The Solvation Shell of Small Solutes in Aqueous-Organic Solvent Mixtures and Its Implications for Reversed-Phase Liquid Chromatography

Reversed-phase liquid chromatography (RPLC) operates with water-organic solvent (W-OS) mobile phases where preferential solvation (PS) of solutes is likely. To investigate the relevance of the solute solvation shell in the mobile phase for RPLC retention, we combine data from molecular dynamics simulations of small, neutral solutes (six analytes and two dead time markers) in W-methanol (MeOH) and W-acetonitrile (ACN) mixtures with corresponding retention data obtained on an RPLC column over a wide range of W/OS ratios. Data derived from Kirkwood-Buff integrals show PS by the OS for analytes vs low or negative PS for dead time markers. W-ACN mixtures generate a higher amount of PS than W-MeOH mixtures, which contributes to the higher eluent strength of ACN in RPLC. Difference spatial distribution functions reveal anisotropic solvation shells with OS excess at hydrocarbon elements and W excess at functional groups, predicting that retention by the hydrophobic stationary phase is favored by hydrocarbon elements and limited by functional groups. Analysis of solute-solvent hydrogen bonds pinpoints the hydrogen-bond requirements toward W as the retention-limiting factor. The relation between the solute solvation shell and retention confirms the importance of W-OS and solute-W hydrogen bonding for RPLC retention.

Mobile-Phase Contributions to Organic-Solvent Excess Adsorption and Surface Diffusion in Reversed-Phase Liquid Chromatography

Fast transport of retained analytes in reversed-phase liquid chromatography occurs through surface diffusion in the organic-solvent (OS)-enriched interfacial "ditch" region between the hydrophobic stationary phase and the water (W)-OS mobile phase. Through molecular dynamics simulations that recover the OS excess adsorption isotherms of a typical C₁₈-stationary phase for methanol and acetonitrile, we explore the relation between OS properties, OS excess adsorption, and surface diffusion. The emerging molecular-level picture attributes the mobile-phase contribution to surface diffusion to the hydrogen-bond capability and the eluting power of the OS. The higher affinity of methanol for the formation of W-OS hydrogen bonds at the soft, hydrophobic surface presented by the bonded-phase (C₁₈) chains reduces the OS excess and the related viscosity drop in the ditch. The lower eluting power of methanol, however, translates to increased bonded-phase contacts for analytes, which can increase their mobility gain from surface diffusion above the gain observed with acetonitrile.

Control of structure and spin texture in the van der Waals layered magnet CrSBr

Controlling magnetism at nanometer length scales is essential for realizing high-performance spintronic, magneto-electric and topological devices and creating on-demand spin Hamiltonians probing fundamental concepts in physics. Van der Waals (vdW)-bonded layered magnets offer exceptional opportunities for such spin texture engineering. Here, we demonstrate nanoscale structural control in the layered magnet CrSBr with the potential to create spin patterns without the environmental sensitivity that has hindered such manipulations in other vdW magnets. We drive a local phase transformation using an electron beam that moves atoms and exchanges bond directions, effectively creating regions that have vertical vdW layers embedded within the initial horizontally vdW bonded exfoliated flakes. We calculate that the newly formed two-dimensional structure is ferromagnetically ordered in-plane with an energy gap in the visible spectrum, and weak antiferromagnetism between the planes, suggesting possibilities for creating spin textures and quantum magnetic phases.

