Carbonyl Vibrations Research Articles

Effects of temperature and pH on the structure of a metalloprotease from Lactobacillus fermentum R6 isolated from Harbin dry sausages and molecular docking between protease and meat protein.

Microbial protease can interact with meat protein in fermented meat products at a certain pH and temperature. To investigate the effects of various pH values and temperatures on the structural characteristics of Lactobacillus fermentum R6 protease, which was isolated from Harbin dry sausages, spectroscopy techniques and molecular dynamics were utilized to evaluate structural changes. The protease exhibited a stable spatial structure at pH 7 and 40 °C, and the extension of the protease structure was also promoted. Although the structure of the protease could be changed or destroyed by pH 8 and 70 °C, it was mainly determined by the changes of secondary and tertiary structures such as α-helix, β-sheet, β-turn and random coil. In addition, carbonyl vibration, -NH vibration, C-H stretching vibration and disulphide bonds were present in L. fermentum R6 protease under various pH and temperature conditions. Molecular docking showed that the protease can interact with myosin light chain, myosin heavy chain, actin and myoglobin. The protease can maintain stable structure and interact with meat protein, which reflected certain application prospects in the fermentation of Harbin dry sausages. © 2021 Society of Chemical Industry.

Molecular characteristics and digestion properties of corn starch esterified by l ‐malic acid

Malate starch was prepared by dry heat treatment of corn starch with l-malic acid. Malate starch has lower swelling degree and gelatinization property than the original starch. The polarization cross gradually disappears, and the particle size becomes larger. However, as the degree of substitution increased, the polarization cross became weak and eventually disappeared due to the destruction of the crystal structure. The results of infrared spectroscopy indicated that malate starch showed a characteristic peak of carbonyl vibration at 1,739 cm−1, and the peak value of the substitution increased significantly. The weak peak in the 165–180 region of the nuclear magnetic carbon spectrum is the chemical shift of the ester carbonyl carbon formed by esterification. The 13C NMR results speculated that the hydroxyl group of l-malic acid C9 and starch C6 was esterified to form malate starch. The digestion experiments showed that the content of resistant starch after esterification increased significantly. Practical applications Esterified starch is an important part of modified starch. After organic acid treatment, starch can be more widely used in various industries according to its different properties. In this study, the low degree of substitution malate starches were constructed by combining the chemical bonds of corn starch and l-malic acid, and the effects on physical and chemical properties, molecular characteristics, and digestion characteristics were studied to improve the processing characteristics of starch and improve the product addition value.

Impacts of pH and temperature on the conformation of a protease from Pediococcus pentosaceus R1 isolated from Harbin dry sausage

The aim of this work was to investigate the effects of pH and temperature on the structural characteristics of the Pediococcus pentosaceus R1 protease, which was isolated from Harbin dry sausage. UV–vis, fluorescence, circular dichroism and Fourier transform infrared spectroscopy were used to evaluate the structural changes as a function of pH and temperature. The protease had a stable spatial structure at pH 5 and 30 °C, and the extended secondary structures of the protease were identified. The structure of protease was changed at pH 8 and 70 °C, with changes predominantly manifested as changes in secondary structure components, the α-helices, β-sheets, β-turns and random coils contents at pH 8 were 5.32%, 37.08%, 19.45% and 38.22%, respectively; and at 70 °C the contents were 5.47%, 40.62%, 19.56% and 34.35% respectively, which were significantly different from that at pH 5, 30 °C. Carbonyl vibration (1651 cm−1), –NH vibration (1540 cm−1), C–H stretching vibration (2959-2857 cm−1) and disulfide bonds (560-460 cm−1)were identified in P. pentosaceus R1 protease under various pH and temperature conditions. Molecular docking showed that the protease can interact with actin and myoglobin, which indicates certain options for the application of this enzyme in the fermentation of Harbin dry sausage.

