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The optimum experimental geometry for visible-infrared sum-frequency generation experiments depends rather sensitively on the molecules adsorbed at the surface, their orientation, and the nature of the adjacent bulk media. We consider the commonly encountered case of methyl groups situated at air-water, air-gold, and polymer-water interfaces. We provide expressions that may be used to determine the optimal visible and IR beam incident angles, considering the symmetric and antisymmetric modes separately and then together. The analysis is carried out for co-propagating (collinear and non-collinear geometries) and counter-propagating configurations. We first consider that one or more vibrational modes are of interest, and the goal is to study them quantitatively under a single polarization scheme; our results enable the user to set the beam angles for such an experiment. In the second case, molecular orientation information is desired, and so the calibrated response is required in all accessible polarization schemes for full characterization of the nonlinear susceptibility tensor. [ABSTRACT FROM AUTHOR]

A detailed model is presented that describes the temporal and spectral interference patterns resulting from phase-recovery infrared-visible sum-frequency spectroscopy. Included in this model are the effects of dispersive elements other than the phase shifting unit placed between the sample and local oscillator signals. This inclusion is critical when considering the interference patterns arising from studies of buried interfaces. Furthermore, in the midinfrared where it is difficult to have high visibility of the fringes, it is demonstrated that local field corrections have a significant effect on the shape of the interference pattern. By collecting and subsequently fitting a two-dimensional interference pattern displaying both temporal and spectral fringes, a complete characterization of all these effects is possible. [ABSTRACT FROM AUTHOR]

The intriguing network of antibody–antigen (Ab–Ag) interactions is highly governed by environmental perturbations and the nature of biomolecular interaction. Protein–protein interactions (PPIs) have potential applications in developing protein-adsorption-based sensors and nano-scale materials. Therefore, characterizing PPIs in the presence of a nanomaterial at the molecular level becomes imperative. The present work involves the investigation of antiferritin–ferritin (Ab–Ag) protein interactions under the influence of tungsten disulfide quantum dots (WS2 QDs). Isothermal calorimetry and contact angle measurements validated the strong influence of WS2 QDs on Ab–Ag interactions. The interfacial signatures of nano–bio-interactions were evaluated using sum frequency generation vibration spectroscopy (SFG-VS) at the air–water interface. Our SFG results reveal a variation in the tilt angle of methyl groups by ∼12° ± 2° for the Ab–Ag system in the presence of WS2 QDs. The results illustrated an enhanced ordering of water molecules in the presence of QDs, which underpins the active role of interfacial water molecules during nano–bio-interactions. We have also witnessed a differential impact of QDs on Ab–Ag by raising the concentration of the Ab–Ag combination, which showcased an increased inter-molecular interaction among the Ab and Ag molecules and a minimal influence on the methyl tilt angle. These findings suggest the formation of stronger and ordered Ab–Ag complexes upon introducing WS2 QDs in the aqueous medium and signify the potentiality of WS2 QDs relevant to protein-based sensing assays. [ABSTRACT FROM AUTHOR]

Quantitative measurements in nonlinear surface vibrational spectroscopy enable the investigation of the orientation of molecules through analysis of the observed bands in resonance with specific chemical functional groups. Thin polymer films are commonly used to create a specific chemical environment or degree of hydrophobicity. We illustrate the effect of multiple beam interference in the thin films on the structural analysis of free-surface molecules, even in the case where the overlaying molecules are the only source term in the nonlinear polarization. Our findings illustrate that neglect of the modulation of the local field due to interference results in a substantial error in the determination of the molecular tilt angle. In cases where the phase of the response is of interest, the results are substantially influenced as well. In both cases, the effects are more pronounced as the refractive index of the solid support increases. We further demonstrate that the insensitivity of these effects to the experimental geometry provides a straightforward route to the treatment of these interference effects. [ABSTRACT FROM AUTHOR]

Attenuated total reflectance Fourier transform infrared spectroscopy and sum frequency generation (SFG) vibrational spectroscopy have been employed to probe the molecular structure of N,N-dimethylformamide (DMF) and water mixture by varying the concentration of DMF. From the bulk studies, we observed a gradual decrease in the intensity with a continuous blue shift in the OH-stretch region with the increase in the DMF concentration. In contrast, no significant blue shift in the OH-stretch region is noticed from the SFG spectra collected from the air–aqueous binary mixture interface as a function of DMF concentration. However, the impact of DMF is found to be disruptive in nature toward the existing hydrogen bonding network of the pristine water at the interfacial region. Interestingly, in the CH-stretch region, the vibrational signatures of the DMF molecule show blue shifts, as proposed in earlier studies. We have calculated the molecular tilt angle of the methyl group of the DMF molecule as a function of DMF concentration. For the case of neat DMF, the observed tilt angle is ∼17.7° with respect to the surface normal. The value of tilt angle decreases with the decrease in DMF concentration and reaches a value of ∼1.7° for a mole fraction of 0.5, and it further increases with the decrease in DMF concentration. It achieves a value of ∼20° for the dilute DMF mole fraction of 0.05 in the binary mixture. This indicates that DMF molecules at the air–binary mixture interface are placing their methyl groups more toward the normal for the intermediate DMF concentrations. [ABSTRACT FROM AUTHOR]

