Determination of Vapor Pressures Using Extrapolation of Adjusted Retention Times

Vapor pressure is one of the fundamental properties which govern the distribution of organic compounds in the environment. This property is estimated for five series of homologous substituted alkanes of the type H—(CH₂)_n—Y, where Y denotes Cl, Br, CHO, COOCH₃, OCOCH₃ and n varies from 5 to 14 using extrapolation of adjusted retention times to 25 °C. The results are compared with those obtained by using indirect methods for 40 compounds and a significant improvement is obtained. Indeed, the absolute average error percentage for the same series does not exceed 2.6%     

Molecular docking/dynamic simulations,MEP, ADME-TOX-based analysis of xanthone derivatives as CHK1 inhibitors

Structural Chemistry - CHK1 is a promising molecular target that gained immense attention recently for the development of cancer therapeutics. In this study, a simulation-based investigation was...     

Green and sustainable carboxymethyl cellulose-chitosan composite hydrogels: Effect of crosslinker on microstructure

Cellulose - The toxicity level of conventional hydrogels is considerably high for most applications. To date, very few studies on hydrogels synthesized using only safe materials and simple,...     

A simple, sensitive, and rapid method for the determination of cotinine in urine by high-performance liquid chromatography with UV detection

Cotinine levels in biological fluids are a reliable indicator of the presence of nicotine. In this paper, a simple and sensitive high-performance liquid chromatography (HPLC) procedure for the determination of cotinine in urine following liquid-liquid extraction with dichloromethane in an alkaline medium is described. Calibration curves show linearity over the 50 to 3000 ng/mL range with low intra- and interday variability as well as good selectivity and specificity. No solid-phase extraction is performed because the liquid dichloromethane extraction step yields excellent results. This method is a good alternative for routine analysis of urinary cotinine in laboratories where gas chromatography or HPLC-mass spectrometry is not available.     

An efficient and novel numerical method for quasiconformal mappings of doubly connected domains

A numerical method for quasiconformal mapping of doubly connected domains onto annuli is presented. The ratio R of the radii of the annulus is not known a priori and is determined as part of the solution procedure. The numerical method presented in this paper requires solving iteratively a sequence of inhomogeneous Beltrami equations, each for a different R. R is updated using a procedure based on the bisection method. The new method is an extension of Daripas method for the quasiconformal mapping of the exterior of simply connected domains onto the interior of unit disks [15]. It uses fast and accurate algorithms for evaluating certain singular integrals and is, thus, very efficient and accurate. Its performance is demonstrated for several doubly connected domains.     

Vibrational study of hydrogen bonding and structural disorder in Na2H(SO4)2, K3H(SO4)2 and (NH4)3H(SO4)2 crystals

Infrared and Raman spectra on Na₃H(SO₄)₂, K₃ H(SO₄)₂ and (NH₄)₃ H(SO₄)₂ crystals have been investigated at 300 and 100 K in the 4000 to 30 cm⁻¹ region. An assignment of bands in terms of OH group frequencies and more or less distorted tetrahedra of ammonium and sulphate ions is given. The crystallographic and spectroscopic symmetry and/or dissymetry of OHO hydrogen bonds linking sulphate ions into dimers is discussed using OH group frequencies and the splitting of the v₁ (SO₄) Raman bands as criteria. In the particular case of (NH₄)₃H(SO₄)₁ compound containing several solid phases it can be shown that the room temperature phase (II) is strongly disordered, principally because of an orientational disorder of ammonium ions, and that a progressive ordering takes place with temperature lowering.     

