Spin 0 and Spin 1/2 Particles in a Spherically Symmetric Static Gravity and a Coulomb Field

A relativistic particle in an attractive Coulomb field as well as a static and spherically symmetric gravitational field is studied. The gravitational field is treated perturbatively and the energy levels are obtained for both spin 0 (Klein-Gordon) and spin 1/2 (Dirac) particles. The results are shown to coincide with each other as well as the result of the nonrelativistic (Schr?dinger) equation in the nonrelativistic limit.     

New poly(ester amide ether amide)s from a novel flexible diamine and different diacid chlorides using TMSCl for in situ silylation

A novel flexible diamine with built-in ester, amide and ether groups named terephthalic acid bis(4-{2-[2-(2-amino ethoxy)ethoxy]ethyl carbamoyl}phenyl) ester (TABE), was synthesized via two steps. Nucleophilic reaction of 4-hydroxybenzoic acid with terephthaloyl chloride in the presence of NaOH yielded terephthaloyl bis (4-oxybenzoic) acid (TOBA). The diamine (TABE) was prepared via two direct and indirect methods. In the indirect method TOBA was converted to related diacid chloride and reacted with 1,8-diamino-3,6-dioxaoctane (DADO). Direct method was achieved through the reaction of TOBA with DADO via Yamazaki method. TOBA and TABE were fully characterized and TABE was used to prepare new poly(ester amide ether amide)s through polycondensation with different diacid chlorides in the presence of trimethylchlorosilane (TMSCl). The polymers were characterized using conventional methods and their physical properties including inherent viscosity, thermal behavior, thermal stability, crystallinity, and solubility were studied. The polymers showed good thermal stability and improved solubility.     

Adsorption of carbon dioxide by X zeolites exchanged with Ni2+ and Cr3+: isotherms and isosteric heat

The adsorption of CO2, at intervals of 30 K from 303 K was carried out on M(n+)X zeolites (M(n+)=Ni2+ or Cr3+) exchanged at different degrees. The structural regularity of the zeolite lattice of NaX and the existence of well-defined cavities within which the adsorbate molecules are lodged suggest that it should be possible to use various isotherm equations. Several models were thus used to describe the experimental isotherms. The best fit of adsorption isotherm data is obtained with the Sips model. The Volmer model also describes satisfactorily the isotherms of CO2 adsorption by NaX, Ni(x)X, and Cr(x)X. Analysis of the isosteric heat reveals a character energetically heterogeneous for NaX and Ni(x)X samples exchanged at a higher degree of Ni2+ exchange and at low coverage. Specific interaction is also obtained between the adsorbate molecules and Cr(x)X exchanged at a lower degree. From these considerations, hypotheses will be advanced to describe the behavior of the adsorbed phase within zeolitic cavities.     

Characterization of a novel crown ether-bearing near-infrared heptamethine cyanine dye. A study of fluorescence quenching by lithium

The spectral characteristics of a crown ether-bearing heptamethine cyanine dye (JCM-15C5) and its quenching by lithium ion are reported. The absorbance maximum of the dye is at 776 nm in acetonitrile. This value matches the output of a commercially available laser diode (780 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in acetonitrile is at 799 nm. It was found that Li⁺ ion selectively quenches the fluorescence intensity of JCM-15C5 by the static quenching mechanism. The Stern-Volmer quenching constant (K_sv) was calculated from the Stern-Volmer plot and found to be 1.17×10⁷ M⁻¹ at room temperature. The detection limit for Li⁺ ion was found to be 7.43×10⁻² ppb. The stability constant (K_s) of the metal-dye complex was determined by fluorometric titration and found to be 5.40×10⁷ M⁻¹.     

Diastereoselectivity in the Mukaiyama-Michael Reaction Employing alpha-Acyl beta,gamma-Unsaturated Phosphonates

The unique electronic and structural nature of the alpha-acylphosphonate functional group affords both dimeric and chelated complexes of diethyl crotonyl phosphonate (1; DECP) with stannic chloride (SnCl(4)). The dimeric complex, SnCl(4).(DECP)(2) (5) results from the coordination of two DECP molecules, ligated via the phosphoryl oxygens to the tin atom. The chelated complex, SnCl(4).(DECP) (6), is best represented with both phosphoryl and carbonyl oxygens coordinated to the metal center. Both metal ligated and chelated complexes have unique (13)C (31)P, and (119)Sn NMR spectra. In complex 5, the (13)C NMR resonances attributed to the carbonyl carbons were shifted upfield of free DECP. A monocoordinating Lewis acid, BF(3).OEt(2), produced a similar chemical shift trend in both the (13)C and (31)P NMR spectra of the BF(3).DECP complex. Essentially quantitative yields and moderate diastereomeric excesses favoring anti (or trans) diethyl 6-phenyl-4,5-dimethyl-6-(trimethylsilyloxy)-2-dihydropyranphosphonate (3) and diethyl 5-phenyl-3,4-dimethyl-1,5-dioxopentanephosphonate (4) were obtained from both chelated and dimeric SnCl(4).(DECP)(n) (n = 1, 2) when treated with either diastereomeric (Z)- or (E)-1-phenyl-1-(trimethylsilyloxy)-1-propene 2. Diethyl crotonylphosphonate (1), 3, and 4 were fully characterized.     