Insights from molecular simulations about dead time markers in reversed-phase liquid chromatography

Among the most popular compounds to estimate the hold-up time in reversed-phase liquid chromatography (RPLC) are acetone and uracil, which are considered as too small and too polar, respectively, for retention by the hydrophobic stationary phase, although their observed elution behavior does not fully support this assumption. We investigate how acetone and uracil as solutes interact with the chromatographic interface through molecular dynamics simulations in an RPLC mesopore model of a silica-supported, endcapped, C₁₈ phase equilibrated with a water (W)‒acetonitrile (ACN) mobile phase. The simulation results provide a molecular-level explanation for the observed elution behavior of acetone and uracil, but also question whether true dead time markers for RPLC exist. Both solutes have a density maximum in the interfacial region in addition to a low presence in the bonded-phase region, but these density peaks clearly differ from the adsorption and partitioning peaks of true analytes. Acetone partially behaves like a co-solvent of ACN and partially like the analyte acetophenone. Like ACN, acetone can be found in the first and second layer of solvent molecules at the silica surface; like acetophenone, acetone adsorbs to the bonded-phase chains by orienting its polar group to the bulk region to sustain hydrogen bonds with W molecules. Uracil behavior is governed by a need for extensive hydrogen-bond coordination by W molecules. Uracil adsorbs to the very edge of the bonded-phase chains, on the bulk-region side of the ACN density maximum in the interfacial region. Further penetration into the chains is prevented by the absence of W molecules, which are not found deeper in the bonded phase, except at the silica surface. Contrary to true analytes, accumulation of uracil and acetone in the interfacial region ceases at an equimolar presence of W and ACN in the mobile phase (at 70‒80% ACN volume fraction). Uracil achieves a closer approximation of the stationary-phase limit than acetone, but carries the risk of HILIC retention at high ACN fraction in the mobile phase.

Prospects and Limitations of Transition Metal Dichalcogenide Laser Gain Materials

Nanolasers operate with a minimal amount of active material and low losses. In this regime, single layers of transition-metal dichalcogenides (TMDs) are being investigated as next generation gain materials due to their high quantum efficiency. We provide results from microscopic gain calculations of highly excited TMD monolayers and specify requirements to achieve lasing with four commonly used TMD semiconductors. Our approach includes band-structure renormalizations due to excited carriers that trigger a direct-to-indirect band gap transition. As a consequence, we predict a rollover for the gain that limits the excitation regime where laser operation is possible. A parametrization of the peak gain is provided that is used in combination with a rate-equation theory to discuss consequences for experimentally accessible laser characteristics.

Electric-Field Switchable Second-Harmonic Generation in Bilayer MoS2 by Inversion Symmetry Breaking

We demonstrate pronounced electric-field-induced second-harmonic generation in naturally inversion symmetric 2H stacked bilayer MoS₂ embedded into microcapacitor devices. By applying strong external electric field perturbations (|F| = ±2.6 MV cm^-1) perpendicular to the basal plane of the crystal, we control the inversion symmetry breaking and, hereby, tune the nonlinear conversion efficiency. Strong tunability of the nonlinear response is observed throughout the energy range (E_ω ∼ 1.25-1.47 eV) probed by measuring the second-harmonic response at E_2ω, spectrally detuned from both the A- and B-exciton resonances. A 60-fold enhancement of the second-order nonlinear signal is obtained for emission at E_2ω = 2.49 eV, energetically detuned by ΔE = E_2ω - E_C = -0.26 eV from the C-resonance (E_C = 2.75 eV). The pronounced spectral dependence of the electric-field-induced second-harmonic generation signal reflects the bandstructure and wave function admixture and exhibits particularly strong tunability below the C-resonance, in good agreement with density functional theory calculations. Moreover, we show that the field-induced second-harmonic generation relies on the interlayer coupling in the bilayer. Our findings strongly suggest that the strong tunability of the electric-field-induced second-harmonic generation signal in bilayer transition metal dichalcogenides may find applications in miniaturized electrically switchable nonlinear devices.

