Coordination studies of Al-EDTA in aqueous solution

The degree of aluminum toxicity is based on its complexation with organic ligands. One of these complexes is AlEDTA- (Al = aluminum, EDTA = ethylenediaminetetraacetate), the structure of which in aqueous solution has been debated on the basis of X-ray absorption and NMR measurements with different interpretations proposing different coordination. In addition, there is a lack of consensus regarding the relationship of crystalline AlEDTA- and its geometry in solution. This debate must be resolved, not merely for scientific interest, but because the use of an incorrect coordination might lead to the wrong interpretation of bioactivity and kinetics data. In this work, we predict the coordination of Al in aqueous AlEDTA- by employing ab initio calculations and Car-Parrinello molecular dynamics simulations. Our results indicate that AlEDTA- favors Al in octahedral coordination in aqueous solution. Furthermore, the predicted crystalline and solution-phase structures of AlEDTA- are similar and agree well with recent X-ray measurements, supporting the strong chelating nature of this metal-organic complex in aqueous solution.     

Achieving Molecular Recognition of Structural Analogues in Surface-Enhanced Raman Spectroscopy: Inducing Charge and Geometry Complementarity to Mimic Molecular Docking

Molecular recognition of complex isomeric biomolecules remains challenging in surface-enhanced Raman scattering (SERS) spectroscopy due to their small Raman cross-sections and/or poor surface affinities. To date, the use of molecular probes has achieved excellent molecular sensitivities but still suffers from poor spectral specificity. Here, we induce “charge and geometry complementarity” between probe and analyte as a key strategy to achieve high spectral specificity for effective SERS molecular recognition of structural analogues. We employ 4-mercaptopyridine (MPY) as the probe, and chondroitin sulfate (CS) disaccharides with isomeric sulfation patterns as our proof-of-concept study. Our experimental and in silico studies reveal that “charge and geometry complementarity” between MPY's binding pocket and the CS sulfation patterns drives the formation of site-specific, multidentate interactions at the respective CS isomerism sites, which “locks” each CS in its analogue-specific complex geometry, akin to molecular docking events. Leveraging the resultant spectral fingerprints, we achieve > 97 % classification accuracy for 4 CSs and 5 potential structural interferences, as well as attain multiplex CS quantification with < 3 % prediction error. These insights could enable practical SERS differentiation of biologically important isomers to meet the burgeoning demand for fast-responding applications across various fields such as biodiagnostics, food and environmental surveillance.     

Isolation, structure, and antibacterial activity of philipimycin, a thiazolyl peptide discovered from Actinoplanes philippinensis MA7347

Bacterial resistance to antibiotics, particularly to multiple drug resistant antibiotics, is becoming cause for significant concern. The only really viable course of action is to discover new antibiotics with novel mode of actions. Thiazolyl peptides are a class of natural products that are architecturally complex potent antibiotics but generally suffer from poor solubility and pharmaceutical properties. To discover new thiazolyl peptides potentially with better desired properties, we designed a highly specific assay with a pair of thiazomycin sensitive and resistant strains of Staphylococcus aureus, which led to the discovery of philipimycin, a new thiazolyl peptide glycoside. It was isolated along with an acid-catalyzed degradation product by bioassay-guided fractionation. Structure of both compounds was elucidated by extensive application of 2D NMR, 1D TOCSY, and HRESIFT-MS/MS. Both compounds showed strong antibacterial activities against gram-positive bacteria including MRSA and exhibited MIC values ranging from 0.015 to 1 microg/mL. Philipimycin was significantly more potent than the degradation product. Both compounds showed selective inhibition of protein synthesis, indicating that they targeted the ribosome. Philipimycin was effective in vivo in a mouse model of S. aureus infection exhibiting an ED50 value of 8.4 mg/kg. The docking studies of philipimycin suggested that a part of the molecule interacts with the ribosome and another part with Pro23, Pro22, and Pro26 of L11 protein, which helped in explaining the differential of activities between the sensitive and resistant strains. The design and execution of the bioassay, the isolation, structure, in vitro and in vivo antibacterial activity, and docking studies of philipimycin and its degradation product are described.     

Water at the surfaces of aligned phospholipid multibilayer model membranes probed with ultrafast vibrational spectroscopy

The dynamics of water at the surface of artificial membranes composed of aligned multibilayers of the phospholipid dilauroyl phosphatidylcholine (DLPC) are probed with ultrafast polarization selective vibrational pump-probe spectroscopy. The experiments are performed at various hydration levels, x = 2 - 16 water molecules per lipid at 37 degrees C. The water molecules are approximately 1 nm above or below the membrane surface. The experiments are conducted on the OD stretching mode of dilute HOD in H 2O to eliminate vibrational excitation transfer. The FT-IR absorption spectra of the OD stretch in the DLPC bilayer system at low hydration levels shows a red-shift in frequency relative to bulk water, which is in contrast to the blue-shift often observed in systems such as water nanopools in reverse micelles. The spectra for x = 4 - 16 can be reproduced by a superposition of the spectra for x = 2 and bulk water. IR Pump-probe measurements reveal that the vibrational population decays (lifetimes) become longer as the hydration level is decreased. The population decays are fit well by biexponential functions. The population decays, measured as a function of the OD stretch frequency, suggest the existence of two major types of water molecules in the interfacial region of the lipid bilayers. One component may be a clathrate-like water cluster near the hydrophobic choline group and the other may be related to the hydration water molecules mainly associated with the phosphate group. As the hydration level increases, the vibrational lifetimes of these two components decrease, suggesting a continuous evolution of the hydration structures in the two components associated with the swelling of the bilayers. The agreement of the magnitudes of the two components obtained from IR spectra with those from vibrational lifetime measurements further supports the two-component model. The vibrational population decay fitting also gives an estimation of the number of phosphate-associated water molecules and choline-associated water molecules, which range from 1 to 4 and 1 to 12, respectively, as x increases from 2 to 16. Time-dependent anisotropy measurements yield the rate of orientational relaxation as a function of x. The anisotropy decay is biexponential. The fast component is almost independent of x, and is interpreted as small orientational fluctuations that occur without hydrogen-bond rearrangement. The slower component becomes very long as the hydration level decreases. This component is a measure of the rate of complete orientational randomization, which requires H-bond rearrangement and is discussed in terms of a jump reorientation model.     

