Raman spectroscopic study of serum albumins: an effect of proton‐ and γ‐irradiation

Raman spectroscopy was applied to analyse structural changes in serum albumins (bovine serum albumin, BSA; human serum albumin, HSA) following proton and γ‐irradiation (0.5, 5 and 50 Gy). Characteristic Raman bands of both polypeptide backbone and amino acid residues were sensitive to irradiation. Significant damage of HSA/BSA was observed only at the highest dose (50 Gy). Raman spectra confirmed radiation‐induced denaturation, destruction of helical structures and aggregation of serum albumins. The differences in the dose‐dependent effects of proton and γ‐radiation on studied proteins are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Understanding tip‐enhanced Raman spectra of biological molecules: a combined Raman,SERS and TERS study

Although conventional Raman, surface‐enhanced Raman (SERS) and tip‐enhanced Raman spectroscopy (TERS) have been known for a long time, a direct, thorough comparison of these three methods has never been carried out. In this paper, spectra that were obtained by conventional Raman, SERS (on gold and silver substrates) and TERS (in ‘gap mode’ with silver tips and gold substrates) are compared to learn from their differences and similarities. Because the investigation of biological samples by TERS has recently become a hot topic, this work focuses on biologically relevant substances. Starting from the TER spectra of bovine serum albumin as an example for a protein, the dipeptides Phe–Phe and Tyr–Tyr and the tripeptide Tyr–Tyr–Tyr were investigated. The major findings were as follows. (1) We show that the widely used assumption that spectral bands do not shift when comparing SER, TER and conventional Raman spectra (except due to binding to the metal surface in SERS or TERS) is valid. However, band intensity ratios can differ significantly between these three methods. (2) Marker bands can be assigned, which should allow one to identify and localize proteins in complex biological environments in future investigations. From our results, general guidelines for the interpretation of TER spectra are proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental determination of vibrational anharmonic contributions

This article deals with the experimental determination of separate vibrational anharmonic contributions to the self‐energy of phonons in any crystals based on temperature dependence of their Raman spectra. We propose a new approach to find each anharmonic contribution by using special temperature points. We apply the approach to diamond, silicon, and crystalline α‐S₈ and show that our results for summarized anharmonicity in diamond and silicon are in good agreement with the values obtained previously for these systems by other researchers. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman spectroscopy at different excitation wavelengths (1064, 785 and 532 nm) as a tool for diagnosis of colon cancer

Raman spectroscopy is structure sensitive non‐destructive method that allows observing the status of biological tissues with minimal impact. This method has a great potential in the diagnosis of various types of degenerative diseases including cancer damages. Near‐infrared Fourier transform (NIR‐FT)‐Raman (λ_ex ~1064 nm), NIR‐visible (Vis)‐Raman (λ_ex ~785 nm) and Vis‐Raman (λ_ex ~532 nm) spectra of normal and colorectal carcinoma colon tissue samples were recorded in macroscopic mode at 10–20 randomly chosen independent sites. In the cases of NIR‐Vis‐ and Vis‐Raman spectra, enhanced resonance effects were observed for tissue chromophores absorbing in the visible area. Evident spectral differences were noticed for Raman spectra of normal colon tissue samples in comparison with abnormal samples. The average Raman spectra of colon tissue samples were analysed by principal component analysis (PCA) to discriminate normal and abnormal tissues. PCA of combined dataset containing Raman intensities of chosen NIR‐FT, NIR‐Vis or Vis‐Raman bands led to discrimination of normal and abnormal colon tissue samples. Therefore, combination of these three Raman methods can be helpful for recognizing cancer lesions in colon for diagnostic purposes. Copyright © 2014 John Wiley & Sons, Ltd.     

Raman spectroscopic study of calf thymus DNA: an effect of proton‐ and γ‐irradiation

Raman spectroscopy was applied to analyse structural changes in calf thymus double‐stranded deoxyribonucleic acid (dsDNA) after proton‐ and γ‐irradiation (0.5, 5 and 50 Gy). Characteristic Raman bands of phosphodiester linkages, nucleic bases and deoxyribose moieties were sensitive to irradiation. A significant damage of the macromolecules was observed only at the highest dose (50 Gy) of both types of radiations. Spectral changes confirmed a radiation‐induced alteration of the native structure of dsDNA. Nucleic bases, especially pyrimidines, were the most sensitive to radiation, while some alterations in the sugar–phosphate backbone were also detected. The differences in the dose‐dependent effects of proton vs γ‐irradiation on studied biomolecule are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

