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The Raman spectra of several surfactants such as didodecyldimethylammonium bromide (DDAB), cetyltrimethylammonium bromide (CTAB), dimyristoylphosphatidylcholine (DMPC), cetylpyridinium chloride (CPC), dihexadecyl phosphate (DHP), and sodium laurate (NaL) have been investigated in the solid, multilayer, micellar, and multibilayer forms. The first four are cationic surfactants while DHP and NaL are anionic. Raman spectra show that they all exist in an all-trans configuration in the crystalline state while their structure in the micellar, monolayer, and multibilayer (film) forms is a mixture of gauche and trans configurations. Surface-enhanced Raman scattering (SERS) spectra of the above surfactants (with the exception of CPC) show an unexpected enhancement for C−H stretching modes at potentials more negative than −0.8 V versus the saturated calomel electrode along with the appearance of two new SERS vibration bands at 2710 and 2815 cm^-1. In the multibilayer film, the SERS spectra of some of these surfactants (DDAB, CTAB, DMPC) are dominated by two intense bands located at 1130 cm^-1 and 1530 cm^-1. The 1130 cm^-1 band corresponds to the all-trans alkyl structure, which is common in the Raman spectra of all of these surfactants, while the 1530 cm^-1 band is a totally new band. We associate it with a bending mode of the quaternary nitrogen methyl groups. Ab initio Hartree−Fock/6-311G calculations of CTAB in the trans and gauche configurations are used to support the band assignments.

The surface-enhanced Raman scattering (SERS) spectra of nicotinamide adenine dinucleotide (NAD⁺) at different pH values and electrode potentials were investigated at a silver electrode. For comparison purposes, the spectra of adenine, N-methylnicotinamide, and nicotinamide mononucleotide were also recorded. Good quality spectra are reported, and NAD⁺ adsorbs spontaneously onto the electrode at all of the pH values (9.3−3.6) studied. Normal mode calculations of the in-plane vibrations of adenine were performed to assist in band assignments and determination of adsorbate orientation. These calculations utilized Urey−Bradley force field calculations and the PM3 semiempirical molecular orbital method. From these calculations, it is concluded that at physiological pH values NAD⁺ adsorbs on the silver electrode in a conformer in which the adenine ring binds to the surface through the external amino group on carbon 6 and through nitrogen 7. The ribose and phosphate parts of the molecule are also involved in adsorption. In the surface conformer NAD⁺ is in an extended configuration with the adenine ring oriented normal (side on) with respect to the surface and the nicotinamide ring oriented flat with respect to the surface much like in an enzyme bound case.

In this study, surface-enhanced resonance Raman scattering, SERRS, and voltammetric techniques (cyclic voltammetry, rotating disk electrochemistry, and rotating ring disk electrochemistry) are used to elucidate the mechanism of oxygen reduction on a silver electrode with iron(III) tetra-4-N-methylpyridylporphyrin. The results indicate that after the oxidation reduction cycle at pH 10 and pH 4, the iron porphyrin is adsorbed on the silver surface as a high-spin, five-coordinated μ-oxo-bridged dimer. On the forward voltage scan, this dimer undergoes two successive one-electron reductions at about −0.3 and −0.5 V to form a high-spin fully reduced Fe(II) μ-oxo-bridged dimer. SERRS spectra show that the first electron transfer forms a mixed-valence Fe(II)−O−Fe(III) μ-oxo-bridged dimer system. At pH 2, only the high-spin reduced Fe(II) monomer is adsorbed on the surface. At pH 4 and pH 10, a shift in the reduction of the oxygen overpotential by approximately +150 mV is observed and the active catalyst in this process is attributed to the partially reduced μ-oxo dimer. A value of n ≈ 4 was calculated for the number of electrons involved in this catalytic reaction, and rotating ring disk voltammetry showed that only 10% stable hydrogen peroxide species is produced on the dimer-modified surface. These results are used to formulate a mechanism for the catalytic reduction of oxygen.

Surface-enhanced Raman spectroscopy (SERS) at a silver electrode was used to obtain the Raman spectrum of lumazine free of interference from fluorescence. The study was carried out varying the experimental conditions of voltage and pH. SERS spectra were compared with Fourier transform infrared (FTIR), coherent anti-Stokes Raman spectroscopy (CARS), normal Raman spectroscopy (NRS), and ultraviolet resonance Raman spectroscopy (UV RRS) spectra. Ab initio calculations at the Hartree−Fock/6-31G(d) level were made of the vibrational spectra of lumazine [2,4(3H,8H)-pterdinedione, LUM] and dimethyllumazine [6,7-dimethyl-,2,4(3H,8H)-pterdinedione, DML], and these were compared with the experimental results. Band assignments were made for LUM and DML. In addition, to determine the structure of the molecules on the metal surface as well as to examine the effects of the surface on the observed spectrum, we compared the results with the FTIR spectrum of a known metal complex of LUM. We also analyzed band shifts and the intensity ratio of in-plane and out-of-plane modes as a function of potential. This analysis indicates that the LUM molecules are tilted at an angle of ca. 45° (0.0 to −0.3 V) to the surface interacting as dimers with silver (Ag) sites through the lone pairs on the 1N or 5N atoms of the LUM ring. The tilt angle moves to ca. 50° as the potential is made more negative (−0.6 to −0.7 V).

Summary.To examine the influence of cellular immunity to spermatozoa on the fertility of inbred mice, leucocytes were transferred from other female mice that had been immunized with spermatozoa. Both syngeneic and allogeneic systems were investigated. The cellular immune reaction was estimated using a footpad swelling test before and after the cell transfer. There was a significant increase of the paw thickness and a statistically significant reduction in fertility only for C3H mice immunized with C57BL spermatozoa.

The electroreduction processes of both 4-pyridinecarboxaldehyde, 4-ALPY, and 4-(hydroxymethyl)pyridine, 4-HMPY, have been studied in aqueous solution on a Ag electrode using surface-enhanced Raman spectroscopy, SERS, and cyclic voltammetry, CV. Each electrode process was investigated at pH 3 and at pH 7 in 0.1M KCl electrolyte. SERS spectra show that both the neutral 4-ALPY and a species which is protonated on the aldehyde group (Py−CHOH⁺) adsorb on the roughened Ag electrode surface with an end-on orientation through the pyridine nitrogen, but the species with a protonated ring (H⁺Py−CHO) prefers adsorption with a face-on orientation through its π-system. The electrochemical reduction of ALPY produces a common product, 1,2-bis(4-pyridyl)ethane (BPE), in both acidic and basic media. The major reaction process was studied by time-resolved SERS, TR-SERS, in the time range of 0.1 to 30 ms. A transient intermediate appears at 3.0 ms and is suggested to be the pinicol Py−CH(OH)CH(OH)−Py on the basis of a Gaussian 94 ab initio frequency calculation. It disappears by 10 ms, at which time the BPE product spectrum is established. The reduction of HMPY also undergoes similar reaction pathways in both acidic and neutral pH conditions, and the major product is the same in either condition. A striking fact is that the reduction of HMPY on Ag produces the same product as that of the ALPY, i.e., 1,2-bis(4-pyridyl)ethane (BPE). The surface species for the reactants and the product on the Ag electrode have been identified by SERS, and vibrational assignments of these species have been made.