625. Anionotropic systems. Part IV. The kinetics of the rearrangement of 3-hydroxy-3: 5-dimethylhex-4-en-2-one. The effect of an acetyl group on anionotropic mobility

1953 ◽  
pp. 3138 ◽  
Author(s):  
E. A. Braude ◽  
C. J. Timmons
Keyword(s):  
Acetyl Group ◽  
Kinetics Of

Structural effects on epimerization of bacteriochlorophyll a and chlorophyll a revealed using 3-acetyl chlorophyll a

2020 ◽  
Vol 24 (04) ◽  
pp. 499-504 ◽  
Author(s):  
Yoshitaka Saga ◽  
Shiori Nakagawa
Keyword(s):  
Physicochemical Properties ◽  
Chlorophyll A ◽  
Photosynthetic Reaction Center ◽  
Molecular Structures ◽  
Structural Factors ◽  
Structural Effects ◽  
Photosynthetic Organisms ◽  
Acetyl Group ◽  
Kinetics Of

Chlorophyll (Chl) and bacteriochlorophyll (BChl) pigments, which are crucial cyclic tetrapyrroles in photosynthesis, generally have a chiral center in their exo-cyclic five-membered E-ring. Although [Formula: see text]-epimers (primed-type) of (B)Chl pigments are rarely present in photosynthetic organisms, they play key roles in photosynthetic reaction center complexes. The epimerization mechanism of (B)Chl pigments in vivo has not been unraveled. The structural effects on the physicochemical properties of (B)Chl epimerization reactions provide useful information to tackle this question. We analyzed epimerization of three pigments, BChl [Formula: see text], Chl [Formula: see text], and 3-acetyl Chl [Formula: see text], to elucidate the structural factors that are responsible for epimerization reactions. We compared the epimerization kinetics of the three pigments and concluded that the bacteriochlorin skeleton (7,8,17,18-tetrahydroporphyrin) significantly retarded the epimerization kinetics. Thus, BChl [Formula: see text] exhibited slower epimerization kinetics than Chl [Formula: see text] in spite of the presence of the electron-withdrawing 3-acetyl group that accelerates epimerization. In contrast to the large structural effects of (B)Chl molecules on epimerization kinetics, the thermodynamic properties at equilibrium in the epimerization of the three pigments were barely influenced by their molecular structures. This study also demonstrates that a semi-synthetic pigment, 3-acetyl Chl [Formula: see text], is appropriate for comparative analyses of the structural effects of BChl [Formula: see text] and Chl [Formula: see text] on their physicochemical properties.

Synthesis and Characteristics of Dental Composites with Novel Bis-GMA Derivate as a Resin Base

2013 ◽  
Vol 745-746 ◽  
pp. 442-446 ◽  
Author(s):  
Rui Li Wang ◽  
Mo Zhu ◽  
Sheng Liu ◽  
Feng Wei Liu ◽  
Xiao Ze Jiang ◽  
...  
Keyword(s):  
Adverse Effects ◽  
Triethylene Glycol ◽  
High Viscosity ◽  
Dental Composites ◽  
Resin Matrix ◽  
Hydroxyl Groups ◽  
Acetyl Group ◽  
Matrix Differential ◽  
Dental Restorative ◽  
Kinetics Of

2,2-bis [4-(2-hydroxy-3-methacryloyloxypropoxy) pheny propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) have been commonly used as a viscous monomer and a reactive diluent in the organic phase of dental restorative composites, respectively. The purpose of addition of TEGDMA is mainly to decrease the high viscosity of Bis-GMA caused by hydrogen bonding between hydroxyl groups. However, some adverse effects will accompany with increased amounts of the TEGDMA, such as higher values of polymerization shrinkage, which is not undesirable for the clinical application. Therefore, substituting hydroxyl groups of Bis-GMA might be an appropriate and effective way to reduce the amount of diluents and weaken the accompanied adverse effects. This work focuses on the synthesis of a novel Bis-GMA derivate, substituting acetyl groups for hydroxyl groups in Bis-GMA. The viscosity of Bis-GMA characterized with rotational rheometer was significantly decreased from 820 Pa.s to 11 Pa.s by substitution of acetyl group, leading to the low amount of TEGDMA in resin matrix. Differential Scanning Calorimeter (DSC) was used for investigating the reaction kinetics of this novel monomer with different mass ratios of TEGDMA. The results suggested that the maximum conversion of the Ac-Bis-GMA can reach 88% while the corresponding value for Bis-GMA is 75%. Dental composites were prepared from 2,2-bis [4-(2-acetyl-3-methacryloyloxypropoxy) pheny propane (Ac-Bis-GMA) or Bis-GMA resin mixtures with TEGDMA filled with 70 wt% silica co-fillers. The results presented that dental composites prepared from new resin matrixes exhibited adequate mechanical properties.

