A study of the quenching of PCl(b1∑+) by the E-V model

Using the reaction of Ar(3Po,2) + PCl3 as a source of PCl(b1 +), we have measured the quenching rate constants of PCl(b,v'=0) for more than 20 quenchers. The E-V model is used to calculate the rate constants. The comparison of the calculated values with the experimental ones shows that the quenching of PCl(b) by the reagent molecules results from the electronic to vi-brational energy near resonance transfer and has been related to the Franck-Condon factors for the PCl(b,v'=0-a,v"=m) transition and to the anharmonicities of the terminal bonds of the quenchers. In addition, the influence of the polarizability of the reagent molecule on the quenching rate constant is discussed.     

Efficient Synthesis of the C1-C7 Fragment of Didemnaketal A

The stereoselective synthesis of the CI-C7 fragment (3R,4S,6R)-3,4-di[(tert-butyldimethylsilyl)oxy]-7-hydroxy-6-methylheptan-2-one, which is the crucial intermediate for synthesis ofthe HIV-1 protease inhibitive didemnaketals, was developed via 12 steps from the natural ( )-pulegone.     

A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.     

A study of the perturbations between the A1Σ+u and b3Πu states of Na2

The interaction between the A¹Σ⁺_u and b³Π_Ωu states of Na₂ is explored by resonantly exciting A states via A-X transitions and, after an adjustable delay time, photoionizing them. For long delays signals arise only from states with significant fractions of both A and b state character. Thus the regions where the interaction is important stand out clearly in the spectrum. Using this technique we have investigated perturbations of the A v' = 3, 7 and 8 states by the b v' = 10, 13 and 14 states.     

Adiabatic scanning calorimetry of the nematic-smectic A1 and the smectic A1–smectic A transitions in frustrated smectic mixtures at low temperatures

Abstract

Phase diagram results and high resolution adiabatic scanning calorimetric data are presented for several binary mixtures of 4-cyanocyclohexyl-4'-n-butyl-cyclohexane and 1 amino-9-fluorenone showing smectic A₁ and smectic à phases at low temperatures. Contrary to present theoretical expectations and experimental evidence for other systems, we find strongly first order nematic to smectic A₁ transitions with a latent heat of about 2 kJ/mol for all the mixtures investigated. The enthalpy change related to the smectic A₁ to smectic à transitions is two orders of magnitude smaller and corresponds most likely to a fluctuation induced first order transition.     

A Convenient Method for the Synthesis of Chiral N-Protected 1, 2-Amino Alcohols via the Reduction of the Aminoketones

A series of optically active N-protected 1,2-amino alcohols were synthesized via the reduction of the corresponding α-aminoketones starting from the readily available L-amino acids.     

A synthetic approach to the phorboxazoles – A strategy for the synthesis of the C1–C19 polyketide fragment

A synthetic approach to the C1–C19 polyketide fragment of the phorboxazoles is disclosed here. While an initial two-directional approach was efficient, it did not proceed in a high enough yield to justify moving forward. A subsequent successful strategy for the generation of the C11–C15 pyrans of both of the phorboxazoles was achieved, and the installation of the C9 stereocenter was able to be demonstrated. Furthermore, an efficient route for the preparation of the C1–C8 fragment with suitable functionality to allow for elaboration into the complete C1–C19 fragment, with the capricious C2–C3 Z-geometry installed, was also achieved.     

Inhibition of the Fibrillation of Amyloid Aβ1-40 by Hybrid-Lipid-Polymer Vesicles

The transformation of functional proteins into amyloidic plaques is responsible for the impairment of neurological functions in patients fallen victim to debilitating neurological conditions like Alzheimer's, Parkinson's, and Huntington's diseases. The nucleating role of amyloid beta (Aβ_1-40) peptide into amyloids is well established. Herein, lipid hybrid-vesicles are generated with glycerol/cholesterol-bearing polymers aiming to alter the nucleation process and modulate the early phases of Aβ_1-40 fibrillation. Hybrid-vesicles (±100 nm) are prepared by incorporating variable amounts of cholesterol-/glycerol-conjugated poly(di(ethylene glycol)_macrylates)_n polymers into 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membranes. The in vitro fibrillation kinetics coupled to transmission electron microscopy (TEM) is employed to investigate the role of hybrid-vesicles on Aβ_1-40 fibrillation without destroying the vesicular membrane. Both polymers, when embedded in hybrid-vesicles (up to 20%) significantly prolonged the fibrillation lag phase (t_lag) compared to a small acceleration in the presence of DOPC vesicles, irrespective of the amount of polymers inside the hybrid-vesicles. Along with this notable retardation effect, a morphological transformation of the amyloid's secondary structures to amorphous aggregates or the absence of fibrillar structures when interacting with the hybrid-vesicles is confirmed by TEM and circular dichroism (CD) spectroscopy.     

