Origin of the variability of the mechanical properties of silk fibres: 3. Order and macromolecule orientation in Bombyx mori bave,hand‐stretched strings and Nephila madagascarensis spider fibres

The comparison of the low wavenumber of polarized Raman spectra (50–300 cm^–1) from Bombyx mori (fresh cocoons fibres, hand‐stretched ‘Crins de Florence’ strings from the gland content, dried gland, regenerated silk films) and Nephila madagascarensis silks reveals the high polarisation of fibre modes and the absence of polarisation for dried gland and regenerated silk films. This is consistent with X‐ray diffraction measurements. The orientation of the fibroin/spidroin chains is due to the stretching during production, as for advanced synthetic fibres. The bandwidth of the ‘ordered chains’ signature is almost the same for the different fibres. However, the degree of polarisation seems to be higher in the case of spider fibre. The huge bandwidth of low wavenumber components of regenerated films indicates high disorder. Measurements along the fibre point out conformation changes with a periodicity (~20 mm) related to the silkworm head motion during the fabrication of the cocoon. Copyright © 2012 John Wiley & Sons, Ltd.     

Nanomechanics of single silkworm and spider fibres: a Raman and micro‐mechanical in situ study of the conformation change with stress

The combination of micro‐Raman spectroscopy and an advanced universal fibre tester (UFT) made it possible to probe at the nanoscale (through monitoring the modification of chemical bonds) the change in conformation (α‐helix, β‐sheet, etc.), macromolecular fibroin chain orientation and coupling during the application of stress, quantitatively. Different single fibres of silkworms (Bombyx mori, Gonometa rufobrunea, Gonometa postica) and a spider (Nephila madagascariensis) were tested in a dry environment and compared with the behaviour of keratin fibre. As observed previously for single keratin fibres, a direct relationship is observed between nano‐ and micro‐mechanical tensile behaviour. The phase transition plateau, well defined for some pristine B. mori fibres, disappears in degummed fibres, which indicates a structural modification and increasing disorder with chemical treatments. Stress‐controlled micro‐Raman analysis shows that a few modes involving CH₂ and/or amide groups of β‐conformation chains undergo a wavenumber softening during the elastic behaviour (∼0–3%), although most of the modes are not affected. A different behaviour is observed for modes associated with ‘ordered’ and ‘disordered’ β‐sheets and helical chains. Larger softening is observed for lattice modes with increasing stress/strain, as expected. Structural changes and relationships with mechanical behaviour are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman imaging and stress quantification in self‐assembled graphene oxide fiber ‘Latin Letters’

To probe the intrinsic stress distribution in terms of spatial Raman shift (ω) and change in the phonon linewidth (Γ), here we analyze self‐assembled graphene oxide fibers (GOF) ‘Latin letters’ by confocal Raman spectroscopy. The self‐assembly of GOF ‘Latin letters’ has been explained through surface tension, π–π stacking, van der Waals interaction at the air–water interface and by systematic time‐dependent investigation using field emission scanning electron microscopy analysis. Intrinsic residual stress due to structural joints and bending is playing a distinct role affecting the E_2g mode (G band) at and away from the physical interface of GOF segments with broadening of phonon linewidth, indicating prominent phonon softening. Linescan across an interface of the GOF ‘letters’ reveals Raman shift to lower wavenumber in all cases but more so in ‘Z’ fiber exhibiting a broader region. Furthermore, intrinsic stress homogeneity is observed for ‘G’ fiber distributed throughout its curvature with negligible shift corresponding to E_2g mode vibration. This article demonstrates the significance of morphology in stress distribution across the self‐assembled and ‘smart‐integrable’ GOF ‘Latin letters’. Copyright © 2016 John Wiley & Sons, Ltd.     