Three types of alpha-melanocyte-stimulating hormone: bioactivities and half-lives

1983 ◽  
Vol 245 (1) ◽  
pp. E47-E54 ◽  
Author(s):  
D. Rudman ◽  
B. M. Hollins ◽  
M. H. Kutner ◽  
S. D. Moffitt ◽  
M. J. Lynn
Keyword(s):  
Tissue Slices ◽  
Melanocyte Stimulating Hormone ◽  
Lipolytic Action ◽  
Acetyl Group ◽  
Isolated Adipocytes ◽  
Hydroxy Groups ◽  
Kinetics Of ◽  
Stimulating Hormone

Three types of alpha-melanocyte-stimulating hormone (alpha MSH) that differ in the acetyl status of the N-terminal serine have been found in the neurointermediate lobe of the pituitary gland and in the brain: desacetyl alpha MSH, which lacks an acetyl group; monoacetyl alpha MSH, in which the amino group of the serine is acetylated; and diacetyl alpha MSH, in which both amino and hydroxy groups of the serine are acetylated. We compared the lipolytic and melanotropic actions of these three peptides, and their rates of disappearance from plasma, both in vitro and in vivo. The following differences were found. a) For in vitro lipolytic actions on rabbit adipose tissue slices, the potencies differed according to the order diacetyl = monoacetyl greater than desacetyl. On rabbit isolated adipocytes, however, the three peptides were equipotent. b) For in vivo lipolytic action in the rabbit, not only potency but also kinetics differed. Diacetyl alpha MSH had the slowest onset, longest duration, and greatest potency. The desacetyl variant had the quickest onset, shortest duration, and least potency. c) The half-life for elimination from rabbit plasma both in vitro and in vivo was shortest for the desacetyl form and longest for the diacetyl peptide. d) For in vitro melanotropic effect on frog skin, kinetics of action were the same for all three peptides, but potency differed according to the order diacetyl = monoacetyl greater than desacetyl. Thus acetylation of alpha MSH alters lipolytic and melanotropic potencies in vitro and lipolytic potency and kinetics in vivo. These differences result in part from the fact that acetylation slows the degradation of the tridecapeptide both inside and outside the circulation.

Kinetics of glycoluril template-directed Claisen condensations — Effect of thionation of the glycoluril

2005 ◽  
Vol 83 (9) ◽  
pp. 1253-1260 ◽  
Author(s):  
Karen Kam ◽  
Mohammad Rahimizadeh ◽  
Robert S McDonald ◽  
Paul HM Harrison ◽  
Hao Chen ◽  
...  
Keyword(s):  
Carbonyl Group ◽  
Isotope Effect ◽  
Rate Constants ◽  
Uv Spectroscopy ◽  
Claisen Condensation ◽  
Bond Forming ◽  
Deuterium Substitution ◽  
Acetyl Group ◽  
Electron Donating Groups ◽  
Kinetics Of

Apparent rate constants for the tert-butoxide promoted Claisen-like condensation of a series of N1-acetyl-N6-aroyl-2,5-dithio-3,4,7,8-tetramethylglycolurils (9a–9f) to give N1-(3′-aroyl-3′-oxopropionyl)-2,5-dithio-3,4,7,8-tetramethylglycolurils (10a–10f) were determined by UV spectroscopy. Overall rate accelerations of 3.5- to 18-fold were found relative to the corresponding reactions of the 2,5-dioxo compounds (7a–7f). Analysis of the Hammett plot for 9 and comparison with that for 7 shows that the key C—C bond-forming step, where the enolate of the acetyl group of the substrate attacks the aroyl carbonyl group, is accelerated by the thio substitution. For electron-withdrawing substituents in the aroyl group, the acceleration is sufficient to make this step nonrate limiting: the Hammett ρ value drops from approx. 1.5 for electron-donating groups to 0.27 for electron-withdrawing groups. Deuterium substitution in the acetyl group reduces the rate slightly, a result consistent with a slow but partially reversible first step in which substrate is deprotonated. A similar acceleration and isotope effect are found when diacetyl glycoluril (2) and diacetyl dithio glycoluril (5) are compared. The implications of these results are discussed.Key words: glycoluril, Claisen condensation, kinetics, mechanism.

Direct observations of radiation-enhanced transformations in glass

1983 ◽  
Vol 41 ◽  
pp. 354-355
Author(s):  
J. F. DeNatale ◽  
D. G. Howitt
Keyword(s):  
Glass Matrix ◽  
Diffusion Mechanism ◽  
Bubble Formation ◽  
Silicate Glasses ◽  
Phase Decomposition ◽  
Direct Observations ◽  
Thin Foils ◽  
Oxygen Bubble ◽  
Electron Energy Loss ◽  
Kinetics Of

The electron irradiation of silicate glasses containing metal cations produces various types of phase separation and decomposition which includes oxygen bubble formation at intermediate temperatures figure I. The kinetics of bubble formation are too rapid to be accounted for by oxygen diffusion but the behavior is consistent with a cation diffusion mechanism if the amount of oxygen in the bubble is not significantly different from that in the same volume of silicate glass. The formation of oxygen bubbles is often accompanied by precipitation of crystalline phases and/or amorphous phase decomposition in the regions between the bubbles and the detection of differences in oxygen concentration between the bubble and matrix by electron energy loss spectroscopy cannot be discerned (figure 2) even when the bubble occupies the majority of the foil depth.The oxygen bubbles are stable, even in the thin foils, months after irradiation and if van der Waals behavior of the interior gas is assumed an oxygen pressure of about 4000 atmospheres must be sustained for a 100 bubble if the surface tension with the glass matrix is to balance against it at intermediate temperatures.