Essential Oil Quality and Purity Evaluation via FT-IR Spectroscopy and Pattern Recognition Techniques

Essential oils are highly volatile, aromatic concentrated extracts from plants with wide applications. In this study, fast, easy-to-use attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was combined with chemometric techniques to verify essential oils’ taxonomy and purity. Principal component analysis (PCA) clustered 30 essential oil samples into three different groups based on plant botanical family and concentration. The first group contained highly concentrated oils from the Asteraceae family, the second group contained highly concentrated oils from the Lamiaceae family, while the last group contained three highly concentrated essential oils from different botanical families and commercial-grade essential oils. Thus, commercial-grade oil samples did not cluster with the corresponding concentrated oil samples despite their similar spectral patterns or botanical family. A loading plot identified infrared (IR) bands that correspond to carbonyl, vinyl, methyl and methylene group vibrations as the most important spectral bands that can be used as marker bands for discrimination between different botanical plant family groups. Hierarchical cluster analysis (HCA) confirmed the results obtained by PCA. ATR-FTIR spectroscopy combined with chemometric algorithms provides a direct and non-destructive method for chemotaxonomic classification of medicinal and aromatic essential oils and an assessment of their purity.

Renewable and Tough Poly(l-lactic acid)/Polyurethane Blends Prepared by Dynamic Vulcanization.

Melt blending of homopolymers is an effective way to achieve an attractive combination of polymer properties. Dynamic vulcanization of fatty-acid-based polyester polyol with glycerol and poly(l-lactic acid) (PLLA) in the presence of hexamethylene diisocyanate (HDI) was performed with the aim of toughening PLLA. The dynamic vulcanization in an internal mixer led to the formation of a PLLA/PU biobased blend. Melt torque, Fourier transform infrared (FTIR), and gel fraction analysis demonstrated the successful formation of cross-linked polyurethane (PU) inside the PLLA matrix. Scanning electron microscopy (SEM) analysis showed that the PLLA/PU blends exhibit a sea–island morphology. Gel fraction analysis revealed that a rubbery phase was formed inside the PLLA matrix, which was insoluble in chloroform. FTIR analysis of the insoluble part shows the appearance of an absorption band centered at 1758 cm–1, related to the crystalline carbonyl vibration of the PLLA component, thus suggesting the partial involvement of PLLA chains in the cross-linking reaction. The overall content of the PU phase in the blends significantly affected the mechanical properties, thermal stability, and crystallization behavior of the materials. The overall crystallization rate of PLLA was noticeably decreased by the incorporation of PU. At the same time, polarized light optical microscopy (PLOM) analysis revealed that the presence of the PU rubbery phase inside the PLLA matrix promoted PLLA nucleation. With the formation of the PU network, the impact strength showed a remarkable increase while Young’s modulus correspondingly decreased. The blends showed slightly reduced thermal stability compared to the neat PLLA.

Ultrafast Dynamics at Lipid-Water Interfaces.

Lipid membranes are more than just barriers between cell compartments; they provide molecular environments with a finely tuned balance between hydrophilic and hydrophobic interactions that enable proteins to dynamically fold and self-assemble to regulate biological function. Characterizing dynamics at the lipid-water interface is essential to understanding molecular complexities from the thermodynamics of liquid-liquid phase separation down to picosecond-scale reorganization of interfacial hydrogen-bond networks.Ultrafast vibrational spectroscopy, including two-dimensional infrared (2D IR) and vibrational sum-frequency generation (VSFG) spectroscopies, is a powerful tool to examine picosecond interfacial dynamics. Two-dimensional IR spectroscopy provides a bond-centered view of dynamics with subpicosecond time resolutions, as vibrational frequencies are highly sensitive to the local environment. Recently, 2D IR spectroscopy has been applied to carbonyl and phosphate vibrations intrinsically located at the lipid-water interface. Interface-specific VSFG spectroscopy probes the water vibrational modes directly, accessing H-bond strength and water organization at lipid headgroup positions. Signals in VSFG arise from the interfacial dipole contributions, directly probing headgroup ordering and water orientation to provide a structural view of the interface.In this Account we discuss novel applications of ultrafast spectroscopy to lipid membranes, a field that has experienced significant growth over the past decade. In particular, ultrafast experiments now offer a molecular perspective on increasingly complex membranes. The powerful combination of ultrafast, interface-selective spectroscopy and simulations opens up new routes to understanding multicomponent membranes and their function. This Account highlights key prevailing views that have emerged from recent experiments: (1) Water dynamics at the lipid-water interface are slow compared to those of bulk water as a result of disrupted H-bond networks near the headgroups. (2) Peptides, ions, osmolytes, and cosolvents perturb interfacial dynamics, indicating that dynamics at the interface are affected by bulk solvent dynamics and vice versa. (3) The interfacial environment is generally dictated by the headgroup structure and orientation, but hydrophobic interactions within the acyl chains also modulate interfacial dynamics. Ultrafast spectroscopy has been essential to characterizing the biophysical chemistry of the lipid-water interface; however, challenges remain in interpreting congested spectra as well as designing appropriate model systems to capture the complexity of a membrane environment.