CARS investigation of collisional shift of the hydrogen Q‐branch transitions by water at high temperatures

A high‐resolution (∼0.1 cm⁻¹) spectroscopic method based on the application of a Fabry–Pérot interferometer to the spectral analysis of the coherent anti‐Stokes Raman scattering (CARS) signal from an individual Raman transition was used to obtain single‐shot spectra of hydrogen Q‐branch transitions directly in the flame of a pulsed, high‐pressure H₂/O₂ combustion chamber. Simultaneously with the Fabry–Pérot pattern, a broadband CARS spectrum of the complete H₂Q ‐branch structure was recorded in order to measure the temperature of the probe volume. During every cycle of the combustion chamber, a pressure pulse together with single‐shot CARS spectra, providing information on individual line shapes and medium temperature, was recorded. On the basis of the experimental data, the temperature dependences of lineshift coefficients for several Q‐branch lines of hydrogen molecules under collisions with water molecules were determined in the temperature range 2100 < T < 3500 K, and an empirical ‘fitting law’ for H₂ H₂O lineshift coefficients is proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Phonon anomalies and structural transition in spin ice Dy2Ti2O7: a simultaneous pressure‐dependent and temperature‐dependent Raman study

We revisit the assignment of Raman phonons of rare‐earth titanates by performing Raman measurements on single crystals of O¹⁸ isotope‐rich spin ice and nonmagnetic pyrochlores and compare the results with their O¹⁶ counterparts. We show that the low‐wavenumber Raman modes below 250 cm⁻¹ are not due to oxygen vibrations. A mode near 200 cm⁻¹, commonly assigned as F_2g phonon, which shows highly anomalous temperature dependence, is now assigned to a disorder‐induced Raman active mode involving Ti⁴⁺ vibrations. Moreover, we address here the origin of the ‘new’ Raman mode, observed below T_C ~ 110 K in Dy₂Ti₂O₇, through a simultaneous pressure‐dependent and temperature‐dependent Raman study. Our study confirms the ‘new’ mode to be a phonon mode. We find that dT_C/dP = + 5.9 K/GPa. Temperature dependence of other phonons has also been studied at various pressures up to ~8 GPa. We find that pressure suppresses the anomalous temperature dependence. The role of the inherent vacant sites present in the pyrochlore structure in the anomalous temperature dependence is also discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Involvement of weak C?H···X hydrogen bonds in metal‐to‐semiconductor regime change in one‐dimensional organic conductors (o‐DMTTF)2X (X = Cl,Br, and I): combined IR and Raman studies

We report on the infrared (IR) and Raman studies of the three isostructural quasi‐one‐dimensional cation radical salts of 3,4‐dimethyl‐tetrathiafulvalene (o‐DMTTF)₂X (X = Cl, Br, and I), which all exhibit metallic properties at room temperature and undergo transitions to a semiconducting state in two steps: a soft metal‐to‐semiconductor regime change in the temperature region T_ρ = 5–200 K and then a sharp phase transition at about T_MI = 50 K. Polarized IR reflectance spectra (700–16 000 cm⁻¹) and Raman spectra (50–3500 cm⁻¹, excitation λ = 632.8 nm) of single crystals were measured as a function of temperature (T = 5–300 K) to assess the eventual formation of a charge‐ordered state below 50 K. Additionally, the temperature dependence of the IR absorption spectra of powdered crystals in KBr discs was also studied. The Raman spectra and especially the bands related to the CC stretching vibration of o‐DMTTF provide unambiguous evidence of uniform charge distribution on o‐DMTTF down to the lowest temperatures, without any modification below 50 K. However, the temperature dependence of Raman spectra indicates a regime change below about 200 K. Temperature dependence of both electronic dispersion and vibrational features observed in the IR spectra also clearly confirms the regime change below about 200 K and shows the involvement of C H···X hydrogen bonds in the electronic localization; some spectral changes can be also related with the phase transition at 50 K. Additionally, using density functional theory methods, the normal vibrational modes of the neutral o‐DMTTF⁰ and cationic o‐DMTTF⁺ species, as well as their theoretical IR and Raman spectra, were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral o‐DMTTF molecule. Copyright © 2011 John Wiley & Sons, Ltd.     

