Cleavage Process (cleavage + process)

Distribution by Scientific Domains


Selected Abstracts


A Facile Route to Synthesize the Ti5NbO14 Nanosheets by Mechanical Cleavage Process

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010
Na Zhang
Layered and rod-like K3Ti5NbO14 was synthesized via the solid-state chemistry, and it was exfoliated into nanosheets through a novel mechanical cleavage technology. X-ray diffraction was utilized to determine the phase changes of all the specimen during the total process, and the microstructure of the samples was analyzed by scanning electron microscope and transmission electron microscope. The formation mechanism was also discussed in detail, the results indicated that the compression and shearing should play a main function in the crack and the cleavage of the aggregated layered compound. UV,vis absorption spectroscopy was used to monitor the consecutive buildup of the (PEI/Ti5NbO14)n film. The resulting quasi-linear increase at the top absorbance as a function of the sequential assembly number for the multilayer film indicated that the nanosheet had deposited uniformly in each dipping cycle. The photocatalytic activity of K3Ti5NbO14 -related products was examined. Compared with original layered compound, nanosheet precipitate had good property under irradiation of ultraviolet light. [source]


ChemInform Abstract: A Novel Approach for Mannich-Type Bases Having a Terminal Olefin: Zinc Triflate and Water-Promoted Cyclization/C,N Bond Cleavage Process.

CHEMINFORM, Issue 16 2001
Kaori Ishimaru
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


Photochemical cleavage of a tattoo pigment by UVB radiation or natural sunlight

JOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, Issue 7 2007
Eva Engel
Summary Background: Millions of people have at least one tattoo. Complex and light absorbing molecules are implanted in the skin. When tattooed skin receives UV radiation or natural sunlight, photochemical cleavage of the pigments may occur. As a first step, we dissolved pigments in a suitable solvent and analyzed them after light irradiation. Methods: The widespread Pigment Red 22 was dissolved in different solvents. The solutions were irradiated with either UVB radiation (up to 8 h) or with natural sunlight (110 days). After irradiation, the solutions were analyzed by means of liquid chromatography and mass spectrometry. Results: A clear cleavage of the pigment was detected in all solvents and the primary decomposition products were identified. In tetrahydrofuran and dioxane, the pigment concentration decreased significantly during UVB irradiation, whereas the pigment was completely destroyed during sunlight exposure. In chloroform and dichloromethane, the pigment concentration decreased slightly during UVB irradiation, whereas the pigment was almost completely destroyed during sunlight exposure. Conclusion: Since chloroform and dichloromethane do not affect the cleavage process, these solvents are optimal for such in vitro experiments. We have shown the cleavage of the tattoo pigment Red 22 when exposed to UVB radiation or natural sunlight. The decomposition products are hazardous showing a potential risk of being toxic or even carcinogenic. At present, a risk assessment is not feasible since the concentration of pigments and their decomposition products in skin are unknown. [source]


Transformation of antimicrobial into bradykinin-potentiating peptides during peptic hydrolysis of bovine haemoglobin: identification, release kinetics and reaction network of peptides

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2007
Wei Qi
Abstract The precursor cleavage of the antimicrobial peptide ,107,136 into the bradykinin-potentiating peptide ,110,125 during peptic hydrolysis of bovine haemoglobin was investigated by reverse phase high-performance liquid chromatography coupled with tandem mass spectrometry. The optimal conditions for the preparation of ,107,136 and ,110,125 were found to be low and high degrees of hydrolysis respectively. A total of six peptides were identified as being involved in the cleavage process. Moreover, the reaction network of these peptides was developed according to the sequence alignment and their release kinetics. The affinity of pepsin towards different peptide bonds of bovine haemoglobin was also compared based on data from the release kinetics of peptides. In addition, some potentially bioactive peptides were predicted by means of sequence analysis and secondary structure calculations. Copyright © 2006 Society of Chemical Industry [source]