Dynamic Covalent Synthesis of Crystalline Porous Graphitic Frameworks

Summary Porous graphitic framework (PGF) is a two-dimensional (2D) material that has emerging energy applications. An archetype contains stacked 2D layers, the structure of which features a fully annulated aromatic skeleton with embedded heteroatoms and periodic pores. Due to the lack of a rational approach in establishing in-plane order under mild synthetic conditions, the structural integrity of PGF has remained elusive and ultimately limited its material performance. Here, we report the discovery of the unusual dynamic character of the C=N bonds in the aromatic pyrazine ring system under basic aqueous conditions, which enables the successful synthesis of a crystalline porous nitrogenous graphitic framework with remarkable in-plane order, as evidenced by powder X-ray diffraction studies and direct visualization using high-resolution transmission electron microscopy. The crystalline framework displays superior performance as a cathode material for lithium-ion batteries, outperforming the amorphous counterparts in terms of capacity and cycle stability.

Cryoprotectants Disrupt Hydrogen-Bond Networks at the Lipid-Water Interface

Cryoprotectant agents (CPAs) are mixtures of small organic compounds used to inhibit ice-crystal growth during cell and tissue freezing and storage, but these compounds can be themselves toxic to cells. Increased membrane permeability, caused by partial disruption of lipid-lipid interactions, combined with dehydration, have been hypothesized to be the main driver of cell toxicity, but the specific interactions between lipids and cryoprotectants are poorly understood. In this study, we investigate the effects of dimethyl sulfoxide (DMSO) on phosphatidylcholine bilayers. We have measured ultrafast two-dimensional infrared (2D IR) spectra of the ester carbonyl vibrations to directly probe the interfacial hydrogen bond networks. Our measurements directly quantify the picosecond hydrogen bond lifetimes at the ester carbonyl positions. Spectra are interpreted at an atomistic level using molecular dynamics simulations, which are in semi-quantitative agreement with experiment. Our results show that biologically relevant cryoprotectant concentrations (<20 mol%), partially dehydrate the interface, but surprisingly, hydrogen-bond lifetimes are non-monotonic with increasing concentration: 1. Low DMSO concentrations (<10%) severely disrupt the otherwise ice-like interfacial hydrogen bond networks, without altering the lipid-lipid interactions, leading to faster overall hydrogen bond dynamics at the ester carbonyls. 2. Above >10 mol%, dynamics become slower as a result of dehydration, more rigid H-bond conformations, trapped water, and stronger headgroup-headgroup interactions. Together, these results provide an atomistic foundation for understanding the complex effects of cryoprotectants on lipid membranes, showing that different effects dictate the properties of membranes within various cryoprotectant concentration regimes.

Structural and spectral characterisation of 2-amino-2H-[1,2,3]triazolo[4,5-g]quinoline-4,9-dione polymorphs. Cytotoxic activity and molecular docking study with NQO1 enzyme.

