Home About us Contact
|
Home About us Contact | ||
|
|
||
Unimolecular Reaction (unimolecular + reaction)
Selected AbstractsAggregation kinetics of recombinant human FVIII (rFVIII)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Karthik Ramani Abstract The physical phenomenon of aggregation can have profound impact on the stability of therapeutic proteins. This study focuses on the aggregation behavior of recombinant human FVIII (rFVIII), a multi-domain protein used as the first line of therapy for hemophilia A, a bleeding disorder caused by the deficiency or dysfunction of factor VIII (FVIII). Thermal denaturation of rFVIII was investigated using circular dichroism (CD) spectroscopy and size exclusion chromatography (SEC). The dependence of unfolding on heating rate indicated that the thermal denaturation of the protein was at least partly under kinetic control. The data was interpreted in terms of a simple two-state kinetic model, , where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation. Analysis of the data in terms of the above scheme suggested that under the experimental conditions used in this study, the rate-controlling step in the aggregation of rFVIII may be a unimolecular reaction involving conformational changes. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2023,2029, 2005 [source] Synthesis and structural analysis of 1,4-bis[n -(N,N -dimethylamino)phenyl]buta-1,3-diynes and charge-transfer complexes with TCNEJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2001J. Gonzalo Rodríguez Abstract n -(N,N -Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n -(N,N -dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate dimers 1,4-bis[n -(N,N -dimethylamino)phenyl]buta-1,3-diyne were obtained by oxidative dimerization with copper(I) chloride. X-ray molecular structure analysis of the dimer 1,4-bis[2 -(N,N -dimethylamino)phenyl]buta-1,3-diyne corroborated the resonance contribution of the o -dimethylamino substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o - and p -(N,N -dimethylamino) conjugate dimers develop 1:1 charge-transfer complexes with TCNE and their structure was identified by NMR, IR and UV,visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3-diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright © 2001 John Wiley & Sons, Ltd. [source] Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociationsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003Jongwoo Lee Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH2CO) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H2CHO) and the acetyl radicals (CH3C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (,Hf°298) were determined using isodesmic reaction analysis at the CBS-QCI/APNO and the CBSQ levels. Entropies (S°298) and heat capacities (Cp°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6-311G(d,p) level of theory. Internal rotor contributions were included in the S and Cp(T) values. A hydrogen atom can add to the CH2 -group of the ketene to form the acetyl radical, CH3C·O (Ea = 2.49 in CBS-QCI/APNO, units: kcal/mol). The acetyl radical can undergo ,-scission back to reactants, CH2CO + H (Ea = 45.97), isomerize via hydrogen shift (Ea = 46.35) to form the slight higher energy, formyl methyl radical, C·H2CHO, or decompose to CH3 + CO (Ea = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H2CHO (Ea = 6.72). This formyl methyl radical can undergo , scission back to reactants, CH2CO + H (Ea = 43.85), or isomerize via hydrogen shift (Ea = 40.00) to form the acetyl radical isomer, CH3C·O, which can decompose to CH3 + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice,Ramsperger,Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH3 + CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH2CO by H to form, ketenyl radical plus H2 is identified with a barrier of 12.27, at the CBS-QCI/APNO level. ,Hf°298 values are estimated for the following compounds at the CBS-QCI/APNO level: CH3C·O (,3.27), C·H2CHO (3.08), CH2CO (,11.89), HC·CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 20,44, 2003 [source] Ultrasonic Spectrometry of Aqueous Solutions of Alkyl Maltosides: Kinetics of Micelle Formation and Head-Group IsomerizationCHEMPHYSCHEM, Issue 15 2009Julian Haller Abstract At frequencies between 100 kHz and 400 MHz, ultrasonic attenuation spectra are measured at 25,°C for aqueous solutions of hexyl-, heptyl-, octyl-, nonyl-, and decyl-,- D -maltopyranoside as well as of decyl-,- D -maltopyranoside. The spectra with surfactant concentration c above the relevant critical micelle concentration (cmc) display three relaxation terms with discrete relaxation times. That with a relaxation time between 0.1 and 1.2 ,s is due to exchange of monomers between micelles and the suspending phase. It is discussed in the light of the Teubner,Kahlweit,Aniansson,Wall model of the formation/decay kinetics of systems with Gaussian size distribution of micelles. The relaxation parameters are compared to those for solutions of other non-ionic surfactants, such as alkyl monoglycosides and poly(ethylene glycol) monoalkyl ethers. At c
| | |||||||||