Specific Chemical Bonds Research Articles

Vast scope of raman spectroscopy in oral cancers and head & neck regions: A review

Higher rates of local recurrences and second primaries, ascribable to field cancerization, are known problems in oral cancers. The present review explored utility of identification of potential recurrences by Raman spectroscopy, which has been shown to identify oral precancers, cancers, and field cancerization in humans and micro-sized mechanical irritation-induced tumours in animals. There is an urgent need for improved techniques for disease detection. The focus here, in vivo Raman spectroscopy (RS), measures inelastic light scattering with the vibrational and rotational modes of molecular bonds in cells/tissue. The Raman ‘signature’ can be used to assess physiological and/or altered pathological statuses. This information can supplement existing diagnostic techniques for screening and diagnosis, in interventional guidance for identifying disease margins, and in monitoring treatment responses. Using fiberoptic-based light delivery and collection, RS is performed on accessible tissue surfaces, either on the skin, in hollow organs or intraoperatively. The strength of RS lies in the high biochemical information content of the spectra, that show an array of narrow peaks associated with specific chemical bonds. This results in high sensitivity and specificity, e.g., to distinguish malignant/premalignant from normal tissues. An issue with Raman signal is that it is often weak, limiting clinical use to point-by-point measurements. Recent advances in instrumentation and spectral analysis have improved the feasibility of RS, so that it is now being investigated with increased success in cancer types, locations and for non-oncological conditions. This review covers recent advances and continuing challenges, with emphasis on clinical translation.

Rationalizing Structural Hierarchy in the Design of Fuel Cell Electrode and Electrolyte Materials Derived from Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are arguably a class of highly tuneable polymer-based materials with wide applicability. The arrangement of chemical components and the bonds they form through specific chemical bond associations are critical determining factors in their functionality. In particular, crystalline porous materials continue to inspire their development and advancement towards sustainable and renewable materials for clean energy conversion and storage. An important area of development is the application of MOFs in proton-exchange membrane fuel cells (PEMFCs) and are attractive for efficient low-temperature energy conversion. The practical implementation of fuel cells, however, is faced by performance challenges. To address some of the technical issues, a more critical consideration of key problems is now driving a conceptualised approach to advance the application of PEMFCs. Central to this idea is the emerging field MOF-based systems, which are currently being adopted and proving to be a more efficient and durable means of creating electrodes and electrolytes for proton-exchange membrane fuel cells. This review proposes to discuss some of the key advancements in the modification of PEMs and electrodes, which primarily use functionally important MOFs. Further, we propose to correlate MOF-based PEMFC design and the deeper correlation with performance by comparing proton conductivities and catalytic activities for selected works.

Ultrafast Simultaneous and Selective Depolymerization of Heterogeneous Streams of Polyethylene Terephthalate and Polycarbonate: Towards Industrially Feasible Chemical Recycling.

Mixed plastic waste-streams are a main obstacle to a more extensive implementation of polymer recycling. Separating mixed-plastic waste streams demands time and effort at collection or in the recycling plant, while many products consist of multiple polymers that cannot be readily separated. Chemical recycling could provide the key to overcome this issue by targeting specific chemical bonds, enabling selective depolymerization of a single polymer class in a mixture. This work explores the depolymerization of polycarbonate (PC) and polyethylene terephthalate (PET) in separate and in mixed streams. Selective depolymerization of mixed streams composed of PET and PC and one-step separation of their constituent monomers are carried out with outstanding energy efficiency through an inexpensive KOH-in-methanol hydrolysis (KMH) process developed for instantaneous PET hydrolysis. The activation energies for depolymerization of PC and PET pellets are 68.6 and 131.4 kJ mol-1 , respectively. Randomly mixed streams are fully depolymerized within 2 min at 120 °C using 30 mL of depolymerization solution per gram of polymer. The separation of bisphenol A and terephthalic acid is demonstrated in a one-step separation process, yielding 98 and 97 % purity without any secondary reactions detected. Simultaneous depolymerization and selective one-step separation of monomers are also demonstrated for a PET/PC polymer blend prepared by solution casting, showing that this process also works for intimately mixed PET/PC mixtures.

The Infrared Spectra of Polymers, VI: Polymers With C-O Bonds

This column series has been organized into sections based on the infrared (IR) spectroscopy of specific chemical bonds. We have discussed functional groups containing C-H, C-O, and C=O bonds. Here, in the sixth installment of our survey of the IR spectra of polymers, we discuss polymers that contain C-O bonds. The spectra we will examine include polyvinyl alcohol, cellulose, starch, and copolymers that contain C-O bonds such as polyethetherketone, polyurethanes, and polyimides. The unifying theme of all these spectra is that they all contain one or more large C-O stretching peaks between 1300–1000 cm-1.