The Raman spectrum of the γ′‐V2O5 polymorph: a combined experimental and DFT study

Structure and vibrational dynamics of γ′‐V₂O₅ synthesized from a pristine γ‐LiV₂O₅ sample via a chemical oxidation route was studied by means of Raman spectroscopy and quantum‐chemical calculations. The calculations based on density functional theory reliably reproduce the experimental structure of the γ′‐V₂O₅ lattice. The calculated Raman spectrum agrees remarkably well with the experimental one. Making use of the agreement, a complete assignment of Raman bands to vibrations of particular structural units is proposed. The comparison of Raman spectra and structural features of α‐V₂O₅ and γ′‐V₂O₅ polymorphs allowed establishing reliable ‘structure–spectrum’ correlations and identifying Raman peaks characteristic for different structural units. Copyright © 2015 John Wiley & Sons, Ltd.     

SERS spectrum of the peptide thymosin‐β4 obtained with Ag nanorod substrate

Thymosin‐β4 is a peptide found at high concentrations in a wide range of mammalian cells. It has been shown to be elevated in metastatic cells. In this study, the surface‐enhanced Raman spectrum of thymosin‐β4 was obtained using a silver nanorod array surface‐enhanced Raman scattering substrate. Significant Raman peaks were found, and the corresponding vibrational modes were assigned based on previously published literature, with amide A–B, amide I, and amide III modes all identified. The majority of the remaining peaks were assigned modes based on the spectra of lysine and glutamic acid, the two most abundant amino acids in the thymosin‐β4 sequence. A standard Raman spectrum of thymosin‐β4 was also obtained and analyzed for comparison. Because thymosin‐β4 plays a significant role in regulating the formation of cellular cytoskeleton and other several biological processes, its Raman spectrum will be of use to researchers. Copyright © 2014 John Wiley & Sons, Ltd.     

Large‐area Ag nanorod array substrates for SERS: AAO template‐assisted fabrication,functionalization, and application in detection PCBs

Highly ordered arrays of thiolated β‐cyclodextrin (HS‐β‐CD) functionalized Ag‐nanorods (Ag‐NRs) with plasmonic antennae enhancement of electrical field have been achieved for encapsulation and rapid detection of polychlorinated biphenyls (PCBs). The large‐area ordered arrays of rigid Ag‐NRs supported on copper base were fabricated via porous anodic aluminum oxide (AAO) template‐assisted electrochemical deposition. The inter‐nanorod gaps between the neighboring Ag‐NRs were tuned to sub‐10 nm by thinning the pore‐wall thickness of the AAO template using diluted H₃PO₄. The nearly perfect large‐area ordered arrays of Ag‐NRs supported on copper base render these systems excellent in surface‐enhanced Raman scattering (SERS) performance with uniform electric field enhancement, as testified by the SERS spectra and Raman mappings of rhodamine 6 G. Furthermore, the Ag‐NRs were functionalized with HS‐β‐CD molecules so as to capture the apolar PCB molecules in the hydrophobic cavity of the CD. Compared to the ordinary undecorated SERS substrates, the HS‐β‐CD modified Ag‐NR arrays exhibit better capture ability and higher sensitivity in rapid detection of PCBs. Copyright © 2012 John Wiley & Sons, Ltd.     

A shifted‐excitation Raman difference spectroscopy (SERDS) evaluation strategy for the efficient isolation of Raman spectra from extreme fluorescence interference

A biochemical characterization of pathologies in biological tissue can be provided by Raman spectroscopy. Often, the raw spectrum is severely affected by fluorescence interference. We report and compare various spectra‐processing approaches required for the purification of Raman spectra from heavily fluorescence‐interfered raw spectra according to the shifted‐excitation Raman difference spectroscopy method. These approaches cover the entire spectra‐processing chain from the raw spectra to the purified Raman spectra. In detail, we compared (1) area normalization versus z‐score normalization, (2) direct reconstruction of the difference spectra versus reconstruction of zero‐centered difference spectra and (3) collective baseline correction of the reconstructed spectra versus piecewise baseline correction of the reconstructed spectra and, finally, (4) analyzed the influence of the shift of the excitation wavelength on the quality of the reconstructed spectra. Statistical analysis of the spectra showed that – in our experiments – the best results were obtained for the z‐score normalization before subtraction of the normalized spectra, followed by zero‐centering of the difference spectra before reconstruction and a piecewise baseline correction of the pure Raman spectra. With our equipment, a wavelength shift from 784 to 785 nm provided reconstructed spectra of best quality. The analyzed specimens were different tissue types of pigs, tissue from the oral cavity of humans and a model solution of dye dissolved in ethanol. © 2015 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd.     