Solvation of AgTFSI in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid investigated by vibrational spectroscopy and DFT calculations

In this paper we investigate the solvation of silver bis(trifluoromethylsulfonyl)imide salt (AgTFSI) in 1‐ethyl‐3‐methylimidazolium TFSI [EMI][TFSI] ionic liquid by combining Raman and infrared (IR) spectroscopies with density functional theory (DFT) calculations. The IR and Raman spectra were measured in the 200–4000 cm⁻¹ spectral region for AgTFSI/[EMI][TFSI] solutions with different concentrations ([AgTFSI] <0.2 mole fraction). The analysis of the spectra shows that the spectral features observed by dissolution of AgTFSI in [EMI][TFSI] solution originate from interactions between the Ag⁺ cation and the first neighboring TFSI anions to form relatively stable Ag complexes. The ‘gas phase’ interaction energy of a type [Ag(TFSI)₃]²⁻ complex was evaluated by DFT calculations and compared with other interionic interaction energy contributions. The predicted spectral signatures because of the [Ag(TFSI)₃]²⁻ complex were assessed in order to interpret the main IR and Raman spectral features observed. The formation of such complexes leads to the appearance of new interaction‐induced bands situated at 753 cm⁻¹ in Raman and at 1015 and 1371 cm⁻¹ in IR, respectively. These specific spectral signatures are associated with the ‘breathing’ mode and the S–N–S and S–O stretching modes of the TFSI anions engaged in the complex. Finally, all these findings are discussed in terms of interaction mechanisms enabling the electrodeposition characteristics of silver from AgTFSI/[EMI][TFSI] IL‐based electrolytic solutions. Copyright © 2015 John Wiley & Sons, Ltd.     

Origin of the variability of the mechanical properties of silk fibres: 1 ‐ The relationship between disorder,hydration and stress/strain behaviour

The causes of the variability in mechanical behaviour of various silks obtained from silkworms (Bombyx mori, Antheraea/Tussah) and spiders (Nephila madagascarensis) have been studied by tensile uniaxial tests, differential scanning calorimetry and Raman microspectrometry. Analyses of tensile stress–strain curves recorded for different silkworm and spider baves and single fibres, undergoing different histories (age, degumming, thermal/chemical treatments), allow the behaviour to be classified into five groups and correlated with the fibroin/spidroin structural status: (1) Type I exhibits linear elastic behaviour and then a quasi plateau, (2) Type II has a two‐step linear elastic behaviour with kinks then a quasi plateau, (3) Type III exhibits a smooth transition from a linear behaviour to a plateau, (4) Type IV has a behaviour rather similar to that of Type I but above ~8–12% hardening occurs, and (5) Type V results in the breakage of fibres during the first elastic stage. Unambiguously, Type IV is more frequent for degummed, very dried fibres and Type III for water‐saturated fibres. The most striking Raman signature differences are observed in the Raman intensity of the amorphous/‘ordered’ νN–H and H₂O band components and correlated to the water content and disorder degree according to the calorimetry study. Types I and II are frequently observed for fresh (largely amorphous) spun fibres/baves. Type V is characteristic of degraded fibres. Type IV represents the most ordered state. The similar stress–strain types for dried silkworm and spider fibres show that the general difference in amino acid contents is not the most pertinent parameter for the mechanical behaviour. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman response function and Raman fraction of phosphosilicate fibers

The Raman response function and Raman nonlinear index of phosphosilicate fibers are calculated for several P₂O₅ concentrations. The nonlinear index of phosphosilicate fiber is estimated by using the Boling formula, and it is used to calculate the Raman fraction of the nonlinear index. On the other hand, the Raman response function of the phosphosilicate fibers is fitted to a superposition of six phase-shifted under-damped functions in order to use it in the numerical simulation of ultra-short pulse propagation. We show through numerical simulations that phosphosilicate fibers are a suitable medium to observe a scaling up of the Raman self-frequency shift when compared to silica fibers.     

