Crystal structure and aqueous solubility of ammonium D-glucarate

Ammonium D-glucarate, NH(4)(C(6)H(9)O(8)) [ammonium D-saccharate, NH(4)-SAC], has been synthesized, and its crystal structure solved by single-crystal X-ray diffraction methods. NH(4)-SAC crystallizes in the monoclinic space group P2(1) (#4) with cell parameters a = 4.8350(4) Angstroms, b = 11.0477(8) Angstroms, c = 16.7268(12) Angstroms, beta = 90.973(1) degrees, V = 894.34(12) Angstroms(3), Z = 3. The structure was refined by full-matrix least-squares on F(2) yielding final R-values (all data) R1 = 0.0353 and R(w)2 = 0.0870. The structure consists of alternating (NH(4))(+) and (C(6)H(11)O(6))(-) layers parallel to the bc plane. An extended network of N-H...O(SAC) and O(SAC)-H...O(SAC) hydrogen bonds provide the 3-D connectivity. The aqueous solubility (S(w)) has been shown to be pH independent at ambient conditions within the range 4.5 < pH < 10 with S(w) = 2.19 M/L, whose value is about a factor of two lower than that of the ammonium isosaccharate analogue.     

Environmentally friendly C-glycosylation of phloroacetophenone with unprotected D-glucose using scandium(III) trifluoromethanesulfonate in aqueous media: key compounds for the syntheses of mono- and di-C-glucosylflavonoids

The direct C-glycosylation of phloroacetophenone with an unprotected d-glucose in aqueous media using scandium(III) trifluoromethanesulfonate (Sc(OTf)3) as the catalyst, gave mono- and bis-C-beta-glycosylic compounds in highest total yield of 81%. The second and third use of the recovered Sc(OTf)3 afforded them in total yields of 56% and 53%, respectively.     

A kinetic study of the growth of fatty acid vesicles

Membrane vesicles composed of fatty acids can be made to grow and divide under laboratory conditions, and thus provide a model system relevant to the emergence of cellular life. Fatty acid vesicles grow spontaneously when alkaline micelles are added to buffered vesicles. To investigate the mechanism of this process, we used stopped-flow kinetics to analyze the dilution of non-exchanging FRET probes incorporated into preformed vesicles during growth. Oleate vesicle growth occurs in two phases (fast and slow), indicating two pathways for the incorporation of fatty acid into preformed vesicles. We propose that the fast phase, which is stoichiometrically limited by the preformed vesicles, results from the formation of a "shell" of fatty acid around a vesicle, followed by rapid transfer of this fatty acid into the preformed vesicle. The slower phase may result from incorporation of fatty acid which had been trapped in an intermediate state. We provide independent evidence for the rapid transformation of micelles into an aggregated intermediate form after transfer from high to low pH. Our results show that the most efficient incorporation of added oleate into oleic acid/oleate vesicles occurs under conditions that avoid a large transient increase in the micelle/vesicle ratio.     

Carbon nanotube aqueous sol-gel composites: enzyme-friendly platforms for the development of stable biosensors

A new type of composite material based on carbon nanotubes and an aqueous sol-gel process has been developed. The electrochemical characteristics of these composites were investigated and compared to composites made with an alkoxy silane sol-gel process. The use of carbon nanotubes, as the conductive part of the composite, facilitated fast electron transfer rates. The feasibility of this type of composite for the development of biosensors was demonstrated using l-amino acid oxidase. The stability of the enzyme was increased when it was encapsulated in the aqueous sol-gel, and the sensor retained more that 50% of its response after 1 month of testing.     

Aggregation of cyclodextrins as an important factor to determine their complexation behavior

Here, we report a study on the complexation behavior of carotenoids with cyclodextrins (CDs) using solubility experiments and molecular-modelling methods. Carotenoids are an important group of naturally occurring dyes found in vegetables and fruits. Their antioxidant property has initiated investigations on their possible use as drugs. However, carotenoids are lipophilic molecules with very little inherent aqueous solubility. Cyclodextrin complexation has been widely used in order to increase the potential applications of hydrophobic compounds. Thus, the aim of our investigation was to design carotenoids with enhanced water solubility by cyclodextrin complexation. Molecular modelling of carotenoid-cyclodextrin complexes with a 1 : 1 stoichiometry successfully explained the experimentally observed capability of beta-cyclodextrins (beta-CDs) to form complexes with carotenoids as opposed to alpha-cyclodextrins (alpha-CDs) and gamma-cyclodextrins (gamma-CDs). Furthermore, molecular-dynamics calculations revealed that the aggregation properties of CD derivatives significantly influence their complexation behavior. Our docking calculations showed that RAMEB (random methylated beta-CD) is the beta-CD derivative that possesses the lowest tendency to aggregate. Solubility experiments yielded the same results, namely, RAMEB complexes possess the best water solubility. Our results showed that complexation of a ligand not buried inside of the CD cavity is dependent on two factors: i) the geometry of the inclusion part of the complex; ii) the self-aggregation property of the CD itself. The lower affinity the CDs possess for self-aggregation, the more likely are they involved in interactions with carotenoids. These results suggest that self-aggregation of CDs should be considered as an important parameter determining complexation in general.     