Raman spectroscopic characterization of corrosion products of archaeological iron

Abstract Raman spectroscopy is a versatile analytical technique which allows the detection of different molecules analysing the vibrational modes. As a matter of facts, the vibrational frequencies are typical of a specific chemical bond or of a structural symmetry. In this study, the Raman technique is used for the determination of iron corrosion products, mainly oxides and hydroxides. Metallic artefacts buried in soil are affected, in dependence of their electrochemical nobility, by corrosion phenomena of various entities, which partially modify their chemical composition and their structure. The process may occur both during burial time and after the extraction from the archaeological site, implying the potential loss of information about the metallurgical technology and structure of the object. The study of the corrosion phenomena allows to propose tailored strategies for the restoration and conservation of the artefacts, especially in view of the storage of the artefacts in a museum. This study validates the use of the Raman technique for this purpose, showing its efficiency in the identification of the iron corrosion products in favourable conditions for the analysis of Cultural Heritage artefacts, as the possibility of performing in situ analysis without the need of a previous sample preparation.

Probing effect of solvation on photoexcited quadrupolar donor-acceptor-donor molecule via ultrafast Raman spectroscopy

The symmetric and quadrupolar donor-acceptor-donor (D-A-D) molecules usually exhibit excited-state charge redistribution process from delocalized intramolecular charge transfer (ICT) state to localized ICT state. Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies. Femtosecond stimulated Raman spectroscopy (FSRS) is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules. Herein, a molecule, 4,4′-(buta-1,3-diyne-1,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline), that consists of two central adjacent alkyne (-C≡C-) groups as electron-acceptors and two separated, symmetric N,N-bis(4-methoxyphenyl)aniline at both branches as electron-donors, is chosen to investigate the excited-state photophysical properties. It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy. The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.

Specific chemical bond relaxation unraveled by analysis of shake-up satellites in the oxygen single site double core hole spectrum of CO2

Important electronic relaxation and reorganization effects induced by single site double core hole formation and associated shake-up excitation are investigated in CO2 by means of an highly accurate computation method using non orthogonal basis set. Connection between the two main satellite bands and the two (non equivalent) carbon oxygen bonds are highlighted.

Pyrolysis mechanisms of coal extracts based on TG-FTIR and ReaxFF MD study

The decomposition of small molecules in coal dominates the initial pyrolysis stage, which further influences the ignition, combustion, and pollutant emissions. In this work, the detailed composition of the coal extracts was obtained through the gas chromatograph-mass spectrometer (GC–MS) and nuclear magnetic resonance (NMR) analyses. Furthermore, the coal extract molecular models were successfully constructed. Then, the microscopic pyrolysis mechanisms of coal extracts were elucidated through the reactive force field molecular dynamics (ReaxFF MD) simulations. More importantly, the evolution of specific chemical bonds and the decomposition of selected crucial molecular fragments were discussed. Meanwhile, the weight loss characteristics were investigated accordingly through TG-FTIR. The results indicate there are three main reaction stages including the low-temperature reaction, rapid thermal decomposition, and molecular condensation reaction. During the rapid thermal decomposition, the cleavages of CC and CO bonds cooperatively contribute to the formation of CH4 and CO2. As the temperature increases to the molecular condensation stage, the pyrolysis process is governed by the dehydrogenation condensation, accompanied by the increase of CC and HH bonds and decrease of CO bonds. Additionally, phenolic ethers can accelerate molecular condensation reactions. Furthermore, butylated hydroxytoluene primarily undergoes the demethylation reaction during rapid thermal decomposition.

Clinical Translation of Stimulated Raman Histology.

Stimulated Raman histology (SRH) images are created by the label-free, nondestructive imaging of tissue using stimulated Raman scattering (SRS) microscopy. In a matter of seconds, these images provide real-time histologic information on biopsied tissue in the operating room. SRS microscopy uses two lasers (pump beam and Stokes beam) to amplify the Raman signal of specific chemical bonds found in macromolecules (lipids, proteins, and nucleic acids) in these tissues. The concentrations of these macromolecules are used to produce image contrast. These images are acquired and displayed using an imaging system with five main components: (1) fiber coupled microscope, (2) dual-wavelength fiber-laser module, (3) laser control module, (4) microscope control module, and (5) a computer. This manuscript details how to assemble the dual-wavelength fiber-laser module and how to generate an SRH image.

