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This paper gives a summary of this special issue on 'Pharmaceutical Applications of Raman Spectroscopy'. It summarizes the papers collected and introduces the possible applications of classical Raman spectroscopy (macro and micro) and surface-enhanced Raman spectroscopy to the identification of pharmacologically active substances, their qualitative and quantitative analysis, characterization of crystalline forms and structure determination.

The C=O stretching frequency of liquid ethylene and propylene carbonates is higher in the infrared than in the Raman spectrum. The difference amounts to 13 cm-I for ethylene carbonate at 313 K. This effect is explained as the consequence of a coupling between the transition dipoles of neighbouring molecules, which is made possible by some degree of alignment of molecular dipoles due to the high dipole moment of these molecules (about 16 x C m). A study of dilution and temperature effects confirms this interpretation.

A comparative Raman and FTIR study of histamine (Hm), a small hormone present in a wide selection of living organisms, and its complexes with copper(II) at different pH values was carried out. Both the Raman and IR spectra present some marker bands useful for the identification of the structure of the species predominating in the Cu(II) aqueous and alcoholic systems. In particular, Raman spectroscopy appears to be a useful tool for analyzing the tautomeric equilibrium of the imidazole ring of Hm, because some bands (i.e., nuC(4)dbond;C(5)) appear at different wavenumbers, depending on whether the imidazole moiety is in the N(tau)-H (tautomer I) or N(pi)-H (tautomer II) protonated form. In aqueous solutions the manner in which Hm binds to Cu(II) depends on the pH. At basic pH the most relevant species formed are a dimer, [Cu(2)L(2)H(-2)](2+), and a monomeric complex, [CuL](2-) or [CuL(2)](+). On the contrary, by decreasing the pH, Hm acts as a mono- or bidentate ligand, giving rise to two types of monomeric complexes, [CuLH](2-) and [CuL](2-) or [CuL(2)](+). With respect to the Cu(II)-Hm alcoholic system, both the aminic group and the imidazole ring (tautomer I) take part in the Cu(II) coordination, leading to the formation of the [CuL](2-) or [CuL(2)](+) monomeric complex.

The zinc(II)–L‐carnosine system was investigated at different pH and metal/ligand ratios by Raman and IR spectroscopy. The Raman and IR spectra present some marker bands useful to identify the sites involved in metal chelation at a specific pH value. In particular, the neutral imidazole group gives rise to some Raman bands, such as the νC4C5 band, that change in wave number, depending on whether the imidazole ring takes the tautomeric form I or II. Even if tautomer I is predominant in the free ligand, metal coordination can upset tautomeric preference and Nτ‐ and Nπ‐ligated complexes can be identified. Although weak compared to those of aromatic residues, these Raman marker bands may be useful in analyzing metal–histidine interaction in peptides and proteins. On the basis of the vibrational results, conclusions can be drawn on the species existing in the system. Depending on the available nitrogen atoms, various complexes can be formed and the prevalent form of the species depends mainly on the pH. At basic pH carnosine gives rise to two different neutral complexes: a water‐insoluble polymeric species, [ZnH−1L] 0italicn, and a dimer, [Zn2H−2L2]0. The first is predominant and involves the tautomeric I form of the imidazole ring in metal chelation; the second contains tautomer II and increases its percentage by going from a 2 to 0.25 metal/ligand ratio. Conversely, the dimeric species dominates at pH 7, whereas two charged species, [ZnHL]2+ and [ZnL]+, are formed under slightly acidic conditions. In the [ZnHL]2+ complex the imidazole ring takes part in the Zn(II) coordination in the tautomeric I form, whereas in [ZnL]+ the ring is protonated and not bound to the Zn(II) ion. In addition, the curve fitting analysis of the 1700–1530 cm−1 Raman region was helpful in indicating the predominant species at each pH. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 352–364, 2000

Multinuclear ((1)H, (13)C, and (31)P) magnetic resonance spectroscopy are applied to the biochemical characterization of the total lipid fraction of healthy and neoplastic human brain tissues. Lipid extracts from normal brains, glioblastomas, anaplastic oligodendrogliomas, oligodendrogliomas, and meningiomas are examined. Moreover, the unknown liquid content of a cyst adjacent to a meningioma is analyzed. Two biopsies from glioblastomas are directly studied by (1)H-NMR without any treatment (ex vivo NMR). The (1)H- and (13)C-NMR analysis allows full characterization of the lipid component of the cerebral tissues. In particular, the presence of cholesteryl esters and triglycerides in the extracts of high grade tumors is correlated to the vascular proliferation degree, which is different from normal brain tissue and low grade neoplasms. The (31)P spectra show that phosphatidylcholine is the prominent phospholipid and its relative amount, which is higher in gliomas, is correlated to the low grade of differentiation of tumor cells and an altered membrane turnover. The ex vivo (1)H-NMR data on the glioblastoma samples show the presence of mobile lipids that are correlated to cell necrotic phenomena. Our data allow a direct correlation between biochemical results obtained by NMR and the histopathological factors (vascular and cell proliferations, differentiation, and necrosis) that are prominent in determining brain tumor grading.

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In the Ranian spectrum of pure liquids, the anisotropic component of the C-0 stretching band falls at a higher frequency than the isotropic component. In the same liquids the infra-red band maximum appears at almost the same frequency as the Raman anisotropic component. In some cases the infra-red band may be resolved into two components, the stronger coinciding with the anisotropic, the weaker with the isotropic Raman band. These effects disappear with dilution and are reduced with increasing temperature.This behaviour is explained in terms of a model which assumes that dipolar aprotic liquids are composed of clusters cf molecules oriented in an (at least partially) ordered way.In pure liquids equal vibrations of neighbouring molecules are coupled. When the orientation of the molecules is entirely random, this coupling only causes a band broadening1'On the other hand, if some degree of order occurs in the molecular orientation, then correlation splitting effects of the same nature as those observed in molecular crystals become possible.In the first paper of this series we reported that the C=O stretching vibration of 1iqu;d ethylene carbonate exhibits an infra-red absorption 13 CM-' higher than its Raman counterpart, and we showed that this difference could be explained by assuming the presence in the liquid of a short-range order partially reproducing the structure of the crystal (in the solid phase the separation between the infra-red and Raman C=O stretching bands is about 70 c~I I -~) .~ Liquid propylene carbonate behaves similarly.In ethylene and propylene carbonates the ordered molecular orientation is ascribed to the large dipole moment of these molecules (about 16 x C m). However, less polar liquids should also possess a degree of order able to produce measurable effects in the vibrational spectrum : indeed the orientational order will extend up to such a distance that the energy of electrostatic interaction between two dipoles equals the thermal agitation energy, i.e. approximately : p 2 / r 3 = kT.C m, T = 300 M, we obtain r = 0.6 nm; for not too large molecules this implies that at least the molecules in the first coordination shell should attain a preferential orientation with respect to the central molecule. Furthermore, if the coupling mechanism is mainly of an excitonic character,' the effects on the vibrational spectrum should be especially marked for the most intense absorption bands, as, for example, the C=O stretching.In 1947, on the basis of the data then available on the Raman and infra-red C=O stretching frequencies of ketones, Lecomte set forth the hypothesis of electrostatic coupling between C=O oscillators of neighbouring molecules.6 This hypothesis was apparently confirmed by subsequent observations of Josien and Lascombe on liquid 1776