Fourier‐transform surface‐enhanced Raman spectroscopy (FT‐SERS) applied to the identification of natural dyes in textile fibers: an extractionless approach to the analysis

In the present study, an application of a silver colloid substrate in order to obtain Fourier‐transform surface‐enhanced Raman (FT‐SER) spectra of natural historical dyes is presented. In detail, we collected a spectral database from solutions of pure dyes and then we carried out extractionless both hydrolysis and non‐hydrolysis FT‐SERS analyses on wool fibers previously dyed in our laboratory and on ancient textiles. The term ‘extractionless’ refers to a method of SERS analysis applied directly on the fiber, thus avoiding the extraction of dyes from textile samples. The combination of a low‐energy source of radiation, as in the FT‐Raman technique, with SER spectroscopy can bring the important advantage of reducing the fluorescence typical of ancient samples and organic dyes. In some historical textile samples, for which SER spectra by use of visible excitation could not be obtained, the FT‐SER spectrum of an iron‐gall dye was recorded without hydrolysis, while, with an HF hydrolysis pre‐treatment on ancient fibers, madder, lac dye and brazilwood were clearly recognized. Copyright © 2014 John Wiley & Sons, Ltd.     

Polarization behaviors of twisted carbon nanotube fibers

Polarization behaviors of carbon nanotube (CNT) fibers with different twisting were reported. Scanning electron microscope and polarized Raman spectroscopy were used to investigate the prepared samples. Results indicate that surface twisting angle affects greatly the polarization angle and I_///I_⊥ ratio of twisted CNT fibers. Raman depth profile measurements imply that the twisted fibers consist of non‐uniform CNT alignments. A simplified two‐CNT‐alignment geometric model was proposed to illuminate the experimental observations. The results suggest that polarized Raman depth profile measurement would be a very useful approach for determining the distribution of CNT alignments in CNT fibers. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies of the structure of di‐amino acid peptides. Part II: cyclo(L‐Asp‐L‐Asp) in the solid state and in aqueous solution

Solid‐state protonated and N,O‐deuterated Fourier transform infrared (IR) and Raman scattering spectra together with the protonated and deuterated Raman spectra in aqueous solution of the cyclic di‐amino acid peptide cyclo(L ‐Asp‐L ‐Asp) are reported. Vibrational band assignments have been made on the basis of comparisons with previously cited literature values for diketopiperazine (DKP) derivatives and normal coordinate analyses for both the protonated and deuterated species based upon DFT calculations at the B3‐LYP/cc‐pVDZ level of the isolated molecule in the gas phase. The calculated minimum energy structure for cyclo(L ‐Asp‐L ‐Asp), assuming C₂ symmetry, predicts a boat conformation for the DKP ring with both the two L ‐aspartyl side chains being folded slightly above the ring. The CO stretching vibrations have been assigned for the side‐chain carboxylic acid group (e.g. at 1693 and 1670 cm⁻¹ in the Raman spectrum) and the cis amide I bands (e.g. at 1660 cm⁻¹ in the Raman spectrum). The presence of two bands for the carboxylic acid CO stretching modes in the solid‐state Raman spectrum can be accounted for by factor group splitting of the two nonequivalent molecules in a crystallographic unit cell. The cis amide II band is observed at 1489 cm⁻¹ in the solid‐state Raman spectrum, which is in agreement with results for cyclic di‐amino acid peptide molecules examined previously in the solid state, where the DKP ring adopts a boat conformation. Additionally, it also appears that as the molecular mass of the substituent on the C^α atom is increased, the amide II band wavenumber decreases to below 1500 cm⁻¹; this may be a consequence of increased strain on the DKP ring. The cis amide II Raman band is characterized by its relatively small deuterium shift (29 cm⁻¹), which indicates that this band has a smaller N H bending contribution than the trans amide II vibrational band observed for linear peptides. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature‐dependent Raman study of PrFeO3thin film

Low‐temperature Raman study of (001)‐oriented PrFeO₃ thin film of around 200 nm thickness deposited on a LaAlO₃ (001) substrate by using the pulsed‐laser deposition technique is presented. X‐ray diffraction analysis of this film shows an orthorhombic structure with Pbnm space group. The observed substrate‐induced strain is found to be small. In the room temperature Raman spectra, different Raman modes were observed that were classified according to the orthorhombic structure. All the observed modes show a decrease in wavenumber with rise in temperature, except the B_1g mode (624 cm⁻¹) which shows some anomalous behavior. We tried to correlate the variations in linewidth and position with temperature for the observed modes with the octahedral disorder of FeO₆. Many possibilities are presented to explain the observed results. Copyright © 2010 John Wiley & Sons, Ltd.     

