Ultraviolet absorption and vibrational spectra of 2-fluoro-5-bromopyridine

The ultraviolet absorption spectrum in the range 340-185 nm in the vapour and solution phase has been measured for 2-fluoro-5-bromopyridine. Three fairly intense band systems identified as the pi* <-- pi transitions II, III and IV have been observed. A detailed vibronic analysis of the vapor and solution spectra is presented. The first system of bands is resolved into about sixty-two distinct vibronic bands in the vapour-phase spectrum. The 0,0 band is located at 35944 cm(-1). Two well-developed progressions, in which the excited state frequencies nu'25 (283 cm(-1)) and nu'19 (550 cm(-1)) are excited by several quanta, have been observed. The corresponding excited state vibrational and anharmonicity constants are found to be omega'i = 292 cm(-1), x'ii = 4.5 cm(-1) (i = 25) and omega'i = 563.8 cm(-1), x'ii = 6.9 cm(-1) (i = 19). The other two band systems show no vibronic structure, the band maxima being located at 48346 and 52701 cm(-1), respectively. The oscillator strength of the band systems in different solutions and the excited state dipole moments associated with the first two transitions have been determined by the solvent-shift method. The infrared spectrum in the region 4000-130 cm(-1) and the laser Raman spectrum of the molecule in the liquid state have been measured and a complete vibrational assignment of the observed frequencies is given. A correlation of the ground and excited state fundamental frequencies observed in the UV absorption spectrum with the Raman or infrared frequencies is presented.     

Parallel bundle-based decomposition for large-scale structured mathematical programming problems

In this paper, we present parallel bundle-based decomposition algorithms to solve a class of structured large-scale convex optimization problems. An example in this class of problems is the block-angular linear programming problem. By dualizing, we transform the original problem to an unconstrained nonsmooth concave optimization problem which is in turn solved by using a modified bundle method. Further, this dual problem consists of a collection of smaller independent subproblems which give rise to the parallel algorithms. We discuss the implementation on the CRYSTAL multi-computer. Finally, we present computational experience with block-angular linear programming problems and observe that more than 70% efficiency can be obtained using up to eleven processors for one group of test problems, and more than 60% efficiency can be obtained for relatively smaller problems using up to five processors for another group of problems.     

Bundle-based decomposition for large-scale convex optimization: Error estimate and application to block-angular linear programs

Robinson has proposed the bundle-based decomposition algorithm to solve a class of structured large-scale convex optimization problems. In this method, the original problem is transformed (by dualization) to an unconstrained nonsmooth concave optimization problem which is in turn solved by using a modified bundle method. In this paper, we give a posteriori error estimates on the approximate primal optimal solution and on the duality gap. We describe implementation and present computational experience with a special case of this class of problems, namely, block-angular linear programming problems. We observe that the method is efficient in obtaining the approximate optimal solution and compares favorably with MINOS and an advanced implementation of the Dantzig—Wolfe decomposition method.     

Handling of intrinsic divergence in the orthogonal gradient method of orbital optimization in an MC-SCF framework and geometry optimization in pathological cases: I (propynal in excited states)

It is demonstrated that a generalized version of the orthogonal gradient method of orbital optimization may sometimes encounter a specific divergence problem which may be termed intrinsic to the first order method. Instead of switching over to a more sophisticated second order method one can cure the divergence problem at the first order level itself by suitably tailoring the MC-SCF operator or the MC-SCF energy matrix. Results of complete geometry optimization of propynal in^l,3nπ* and³ππ* states (pathological cases) are reported to demonstrate the usefulness of the method at an INDO-MCSCF level of approximation. The results of structure calculations are further rationalized from generalized quantum chemical bond order indices.     

