Vibrational Spectroscopy of N-Methyliminodiacetic Acid (MIDA)-Protected Boronate Ester: Examination of the B–N Dative Bond

Glucose sandwich assay based on surface-enhanced Raman spectroscopy

A facile and sensitive glucose sandwich assay using surface-enhanced Raman scattering (SERS) has been developed. Glucose was captured by 3-aminopheyonyl boronic acid (APBA) modified Ag nanoparticles decorated onto a polyamide surface. Then, Ag nanoparticles modified with 3-amino-6-ethynylpicolinonitrile (AEPO) and APBA were used as SERS tags. APBA forms specific cis-diol compounds with glucose molecules avoiding interference by other saccharides and biomolecules in urine enabling its selective detection. As the actual Raman reporter, AEPO exhibited a distinctive SERS peak in the Raman silent region, thus increasing the sensitivity of the glucose detection to 10-11 M. Additionally, the developed SERS assay was reusable, and its applicability in artificial urine samples demonstrated future clinical utility confirming the potential of this innovative technology as a diagnostic tool for glucose sensing.

Raman Spectroscopic and Quantum Chemical Investigation of the Pyridine-Borane Complex and the Effects of Dative Bonding on the Normal Modes of Pyridine

The pyridine-borane (PyBH₃) complex was analyzed by Raman vibrational spectroscopy and density functional theory to elucidate its structural and vibrational properties and to compare these with those for neat pyridine (Py). The borane-nitrogen (BN) bond length, the BN dative bond stretching frequency, and the effects of dative-bonded complex formation on Py are presented. Rather than having a single isolated stretching motion, the complex exhibits multiple BN dative bond stretches that are coupled to Py's vibrations. These modes exhibit large shifts that are higher in energy relative to neat Py, similar to previous observations of Py/water mixtures. However, significantly higher charge transfer was observed in the dative-bonded complex when compared to the hydrogen-bonded complex with water. A linear relationship between charge transfer and shifts to higher frequencies of pyridine's vibrational modes agrees well with earlier observations. The present work is of interest to those seeking a stronger relationship between charge-transfer events and concomitant changes in molecular properties.

Ability of Boron to Act as a Nucleophile and an Electrophile in Boryl Shift Reactions Unveiled by Electron Density Distribution Analysis

The behavior of the tetracoordinate boron of N-methyliminodiacetic acid (MIDA) boronates as a nucleophile and an electrophile during the 1,2-boryl migration promoted by a Lewis acid and the 1,4-boryl migration promoted by a neighboring atom, respectively, have been investigated using density functional theory and the quantum theory of atoms in molecules. We found that when boron acts as a nucleophile, the electron density of the B-N interaction of the BMIDA moiety maintains the charge concentration over the boron atom, facilitating its transport toward the electron-deficient center. In this process, the BMIDA remains as a tetracoordinate. On the other hand, the B-N weakening generates a charge depletion region over the boron, allowing it to interact with the electron-rich center of O₁, developing the boron atom, a pentacoordinate form. Then, the B-N bond breaking triggers a series of changes in the electronic structure of the boron atom. Our results explain the role of the MIDA ligand upon the remarkable susceptibility of the boron atom for switching its structural and electronic characteristics in the migration processes. In addition, the dichotomous behavior was evaluated with a different scenario, considering tricoordinate pinacol boronate as a boryl migrating group.

Organic nanoparticles based on Lewis-pair formation: observation of prototropically controlled dual fluorescence

We successfully synthesize fluorescent organic nanoparticles of a Lewis-pair consisting of an amino-type hydrogen-bonding molecule (Lewis base) and a borinate derivative (Lewis acid). 2-(2'-Aminophenyl)benzothiazole (o-ABT) is chosen as the fluorophore. This molecule has a transferable proton in the amino group, but it does not exhibit ESIPT (excited-state intramolecular proton transfer) reaction in solution and thus shows a single normal emission solely from the enamine form. Organic nanoparticles are prepared by the reprecipitation method in which the fluorophore (o-ABT) in conjunction with a Lewis acid (diphenylborinic anhydride; DPBA) dissolved in a good solvent is rapidly injected into water under sonication. Interestingly, the nanoparticles produced exhibit a characteristic dual fluorescence that can be ascribed to the enamine and imine tautomers of o-ABT generated in the ground-state prototropy, which can be revealed by UV-vis absorption and excitation spectroscopy, IR spectroscopy and computational approaches. In the o-ABT/DPBA Lewis-pair nanoparticles, highly Stokes-shifted emission from the imine tautomer is enhanced in comparison with that from the molecularly dissolved state, suggesting that the present nanofabrication methodology based on Lewis acid-base chemistry (or N-B bonding interaction) plays a key role in tuning the fluorescence colour for the new type of organic nanoparticle.