Vibrationalsum-frequency generation spectroscopy is valued forits ability to selectively probe molecules at a variety of interfaceswithout the use of extrinsic chromophores. The spectra contain valuableinformation regarding the molecular structure and the interfacialenvironment through the observation of vibrational resonances associatedwith specific moieties. Chemical information is obtained by closeinspection of the frequencies of these bands and the amplitude ofthe response under conditions of different beam polarizations. Suchsensitivity motivates the development of techniques that can providestructural details. We illustrate several approaches by which varioustypes of calculations and molecular simulations may be used to enhancethe sought structural interpretation of experimental data. By applyingthese techniques to the adsorbate molecules, interfacial water, andthe substrate surfaces themselves, we are able to achieve a holisticpicture of the adsorption environment. [ABSTRACT FROM AUTHOR]

We demonstrate that the thickness of a polymer film may be determined by a simple analysis of the interference fringes observed in a transparent region of its transmission spectrum. By measuring the transmission spectrum of the uncoated substrate in the same wavelength region, we can determine the dispersion of the refractive index for the substrate and film and the thickness of the film, without prior knowledge of the optical constants of any of the materials. The results of our approach agree with measurements obtained by a direct contact method. This analysis provides a fast, simple, and nondestructive method of thickness measurement using equipment available in many teaching laboratories. The method enables students to make routine thickness measurements while introducing them to refractive index dispersion, Fresnel coefficients, thin film interference, and regression analysis. [ABSTRACT FROM AUTHOR]

Abstract: The phase conjugation geometry of degenerate four wave mixing (DFWM) technique has been employed to study the third-order optical nonlinear susceptibility (χ 3) and second-order hyperpolarizability of multi-wall carbon nanotubes (MWCNTs). MWCNTs were grown by thermal chemical vapor deposition method and, subsequently functionalized with carboxylic acid group to improve their solubility in an organic solvent, ethylene glycol. The average hyperpolarizability for each carbon atom has been found to be 4.74×10−46 m5/V2 for the pump pulse of 8ns at 532nm. Decreasing the pulse width of the pump laser decreases the average value of hyperpolarizability. The absorption spectra show a monotonous increase from IR through visible and give an opportunity to estimate the imaginary part of the χ 3 by the open aperture Z-scan technique. [Copyright &y& Elsevier]

Jet velocity and jet power are the crucial parameters that govern the release profile of drugs/vaccines in needle-free injection systems, where salts are considered as one of the essential constituents of drugs/vaccines as adjuvants. However, the impact of salts on the generation of laser-induced liquid microjets that have shown tremendous potential for drug delivery has remained unexplored. Here, we have investigated the influence of Hofmeister ions on the velocity of laser-induced liquid jets in rhodamine 6G (Rh6G) dye solution. A comprehensive experimental approach is adopted to find out the values of the liquid microjet velocity by varying the parameters, such as input energy of the laser beam, concentrations of the dye, and specific Hofmeister ions in the aqueous solution. From our experimental findings, it is observed that the presence of ions significantly influences the jet velocity that follows the Hofmeister series: SO 4 2 − > I − > SCN − . This, in turn, governs the ion-specific penetration depth of liquid jets as simulated for the model soft tissues. The observed Hofmeister trend in the jet velocity values showcases the possible specific-ion interactions between anions and Rh6G molecules in the aqueous solution. Our detailed experimental findings on ion-specific jet velocity and jet power could be beneficial in designing needle-free drug delivery systems with controlled penetration depths. [ABSTRACT FROM AUTHOR]

The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena. [ABSTRACT FROM AUTHOR]