氯霉素包合物的拉曼光谱和红外光谱研究

研究应用拉曼光谱法分析验证氯霉素包合物的可行性。采用拉曼光谱仪和傅里叶红外光谱仪分别测得β-环糊精、氯霉素、β-环糊精和氯霉素物理混合物、氯霉素包合物四种物质固体粉末的拉曼图谱和红外图谱, 并对其进行对照分析。 结果表明拉曼光谱法可获得与红外光谱法一致的结果, 结果表明氯霉素的苯环结构和易水解基团二氯乙酰胺基通过氢键作用被包裹在β-环糊精的空穴结构中形成包合物, 增加了氯霉素的稳定性和溶出度, 并且拉曼光谱法具有快速、准确、简便、无损测量等显著优势, 可作为验证药物包合物的形成重要手段。     

Deep UV resonance Raman spectroscopic study of CnF2n+2 molecules: the excitation of C–C σ bond

The σ–σ* transition of C–C bond in C_nF_2n+2 molecules was studied by deep UV resonance Raman spectroscopy. With the C–C σ bond selectively excited by the deep UV laser at 177.3 nm, the resonance Raman spectra of C_nF_2n+2 molecules were obtained on our home‐assembled deep UV Raman spectrograph. The Raman bands at 1299, 1380 and 2586 cm⁻¹ due to the C–C skeletal stretching modes are evidently enhanced owing to the resonance Raman effect. Based on the resonance Raman spectra and theoretical calculation results, it is proposed that the electronic geometry of C_nF_2n+2 molecules at the σσ* excited state is displaced along the directions perpendicular and parallel to the C–C skeleton, and the excited C–C bond is not dissociative due to the delocalization of the excited electron in σ* orbital. Copyright © 2012 John Wiley & Sons, Ltd.     

Molecular structure,spectroscopic (FTIR,FTIR gas phase,FT‐Raman) first‐order hyperpolarizability and HOMO–LUMO analysis of 4‐methoxy‐2‐methyl benzoic acid

Vibrational spectral analysis was carried out for 4‐methoxy‐2‐methyl benzoic acid (4M2MBA) by using Fourier transform infrared (FT‐IR) (solid, gas phase) and FT‐Raman spectroscopy in the range of 400–4000 and 10–3500 cm⁻¹ respectively. The effects of molecular association through O H···O hydrogen bonding have been described by the single dimer structure. The theoretical computational density functional theory (DFT) and Hatree‐Fock (HF) method were performed at 6–311++G(d,p) levels to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The scaled theoretical wavenumbers were also shown to be in good agreement with experimental data. The first‐order hyperpolarizability (β₀) of this novel molecular system and related properties (β, α₀ and Δα) of 4M2MBA are calculated using the B3LYP/cc‐pvdz basis set, based on the finite‐field approach. A detailed interpretation of the infrared and Raman spectra of 4M2MBA is reported. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule were also constructed and compared with the experimental one. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study on sodium hyaluronate: an effect of proton and γ irradiation

Raman spectroscopy was applied to the analysis of structural changes in lyophilised sodium hyaluronate after proton and γ irradiation (0.5, 5, 50, 100, 200 and 600 Gy). Characteristic Raman bands of the polysaccharide were sensitive to irradiation. Significant damage was observed at doses of 50 Gy or higher. The spectral changes confirmed radiation‐induced loss of native solution conformation, destruction of primary structure, fragmentation, cross‐linking and elimination of functional groups. Differences in the effects of proton and γ radiation on sodium hyaluronate are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

UV resonance Raman study of TrpZip2 and related peptides: π‐π interactions of tryptophan