Posttranslational hydroxylation of human phenylalanine hydroxylase is a novel example of enzyme self-repair within the second coordination sphere of catalytic iron

Phenylalanine hydroxylase, a mononuclear non-heme iron enzyme, catalyzes the hydroxylation of phenylalanine to tyrosine in the presence of oxygen and reduced pterin cofactor. X-ray structural studies have established the coordination around the iron metal center and point to significant interactions within the second coordination sphere. One such interaction involves Tyr325 in human phenylalanine hydroxylase (hPAH), which forms a hydrogen-bonding network with an aqua ligand on iron and the pterin cofactor. The full-length tetramer (1-452) and truncated dimer (117-424) Tyr325Phe hPAH mutant enzymes showed similar kinetics, thermal stabilities, and oligomerization profiles as their corresponding wild-type proteins. The possibility of in vivo posttranslational hydroxylation that would restore the activity of hPAH was examined by mass spectrometry on the trypsin digested full-length (1-452) hPAH Tyr325Phe point mutant. The amino acid tags obtained by ESI-MS/MS confirmed the presence of a Phe325 in the peptide corresponding to the doubly charged precursor ion at m/z 916.4 (L A T I F W F T V E F G L C K), and its hydroxylated counterpart in the peptide corresponding to the m/z 924.4 (L A T I F-OH W F T V E F G L C K) byproduct ion series comprising the fragments y(5)-y(12). Furthermore, the point mutation Tyr325Ala resulted in an enzyme that was totally inactive and did not display any evidence of hydroxylation. These results demonstrate the importance of Tyr325 for proper conformation of the active site, substrate binding, and catalysis. The rescue of the Tyr325Phe mutant in hPAH via self-hydroxylation presents a novel example of oxidative repair on the molecular level.     

1,2,3‐ and 1,2,4‐triazolium salts,pyrazoles, and quinoxalines from diarylnitrilimines and isocyanides: A study of the scope

Formation of the four title compounds has been found to be strongly dependent on substituents: 1,2,3‐Triazolium salts 6 do not arise from nitrilimines 2 that have an electron‐acceptor attached to either the C‐ or the N‐phenyl group. Likewise tert‐butyl and aryl isocyanides do not afford this class of compounds; from the former isocyanide, dequaternization products 7 are obtained instead, whereas from the latter 1,2,4‐triazolium salts 11 are formed. Compounds 11 with tert‐butyl group at the ring are unstable too, giving rise to triazoles 13 . Pyrazole formation (analogues of 14 ) is completely suppressed when both tert‐butyl and aryl isocyanides are used, whereas access to this ring system works best with see‐alkyl isocyanides (the influence of substituents of 2 being almost negligible in this case). Formation of quinoxalines 23 which arise from intermediary 1,2‐diazets 22 by ring expansion is much favoured on employment of 2 that bears a donator substituent at the N‐phenyl group, and under this premise ring closure to 22 is virtually independent on the nature of the isocyanide. Formation of 23 is not observed with 2 having acceptor groups.     

Synthesis, DTA, IR and Raman spectra of penthylenediammonium hexachlorostannate NH3(CH2)5NH3SnCl6.

The Raman and IR spectra of NH3(CH2)5NH3SnCl6 have been measured at ambient temperature. It is shown that the cations in the compound assume a symmetry lower than C2v. Combination bands observed in the 2100-1800 cm(-1) region in the IR spectrum of NH3(CH2)5NH3SnCl6 indicate that the compound contains the C-NH3 grouping, the bands are discussed and their assignment are suggested. No evidence of existence of hydrogen bonding is found from the infrared spectrum in the region of 2800-3200 cm(-1); anions and cations are found not connected by hydrogen bonding and are therfore isolated. The Raman spectrum of anions can be interpreted in terms of disordered groups, not clearly showing the predicted splitting of bands.     

An integrated production and preventive maintenance planning model

We are given a set of items that must be produced in lots on a capacitated production system throughout a specified finite planning horizon. We assume that the production system is subject to random failures, and that any maintenance action carried out on the system, in a period, reduces the system’s available production capacity during that period. The objective is to find an integrated lot-sizing and preventive maintenance strategy of the system that satisfies the demand for all items over the entire horizon without backlogging, and which minimizes the expected sum of production and maintenance costs. We show how this problem can be formulated and solved as a multi-item capacitated lot-sizing problem on a system that is periodically renewed and minimally repaired at failure. We also provide an illustrative example that shows the steps to obtain an optimal integrated production and maintenance strategy.