Depending on temperature, the 2-amino-2H-[1,2,3]triazolo[4,5-g]quinoline-4,9-dione forms two polymorphic structures, which differ in the spatial arrangement of the amine group. Both polymorphs were investigated using different experimental methods as well as various quantum chemical calculations in order to characterise their molecular structures. We used X-ray diffraction, FT-IR and NMR (solid-state and liquid) methods supplemented by the density functional theory (DFT) calculations, molecular electrostatic potential (MEP) and molecular orbital (HOMO, LUMO) analyses. It was found that the arrangement of the amine group affected the crystal structure, formation of H-bonds, the amine and carbonyl vibration bands in the FT-IR spectra, chemical shift of amine group in 15N CP/MAS NMR and chemical shift of amine protons in 1H NMR spectra. Both polymorphs were tested on anticancer activity against a panel of human cancer cell lines. Comparing the activity of both compounds showed that activity against MCF-7, MDA-MB-231 and Caco-2 lines depend on the arrangement of the amine group. Moreover, both polymorphs exhibited the highest activity against cell line with high NQO1 protein level, such as: A549, MCF-7 and Caco-2. The molecular docking was used to examine the probable interaction between the ligand of the tested polymorphs and the NQO1 enzyme. The analysis showed that ligands formed a hydrophobic interaction with tryptophan (Trp105), phenylalanine (Phe126 and Phe178) and tyrosine (Tyr 126).

A quantum cascade laser setup for studying irreversible photoreactions in H2O with nanosecond resolution and microlitre consumption.

Time-resolved infrared spectroscopy on irreversible reactions requires in general an exchange of sample for thousands of acquisitions leading to high sample consumption. Here, we present a setup employing a modern quantum cascade laser (QCL) as a probe light source to record time-resolved difference spectra of irreversible photoreactions in H2O. The combination of the focused QCL with a pressure-tolerant flow cell and a micrometre stage orthogonal to the flow allowed us to drastically reduce the sample consumption. We investigated the irreversible photoreduction of the cofactor flavin mononucleotide (FMN) in H2O, which is a common reaction taking place in biological photoreceptors. A broad time range from 20 nanoseconds to 1 second was accessible, because the approach minimized any signal drift by the flow. Kinetics were recorded at 46 selected wavenumbers consuming 12 microlitres for a complete dataset. The tuning range of 1490-1740 cm-1 included relevant carbonyl vibrations and the region of strong water absorption at around 1650 cm-1. A continuous dataset in the spectral dimension was generated by applying a fit with a sum of Lorentzians. Subsequent global analysis allowed us to resolve reference spectra and kinetics of the photoreaction proceeding from the triplet excited state via the intermediate flavin anion radical to the product, the fully reduced state of FMN. Accordingly, the neutral radical state is not populated in the disproportionation. The approach strongly facilitates the spectroscopic access to irreversible reactions of flavin-containing photoreceptors and photoenzymes with high time resolution and small sample consumption.

Photoluminescence in non-conjugated polyelectrolyte films containing 7-hydroxy-flavylium cation

Chitosan–carboxymethylcellulose/flavylium salt (Ch–CMC/FS) films were obtained at different flavylium salt (FS) concentrations under acidic conditions in order to maintain de benzopyrylium form of the flavylium organic cation. Films were characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–Vis diffuse reflectance (DRUV) and emission spectroscopy. Thermal properties were also recorded by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. FTIR and Raman spectra showed shifting of the carbonyl vibrations after addition of flavylium salt compound. Thermal stability prevailed even after addition of FS as was determined by TGA and DSC analysis. Ch–CMC/FS showed strong absorption in the visible part of the electromagnetic spectrum centred around λ = 450 nm. Luminescence profile after excitation at λ = 450 nm showed an emission centred around λ = 507 nm. FS appears to be chemically stabilized by the interaction with polyelectrolyte chains.

Interfacial H-Bond Dynamics in Reverse Micelles: The Role of Surfactant Heterogeneity.

