Jose Ramos

Temperature-sensitive nanogels: poly(N-vinylcaprolactam) versus poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinylcaprolactam) (PVCL) are temperature-responsive polymers which show a lower critical solution temperature (LCST) around 32 °C in aqueous solutions. Nanogels based on these temperature sensitive polymers swell at low temperatures and collapse at high ones, showing a volume phase transition temperature (VPTT) near physiological temperature. This unique behavior makes these nanogels attractive for biotechnological applications. PNIPAM is the building block of a huge amount of nanogels reported in the literature. However, PVCL is especially interesting due to the fact that it is very stable against hydrolysis and biocompatible. In this mini-review, various synthesis procedures together with the functionalization of different PNIPAM- and PVCL-based nanogels are revised and compared.

Cationic polymer nanoparticles and nanogels: from synthesis to biotechnological applications.

Biotechnological Applications Jose Ramos,† Jacqueline Forcada,*,† and Roque Hidalgo-Alvarez*,‡ †POLYMAT, Bionanoparticles Group, Departamento de Química Aplicada, UFI 11/56, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, Apdo. 1072, 20080 Donostia-San Sebastiań, Spain ‡Grupo de Física de Fluidos y Biocoloides, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain

Soft nanoparticles (thermo-responsive nanogels and bicelles) with biotechnological applications: from synthesis to simulation through colloidal characterization

The use of nanotechnology in biotechnological applications has attracted tremendous attention from researchers. Currently many nanomaterials, such as soft nanoparticles, are under investigation and development for their use in biomedicine. Among soft nanoparticles, polymeric gels in the nanometre range, known as nanogel particles, have received considerable attention. Nanogel particles, which are formed by polymeric chains loosely cross-linked to form a three-dimensional network, swell by a thermodynamically good solvent but do not dissolve in it. Nanogels are composed of hydrophilic polymers capable of undergoing reversible volume-phase transitions in response to environmental stimuli. Among them, temperature-sensitive nanogels showing a volume phase transition temperature (VPTT) near physiological temperature have been investigated in detail. Nanogels based on biocompatible and temperature-sensitive polymers having a lower critical solution temperature (LCST) around 32 °C in aqueous solutions swell at low temperatures and collapse at high ones. This unique behavior makes these nanogels attractive for pharmaceutical, therapeutical, and biomedical applications. In this review, different synthesis strategies to produce this type of nanogels in dispersed media are revised. Special attention is paid to poly(N-vinylcaprolactam) (PVCL)-based nanogels due to their proven biocompatibility. On the other hand, an extensive review on the characteristics, preparation, and physicochemical properties of another type of soft nanoparticles, which are the bicelles, is presented. The different morphologies obtained depending on experimental conditions such as temperature, lipid concentration, and long- and short-chain phospholipids molar ratio are revised, emphasizing on an important property of bicelles: their alignment in the presence of a magnetic field, and presenting the most important applications of bicelles as membrane models in diverse conformational studies of proteins and membrane peptides, together with the possibilities of administration of such vesicles by systemic routes. A key challenge for the characterization of both soft nanoparticles (nanogels and bicelles) involves the elucidation of their colloidal properties. In this work, some colloidal features of these nanoparticles such as their size, electric double layer or the internal structure and motions of their chains are analyzed. In addition, an overview on the previous and current understanding of the methods and techniques employed in this colloidal characterization is presented, mainly from an experimental point of view. Finally, the most recent results on polyelectrolyte gels and bicelles obtained from computer simulations are also briefly commented. Concerning polyelectrolyte gels, this review is mainly focused on the most important feature of these systems, their large capacity of swelling, which has been explored by simulation in the last decade.

Synthesis of biologically active drimanes and homodrimanes from (−)-sclareol

Abstract Three drimanes, polygodial (2), albicanyl acetate (3) and 7-oxo-8,12-drimen-11-al (5), and two homodrimanes, 13,14,15,16-tetranorlabd-7-en-12,17-dial (6) and 7-oxo-13,14,15,16-tetranorlabd-8(17)-en-12-al (7), were synthesized from (−)-sclareol (1), and their antifeedant, antitumor and antimicrobial properties tested. In most cases, 6 and 7 were found to be more active than 2.