A Photodissociation Reaction: Experimental and Computational Study of 2-Hydroxy-2,2-dimethylacetophenone,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006
X. Allonas
ABSTRACT The photophysical parameters controlling the cleavage process of 2-hydroxy-2,2-dimethylacetophenone (HDMA) were investigated in detail. Time-resolved picosecond absorption experiments show that the formation of the triplet state occurs within 20 ps after excitation and decays within hundreds of picoseconds depending on the solvent polarity. Molecular modeling reveals that three stable conformations exist in the ground state, the most stable one exhibiting an intramolecular hydrogen bond that modifies the electronic properties of the molecule. This explains quite well the steady-state absorption properties. The conformation of the most stable triplet state is twisted by 180° with respect to the ground state. Computation of the potential energy surface along the molecular coordinate for the dissociation reaction evidences an electronic state crossing yielding a final ,,* state, in perfect agreement with the state correlation diagram. Optimization of the transition state allows the calculation of the activation energy and the use of the transition-state theory leads to an estimate of 100 ps for the cleavage process in the gas phase. Single-point energy calculations using a solvent model predict an increase of the dissociation rate constant with the increase of the solvent polarity, in good agreement with the value deduced from kinetic measurements. [source]


Ferrocene-bridging dinuclear cyclen copper(II) complexes as high efficient artificial nucleases: design, synthesis and interaction with DNA

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2008
Kun Li
Abstract Two novel cyclen copper(II) complexes bridged by ferrocene were designed and synthesized. Both of these complexes exhibited excellent cleavage ability towards plasmid DNA via an oxidative pathway without the presence of any additives. Cyclic voltammetry was used to investigate the electrochemistry characters of the interaction between the complexes and DNA. Agarose gel electrophoresis was carried out to study the DNA restriction ability of these complexes, and the results indicated that the complexes showed higher cleavage efficiency via an oxidative pathway without the presence of any additives. The mechanism of DNA cleavage catalyzed by these complexes was examined by the addition of various scavengers, and the results showed that singlet oxygen and hydroxyl radical might be responsible for the cleavage process. Copyright © 2008 John Wiley & Sons, Ltd. [source]


The Effect of an Amino-Acid Bridge on Binding Affinity and Cleavage Efficiency of Pyrenyl-Macrocyclic Polyamine Conjugates toward DNA

CHEMISTRY & BIODIVERSITY, Issue 8 2009
Qiao-Sen Lu
Abstract A series of pyrenyl-macrocyclic polyamines 5a,5c have been prepared and characterized. Their DNA-cleavage properties were examined under physiological conditions. Without the presence of other additives, the DNA cleavage ability of 5a,5c showed the order of 5c>5a>5b. Absorption and fluorescence experiments showed the binding affinity of 5a,5c to DNA. The interactions of 5a,5c with CT-DNA indicated that the DNA binding ability followed an order according to their cleavage efficiency. All the results indicated that the structures of amino-acid bridge in the ligands may affect the DNA binding and cleavage ability. The cleavage-mechanism studies indicated that singlet oxygen and superoxide free radicals were involved in the catalytic DNA cleavage process. [source]


Negative ion fragmentations of deprotonated peptides.

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2009
The unusual case of isoAsp: a joint experimental, theoretical study.
The following peptides have been examined in this study: GLDFG(OH), caeridin 1.1 [GLLDGLLGLGGL(NH2)], 11 Ala citropin 1.1 [GLFDVIKKVAAVIGGL(NH2)], Crinia angiotensin [APGDRIYVHPF(OH)] and their isoAsp isomers. It is not possible to differentiate between Asp- and isoAsp-containing peptides (used in this study) using negative ion electrospray mass spectrometry. This is because the isoAsp residue cleaves to give the same fragment anions as those formed by , and , backbone cleavage of Asp. The isoAsp fragmentations are as follows: RNHCH(CO2H),CHCONHR,,,,[RNH,(HO2CCHCHCONHR,)],,,RNH,+HO2CCHCHCONHR, and RNHCH(CO2H),CHCONHR,,,,[RNH,(HO2CCHCHCONHR,],,,,O2CCHCHCONHR,+RNH2. Calculations at the HF/6-31+G(d)//AM1 level of theory indicate that the first of these isoAsp cleavage processes is endothermic (by +115,kJ mol,1), while the second is exothermic (,85,kJ mol,1). The barrier to the highest transition state is 42,kJ mol,1. No diagnostic cleavage cations were observed in the electrospray mass spectra of the MH+ ion of the Asp- and isoAsp-containing peptides (used in this study) to allow differentiation between these two amino acid residues. Copyright © 2009 John Wiley & Sons, Ltd. [source]