A structure determination protocol based on combined analysis of 3D-ED data, powder XRD data, solid-state NMR data and DFT-D calculations reveals the structure of a new polymorph of l-tyrosine.

We report the crystal structure of a new polymorph of l-tyrosine (denoted the ß polymorph), prepared by crystallization from the gas phase following vacuum sublimation. Structure determination was carried out by combined analysis of three-dimensional electron diffraction (3D-ED) data and powder X-ray diffraction (XRD) data. Specifically, 3D-ED data were required for reliable unit cell determination and space group assignment, with structure solution carried out independently from both 3D-ED data and powder XRD data, using the direct-space strategy for structure solution implemented using a genetic algorithm. Structure refinement was carried out both from powder XRD data, using the Rietveld profile refinement technique, and from 3D-ED data. The final refined structure was validated both by periodic DFT-D calculations, which confirm that the structure corresponds to an energy minimum on the energy landscape, and by the fact that the values of isotropic 13C NMR chemical shifts calculated for the crystal structure using DFT-D methodology are in good agreement with the experimental high-resolution solid-state 13C NMR spectrum. Based on DFT-D calculations using the PBE0-MBD method, the ß polymorph is meta-stable with respect to the previously reported crystal structure of l-tyrosine (now denoted the α polymorph). Crystal structure prediction calculations using the AIRSS approach suggest that there are three other plausible crystalline polymorphs of l-tyrosine, with higher energy than the α and ß polymorphs.

Contact hypersensitivity: quantitative aspects, susceptibility and risk factors.

The development of allergic sensitisation by environmental chemicals results in allergic contact dermatitis and highly undesirable morbidity and disability. This form of hypersensitivity is mediated by specific T lymphocytes that recognise the chemical sensitiser bound to self-proteins. Use of deliberate experimental contact sensitisation with dinitrochlorobenzene (DNCB) has been used to investigate the human immune system which exhibits dose-related responses. Many factors contribute to whether sensitisation occurs and the nature and magnitude of the immune response. Chemicals vary in sensitising potency, mainly reflecting their intrinsic protein-binding properties. The amount of sensitiser reaching the immune system is determined by many factors of which the concentration (dose per unit area), the relative lipid solubility and molecular weight are the most critical. Host-related factors contributing to the nature and magnitude of immune responses are mainly genetically determined including gender, age, the biochemical/physical integrity of the epidermal barrier and the quality of the innate and adaptive immune systems. The underlying mechanisms must be elucidated before it will be possible to make reliable predictions of whether a given individual will develop allergic sensitisation by a given chemical.

Sensitization via healthy skin programs Th2 responses in individuals with atopic dermatitis.

Allergen-specific responses in atopic dermatitis (AD) are skewed toward a Th2 profile. However, individuals with AD have been shown to make effective virus-specific Th1 responses, raising the possibility that the skin itself contributes to driving the AD Th2 immunophenotype. Therefore, to explore the programming of immunological sensitization by the skin, we examined the outcome of sensitization through non-lesional skin of individuals with AD and healthy controls. Volunteers (controls, AD individuals with filaggrin gene (FLG) mutations (ADFM), and AD individuals without FLG mutations (ADWT)) were sensitized by cutaneous application of 2,4-dinitrochlorobenzene (DNCB), a small, highly lipophilic chemical sensitizer. At the doses tested, DNCB showed equal penetration into skin of all groups. Clinical reactions to DNCB were significantly reduced in AD. Although both controls and AD made systemic DNCB-specific Th1 responses, these were reduced in AD and associated with significantly Th2-skewed DNCB-specific T-cell responses. Th2 skewing was seen in both ADFM and ADWT, with no difference between these groups. After 3 months, DNCB-specific Th2 responses were persistent in individuals with AD, and Th1 responses persisted in controls. These data provide evidence that when antigen penetration is not limiting, AD skin has a specific propensity to Th2 programming, suggesting the existence of altered skin immune signaling that is AD-specific and independent of FLG status.

CD70-CD27 interaction augments CD8+ T-cell activation by human epidermal Langerhans cells.