Poly(sulfone ether amide amide)s as a new generation of soluble, thermally stable polymers

A new sulfone ether amide diamine was synthesized via three steps, starting from reaction of 4-aminophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide afforded N-(4-hydroxy phenyl)-4-nitrobenzamide (HPNB). In the next step, reduction of nitro group resulted in preparation of 4-amino-N-(4-hydroxy phenyl) benzamide (AHPB). Final step in the preparation of diamine was the reaction of AHPB with bis(4-chlorophenyl) sulfone in the presence of K₂CO₃. All the materials were characterized using conventional spectroscopic methods. Poly(sulfone ether amide amide)s were synthesized by polycondensation reactions of prepared diamine with different diacid chlorides (aromatic and aliphatic ones). The obtained polymers were fully characterized and their physical properties including thermal behavior, thermal stability, solubility, and inherent viscosity were studied.     

Characterization of chromium-induced apoptosis in cultured mammalian cells:: A differential scanning calorimetry study

The present study examined the cytotoxic effect of increasing Cr(VI) concentrations on cultured cells by a combination of biochemical methods and DSC, a novel use of DSC in the study of cell death. The characteristics of apoptotic cells are compared with normal cells. Chromatin in human epithelial-like L-41 cells has two thermal transitions at 100 and 105 °C. The heat from these endotherms is 90.5 ± 11.0 J/g DNA. The total heat of denaturation (Q_d) is 27.5 ± 3.5 J/g dry biomass. The heat evolved (−Q) is 15.6 ± 3.0 J/g dry biomass. The treatment of cells with 20 μM Cr(VI) for 2 and 4 h has not revealed any changes in heat of denaturation and heat evolution (−Q). However increased treatment time with Cr(VI) at 20 μM resulted in significant changes to the thermal profile and a sharp linear decrease of (−Q) and Q_d values. The Q_d and (−Q) values of cells treated with 20 μM Cr(VI) for 48 h are equal to 15.5 ± 2.0 and 2.1 ± 0.4 J/g dry biomass, respectively. The changes in chromatin conformation, Bax expression and the collapse of the mitochondrial membrane permeability coincide with the time point from which the action of chromium is irreversible.     

Study of thermodynamic parameters in amphiphilic systems by lattice Monte Carlo: effect of tails and heads

Results from three-dimensional lattice Monte Carlo simulations of amphiphile–solvent mixtures are presented. The chemical potential is derived from the monomer distribution in different clusters rather than using a Widom particle insertion approach. The effect of tail and head characteristics on the non-ideality of these systems, aggregation number, and premicellar phenomena is considered. The aggregation number and CMC behavior of the simulated amphiphilic systems are compared with existing experimental results for non-ionic amphiphiles. Two kinds of polydispersity changing with total concentration of surfactants are observed which are related to phase transition phenomena. Shape variations in clusters are studied by calculating the eigenvalues of the gyration matrix; it is shown that large clusters are non-spherical. With the Maclaurin’s expansion of activity coefficient into volume fraction, the distribution of excess chemical potential with changing aggregation number is considered. Study of the degree of non-ideality of these amphiphiles reveals that asymmetric amphiphiles are characterized by greater non-ideality than symmetric amphiphiles. Goldstein’s parameters are calculated taking non-ideality into consideration. The difference between the phenomenological model and the simulation data is investigated.     