Singlet 1A″ methylnitrene: A possible intermediate in the photochemical decomposition of methylazide

The interconversion of methylnitrene and methylenimine is studied in the singlet excited state ¹A″ using ab initio methods. At the MP4SDQ/6-31G**//HF/3-21G level plus zero-point energy contributions, the energy barrier for the rearrangement to methylenimine is calculated to be 9.5 kcal/mol. The ¹A″ methylnitrene lies only about 8 kcal/mol above the closed-shell singlet ¹A′ state which is a saddle point on the energy surface. This suggests that the open-shell singlet ¹A″ methylnitrene might constitute a short-lived intermediate during the direct photolytic decomposition of methylazide in the presence of collisions.     

A Novel Oligosaccharide from the Mucus of the Loach

A novel oligosaccharide was isolated and purified from the mucus of the loach, Misgurnus anguillicaudatus. Its was identified by several qualitative tests and characterized by elementary analysis,UV and IR spectrum. Its average molecular weight(Mw=1539.4) was determined by gel permeation chromatography. The major structural monomers of Misgurnus anguillicaudatus oligosaccharide were identified to be D-galactose and L-fucose by paper chromatography and gas chromatography.     

Synthesis of the Methyl α-Glycoside of the Intracatenary Disaccharide Repeating Unit of the O-Polysaccharide of Vibrio Cholerae O:1. A Comparison of two Assembly Strategies

Abstract

The two strategies engaged in the construction of the title disaccharide 17 comprise: 1. assembly of a diamino disaccharide and its N-acylation using chiral reagents to introduce the 4-(3-deoxy-l-glycero-tetronyl) group, followed by deprotection, and 2. preparation of a glycosyl acceptor and a glycosyl donor both having the chiral 3-deoxy-l-glycero-tetronamido group already in place, their condensation to give a fully substituted disaccharide, and deprotection. Accordingly, the crystalline diamino disaccharide methyl 2-O-(4-amino-3-O-benzyl-4, 6-dideoxy-α-d-mannopyranosyl)-4-amino-3-O-benzyl-4, 6-dideoxy-α-d-mannopyranoside, (14), was prepared from the known [Bundle, D. R. et al., Carbohydr. Res. 174, 239 (1988)] diazido disaccharide 12, and treated with the lactone 30, or its acetylated or benzylated analogs 31 and 32, respectively, as the N-acylating reagents. Subsequent deprotection of the respective products applying standard chemistry gave 17. Alternatively, the methyl α-glycoside of the monomeric intracatenary repeating unit of Vibrio cholerae 0:1 (2) was converted to the fully benzoylated glycosyl chloride 26, and the latter glycosyl donor was condensed with methyl 3-O-benzyl-4,6-dideoxy-4-(2,4-di-O-benzoyl-3-deoxy- l-glycero-tetronamido)-α-d-mannopyranoside (24), to give the corresponding, fully protected derivative 27. Deprotection then readily gave 17. It appears that the title disaccharide can be most efficiently synthesized using synthons 24 and 26. The lactones 30 and 32 appear to be promising acylating reagents for the introduction of the 3-deoxy-l-glycero-tetronamido group when higher oligosaccharides in this series will be synthesized via their (poly)amino precursors.     

A Versatile Approach for the Asymmetric Synthesis of 3-Alkyl-isoindolin-1-ones

3 Ｓｕｂｓｔｉｔｕｔｅｄｉｓｏｉｎｄｏｌｉｎ 1 ｏｎｅｓ (2 ,3 ｄｉｈｙｄｒｏ 1Ｈ ｉｓｏｉｎｄｏｌｉｎ 1 ｏｎｅｓ)ｏｆｇｅｎｅｒａｌｓｔｒｕｃｔｕｒｅ (1)ｃｏｎｓｔｉｔｕｔｅｔｈｅｋｅｙｓｔｒｕｃｔｕｒａｌｆｅａｔｕｒｅｏｆａｌａｒｇｅｎｕｍｂｅｒｏｆｂｉｏａｃｔｉｖｅｍｏｌｅｃｕｌｅｓｏｆｎａｔｕｒａｌｏｒｓｙｎｔｈｅｔｉｃｏｒｉｇｉｎ .Ｆｏｒｅｘａｍｐｌｅ ,ｌｅｎｎｏｘａｍｉｎｅ (2 ) ,1ｎｕｅｖａｍｉｎｅａｎｄｃｈｉｌｅｎｉｎｅａｒｅａｌｋａｌｏｉｄｓｉｓｏｌａｔｅｄｆｒｏｍｖａｒｉｏｕｓ…     