Aromatic interactions are important stabilizing forces in proteins but are difficult to detect in the absence of high‐resolution structures. Ultraviolet resonance Raman spectroscopy is used to probe the vibrational signatures of aromatic interactions in TrpZip2, a synthetic β‐hairpin peptide that is stabilized by edge‐to‐face and face‐to‐face tryptophan π‐π interactions. The vibrational markers of isolated edge‐to‐face π‐π interactions are investigated in the related β‐hairpin peptide W2W11. The bands that comprise the Fermi doublet exhibit systematic shifts in position and intensity for TrpZip2 and W2W11 relative to the model peptide, W2W9, which does not form aromatic interactions. Additionally, hypochromism of the B_b absorption band of tryptophan in TrpZip2 leads to a decrease in the relative Raman cross‐sections of B_b‐coupled Raman bands. These results reveal spectral markers for stabilizing tryptophan π‐π interactions and indicate that ultraviolet resonance Raman may be an important tool for the characterization of these biological forces. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of a sensitive,stable and EGFR‐specific molecular imaging agent for surface enhanced Raman spectroscopy

We created and studied a novel nanoprobe for spectroscopic molecular imaging of the epidermal growth factor (EGF) receptor, whose over‐expression is a hallmark of a wide range of cancers. Silver nanoparticles (AgNPs) of 45 nm diameter were synthesized and coupled to EGF by α‐lipoic acid, a short ligand that exhibits excellent silver binding affinity. Time‐of‐flight mass spectroscopy demonstrates formation of the protein complex. Enzyme‐linked immunosorbent assay verifies the protein complex is 100% active for the EGF receptor, alone and, following conjugation to silver nanoparticles. Compared with its monosulfide analog, 6‐mercaptohexanoic acid, α‐lipoic acid is stabilized by binding to silver with a total energy that is lower by 1.38 eV, as found from Density Functional Theory (DFT)/natural bond analysis calculations. A Highest Occupied Molecular Orbital (HOMO)‐Lowest Unoccupied Molecular Orbital (LUMO) gap energy of 5.25 (spin‐up electrons) and 5.74 eV (spin‐down electrons) was obtained for the silver‐α‐lipoic acid complex. This is the first report of silver nanoparticles being attached to EGF, and the first theoretical and experimental report on the surface enhanced Raman spectroscopy spectral interpretation of α‐lipoic acid bound to silver. These nanoprobes exhibit surface enhanced Raman spectroscopy, when aggregated in solution, at picomolar concentrations and have the necessary properties – specificity, sensitivity and stability – to serve as molecular imaging agents. Copyright © 2015 John Wiley & Sons, Ltd.     

Solid phase synthesis of novel α/β‐tetrapeptides,electrospray ionization mass spectrometric evaluation of their metal cation complexation behavior,and conformational analysis using density functional theory (DFT)

Thirty‐four novel α/β‐tetrapeptides ( 1–34 ) have been prepared employing solid‐phase and in‐parallel synthetic protocols. α/β ‐Tetrapeptides 1 – 34 were prepared by a combination of three α‐amino acid residues (alanine (Ala), phenylalanine (Phe), and isoleucine (Ile)) with one β‐amino acid residue (β³‐homophenylglycine). The corresponding complexes of several selected α/β‐tetrapeptides with alkali, alkaline earth, and transition metals, [tP + M⁺], were evaluated using ion electrospray‐ionization mass spectrometry (ESI‐MS). According to the results from analysis of mixtures, we can conclude that the position of the β‐amino acid is determinant in the affinity toward different metal cations. Computational modeling (DFT, B3LYP 6‐311++G) provided useful information regarding the most likely coordination sites of the metal ions on the receptor α/β‐tetrapeptide 12 , HO₂C‐α‐Phe‐α‐Phe‐α‐Ile‐β³‐hPhg‐NH₂, as well as the conformational changes induced by the metal upon [tP + M⁺] complex formation. Copyright © 2008 John Wiley & Sons, Ltd.     

基于拉曼光谱技术的枇杷果实β-胡萝卜素含量无损测定研究

β-胡萝卜素作为一种重要的营养元素,其在果蔬活体内的测定方法通常必须对样品进行破坏,并且耗时、费力。采用拉曼光谱技术预测活体枇杷果实内β-胡萝卜素含量,以高效液相色谱法(HPLC)检测值作为参考值,采用高斯平滑对光谱数据进行预处理,同时使用多项式拟合(PF)的方法对光谱数据进行背景荧光扣除,以标准β-胡萝卜素的拉曼图谱为基础,选取了三个特征频移,以特征频移和截取的光谱建立了MLR模型、PLSR模型以及LS-SVM模型,取得了比较好的预测精度。其中LS-SVM模型的预测精度最高,其预测相关系数R2_p达到了0.91,表明通过拉曼光谱对活体枇杷内β-胡萝卜素的含量检测是实际可行的。     