A comparison between ab initio calculated and measured Raman spectrum of triclinic albite (NaAlSi3O8)

Albite is one of the most common minerals in the Earth's crust, and its polymorphs can be found in rocks with different cooling histories. The characteristic spectrum of vibration of the albite mineral reflects its structural Si/Al ordering. In this study, we report on the comparison between the Raman spectra measured on a natural and fully ordered (as deduced on the basis of single‐crystal X‐ray diffraction data) ‘low albite’, NaAlSi₃O₈, and those calculated at the hybrid Hartree–Fock/density functional theory level by employing the WC1LYP Hamiltonian, which has proven to give excellent agreement between calculated and experimentally measured vibrational wavenumbers in silicate minerals. All the 39 expected A_g modes are identified in the Raman spectra, and their wavenumbers and intensities, in different scattering configurations, correspond well to the calculated ones. The average absolute discrepancy is ~3.4 cm⁻¹, being the maximum discrepancy |Δv|_max ~ 10.3 cm⁻¹. The very good quality of the WC1LYP results allows for reliable assignments of the Raman features to specific patterns of atomic vibrational motion. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparative Raman spectroscopic analysis of orientation in fibers and regenerated films of Bombyx mori silk fibroin

This study is focused on the Raman spectroscopic analysis of degummed silk fibroin (SF) fibers and regenerated Bombyx mori silk fibroin films: a correlation was found between some spectral features related to the methylene deformation modes and the molecular orientation of the samples. Polarized Raman spectra on SF fibers were used to obtain the orientation distribution function of carbonyl groups along the protein backbone. The variation of the intensity ratio of 1400/1450 cm⁻¹ for the peaks attributed to the wagging and bending deformation modes of CH₂ groups with respect to the angular orientation of the fiber was measured and quantitatively correlated with the orientation distribution function of the carbonyl groups. Unpolarized Raman spectra were measured for regenerated silk fibroin films and lyophilized solutions. The variation of the intensity ratio of 1415/1455 cm⁻¹, which is related to the deformation modes of CH₂ groups in SF regenerated materials, was qualitatively related to the microstructural orientation of the samples observed by scanning electron microscopy (SEM), and to the presence of Silk I phase as suggested by the analysis of samples obtained in different casting conditions and also by the measurements on mechanically deformed films. The results obtained showed the utility of the spectroscopic intensity ratio of 1400/1450 cm⁻¹ for the rapid assessment of molecular orientation in silk fibers, which could be useful for quality and process control of regenerated silk‐based textiles. Moreover, the qualitative dependence of the intensity ratio of 1415/1455 cm⁻¹ was found to be sensitive to both the microstructural orientation and Silk I content of regenerated silk fibroin films, suggesting a possible correlation of this Raman marker of the Silk I phase with the degree of molecular order brought about by this polymorph. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman studies of α‐aminophosphinic inhibitors of metalloenzymes

