Ina Baļķe, Gunta Resēviča, Dace Skrastiņa and Andris Zeltiņš
Expression and characterisation of the ryegrass mottle virus non-structural proteins
The Ryegrass mottle virus (RGMoV) single-stranded RNA genome is organised into four open reading frames (ORF) which encode several proteins: ORF1 encodes protein P1, ORF2a contains the membrane-associated 3C-like serine protease, genome-linked protein VPg and a P16 protein gene. ORF2b encodes replicase RdRP and the only structural protein, coat protein, is synthesised from ORF3. To obtain the non-structural proteins in preparative quantities and to characterise them, the corresponding RGMoV gene cDNAs were cloned in pET- and pColdI-derived expression vectors and overexpressed in several E. coli host cells. For protease and RdRP, the best expression system containing pColdI vector and E. coli WK6 strain was determined. VPg and P16 proteins were obtained from the pET- or pACYC- vectors and E. coli BL21 (DE3) host cells and purified using Ni-Sepharose affinity chromatography. Attempts to crystallize VPg and P16 were unsuccessful, possibly due to non-structured amino acid sequences in both protein structures. Methods based on bioinformatic analysis indicated that the entire VPg domain and the C-terminal part of the P16 contain unstructured amino acid stretches, which possibly prevented the formation of crystals.
Mikelis Kirpluks, Ugis Cabulis, Viesturs Zeltins, Laura Stiebra and Andris Avots
One of the biggest disadvantages of rigid polyurethane (PU) foams is its low thermal resistance, high flammability and high smoke production. Greatest advantage of this thermal insulation material is its low thermal conductivity (λ), which at 18-28 mW/(m•K) is superior to other materials. To lower the flammability of PU foams, different flame retardants (FR) are used. Usually, industrially viable are halogenated liquid FRs but recent trends in EU regulations show that they are not desirable any more. Main concern is toxicity of smoke and health hazard form volatiles in PU foam materials. Development of intumescent passive fire protection for foam materials would answer problems with flammability without using halogenated FRs. It is possible to add expandable graphite (EG) into PU foam structure but this increases the thermal conductivity greatly. Thus, the main advantage of PU foam is lost. To decrease the flammability of PU foams, three different contents 3%; 9% and 15% of EG were added to PU foam formulation. Sample with 15% of EG increased λ of PU foam from 24.0 to 30.0 mW/(m•K). This paper describes the study where PU foam developed from renewable resources is protected with thermally expandable intumescent mat from Technical Fibre Products Ltd. (TFP) as an alternative to EG added into PU material. TFP produces range of mineral fibre mats with EG that produce passive fire barrier. Two type mats were used to develop sandwich-type PU foams. Also, synergy effect of non-halogenated FR, dimethyl propyl phosphate and EG was studied. Flammability of developed materials was assessed using Cone Calorimeter equipment. Density, thermal conductivity, compression strength and modulus of elasticity were tested for developed PU foams. PU foam morphology was assessed from scanning electron microscopy images.