Comparison of Chromatographic Performance for L-Phenylalanine-Derived Organic Phases on Silica by “Grafting from” and “Grafting to” Strategies

L-phenylalanine-derived polymerizable organogel, N’-octadecyl-Nα-(4-vinyl)-benzoyl-L-phenylalanineami- de (4) has been prepared according to the procedure described elsewhere. Compound 4 was successfully polymerized by surface initiated atom transfer radical polymerization (ATRP) from the initiator grafted silica particles (sil-poly4). It was also telomerized with 3-mercaptopropyltrimethoxysilane (MPS) and the telomer (T4) was grafted on to silica (sil-T4). TGA and elemental analysis measurement revealed that higher amount of polymer can graft by ATRP process than that of “grafting to” strategy. The results of 13C CP/MAS NMR measurement showed that the N-alkyl chain of the grafted polymers for both sil-poly4 and sil-T4 remained as less ordered gauche conformational form on silica surface and no inversion to trans form was occurred until temperature is increased up to 50?C. The retention of alkylbenzene samples showed that sil-poly4 prepared by “grafting from” method yielded extremely higher retention than conventional C18 phase however, sil-T4 prepared by conventional “grafting to” method showed lower retention than C18 phase. Aspects of molecular recognition were evaluated by the retention studies of a series of polycyclic aromatic hydrocarbons (PAHs) and aromatic positional isomers. We have observed sil-T4 yielded slightly higher selectivity for PAHs than sil-poly4 regardless the fact that it has low surface coverage and lower hydrophobic interactions. The enhanced selectivity observed for sil-T4 than C18 phases and sil-poly4 can be explained by the π - π interactions between the guest PAHs and carbonyl groups present in the polymer chain. In addition the aromatic moieties of compound 4 that aggregates through π - π interactions also contribute to the separation of PAHs for both sil-poly4 and sil-T4. The minimal π - π interactions between the carbonyl groups and guest molecules for sil-poly4 probably due to the presence of long chain initiator which restrict the polymer to form order thin layer over silica surface.

Preparation of Chitin-PLA laminated composite for implantable application

The present study explores the possibilities of using locally available inexpensive waste prawn shell derived chitin reinforced and bioabsorbable polylactic acid(PLA)laminated composites to develop new materials with excellent mechanical and thermal properties for implantable application such as in bone or dental implant.Chitin at different concentration(1e20%of PLA)reinforced PLA films(CTP)were fabricated by solvent casting process and laminated chitin-PLA composites(LCTP)were prepared by laminating PLA film(obtained by hot press method)with CTP also by hot press method at 160
C.The effect of variation of chitin concentration on the resulting laminated composite's behavior was investigated.The detailed physico-mechanical,surface morphology and thermal were assessed with different characterization technique such as FT-IR,XRD,SEM and TGA.The FTIR spectra showed the characteristic peaks for chitin and PLA in the composites.SEM images showed an excellent dispersion of chitin in the films and composites.Thermogravimetric analysis(TGA)showed that the complete degradation of chitin,PLA film,5%chitin reinforced PLA film(CTP2)and LCTP are 98%,95%,87%and 98%respectively at temperature of 500
C.The tensile strength of the LCTP was found 25.09 MPa which is significantly higher than pure PLA film(18.55 MPa)and CTP2 film(8.83 MPa).After lamination of pure PLA and CTP2 film,the composite(LCTP)yielded 0.265e1.061%water absorption from 30 min to 24 h immerse in water that is much lower than PLA and CTP.The increased mechanical properties of the laminated films with the increase of chitin content indicated good dispersion of chitin into PLA and strong interfacial actions between the polymer and chitin.The improvement of mechanical properties and the results of antimicrobial and cytotoxicity of the composites also evaluated and revealed the composite would be a suitable candidate for implant application in biomedical sector.