Study of the Degradation of Biobased Plastic after Stress Tests in Water

Research on compostable bioplastics has recently obtained performances comparable to traditional plastics, like water vapor permeability, sealability, and UV transmission. Therefore, it is crucial to create new tools that help the developers of new polymeric composites study them quickly and cost-effectively. In this work, Raman spectroscopy (RS) was proposed as a versatile tool to investigate the degradation of biobased plastics after a stress test in water: this approach is a novelty for food packaging. Treatments at room temperature (RT) and 80 °C were selected, considering that these biopolymers can be used to packaging ready meals. The investigation was carried out on single-layer sheets of poly-lactic acid (PLA), cellulose ester (CE), poly-butylene succinate (PBS), poly-butylene adipate-co-terephthalate (PBAT), and a new composite material obtained by coupling CE and PBS (BB951) and PLA and CE (BB961). The vibrational modes of the water-treated materials at RT and 80 °C were compared to the Raman spectra of the pristine bioplastic, and the morphologies of the polymers were analyzed by scanning electron microscopy (SEM) and optical microscopy. Composite sheets were the plastics which were mostly affected by the 80 °C treatment in water, through changes in morphology (wrinkling with alternate white and transparent zones), as was especially the case for BB951. The Raman spectra acquired in different zones showed that the vibrations of BB951 were generally maintained in transparent zones but reduced or lacking in white zones. At the same time, the single-layer materials were almost unchanged. For BB961, the Raman vibrations were only slightly modified, in agreement with the visual inspection. The results suggest that RS detects the specific chemical bond that was modified, helping us understand the degradation process of biobased plastics after water treatment.

Characterization of Escherichia coli RNase H Discrimination of DNA Phosphorothioate Stereoisomers.

Phosphorothioate (PS) modification of antisense oligonucleotides (ASOs) is a critical factor enabling their therapeutic use. Standard chemical synthesis incorporates this group in a stereorandom manner; however, significant effort was made over the years to establish and characterize the impact of chiral control. In this work, we present our in-depth characterization of interactions between Escherichia coli RNase H and RNA-DNA heteroduplexes carrying chirally defined PS groups. First, using a massive parallel assay, we showed that at least a single Rp-PS group is necessary for efficient RNase H-mediated cleavage. We followed by demonstrating that this group needs to be aligned to the phosphate-binding pocket of RNase H, and that chiral status of other PS groups in close proximity to RNase H does not affect cleavage efficiency. We have shown that RNase H's PS chiral preference can be utilized to guide cleavage to a specific chemical bond. Finally, we present a strategy for ASO optimization by mapping preferred RNase H cleavage sites of a non-thioated compound, followed by introduction of Rp-PS in a strategic position. This results in a cleaner cleavage profile and higher knockdown activity compared with a compound carrying an Sp-PS at the same location.

Hot-Hole-Induced Molecular Scissoring: A Case Study of Plasmon-Driven Decarboxylation of Aromatic Carboxylates

Optically excited plasmonic nanostructures may function as molecular scissors with unique capabilities to cleave specific chemical bonds in molecular adsorbates through either plasmon-enhanced intramolecular electronic excitations or injection of photoexcited hot electrons into adsorbate orbitals. Here we chose plasmon-driven decarboxylation of aromatic carboxylates as a model reaction system to demonstrate that plasmonic hot holes, instead of electrons, could also be effectively harnessed to trigger regioselective bond cleavage in molecular adsorbates. We used surface-enhanced Raman scattering as an in situ spectroscopic tool to precisely monitor the decarboxylation reactions in real time and further correlate the reaction kinetics to local-field enhancements. The apparent rate constants were proportional to the fourth power of the local-field enhancements and exhibited a superlinear dependence on the excitation powers. Such a non-linear power dependence of reaction rates was a hallmark of hot-carrier-driven reactions involving multiphoton absorption rather than photothermally triggered processes, as inferred by the results of Raman thermometry. The decarboxylation reactions took place only at the surface sites with local-field intensities exceeding a certain threshold value, whereas the molecules experiencing weaker local fields below the threshold remained essentially unreactive. With the aid of density functional theory calculations, we were able to further relate the experimentally observed pH dependence of reaction kinetics to the frontier orbital energies of the hole-accepting adsorbates and the redox potentials of the electron-accepting protons, both of which could be modulated by adjusting the pH of the reaction medium.