A theoretical form of the Martin-Hou equation of state

A new equation of state is derived from the Barker-Henderson hard-sphere perturbation theory. It has the form similar to the Martin-Hou equation of state. The numerical values of the characteristic constants in the equation can be calculated by the method of Martin and Hou. The equation can be used to predict P-V-T properties accurately for fluids when the critical parameters (T_c, P_c and V_c) and one point on the vapor pressure cure are given. By using the functional relationships between the characteristic constants and the microscopic parameters, the molecular microscopic parameters of the substance can be obtained.     

Aplysqualenol A binds to the light chain of dynein type 1 (DYNLL1)

A bidirectional affinity system has been developed for the identification of cancer-related natural products and their biological targets. Aplysqualenol A is thus selectively identified as a ligand of the dynein light chain. The use of forward and reverse affinity methods suggests that both small-molecule isolation and target identification can be conducted using conventional molecular biological methods.     

A Kind of Electrode Enhanced the Electrochemiluminescence

Electrochemiluminescence (ECL), like other chemiluminescence technique, offers high signal-to-noise ratio. Furthermore, it has the advantage over other chemiluminescence techniques of being initiated by a voltage potential. Thus, it provides a better-controlled luminescence. This technique has been used in measuring many kinds of organic and inorganic matters, and analyzing many kinds of antigen, antibody and hapten, such as carcinoembryonic antigen and alpha-fetoprotein, etc1-6. The ele…     

Synthesis of the 8,19-Epoxysteroid Eurysterol A

We report the first chemical synthesis of eurysterol A, a cytotoxic and antifungal marine steroidal sulfate with a unique C8−C19 oxy-bridged cholestane skeleton. After C19 hydroxylation of cholesteryl acetate, used as an inexpensive commercial starting material, the challenging oxidative functionalization of ring B was achieved by two different routes to set up a 5α-hydroxy-7-en-6-one moiety. As a key step, an intramolecular oxa-Michael addition was exploited to close the oxy-bridge (8β,19-epoxy unit). DFT calculations show this reversible transformation being exergonic by about −30 kJ mol⁻¹. Along the optimized (scalable) synthetic sequence, the target natural product was obtained in only 11 steps in 5 % overall yield. In addition, an access to (isomeric) 7β,19-epoxy steroids with a previously unknown pentacyclic ring system was discovered.     

A Statistical Mechanical View of the Determination of the Composition of Multi‐Temperature Plasmas

It is important that plasma composition is calculated in a manner consistent with statistical mechanics, particularly since the Boltzmann equation is the basis from which transport coefficients and the fluiddynamic equations are derived. It is shown from statistical mechanical considerations based on the Boltzmann equation and the Htheorem that it is (i) not possible for a plasma to have more than one temperature in equilibrium in the absence of external forces and gradients, and (ii) not possible to draw conclusions about the change in entropy of a plasma in the presence of external forces and gradients. Derivations of the twotemperature Saha equation, and more generally calculations of the composition of a multitemperature plasma, that are based on entropy maximization are therefore invalid. A thermodynamic derivation of the composition of a multitemperature plasma that is consistent with the statistical mechanical results is presented. The derivation shows that the equilibrium composition of a plasma can be correctly calculated by minimization of the internal or free energy.     

Study of catalytic properties of recombinant β-lactamases TEM-1 and TEM-171 of the molecular class A

Homogeneous preparations of recombinant β-lactamases TEM-1 and TEM-171 of molecular class A, differing by an amino acid substitution of valine at position 84 to isoleucine (Val84Ile), was obtained. The kinetic parameters of the β-lactamase TEM-171 were determined using a chromogenic substrate CENTA (K _{M eff} = 23 μM, K _cat = 102 s^–1). The competitive inhibition of recombinant β-lactamases TEM-1 and TEM-171 by tazobactam was ascertained. The values of the inhibition constants in the hydrolysis of the CENTA substrate amount to 0.057 and 0.047 μM for TEM-1 and TEM-171, respectively. It was shown that the Val84Ile mutation leads to a decrease of TEM-171 enzyme thermal stability by 1.5 times.