Histidine‐naphthalimide based receptors were prepared with variation of the side chain amine having morpholine and 1,1‐dimethylethylenediamine. The prepared organic compounds were then employed as a framework for the fabrication of organic‐inorganic nanohybrid assembly with the aim of detection of environmentally essential anions in the aqueous medium. The size and morphology of the nanohybrid particles were confirmed with TEM and DLS analysis. Hybrid nanoparticles of morpholine naphthalimide show selective and sensitive response with cyanide ion. Subsequently, the hybrid nanoparticles of 1,1‐dimethylethylenediamine naphthalimide display visible difference with iodide ions and the response was electrochemically detected. Both the hybrid nanoparticles were utilized for the selective and sensitive detection of CN− and I− ions; with quite low detection limits. [ABSTRACT FROM AUTHOR]

Environmental contamination due to increase in drug levels is reaching an alarming stage. An array of drugs, such as antibiotics, antidepressants, analgesics, and chemotherapy drugs, have been found to be polluting agriculture soils and rivers. Here we developed optical sensors based on terbium(III)-coated carbon quantum dots (Tb-CQDs) synthesized by carrying out a single-step one-pot hydrothermal process in an aqueous medium and characterized by using UV-visible, fluorescence, DLS, HRTEM and XRD measurements. Photophysical studies showed the ability of CQD-Tb to act as a chemosensor of the antidepressant drug clomipramine in aqueous medium. A competitive binding assay using CQD-Tb and clomipramine was carried out in the presence of other drugs. No interference resulted from the presence of the other drugs; and hence, the developed chemosensor can be used for selective detection of clomipramine. A functional group analysis was done using FTIR spectroscopy and a mechanism for drug binding with the chemosensor was derived. To target the interfacial behavior with different drugs, vibrational sum-frequency generation (VSFG) spectroscopy was carried out and further confirmed the ability of the synthesized CQD-Tb to act as a chemosensor for the selective detection of clomipramine in the presence of other drugs. [ABSTRACT FROM AUTHOR]

Advancement in molecularly imprinted biomimetics has aided in developing robust artificial recognition-based materials, which can be customized for bio/chemo-sensing of distinct molecules. The present study reports a simple one-step synthesis and analysis of protein-imprinted polymer thin films as a recognition element directly onto a solid support. Dopamine has been explored as a versatile functional monomer for a molecularly imprinted polymer (MIP) matrix to fabricate polydopamine (PDA) thin films with bovine hemoglobin as a template protein molecule. A detailed molecular-level insight into the recognition of the template molecule at each step has been investigated using vibrational sum frequency generation (VSFG) spectroscopy. A suitable PDA-coated thin film is selected based on the extent of polymerized intermediates formed after non-imprinted polymer fabrication at different time durations. An optimally prepared film of MIP is specified by observing the spectral signature of the methyl groups from protein molecules at the air–polymer interface. The template removal from MIP films after the washing procedure and subsequent re-binding of the protein molecules were evaluated by VSFG spectroscopy. The insightful molecular-level findings from SFG spectroscopy demonstrate the fabrication of an imprinted matrix as a label-free chemical sensor. [ABSTRACT FROM AUTHOR]

Wehave investigated the roles of structural modification and polareffects in the optical nonlinearities of a series of selectively mixedβ-pyrrole functionalized tetraphenylporphyrin, MTPP(CHO)(R)2(R = H, Br, 2-thienyl, phenyl (Ph), phenylethynyl (PE) compoundsand their metal (Cu(II), Zn(II)) complexes in toluene. In the presentstudy, we have used phase conjugation geometry of the four wave mixingprocess to measure the third order nonlinear susceptibility (χ(3)) and the second order hyperpolarizabilty (⟨γ⟩)with picosecond laser pulse excitation at 532 nm. An increase in thevalues of χ(3)and ⟨γ⟩ for electron-withdrawinggroups was observed whereas an opposite trend was noticed for theelectron-donating groups at the β-pyrrole positions. In theCu(II) and Zn(II) complexes of substituted free base porphyrins, thedistortion of the macrocyclic ring may be responsible for the reductionof the values of χ(3)and ⟨γ⟩.From fluorescence measurements, it has been found that the electron-donatingand electron-withdrawing substituted groups at β-pyrrole positionsand also the macrocyclic ring distortion of the porphyrin lead toincreased radiationless transitions. [ABSTRACT FROM AUTHOR]

