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Molecular Groups (molecular + groups)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

In Situ Characterization of Thermo-Responsive Poly(N -Isopropylacrylamide) Films with Sum-Frequency Generation Spectroscopy

CHEMPHYSCHEM, Issue 7 2010
Volker Kurz
Abstract The thermo-responsive behaviour of thiol modified poly(N -isopropylacrylamide) (pNIPAM) films immobilized on gold are probed by in situ broadband sum-frequency generation (SFG) spectroscopy. The pNIPAM films were prepared by atom transfer radical polymerization (ATRP) using a nitro-biphenyl-thiol (NBT)-SAM on a polycrystalline gold surface as a substrate. Additionally, Raman and infrared reflection absorption spectroscopy (IRRAS) are applied to spin-coated pNIPAM films. Molecular groups involved in the reorientation and disordering of the polymer chains during the LCST (lower critical solution temperature) transition of pNIPAM are identified. The characteristic vibrations of the CH3 groups show a gradual reorientation of the isopropyl groups within the pNIPAM film and instantaneous reorientation of the outermost CH3 groups around 32,°C. [source]

Molecular epidemiology of HIV in Ghana: Dominance of CRF02_AG

JOURNAL OF MEDICAL VIROLOGY, Issue 2 2004
Lucia Fischetti
Abstract Recent studies showed the importance of CRF02_AG in West Africa, although the clinical relevance of these recombinant forms of HIV remains unknown. The present study aimed at determining the molecular diversity of HIV in Ghana and investigating the possible epidemiologic advantage of recombinant HIV-1. Plasma samples collected in 1999,2002 from two populations of HIV infected individuals (144 asymptomatic candidate blood donors and 169 AIDS patients) were studied and 249 of them were molecularly characterised in gag, pol, and env regions. Five molecular groups were identified: strains clustering with CRF02_AG in all regions (147/249 or 59%), recombinant strains clustering with CRF02_AG in one or two regions (50/249 or 20%), other subtypes, pure or recombinant, but not involving CRF02_AG (37/249 or 15%), HIV-2 (11/249 or 4.5%), and double infections (4/249 or 1.5%). There was no significant difference in the distribution of HIV-1 recombinant strains according to clinical presentation. No evidence of a significant increase in CRF02_AG prevalence between 1999 and 2002 was found. Irrespective of clinical condition, CRF02_AG is the predominant molecular form of HIV-1 in Kumasi, Ghana. J. Med. Virol. 73:158,166, 2004. © 2004 Wiley-Liss, Inc. [source]

Heavy atom motions and tunneling in hydrogen transfer reactions: the importance of the pre-tunneling state

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2010
Hans-Heinrich Limbach
Abstract Arrhenius curves of selected hydrogen transfer reactions in organic molecules and enzymes are reviewed with the focus on systems exhibiting temperature-independent kinetic isotope effects. The latter can be rationalized in terms of a ,pre-tunneling state' which is formed from the reactants by heavy atom motions and which represents a suitable molecular configuration for tunneling to occur. Within the Bell,Limbach tunneling model, formation of the pre-tunneling state dominates the Arrhenius curves of the H and the D transfer even at higher temperatures if a large energy Em is required to reach the pre-tunneling state. Tunneling from higher vibrational levels and the over-barrier reaction via the transition state which lead to temperature-dependent kinetic isotope effects dominate the Arrhenius curves only if Em is small compared to the energy of the transition state. Using published data on several hydrogen transfer systems, the type of motions leading to the pre-tunneling state is explored. Among the phenomena which lead to large energies of the pre-tunneling state are (i) cleavage of hydrogen bonds or coordination bonds of the donor or acceptor atoms to molecules or molecular groups in order to allow the formation of the pre-tunneling state, (ii) the occurrence of an energetic intermediate on the reaction pathway within which tunneling takes place, and (iii) major reorganization of a molecular skeleton, requiring the excitation of specific vibrations in order to reach the pre-tunneling state. This model suggests a solution to the puzzle of Kwart's findings of temperature-independent kinetic isotope effects for hydrogen transfer in small organic molecules. Copyright © 2010 John Wiley & Sons, Ltd. [source]

An overview of the antifungal properties of allicin and its breakdown products , the possibility of a safe and effective antifungal prophylactic

MYCOSES, Issue 2 2005
Stephen R Davis
Summary Reports about the safe and successful intravenous (i.v.) use of garlic derivatives in China against invasive fungal infections have been made, but little has been done to seriously investigate the in vivo use of these derivatives in the West. Laboratories have demonstrated impressive in vitro MICs using allitridium, one of these derivatives, against a range of medically important fungi. In addition, it has been demonstrated that allitridium shows in vitro synergy with amphotericin B, one of the main i.v. antifungal agents. Some of the breakdown products of allicin, the main parent antifungal compound in garlic, have been investigated for their general antimicrobial, anticancer and anticholesterol properties, and it appears that there is a common mode of action that underlies these activities. It appears that these small molecules have the ability to cross cell membranes and combine with sulfur-containing molecular groups in amino acids and proteins, thus interfering with cell metabolism. It has been suggested that the reason human cells are not poisoned by allicin derivatives is that they contain glutathione, a sulfur-containing amino acid that combines with the allicin derivative, thus preventing cell damage. In addition to their biochemical mechanism, these derivatives appear to stimulate cellular immunity, an important ability lacking in conventional antifungal chemotherapy. These derivatives appear to be safe, cheap, wide-spectrum and immunostimulatory, as well as possibly synergistic with conventional antifungal therapy, making them ideal candidates for investigation into their use as prophylactic antifungal agents. [source]