Characterizing the hydrogen bond structure and dynamics at surfactant interfaces is essential for understanding how microscopic interactions translate to bulk microemulsion properties. Heterogeneous blends containing tens or hundreds of surfactants are common in the industry, but the most fundamental studies have been carried out on micelles composed of a single surfactant species. Therefore, the effect of surfactant heterogeneity on the interfacial structure and dynamics remains poorly understood. Here, we use ultrafast two-dimensional infrared spectroscopy and molecular dynamics simulations to characterize sub-picosecond solvation dynamics as a function of the surfactant composition in ∼120 nm water-in-oil reverse micelles. We probe the ester carbonyl vibrations of nonionic sorbitan surfactants, which are located precisely at the interface between the polar and nonpolar regions, and as such, report on the interfacial water dynamics. We show a 7% increase in hydrogen bond populations together with a 37% slowdown of interfacial hydrogen bond dynamics in heterogeneous mixtures containing hundreds of species, compared to more uniform compositions. Simulations, which are in semiquantitative agreement with experiments, indicate that structural diversity leads to decreased packing efficiency, which in turn drives water further into the otherwise hydrophobic region. Interestingly, this increase in hydration is accompanied by a slowdown of dynamics, indicating that water molecules solvating surfactants are conformationally constrained. These studies demonstrate that the composition and heterogeneity are key factors in determining interfacial properties.

Vibrational solvatochromism of the ester carbonyl vibration of PCBM in organic solutions

Ester carbonyl stretch in a widely used organic semiconducting material, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), has been utilized as a vibrational probe of molecular morphology in emerging electronic materials due to the sensitivity of its vibrational frequency to the local environment. Vibrational solvatochromic shift has been observed for dilute PCBM in organic solvents of varying polarity, but the spectral shift does not follow the order of solvent polarity, and its microscopic origin remains elusive. Here, we applied a mixed quantum/classical approach to simulate the infrared (IR) spectra for the ester carbonyl stretch of PCBM in dichloromethane, chloroform, and benzene. In this approach, the ester carbonyl group is treated quantum mechanically with a frequency map, and the rest of the system is described by molecular dynamics simulations. Based on the reasonable agreement with experimental IR spectra, we show that the specific directional interaction between the ester carbonyl group and its neighboring solvent molecules, which is not well captured by the solvent polarity, is primarily responsible for the observed solvatochromic shift. Furthermore, we find that the strength of this interaction also governs the solvation dynamics of the ester carbonyl group and the resulting frequency fluctuation, leading to a more inhomogeneously broadened spectrum for PCBM in chloroform compared to that in dichloromethane and benzene.

Active-Site Heterogeneity of Lactate Dehydrogenase

Molecular dynamics simulation of human heart lactate dehydrogenase (LDH) has been carried out to determine the linear and two-dimensional Fourier transform infrared (2D-FTIR) spectra for the carbonyl stretch vibration of pyruvate in the tetrameric enzyme, using quantum vibrational perturbation theory. The computed line-shapes of individual subunits are inhomogeneously broadened and span the entire absorption range of the carbonyl vibration of the full enzyme, indicating the similar conformation heterogeneity in the four active sites of LDH. However, each subunit line-shape has different width and peak maximum due to variations in conformation equilibrium in different subunits, corresponding to the spectral multiplets observed experimentally. Since there is a finite time interval before a substrate is converted into products in a given active site, the distribution of such a time coarse-grained average of Michaelis complexes is called active-site heterogeneity. Active-site heterogeneity is distinguished fr...

Solvent Quality Controls Macromolecular Structural Dynamics of a Dendrimeric Hydrogenase Model.

We report a spectroscopic investigation of the ultrafast dynamics of the second-generation poly(aryl ether) dendritic hydrogenase model using two-dimensional infrared (2D-IR) spectroscopy to probe the metal carbonyl vibrations of the dendrimer and a reference small molecule, [Fe(μ-S)(CO)3]2. We find that the structural dynamics of the dendrimer are reflected in a slow phase of the spectral diffusion, which is absent from [Fe(μ-S)(CO)3]2, and we relate the slow phase to the quality of the solvent for poly(aryl ether) dendrimers. We observe a solvent-dependent modulation of the initial phase of vibrational relaxation of the carbonyl groups, which we attribute to an inhibition of solvent assistance in the intramolecular vibrational redistribution process for the dendrimer. There is also a clear solvent dependence of the vibrational frequencies of both the dendrimer and [Fe(μ-S)(CO)3]2. Our data represent the first 2D-IR study of a dendritic complex and provide insight into the solvent dependence of molecular conformation in solution and the ultrafast dynamics of moderately sized, conformationally mobile compounds.