Human cutaneous dendritic cells (DCs) from epidermal and dermal compartments exhibit functional differences in their induction of CD4+ T-cell and humoral immune responses; however, differences in the regulation of memory CD8+ T-cell responses by human skin DCs remain poorly characterized. We tested the capacity of human Langerhans cells (LCs) and dermal dendritic cells (DDCs) to induce antigen-specific cytokine production and proliferation of memory CD8+ cells. Although tumor necrosis factor-α-matured human DCs from both epidermal and dermal compartments showed efficient potential to activate CD8+ cells, LCs were constitutively more efficient than DDCs in cross-presenting CD8+ epitopes, as well as direct presentation of viral antigen to Epstein-Barr virus-specific CD8+ T cells. LCs showed greater expression of CD70, and blockade of CD70-CD27 signaling demonstrated that superiority of CD8+ activation by epidermal LC is CD70 dependent. This CD70-related activation of CD8+ cells by LCs denotes a central role of LCs in CD8+ immunity in skin, and suggests that regulation of LC CD70 expression is important in enhancing immunity against cutaneous epithelial pathogens and cancer.

Quantifying human susceptibility to contact sensitization; risk assessments now and in the future.

Assessment and quantification of the risk that a chemical will induce allergic contact sensitization presently depend heavily on background data from animal tests. Following the banning of animal testing of chemicals used in cosmetics and personal products in Europe after 2013, alternative approaches will be required. The chemical properties likely to make a given compound a sensitizer can be determined in vitro with reasonable certainty, but confirmation that it is a sensitizer comes only from in vivo exposure to it. Assessment of the sensitization risks involves consideration of how much of the compound will be applied to skin, for how long, and at which sites. However, the in vivo interactions of the chemical with the skin, with regard to its permeability, and biochemical and immune defences, cannot be predicted from a theoretical position. The xenobiotic-metabolizing enzymes and antioxidant defences may degrade chemicals or may generate potentially immunogenic haptens. Many factors can modify the skin and the immune response, including sex, race, age, genetic programming of epidermal permeability, and/or antioxidant and drug-metabolizing pathways. The only certain way to evaluate whether a chemical will sensitize is in vivo exposure, and the nature of the hazard is revealed by determination of the dose-response relationship. This review shows there is still a serious gap in our understanding of the biological factors and variables involved in conferring resistance or susceptibility to the development of allergic sensitization by chemicals. We are not yet in a position to predict sensitization by chemicals from a theoretical starting point.

Drug-induced exanthemata: a source of clinical and intellectual confusion.

Drug rashes are a common problem occurring in patients across the whole spectrum of medical specialties. They are a source of confusion not only to the wider medical community but even among dermatologists there is lack of clarity about how to describe, classify and approach them. Common patterns of drug rash, apart from the "classical" maculo-papular eruptions (MPE), include urticarial wheals and urticaria-like rashes which it is important to distinguish, because of differences in pathogenetic mechanisms, therapeutic response and prognostic significance. The purpose of this article is to try to offer some structure both from the point of view of clinical classification and also of underlying mechanisms.

Crystal structure of ammonia monohydrate phase II.

We have determined the crystal structure of ammonia monohydrate phase II (AMH II) employing a combination of ab initio computational structure prediction and structure solution from neutron powder diffraction data using direct space methods. Neutron powder diffraction data were collected from perdeuterated AMH II using the D2B high-resolution diffractometer at the Institut Laue-Langevin. AMH II crystallizes in space-group Pbca with 16 formula units in a unit-cell of dimensions a = 18.8285(4) A, b = 6.9415(2) A, c = 6.8449(2) A, and V = 894.61(3) A3 [rho(calc)(deuterated) = 1187.56(4) kg m(-3)] at 502 MPa, 180 K. The structure is characterized by sheets of tessellated pentagons formed by orientationally ordered O-D...O, O-D...N, and N-D...O hydrogen-bonds; these sheets are stacked along the a-axis and connected by N-D...O hydrogen bonds alone. With the exception of the simple body-centered-cubic high-pressure phases of ammonia monohydrate and ammonia dihydrate, this is the first complex molecular structure of any of the high-pressure stoichiometric ammonia hydrates to be determined. The powder structure solution is complemented by an ab initio structure prediction using density functional theory which gives an almost identical hydrogen bonding network.

Equation of state and phase transition of deuterated ammonia monohydrate (ND3.D2O) measured by high-resolution neutron powder diffraction up to 500 MPa.

We describe the results of a neutron powder diffraction study of perdeuterated ammonia monohydrate (AMH, ND(3).D(2)O) carried out in the range 102