Fluid Mechanics of the Human Eye: Aqueous Humour Flow in The Anterior Chamber

We consider and compare the various different kinds of flow that may take place in the anterior chamber of a human eye. The physical mechanisms responsible for causing such flows may be classified as follows: (i) buoyancy-driven flow arising from the temperature difference between the anterior surface of the cornea and the iris, (ii) flow generated by the aqueous production of the ciliary body, (iii) flow generated by the interaction between buoyancy and gravity while sleeping while sleeping in a face-up position, (iv) flow generated by phakodenesis (lens tremor), (v) flow generated by Rapid Eye Movement (REM) during sleep. Each flow is studied using a traditional fluid mechanics/asymptotic analysis approach. We also assess the veracity of a hypothesis that was recently advanced [see Maurice, D.M., 1998. The Von Sallman Lecture 1996: An ophthalmological explanation of REM sleep. Exp. Eye. Res. 66, 139–145, for details] to suggest that, contrary to previous opinion, the purpose of REM during sleep is to ensure corneal respiration in the absence of the buoyant mixing that routinely takes place due to (i) above during waking conditions.     

Allene oxide synthase from Arabidopsis thaliana (CYP74A1) exhibits dual specificity that is regulated by monomer-micelle association

We investigate the effects of detergent on the kinetics and oligomeric state of allene oxide synthase (AOS) from Arabidopsis thaliana (CYP74A1). We show that detergent-free CYP74A1 is monomeric and highly water soluble with dual specificity, but has relatively low activity. Detergent micelles promote a 48-fold increase in k(cat)/K(m) (to 5.9 x 10(7)M(-1)s(-1)) with concomitant changes in the spin state equilibrium of the haem-iron due to the binding of a single detergent micelle to the protein monomer, which is atypical of P450 enzymes. This mechanism is shown to be an important determinant of the substrate specificity of CYP74A1. CYP74A1 may be suited for structural resolution of the first plant cytochrome P450 and its 9-AOS activity and behaviour in vitro has implications for its role in planta.     

Combined hydrophobic-metal binding fusion tags for applications in aqueous two-phase partitioning

In this work, we studied the influence of fusion affinity tags containing both hydrophobic and histidines residues on the partitioning of the green fluorescent protein, GFPuv, in aqueous two-phase system. The tags were fused to the N-terminal of GFPuv and tested by immobilized metal affinity partitioning, in a PEG/salt system. The presence of both types of residues in the tag increased the partitioning greatly. Particularly, four engineered tags (H6, FH6, WH6, and YH6) containing a hexa-histidine sequence as well as different hydrophobic residues, all increased partitioning more than twice, reaching K values around 20, as compared to another construct (His6-GFP) containing an isolated hexa-histidine sequence. YH6, also proved be beneficial for protein expression.     

Delayed luminescence: a novel technique to obtain new insights into water structure

Fully understanding the structure of water is a crucial point in biophysics because this liquid is essential in the operation of the engines of life. Many of its amazing anomalies seem to be tailored to support biological processes and, during about a century, several models have been developed to describe the water structuring. In particular, a theory assumes that water is a mixture of domains constituted by two distinct and inter-converting structural species, the low-density water (LDW) and the high-density water (HDW). According to this theory, by using some particular solutes or changing the water temperature, it should be possible to modify the equilibrium between the two species, changing in this way the water behavior in specific biological processes, as in governing the shape and stability of the structures of proteins. In this work, we assess the possibility of obtaining information on the structures induced in water by specific salts or by temperature by measuring the delayed luminescence (DL) of some salt solutions and of water in the super-cooled regime. Previous works have demonstrated that the delayed luminescence of a system is correlated with its dynamic ordered structures. The results show significant DL signals only when the formation of LDW domains is expected. The measurement reveals a similar activation energy for the domains both in aqueous salt solutions and super-cooled water. It is worth noting that the time trend of DL signals suggests the existence of structures unusually long-lasting in time, up to the microsecond range.