Chlorophyll and pheophytin protonated and deprotonated ions: Observation and theory

Pheophytin a and chlorophyll a have been investigated by electrospray mass spectrometry in the positive and negative modes, in view of the importance of the knowledge of their properties in photosynthesis. Pheophytin and chlorophyll are both observed intensely in the protonated mode, and their main fragmentation route is the loss of their phytyl chain. Pheophytin is observed intact in the negative mode, while under collisions, it is primarily cleaved beyond the phytyl chain and loses the attaching propionate group. Chlorophyll is not detected in normal conditions in the negative mode, but addition of methanol solvent molecule is detected. Fragmentation of this adduct primarily forms a product (-30 amu) that dissociates into dephytyllated deprotonated chlorophyll. Semi-empirical molecular dynamics calculations show that the phytyl chain is unfolded from the chlorin cycle in pheophytin a and folded in chlorophyll a. Density functional theory calculations have been conducted to locate the charges on protonated and deprotonated pheophytin a and chlorophyll a and have found the major location sites that are notably more stable in energy by more than 0.5 eV than the others. The deprotonation site is found identical for pheophytin a and the chlorophyll a-methanol adduct. This is in line with experiment and calculation locating the addition of methanol on a double bond of deprotonated chlorophyll a.

Experimental and theoretical study of resonant core-hole spectroscopies of gas-phase free-base phthalocyanine

We studied N 1s^-1 inner-shell processes of the free base Phthalocyanine molecule, H₂Pc, in the gas-phase. This complex organic molecule contains three different nitrogen sites defined by their covalent bonds. We identify the contribution of each site in ionized, core-shell excited or relaxed electronic states by the use of different theoretical methods. In particular, we present resonant Auger spectra along with a tentative new theoretical approach based on multiconfiguration self-consistent field calculations to simulate them. These calculations may pave the road towards resonant Auger spectroscopy in complex molecules.

Action spectroscopy of spin forbidden states in the gas phase: A powerful probe for large non-luminescent molecules

Triplet action spectra of two similar copper porphyrins, copper tetraphenylporphyrin (CuTPP) and copper octaethylporphyrin (CuOEP), have been studied in the gas phase at low temperatures in the absence of external perturbations by using a resonant pump and a 193 nm probe, ionizing the ³ππ^* orbital localized on the porphyrin cycle. The molecules were prepared by laser desorption in a disk source, then cooled in a helium supersonic expansion, and finally excited in the Q band system (S₁ ← S₀). This type of experiment allows the spectroscopic characterization of large non-luminescent molecules in the absence of solvent perturbations. The two copper porphyrins exhibit a broad electronic origin Q₀₀ absorption spectrum, partly caused by the short lifetime of the excited (S₁) state. The two porphyrins differ strongly with a strong Q₀₀ band for CuOEP and a weak one for CuTPP, in agreement with the Gouterman four-orbital model. The two molecules exhibit different solvent shifts: CuOEP is blue shifted in non-polar solvents owing to its alkyl substituents, while CuTPP is red shifted as for regular transitions to ππ^* orbitals. The decay dynamics of the triplet state exhibit a collision-free lifetime of 70 ± 7 ns for CuTPP atop a microsecond decay. This non-exponential decay can be viewed as evidence of time evolution of two states combining the state with spin 1 borne by the porphyrin ring and that by the Cu atom 12. Therefore, this method allows solvent-free spectrodynamics of large molecules in a short microsecond time range.

Predicting the size of unerupted canines and premolars using primary maxillary first molar

AIM

One of the most important aspects of interceptive orthodontic diagnosis and treatment planning is space analysis. To date all methods use the size of permanent teeth to predict the dimensions of unerupted teeth. The aim of this study was to predict the permanent teeth size using maxillary primary first molar.

METHODS

The size of primary maxillary first molars and permanent canines and premolars of 80 subjects was measured on their dental casts. Regression equations were determined between the size of primary maxillary first molars and permanent canines and premolars.

RESULTS

The new regression equations for predicting permanent tooth size in the maxilla and mandible were, respectively, Y = 2.2X + 13 and Y = 2.4X + 9.5 among females and Y = 2.7X + 5.5 and Y = 2.4X + 9.5 among males.

CONCLUSIONS

The results show that the primary maxillary first molar size can be used to predict the size of unerupted permanent teeth.