A study on the binding of two water-soluble tetrapyridinoporphyrazinato copper(II) complexes to DNA

Interaction of N,N′,N″,N-tetramethyltetra-2,3-pyridinoporphyrazinatocopper(II), ([Cu(2,3-tmtppa)]⁴⁺) and N,N′,N″,N-tetramethyltetra-3,4-pyridinoporphyrazinatocopper(II), ([Cu(3,4-tmtppa)]⁴⁺) with calf thymus DNA was studied in 1 mM phosphate buffer and low ionic strength (5 mM NaCl) at various temperatures by UV-visible and circular dichroism (CD) spectroscopies and viscometric method. The binding constants were determined from the changes in the visible part of porphyrazine complexes spectra using SQUAD software. The values of K have been obtained (7.9±0.4)×10⁴ and (2.2±0.1)×10⁵ M⁻¹ for [Cu(2,3-tmtppa)]⁴⁺ and [Cu(3,4-tmtppa)]⁴⁺, respectively at 27 °C. The higher affinity of 3,4-isomer of Cu complex towards DNA with respect to the 2,3-isomer was attributed to favorable external positioning of the cationic charges in former, which enables superior interaction with the DNA duplex. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated by van't Hoff equation. The enthalpy and entropy changes were determined, +34.2±3.6 kJ mol⁻¹ and +207.8±12.70 J mol⁻¹ K⁻¹ for [Cu(2,3-tmtppa)]⁴⁺ and +49.7±2.1 kJ mol⁻¹ and +267.8±7.9 J mol⁻¹ K⁻¹ for [Cu(3,4-tmtppa)]⁴⁺. The existence of extensive hypochromicity, large red shift and negative CD in the visible part of [Cu(3,4-tmtppa)]⁴⁺ spectra suggested an intercalation binding mode. Analysis of the moderate hypochromicity, red shift and bisignate CD in the Q-band absorption region of [Cu(2,3-tmtppa)]⁴⁺ spectra possibly led us to the coexistence of intercalation and outside binding modes. The influence of the ionic strength on the binding parameters and binding modes was investigated. The results show that increase in ionic strength causes the decrease in the binding constants. It was also concluded that increase in ionic strength affects the binding characteristics of positively charged complexes with DNA.

The increase in DNA viscosity in the presence of Cu–tmtppa complexes is attributed to the lengthening of DNA helix due to the intercalation. This result is consistent with conclusions obtained from the spectroscopic techniques.     

Structurally distinct active sites in the copper(II)-substituted aminopeptidases from Aeromonas proteolytica and Escherichia coli

The aminopeptidase from Aeromonas proteolytica (AAP) was titrated with copper, which bound sequentially at two distinct sites. Both the mono- and disubstituted forms of AAP exhibited catalytic hyperactivity relative to the native dizinc enzyme. Monosubstituted AAP exhibited an axial Cu(II) EPR spectrum with slight pH dependence: at pH 6.0 g(parallel) = 2.249, g( perpendicular ) = 2.055, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1), whereas at pH 9.65 g(parallel) = 2.245, g( perpendicular ) = 2.056, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1). These data indicate oxygen and nitrogen ligation of Cu. AAP further substituted with copper exhibited a complex signal with features around g approximately 2 and 4. The features at g approximately 4 were relatively weak in the B(0) perpendicular B(1) (perpendicular) mode EPR spectrum but were intense in the B(0) parallel B(1) (parallel) mode spectrum. The g approximately 2 region of the perpendicular mode spectrum exhibited two components, one corresponding to mononuclear Cu(II) with g(parallel) = 2.218, g( perpendicular ) = 2.023, and A(parallel)((63/65)Cu) = 1.55 x 10(-)(2) cm(-)(1) and likely due to adventitious binding of Cu(II) to a site distant from the active site. Excellent simulations were obtained for the second component of the spectrum assuming that two Cu(II) ions experience dipolar coupling corresponding to an inter-copper distance of 5 A with the two Cu(II) g(z)() directions parallel to each other and at an angle of approximately 17 degrees to the inter-copper vector (H = betaB.g(CuA).S(CuA) + betaB.g(CuB).S(CuB) + [S.A.I](CuA) + [S.A.I](CuB) + [S(CuA).J.S(CuB)]; g(parallel(CuA,CuB)) = 2.218, g( perpendicular )((CuA,CuB)) = 2.060; A(parallel(CuA,CuB))((63/65)Cu) = 1.59 x 10(-)(2) cm(-)(1), J(isotropic) = 50 cm(-)(1), r(Cu)(-)(Cu) = 4.93 A, and chi = 17 degrees ). The exchange coupling between the two copper ions was found to be ferromagnetic as the signals exhibited Curie law temperature dependence. The Cu-Cu distance of approximately 5 A indicated by EPR was significantly higher than the inter-zinc distance of 3.5 A in the native enzyme, and the dicopper species therefore represents a novel dinuclear site capable of catalysis of hydrolysis. In contrast to AAP, the related methionyl aminopeptidase from Escherichia coli (EcMetAP) was found to bind only one Cu(II) ion despite possessing a dinuclear binding site motif. A further difference was the marked pH dependence of the signal in EcMetAP, suggestive of a change in ligation. The structural motifs of these two Cu(II)-substituted aminopeptidases provide important insight into the observed catalytic activity.