Irradiation behavior of pyrolytic silicon carbide

1983 ◽  
Vol 41 ◽  
pp. 72-73
Author(s):  
R. J. Lauf
Keyword(s):  
Silicon Carbide ◽  
Fission Products ◽  
Thermodynamics And Kinetics ◽  
Neutron Fluences ◽  
Fuel Particles ◽  
Sic Coatings ◽  
Irradiation Behavior ◽  
Kinetics Of ◽  
Htgr Fuel

Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission product barrier. Optimization of the SiC with respect to fuel performance involves four areas of study: (a) characterization of as-deposited SiC coatings; (b) thermodynamics and kinetics of chemical reactions between SiC and fission products; (c) irradiation behavior of SiC in the absence of fission products; and (d) combined effects of irradiation and fission products. This paper reports the behavior of SiC deposited on inert microspheres and irradiated to fast neutron fluences typical of HTGR fuel at end-of-life.

The Ordered Phase Formation in Ti-Al-Ga Alloys

1970 ◽  
Vol 28 ◽  
pp. 440-441
Author(s):  
Shiro Fujishiro ◽  
Harold L. Gegel
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Titanium Alloys ◽  
Growth Kinetics ◽  
Stoichiometric Composition ◽  
Good Potential ◽  
Alpha Titanium ◽  
Cold Rolled ◽  
Kinetics Of ◽  
Thermal Stability Of

Ordered-alpha titanium alloys having a DO19 type structure have good potential for high temperature (600°C) applications, due to the thermal stability of the ordered phase and the inherent resistance to recrystallization of these alloys. Five different Ti-Al-Ga alloys consisting of equal atomic percents of aluminum and gallium solute additions up to the stoichiometric composition, Ti3(Al, Ga), were used to study the growth kinetics of the ordered phase and the nature of its interface.The alloys were homogenized in the beta region in a vacuum of about 5×10-7 torr, furnace cooled; reheated in air to 50°C below the alpha transus for hot working. The alloys were subsequently acid cleaned, annealed in vacuo, and cold rolled to about. 050 inch prior to additional homogenization

Ion Beam Induced Interfacial Reactions in Molybdenum Thin Films on Silicon

1981 ◽  
Vol 39 ◽  
pp. 162-163
Author(s):  
L. J. Chen ◽  
L. S. Hung ◽  
J. W. Mayer
Keyword(s):  
Ion Beam ◽  
Chemical Vapor ◽  
Interfacial Reactions ◽  
Practical Applications ◽  
Microelectronic Devices ◽  
Recent Emergence ◽  
Chemical Vapor Deposited ◽  
Atomic Mixing ◽  
Silicon Interface ◽  
Kinetics Of

When an energetic ion penetrates through an interface between a thin film (of species A) and a substrate (of species B), ion induced atomic mixing may result in an intermixed region (which contains A and B) near the interface. Most ion beam mixing experiments have been directed toward metal-silicon systems, silicide phases are generally obtained, and they are the same as those formed by thermal treatment.Recent emergence of silicide compound as contact material in silicon microelectronic devices is mainly due to the superiority of the silicide-silicon interface in terms of uniformity and thermal stability. It is of great interest to understand the kinetics of the interfacial reactions to provide insights into the nature of ion beam-solid interactions as well as to explore its practical applications in device technology.About 500 Å thick molybdenum was chemical vapor deposited in hydrogen ambient on (001) n-type silicon wafer with substrate temperature maintained at 650-700°C. Samples were supplied by D. M. Brown of General Electric Research & Development Laboratory, Schenectady, NY.

In situ study of electron beam-induced chemical vapor deposition of Au in an environmental TEM

1995 ◽  
Vol 53 ◽  
pp. 256-257
Author(s):  
J. Drucker ◽  
R. Sharma ◽  
J. Kouvetakis ◽  
K.H.J. Weiss
Keyword(s):  
Electron Beam ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Quantum Effect ◽  
Line Drawing ◽  
Chemical Vapor ◽  
Environmental Cell ◽  
Engineering Changes ◽  
Kinetics Of

Patterning of metals is a key element in the fabrication of integrated microelectronics. For circuit repair and engineering changes constructive lithography, writing techniques, based on electron, ion or photon beam-induced decomposition of precursor molecule and its deposition on top of a structure have gained wide acceptance Recently, scanning probe techniques have been used for line drawing and wire growth of W on a silicon substrate for quantum effect devices. The kinetics of electron beam induced W deposition from WF6 gas has been studied by adsorbing the gas on SiO2 surface and measuring the growth in a TEM for various exposure times. Our environmental cell allows us to control not only electron exposure time but also the gas pressure flow and the temperature. We have studied the growth kinetics of Au Chemical vapor deposition (CVD), in situ, at different temperatures with/without the electron beam on highly clean Si surfaces in an environmental cell fitted inside a TEM column.

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