* These authors contributed equally to this work. The molecular-level insight of protein adsorption and its kinetics at interfaces is crucial because of its multifold role in diverse fundamental biological processes and applications. In the present study, the sum frequency generation (SFG) vibrational spectroscopy has been employed to demonstrate the adsorption process of bovine hemoglobin (BHb) protein molecules at the air–water interface at interfacial isoelectric point of the protein. It has been observed that surface coverage of BHb molecules significantly influences the arrangement of the protein molecules at the interface. The time-dependent SFG studies at two different frequencies in the fingerprint region elucidate the kinetics of protein denaturation process and its influence on the hydrogen-bonding network of interfacial water molecules at the air–water interface. The initial growth kinetics suggests the synchronized behavior of protein adsorption process with the structural changes in the interfacial water molecules. Interestingly, both the events carry similar characteristic time constants. However, the conformational changes in the protein structure due to the denaturation process stay for a long time, whereas the changes in water structure reconcile quickly. It is revealed that the protein denaturation process is followed by the advent of strongly hydrogen-bonded water molecules at the interface. In addition, we have also carried out the surface tension kinetics measurements to complement the findings of our SFG spectroscopic results. [ABSTRACT FROM AUTHOR]

The exponential growth in the research field of water pollution control demands the evolution of novel sensing materials for regulation and quantification of metals ions. Within this context, the current work reports a new strategy for the synthesis of carbon dots from the hydrothermal treatment of organic nanoparticles. The organic nanoparticles are found to be selective towards Cs(I) ions with a detection limit of 5.3 nM, whereas the highly fluorescent carbon dots are found to be selective towards Ag(I) ions with a detection limit of 4.8 nM. Both sensing systems illustrate rapid sensing with a working pH range from 4–9. The interfacial molecular restructuring of the sensing systems in the aqueous phase has been investigated in the absence and presence of targeted metal ions using a sum frequency generation vibrational spectroscopic tool. The practical applicability of the sensors was checked in environmental samples. This work opens new avenues for the exploration of temperature‐guided sensing modulation in nanomaterials. [ABSTRACT FROM AUTHOR]

Carbon Quantum Dots (CQDs) have been extensively employed in various fields of science such as sensing, catalysis, and drug delivery. In this work, ionic liquid coated CQDs (IL@CQDs) have been used as catalysts for the rearrangement of a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) amide coupling intermediate. The rearranged product was confirmed by single crystal structure analysis and it was processed into organic nanoparticles (ONPs). An optical detection method was used to scrutinize the anion sensing properties. The ONPs were found to be sensitive and selective for the recognition of highly toxic cyanide ions through enhancement in the fluorescence intensity. The cyanide ion co-ordinates with the –NH groups of the product and restricts the rotation of molecules around the single bond. The ONPs coated over silica-beads were also showing CN− recognition in the solid state. The detection limit for CN− sensing was found to be 3.8 nM, and real sample analysis depicts more than 90% accuracy in detection. [ABSTRACT FROM AUTHOR]

The article focuses on the status of charge asymmetry under aqueous hydrophobic interfaces and hydration shells. Topics discussed include the differences of the structures of hydration shells and hydrophobic/water interfaces which were induced by the ions of opposite charge, the relation of implied charge asymmetry to the dipolar character of water, and hydration-shell spectra of oxygen (O)-hydrogen (H).

The article focuses on the quantification of the charge asymmetry associated with the hydration of two oppositely charged ions on the hydrophobic/water interface. Topics discussed include interactions of electrostatic forces and hydrogen bonding, role of the nanoscopic liquid hexadecane droplets in an aqueous solution of the tetraphenylborate and tetraphenylarsonium ions and role of Raman spectroscopy in the study of the hydration shells.

Supersaturation as a formulation principle relates to the aqueous solubility of poorly soluble drugs in solution. However, supersaturation state of drugs tends to crystallize because of its thermodynamic instability thereby compromising the solubility and biopharmaceutical performance of drugs. The present study aims to investigate the supersaturation potential of albendazole (ABZ) and its precipitation via nucleation and crystal growth. We hypothesized the use of polymers will avoid ABZ precipitation by interacting with drug molecules. The drug polymer interactions are characterized using conventional methods of Fourier transform infrared (FTIR), Nuclear magnetic resonance (NMR) and Polarized light microscopy (PLM). We have used a novel approach of sum frequency generation (SFG) vibrational spectroscopic in exploring the drug polymer interactions at air-water interface. Recently we have reported the SFG for e rifaximin-polymer interactions (Singh et al., 2021). The supersaturation assay, saturation solubility studies and nucleation induction time analysis revealed polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP K30) as effective precipitation inhibitors thereby enhancing the ABZ equilibrium solubility and in vitro supersaturation maintenance of ABZ. Further, modification in the solid state of ABZ has confirmed the influence of polymers on its precipitation behaviour. We conclude that PVA and PVP K30 act as nucleation and crystal growth inhibitor, respectively for the precipitation inhibition of ABZ. [Display omitted] [ABSTRACT FROM AUTHOR]