Some INDO calculations of fluorine-nitrogen spin–spin coupling constants

INDO parameterized calculations of ⁿJ(¹⁹F¹⁵N) are reported where n=1, 2, 3, 4 and 5. The calculations are performed within the sum-over-states perturbation and self-consistent perturbation frameworks. In general, satisfactory agreement between both sets of calculated results and the available experimental data is obtained. All of the ¹ J(¹⁹F¹⁵N) and ⁴J(¹⁹F¹⁵N) couplings can be of either sign. Most of the couplings considered are dominated by the contact contribution but the non-contact interactions can be very important in certain cases.     

Characterization of the Binding of Metoprolol Tartrate and Guaifenesin Drugs to Human Serum Albumin and Human Hemoglobin Proteins by Fluorescence and Circular Dichroism Spectroscopy

The interactions of metoprolol tartrate (MPT) and guaifenesin (GF) drugs with human serum albumin (HSA) and human hemoglobin (HMG) proteins at pH?7.4 were studied by fluorescence and circular dichroism (CD) spectroscopy. Drugs quenched the fluorescence spectra of HSA and HMG proteins through a static quenching mechanism. For each protein-drug system, the values of Stern-Volmer quenching constant, bimolecular quenching constant, binding constant and number of binding site on the protein molecules were determined at 288.15, 298.15, 310.15 and 318.15 K. It was found that the binding constants of HSA-MPT and HSA-GF systems were smaller than those of HMG-MPT and HMG-GF systems. For both drugs, the affinity of HMG was much higher than that of HSA. An increase in temperature caused a negative effect on the binding reactions. The number of binding site on blood proteins for MPT and GF drugs was approximately one. Thermodynamic parameters showed that MPT interacted with HSA through electrostatic attraction forces. However, hydrogen bonds and van der Waals forces were the main interaction forces in the formation of HSA-GF, HMG-MPT and HMG-GF complexes. The binding processes between protein and drug molecules were exothermic and spontaneous owing to negative ?H and ?G values, respectively. The values of binding distance between protein and drug molecules were calculated from Förster resonance energy transfer theory. It was found from CD analysis that the bindings of MPT and GF drugs to HSA and HMG proteins altered the secondary structure of HSA and HMG proteins.     

Some self-consistent perturbation calculations of 1J(CC)

Self-consistent perturbation calculations of 70 ¹J(CC) values are reported within the INDO framework. A least-squares agreement between the calculated and observed couplings, for a variety of bond multiplicities, provides values of 13.503 au^?6 and 5.072 au^?6 for (S_C²(O))² and 〈r^?3〉_C², respectively. The non-contact terms are found to be important in cases of multiple bonding.     

Some self-consistent perturbation calculations of 15N?13C coupling constants

Self-consistent perturbation calculations within the INDO framework are reported for 63 ¹⁵N? ¹³C coupling constants. Examples are presented for which each of the contact, orbital and dipolar terms provides the dominant contribution to the observed coupling constant. In general, good agreement with the experimental data is obtained when the integral products S_N²(O)S_C²(O) and 〈r^?3〉_N〈r^?3〉_C take the values 14.480 au^?6 and 2.446 au^?6 for ¹J(¹⁵N? ¹³C), and the corresponding values of 10.444 au^?6 and 17.664 au^?6 for ¹J(¹⁵N?¹³C). All 19 of the ¹J(¹⁵N?¹³C) couplings considered are predicted to have a negative sign.     

Some Fundamental Properties of Successive Convex Relaxation Methods on LCP and Related Problems

General successive convex relaxation methods (SRCMs) can be used to compute the convex hull of any compact set, in an Euclidean space, described by a system of quadratic inequalities and a compact convex set. Linear complementarity problems (LCPs) make an interesting and rich class of structured nonconvex optimization problems. In this paper, we study a few of the specialized lift-and-project methods and some of the possible ways of applying the general SCRMs to LCPs and related problems.     

Evaluation of pressure levels in pipelines due to solar heat gains

A detailed numerical model based on a lumped capacity analysis, is developed for assessing potential pressure increases in pipelines due to solar energy gains. Test computations for gasoline and water show that for operational conditions of no pipeline flow, pressures reach levels for which structural damage may occur.     

The structure of ethyl allyl 1,4-dihydro-2,6-dimethyl-4-[4-(4H-4-oxo-1-benzopyran-2-yl)phenyl]-3,5-pyridine dicarboxylate

The crystal and molecular structure of the title compound has been determined by direct methods, and refined to a finalR of 0.070 for 1466 observed reflections. The compound crystallizes in space group P2_l/n with cell dimensionsa=10.706(8),b=21.127(11),c=12.038(10) Å, Z=4.1,4-dihydropyridine ring adopts a boat shaped conformation. The flavon molecule is planar and it's phenyl ring is almost perpendicular to the 1,4-DHP. The C36 atom of the allyl group shows disorder.     

From Open‐Shell Singlet Diradicaloid to Closed‐Shell Global Antiaromatic Macrocycles

A dithieno[a,h]‐s‐indacene‐ (DTI‐) based diradicaloid DTI‐2Br was synthesized and its open‐shell singlet diradical character was validated by magnetic measurements. On the other hand, its macrocyclic trimer DTI‐MC3 and tetramer DTI‐MC4 turned out to be closed‐shell compounds with global antiaromaticity, which was supported by X‐ray crystallographic analysis and NMR spectroscopy, assisted by ACID and 2D‐ICSS calculations. Such change can be explained by a subtle balance between two types of antiferromagnetic spin–spin coupling along the π‐conjugated macrocycles. The dications of DTI‐MC3 and DTI‐MC4 turned out to be open‐shell singlet diradical dications, with a singlet–triplet energy gap of ?2.90 and ?2.60 kcal mol^?1, respectively. At the same time, they are both global aromatic. Our studies show that intramolecular spin–spin interactions play important roles on electronic properties of π‐conjugated macrocycles.     

Effects of cosolvents cetyltrimethylammonium bromide on the thresholds for nucleation of nitrogen in aqueous solutions

The decomposition of ammonium nitrite in water creates a supersaturated solution of nitrogen. The same process occurs in water-organic solvent mixtures. Acetone, dioxane, dimethylsulfoxide (DMSO) and dimethylformamide (DMF) are the cosolvents used in this study. The limits of supersaturation of nitrogen (C _SL /mol L^–1) were determined in all of these solvent mixtures by releasing the dissolved gas sonicationally and measuring the volume of released gas. C _SL was generally increased in the presence of cosolvents. The effectiveness sequence of organic solvents was found to be as DMF SL and all of the measured quantities of this study were generally affected by micelle formation.