Efficient Excitonic Photoluminescence in Direct and Indirect Band Gap Monolayer MoS2

We discuss the photoluminescence (PL) of semiconducting transition metal dichalcogenides on the basis of experiments and a microscopic theory. The latter connects ab initio calculations of the single-particle states and Coulomb matrix elements with a many-body description of optical emission spectra. For monolayer MoS2, we study the PL efficiency at the excitonic A and B transitions in terms of carrier populations in the band structure and provide a quantitative comparison to an (In)GaAs quantum well-structure. Suppression and enhancement of PL under biaxial strain is quantified in terms of changes in the local extrema of the conduction and valence bands. The large exciton binding energy in MoS2 enables two distinctly different excitation methods: above-band gap excitation and quasi-resonant excitation of excitonic resonances below the single-particle band gap. The latter case creates a nonequilibrium distribution of carriers predominantly in the K-valleys, which leads to strong emission from the A-exciton transition and a visible B-peak even if the band gap is indirect. For above-band gap excitation, we predict a strongly reduced emission intensity at comparable carrier densities and the absence of B-exciton emission. The results agree well with PL measurements performed on monolayer MoS2 at excitation wavelengths of 405 nm (above) and 532 nm (below the band gap).

Influence of excited carriers on the optical and electronic properties of MoS₂

We study the ground-state and finite-density optical response of molybdenum disulfide by solving the semiconductor Bloch equations, using ab initio band structures and Coulomb interaction matrix elements. Spectra for excited carrier densities up to 10(13) cm(-2) reveal a redshift of the excitonic ground-state absorption, whereas higher excitonic lines are found to disappear successively due to Coulomb-induced band gap shrinkage of more than 500 meV and binding-energy reduction. Strain-induced band variations lead to a redshift of the lowest exciton line by ∼110 meV/% and change the direct transition to indirect while maintaining the magnitude of the optical response.

Komplexe offenkettiger und zyklischer Diazathiaalkane. Die Kristallstrukturen von 1,7-Diaza-4-thiaheptan-tricarbonyl-molybdän(0), 1-Thia-4,7-diazacycIononan-tricarbonyI-molybdän(0) und 1-Thia-4,7-diazacyclononan-tricarbonyl-rhenium(I)-bromid

The reactions of Mo(CO)6, W(CO)6 and Re(CO)6Br with the ligand l-thia-4,7-diazacyclononane (C6H14N2S = L) yield crystals of LMo(CO)3 (4a), LW(CO)3 (4b) and LRe(CO)3Br (5). A n improved synthesis of L has been developed, and the structures of 4a and 5 have been determined. Crystal data: 4a, monoclinic, space group P21/n, a = 791.3(4), b - 1332.6(4), c = 1149.2(6) pm, β - 98.96(4)°, Z = 4.1841 reflexions, R = 0.045. 5, orthorhombic, space group Pbca, a = 1413.4(5), b = 1398.0(5), c = 1409.5(5) pm, Z = 8.2619 reflexions, R = 0.038. Both crystals contain pseudooctahedral LM(CO)3 moieties, with facial coordination of the CO molecules. The Re - N bond lengths (average 220.3(4) pm) are rather short. The structure of L 'Mo(CO)3 (3) with the acyclic ligand 1,7-diaza-4-thiaheptane (C4H10N2S = L') was also determined. Crystal data: monoclinic, space group P21/c, a = 682.8(2), b = 1213.0(3), c = 1253.0(3), β = 99.74°, Z = 4.1889 reflexions, R = 0.023.

Indirect RT-PCR in-situ hybridization: a novel non-radioactive method for detecting glucose-dependent insulinotropic peptide

To establish indirect in-situ PCR for the detection of intestinal peptide hormones, rat intestine and a murine intestinal tumor cell line, STC 1, were used. The results exhibited intensive staining of GIP-producing K-cells. Paraformaldehyde-fixed cryostat sections yielded the best results in signal to background ratio with RT-PCR in-situ hybridization. Moreover, it was possible to elevate the positive staining signal and to reduce background staining. Digoxigenin-labeled in-situ hybridization served as a control for specificity and sensitivity of GIP (glucose-dependent insulinotropic peptide) mRNA expression on cryostat as well as paraffin sections. In conclusion, this RT-PCR in-situ hybridization protocol proves to be a specific, sensitive and reliable non-radioactive technique for the detection of intestinal peptide hormone mRNA, especially in tissues or tumor cells where the application of ISH is limited.

