Norcaradiene-cycloheptatriene substituted in position 7: Investigation of the valence isomerization equilibrium

Summary The valence isomerism of a series of noncaradiene-cycloheptatriene compounds is investigated. Geometry and energy calculations allow to explain the nature of the transitions. Peculiarities of equilibrium shifts between different structures depending on the substituent at position 7 (X=CH₃, NH₂, CHO, CN) are discussed. Th nature of the interaction between the substituentX and the ring (- or -interaction) is investigated.

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Norcaradiene-Cycloheptatrien mit Substituenten in Position 7: Untersuchungen der Valenzisomeriegleichgewichte (Kurze Mitt.)

Zusammenfassung Es wurden Gleichgewichte zwischen Norcaradien und Cycloheptatrien mit Hilfe der semiempirischen Methoden MNDO und AM1 untersucht. Die Elektronendichteverteilungen und H _f-Werte der untersuchten Verbindungen werden in Abhängigkeit der Substituenten diskutiert.

     

Quasi-Steady State Kinetics of Simple Sequential Multienzyme Reactions with Single Substrates

Applications of computer algebra technique to kinetic analysis of multienzyme reaction including two and three distinct enzymes were described in the literature, which mainly depend on Gröbner Basis theory. In the present study, we have applied the same methodology to a hypothetical system with four enzymes. After deriving a composite rate law for a reaction system with four distinct enzymes using the computer algebra system MAPLE, the composite rate law was fitted to simulated data for time versus product concentration to yield estimates of the kinetic parameters.     

Developing a Novel Platelet-Rich Plasma-Laden Bioadhesive Hydrogel Contact Lens for the Treatment of Ocular Surface Chemical Injuries

Permanent injury to corneal limbal stem cells after ocular surface chemical and thermal injuries is a major cause of corneal blindness. In this study, a PRP-laden GelMA hydrogel contact lens is manufactured which is aimed to support the limbal niche after ocular surface insults thereby preventing limbal stem cell failure. GelMA with varying platelet-rich plasma (PRP) concentrations (5%, 10%, and 20%) is photopolymerized using a visible light crosslinking system followed by characterizations of mechanical properties, growth factor release, enzymatic degradation, and in vitro cytotoxicity. The addition of 10% PRP into 10% GelMA hydrogel precursor solution results in the highest tensile and compressive modulus (38 and 110 kPa, respectively) and burst pressure (251±37.66 mmHg). Degradation time varies according to the concentration of the collagenase enzyme tested (0, 2.5, 5, and 40 µg/mL) and is most prolonged with 20% PRP. EGF and TGF-β release profiles suggest an initial burst release followed by sustained release, most consistent in the 10% PRP sample. Although cell viability decreases on day 1, rapid recovery is observed and is approximately 120% after day 21. PRP-laden GelMA in the form of a contact lens may be a promising biomaterial-based treatment approach for the maintenance of limbal epithelial stem cells after ocular surface insults.     

Voltammetric determination of mercury(II) using a modified pencil graphite electrode with 4-(4-methylphenyl aminoisonitrosoacetyl)biphenyl

A sensitive and selective method for determination of mercury(II) with “4-(4-methylphenyl aminoisonitrosoacetyl)biphenyl (TKO)-modified pencil graphite electrode” was developed. All factors affecting determination process were optimized. Differential pulse voltammetry with 4-(4-methylphenyl aminoisonitrosoacetyl)biphenyl-modified electrode showed a linear response between 1.0 × 10^?5 and 1.0 × 10^?3 M (R ² = 0.9994). The detection limit of this electrode was found as 5.85 × 10^?7 M (S/N = 3). The effects of different cations on the determination of mercury(II) were investigated and found that modified electrode is highly selective. The developed method was applied for mercury determination in different water samples.     

New saccharinate complexes with 3,3′-azobispyridine ligand: synthesis,characterization, and spectroscopic properties

The new metal complexes with saccharinate (sac) and 3,3′-azobispyridine (3,3′-abpy), [Ni(H₂O)₄(3,3′-abpy)₂](sac)₂ (1), [Cu(sac)₂(H₂O)(μ-3,3′-abpy)]_n (2), [Zn(H₂O)₄(3,3′-abpy)₂](sac)₂ (3), [Cd(sac)₂(H₂O)₂(μ-3,3′-abpy)]_n (4), and [Hg₂(μ-sac)₂(sac)₂(μ-3,3′-abpy)(3,3′-abpy)₂]_n (5), were synthesized and characterized by IR spectra, elemental analysis, and single-crystal X-ray diffraction. Spectroscopic (UV–vis and photoluminescence) and thermal properties were also investigated. Single-crystal X-ray analysis reveals that Ni(II) and Zn(II) are coordinated by four aqua ligands and two nitrogens of 3,3′-abpy, while sac is a counter-ion in 1 and 3. In 2, Cu(II) and all ligands are linked by coordination bonds and 3,3′-abpy ligands connect the Cu(II) centers forming a 1-D coordination polymer. In 4, sac N-coordinated to Cd(II) and distorted octahedral geometry of Cd(II) ion is completed by two aqua and bridging 3,3′-abpy ligands. In 5, sac bridges two Hg(II) ions to generate dinuclear [Hg₂(μ-sac)₂] units. These dinuclear units are connected by 3,3′-abpy to form a 1-D coordination polymer. The photoluminescence spectra of 3 and 5 show blue fluorescent emission bands, and these emissions can probably be assigned to intraligand fluorescent emissions. Thermal decompositions of the compounds are also discussed. For all complexes, magnetic susceptibility measurements show expected magnetic behavior.     

Synthesis of highly ordered hBN in presence of group I/IIA carbonates by solid state reaction

This comprehensive study declares experimentally the effects of IA/IIA metal carbonates on the formation of hexagonal boron nitride (hBN) with the aid of the available experimental methods as regards Fourier transform infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM). hBN is synthesized in the existence of the metal carbonates at the low temperature by modified O'Connor method. The experimental findings of FT‐IR and XRD investigations show that the addition of metal carbonates affects considerably the crystallization of hBN powder during the synthesis process. The presence of the high concentration level of the additions improves harshly the crystallinity. In this respect, the graphitization index deduced from the XRD patterns reduces with the enhancement in the amount of the dopant content. At the same time, the differentiation between the products is analyzed by the SEM surveys. According to the results, the materials synthesized by the Li₂CO₃ powder exhibit both the tubular form and rod‐like while the other samples prepared by the CaCO₃ chemical dopant display the homogeneous plates. Even, the TEM images confirm the nanowires and nanotubes structures such as multi‐walled cylindrical, bamboo nanotubes in all the materials studied in this work.     

Effect of heat transfer augmentation on two-phase flow instabilities in a vertical boiling channel

The effect of different heater surface configurations on two-phase flow instabilities has been investigated in a single channel, forced convection, open loop, up-flow system. Freon-11 is used as the test fluid, and six different heater tubes with various inside surface configurations have been tested at five different heat inputs. In addition to temperature and pressure recordings, high speed motion pictures of the two-phase flow were taken for some of the experiments to study the two-phase flow behavior at different operating points. Experimental results are shown on system pressure drop versus mass flow rate curves, and stability boundaries are also indicated on these curves. Comparison of different heater tubes is made by the use of the stability boundary maps and the plots of inlet throttling necessary to stabilize the system versus mass flow rate. Tubes with internal springs were found to be more stable than the other tubes.