Here, we report the nature of new di‐α‐amino (L¹–L³) and α‐amino‐α‐hydroxyphosphinic (L⁴–L⁶) acids, which are considered potential inhibitors of the aminopeptidase N, adsorbed on a colloidal silver surface by means of surface‐enhanced Raman scattering (SERS) spectroscopy. In order to reveal the adsorption mechanism of these species from their SERS spectra, Fourier‐transform Raman (FT‐RS) spectra of these nonadsorbed molecules were measured. By examining the enhancement, shift in wavenumbers, and changes in breadth of the SERS bands due to the adsorption process, we revealed that the tilted compounds interact with the colloidal silver substrate mainly through the benzene ring, amino group, and phosphinic moiety in the following way. The benzene ring of L² and L³ is ‘standing up’ on the colloidal silver surface, and the C N bond is almost vertical to it, while the tilt angle between the O PO bond and this surface is greater than 45°. On the other hand, for L¹, L⁴, and L⁵, the aromatic ring and C N bond are arranged more or less tilted, and the tilt angle between the O PO bond and the silver substrate is smaller than 45°. The elongation of the bond to the benzene ring, the L⁶ case, produces an almost horizontal orientation of the benzene ring and the O PO bond on the silver nanoparticles. For these ligands, the complement inhibition IC₅₀ tested in vitro using porcine kidney leucine aminopeptidase was correlated mainly with the behavior of the O PO and C CH N fragments on the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Stability toward alkaline hydrolysis of B. mori silk fibroin grafted with methacrylamide

Bombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH₂ groups into COOH and COO⁻ groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β‐sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH⁻ attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high‐performing silk‐based materials. The A₇₃₁/A₁₀₀₄ Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R² = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd.     

Raman scattering of L‐tryptophan enhanced by surface plasmon of silver nanoparticles: vibrational assignment and structural determination

Vibrational bands of L ‐tryptophan which was adsorbed on Ag nanoparticles (∼10 nm in diameter) have been investigated in the spectral range of 200–1700 cm⁻¹ using surface‐enhanced Raman scattering (SERS) spectroscopy. Compared with the normal Raman scattering (NRS) of L ‐tryptophan in either 0.5 M aqueous solution (NRS‐AS) or solid powder (NRS‐SP), the intensified signals by SERS have made the SERS investigation at a lower molecular concentration (5 × 10⁻⁴ M ) possible. Ab initio calculations at the B3LYP/6‐311G level have been carried out to predict the optimal structure and vibrational wavenumbers for the zwitterionic form of L ‐tryptophan. Facilitated with the theoretical prediction, the observed vibrational modes of L ‐tryptophan in the NRS‐AS, NRS‐SP, and SERS spectra have been analyzed. In the spectroscopic observations, there are no significant changes for the vibrational bands of the indole ring in either NRS‐AS, NRS‐SP, or SERS. In contrast, spectral intensities involving the vibrations of carboxylate and amino groups are weak in NRS‐AS and NRS‐SP, but strong in SERS. The intensity enhancement in the SERS spectrum can reach 10³–10⁴‐fold magnification. On the basis of spectroscopic analysis, the carboxylate and amino groups of L ‐tryptophan are determined to be the preferential terminal groups to attach onto the surfaces of Ag nanoparticles in the SERS measurement. Copyright © 2008 John Wiley & Sons, Ltd.     

The study of the structure and bioactivity of the B2O3 • Na2O • P2O5 system

In this study, we have investigated calcium and silicate‐free samples over a wide compositional range in the xB₂O₃·30 Na₂O·(70−x)P₂O₅ system, with 0 ≤ x ≤ 70 mol%, in order to determine the influence of the chemical composition on their structure and bioactive response in simulated body fluid. Information related to the chemical structures present in the network was obtained by means of Raman and infrared spectroscopy. For samples containing small amounts of P₂O₅, boron structures are preponderant. Upon increasing the phosphorus content, the samples' network is based on phosphate chains linked by boron groups through ‘P–O–B’ bridges. For high concentration of P₂O₅, the Q³ units form three‐dimensional network, whereas Q² units assist the chain formation. Regarding the in vitro assessment of bioactivity, the clear print of PO₄ asymmetric bending vibrations of apatite‐like layer in the 540–680 cm⁻¹ spectral domain, the scanning electron micrographs and energy dispersive x‐ray analysis spectra demonstrate that the studied borophosphate samples exhibit good bioactive response only for certain chemical compositions. More exactly, the highest bioactivity is obtained for 30% and 20% B₂O₃ (mol%) after 3 and 11 days of immersion, respectively. Therefore, the samples with 20–30 mol% boron content are valuable candidates that can be used as materials for tissue engineering applications. Copyright © 2013 John Wiley & Sons, Ltd.