Comparison of the TEMPO+ ear-level speech processor and the cis pro+ body-worn processor in adult MED-EL cochlear implant users

A study was conducted to compare the new MED-EL TEMPO+ ear-level speech processor with the CIS PRO+ body-worn processor in the COMBI 40/COMBI 40+ implant system. Speech tests were performed in 46 experienced subjects in two test sessions approximately 4 weeks apart. Subjects were switched over from the CIS PRO+ to the TEMPO+ in the first session and used only the TEMPO+ in the time between the two sessions. Speech tests included monosyllabic word tests and sentence tests via the telephone. An adaptive noise method was used to adjust each subject's scores to approximately 50%. Additionally, subjects had to complete a questionnaire based on their 4 weeks of experience with the TEMPO+. The speech test results showed a statistically significant improvement in the monosyllabic word scores with the TEMPO+. In addition, in the second session, subjects showed a significant improvement when using the telephone with the TEMPO+, indicating some learning in this task. In the questionnaire, the vast majority of subjects found that the TEMPO+ allows equal or better speech understanding and rated the sound quality of the TEMPO+ higher. All these objective and subjective results indicate the superiority of the TEMPO+ and are mainly attributed to a new coding strategy called CIS+ and its implementation in the TEMPO+. In other words, based on the results of this study, it appears that after switching over from the CIS PRO+ to the TEMPO+, subjects are able to maintain or even improve their own speech understanding capability.

Evidence for a role of macrophage migration inhibitory factor in psoriatic skin disease

Macrophage migration inhibitory factor (MIF) was originally described as a T-cell-derived lymphokine with the potential to inhibit the random migration of macrophages. However, recent reports have shown a much broader tissue distribution, including the skin. Functionally, MIF appears to act as an antagonist of anti-inflammatory glucocorticoid action. To elucidate the role of MIF in inflammatory skin diseases, we investigated the production and localization of this cytokine in human skin of patients with psoriasis by means of reverse transcription-polymerase chain reaction, immunohistochemistry and Western blot analysis. In normal skin, our results showed a moderate but homogeneous MIF immunoreactivity in all epidermal layers. Endothelial cells and the outer root sheath of hair follicles were also positive for MIF. In lesional psoriatic human skin, a significant increase in MIF immunoreactivity was visible in suprabasal keratinocytes, especially of the spinous layer. In addition, endothelial cells also showed increased immunolabelling for MIF in psoriatic lesions, indicating a cell-specific upregulation of this mediator in untreated psoriasis. Western blot analysis also revealed a clear increase in MIF in homogenates of lesional skin from psoriasis patients. These results suggest a role for MIF in the inflammatory skin disease psoriasis.

Identification of pituitary adenylate cyclase activating polypeptide (PACAP) and PACAP type 1 receptor in human skin: expression of PACAP-38 is increased in patients with psoriasis

Morphological and biochemical evidence is presented for the presence of pituitary adenylate cyclase activating peptide (PACAP) and the high-affinity PACAP-1 receptor subtype in human skin. Immunohistochemical analysis revealed PACAP-immunoreactivity (IR) to be present predominantly in dermal nerve fibers close to the dermal-epidermal border, hair follicles, blood vessels and sweat glands. Radioimmunoassay, chromatographic analysis and Western blotting revealed this PACAP-IR to be PACAP-38 whereas the second molecular form, PACAP-27, is absent. In tissue of psoriasis patients significantly more PACAP-38 protein was detected as compared to normal skin. Using RT-PCR, the expression of a high-affinity PACAP-1 receptor in human skin was observed. These results indicate a possible role for PACAP-38 in inflammatory processes of psoriasis.

