benzoyl-1,1,4-trichloro-1,2,3,4-tetrahydro-phenazine 6ea, and 1,7-dichlorophenazine 10db have been determined.     

Electric properties of the water molecule in 1A1, 1B1, and 3B1 electronic states: Refined CASSCF and CASPT2 calculations

Summary The dipole moments and dipole polarizabilities of the ¹A₁, ¹B₁, and ³B₁ electronic states of the water molecule have been calculated by using the CASSCF approach followed by the evaluation of the dynamic electron correlation contribution by the second-order perturbation scheme CASPT2. All calculations have been carried out in a specifically extended ANO basis set which accounts for the Rydberg character of the two excited states. In order to estimate the correctness and accuracy of the present data a scan over a variety of different active spaces for the CASSCF wave function has been made. The present results are superior to earlier CASSCF calculations, although their qualitative features remain essentially the same. The dipole moments in ¹B₁ and ³B₁ states are predicted to be about 0.49 a.u. and 0.33 a.u., respectively, and have the opposite orientation with respect to the ground state dipole moment. The dipole polarizability tensors of the excited states are characterized by high anisotropy and are dominated by the in-plane component perpendicular to the symmetry axis. All their components are found to be about an order of magnitude larger than those of the ground state polarizability tensor. The excitation energy dependence on the choice of the active orbital space in the CASSCF reference function is also considered and the analysis of the present data concludes in the concept of what is called the mutually compatible active spaces for the two states involved in excitation. All CASPT2 results are in good agreement with the results of recent calculations carried out in the framework of the open-shell coupled cluster formalism. This agreement confirms the high efficiency of the CASSCF/CASPT2 approach to the treatment of the electron correlation effects.     

An efficient peptide ligation using azido-protected peptides via the thioester method

Azido-protected Fmoc-Lys-OH (Fmoc-Lys(N₃)-OH) was synthesized from Fmoc-Lys-OH by the copper(II)-catalyzed diazo transfer method, and introduced to a peptide by the ordinary Fmoc-based solid-phase peptide synthesis. This azido peptide could be condensed with a peptide thioester by the Ag⁺-free thioester method without any significant side reactions. The azido group was easily reduced to an amino group by Zn powder after peptide condensation.     

An efficient method based on indoles for the synthesis of isatins by taking advantage of I2O5 as oxidant

An efficient method to synthesize isatins based on indoles by using inorganic hypervalent I₂O₅ has been explored in good yields, which successfully realized the transformation from indoles to isatins under metal-free, mild condition with broad substrate scope.     

An efficient data compression method for the Davidson subspace diagonalization scheme

Summary A flexible and efficient compression scheme for the expansion and product vectors Hamiltonian matrix times expansion vectors is presented within the Davidson diagonalization method. Our approach is based on an error analysis of the energy in terms of the aforementioned vectors and on a compression scheme for representing floating point numbers with a variable length mantissa. For a selection of typical quantum chemical test cases total saving factors of up to ten are reported. The method is expected to work especially well for extended multi-reference CI and full CI cases. As a general outcome of our analysis we obtain limits of possible sizes of a CI expansion within the Davidson procedure in relation to the energy and the desired accuracy of the energy assuming the usual IEEE floating point standard.     

An efficient method for computing the QTAIM topology of a scalar field: The electron density case

An efficient method for computing the quantum theory of atoms in molecules (QTAIM) topology of the electron density (or other scalar field) is presented. A modified Newton–Raphson algorithm was implemented for finding the critical points (CP) of the electron density. Bond paths were constructed with the second‐order Runge–Kutta method. Vectorization of the present algorithm makes it to scale linearly with the system size. The parallel efficiency decreases with the number of processors (from 70% to 50%) with an average of 54%. The accuracy and performance of the method are demonstrated by computing the QTAIM topology of the electron density of a series of representative molecules. Our results show that our algorithm might allow to apply QTAIM analysis to large systems (carbon nanotubes, polymers, fullerenes) considered unreachable until now. © 2012 Wiley Periodicals, Inc.     

An efficient green procedure for the synthesis of chalcones using C-200 as solid support under grinding conditions

Abstract

A simple, rapid, efficient and environmentally benign procedure for the synthesis of chalcones has been achieved by grinding aryl aldehydes and acetophenones with anhydrous barium hydroxide (C-200) in the absence of any solvent. The use of organic solvent for extraction of compound is also avoided. This present method is highly useful for the synthesis of 2′-hydroxy chalcones, required intermediates for the synthesis of flavanoids.