Engineering reversible isomerization at the nanoscale via intermolecular interactions

Engineering reversible isomerization at the nanoscale via intermolecular interactions

The Effect of SAP Polymer on The Properties of Concrete

Superabsorbent polymer (SAP), also known as hydrogels, is a group of cross-linked, puffable polymeric materials. Due to the structure of the three-dimensional cross-linked polymeric network, it can absorb large quantities (can reach 1000g / g) of different activation fluids and swell up based on its specific chemical bonds. Incorporation of superabsorbent polymer particles (SAP) into cement-based materials, is more convenient as the shape, size and distribution of voids and defects can be controlled. In this study we use a super absorbent polymer which is sodium polyacrylate (sp) in several forms, solid (powder) at a rate of (80-100) mesh and 1% of the cement weight, then in balls with a diameter from (2.61 mm) to (3.25 mm) saturated. . Samples were treated (with treated water and air) to compare the effect of the presence of the polymer on the internal treatment and to compare the experimental compressive strength with theoretical ultrasound examination. The results indicated that the samples containing powder and balls maintained good pressure resistance with significantly light weight.

Chemical targets to deactivate biological and chemical toxins using surfaces and fabrics.

The most recent global health and economic crisis caused by the SARS-CoV-2 outbreak has shown us that it is vital to be prepared for the next global threat, be it caused by pollutants, chemical toxins or biohazards. Therefore, we need to develop environments in which infectious diseases and dangerous chemicals cannot be spread or misused so easily. Especially, those who put themselves in situations of most exposure — doctors, nurses and those protecting and caring for the safety of others — should be adequately protected. In this Review, we explore how the development of coatings for surfaces and functionalized fabrics can help to accelerate the inactivation of biological and chemical toxins. We start by looking at recent advancements in the use of metal and metal-oxide-based catalysts for the inactivation of pathogenic threats, with a focus on identifying specific chemical bonds that can be targeted. We then discuss the use of metal–organic frameworks on textiles for the capture and degradation of various chemical warfare agents and their simulants, their long-term efficacy and the challenges they face.

Deployment of response surface methodology to optimize microencapsulation of peroxidases from turnip roots (Brassica rapa L.) by double emulsion in PLA polymer.

In order to improve the preservation conditions and stability of peroxidase catalytic properties, a number of immobilization techniques have been widely developed. In this context, we set as objective, the optimization of synthesis and stability of microcapsules of peroxidases (POD) from turnip using polylactic acid (PLA) polymer with the double emulsion technique. The surfactant, polymer, and peroxidase concentrations were the optimized parameters. According to the results obtained using the Box-Behnken design, the optimal parameters found were 1.55% of PVA, 55mg/mL of peroxidases, and 30mg/mL of PLA polymer with an encapsulation efficiency of 57.29%. The scanning electron microscopy morphological characterization of the optimized microcapsules showed a regular spherical structure. Fourier transform infrared spectroscopy identified the specific functional groups and chemical bonds before and after microencapsulation. The elaborated microcapsules were characterized by an average size of 200µm(mainly from 150 to 500µm)with a low residual moisture content (2.26%) and the encapsulated peroxidases showed better thermal stability. The in vitro release of peroxidases confirmed that the microcapsules have an excellent sustained release in simulated gastric digestion. Encapsulated peroxidases' storage under 25 and 4°C displays a good residual POD activity with about 60% of initial activities during 80 days of storage, whereas free POD losses its initial activity within 15 and 30 days, respectively. The obtained results are promising for the development of effective therapeutic treatment of some intestinal troubles due to oxidative stress. PRACTICAL APPLICATION: Brassica rapa L. root is well known for its richness on peroxidases and thus presents an interesting potential for developing high added value products. In order to preserve the activity of extracted peroxidases (POD) from turnip roots, microencapsulation was optimized using a polylactic acid polymer. The encapsulated POD showed the maintenance of its activity under the effect of different storage conditions (time and temperature) and demonstrated resistance to gastric acidity. According to the obtained results, the encapsulation of peroxidases opens up medicine and pharmaceutical applications such as intestinal and colic protection against inflammations.

Research Progress in Organic Synthesis by Means of Photoelectrocatalysis.