Infrared Spectroscopic Quantification of Methacrylation of Hyaluronic Acid: A Scaffold for Tissue Engineering Applications.

Methacrylated hyaluronic acid (MeHA) has been used extensively in tissue engineering and drug delivery applications. The degree of methacrylation (DM) of HA impacts hydrogel crosslinking, which is of pivotal importance for cell interactions. The methacrylation reaction occurs over several hours, and DM is currently assessed post reaction and after dialysis of the solution, using nuclear magnetic resonance (1H NMR) data. Thus, there is little control over exact DM in a specific reaction. Here, infrared (IR) spectroscopy in attenuated total reflection (ATR) mode was investigated as an alternate modality for assessment of the DM of HA hydrogels, including during the reaction progression. Attenuated total reflection is a low-cost technique that is widely available in research and industry labs that can be used online during the reaction process. Strong correlations were achieved with IR-derived peak heights from dialyzed and lyophilized samples at 1708 cm-1 (from the methacrylic ester carbonyl vibration), and 1H NMR values ( R = 0.92, P = 6.56E-11). Additional IR peaks of importance were identified using principal component analysis and resulted in significant correlations with the 1H NMR DM parameter: 1454 cm-1 ( R = 0.85, P = 2.81E-8), 1300 cm-1 ( R = 0.95, P = 4.50E-14), 950 ( R = 0.85, P = 3.55E-8), 856 cm-1 ( R = 0.94, P = 1.20E-12), and 809 cm-1 ( R = 0.93, P = 3.54E-12). A multiple linear regression model to predict 1H NMR-derived DM using the 1708, 1300, and 1200 cm-1 peak heights as independent variables resulted in prediction with an error of 3.2% using dialyzed and lyophilized samples ( P < 0.001). Additionally, a multilinear regression model to predict the DM in undialyzed liquid MeHA samples obtained during the reaction process using similar peak height positions as independent variables resulted in a prediction error of 0.81% ( P < 0.05). Thus, IR spectroscopy can be utilized as an alternate modality to 1H NMR for quantification of the DM of MeHA while sampling either on-line during the methacrylation reaction as well as in post-lyophilized products. This could greatly simplify workflow for tissue engineering and other applications.

Development of chitosan based optimized edible coating for tomato (Solanum lycopersicum) and its characterization.

In the present work experiments were carried out to optimize coating formulation in central composite rotatable design varying chitosan and glycerol concentration from 0.5 to 3% (w/w) and 0 to 3% (w/w) respectively as two independent factors. Total color difference and respiration rate was selected for tomato parameters and water vapor permeability and percentage solubility was selected for coating parameters as response. Quadratic polynomial models generated was adequate to explain the effects of the chitosan and glycerol concentrations on response variables. Experimental validation confirmed the adequacy of the coating formulation for tomato optimized by response surface methodology with 2.15% chitosan and 0.50% glycerol. Characterization of the optimized coating was undertaken in scanning electron microscope, X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) spectroscopy. Microstructure image revealed proper continuity, integrity and surface micro structure of the developed coating. XRD and FTIR spectra revealed the pattern of ideal chitosan based coatings and also unfolded various crystallographic, structural and molecular involvement and couplings in coating properties. XRD pattern reflected semicrystalline structure of chitosan based developed edible coating having crystal form-1 and crystal form-II. In addition to other expected ideal peaks, FTIR also confirmed the presence of water in the coating. Residual acetic acid (solvent for coating formulation) is also evident at around 1700cm-1 of FTIR spectra, corresponding to carbonyl vibration of the carboxylic acid.