Trisomy 3 is not a common feature in malignant lymphomas of mucosa-associated lymphoid tissue type

The genetic background of extranodal marginal zone B-cell non-Hodgkin's lymphoma (NHL) of mucosa-associated lymphoid tissue (MALT) type is poorly understood. In contrast to most entities of primary nodal lymphomas, few cytogenetic data are available, and gene rearrangements frequently encountered in and highly characteristic of certain entities of systemic NHL are absent in this type of lymphoma. Recently, it was suggested that MALT-type NHLs are associated with certain numerical chromosome aberrations and especially with trisomy 3. We performed an extensive study using a sensitive double (bicolor) fluorescence in situ hybridization technique for the analysis of trisomies for chromosomes 3, 7, 12, and 18 in 60 samples of low-grade and 45 high-grade MALT-type tumors. In the low-grade cases, trisomy 3 was found in a frequency of only 20%. High-grade lymphomas of MALT type were associated with trisomies 3, 7, 12, and 18 in 36, 20, 18, and 13% of the cases, respectively. Whereas no difference was encountered for trisomy 3 in primary and secondary/simultaneous high-grade lymphomas, +7 and +12 were associated with primary lymphomas, and a +18 was predominantly found in secondary/simultaneous high-grade NHL. These results challenge earlier reports describing a high frequency of +3 in low-grade MALT-type NHL and indicate a possibly different genetic evolution pattern of primary and secondary/simultaneous high-grade lymphomas of primary mucosal origin.

Pharmacokinetics of doxorubicin in man: dose and schedule dependence

Doxorubicin serum elimination kinetics were measured by HPLC in three different patient groups. A dose of (a) 30 mg/m2; (b) 50 mg/m2, and (c) 4 x 15 mg/m2 every 10 h was administered by bolus injection to (a) 10, (b) 6, and (c) 8 patients. The results obtained provided strong evidence for a nonlinear dependence of doxorubicin serum elimination on the dose and administration schedule used. Comparing the 15 and 30 mg/m2 dose there was no significant increase in early drug levels but a marked increase in terminal half-life. At doses higher than 30 mg/m2, however, there was a steep increase in early drug levels, too. Moreover a marked cumulation of the anthracycline in the central compartment following short-term (4 x 15 mg/m2 every 10 h) consecutive administration was found. To obtain an optimal concentration x time product by single bolus injection a dose equal or higher than 30 mg/m2 should be used. However, in this dose range a steep dose-dependent rise in early drug levels is to be expected. As early high serum levels correlate with congestive heart failure, administration schedules reaching effective concentration x time products without high peak levels such as continuous infusion or consecutive administration of low doses seem to be necessary.

[Significance of procarbazine in the chemotherapy of Hodgkin's disease--a report of the Cooperative Therapy Study DAL-HD-85]

It was the objective of the DAL study HD-85 to examine the possibility of a reduction of chemotherapy, compared to the study HD-82 which had applied a combined treatment strategy resulting in a relapse rate of only 2.5% after 4 years, and a proportion of intercurrent deaths of 1.5%, in a total of 203 patients. Procarbazine was eliminated in the OPPA-therapy (OPA) and replaced by methotrexate in the COPP-cycles (COMP). Chemotherapy consisted in 2 cycles of OPA for stage I/IIA (group 1), 2 cycles of OPA and 2 cycles of COMP for stage IIB/IIIA (including IEA/IIEA) (group 2), and 2 cycles of OPA and 4 cycles of COMP for stage IIIB/IV (group 3). The subsequent radiotherapy was limited to the initially involved fields, the dosage of 35, 30 or 25 Gy depending on the extent of chemotherapy. Regions showing incomplete tumor regression after chemotherapy received another 5 Gy, in patients of groups 2 and 3. Between Jan. 1985 to Nov. 1986, 103 children with Hodgkin's disease from 42 participating hospitals were enrolled in this study. 98 patients were treated according to protocol (59 boys, 39 girls). A specific strategy for the selective indication of laparotomy and splenectomy was applied. With this strategy no laparotomy was performed in 39/98 patients (40%). 67 patients (68%) retained their spleen. 4 patients showed progression of the disease under chemotherapy, all others achieved remission. 16 patients relapsed before Dec. 31, 1987. So far no child of this study has died.(ABSTRACT TRUNCATED AT 250 WORDS)