Intramolecular enantiomerism as revealed from Raman optical activity spectrum

An algorithm is employed to retrieve the differential bond polarizabilities (DBP) of the C‐C bonds from the Raman optical activity spectrum of (‐)β‐pinene. (‐)β‐pinene possesses two stereo centers (chiral centers) and a local mirror reflection that interchanges the S type part and R type part in one molecular. It is demonstrated that this local mirror reflection could induce an approximate (or symmetry breaking) mirror reflection that reverses the signs of the DBP of the pair bond coordinates that are related to each other by the mirror reflection.This can be called intramolecular enantiomerism (IE). More cases of IE are discussed by the analysis of (‐)α‐pinene, (R)‐(+)‐4‐isopropyl‐1‐methylcyclohexene and (R)‐(+)‐3‐methylcyclohexanone together with previously studied limonene case. Copyright © 2015 John Wiley & Sons, Ltd.     

Food additives characterization by infrared,Raman, and surface‐enhanced Raman spectroscopies

Fourier‐transform infrared (FT‐IR), Raman (RS), and surface‐enhanced Raman scattering (SERS) spectra of β‐hydroxy‐β‐methylobutanoic acid (HMB), L ‐carnitine, and N‐methylglycocyamine (creatine) have been measured. The SERS spectra have been taken from species adsorbed on a colloidal silver surface. The respective FT‐IR and RS band assignments (solid‐state samples) based on the literature data have been proposed. The strongest absorptions in the FT‐IR spectrum of creatine are observed at 1398, 1615, and 1699 cm⁻¹, which are due to ν_s(COOH) + ν(CN) + δ(CN), ρ_s(NH₂), and ν(C O) modes, respectively, whereas those of L ‐carnitine (at 1396/1586 cm⁻¹ and 1480 cm⁻¹) and HMB (at 1405/1555/1585 cm⁻¹ and 1437–1473 cm⁻¹) are associated with carboxyl and methyl/methylene group vibrations, respectively. On the other hand, the strongest bands in the RS spectrum of HMB observed at 748/1442/1462 cm⁻¹ and 1408 cm⁻¹ are due to methyl/methylene deformations and carboxyl group vibrations, respectively. The strongest Raman band of creatine at 831 cm⁻¹ (ρ_w(R NH₂)) is accompanied by two weaker bands at 1054 and 1397 cm⁻¹ due to ν(CN) + ν(R NH₂) and ν_s(COOH) + ν(CN) + δ(CN) modes, respectively. In the case of L ‐carnitine, its RS spectrum is dominated by bands at 772 and 1461 cm⁻¹ assigned to ρ_r(CH₂) and δ(CH₃), respectively. The analysis of the SERS spectra shows that HMB interacts with the silver surface mainly through the  COO⁻, hydroxyl, and  CH₂ groups, whereas L ‐carnitine binds to the surface via  COO⁻ and  N⁺(CH₃)₃ which is rarely enhanced at pH = 8.3. On the other hand, it seems that creatine binds weakly to the silver surface mainly by  NH₂, and C O from the  COO⁻ group. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopy of dipyrrins: nonresonant,resonant and surface‐enhanced cross‐sections and enhancement factors

Detailed studies of the mechanism of surface‐enhanced (resonance) Raman spectroscopy (SE(R)RS), and its applications, place a number of demands on the properties of SERS scatterers. With large Raman cross‐sections, versatile synthetic chemistry and complete lack of fluorescence, free dipyrrins meet these demands but the Raman and SE(R)RS spectroscopy of free dipyrrins is largely unknown. The first study of the Raman spectroscopy of free dipyrrins is therefore presented in this work. The nonresonant Raman, resonant Raman and surface‐enhanced Raman spectra of a typical meso aryl‐substituted‐dipyrrin are reported. Absolute differential cross‐sections are obtained for excitation wavelengths in the near infrared and visible region, in solution phase and for dipyrrin adsorbed on the surface of silver nanoparticles. Raman enhancement factors for SERRS and resonance Raman are calculated from the observed differential cross‐sections. The magnitudes of the resonantly enhanced cross‐sections are similar to those recently reported for strong SERS dyes such as Rhodamine 6G and Crystal Violet. Free dipyrrins offer the advantages of existing SERS dyes but without the drawback of strong fluorescence. Free dipyrrins should therefore find applications in all areas of Raman spectroscopy including fundamental studies of the mechanisms of SERS and bioanalytical and environmental applications. Copyright © 2011 John Wiley & Sons, Ltd.