Microrheology to Understand the Viscosity Behavior of a Sophorolipid Biosurfactant

The microstructure of the aqueous solutions of purified acidic Sophorolipid (SL) has previously been studied using highly sophisticated methods such as SANS and Cryo-TEM. We were interested in whether (a) the main findings also apply to commercially available SL (which is a mixture of acidic and lactonic SL) and (b) more readily available methods such as DLS can be used to gain insight into the molecular aggregation of SL. Our work was motivated by the increasing interest in biosurfactants for applications in personal and household care. Moreover, the origin behind the more or less lack of rheological response to changes in pH is of practical relevance, as it is somewhat unusual for a carboxylate-group containing surfactant. By using DLS microrheology, we could elucidate the aggregation structure and dynamics of the surfactant on a microscopic scale. Surprisingly, the different degrees of protonation only impacted the microscopic properties such as exchange kinetics and the plateau values of the storage moduli.

Nickel(II)-Complex of Ceftibuten Dihydrate: Synthesis, Characterization and Thermal Study

Ceftibuten dihydrate is a semisynthetic, orally administered, third generation cephalosporin antibiotic which is effective against most of the pathogens causing infections in the respiratory tract. Complexation of ceftibuten dehydrate (Ligand, L) was performed with hydrated Ni(II) salt (Metal, M) in the ratio of 2:1 (L:M) in aqueous medium at 90 oC. The metal complex was then characterized by spectral techniques and thermal analyses. The FT-IR spectral data of metal complex suggested the monodentate bonding of metal ion to carboxylate group. Spectral evidence also supported the formation of five-membered ring via coordination of metal ion to β-lactam nitrogen and carboxylate group of parent drug. Thermal behavior of ligand and complex were studied. Thus, thermoanalytical (DSC and TGA) results also supported the formation of new metal complex, indicating the successful interaction of metal ion to ligand. Dhaka Univ. J. Pharm. Sci. 20(2): 219-225, 2021 (December)

Lithium dipotassium citrate monohydrate, LiK2C6H5O7(H2O)

The crystal structure of dilithium potassium citrate monohydrate, Li+·2K+·C6H5O7 3−·H2O or LiK2C6H5O7·H2O, has been solved by direct methods and refined against laboratory X-ray powder diffraction data, and optimized using density functional techniques. The complete citrate trianion is generated by a crystallographic mirror plane, with two C and three O atoms lying on the reflecting plane, and chelates to three different K cations. The KO8 and LiO4 coordination polyhedra share edges and corners to form layers lying parallel to the ac plane. An intramolecular O—H...O hydrogen bond occurs between the hydroxyl group and the central carboxylate group of the citrate anion as well as a charge-assisted intermolecular O—H...O link between the water molecule and the terminal carboxylate group. There is also a weak C—H...O hydrogen bond.

Formulation and Characterization of Alginate-Based Membranes for the Potential Transdermal Delivery of Methotrexate

The aim of this study is to obtain and characterize of alginate-based membranes, as well as to choose the most suitable membrane type for the transdermal release of methotrexate. The paper presents the synthesis of four types of membranes based on alginate to which are added other copolymers (Carbopol, Tween, and Polyvinylpyrrolidone) as well as other components with different roles. Membranes and binary mixtures made between the components used in membrane synthesis and methotrexate are analyzed by thermogravimetric techniques, FTIR and UV spectroscopic techniques as well as SEM. The analyses aim to establish the type of membrane most indicated in the use of the controlled release of methotrexate, namely those membranes in which there are no interactions that could inactivate the active substance. Following these studies, it was concluded that membranes obtained from alginate/alginate and Tw can be used for methotrexate release. The membrane obtained from alginate and carbopol was excluded from the beginning because it is not homogeneous. Regarding the AGP-MTX membrane, it presents interactions with the active substance, carboxylate group interactions argued by TGA and FTIR studies, and interactions that occur in aqueous medium.

Synthesis, molecular and crystal structure of a heterometallic Cu(II)–Ge(IV) complex with 2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetracetic acid and 2,2'-bipyridine

A novel synthesis method was developed which allows isolating a new coordination compound with polymeric structure {[Ge2(OH)2(3-hpdta)2Cu2(bipy)2]2Н2О}n (І) (where hpdta5– – anion of 2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetracetic acid, bipy – 2,2'-bipyridine) in solid state. Elemental composition, features of thermal decomposition, and molecular and crystalline structure of the synthesized complex were established. According to the data of X-ray diffraction analysis, complex I is a coordination polymer. The polymer chain is formed due to the bridging function of deprotonated ligands hpdta5–, which are simultaneously coordinated with germanium and copper atoms. Ge(1) and Ge(2) atoms have the same coordination environment and distorted octahedral polyhedrons. The coordination polyhedron of Ge(2) is formed due to the coordination of oxygen atoms of two carboxylate and one deprotonated hydroxyl groups of one ligand hpdta5–_1 and carboxylate group of the second ligand hpdta5–_2 in the equatorial direction. In the axial direction, the Ge atom coordinates with the nitrogen atom of the ligand hpdta5–_1 and the hydroxo-ligand. The coordination polyhedrons of Cu(1) and Cu(2) are square pyramids, in which molecules of bipy are coordinated with Cu2+ by two nitrogen atoms. One nitrogen atom and one oxygen atom of the carboxylate group of the hpdta5– ligand are located in the base of a square pyramid. In the apical direction, copper coordinates with deprotonated hydroxyl group of the same hpdta5– ligand. A –-stacking interaction was detected in the crystal between the -systems of bipyridines of two neighboring coordination polymer chains directed along the crystallographic axis a that form double chains with the cavities of 623.04 Å3.

Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor- Free Decarboxylase

<div> <div> <p> </p><div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div> </div> </div>

Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor- Free Decarboxylase

<div> <div> <p> </p><div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div> </div> </div>

Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor- Free Decarboxylase

<div> <div> <p> </p><div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div> </div> </div>