The rapid development of radical chemistry has spurred several innovative strategies for organic synthesis. The novel approaches for organic synthesis play a critical role in promoting and regulating the single-electron redox activity. Among them, photoelectrocatalysis (PEC) has attained considerable attention as the most promising strategy to convert organic compounds into fine chemicals. This review highlights the current progress in organic synthesis through PEC, including various catalytic reactions, catalyst systems and practical applications. The numerous catalytic reactions suffer the high overpotential and poor conversion efficiency, depending on the design of electrolyzers and the reaction mechanisms. We also considered the recent developments with special emphasis on scientific problems and efficient solutions, which enhance accessibility to utilize and further develop the photoelectrocatalytic technology for the specific chemical bonds formation and the fabrication of numerous catalytic systems.

Simulation of stimulated Raman scattering signal generation in scattering tissues excited by Bessel beams

Stimulated Raman scattering (SRS) microscopy has the ability of noninvasive imaging of specific chemical bonds and been increasingly used in biomedicine in recent years. Two pulsed Gaussian beams are used in traditional SRS microscopes, providing with high lateral and axial spatial resolution. Because of the tight focus of the Gaussian beam, such an SRS microscopy is difficult to be used for imaging deep targets in scattering tissues. The SRS microscopy based on Bessel beams can solve the imaging problem to a certain extent. Here, we establish a theoretical model to calculate the SRS signal excited by two Bessel beams by integrating the SRS signal generation theory with the fractal propagation method. The fractal model of refractive index turbulence is employed to generate the scattering tissues where the light transport is modeled by the beam propagation method. We model the scattering tissues containing chemicals, calculate the SRS signals stimulated by two Bessel beams, discuss the influence of the fractal model parameters on signal generation, and compare them with those generated by the Gaussian beams. The results show that, even though the modeling parameters have great influence on SRS signal generation, the Bessel beams-based SRS can generate signals in deeper scattering tissues.

Label-free brain tumor imaging using Raman-based methods.

Label-free Raman-based imaging techniques create the possibility of bringing chemical and histologic data into the operation room. Relying on the intrinsic biochemical properties of tissues to generate image contrast and optical tissue sectioning, Raman-based imaging methods can be used to detect microscopic tumor infiltration and diagnose brain tumor subtypes. Here, we review the application of three Raman-based imaging methods to neurosurgical oncology: Raman spectroscopy, coherent anti-Stokes Raman scattering (CARS) microscopy, and stimulated Raman histology (SRH). Raman spectroscopy allows for chemical characterization of tissue and can differentiate normal and tumor-infiltrated tissue based on variations in macromolecule content, both ex vivo and in vivo. To improve signal-to-noise ratio compared to conventional Raman spectroscopy, a second pulsed excitation laser can be used to coherently drive the vibrational frequency of specific Raman active chemical bonds (i.e. symmetric stretching of -CH2 bonds). Coherent Raman imaging, including CARS and stimulated Raman scattering microscopy, has been shown to detect microscopic brain tumor infiltration in fresh brain tumor specimens with submicron image resolution. Advances in fiber-laser technology have allowed for the development of intraoperative SRH as well as artificial intelligence algorithms to facilitate interpretation of SRH images. With molecular diagnostics becoming an essential part of brain tumor classification, preliminary studies have demonstrated that Raman-based methods can be used to diagnose glioma molecular classes intraoperatively. These results demonstrate how label-free Raman-based imaging methods can be used to improve the management of brain tumor patients by detecting tumor infiltration, guiding tumor biopsy/resection, and providing images for histopathologic and molecular diagnosis.

Evaluation of degradation of pigments formed during garlic discoloration in different pH

The specific chemical bond changes of green pigment formed in garlic discoloration were investigated in our study. Multiple analysis methods were used in the degradation of pigment, including ultraviolet–visible (UV–Vis) spectrophotometry, attenuated total reflection Fourier transform infrared (ATR-FTIR) and Fourier transform infrared near infrared (FT-NIR). Green pigments were treated at 40 °C for 7 days in the pH range of 5.0–8.0. Principal component analysis of the ATR-FTIR and FT-NIR spectra indicated the similarities and differences during pigment degradation. It was found that the degradation degree of green pigments in a solution with pH 5.0 was the lowest. Changes in the absorptions of CO, COO−, CN, CN, OCOCH, COC, COOH, and NH bonds vibrations are attributed to the decomposition of the pigments. The absorption at 5170 cm−1 (NH bond first overtone) and 4871 cm−1 (OCH stretching) correlated to pigment degradation were confirmed by FT-NIR spectra. One proposed pathway of the pigment decomposition was explored.