Improved methodology for the microwave digestion of carbonate-rich environmental samples

Microwave-assisted digestion permits a rapid and total dissolution of sediments and various other sample types, allowing easier and more accurate multi-element determinations. In this study, we present an optimised microwave digestion method for the complete digestion of 200 mg of carbonate-rich sediments. The optimised method prevents the formation of precipitates and assures a complete dissolution of the material. The optimised method involves treatment with concentrated hydrochloric acid (HCl) prior to microwave digestion, which prevents the formation of an insoluble calcium fluoride precipitate associated with the use of hydrofluoric acid (HF). Three different certified reference samples along with a pure calcium carbonate standard and a carbonate-rich in-house marine sediment sample were considered. Sediments were found to only be partially digested if insufficient HF was present, while a noticeable fluoride-based precipitate was found if excess HF was present. Twenty elements were analysed using sector field inductively coupled plasma mass spectrometry (ICP-MS) (Al, Ag, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, Sr, Th, Ti, U, V and Zn). A total sample digestion with average elemental recoveries above 90% was obtained by reacting carbonate-rich samples with HCl on a hotplate at 150°C for 2 h (time for the total release of generated CO₂), prior to any microwave digestion step. This extra step prevented the accumulation of gas in the sealed vessels during digestion, which would otherwise influence the carbonate chemical equilibria and make insoluble calcium available for precipitation. After this initial treatment, the improved digestion method consisted of microwave attack employing a mix of concentrated HCl, nitric acid (HNO₃) and HF (4 mL/10 mL/2 mL), followed by evaporation on a hotplate. The limits of detection (LOD) obtained using the optimised microwave protocol and ICP-MS measurements were below 0.1 µg/kg for the trace elements and below 0.2 mg/kg for major elements.     

ATP‐Releasing Nucleotides: Linking DNA Synthesis to Luciferase Signaling

A new strategy is reported for the production of luminescence signals from DNA synthesis through the use of chimeric nucleoside tetraphosphate dimers in which ATP, rather than pyrophosphate, is the leaving group. ATP‐releasing nucleotides (ARNs) were synthesized as derivatives of the four canonical nucleotides. All four derivatives are good substrates for DNA polymerase, with K_m values averaging 13‐fold higher than those of natural dNTPs, and k_cat values within 1.5‐fold of those of native nucleotides. Importantly, ARNs were found to yield very little background signal with luciferase. DNA synthesis experiments show that the ATP byproduct can be harnessed to elicit a chemiluminescence signal in the presence of luciferase. When using a polymerase together with the chimeric nucleotides, target DNAs/RNAs trigger the release of stoichiometrically large quantities of ATP, thereby allowing sensitive isothermal luminescence detection of nucleic acids as diverse as phage DNAs and short miRNAs.     

Photoenolization of o‐Methylvalerophenone Ester Derivative

Photolysis of ester 1 in argon‐saturated methanol and acetonitrile does not produce any product, whereas irradiation of 1 in oxygen‐saturated methanol yields peroxide 2 . Laser flash photolysis studies demonstrate that 1 undergoes intramolecular H atom abstraction to form biradical 3 (λ _max ~ 340   nm), which intersystem crosses to form photoenols Z ‐ 4 and E ‐ 4 (λ _max ~ 380   nm). Photoenols 4 decay by regenerating ester 1 . With the aid of density functional theory calculations, it was concluded the photoenol E ‐ 4 does not undergo spontaneous lactonization or electrocyclic ring closure because the transition state barriers for these reactions are too large to compete with reketonization of E ‐ 4 to form 1 .     

Development and Validation of the Mathematics Teachers' Beliefs About English Language Learners Survey (MTBELL)

Given the increasing number of English Language Learners (ELLs) in secondary mathematics classrooms, it is imperative that mathematics teacher educators develop measures for determining how and why secondary mathematics teachers (SMTs) understand and respond instructionally to these students. This paper reports on the initial development and validation of the Mathematics Teachers' Beliefs about English Language Learners survey, an instrument that measures SMTs beliefs, attitudes, knowledge base, and instructional practices in relation to meeting the academic and language needs of ELLs. Through piloting processes, the instrument was refined for a research study through which reliability and validity were established. The five constructs identified from exploratory factor analysis illustrate perceived opportunities and barriers in meeting ELLs' academic and language needs among SMTs. This article features a Research to Practice Companion Article . Please click on the supporting information link below to access.     

Organocatalytic enantioselective Friedel-Crafts reaction of pyrrole derivatives with imines

A highly enantioselective Friedel-Crafts reaction of pyrrole derivatives with N-acyl imines catalyzed by chiral phosphoric acids was developed. The reactions produced the pyrrole derivatives in high yields and enantioselectivity.     

Using ionic strength to control liquid-ordered/liquid-disordered separation

In this Letter, we will show that liquid-ordered/liquid-disordered separation can be controlled with ionic strength. Using this observation, a robust method was developed for creating visible, by fluorescence microscopy, liquid-ordered domains in supported lipid bilayers. The details of the method will be discussed.