RESUMO
Melting and premelting phenomena in self-organized organic systems have been extensively explored in the literature, exploring distinct behaviors of different molecule lengths and morphologies. Nevertheless, the influence of the supramolecular assembly configuration on the occurrence of premelting remains poorly explored. Here we use phosphonic acids as model systems for self-organized molecular assemblies. These molecules exhibit long-range order on different types of substrates. The balance between chain-to-chain and head-to-head interactions leads to distinct types of stackings. Although their structural configurations are well understood, very little is known about their behavior near the melting transition. We show here that premelting occurs in lamellar structures and that its behavior depends directly on the ordered configuration assumed in the studied multilayers. Two molecules with different chain lengths were investigated: octadecyl phosphonic and octyl phosphonic acids. Although almost no dependence on the molecule length was observed, the occurrence of premelting is strongly influenced by their lamellar packing configuration. For tilted packings premelting is unfavored while in straight configurations, where alkyl chain interactions are weakened with respect to head-to-head interactions, strong premelting is observed. We find that the onset of premelting occurs at the domain boundaries with straight lamellar configurations and the domain sizes exhibit power law temperature dependences.
Assuntos
Cristalização/métodos , Modelos Químicos , Modelos Moleculares , Ácidos Fosforosos/química , Simulação por Computador , Transição de FaseRESUMO
An immune mechanism has been suggested in the pathogenesis of periodontal disease. Actinobacillus actinomycetemcomitants (Aa) has been implicated as one of the etiological agents that induces the major immune response together with a dense infiltrate of inflammatory cells. But the exact role of these immune cells in periodontal disease has not yet been clarified. In this study the T lymphocyte (TL) proliferative response was evaluated after having being exposed to free cell supernatant (SN) from Aa. Aa SN increased TL proliferation. This mitogenic effect of Aa SN was attenuated by pretreating TL with indomethacin (INDO) or acetylsalicylic acid (ASA) but not by polymyxin B. The inhibitory effect of INDO on cell proliferation was reversed by the addition of prostaglandin E2 (PGE2) to the culture assay. Moreover, when immune cells were exposed to Aa SN they were able to generate PGE2 at the same time as intracellular levels of cAMP decreased. Both, PGE2 release and decrease accumulation of cAMP in TL were blunted by treated lymphocytes with INDO. In this paper we demonstrate that cell free SN from Aa induces a mitogenic effect on murine lymphocytes. The mechanism involves the host's immunecompetent cells and the release of PGE2 and appears not to be induced by capsular-like polysaccharide antigen. Results show a paradoxical mitogenic effect of Aa SN accompanied by increased generation of PGE2 and decreased production of cAMP by lymphocytes.
Assuntos
Aggregatibacter actinomycetemcomitans/química , AMP Cíclico/fisiologia , Dinoprostona/fisiologia , Linfócitos T/microbiologia , Animais , Aspirina/farmacologia , Divisão Celular/efeitos dos fármacos , Meios de Cultivo Condicionados/farmacologia , AMP Cíclico/metabolismo , Inibidores de Ciclo-Oxigenase/farmacologia , Dinoprostona/metabolismo , Indometacina/farmacologia , Cinética , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Polimixina B/farmacologia , Linfócitos T/citologia , Linfócitos T/metabolismoRESUMO
The mutans group of streptococci is considered to play a key role in the etiology of dental caries. We have evaluated the ability of different substances to prevent dental plaque formation without affecting Streptococcus sobrinus viability. Viable organisms were detected as CFU/mL in agar plates and bacterial adherence was assessed by dry weight. We studied 23 compounds and we demonstrated that phenyl salicylate, phenylmercuric nitrate and potassium iodate are more effective to inhibit adhesion without showing antibacterial activity.