Synthesis of N-vinylpyrrolidone/Acrylic acid nanoparticles for drug delivery: Method optimization

There are various approaches to deliver therapeutic agents to the preferred target. Polymeric nanoparticles were found to have pleasing suitability as a drug carrier. The goal of this research was to optimize the synthesis method to obtain the desirable %yield and particle properties of the new biocompatible polymer-based nanoparticles. The non-toxic polymer, N-vinyl pyrrolidone (NVP) and a widely used hydrophilic biocompatible acrylic acid (AA) monomer were used to form the drug nanocarriers. The synthesis method was optimized by changing the types of initiator (KPS or V50) and the monomers molar ratio (NVP:AA). It was found that by varying both the monomer molar ratio and the type of reaction initiator, did not have significant effect on the physicochemical characteristics of the nanocarriers. The FTIR spectra of all products exhibited the peaks of carboxylic acid, carbonyl, and tertiary amine functional group vibration. The particle size of the nanocarriers was in the range of 173.6 ± 18.4 to 201.4 ± 17.1 nm with negative surface charge. However, the yield obtained increased as the initiator was altered from KPS to V50, and when the acrylic acid molar ratio was increased from 1:1 to 1:3. In conclusion, changing the initiator and monomer molar ratio may affect the physicochemical properties of the nanocarriers and the %yield of the nanocarrier product. Further investigations are essential to obtain the favorable drug nanocarriers for drug delivery.

Central-metal effect on intramolecular vibrational energy transfer of M(CO)5Br (M = Mn, Re) probed by two-dimensional infrared spectroscopy.

Vibrational energy transfer in transition metal complexes with flexible structures in condensed phases is of central importance to catalytical chemistry processes. In this work, two molecules with different metal atoms, M(CO)5Br (where M = Mn, Re), were used as model systems, and their axial and radial carbonyl stretching modes as infrared probes. The central-metal effect on intramolecular vibrational energy redistribution (IVR) in M(CO)5Br was investigated in polar and nonpolar solvents. The linear infrared (IR) peak splitting between carbonyl vibrations increases as the metal atom changes from Mn to Re. The waiting-time dependent two-dimensional infrared diagonal- and off-diagonal peak amplitudes reveal a faster IVR process in Re(CO)5Br than in Mn(CO)5Br. With the aid of density functional theory (DFT) calculations, the central-metal effect on IVR time linearly correlates with the vibrational coupling strength between the two involved modes. In addition, the polar solvent is found to accelerate the IVR process by affecting the anharmonic vibrational potentials of a solute vibration mode.

Infrared spectroscopy of flavones and flavonols. Reexamination of the hydroxyl and carbonyl vibrations in relation to the interactions of flavonoids with membrane lipids

Detailed vibrational assignments for twelve flavonoids (seven flavones (flavone, 3- and 5-hydroxyflavone, chrysin, apigenin, fisetin and luteolin) and five flavonols (galangin, kaempferol, quercetin, morin and myricetin)) have been made based on own and reported experimental data and calculations at the B3LYP/6-31+G(d,p) level of theory. All the molecules are treated in a uniform way by using the same set of redundancy-free set of internal coordinates. A generalized harmonic mode mixing is used to corroborate the vibrational characteristics of this important class of molecules. Each flavonoid molecule can be treated from the vibrational point of view as made of relatively weakly coupled chromone and phenyl part. It has been shown that the strongest band around 1600cm−1 need not be attributable to the CO stretching. The way the vibrations of any of the hydroxyl groups are mixed with ring vibrations and vibrations of other neighboring hydroxyl groups is rather involved. This imposes severe limitations on any attempt to describe normal modes of a flavonol in terms of hydroxyl or carbonyl group vibrations. The role of water molecules in the appearance of flavonoid IR spectra is emphasized. Knowing for the great affinity of phosphate groups in lipids towards water, the immediate consequence is a reasonable assumption that flavonoid lipid interactions is mediated by water.