Synthesis of Ambrox® from(-)-sclareol and (+)cis-abienol

Abstract Short and efficient syntheses of (−)-Ambrox® (12) from (−)-sclareol (1) and (+)-cis-abienol (11) are described. In constrast to previously described procedures, the transformation of 1 to 12, involving in the key step, an oxidative degradation by catalytic osmium tetroxide, in the presence of sodium periodate, has the advantage of using the more suitable sodium borohydride, as the reducing agent. The isolation and characterization of some reaction intermediates allowed us to confirm the degradation mechanism.

Computer simulations of thermo-sensitive microgels: quantitative comparison with experimental swelling data.

In this work, a quantitative comparison between experimental swelling data of thermo-sensitive microgels and computer simulation results obtained from a coarse-grained model of polyelectrolyte network and the primitive model of electrolyte is carried out. Polymer-polymer hydrophobic forces are considered in the model through a solvent-mediated interaction potential whose depth increases with temperature. The qualitative agreement between simulation and experiment is very good. In particular, our simulations predict a gradual shrinkage with temperature, which is actually observed for the microgels studied in this survey. In addition, the model can explain the swelling behavior for different contents of ionizable groups without requiring changes in the hydrophobic parameters. Our work also reveals that the abruptness of the shrinkage of charged gels is considerably conditioned by the number of monomeric units per chain. The swelling data are also analyzed with the Flory-Rhener theory, confirming some limitations of this classical formalism.

Surfactant-Free Miniemulsion Polymerization as a Simple Synthetic Route to a Successful Encapsulation of Magnetite Nanoparticles

Due to the existing interest in new hybrid particles in the colloidal range based on both magnetic and polymeric materials for applications in biotechnological fields, this work is focused on the preparation of magnetic polymer nanoparticles (MPNPs) by a single-step miniemulsion process developed to achieve better control of the morphology of the magnetic nanocomposite particles. MPNPs are prepared by surfactant-free miniemulsion polymerization using styrene (St) as a monomer, hexadecane (HD) as a hydrophobe, and potassium persulfate (KPS) as an initiator in the presence of oleic acid (OA)-modified magnetite nanoparticles. The effect of the type of cross-linker used [divinylbenzene (DVB) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP)] together with the effect of the amount of an aid stabilizer (dextran) on size, particle size distribution (PSD), and morphology of the hybrid nanoparticles synthesized is analyzed in detail. The mixture of different surface modifiers produces hybrid nanocolloids with various morphologies: from a typical core-shell composed by a magnetite core surrounded by a polymer shell to a homogeneously distributed morphology where the magnetite is uniformly distributed throughout the entire nanocomposite.

Synthesis of Ambrox® from communic acids

Two routes for preparing Ambrox® (1) from the methyl esters of trans-communic acid (2b) and/or cis-communic acid (3b), via selective degradation of their side chains, stereoselective formation of the tetrahydrofurane ring, and reduction of the axial methoxycarbonyl group, are described.

Steady shear magnetorheology of inverse ferrofluids

Silica-based inverse ferrofluids (IFFs) are synthesized and their pre-yield and post-yield rheological properties are investigated as a function of magnetic field strength (8.8–276 kA/m), volume fraction (12.6–26.1 vol %), silica particle size (104–378 nm radius), and ferrofluid Newtonian viscosity (44–559 mPa s). The Mason number (Mn) provides a good scaling of the data in the steady simple shear flow regime. Special emphasis is made on the low and moderate Mason number region. At low Mn values, two different behaviors are observed depending on the IFF formulation and magnetic field strength applied: (i) either the viscosity monotonically increases with decreasing shear rate suggesting the existence of a yield stress (ii) or a low-shear plateau is reached. At medium Mn values, a power law behavior is found η/η∞∝MnΔ with −1<Δ<−2/3. Yielding behavior is modeled by using both macroscopic and microscopic approaches under the assumption of spheroidal, cylindrical, and single-width particle chain models.

Long-term study on the evaluation of yield and economic losses caused by Prays oleae Bern. in the olive crop of Granada (southern Spain)

Abstract A 28-year study (1970–1997) of olive trees grown in Granada (southern Spain) has revealed the levels of attack by the olive moth (Prays oleae Bern.), as well as the beneficial action of oophagous predators (Chrysopidae). On the basis of the results, the damage caused by the moth has been divided into three categories, and the yield and economic losses have been evaluated. When the final attack is ‘high’ (more than 40% fruit fall), which occurs approximately one in every three years, the necessity of control methods against the pest should be considered.