Solid-state characterization of Felodipine-Soluplus amorphous solid dispersions

The aim of the current study is to develop amorphous solid dispersion (SD) via hot melt extrusion technology to improve the solubility of a water-insoluble compound, felodipine (FEL). The solubility was dramatically increased by preparation of amorphous SDs via hot-melt extrusion with an amphiphilic polymer, Soluplus® (SOL). FEL was found to be miscible with SOL by calculating the solubility parameters. The solubility of FEL within SOL was determined to be in the range of 6.2-9.9% (w/w). Various techniques were applied to characterize the solid-state properties of the amorphous SDs. These included Fourier Transform Infrared Spectrometry spectroscopy and Raman spectroscopy to detect the formation of hydrogen bonding between the drug and the polymer. Scanning electron microscopy was performed to study the morphology of the SDs. Among all the hot-melt extrudates, FEL was found to be molecularly dispersed within the polymer matrix for the extrudates containing 10% drug, while few small crystals were detected in the 30 and 50% extrudates. In conclusion, solubility of FEL was enhanced while a homogeneous SD was achieved for 10% drug loading.

Synthesis, characterization, photophysical properties, and catalytic activity of an SCS bis(N-heterocyclic thione) (SCS-NHT) Pd pincer complex

Treatment of 1,3-bis(3'-butylimidazolyl-1'-yl)benzene diiodide with elemental sulfur in the presence of a base produced a bis(N-heterocyclic thione) (NHT) pincer ligand precursor. Its reaction with PdCl2(CH3CN)2 produced chloro[1,3-bis(3'-butylimidazole-2'-thione-κ-S)benzene-κ-C]palladium(ii), a 6,6-fused ring SCS-NHT palladium pincer complex. This air stable compound is, to our knowledge, the first SCS pincer complex that utilizes N-heterocyclic thione (NHT) donor groups. The molecular structures of the ligand precursor and the palladium complex were determined by X-ray crystallography and computational studies provided insight into the interconversion between its rac and meso conformations. The photophysical properties of the complex were established, and its catalytic activity in Suzuki, Heck, and Sonogashira cross-coupling reactions was evaluated.

Characterizing the B-P stretching vibration in phosphorus-substituted phosphine boranes

The experimental Raman spectra of three phosphorus-substituted phosphine boranes with bulky hydrocarbon substituents are presented and compared to the results of electronic structure computations by using the M06-2X method and the 6-311G(2df, 2pd) basis set. Total-energy distributions (TEDs) are calculated to describe the degree of mixing of the dative-bond stretching vibration with other simple internal coordinates. This level of theory is found to accurately reproduce the B-P stretching frequency in all three crystalline solids. The Raman spectra of five smaller B-P-containing molecules, including BH(3) PH(3), are also simulated at this level of theory and compared to previous experimental results.

Sensitive SERS glucose sensing in biological media using alkyne functionalized boronic acid on planar substrates

In this work, we propose a novel glucose binding mechanism on a highly sensitive SERS substrate, in order to overcome challenges in specific glucose detection in bio-fluids. We make use of phenylboronic acid as a receptor for saccharide capture onto the substrate and the ability of the captured glucose molecule to undergo secondary binding with an alkyne-functionalized boronic acid to form a glucose-alkyne-boronic acid complex. The formation of this complex shows high selectivity for glucose, over other saccharides. In addition, the alkyne group of the alkyne-functionalized boronic acid exhibits a distinct Raman peak at 1996 cm(-1) in a biological silent region (1800-2800 cm(-1)) where most endogenous molecules, including glucose, show no Raman scattering, thus offering a high sensitivity over other SERS glucose sensing. The substrate offers long-term stability, as well as high SERS enhancement to the glucose-alkyne boronic acid complex on substrate. In addition, the reversibility of SERS signals at various incubation stages also shows reusability capabilities, whereas positive results in clinical urine samples demonstrate clinical feasibility. All these strongly suggest that this newly developed SERS-based assay offers great potential in glucose sensing.