A Kinetic Dearomatization Strategy for an Expedient Biomimetic Route to the Bielschowskysin Skeleton

Bielschowskysin ( 1 ), the flagship of the furanocembranoid diterpene family, has attracted attention from chemists owing to its intriguing and daunting polycyclic architecture and medicinal potential against lung cancer. The high level of functionalization of 1 poses a considerable challenge to synthesis. Herein, a stereoselective furan dearomatization strategy of furanocembranoids was achieved via the intermediacy of chlorohydrins. The stereochemical course of the kinetic dearomatization was established, and the C3 configuration of the resulting exo‐enol ether intermediates proved to be essential to complete the late‐stage transannular [2+2] photocycloaddition. Overall, this biomimetic strategy starting from the natural product acerosolide ( 9 ) featured an unprecedented regio‐ and highly stereoselective furan dearomatization, which provided rapid access to the pivotal exo‐enol ethers en route to the intricate bielschowskyane skeleton.     

Perturbing π-clouds with Substituents to Study the Effects on Reaction Dynamics of gauche-1,3-Butadiene to Bicyclobutane Electrocyclization

The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (−F) and donating (−CH₃) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multi-reference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and non-adiabatic dynamics suggest that the −CH₃ substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to −F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with −F or −CH₃, the conversion proceeds via the conrotatory pathway.     

Influence of oxidative injury and monitoring of blood plasma by DSC on breast cancer patients

Damage caused by oxidative stress is involved in many types of diseases, including breast cancer. Our aim was to detect the oxidative stress parameters and blood plasma changes with differential scanning calorimetry (DSC) in breast cancer patients. The study included 40 adult breast cancer women who were grouped according to tumor diameter, regional lymph node metastases, proliferative activity, receptor status and postoperative chemotherapy. To monitor oxidative stress, malondialdehyde, oxygen free radicals (OFRs), activity of myeloperoxidase (MPO), superoxide dismutase (SOD) and catalase (CAT) were measured. Denaturation of plasma components was detected in Setaram Micro DSC-II calorimeter. The total production of OFRs, the MPO activity and lipidperoxidation were significantly increased in each breast cancer patients considering the tumor size, the metastatic lymph nodes, the proliferation activity and receptor status compared with healthy controls (p < 0.05). These pro-oxidants were slightly elevated without chemotherapy, but their values were increased significantly in chemotherapy-receiving group. The activity of SOD and CAT was significantly decreased in all groups, and in regard to the chemotherapy, they were changed significantly parallel to the severity of disease. Regarding to both the increased tumor diameter and the increased number of affected lymph nodes, DSC measurements showed a strong relationship between the maximum excess heat capacity (C_pmax) of the blood plasma and the severity of disease. The study demonstrated that oxidative stress is implicated in breast carcinoma and chemotherapy aggravates these changes which confirmed the plasma DSC measurements also.     

Basicities of some 9-substituted acridine-4-carboxamides: A density functional theory (DFT) calculation

Acid-base properties of drugs are important in understanding the behaviour of these compounds under physiological condition. In order to understand such behaviour the proton affinities of acri-dine 4-carboxamides with substitution (R) at the 9-position are theoretically studied, and considered for the basic sites of both the heterocyclic ring as well as side chain nitrogens. In 9-amino acridine 4-carbox-amide, the -NH₂ group is observed to be an additional basic site. The heterocyclic nitrogen of substituted carboxamides (R =-NH₂, -O-methyl, -O-ethyl, and -O-phenyl) is more basic than the side chain nitrogen, however, side chain nitrogen corresponds to more basic site for some carboxamides (R = -OH and-Cl) and the -NH₂ group represents the least basic site of 9-amino acridine 4-carboxamide. In addition to presenting the basicities of these drugs an indication of another hydrogen-bond between heterocyclic ring N and carboxamide chain O is observed. The difference of basicities with substituents at 9-position are very narrow and carboxamides with substituents at 9-position are found to be suitable for studying intramolecular H-bonds between the heterocyclic N and carboxamide O. The resultant stabilization of a configuration due to such H-bonding is determined     

Infrared and Raman spectra and thermodynamic functions of 4-methoxypyridine N-oxide

The infrared spectrum of 4-methoxypyridine N-oxide in the region 4000-30 cm⁻¹ in the solid and liquid states and the polarized laser Raman spectrum of the molecule in the liquid state have been investigated. A vibrational assignment of the observed frequencies based on the state of polarization of the Raman lines and comparison with the related molecules is presented. Ideal gas state thermodynamic functions of the molecule are calculated in the temperature range 273·15–1500° K.